Electromechanical transducer

Abstract

There is provided an electromechanical transducer, including: a chassis; a drive unit which includes a stationary part, which forms part of the chassis, and a moveable part which is moveable relative to the stationary part, wherein the drive unit is operable to cause the moveable part to move relative to the stationary part along a movement axis in a forward direction and in a rearward direction; a first suspension element and a second suspension element which are respectively configured to deflect along the movement axis, wherein the first suspension element is secured to a first landing surface of the chassis and the second suspension element is secured to a second landing surface of the chassis, and wherein the first suspension element includes a first suspension attachment formation attached to the moveable part and the second suspension element includes a second suspension attachment formation attached to the moveable part; wherein the first suspension attachment formation and the second suspension attachment formation are attached to at least one attachment formation of the moveable part; wherein an axial separation of the first landing surface and the second landing surface, as measured along the movement axis, is greater than an axial separation of the first suspension attachment formation and the second suspension attachment formation, as measured along the movement axis, such that the suspension elements are deflected along the movement axis by their attachment to the moveable part when the moveable part is at a rest position.

Description

[0001] 008861056

[0002] 1

[0003] ELECTROMECHANICAL TRANSDUCER

[0004] This application claims priority from GB2418957.3 filed 23 December 2024, the contents and elements of which are herein incorporated by reference for all purposes.

[0005] Field of the Invention

[0006] The present invention relates to an electromechanical transducer.

[0007] Background

[0008] Electromechanical transducers are devices for converting an electrical signal into a mechanical vibration, known to be used for transmitting vibrations to an application. Herein, an “application” can be understood as any apparatus to which the electromechanical transducer may be attached. For example, the electromechanical transducer may be attached to a sound radiating surface (in which the term “exciter” may be used) or the seat of a road vehicle (in which case the “shaker” may be used).

[0009] If attached to the seat of a road vehicle (e.g. via a frame of the seat, via foam of the seat, or via other coupling features of the seat), an electromechanical transducer can be used for transmitting vibrations to a person sat in the seat. Such vibrations can be used to provide a tactile warning to a person sat in the seat, to provide a massage to a person sat in the seat, and / or to enhance a listening experience to a person sat in the seat (e.g. by helping them “feel” bass sounds more strongly).

[0010] Minimising the dimensions and weight of electromechanical transducers is a challenge, particularly in the context of the automotive industry.

[0011] The present invention has been devised in light of the above considerations.

[0012] Summary of the Invention

[0013] Electromechanical transducers according to a first aspect, a second aspect, and a third aspect are described. These may help reduce dimensions and / or weight over traditional electromechanical transducers. Moreover, the features of the electromechanical transducer according to the first aspect may be combined with the second aspect, and vice versa, which may further help reduce dimensions and / or weight. The features of the electromechanical transducer according to the second aspect may be combined with features of the third aspect, and vice versa.

[0014] According to a first aspect, there is provided an electromechanical transducer, including: a chassis; a drive unit which includes a stationary part which forms part of the chassis, and a moveable part which is moveable relative to the stationary part, wherein the drive unit is operable to cause the moveable part to move along a movement axis relative to the stationary part; the electromechanical transducer includes: a first suspension element and a second suspension element which are respectively configured to deflect008861056

[0015] 2

[0016] along the movement axis, wherein the first suspension element is secured to a first landing surface of the chassis and the second suspension element is secured to a second landing surface of the chassis, and wherein the first suspension element includes a first suspension attachment formation attached to the moveable part and the second suspension element includes a second suspension attachment formation attached to the moveable part; wherein the first suspension attachment formation and the second suspension attachment formation are attached to at least one attachment formation of the moveable part; wherein an axial separation of the first landing surface and the second landing surface, as measured along the movement axis, is greater than an axial separation of the first suspension attachment formation and the second suspension attachment formation, as measured along the movement axis, such that the suspension elements are deflected along the movement axis by their attachment to the moveable part when the moveable part is at a rest position.

[0017] The electromechanical transducer according to the first aspect has a configuration according to which the axial separation of the landing surfaces is greater than the axial separation of the suspension attachment formations attached to the moveable part such that the suspension elements are deflected by their attachment to the moveable part when the moveable part is at a rest position. This configuration may help reduce the size of the space needed to accommodate the electromechanical transducer, since the difference between the axial separation of the landing surfaces and the axial separation of the suspension attachment formations effectively define (at least part of) a clearance space around the moveable part, that the moveable part moves into when the electromechanical transducer is in use. By contrast, traditional electromechanical transducers may have a configuration according to which the moveable part, once moved from the rest position, already has cleared the first landing surface (or the second landing surface) such that the electromechanical transducer needs to be accommodated by giving the moveable part a comparatively large clearance space beyond the first landing surface (and also beyond the second landing surface) since motion of the moveable part in the forward direction takes place entirely beyond the first landing surface (and also beyond the second landing surface for motion in the rearward direction).

[0018] The electromechanical transducer according to the first aspect has a configuration according to which the first suspension element and the second suspension element are attached to the at least one attachment formation of the moveable part of the drive unit. This configuration may provide for improved attachment of the suspension elements to the moveable part. Utilising the at least one attachment formation on the moveable part may improve alignment of the suspension elements relative to the moveable part, since the attachment formation on the moveable part may be used when attaching the suspension elements. Additionally or alternatively, utilising the at least one attachment formation may improve ease of assembly, since the attachment formation may be used when attaching the suspension elements to the moveable part of the drive unit. By contrast, traditional electromechanical transducers may not have an attachment formation but instead may utilise adhesive for attachment of the suspension elements to the moveable part, which may make alignment of the suspension elements relative to the moveable part more difficult.008861056

[0019] 3

[0020] The at least one attachment formation may extend in a direction parallel to the movement axis, e.g. coaxially with the movement axis. For example, the at least one attachment formation may extend into an axial face of the moveable part (e.g. a tapped hole) or may extend from the axial face of the moveable part (e.g. a pin). Said axial face may be perpendicular to the movement axis.

[0021] The moveable part of the drive unit may have a first axial face which faces in the forward direction and a second axial face which faces in the rearward direction. The at least one attachment formation may extend into / from the first axial face and the second axial face.

[0022] The at least one attachment formation may extend from the first axial face in the forward direction and towards the first landing surface, and the at least one attachment formation may extend from the second axial face in the rearward direction and towards the second landing surface.

[0023] The at least one attachment formation may be pre-formed prior to attachment of the first suspension element and / or the second suspension element. The at least one attachment formation of the moveable part may have a first configuration prior to attaching the first suspension element and / or the second suspension element, and may have a second configuration when the first suspension element and / or the second suspension element are attached. The at least one attachment formation may extend in a direction parallel to the movement axis in either or both of the first configuration and the second configuration.

[0024] Changing the at least one attachment formation from the first configuration to the second configuration may include mechanically deforming the at least one attachment formation. For example, the at least one attachment formation may include a pin which is received into one of the suspension elements and is then flattened to attach said suspension element. The pin may extend in a direction along the movement axis prior to and also after being flattened.

[0025] The first suspension attachment formation and the second suspension attachment formation may be mechanically attached to the at least one attachment formation of the moveable part by at least one an attachment member. The at least one attachment member may include, for example, a bolt or a rivet. In some examples, the at least one attachment member may include a bolt and a nut.

[0026] The at least one attachment member may make a threaded connection. For example, the at least one attachment member may make a threaded connection with another attachment member, such as a bolt received into a nut. Alternatively, the at least one attachment member may make a threaded connection with the moveable part of the drive unit, such as a bolt received into a tapped hole. More particularly, the at least one attachment formation may include a tapped hole, and the at least one attachment member may include a threaded member which makes a threaded connection with the tapped hole.

[0027] The first suspension attachment formation and the second suspension attachment formation may be jointly attached by one attachment member, or the first suspension attachment formation and the second suspension attachment formation may each be attached by a respective attachment member. That is to say, the first suspension attachment formation may be attached to the at least one attachment formation008861056

[0028] 4

[0029] by a first attachment member, and the second suspension attachment formation may be attached to the at least one attachment formation by a second attachment member.

[0030] In some examples, there may be provided a plurality of attachment formations on the moveable part of the drive unit, and a plurality of attachment members. For example, the first suspension attachment formation may be attached to a first attachment formation by a first attachment member, and the second suspension attachment formation may be attached a second attachment formation by a second attachment member.

[0031] The drive unit may include a permanent magnet to generate magnetic flux and one or more flux guides to guide the magnetic flux across an air gap, e.g. in a direction perpendicular to the movement axis. More particularly, the moveable part of the drive unit may include the permanent magnet and at least one flux guide. For example, the moveable part may include a first flux guide, a second flux guide and the permanent magnet arranged between the first flux guide and the second flux guide.

[0032] The permanent magnet may have any suitable shape, such as a cylindrical shape or an annular shape. The first flux guide and the second flux guide may have any suitable shape, such as a cylindrical shape or an annular shape. In some examples, the first flux guide and the second flux guide may be (flat) washers or shoulder washers with a protruding shoulder.

[0033] The drive unit may further include a tubular yoke. More particularly, the stationary part of the drive unit may include the tubular yoke, which may form part of the chassis.

[0034] The tubular yoke may extend around the movement axis.

[0035] The tubular yoke may have a first end and, opposite thereto, a second end. The first end and the second end may delimit an axial extent of the tubular yoke along the movement axis. The first end may be a first axial end and the second end may be a second axial end.

[0036] A first air gap may be formed between the first flux guide and the tubular yoke, and a second air gap may be formed between the second flux guide and the tubular yoke. The first air gap and the second air gap may each have an annular shape.

[0037] The first suspension attachment formation may be attached to a first attachment formation of the first flux guide and the second suspension attachment formation may be attached to a second attachment formation of the second flux guide. For example, the first suspension attachment formation may be attached to the hole in a first washer (or shoulder washer), and the second suspension attachment formation may be attached to the hole in the second washer (or shoulder washer), e.g. via the at least one attachment member. Particularly where a shoulder washer is used, the hole may be tapped.

[0038] In some examples, the first attachment formation may extend in the forward direction and the second attachment formation extend in the rearward direction. For example, a shoulder portion of a first shoulder washer may extend in the forward direction, and a shoulder portion of a second shoulder washer may extend in the rearward direction.008861056

[0039] 5

[0040] The stationary part of the drive unit may include a voice coil. The voice coil may be mounted within the tubular yoke. In some examples, the voice coil may be in contact with the tubular yoke. In other examples, there may be an annular clearance space between the voice coil and the tubular yoke (i.e. the annular clearance extends around the voice coil, and the tubular yoke extends around the annular clearance space.

[0041] The voice coil may extend around the movement axis.

[0042] The voice coil may be part of the stationary part of the drive unit and may extend around the moveable part of the drive unit.

[0043] The voice coil may include voice coil windings arranged on a voice coil former. The voice coil former may have a generally tubular shape on which the voice coil windings may be arranged between a first end and a second end of the voice coil. The first end and the second end of the voice coil may delimit an axial extent of the voice coil. The first end may be a first axial end and the second end may be a second axial end.

[0044] The voice coil windings may be located in the air gap defined by the permanent magnet and the one or more flux guides when the moveable part is at the rest position. Where the voice coil windings are arranged into the first set of windings and the second set of windings, the first set of windings may be located in the first air gap and the second set of windings may be located in the second air gap when the moveable part is at the rest position.

[0045] The voice coil windings of the voice coil may be arranged to provide a first set of windings and, spaced therefrom, a second set of windings. The first set of windings and the second set of windings may be spaced apart as measured along the movement axis.

[0046] The first set of windings and the second set of windings may be formed from a single continuous wire. Each of the first set of windings and the second set of windings may have an uneven number of winding layers.

[0047] The voice coil may be electrically connected to a signal source at the first end of the voice coil and may be electrically connected to the signal source at the second end of the voice coil.

[0048] The drive unit may define a force factor BL, where B is the magnetic flux density permeating the voice coil in the air gap and L is the total length of windings of the voice coil in the air gap. The force factor BL is a known measure to quantify the strength of the magnetic interaction between the magnet unit and the voice coil.

[0049] The magnetic flux density B may have a value which is between 1% and 30% of the value of the total length of windings L. Optionally B is between 2% and 10% of L.

[0050] The magnetic flux B in the air gap may have a magnitude such that the resulting magnetic attraction between the stationary part and the moveable part causes a radial static deflection of the moveable part relative to the movement axis of no more than 0.1 millimetres.008861056

[0051] 6

[0052] The terms “stationary” and “moveable” are relative terms and in principle dependent on the particular frame of reference. In this context, the terms “stationary” and “moveable” are intended to refer to a conventional frame of reference according to which the chassis is considered to be stationary, and from which the moveable part of the drive unit is suspended via the suspension elements. As such the moveable part of the drive unit, and any parts which in use move with the moveable part, are referred to as moveable, while other parts of the transducer are referred to as stationary, e.g. the stationary part of the drive unit. Those parts of the transducer which are moveable, i.e. the moveable part of the drive unit and parts that in use move with the moveable part, may collectively be referred to as the moveable part. Herein, a reference to the moveable part of the drive unit being at the rest position may be taken to correspond to a state in which the drive unit is not energised (e.g. an electric current is not being supplied to the voice coil of the drive unit) with the moveable part of the drive unit having been given time to reach a state of rest.

[0053] The first suspension element and the second suspension element may each include a plurality of bridge arms which extend towards the suspension attachment formation.

[0054] Each suspension element may include an outer portion and an inner portion. The inner portion may be located at the movement axis and may include the suspension attachment formation. The outer portion may extend around the movement axis and may be attached to the chassis. The bridge arms may extend between the outer portion and the inner portion.

[0055] The bridge arms may extend towards the suspension attachment formation of the respective suspension element and may extend around the movement axis. That is to say, the bridge arms may curve around the movement axis. In some examples, the bridge arms may extend around the movement axis for less than one full revolution. In some examples, the bridge arms may extend around the movement axis for one full revolution or more than one full revolution.

[0056] Any suitable number of bridge arms may be provided. For example, each suspension element may have at most three bridge arms. In some examples, each suspension element has (exactly) two bridge arms. By providing the suspension element with a small number of bridge arms, especially two bridge arms, the suspension element may better withstand attachment to the moveable part, particularly where such attachment is effected mechanically. For example, where attachment is by means of an attachment member, such as a bolt, the process of securing the attachment member could put strain on the suspension element which could cause damage to a suspension element with a large number of bridge arms. A suspension element with a small number of bridge arms may generally be better suited for withstanding such manipulation.

[0057] The suspension elements may be formed by stamping to provide the bridge arms and the suspension attachment formation. The suspension attachment formation may be an aperture through the respective suspension element.

[0058] Each suspension element may be formed from metal. In some examples, each suspension element may be formed from a single piece of metal, e.g. a stamped piece of sheet metal.008861056

[0059] 1

[0060] The electromechanical transducer may further include: a forward frame portion, which forms part of the chassis, wherein the moveable part of the drive unit is suspended from the forward frame portion by a first suspension element configured to deflect along the movement axis; a rearward frame portion, which forms part of the chassis, wherein the moveable part of the drive unit is suspended from the rearward frame portion by a second suspension element configured to deflect along the movement axis; wherein the forward frame portion is shaped to define a first channel which faces towards the rearward frame portion and extends around the movement axis; wherein the rearward frame portion is shaped to define a second channel which faces towards the forward frame portion and extends around the movement axis; a tubular yoke, which forms part of the chassis, having: a first end received into the first channel of the forward frame portion to thereby align the first suspension element relative to the tubular yoke, and a second end received into the second channel to thereby align the second suspension element relative to the tubular yoke.

[0061] Any feature described below in relation to the second aspect is applicable also to the electromechanical transducer of the first aspect.

[0062] The tubular yoke may be attached to first frame portion and the second frame portion. For example, the tubular yoke may be attached using adhesive. Adhesive may be provided in the first channel to attach the tubular yoke and the first frame portion, and adhesive may be provided in the second channel to attach the tubular yoke and the second frame portion.

[0063] A forward end of the voice coil former may be radially constrained by a first axis-facing inner surface of the forward frame portion and a rearward end of the voice coil former may be radially constrained by a second axis-facing inner surface of the rearward frame portion to thereby align the voice coil with respect to the movement axis.

[0064] The forward frame portion may be shaped to define a first annular surface which faces towards the rearward frame portion and extends around the movement axis. The rearward frame portion may be shaped to define a second annular surface which faces towards the forward frame portion and extends around the movement axis. The voice coil windings may be axially constrained by the first annular surface and the second annular surface.

[0065] The voice coil windings may be attached to the first frame portion and the second frame portion. For example, voice coil windings may be attached using adhesive. Adhesive may be added to the first annular surface to attach the voice coil windings to the first frame portion, and adhesive may be added to the second annular surface to attach the voice coil windings to the second frame portion.

[0066] The forward frame portion may have a first end face which faces away from the tubular yoke and the rearward frame portion may have a second end face which faces away from the tubular yoke.

[0067] A central passage may extend between the first end face and the second end face. In particular, the central passage may extend from the end face and to the end face. That is to say, the central passage may extend between a first opening in the first end face and a second opening in the second end face. The moveable part may be moveable in the central passage along the movement axis.008861056

[0068] 8

[0069] The first landing surface may be recessed into the first end face and the first suspension element may be attached to the first landing surface. A forward clearance space may be formed between the first end face and the first landing surface. The moveable part may be moveable in the forward clearance space.

[0070] The second landing surface may be recessed into the second end face and the second suspension element may be attached to the second landing surface. A rearward clearance space may be formed between the second end face and the second landing surface. The moveable part may be moveable in the rearward clearance space.

[0071] The chassis may include a first closure member attached to the forward frame portion to close the first opening and may include a second closure member attached to the rearward frame portion to close the second opening.

[0072] The chassis may be arranged to provide an airtight seal around the central passage.

[0073] There may be provided a road vehicle including the electromechanical transducer as described above in relation to the first aspect. The road vehicle may include a seat containing a seat foam, and the electromechanical transducer may be mounted to a recess in the seat foam.

[0074] According to a second aspect, there is provided an electromechanical transducer, including: a chassis; a drive unit which includes a stationary part, which forms part of the chassis, and a moveable part which is moveable relative to the stationary part, wherein the drive unit is operable to cause the moveable part to move along a movement axis relative to the stationary part along a movement axis in a forward direction and a rearward direction; a forward frame portion, which forms part of the chassis, wherein the moveable part of the drive unit is suspended from the forward frame portion by a first suspension element configured to deflect along the movement axis; a rearward frame portion, which forms part of the chassis, wherein the moveable part of the drive unit is suspended from the rearward frame portion by a second suspension element configured to deflect along the movement axis; wherein the forward frame portion is shaped to define a first channel which faces towards the rearward frame portion and extends around the movement axis; wherein the rearward frame portion is shaped to define a second channel which faces towards the forward frame portion and extends around the movement axis; a tubular yoke, which forms part of the chassis, having: a first end received into the first channel of the forward frame portion to thereby align the first suspension element relative to the tubular yoke, and a second end received into the second channel to thereby align the second suspension element relative to the tubular yoke.

[0075] The electromechanical transducer according to the second aspect has a configuration according to which the tubular yoke is received in the channels defined by the frame portions. This configuration may help reduce dimensions and / or weight since the frame portions are connected by the tubular yoke and so need not be connected by a further frame portion. By contrast, traditional electromechanical transducers may have a “full” frame, thereby potentially increasing material usage, dimensions and weight.

[0076] The electromechanical transducer according to the second aspect has a configuration according to which the tubular yoke is received in the channels defined by the frame portions to align the suspension elements relative to the tubular yoke. This configuration may improve alignment of the suspension008861056

[0077] 9

[0078] elements relative to the chassis. Additionally or alternatively, ease of assembly may be improved by reducing the need for careful alignment of the tubular yoke relative to the suspension elements since these are aligned relative to the tubular yoke by the frame portions. By contrast, traditional electromechanical transducers may require careful assembly using jigs to achieve alignment to a satisfactory degree.

[0079] The first suspension element may include a first suspension attachment formation attached to the moveable part and the second suspension element may include a second suspension attachment formation attached to the moveable part; wherein the first suspension attachment formation and the second suspension attachment formation may be attached to at least one attachment formation of the moveable part; wherein an axial separation of the first landing surface and the second landing surface, as measured along the movement axis, may be greater than an axial separation of the first suspension attachment formation and the second suspension attachment formation, as measured along the movement axis, such that the suspension elements may be deflected along the movement axis by their attachment to the moveable part when the moveable part is at a rest position.

[0080] The at least one attachment formation may extend in a direction parallel to the movement axis, e.g. coaxially with the movement axis. For example, the at least one attachment formation may extend into an axial face of the moveable part (e.g. a tapped hole) or may extend from the axial face of the moveable part (e.g. a pin). Said axial face may be perpendicular to the movement axis.

[0081] The moveable part of the drive unit may have a first axial face which faces in the forward direction and a second axial face which faces in the rearward direction. The at least one attachment formation may extend into / from the first axial face and the second axial face.

[0082] The at least one attachment formation may extend from the first axial face in the forward direction and towards the first landing surface, and the at least one attachment formation may extend from the second axial face in the rearward direction and towards the second landing surface.

[0083] The at least one attachment formation may be pre-formed prior to attachment of the first suspension element and / or the second suspension element. The at least one attachment formation of the moveable part may have a first configuration prior to attaching the first suspension element and / or the second suspension element, and may have a second configuration when the first suspension element and / or the second suspension element are attached. The at least one attachment formation may extend in a direction parallel to the movement axis in either or both of the first configuration and the second configuration.

[0084] Changing the at least one attachment formation from the first configuration to the second configuration may include mechanically deforming the at least one attachment formation. For example, the at least one attachment formation may include a pin which is received into one of the suspension elements and is then flattened to attach said suspension element. The pin may extend in a direction along the movement axis prior to and also after being flattened.008861056

[0085] 10

[0086] The first suspension attachment formation and the second suspension attachment formation may be mechanically attached to the at least one attachment formation of the moveable part by at least one an attachment member. The at least one attachment member may include, for example, a bolt or a rivet. In some examples, the at least one attachment member may include a bolt and a nut.

[0087] The at least one attachment member may make a threaded connection. For example, the at least one attachment member may make a threaded connection with another attachment member, such as a bolt received into a nut. Alternatively, the at least one attachment member may make a threaded connection with the moveable part of the drive unit, such as a bolt received into a tapped hole. More particularly, the at least one attachment formation may include a tapped hole, and the at least one attachment member may include a threaded member which makes a threaded connection with the tapped hole.

[0088] The first suspension attachment formation and the second suspension attachment formation may be jointly attached by one attachment member, or the first suspension attachment formation and the second suspension attachment formation may each be attached by a respective attachment member. That is to say, the first suspension attachment formation may be attached to the at least one attachment formation by a first attachment member, and the second suspension attachment formation may be attached to the at least one attachment formation by a second attachment member.

[0089] In some examples, there may be provided a plurality of attachment formations on the moveable part of the drive unit, and a plurality of attachment members. For example, the first suspension attachment formation may be attached to a first attachment formation by a first attachment member, and the second suspension attachment formation may be attached a second attachment formation by a second attachment member.

[0090] The drive unit may include a permanent magnet to generate magnetic flux and one or more flux guides (including the aforementioned tubular yoke) to guide the magnetic flux across an airgap, e.g. in a direction perpendicular to the movement axis. More particularly, the moveable part of the drive unit may include the permanent magnet and at least one flux guide. For example, the moveable part may include a first flux guide, a second flux guide and the permanent magnet arranged between the first flux guide and the second flux guide.

[0091] The permanent magnet may have any suitable shape, such as a cylindrical shape or an annular shape. The first flux guide and the second flux guide may have any suitable shape, such as a cylindrical shape or an annular shape. In some examples, the first flux guide and the second flux guide may be (flat) washers or shoulder washers with a protruding shoulder.

[0092] The drive unit includes the aforementioned tubular yoke.

[0093] The tubular yoke may extend around the movement axis.

[0094] The first end and the second end of the tubular yoke may be opposite ends. The first end and the second end may delimit an axial extent of the tubular yoke along the movement axis.008861056

[0095] 11

[0096] A first air gap may be formed between the first flux guide and the tubular yoke, and a second air gap may be formed between the second flux guide and the tubular yoke. The first air gap and the second air gap may each have an annular shape.

[0097] The first suspension attachment formation may be attached to a first attachment formation of the first flux guide and the second suspension attachment formation may be attached to a second attachment formation of the second flux guide. For example, the first suspension attachment formation may be attached to the hole in a first washer (or shoulder washer), and the second suspension attachment formation may be attached to the hole in the second washer (or shoulder washer), e.g. via the at least one attachment member. Particularly where a shoulder washer is used, the hole may be tapped.

[0098] In some examples, the first attachment formation may extend in the forward direction and the second attachment formation extend in the rearward direction. For example, a shoulder portion of a first shoulder washer may extend in the forward direction, and a shoulder portion of a second shoulder washer may extend in the rearward direction.

[0099] The stationary part of the drive unit may include a voice coil. The voice coil may be mounted within the tubular yoke. In some examples, the voice coil may be in contact with the tubular yoke. In other examples, there may be an annular clearance space between the voice coil and the tubular yoke (i.e. the annular clearance extends around the voice coil, and the tubular yoke extends around the annular clearance space.

[0100] The voice coil may extend around the movement axis.

[0101] The voice coil may be part of the stationary part of the drive unit and may extend around the moveable part of the drive unit.

[0102] The voice coil may include voice coil windings arranged on a voice coil former. The voice coil former may have a generally tubular shape on which the voice coil windings may be arranged between the first end and the second end of the voice coil.

[0103] A forward end of the voice coil former may be radially constrained by a first axis-facing inner surface of the forward frame portion and a rearward end of the voice coil former may be radially constrained by a second axis-facing inner surface of the rearward frame portion to thereby align the voice coil with respect to the movement axis.

[0104] The voice coil windings may be located in the air gap defined by the permanent magnet and the one or more flux guides when the moveable part is at the rest position. Where the voice coil windings are arranged into the first set of windings and the second set of windings, the first set of windings may be located in the first air gap and the second set of windings may be located in the second air gap when the moveable part is at the rest position.

[0105] The forward frame portion may be shaped to define a first annular surface which faces towards the rearward frame portion and extends around the movement axis. The rearward frame portion may be008861056

[0106] 12

[0107] shaped to define a second annular surface which faces towards the forward frame portion and extends around the movement axis.

[0108] The voice coil windings may be axially constrained by the first annular surface and the second annular surface.

[0109] The voice coil windings may be attached to the first frame portion and the second frame portion. For example, voice coil windings may be attached using adhesive. Adhesive may be added to the first annular surface to attach the voice coil windings to the first frame portion, and adhesive may be added to the second annular surface to attach the voice coil windings to the second frame portion.

[0110] The voice coil windings of the voice coil may be arranged to provide a first set of windings and, spaced therefrom, a second set of windings. The first set of windings and the second set of windings may be spaced apart as measured along the movement axis.

[0111] The first set of windings and the second set of windings may be formed from a single continuous wire. Each of the first set of windings and the second set of windings may have an uneven number of winding layers.

[0112] The voice coil may be electrically connected to a signal source at the first end of the voice coil and may be electrically connected to the signal source at the second end of the voice coil.

[0113] The drive unit may define a force factor BL, where B is the magnetic flux density permeating the voice coil in the air gap and L is the total length of windings of the voice coil in the air gap. The force factor BL is a known measure to quantify the strength of the magnetic interaction between the magnet unit and the voice coil.

[0114] The magnetic flux density B may have a value which is between 1% and 30% of the value of the total length of windings L. Optionally B is between 2% and 10% of L.

[0115] The magnetic flux B in the air gap may have a magnitude such that the resulting magnetic attraction between the stationary part and the moveable part causes a radial static deflection of the moveable part relative to the movement axis of no more than 0.1 millimetres.

[0116] The tubular yoke may be attached to first frame portion and the second frame portion. For example, the tubular yoke may be attached using adhesive. Adhesive may be provided in the first channel to attach the tubular yoke and the first frame portion, and adhesive may be provided in the second channel to attach the tubular yoke and the second frame portion.

[0117] The forward frame portion may have a first end face which faces away from the tubular yoke and the rearward frame portion may have a second end face which faces away from the tubular yoke.

[0118] A central passage may extend between the first end face and the second end face. In particular, the central passage may extend from the end face and to the end face. That is to say, the central passage may extend between a first opening in the first end face and a second opening in the second end face. The moveable part may be moveable in the central passage along the movement axis.008861056

[0119] 13

[0120] The first landing surface may be recessed into the first end face and the first suspension element may be attached to the first landing surface. A forward clearance space may be formed between the first end face and the first landing surface. The moveable part may be moveable in the forward clearance space. The second landing surface may be recessed into the second end face and the second suspension element may be attached to the second landing surface. A rearward clearance space may be formed between the second end face and the second landing surface. The moveable part may be moveable in the rearward clearance space.

[0121] The chassis may include a first closure member attached to the forward frame portion to close the first opening and may include a second closure member attached to the rearward frame portion to close the second opening.

[0122] The chassis may be arranged to provide an airtight seal around the central passage.

[0123] The first suspension element and the second suspension element may each include a plurality of bridge arms which extend towards the suspension attachment formation.

[0124] Each suspension element may include an outer portion and an inner portion. The inner portion may be located at the movement axis and may include the suspension attachment formation. The outer portion may extend around the movement axis and may be attached to the chassis. The bridge arms may extend between the outer portion and the inner portion.

[0125] The bridge arms may extend towards the suspension attachment formation of the respective suspension element and may extend around the movement axis. That is to say, the bridge arms may curve around the movement axis. In some examples, the bridge arms may extend around the movement axis for less than one full revolution. In some examples, the bridge arms may extend around the movement axis for one full revolution or more than one full revolution.

[0126] Any suitable number of bridge arms may be provided. For example, each suspension element may have at most three bridge arms. In some examples, each suspension element has (exactly) two bridge arms. By providing the suspension element with a small number of bridge arms, especially two bridge arms, the suspension element may better withstand attachment to the moveable part, particularly where such attachment is effected mechanically. For example, where attachment is by means of an attachment member, such as a bolt, the process of securing the attachment member could put strain on the suspension element which could cause damage to a suspension element with a large number of bridge arms. A suspension element with a small number of bridge arms may generally be better suited for withstanding such manipulation.

[0127] The suspension elements may be formed by stamping to provide the bridge arms and the suspension attachment formation. The suspension attachment formation may be an aperture through the respective suspension element.

[0128] Each suspension element may be formed from metal. In some examples, each suspension element may be formed from a single piece of metal, e.g. a stamped piece of sheet metal.008861056

[0129] 14

[0130] The terms “stationary” and “moveable” are relative terms and in principle dependent on the particular frame of reference. In this context, the terms “stationary” and “moveable” are intended to refer to a conventional frame of reference according to which the chassis is considered to be stationary, and from which the moveable part of the drive unit is suspended via the suspension elements. As such the moveable part of the drive unit, and any parts which in use move with the moveable part, are referred to as moveable, while other parts of the transducer are referred to as stationary, e.g. the stationary part of the drive unit. Those parts of the transducer which are moveable, i.e. the moveable part of the drive unit and parts that in use move with the moveable part, may collectively be referred to as the moveable part. Herein, a reference to the moveable part of the drive unit being at the rest position may be taken to correspond to a state in which the drive unit is not energised (e.g. an electric current is not being supplied to the voice coil of the drive unit) with the moveable part of the drive unit having been given time to reach a state of rest.

[0131] There may be provided a road vehicle including the electromechanical transducer as described above in relation to the second aspect. The road vehicle may include a seat containing a seat foam, and the electromechanical transducer may be mounted to a recess in the seat foam.

[0132] Any feature described in relation to the first aspect is applicable also to the electromechanical transducer of the second aspect, and vice versa.

[0133] According to a third aspect, there is provided an electromechanical transducer, including: a chassis; a drive unit which includes a stationary part, which forms part of the chassis, and a moveable part which is moveable relative to the stationary part, wherein the drive unit is operable to cause the moveable part to move relative to the stationary part along a movement axis in a forward direction and in a rearward direction; a first suspension element and a second suspension element which are respectively configured to deflect along the movement axis, wherein the first suspension element includes a first suspension attachment surface which is secured to the chassis and the second suspension element includes a second suspension attachment surface which is secured to the chassis, and wherein the first suspension element includes a first suspension attachment formation attached to the moveable part and the second suspension element includes a second suspension attachment formation attached to the moveable part; wherein the first suspension attachment formation and the second suspension attachment formation are attached to at least one attachment formation of the moveable part.

[0134] The electromechanical transducer according to the third aspect has a configuration according to which the first suspension element and the second suspension element are attached to the at least one attachment formation of the moveable part of the drive unit. This configuration may provide for improved attachment of the suspension elements to the moveable part. Utilising the at least one attachment formation on the moveable part may improve alignment of the suspension elements relative to the moveable part, since the attachment formation on the moveable part may be used when attaching the suspension elements. Additionally or alternatively, utilising the at least one attachment formation may improve ease of assembly, since the attachment formation may be used when attaching the suspension elements to the moveable part of the drive unit. By contrast, traditional electromechanical transducers008861056

[0135] 15

[0136] may not have an attachment formation but instead may utilise adhesive for attachment of the suspension elements to the moveable part, which may make alignment of the suspension elements relative to the moveable part more difficult.

[0137] The at least one attachment formation may extend in a direction parallel to the movement axis, e.g. coaxially with the movement axis. For example, the at least one attachment formation may extend into an axial face of the moveable part (e.g. a tapped hole) or may extend from the axial face of the moveable part (e.g. a pin). Said axial face may be perpendicular to the movement axis.

[0138] The moveable part of the drive unit may have a first axial face which faces in the forward direction and a second axial face which faces in the rearward direction. The at least one attachment formation may extend into / from the first axial face and the second axial face.

[0139] The at least one attachment formation may extend from the first axial face in the forward direction and towards the first suspension attachment surface, and the at least one attachment formation may extend from the second axial face in the rearward direction and towards the second suspension attachment surface.

[0140] The at least one attachment formation may be pre-formed prior to attachment of the first suspension element and / or the second suspension element. The at least one attachment formation of the moveable part may have a first configuration prior to attaching the first suspension element and / or the second suspension element, and may have a second configuration when the first suspension element and / or the second suspension element are attached. The at least one attachment formation may extend in a direction parallel to the movement axis in either or both of the first configuration and the second configuration.

[0141] Changing the at least one attachment formation from the first configuration to the second configuration may include mechanically deforming the at least one attachment formation. For example, the at least one attachment formation may include a pin which is received into one of the suspension elements and is then flattened to attach said suspension element. The pin may extend in a direction along the movement axis prior to and also after being flattened.

[0142] An axial separation of the first suspension attachment surface and the second suspension attachment surface, as measured along the movement axis, may be greater than an axial separation of the first suspension attachment formation and the second suspension attachment formation, as measured along the movement axis, such that the suspension elements are deflected along the movement axis by their attachment to the moveable part when the moveable part is at a rest position.

[0143] Having the axial separation of the first suspension attachment surface and the second suspension attachment surface, as measured along the movement axis, be greater than an axial separation of the first suspension attachment formation and the second suspension attachment formation, as measured along the movement axis, such that the suspension elements are deflected along the movement axis by their attachment to the moveable part when the moveable part is at a rest position, helps reduce the size of the space needed to accommodate the electromechanical transducer, since the difference between the008861056

[0144] 16

[0145] axial separation of the suspension attachment surfaces and the axial separation of the suspension attachment formations effectively define (at least part of) a clearance space around the moveable part, that the moveable part moves into when the electromechanical transducer is in use. By contrast, traditional electromechanical transducers may have a configuration according to which the moveable part, once moved from the rest position, already has cleared the first suspension attachment surface (or the second suspension attachment surface) such that the electromechanical transducer needs to be accommodated by giving the moveable part a comparatively large clearance space beyond the first suspension attachment surface (and also beyond the second suspension attachment surface) since motion of the moveable part in the forward direction takes place entirely beyond the first suspension attachment surface (and also beyond the second suspension attachment surface for motion in the rearward direction).

[0146] An axial separation of the first suspension attachment surface and the second suspension attachment surface, as measured along the movement axis, may be equal to an axial separation of the first suspension attachment formation and the second suspension attachment formation, as measured along the movement axis.

[0147] The first suspension attachment formation and the second suspension attachment formation may be mechanically attached to the at least one attachment formation of the moveable part by at least one attachment member. The at least one attachment member may include, for example, a bolt or a rivet. In some examples, the at least one attachment member may include a bolt and a nut.

[0148] The at least one attachment member may make a threaded connection. For example, the at least one attachment member may make a threaded connection with another attachment member, such as a bolt received into a nut. Alternatively, the at least one attachment member may make a threaded connection with the moveable part of the drive unit, such as a bolt received into a tapped hole. More particularly, the at least one attachment formation may include a tapped hole, and the at least one attachment member may include a threaded member which makes a threaded connection with the tapped hole.

[0149] The first suspension attachment formation and the second suspension attachment formation may be jointly attached by one attachment member, or the first suspension attachment formation and the second suspension attachment formation may each be attached by a respective attachment member. That is to say, the first suspension attachment formation may be attached to the at least one attachment formation by a first attachment member, and the second suspension attachment formation may be attached to the at least one attachment formation by a second attachment member.

[0150] In some examples, there may be provided a plurality of attachment formations on the moveable part of the drive unit, and a plurality of attachment members. For example, the first suspension attachment formation may be attached to a first attachment formation by a first attachment member, and the second suspension attachment formation may be attached a second attachment formation by a second attachment member.008861056

[0151] 17

[0152] The drive unit may include a permanent magnet to generate magnetic flux and one or more flux guides to guide the magnetic flux across an air gap, e.g. in a direction perpendicular to the movement axis. More particularly, the moveable part of the drive unit may include the permanent magnet and at least one flux guide. For example, the moveable part may include a first flux guide, a second flux guide and the permanent magnet arranged between the first flux guide and the second flux guide.

[0153] The permanent magnet may have any suitable shape, such as a cylindrical shape or an annular shape. The first flux guide and the second flux guide may have any suitable shape, such as a cylindrical shape or an annular shape. In some examples, the first flux guide and the second flux guide may be (flat) washers or shoulder washers with a protruding shoulder.

[0154] The drive unit may further include a tubular yoke. More particularly, the stationary part of the drive unit may include the tubular yoke, which may form part of the chassis.

[0155] The tubular yoke may extend around the movement axis.

[0156] The tubular yoke may have a first end and, opposite thereto, a second end. The first end and the second end may delimit an axial extent of the tubular yoke along the movement axis. The first end may be a first axial end and the second end may be a second axial end.

[0157] A first air gap may be formed between the first flux guide and the tubular yoke, and a second air gap may be formed between the second flux guide and the tubular yoke. The first air gap and the second air gap may each have an annular shape.

[0158] The first suspension attachment formation may be attached to a first attachment formation of the first flux guide and the second suspension attachment formation may be attached to a second attachment formation of the second flux guide. For example, the first suspension attachment formation may be attached to the hole in a first washer (or shoulder washer), and the second suspension attachment formation may be attached to the hole in the second washer (or shoulder washer), e.g. via the at least one attachment member. Particularly where a shoulder washer is used, the hole may be tapped.

[0159] In some examples, the first attachment formation may extend in the forward direction (e.g., towards the first suspension attachment surface) and the second attachment formation may extend in the rearward direction (e.g., towards the second suspension attachment surface). For example, a shoulder portion of a first shoulder washer may extend in the forward direction, and a shoulder portion of a second shoulder washer may extend in the rearward direction.

[0160] The stationary part of the drive unit may include a voice coil. The voice coil may be mounted within the tubular yoke. In some examples, the voice coil may be in contact with the tubular yoke. In other examples, there may be an annular clearance space between the voice coil and the tubular yoke (i.e. the annular clearance extends around the voice coil, and the tubular yoke extends around the annular clearance space.

[0161] The voice coil may extend around the movement axis.008861056

[0162] 18

[0163] The voice coil may be part of the stationary part of the drive unit and may extend around the moveable part of the drive unit.

[0164] The voice coil may include voice coil windings arranged on a voice coil former. The voice coil former may have a generally tubular shape on which the voice coil windings may be arranged between a first end and a second end of the voice coil. The first end and the second end of the voice coil may delimit an axial extent of the voice coil. The first end may be a first axial end and the second end may be a second axial end.

[0165] The voice coil windings may be located in the air gap defined by the permanent magnet and the one or more flux guides when the moveable part is at the rest position. Where the voice coil windings are arranged into the first set of windings and the second set of windings, the first set of windings may be located in the first air gap and the second set of windings may be located in the second air gap when the moveable part is at the rest position.

[0166] The voice coil windings of the voice coil may be arranged to provide a first set of windings and, spaced therefrom, a second set of windings. The first set of windings and the second set of windings may be spaced apart as measured along the movement axis.

[0167] The first set of windings and the second set of windings may be formed from a single continuous wire. Each of the first set of windings and the second set of windings may have an uneven number of winding layers.

[0168] The voice coil may be electrically connected to a signal source at the first end of the voice coil and may be electrically connected to the signal source at the second end of the voice coil.

[0169] The voice coil former may have a first end and a second end. The first end and the second end of the voice coil former may delimit an axial extent of the voice coil former. The first end of the voice coil former may be a first axial end and the second end of the voice coil former may be a second axial end.

[0170] The first end of the voice coil former may abut the first suspension element, and / or the second end of the voice coil former may abut the second suspension element.

[0171] The inventors have found that the height of the voice coil former may be controllable / manufacturable within a smaller tolerance range than the height of the voice coil windings. As such, by having the first end of the voice coil former abut the first suspension element and / or the second end of the voice coil former abut the second suspension element, the voice coil may be more accurately positioned within the electromechanical transducer. Alternatively or additionally, the electromechanical transducer may be made easier to manufacture, as a constraining process of the voice coil may be controlled within tighter tolerances.

[0172] Where the first end of the voice coil former abuts the first suspension element, the first end of the voice coil former may be secured to the first suspension element using adhesive. Likewise, where the second end of the voice coil former abuts the second suspension element, the second end of the voice coil former may be secured to the second suspension element using adhesive.008861056

[0173] 19

[0174] The chassis may include a first landing surface that the first suspension attachment surface is secured to, and / or may include a second landing surface that the second suspension attachment surface is secured to.

[0175] The first suspension element may be secured to the first landing surface using adhesive. Where the first end of the voice coil former abuts the first suspension element, the first suspension element may be secured to both the first landing surface and the voice coil former using adhesive.

[0176] The second suspension element may be secured to the second landing surface using adhesive. Where the second end of the voice coil former abuts the second suspension element, the second suspension element may be secured to both the second landing surface and the voice coil former using adhesive. An axial separation of the first end of the voice coil former and the second end of the voice coil former, along the movement axis, may be greater than an axial separation of the first landing surface and the second landing surface, along the movement axis.

[0177] The axial separation of the first end and the second end of the voice coil former may correspond to the axial extent of the voice coil former.

[0178] The first end of the voice coil former, the first suspension attachment surface, and the first landing surface may be secured together by (e.g., a first bead of) adhesive; and / or the second end of the voice coil former, the second suspension attachment surface, and the second landing surface may be secured together by (e.g., a second bead of) adhesive. This may increase the strength of the connection between the voice coil, the suspension elements, and the chassis.

[0179] A forward clearance space may be formed between a forward end of the voice coil windings and the chassis. The forward clearance space may be located forwards of the voice coil windings, in the forward direction.

[0180] A rearward clearance space may be formed between a rearward end of the voice coil windings and the chassis. The rearward clearance space may be located rearwards of the voice coil windings, in the rearward direction.

[0181] Where multiple sets of voice coil windings are provided, the forward end of the voice coil windings may be defined by the forward-most set of voice coil windings and, similarly, the rearward end of the voice coil windings may be defined by the rearward-most set of voice coil windings.

[0182] The drive unit may define a force factor BL, where B is the magnetic flux density permeating the voice coil in the air gap and L is the total length of windings of the voice coil in the air gap. The force factor BL is a known measure to quantify the strength of the magnetic interaction between the magnet unit and the voice coil.

[0183] The magnetic flux density B may have a value which is between 1% and 30% of the value of the total length of windings L. Optionally B is between 2% and 10% of L.008861056

[0184] 20

[0185] The magnetic flux B in the air gap may have a magnitude such that the resulting magnetic attraction between the stationary part and the moveable part causes a radial static deflection of the moveable part relative to the movement axis of no more than 0.1 millimetres.

[0186] The terms “stationary” and “moveable” are relative terms and in principle dependent on the particular frame of reference. In this context, the terms “stationary” and “moveable” are intended to refer to a conventional frame of reference according to which the chassis is considered to be stationary, and from which the moveable part of the drive unit is suspended via the suspension elements. As such the moveable part of the drive unit, and any parts which in use move with the moveable part, are referred to as moveable, while other parts of the transducer are referred to as stationary, e.g. the stationary part of the drive unit. Those parts of the transducer which are moveable, i.e. the moveable part of the drive unit and parts that in use move with the moveable part, may collectively be referred to as the moveable part. Herein, a reference to the moveable part of the drive unit being at the rest position may be taken to correspond to a state in which the drive unit is not energised (e.g. an electric current is not being supplied to the voice coil of the drive unit) with the moveable part of the drive unit having been given time to reach a state of rest.

[0187] The first suspension element and the second suspension element may each include a plurality of bridge arms which extend towards the suspension attachment formation.

[0188] Each suspension element may include an outer portion and an inner portion. The inner portion may be located at the movement axis and may include the suspension attachment formation. The outer portion may extend around the movement axis and may be attached to the chassis. The bridge arms may extend between the outer portion and the inner portion.

[0189] The bridge arms may extend towards the suspension attachment formation of the respective suspension element and may extend around the movement axis. That is to say, the bridge arms may curve around the movement axis. In some examples, the bridge arms may extend around the movement axis for less than one full revolution. In some examples, the bridge arms may extend around the movement axis for one full revolution or more than one full revolution.

[0190] Any suitable number of bridge arms may be provided. For example, each suspension element may have at most three bridge arms. In some examples, each suspension element has (exactly) two bridge arms. By providing the suspension element with a small number of bridge arms, especially two bridge arms, the suspension element may better withstand attachment to the moveable part, particularly where such attachment is effected mechanically. For example, where attachment is by means of an attachment member, such as a bolt, the process of securing the attachment member could put strain on the suspension element which could cause damage to a suspension element with a large number of bridge arms. A suspension element with a small number of bridge arms may generally be better suited for withstanding such manipulation.008861056

[0191] 21

[0192] The suspension elements may be formed by stamping to provide the bridge arms and the suspension attachment formation. The suspension attachment formation may be an aperture through the respective suspension element.

[0193] Each suspension element may be formed from metal. In some examples, each suspension element may be formed from a single piece of metal, e.g. a stamped piece of sheet metal.

[0194] The electromechanical transducer may further include: a forward frame portion, which forms part of the chassis, wherein the moveable part of the drive unit is suspended from the forward frame portion by the first suspension element; and a rearward frame portion, which forms part of the chassis, wherein the moveable part of the drive unit is suspended from the rearward frame portion by the second suspension element.

[0195] The forward frame portion may be shaped to define a first channel which faces towards the rearward frame portion and extends around the movement axis. The rearward frame portion may be shaped to define a second channel which faces towards the forward frame portion and extends around the movement axis. The electromechanical transducer may further comprise the tubular yoke. The tubular yoke may form part of the chassis The tubular yoke may have: a first end received into the first channel of the forward frame portion to thereby align the first suspension element relative to the tubular yoke, and a second end received into the second channel to thereby align the second suspension element relative to the tubular yoke.

[0196] The inventors have found that having the tubular yoke be received in the channels defined by the frame portions may help reduce dimensions and / or weight since the frame portions are connected by the tubular yoke and so need not be connected by a further frame portion. By contrast, traditional electromechanical transducers may have a “full” frame, thereby potentially increasing material usage, dimensions and weight.

[0197] Further, the inventors have found that having the tubular yoke be received in the channels defined by the frame portions so as to align the suspension elements relative to the tubular yoke may improve alignment of the suspension elements relative to the chassis. Additionally or alternatively, ease of assembly may be improved by reducing the need for careful alignment of the tubular yoke relative to the suspension elements since these are aligned relative to the tubular yoke by the frame portions. By contrast, traditional electromechanical transducers may require careful assembly using jigs to achieve alignment to a satisfactory degree.

[0198] The tubular yoke may be attached to the first frame portion and the second frame portion. For example, the tubular yoke may be attached using adhesive. Adhesive may be provided in the first channel to attach the tubular yoke and the first frame portion, and adhesive may be provided in the second channel to attach the tubular yoke and the second frame portion.

[0199] The tubular yoke may be insert moulded into one of the rearward frame portion and the forward frame portion. Insert moulding refers to a manufacturing process where a first component (e.g., the tubular yoke), i.e., the "insert", is placed into a mould before molten plastic is injected around it to create a single,008861056

[0200] 22

[0201] finished part (e.g., the forward or rearward frame portion with the tubular yoke inserted into a channel thereof).

[0202] The first end of the tubular yoke may form an interference fit with the first channel, and / or the second end of the tubular yoke may form an interference fit with the second channel.

[0203] By forming an interference fit with the tubular yoke, the frame may mechanically retain the tubular yoke in the first channel and / or the second channel.

[0204] Each of the first channel and the second channel may include one or more press ribs. The press ribs may be configured to press against the tubular yoke received into the respective channel. The press ribs may be configured to at least partially cause the interference fit. For example, the first channel may include one or more press ribs configured to at least partially cause the interference fit with the first end of the tubular yoke. Additionally or alternatively, the second channel may include one or more press ribs configured to at least partially cause the interference fit with the second end of the tubular yoke.

[0205] A forward clearance space may be formed between the first end of the tubular yoke and the chassis. The forward clearance space may be located forwards of the tubular yoke, in the forward direction.

[0206] A rearward clearance space may be formed between the second end of the tubular yoke and the chassis. The rearward clearance space may be located rearwards of the tubular yoke, in the rearward direction. The clearance space may be contained within the respective channel into which the end of the tubular yoke is received.

[0207] The forward frame portion and the rearward frame portion may be directly secured to one another via: one or more mechanical fastenings; ultrasonic welding; and / or an adhesive.

[0208] When the forward frame portion and the rearward frame portion are directly secured to one another via at least the adhesive, the rearward frame portion may include a first protruding portion that is arranged such that a gutter (e.g., the gutter described above) is created between the first protruding portion and the tubular yoke. The forward frame portion may include a second protruding portion that is arranged to protrude into the gutter. In alternative examples, the above arrangement of the first and second protruding portions may be reversed (e.g., the first protruding portion may be on the forward frame portion, and the second protruding portion may be on the rearward protruding portion). The gutter may be at least partly filled by the adhesive to secure the first protruding portion and second protruding portion together.

[0209] The chassis may further comprise an overflow passage. The overflow passage may be connected to the gutter. The overflow passage may extend alongside the tubular yoke. Adhesive may extend from the gutter into the overflow passage to at least partially (or fully) fill the overflow passage.

[0210] The inventors have found that having an overflow passage that connects to the gutter may prevent adhesive from spilling from the gutter when the forward frame portion and the rearward frame portion are secured together during construction (e.g., decreasing the size of the gutter and so reducing the space for the adhesive). Rather, the adhesive can instead flow into the overflow passage. The adhesive in the008861056

[0211] 23

[0212] overflow passage may also secure the tubular yoke to the chassis (e.g., the forward frame portion and / or the rearward frame portion).

[0213] The electromechanical transducer may include an interior space that is bounded by the chassis and the first and second suspension elements.

[0214] The electromechanical transducer may further comprise a lead wire, wherein the lead wire extends from an interior space of the electromechanical transducer to an exterior space outside of the electromechanical transducer.

[0215] An outer edge of the first suspension element or the second suspension element may include a notch through which the lead wire extends from the interior space to the exterior space.

[0216] The inventors have found that having the lead wire extend through a notch in the suspension element may allow the lead wire to be better isolated from the suspension element. This may be particularly desirable where the suspension element is electrically conductive (for example where the suspension element is made from metal), preventing short circuiting by spacing the lead wire from the suspension element.

[0217] The electromechanical transducer may further comprise a groove.

[0218] The groove may be formed between a pair of spacer elements. The pair of spacer elements may be arranged between the lead wire and the first or second suspension element. The spacer elements may be arranged in the notch in the first suspension element or in the second suspension element. In some examples, spacer elements may be arranged in both notches.

[0219] The groove may extend through the notch in the first suspension element or in the second suspension element.

[0220] The groove may extend from the interior space to the exterior space.

[0221] The lead wire may extend in the groove.

[0222] The electromechanical transducer may further comprise one or more mechanical fasteners for fastening the chassis to another structure. The chassis may include the one or more mechanical fasteners for fastening the chassis to another structure. The mechanical fasteners for fastening the chassis to another structure may be integrated mechanical fasteners. For example, the chassis may include one or more integrated mechanical fasteners for fastening the chassis to another structure. The one or more integrated fasteners may include one or more clips. The one or more integrated mechanical fasteners may be on an external surface of the electromechanical transducer. The one or more integrated mechanical fasteners may be in the exterior space described above.

[0223] The one or more mechanical fasteners may include one or more integrated electrical terminals.

[0224] The forward frame portion may be shaped to define a first annular surface which faces towards the rearward frame portion and extends around the movement axis. The rearward frame portion may be shaped to define a second annular surface which faces towards the forward frame portion and extends008861056

[0225] 24

[0226] around the movement axis. The voice coil windings may be axially constrained by the first annular surface and the second annular surface.

[0227] The voice coil windings may be attached to the first frame portion and the second frame portion. For example, voice coil windings may be attached using adhesive. Adhesive may be added to the first annular surface to attach the voice coil windings to the first frame portion, and adhesive may be added to the second annular surface to attach the voice coil windings to the second frame portion.

[0228] The forward frame portion may have a first end face which faces away from the tubular yoke and the rearward frame portion may have a second end face which faces away from the tubular yoke.

[0229] A central passage may extend between the first end face and the second end face. In particular, the central passage may extend from the end face and to the end face. That is to say, the central passage may extend between a first opening in the first end face and a second opening in the second end face. The moveable part may be moveable in the central passage along the movement axis.

[0230] The first landing surface may be recessed into the first end face and the first suspension element may be attached to the first landing surface. A forward clearance space may be formed between the first end face and the first landing surface. The moveable part may be moveable in the forward clearance space.

[0231] The second landing surface may be recessed into the second end face and the second suspension element may be attached to the second landing surface. A rearward clearance space may be formed between the second end face and the second landing surface. The moveable part may be moveable in the rearward clearance space.

[0232] The chassis may include a first closure member attached to the forward frame portion to close the first opening and may include a second closure member attached to the rearward frame portion to close the second opening.

[0233] The chassis may be arranged to provide an airtight seal around the central passage.

[0234] Any feature described above in relation to the second aspect is applicable also to the electromechanical transducer of the third aspect.

[0235] There may be provided a road vehicle including the electromechanical transducer as described above in relation to the third aspect. The road vehicle may include a seat containing a seat foam, and the electromechanical transducer may be mounted to a recess in the seat foam.

[0236] According to a fourth aspect, there is provided a method for assembly of an electromechanical transducer, the method including: providing a tubular yoke, which forms part of a drive unit, having a first end and a second end; receiving the first end of the tubular yoke into a first annular channel of a forward frame portion; providing a moveable part of the drive unit; attaching a first suspension element to the moveable part; receiving the moveable part into the tubular yoke; attaching the first suspension element to the forward frame portion to thereby align the first suspension element relative to the tubular yoke and wherein the first suspension element is configured to deflect along a movement axis; receiving the second end of the tubular yoke into a second annular channel of a rearward frame portion; wherein the008861056

[0237] 25

[0238] first annular channel faces towards the rearward frame portion and the second annular channel faces towards the forward frame portion; attaching a second suspension element to the rearward frame portion to thereby align the second suspension element relative to the tubular yoke and wherein the second suspension element is configured to deflect along the movement axis; attaching the second suspension element to the moveable part; wherein the drive unit is operable to cause the moveable part to move along the movement axis relative to the stationary part in a forward direction and a rearward direction. The method according to the fourth aspect does not define an ordering of the steps of the method, other than were explicitly required by the claim (e.g. the step of providing a tubular yoke preceding any other steps involving the tubular yoke). For example, the step of providing the tubular yoke may or may not be carried out prior to providing the moveable part.

[0239] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0240] Summary of the Figures

[0241] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0242] Figure 1 is a perspective view of an electromechanical transducer.

[0243] Figure 2 is a sectional view of the transducer.

[0244] Figure 3 is a perspective view of a voice coil of the transducer.

[0245] Figure 4 is a sectional view of the transducer with some components not shown.

[0246] Figure 5 is another sectional view of the transducer, wherein suspension elements of the transducer are not attached.

[0247] Figure 6 is another sectional view of the transducer, where the suspension elements are attached. Figure 7 is another sectional view of the transducer, showing also closure members attached to the transducer.

[0248] Figure 8 shows a suspension element.

[0249] Figure 9 shows another suspension element

[0250] Figure 10 is a graph illustrating radial stiffness dependent on pre-stressing of the suspension element.

[0251] Figure 11 is a graph illustrating axial stiffness dependent on pre-stressing of the suspension element.

[0252] Figure 12 is a graph illustrating axial magnetic stiffness dependent on yoke dimensions.

[0253] Figure 13 is a plan view illustrating a radial shift of a moveable part of transducer.

[0254] Figure 14 is a graph illustrating static radial deflection as a function of air gap size.

[0255] Figure 15 is an illustration of magnetic flux generated by a first drive unit.008861056

[0256] 26

[0257] Figure 16 is an illustration of magnetic flux generated by a second drive unit.

[0258] Figure 17 is a graph illustrating force factor BL as a function of displacement.

[0259] Figure 18 illustrates a method of assembly of the transducer.

[0260] Figure 19 shows a road vehicle including an automotive seat.

[0261] Figure 20 shows the automotive seat with the transducer.

[0262] Figure 21 shows the automotive seat with the transducer.

[0263] Figure 22 shows a conventional automotive seat with a transducer.

[0264] Figure 23 is a perspective view of a second transducer.

[0265] Figure 24 is a sectional view of the second transducer.

[0266] Figure 25 is a sectional view of a third transducer.

[0267] Figure 26 is another sectional view of the third transducer.

[0268] Figure 27 is a sectional view of the fourth transducer.

[0269] Figure 28 is a sectional view of a fifth transducer.

[0270] Figure 29 is a perspective view of the transducer of Figure 28.

[0271] Figure 30 is a second perspective view of the transducer of Figure 28.

[0272] Figure 31 is a sectional view of a sixth transducer.

[0273] Figure 32 is a sectional view of a transducer illustrating a possible electrical short-circuiting path.

[0274] Detailed Description of the Invention

[0275] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0276] Electromechanical transducers (which may also be referred to as vibration actuators) are devices apt at converting an electrical signal into vibration that can be transferred to an application or to a part of the human body, e.g. via a structural medium, to achieve a number of possible objectives. For instance, in the automotive context for instance, it might be desirable to enhance the low frequency content of a music signal by transferring vibrations to the body of the listener, with the aim of enriching the listening experience with additional vibration directly sensed at the body. In a car, vibrations might be transferred via the seat or the car structure to one or more car passengers to deliver wellness content, or any kind of haptic feedback to enhance alertness and driving experience.

[0277] The electromechanical transducers described herein may be particularly suitable for installation in an automotive seat. A challenge for the designer of an automotive seat is ensuring high transduction efficiency while keeping dimensions and weight low. Automotive-grade transducers on the market are008861056

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[0279] commonly of the electrodynamic type, consisting of a magnetic circuit based on a single voice coil and a traditional U-yoke based motor system (see, for example, PCT / EP2023 / 084674). These actuators may typically have a weight in excess of 60 grams, a diameter greater than 50 millimetres, and a height exceeding 18 millimetres. A desired resonance frequency for these devices may be in the range between 40 Hertz and 80 Hertz. The usual approach to achieve this resonance frequency may involve a moveable motor system assembly with a mass commonly between 50 grams and 100 grams, and a coil assembly that is meant to be coupled to the seat’s foam, usually via a plastic bracket. When the motor system vibrates, it generates an equal and opposite reaction force on the coil assembly, thus transferring vibrations to the seat via the plastic coupler. The choice for a relatively high moving mass is generally justified by the will of the designer to have maximum amount of vibration in the frequency range of interest, which may be from 30 Hertz to 500 Hertz and can be narrower (for example, 30 Hertz to 200 Hertz), depending on the specific needs.

[0280] The inventors observed that in the automotive industry there is a tendency to use large plastic modules, which suspended in foam via springs attached to chassis, to house multiple transducers as well as wire harness and other equipment. The inventors found that the plastic modules may be convenient means of attaching multiple components and form modules that can be carried across different vehicles, but may adversely affect coupling condition for the transducers. The transducers described herein may reduce the mass coupled to the transducers and allow for installation closer to the occupant of the automative seat, which may make the vibration transfer path more efficient. For example, a transducer installed directly in a recess in the foam of the automotive seat may benefit of a much higher efficiency, a sharper transient response and a higher frequency extension compared to a transducer installed in a plastic module. Additionally or alternatively, the transducers described below may be provided with reduced bottoming clearances as the total stroke may decrease when installed on a compliant and dampened load, compared to installation in a rigid and heavy environment, where the frame of the device can be considered effectively grounded.

[0281] If the coupling of the transducer to the automotive seat is by installation directly in the foam, the dimensions and moving mass of the transducer may be reduced maintaining desired performance. It may be convenient then to consider a motor system formed by a central assembly consisting in a stack of an upper washer, a magnet and a bottom washer, and an outer yoke (e.g. a highly magnetically permeable steel ring) on the periphery. Inside the outer yoke, a coil assembly may be fixed, consisting of two sets of sets of coil windings, in symmetrical arrangement and wound in opposite winding directions respect to each other. This kind of motor system may generally be known already and suffer from a number of disadvantages:

[0282] - The central stack (washer-magnet-washer) may be radially attracted by magnetic force to the outer yoke. This would not be the case if the central stack were exactly aligned on the movement axis, but this may not be possible in practice, e.g. due to manufacturing tolerances. For a given radial shift of the moveable part from the movement axis, a residual radial magnetic force may be exerted on the moveable part, pulling it towards the outer yoke. The radial magnetic force may increase as the moveable008861056

[0283] 28

[0284] part moves away from the movement axis. The residual radial magnetic force may cause a radial deflection of the suspension of the shaker. This radial deflection may be defined by Hooke’s law as: X = -F_rad / K_rad, where X is displacement (e.g. in millimetres), F_rad is the residual radial magnetic attraction force and K_rad is the combined radial stiffness of the two suspensions composing the suspension system of the transducer.

[0285] - The magnetic circuit may encounter an axial magnetic stiffness due to the reluctance force, which may bias the central stack towards the position of least reluctance. The reluctance force (or “magnetic stiffness”) may add to the mechanical stiffness of the suspensions, thus increasing the resonance frequency of the actuator, which might be undesirable.

[0286] Various proposed solutions to these disadvantages are known.

[0287] One known proposed solution is to rely on exclusively on magnetic stiffness (without any additional suspensions), having the central moveable part sliding axially along a tube made of low friction material, with addition of grease (see, for example, US5973422A). The inventors consider such an arrangement undesirable as the inventors believe that friction may result in unwanted noise and eventually in wear-out. Where additional suspensions are used, a common safety measure employed to prevent the moveable part from shifting radially is that of having a centre slug through the moveable part (e.g. a bearing arrangement), either with moveable part able to slide over the centre slug and the addition of compression springs, or with a fixed centre support to anchor the springs. The inventors consider this approach also undesirable, as it may result in possible wear-out and noise, as well as in an increase in part count and complexity of the design.

[0288] Another known proposed solution is to have the springs connected to a fixed centre holder, with the moveable part able to move axially (see, for example, Fig. 2 of US11341948B2; or EP3597314A1). The inventors also consider this approach undesirable, as implementation of a central holder increases part count and complexity in the design, also adding unwanted friction.

[0289] Another known proposed solution is to have the moveable part suspended on two metal suspensions with the addition of spacers, made of non-ferromagnetic material, which connect the top and bottom washers to the outer yoke. The inventors also consider this approach undesirable, resulting in an increase in component count and in an increase in total height of the actuator.

[0290] The examples of electromechanical transducers described below may solve at least some of the aforementioned limitations resulting from the general motor system design, and may furthermore have reduced dimensions, may have surprisingly high efficiency relative to the package, may be suitable to be used in an automotive environment and may be radially stable, while avoiding at least some of the disadvantageous found in the known proposed solutions (e.g. an increase in part count or unwanted friction).

[0291] Figures 1 and 2 show an electromechanical transducer 10 for transmitting vibrations to an application. The transducer 10 (or “actuator”) is configured to convert electrical signals into mechanical forces to generate vibrations. These vibrations may in use be passed to a user, e.g. passing music information to008861056

[0292] 29

[0293] the user through mechanical vibration on the skin of the user. An example application, described below with reference to Figures 19 to 21 , is an automotive seat.

[0294] The transducer 10 is generally cylindrical with a diameter in the range of 15 and 50 millimetres, optionally between 20 millimetres and 30 millimetres. The total height is preferably between 8 millimetres and 40 millimetres, optionally between 10 millimetres and 20 millimetres.

[0295] The transducer 10 includes a chassis 100. The chassis 100 houses the other components of transducer 10. As seen in Figure 1, the chassis 100 includes a forward frame portion 101 and a rearward frame portion 102.

[0296] The transducer 10 further includes a drive unit 120. The drive unit 120 includes a stationary part 130 which forms part of the chassis 100. The drive unit 120 further includes a moveable part 140 which is moveable relative to the stationary part 130. The drive unit 120 is operable, by supplying an electrical signal to the drive unit 120, to cause the stationary part 130 and the moveable part 140 to magnetically cooperate to cause the moveable part 140 to move relative to the stationary part 130 along a movement axis 11 in a forward direction 12 and a rearward direction 13. Of course, movement of the moveable part 140 relative to the stationary part 130 along the movement axis 11 can also be considered movement of the stationary part 130 relative to the moveable part 140.

[0297] The moveable part 140 of the drive unit 120 includes a permanent magnet 141 to generate magnetic flux, a forward-facing flux guide 142 and a rearward-facing flux guide 143. The permanent magnet 141 is arranged between the forward-facing flux guide 142 and the rearward-facing flux guide 143. More particularly, the forward-facing flux guide 142 is arranged forwards of the permanent magnet 141 and the rearward-facing flux guide 143 is arranged rearwards of the permanent magnet 141.

[0298] The permanent magnet 141 has a cylindrical shape to which the flux guides 142, 143 are attached. The flux guides 142, 143 have a generally annular shape, and are provided here as shoulder washer (as described further below).

[0299] The stationary part 130 of the drive unit 120 includes a tubular yoke 132, which forms part of the chassis 100. The tubular yoke 132 extends around the movement axis 11.

[0300] The tubular yoke 132 has a first end 133 and, opposite thereto, a second end 134. The first end 133 and the second end 134 delimit an axial extent of the tubular yoke 132 along the movement axis 11.

[0301] A first air gap is formed between the forward-facing flux guide 142 and the tubular yoke 132, and a second air gap is formed between the rearward-facing flux guide 143 and the tubular yoke 132. The first air gap and the second air gap each have an annular shape.

[0302] The stationary part 130 of the drive unit 120 includes a voice coil 135.

[0303] Figures 3 and 4 illustrate the voice coil 135. Figure 3 is a perspective view of the voice coil 135. Figure 4 is a sectional view showing the voice coil 135 mounted inside the chassis 100; the moveable part 140 and the suspension elements 160 are not shown in Figure 4.008861056

[0304] 30

[0305] The voice coil includes voice coil windings 136, 137 arranged on a voice coil former 138. The voice coil former 138 has a generally tubular shape on which the voice coil windings 136, 137 are arranged between a first end and a second end of the voice coil 135. In Figure 4, the voice coil former 138 is shown with a dot pattern for ease of reference.

[0306] The voice coil windings 136, 137 are arranged into a first set of windings 136 and, spaced therefrom, a second set of windings 137. The first set of windings 136 and the second set of windings 137 are axially spaced, i.e. spaced apart as measured along the movement axis 11.

[0307] The first set of windings 136 is located in the first air gap and the second set of windings 137 is located in the second air gap when the moveable part 140 is at the rest position shown in Figure 2.

[0308] The first set of windings 136 and the second set of windings 137 are formed from a single continuous wire, and each of the first set of windings 136 and the second set of windings 137 has an uneven number of winding layers such that the wire extends from the first set of windings 136 in the forward direction 12, and extends from the second set of windings 137 in the rearward direction 13. Conveniently, the voice coil 135 is electrically connectable to a signal source at a location towards the first end of the voice coil 135 and is electrically connectable to the signal source at a location towards the second end of the voice coil 135. In this example, electrical terminals 139 (in the form of conductive tabs; cf. Figure 1) are provided on the outside of the chassis 100 for conveniently making such electrical connection.

[0309] The voice coil 135 is mounted within the tubular yoke 132 and extends around the moveable part 140 of the drive unit 120. In some examples, an annular clearance space is formed between the voice coil 135 and in particular the voice coil windings 136, 137, and the tubular yoke 132. Suitably, the outer diameter of the voice coil 135 may be smaller than the inner diameter of the tubular yoke 132.

[0310] The drive unit 120 define a force factor BL, where B is the magnetic flux density permeating the voice coil in the air gap and L is the total length of windings of the voice coil in the air gap. The magnetic flux density B has a value which is between 1% and 30% of the value of the total length of windings L of the voice coil 135 (i.e. including the first set 136 and the second set 137).

[0311] Returning to Figures 1 and 2, the transducer 10 includes a first suspension element 160 and a second suspension element 160 which are respectively configured to deflect along the movement axis 11. The first suspension element 160 is secured to a first landing surface 103 of the chassis 100 and the second suspension element 160 is secured to a second landing surface 103 of the chassis 100.

[0312] The first suspension element 160 includes a first suspension attachment formation 170 attached to the moveable part 140 and the second suspension element 160 includes a second suspension attachment formation 170 attached to the moveable part 140. The first suspension attachment formation 170 and the second suspension attachment formation 170 are each attached to a respective attachment formation 150 of the moveable part 140. More particularly, the first suspension attachment formation 170 is attached to the attachment formation 150 of the forward-facing flux guide 142 and the second suspension attachment formation 170 is attached to the attachment formation 150 of the rearward-facing flux guide 143.008861056

[0313] 31

[0314] An axial separation 105 of the first landing surface 103 and the second landing surface 103, as measured along the movement axis 11 , is greater than an axial separation 145 of the first suspension attachment formation 170 and the second suspension attachment formation 170, as measured along the movement axis 11 , such that the suspension elements 160 are deflected along the movement axis 11 by their attachment to the moveable part 140 when the moveable part 140 is at a rest position. The moveable part 140 is shown in in Figures 1 and 2 at the rest position.

[0315] Figure 5 is another cross-sectional view of the transducer 10. Figure 5 shows the transducer 10 part-assembled with the suspension elements 160 not attached to the moveable part 140.

[0316] According to the present example, the attachment members 180 are pins which are received into the attachment formations 150 of the moveable part 140 (shown in Figure 2) and received into the suspension attachment formations 170 of the suspension elements 160 (shown in Figure 2, whereas Figure 5 shows these detached). Suitably the suspension attachment formations 170 are provided as an aperture through the respective suspension element 160 such that the corresponding pin 180 may be received through said aperture. When the pin 180 is received into the suspension attachment formation 170, the pin 180 is mechanically deformed, e.g. flattened, so that the suspension element 160 is attached to the moveable part 140. The non-deformed configuration of the pins 180 is shown in Figure 5, while the deformed configuration of the pins 180 is shown, for example, in Figure 2.

[0317] Returning to Figures 1 and 2, the attachment formations 150 shown in Figures 1 and 2 extend in directions parallel to the movement axis 11. More particularly, the first attachment formation 150 includes an attachment protrusion 152 which extends in the forward direction 12 and the second attachment formation 150 includes an attachment protrusion 152 which extends in the rearward direction 13. The attachment protrusions 152 extend from a respective axial face 146 of the moveable part 140. Also, the first attachment formation 150 includes an attachment recess 154 which extends in the rearward direction 13 and the second attachment formation 150 includes an attachment recess 154 which extends in the forward direction 12. The attachment recesses 154 extend into the corresponding axial face 146 of the moveable part 140 (and into the corresponding attachment protrusion 152). According to the present example, the attachment recess 154 is a hole which extends through the respective flux guide 142, 143. The first suspension attachment formation 170 and the second suspension attachment formation 170 are mechanically attached to the respective attachment formation 150 of the moveable part 140 by an attachment member 180. The attachment members 180 shown in Figures 1 and 2 are pins which are deformed to respectively attach the suspension attachment formation 170 to the attachment formation 150 of the moveable part 140.

[0318] Figure 6 is another cross-sectional view of the transducer 10.

[0319] The chassis 100 includes the aforementioned frame portions, i.e. the forward frame portion 101 and the rearward frame portion 102. The forward frame portion 101 and the rearward frame portion 102 are formed separately and are joined by the tubular yoke 132 to which both frame portions are suitably attached, e.g. mechanically and / or using adhesive.008861056

[0320] 32

[0321] In this example, the forward frame portion 101 and the rearward frame portion 102 are arranged at the forward end and the rearward end of the transducer 10.

[0322] The moveable part 140 of the drive unit 120 is suspended from the forward frame portion 101 by the first suspension element 160, and is suspended from the rearward frame portion 102 by the second suspension element 160. Suitably, the forward frame portion 101 includes the first landing surface 103 where the first suspension element 160 is attached, and the rearward frame portion 102 includes the second landing surface 103 where the second suspension element 160 is attached.

[0323] The forward frame portion 101 is shaped to define a first channel 104 which faces towards the rearward frame portion 102 and extends around the movement axis 11. Likewise, the rearward frame portion 102 is shaped to define a second channel 104 which faces towards the forward frame portion 101 and extends around the movement axis 11. The first end 133 of the tubular yoke 132 is received into the first channel 104 to thereby align the first suspension element 160 relative to the tubular yoke 132, and the second end 134 of the tubular yoke 132 is received into the second channel 104 to thereby align the second suspension element 160 relative to the tubular yoke 132.

[0324] The tubular yoke may be attached to first frame portion and the second frame portion. For example, the tubular yoke may be attached using adhesive. Adhesive may be provided in the first channel to attach the tubular yoke and the first frame portion, and adhesive may be provided in the second channel to attach the tubular yoke and the second frame portion.

[0325] The forward frame portion 101 includes a first axis-facing inner surface 106. The first axis-facing inner surface 106 extends around the movement axis 11 and, in particular, around the voice coil former 138 such that a forward end of the voice coil former 138 is radially constrained by the first axis-facing inner surface 106. Similarly, the rearward frame portion 102 includes a second axis-facing inner surface 106. The second axis-facing inner surface 106 extends around the movement axis 11 and around the voice coil former 138 such that a rearward end of the voice coil former 138 is radially constrained by the second axis-facing inner surface 106 of the rearward frame portion 102. The described arrangement of the forward frame portion 101 , the rearward frame portion 102 and the voice coil former 138 aligns the voice coil with respect to the movement axis 11.

[0326] The forward frame portion 101 is shaped to define a first annular surface 116 which faces towards the rearward frame portion 102 and extends around the movement axis 11. The rearward frame portion is shaped to define a second annular surface 116 which faces towards the forward frame portion 101 and extends around the movement axis 11. The voice coil windings 136, 137 are arranged between the opposing annular surfaces 116 to thereby axially constrain the voice coil windings 136, 137. In some examples, the voice coil windings are attached to the first annular surface 116 and the second annular surface 117 by adhesive.

[0327] Figure 7 is another sectional view of the transducer 10, including also a pair of closure members 190. The forward frame portion 101 has a first end face 117 which faces away from the tubular yoke 132 and the rearward frame portion 102 has a second end face 117 which faces away from the tubular yoke 132.008861056

[0328] 33

[0329] A central passage 14 extends between the first end face 117 and the second end face 117 and the moveable part 140 of the drive unit 120 is moveable within the central passage 14. In particular, the central passage 14 extends from end face to end face. That is to say, the central passage may extend between a first opening 118 in the first end face 117 and a second opening 118 in the second end face 117 (for openings 118, see Figure 5 in which the openings 118 are indicated by dashed lines).

[0330] The first landing surface 103 is recessed into the first end face 117 such that a forward clearance space 119 is formed between the first end face 117 and the first landing surface 103. Likewise, the second landing surface 103 is recessed into the second end face 117 such that a rearward clearance space 119 is formed between the second end face 117 and the second landing surface 103.

[0331] The moveable part may be moveable in the forward clearance space 119 and in the rearward clearance space 119.

[0332] The chassis 100 includes a first closure member 190 attached to the forward frame portion 101 to close the first opening 118 and a second closure member 190 attached to the rearward frame portion 102 to close the second opening 118. In some examples, the chassis 100 is arranged to provide an airtight seal around the central passage 14.

[0333] Figures 8 and 9 illustrate examples of the suspension elements 160. Figure 8 is a plan view of a first example of the suspension elements 160, while Figure 9 is a plan view of a second example of the suspension elements 160.

[0334] Each suspension element 160 includes an outer portion 162 and an inner portion 164. The inner portion 164 is located at the movement axis 11 and includes the suspension attachment formation 170, which in Figures 8 and 9 is provided as an aperture through the suspension element 160. The outer portion 162 extends around the movement axis 11 and is attached to the chassis 100 at the respective landing surface 103.

[0335] Each suspension element 160 includes a plurality of bridge arms 166 which extend towards and converge at the suspension attachment formation 170. More particularly, the bridge arms 166 connect the outer portion 162, which is attached to the chassis 100, and the inner portion 164, which is attached to the moveable part 140. Figure 8 shows an example with two bridge arms 166, while Figure 9 shows an example with three bridge arms 166.

[0336] The bridge arms 166 extend around the movement axis 11 in a curved or spiralling arrangement.

[0337] The suspension elements 160 shown in Figures 8 and 9 are manufacturable by stamping to form the bridge arms 166 and the suspension attachment formation 170, which in the examples of Figures 8 and 9 is provided as an aperture through the suspension element 160.

[0338] Each suspension element may be formed from metal. In some examples, each suspension element may be formed from a single piece of metal, e.g. a stamped piece of sheet metal.

[0339] The inventors note that suspension elements may be a crucial component and may be very delicate, e.g. where the suspension elements are comparatively small. The inventors found that it may be preferable to008861056

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[0341] use suspension elements with a smaller number of bridge arms 166. The suspension element 160 of Figure 8, which has two bridge arms 166, may have greater robustness compared to the suspension element 160 of Figure 9, which has three bridge arms 166, preventing the bridge arms 166 and / or the suspension attachment formation 170 from being damaged when being attached to the moveable part 140 (e.g. a screw is installed and torque is applied to the screw to fix it to the moveable part 140). In addition, the suspension element 160 with two bridge arms 166 can be formed out of a thinner metal sheet than the suspension element 160 with three bridge arms 166 having the same stiffness. This may help manufacturability, as the stamping tool for the suspension elements 160 may need less force to stamp the suspension element 160. In addition, the gap between the bridge arms 166 can be wider for the suspension element 160 with two bridge arms 166 compared to the suspension element 160 with three bridge arms 166 of the same stiffness, which may help to keep the stamping tool simple. It may be desirable to design suspension elements with adjacent bridge arms having a gap between the bridge arms of at least 1mm, e.g. when stamping springs out of Type 301 steel. Using a suspension element with two bridge arms 166 may be considered as going against the common approach in the art, which can be seen for example in the teaching of US11341948 B2.

[0342] As described above, the suspension elements 160 are attached to the chassis 100 and the moveable part 140 such that the such that the suspension elements 160 are deflected along the movement axis 11 by their attachment when the moveable part 140 is at the rest position. Said deflection may also be referred to as pre-tensioning of the suspension elements 160, or pre-stressing of the suspension elements 160. Pre-stressing the suspension elements 160 may result in drawbacks:

[0343] 1) the radial stiffness of pre-stressed suspensions may be lower than the radial stiffness of suspensions that are not pre-stressed (cf. Figure 10);

[0344] 2) the axial stiffness in the described arrangement, where two suspensions are pre-stressed towards the centre of the moving assembly, may increase (see Figure 11);

[0345] 3) the suspension elements may be prone to deformation if they are dimensionally contained in a transducer of comparatively compact target dimensions; e.g. each suspension element may have an outer diameter comprised between 10 and 50 millimetres, preferably between 15 and 30 millimetres, and a thickness ranging from 0.1 to 0.5 millimetres, preferably 0.2 to 0.4mm, which may make the suspension element prone to deformation and low radial stiffness, especially when used in pre-stress as in this case. The suspension elements and their configuration may therefore be considered critical in some applications.

[0346] For the suspension elements 160 to restrain the moveable part 140 in the radial direction perpendicular to the movement axis 11 , the suspension elements 160 are to have a radial stiffness which is higher than the residual radial magnetic force in the radial direction. Furthermore, it may be desirable to have relatively low axial stiffness, as the stiffness of the two suspensions which hold the moving assembly in the centre sums to the magnetic stiffness coming from the magnetic reluctance force (cf. Figure 12).008861056

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[0348] Figure 13 is a plan view onto the moveable part 140 inside the stationary part 130 of the drive unit 120. In Figure 13, the moveable part 140 is shifted towards the right-hand side, thereby creating a larger gap between the moveable part 140 and the stationary part 130, and closing the gap between the moveable part 140 and the stationary part 130.

[0349] If the central moving stack were perfectly centred in the tubular yoke, there would be no radial magnetic force and the system would be perfectly in balance. In practice it may be difficult to have the central moving stack perfectly centred in the yoke, e.g. because of production tolerances. As a result, for a given radial shift of the moving stack, there will be a certain residual radial magnetic force exerted onto it. This is illustrated by the plot in Figure 14. The plot shows the static deflection of the suspensions for different airgap sizes. The static deflection is defined as deformation of the springs in the radial direction under a certain load, which depends on the residual radial magnetic force, which depends itself on the width of the airgap. Note that static deflection here is a simplification of the matter. In simulations, we have first calculated the residual magnetic attraction force for different airgap sizes, then in a separate simulation we have applied the resulting force as a radial load to the springs so that their static deflection could be quantified. In reality, a radial shift of the moving assembly will cause higher and higher forces to be exerted onto it, so the load is dynamic in nature and increasing with the increase of radial magnetic force. This is to say that the situation shown in Figures 13 and 14 is result of a simplified calculation which shows what may be considered a best-case scenario, when the moving assembly is shifted from the center axis by 0.2mm and additionally shifted by 0.23mm due to the radial static deflection of the suspension system.

[0350] In order to improve the centering of the moveable stack in the airgap, at least one attachment formation is integrated in the moveable part, e.g. integrated each of the washers. This may help limit the component count in the assembly, and may significantly simplify the installation and centering of the suspensions, e.g. allowing to easily apply pre-stress to the springs. The plot in Figure 14 shows that sizing the airgap from 1.7mm onwards results in a negligible static deflection for the suspension. This action results in a loss in radial magnetic flux in the airgap, which may be undesired because it may cause a decrease in force factor of the transducer, thus a decrease in its efficiency. In order to make up for the loss in force factor, the voice coil’s winding width may be maximised so to compensate the decrease in flux density in the air gap. This is illustrated in Figures 15, 16, 17, where the simulation of two motor systems is shown. The motor system of Figure 15 follows the classic design approach, whereas the simulation of Figure 16 shows the approach described. It can be seen that increasing the size of the airgap causes a drop in radial flux density in the airgap from 0.52 Tesla to 0.38 Tesla. Nonetheless, Figure 17 shows that there is a moderate increase of the force factor Bl when comparing the transducer 10 (solid line, 2.8Tm) with a traditional airgap-and-coil setup (dashed line, 2.5Tm). More particularly, according to the traditional airgap-and-coil setup there is a magnetic flux of 0.52 T in the airgap, resulting in a force factor Bl of 2.5Tm for 4.8m of voice coil wire in the air gap. For the transducer 10, the magnetic flux density in the air gap is reduced to 0.38T, which results in a force factor of 2.8Tm for 7.37m of voice coil wire in the air gap.008861056

[0351] 36

[0352] It has been found that when the coil is designed following this approach, the weight of the coil may generally be higher than the weight of the magnet. This may generally not be the case in a conventional transducer design.

[0353] By suitably configuring the magnetic circuit of the drive unit 120, the magnetic flux B in the air gaps is set to have a magnitude such that the resulting magnetic attraction between the stationary part 130 and the moveable part 140 causes a radial static deflection of the moveable part 140 relative to the movement axis 11 of no more than 0.1 millimetres. Such a reduction in magnetic flux B in the air gap may be achieved, for example, by increasing the size of the air gaps. More particularly, the radial extent of the annular air gap may be increased until the desired radial static deflection is obtained. This approach is opposite to the more commonly adopted approaches as described in, for example, US11341948B2 (cf. paragraph 0004).

[0354] That is to say, it is proposed here to increase the size of the air gap, such that the radial stiffness of the suspension is such that their combined static deflection does not exceed 0.1 mm. Since the air gap is made wider, the strength of the magnetic field in the air gap becomes lower. Without further adjustment of the drive unit 120, this would potentially result in in a lower efficiency and lower sensitivity for the transducer 10. However, this can be counterbalanced by increasing the length of wire in the air gap(s), thus compensating the loss in magnetic field with a higher length of wire in the airgap (see Fig.14, 15 and 16). When this is done, typically the total weight of the voice coil 135 may be higher than the weight of the magnet 131.

[0355] The resulting increase in the inductance may not be relevant in this case, e.g. because the preferred frequency range of operation is 20Hz to 500Hz, and more preferably 30Hz to 200Hz. Within such frequency range, the inductive rise is not sufficient to cause a sensitivity drop.

[0356] Also, since the pre-stress on the suspension elements 160 causes an increase in axial stiffness, a balancing act may be needed when determining the amount of pre-stress allowed for a specific design. In the transducer 10 described here, an optimised value of deflection of the suspension elements 160 may be 1.5mm to provide the pre-stress.

[0357] This has been decided based on two targets: a total height of the product of 15mm and a resonance frequency at 80Hz.

[0358] In order to achieve the resonance frequency target, considering that the moveable stack amounts to a moving mass of 15g, the maximum allowable stiffness may be Fs = 1 / (2*pi) * sqrt (K / M), therefore the target K for 80Hz = (4*piA2*80A2*0.014) / 1000 = 3.8N / mm. With reference to the plots of Figures 11 and 12, it can be seen how a suspension pre-stress of 1.5mm, summed to a yoke height of 10.5mm leads to a total stiffness of 2 Newtons / millimetre (mechanical contribution) + 1.8 N / mm (magnetic contribution) = 3.8 N / mm at 0mm displacement, or when the central stack is at rest position in the airgap.

[0359] In this case, setting the yoke height to 10.5mm may be beneficial considering a target height of 15mm, as it gives 4.5mm in addition to install the forward frame portion 101 and the rearward frame portion 102 (or “top and bottom mounting frame”) for the suspension elements 160. The maximum stroke of the central008861056

[0360] 37

[0361] moving stack will amount to 2.4mm, which is fully contained within the defined package (cf. Figure 2 and 7). Since the axial magnetic stiffness and the axial mechanical stiffness are substantially the same, the magnetic circuit contributes to half the target stiffness, allowing for relatively compliant suspension elements, which may be beneficial to their fatigue endurance. In order to keep the product height compact, it may therefore be desirable to set the overhang of the yoke respect to the washer equal to (or up to 2mm more than, or up to 2mm less than) the amount of selected deflection of the suspension elements at rest position, which may help ensure compact dimensions while not making the magnetic stiffness too high. This may lead to an undesired increase in resonance frequency, as it may be difficult to balance the increase in magnetic axial stiffness with more compliant suspensions while keeping their high radial stiffness.

[0362] Once the motor system is sized, the suspension elements may be designed and a certain amount of prestress defined to meet a certain target height and resonance frequency. The size of the airgap may be selected so that the radial stiffness of the suspension elements is high enough to counterbalance the residual radial magnetic force.

[0363] Figure 18 illustrates a method of assembly of an electromechanical transducer.

[0364] The method includes a step S101 of providing a tubular yoke. The tubular yoke forms part of a drive unit, with a first end and a second end.

[0365] The method includes a step S102 of receiving the tubular yoke into a forward frame portion. More particularly, the forward frame portion is shaped to define a first annular channel, and the first end of the tubular yoke is received into the first annular channel. The method may further include receiving a voice coil into the tubular yoke.

[0366] The method includes a step S103 of providing a moveable part of the drive unit.

[0367] The method includes a step S104 of attaching a first suspension element to the moveable part.

[0368] The method includes a step S105 of receiving the moveable part into the tubular yoke, wherein the first suspension element may be attached to the moveable part as per step S104 and the forward frame portion may be attached to the tubular yoke as per step S103.

[0369] The method includes a step S106 of attaching the first suspension element to the forward frame portion. By so attaching the first suspension element, the first suspension element is aligned relative to the tubular yoke and is configured to deflect along a movement axis.

[0370] The method includes a step S107 of receiving the tubular yoke into a rearward frame portion. More particularly, the rearward frame portion is shaped to define a second annular channel, and the second end of the tubular yoke is received into the second annular channel. The tubular yoke is received into the forward frame portion and the rearward frame portion such that the first annular channel faces towards the rearward frame portion and the second annular channel faces towards the forward frame portion.008861056

[0371] 38

[0372] The method includes a step S108 of attaching a second suspension element to the rearward frame portion. By so attaching the second suspension element, the second suspension element is aligned relative to the tubular yoke and is configured to deflect along the movement axis.

[0373] The method includes a step S109 of attaching the second suspension element to the moveable part to suspend the moveable part from the rearward frame portion.

[0374] The drive unit is operable to cause the moveable part to move along the movement axis relative to the stationary part in a forward direction and a rearward direction

[0375] The described method does not define an ordering of the steps of the method, other than were explicitly required by the claim (e.g. the step of providing a tubular yoke S101 preceding any other steps involving the tubular yoke such as steps S103 and S105). For example, step S106 of attaching the first suspension element may or may not be carried out prior to step S107 of attaching the second suspension element. In some examples, the suspension elements may be attached simultaneously.

[0376] In some examples, the following method of assembly may be performed:

[0377] Step 1) Build sub-assembly of moveable part: glue bottom washer, magnet and top washer using a centering jig;

[0378] Step 2) Attach first suspension element (e.g. screw the first metal suspension to the top washer) 3) Prepare top frame-coil-yoke sub-assembly: apply a single glue bead in the yoke holding feature, press the yoke in place. Excess glue will spread on the winding gluing surface. Install the coil in place, routing the bottom exit wire during installation;

[0379] 4) Apply glue on the top frame suspension’s gluing surface and install the moving stack + top suspension sub-assembly;

[0380] 5) Turn product upside-down, and glue the bottom frame on the yoke and bottom coil winding, route the coil wire;

[0381] 6) Apply glue to the bottom frame’s suspension gluing surface, install second suspension element; 7) Attach second suspension element to the bottom washer, e.g. using a second screw, and so prestress both suspension elements by the same amount;

[0382] 8) Solder the coil wire + cable on tags and apply stress relief for the cable;

[0383] 9) Magnetize the transducer.

[0384] As noted from the assembly description, a centering jig is not necessarily needed when the suspensions are installed on the washers (e.g. using screws), and a frame is used such that the voice coil and outer steel ring can be directly centered using centering features integrated in the frame. Figure 2 shows that the frame in cross section has an ‘h’ shape, which helps housing the tubular yoke and acting as gluing surface for the voice coil windings. In addition, the voice coil is centered in the frame via the former, as the frame inner diameter is dimensioned in a way that the former can fit exactly and center in the frame’s inner diameter without significant play.008861056

[0385] 39

[0386] Figures 19, 20 and 21 illustrate an example wherein the electromechanical transducer 10 is installed in a road vehicle 1000.

[0387] The road vehicle 1000 includes an automotive seat 1100 containing a seat foam 1110. The electromechanical transducer 10 is mounted to a recess 1112 in the seat foam 1110.

[0388] Figure 22 shows a conventional automotive seat in which two transducers are mounted within a plastic module in the automotive seat.

[0389] In summary, the electromechanical transducer 10 may be configured such that:

[0390] Suspensions may be pre-stressed such that the stroke of the motor system may be fully contained within the mechanical package. The yoke overhang to the washer may be maximum 2mm more than the amount of pre-stress defined for the suspensions, or may be the same amount.

[0391] The suspensions may be made of metal, and may be made of two spirally shaped arms.

[0392] The width of the airgap may be such that the static deflection of the suspension assembly, resulting from the residual radial magnetic force (definitions in the text below) may be lower than 0.1mm.

[0393] The central moveable stack may be improved by having at least one attachment formation (e.g. integrated screw points in the washers)

[0394] The frame may have integrated housing for the tubular yoke, gluing surface for the coil windings and spacer that may also be used to mount a protective grill or lid, and integrated routing feature for the wire and cable. Optionally the frame may also add an integrated connector and insert-molded terminals for making an electrical connection. The frame so devised may be a simple and compact component, serving multiple functions with reduced usage of material. In addition, the frame may serve as centering element for the voice coil and tubular yoke, so that no centering jigs may be needed in the assembly steps involving the voice coil and the tubular yoke.

[0395] The voice coil may have two sets of windings wound around a coil former; the windings may obtained from the same wire. A first set of windings may be formed in an odd number of layers to continue on to the second set of windings which may be wound in opposite direction respect to the first set of windings. The result is a single coil component, wound on a single former, with exit wires at top and bottom of the former and two sets of windings, each with the same odd number of layers. Between the first and the second sets of windings, a suitable gap may be provided (e.g. of at least 0.5mm) for bending the wire and changing winding direction. The coil formed in this way may have the advantage of being a single component, whose exit wires are easy to manage as they can be arranged symmetrically at top and bottom of the actuator. The coil former, around which the windings are formed, can be used as centering element for the coil, which is assembled to the frame with the windings resting on the dedicated gluing surface.

[0396] The outer ring may have a straight cut, e.g. as a result of being formed out of a sheet.

[0397] Figures 23 and 24 show another example of a transducer. Figure 23 is a perspective view, while Figure 24 is a sectional view of the transducer.008861056

[0398] 40

[0399] The transducer of Figure 23 and 24 is generally identical to the transducer 10 described above but utilises a pair of tapped holes in the moveable part as the attachment formation, and a corresponding pair of bolts as attachment members. In Figures 23 and 24, the bolts are received into the tapped holes but are not screwed in fully such that the suspension elements are not pre-stressed. Upon full insertion of the bolts into the tapped holes, the suspension elements are deflected towards the moveable part.

[0400] More particularly, the washers of the moveable part have integrated screw points which act as mounting points for the suspension elements, which are installed in a situation of pre-stress when the bolts are fully inserted, so that the stroke of the moving assembly can be contained within the total mechanical package of the device.

[0401] Figures 25 and 26 show another example of a transducer. Figure 25 is a sectional view of the transducer with the suspension elements separate from the moveable part, while Figure 26 is a sectional view with the suspension elements attached to the moveable part.

[0402] The transducer of Figure 25 and 26 is generally identical to the transducer 10 described above but utilises riveting features for attaching the suspension elements. More particularly, the moveable part is provided with pins extending therefrom and onto which the suspension elements are received. When so received, the pins are flattened to secure the suspension elements in place in a pre-tension configuration. The stroke of the moving assembly is contained within the mechanical package.

[0403] It is possible to have further variations on the products described above. For example, suspensions are may be made of spring steel, but may be made of plastic, textile, rubber or other suitable suspension material. The frame may have insert moulded terminals and / or suspension. A dust scrim may be applied (for example via ultrasonic welding, or could be glued or could be insert molded) on top and bottom frame to prevent ingress of external particles in the motor system. The coil may be as described above, but it might also consist of a stack of two coils, oppositely connected (for example via a glue joint) and with wires routed to the outer frame, for example via an exit hole in the middle of the yoke. This may provide increased flexibility, with possibility to route coils in series but also in parallel, but may result in a more complex construction. The connection of the suspensions to the moveable part could be implemented using further alternatives. For example, the suspensions could be spot-welded to the washers. In order to improve manufacturability of the tubular yoke, the tubular yoke might have one or multiple straight cuts (or might be formed of multiple steel portions). In particular, having a single straight cut may simplify the manufacturing process, as the component might be formed out of a steel sheet rather than obtained from a rod by CNC process or from a seamless tube.

[0404] The transducers described above could be used as exciters, e.g. to be mounted on a sound radiating surface to emit sound. In such case, it might be desirable to trade efficiency with high frequency extension, as an exciter may be desired to have a range of operation form 20Hzto 10kHz, or more 20Hz to 20kHz. A way to implement such trade off may be that of leaving the airgap width intact, but reducing the number of windings on the coil to decrease the inductance. Figure 27 show a corresponding example of a transducer, noting that in Figure 27 the suspension elements are shown prior full installation of the attachment members (in this example provided as screws).008861056

[0405] 41

[0406] Figures 28-31 show electromechanical transducers 210, 310. More specifically, Figures 28-30 show a fifth example of a transducer 210, and Figure 31 shows a sixth example of a transducer 310. The transducers 210, 310 share several general similarities with the transducer 10 shown and described in relation to Figures 1-27. The skilled person will understand that features described in relation to the transducer 10 may be incorporated into the transducers 210, 310, where appropriate.

[0407] The inventors have found, in relation to electrotechnical transducers, that usage of glue in a coil / yoke gutter to bond a coil and a yoke to a (e.g., plastic) frame can be undesirable. When using a two-component glue, not only the access of the glue nozzle to the coil / yoke gutter to reliably dispense the glue can be very difficult, but also the amount of glue that needs to be purged to keep a good quality in the glue connections can risk being more than the amount of glue needed for the connection. The inventors have found that one possible solution to this would be to use a different kind of glue, for example UV glue, which is a well-established fast curing single component glue used in applications where accuracy is critical and space is limited. For example, UV glue can be used to bond components in a tweeter that are small in size and require high accuracy in the building process. However, one possible limitation of UV glue compared to a two-component glue is cost. Not only can UV glue be more expensive than a two-component glue, but it would also require an at least partially UV-transparent (plastic) frame, so that the glue can cure properly. It is known that transparent plastic is more expensive than traditional plastic. Considering the above, the inventors have found that the usage of glue for the voice coil and yoke connections is to preferably be avoided, e.g., to safeguard costs and / or building quality in at least some designs.

[0408] The inventors have found that one solution to the above problems is to clamp (e.g., constrain) the coil and the yoke between top and bottom frames. The inventors have found that there can be multiple ways to join the top and bottom frame. For example, a standard two component or single component glue could be used to secure the connection. The inventors have also found that it would be possible to implement a mechanical fixation either in addition to or instead of the usage of glue. The inventors have further found that it is possible to use other bonding methods, for example ultrasonic welding between the top and bottom frame.

[0409] However, the inventors have found that production tolerances (for example, the production tolerances on a voice coil’s winding height) can be significant for transducer designs where the frame portions contact the voice coil. For example, the voice coil windings of a voice coil may have a set of tolerances that stack up to an overall tolerance of +- 0.6 mm in the distance between the top of the top set of voice coil windings and the bottom of the bottom set of voice coil windings.

[0410] In some situations, this can make the assembly of the transducer, or the securing of the voice coil windings within the transducer, difficult. For example, if the tolerance is at its highest value, the total distance between a top of a top set of voice coil windings and a bottom of a bottom set of voice coil windings will increase by 0.6mm, which will create an additional 0.6 mm gap between top and bottom portions of a frame. Furthermore, if the tolerance is at its lowest value, the total distance between the sets of voice coil windings would be 0.6 mm smaller than nominal, meaning that, when the top and bottom008861056

[0411] 42

[0412] portions of the frame close, the voice coil may potentially be difficult to properly clamp together, leaving a clearance between the top and bottom of the coils and the top and bottom portions of the frame.

[0413] The transducers 210, 310 have been developed by the inventors in view of the above considerations. Figure 28 shows a sectional view of the transducer 210. Figure 29 shows a perspective view of the transducer 210. Figure 30 shows a second perspective view of the transducer 210, in which also a closure element 290 of the transducer 210 is shown.

[0414] As mentioned above, the transducer 210 shares several similarities with the transducer 10. Like reference signs of the elements of transducer 10, incremented by 100, are applied to like elements of the transducer 210.

[0415] The transducer 210 is configured to convert electrical signals into mechanical forces to generate vibrations. These vibrations may in use be passed to a user, e.g. passing music information to the user through mechanical vibration on the skin of the user. An example application, described above with reference to Figures 19 to 21 , is an automotive seat. A second example application 294 is shown in Figure 30.

[0416] The transducer 210 is generally cylindrical with a diameter in the range of 15 and 50 millimetres, optionally between 20 millimetres and 30 millimetres. The total height is preferably between 8 millimetres and 40 millimetres, optionally between 10 millimetres and 20 millimetres.

[0417] The transducer 210 includes a chassis 200. The chassis 200 houses the other components of transducer 210. As seen in Figure 28, the chassis 200 includes a forward frame portion 201 and a rearward frame portion 202.

[0418] The transducer 210 further includes a drive unit 220. The drive unit 220 includes a stationary part 230 which forms part of the chassis 200. The drive unit 220 further includes a moveable part 240 which is moveable relative to the stationary part 230. The drive unit 220 is operable, by supplying an electrical signal to the drive unit 220, to cause the stationary part 230 and the moveable part 240 to magnetically cooperate to cause the moveable part 240 to move relative to the stationary part 230 along a movement axis 11’ in a forward direction 12’ and a rearward direction 13’. Of course, movement of the moveable part 240 relative to the stationary part 230 along the movement axis 11 ’ can also be considered movement of the stationary part 230 relative to the moveable part 240.

[0419] The moveable part 240 of the drive unit 220 includes a permanent magnet 241 to generate magnetic flux, a forward-facing flux guide 242 and a rearward-facing flux guide 243. The permanent magnet 241 is arranged between the forward-facing flux guide 242 and the rearward-facing flux guide 243. More particularly, the forward-facing flux guide 242 is arranged forwards of the permanent magnet 241 and the rearward-facing flux guide 243 is arranged rearwards of the permanent magnet 241.

[0420] The permanent magnet 241 has a cylindrical shape to which the flux guides 242, 243 are attached. The flux guides 242, 243 have a generally annular shape, and are provided here as shoulder washers. The008861056

[0421] 43

[0422] stationary part 230 of the drive unit 220 includes a tubular yoke 232, which forms part of the chassis 200. The tubular yoke 232 extends around the movement axis 11

[0423] The tubular yoke 232 has a first end 233 and, opposite thereto, a second end 234. The first end 233 and the second end 234 delimit an axial extent of the tubular yoke 232 along the movement axis 11’.

[0424] A first air gap is formed between the forward-facing flux guide 242 and the tubular yoke 232, and a second air gap is formed between the rearward-facing flux guide 243 and the tubular yoke 232. The first air gap and the second air gap each have an annular shape.

[0425] The stationary part 230 of the drive unit 220 includes a voice coil 235.

[0426] The voice coil 235 is similar to the voice coil 135 illustrated in Figures 3 and 4.

[0427] The voice coil 235 includes voice coil windings 236, 237 arranged on a voice coil former 238. The voice coil former 238 has a generally tubular shape on which the voice coil windings 236, 237 are arranged between a first end and a second end of the voice coil 235. The voice coil former 238 includes a first end 238-1 and a second end 238-2, which correspond to the first end and the second end of the voice coil respectively. The voice coil windings 236, 237 are arranged into a first set of windings 236 and, spaced therefrom, a second set of windings 237. The first set of windings 236 and the second set of windings 237 are axially spaced, i.e. spaced apart as measured along the movement axis 11’.

[0428] The first set of windings 236 is located in the first air gap and the second set of windings 237 is located in the second air gap when the moveable part 240 is at the rest position shown in Figure 28.

[0429] The first set of windings 236 and the second set of windings 237 are formed from a single continuous wire, and each of the first set of windings 236 and the second set of windings 237 has an uneven number of winding layers such that the wire extends from the first set of windings 236 in the forward direction 12’, and extends from the second set of windings 237 in the rearward direction 13’. Conveniently, the voice coil 235 is electrically connectable to a signal source at a location towards the first end of the voice coil 235 and is electrically connectable to the signal source at a location towards the second end of the voice coil 235.

[0430] In this example, first and second lead wires 211 are provided for conveniently making such an electrical connection. These are described in more detail below with reference to Figure 29.

[0431] The voice coil 235 is mounted within the tubular yoke 232 and extends around the moveable part 240 of the drive unit 220. In some examples, an annular clearance space is formed between the voice coil 235 and in particular the voice coil windings 236, 237, and the tubular yoke 232. Suitably, the outer diameter of the voice coil 235 may be smaller than the inner diameter of the tubular yoke 232.

[0432] The drive unit 220 defines a force factor BL, where B is the magnetic flux density permeating the voice coil in the air gap and L is the total length of windings of the voice coil in the air gap. The magnetic flux density B has a value which is between 1% and 30% of the value of the total length of windings L of the voice coil 235 (i.e. including the first set of voice coil windings 236 and the second set of voice coil windings 237).008861056

[0433] 44

[0434] The transducer 210 includes a first suspension element 260 and a second suspension element 260 which are respectively configured to deflect along the movement axis 11

[0435] The suspension elements 260 include the features of the suspension elements 160 of Figures 8 and 9. The first suspension element 260 includes a first suspension attachment surface 268 which is secured to a first landing surface 203 of the chassis 200. The second suspension element 260 includes a second suspension attachment surface 268 which is secured to a second landing surface 203 of the chassis 200. The first landing surface 203 is a part of the forward frame portion 201 , and the second landing surface 203 is a part of the rearward frame portion 202.

[0436] Returning to the voice coil 235, as is shown in Figure 28, the first end 238-1 of the voice coil former 238 abuts the first suspension element 260 and the second end 238-2 of the voice coil former 238 abuts the second suspension element 260. More particularly, the first suspension element 260 contacts an axial edge of the first end 238-1 of the voice coil former 238, and the second suspension element 260 contacts an axial edge of the second end 238-1 of the voice coil former 238. An axial separation 207 of the of (e.g., the axial edge of) the first end 238-1 of the voice coil former 238 and (e.g., the axial edge of) the second end 238-2 of the voice coil former 238, along the movement axis 11 ’, is equal to the axial separation 207 of the first suspension attachment surface 268 and the second suspension attachment surface 268, along the movement axis 11 ’. In this configuration, the voice coil former 238, and therefore also the voice coil 235, is constrained between the first and second suspension elements 260.

[0437] In this example, the axial separation 207 of the first end 238-1 of the voice coil former 238 and the second end 238-2 of the voice coil former 238, along the movement axis 11 ’, is greater than an axial separation 208 of the first landing surface 203 and the second landing surface 203, along the movement axis 11’. In other words, the first end 238-1 of the voice coil former 238 extends, in the forward direction 12’, past the first landing surface 203, and the second end 238-2 of the voice coil former 238 extends, in the rearward direction 13’, past the second landing surface 203. Here, the axial separation 207 corresponds to the axial separation of the first suspension attachment surface 268 and the second suspension attachment surface 268, along the movement axis 1 T, which is also greater than the axial separation 208 of the first landing surface 203 and the second landing surface 203, along the movement axis 11’.

[0438] In other examples, the first end 238-1 of the voice coil former 238 and the second end 238-2 of the voice coil former 238, along the movement axis 11 ’, may be equal to the axial separation 208 of the first landing surface 203 and the second landing surface 203, along the movement axis 1 T.

[0439] In still further examples, the first end 238-1 of the voice coil former 238 and the second end 238-2 of the voice coil former 238, along the movement axis 11 ’, may be less than the axial separation 208 of the first landing surface 203 and the second landing surface 203, along the movement axis 11’. An example of this is given in the transducer 310 of Figure 31 below.

[0440] The first end 238-1 of the voice coil former 238, the first suspension attachment surface 268, and the first landing surface 203 are secured together by a first bead of adhesive 269, and the second end 238-2 of008861056

[0441] 45

[0442] the voice coil former 238, the second suspension attachment surface 268, and the second landing surface 203 are secured together by a second bead of adhesive 269.

[0443] Returning to the suspension elements 260, the first suspension element 260 includes a first suspension attachment formation 270 attached to the moveable part 240 and the second suspension element 260 includes a second suspension attachment formation 270 attached to the moveable part 240. The first suspension attachment formation 270 and the second suspension attachment formation 270 are each attached to a respective attachment formation 250 of the moveable part 240. More particularly, the first suspension attachment formation 270 is attached to the attachment formation 250 of the forward-facing flux guide 242 and the second suspension attachment formation 270 is attached to the attachment formation 250 of the rearward-facing flux guide 243.

[0444] The first attachment formation 250 extends in the forward direction 12’ towards the first suspension attachment surface 268 and the second attachment formation 250 extends in the rearward direction 13’ towards the second suspension attachment surface 268.

[0445] The transducer 210 includes attachment members 280. The first suspension attachment formation 270 and the second suspension attachment formation 270 are mechanically attached to the respective attachment formations 250 of the moveable part 240 by the attachment members 280. The attachment members 280 shown in Figures 28 are threaded members (e.g., screws) 280 which make threaded connections with tapped holes (e.g., attachment recesses 254) of the attachment formation 250 respectively to attach each respective suspension attachment formation 270 to the respective attachment formation 250 of the moveable part 240. More particularly, the threaded members 280 are received into the attachment formations 250 of the moveable part 240 and received into the suspension attachment formations 270 of the suspension elements 260. Suitably the suspension attachment formations 270 are provided as an aperture through the respective suspension element 260 such that the corresponding threaded member 280 may be received through said aperture. When the threaded member 280 is received into the suspension attachment formation 270, the threaded member 280 is threaded into the tapped hole, so that the suspension element 260 is attached to the moveable part 240. In other examples, pins may be used in place of the threaded members 280, similarly to as has been described above in relation to Figures 1-7. In still other examples the multiple attachment members 280 may be replaced by a single attachment member that attaches both suspension attachment formations 270 to the moveable part 240.

[0446] Figure 28 shows the transducer 210 assembled with the suspension elements 260 attached to the moveable part 240. In particular, the first suspension attachment formation 270 is attached to the attachment formation 250 of the forward-facing flux guide 242, and the second suspension attachment formation 270 is attached to the attachment formation 250 of the rearward-facing flux guide 243.

[0447] The axial separation 207 of the first suspension attachment surface 268 and the second suspension attachment surface 268, as measured along the movement axis 11 ’, is equal to an axial separation 299 of the first suspension attachment formation 270 and the second suspension attachment formation 270, as measured along the movement axis 11 ’.008861056

[0448] 46

[0449] Here, the attachment members 280 are not fully tightened and, upon fully tightening the attachment members 280, the axial separation 299 between the suspension attachment formations 270 is decreased, such that the axial separation 207 of the first suspension attachment surface 268 and the second suspension attachment surface 268, as measured along the movement axis 11 ’, is greater than the axial separation 299 of the suspension attachment formations 270. Thus, upon fully tightening the attachment member 280, the suspension elements 260 will be deflected along the movement axis 11 ’ by their attachment to the moveable part 240 when the moveable part 240 is at the rest position (shown in Figure 28).

[0450] The transducer 210 demonstrates that the suspension elements of a transducer can be configured with pre-tensioning or without pre-tensioning, without changing the design of the transducer. That is to say, pre-tensioning can be implemented deliberately and can be avoided deliberately, e.g. as part of assembly of the transducer. In some applications, deliberate pre-tensioning can be introduced as part of the assembly process, e.g. to accommodate tolerances and ensure that the suspension elements are suitably attached, e.g. to the landing surfaces and / or the voice coil former. This may result in miniscule pretensioning based on the relevant tolerances, and may have a negligible impact on operational parameters such as the resonant frequency of the transducer.

[0451] The attachment formations 250 shown in Figure 28 extend in directions parallel to the movement axis 11 ’. More particularly, the first attachment formation 250 includes an attachment protrusion 252 which extends in the forward direction 12’ and the second attachment formation 250 includes an attachment protrusion 252 which extends in the rearward direction 13’. The attachment protrusions 252 extend from a respective axial face 246 of the moveable part 240. Also, the first attachment formation 250 includes an attachment recess 254 which extends in the rearward direction 13’ and the second attachment formation 250 includes an attachment recess 254 which extends in the forward direction 12’. The attachment recesses 254 extend into the corresponding axial face 246 of the moveable part 240 (and into the corresponding attachment protrusion 252). According to the present example, the attachment recess 254 are a (e.g., threaded) hole which extends through the respective flux guide 242, 243.

[0452] A first cavity 255 is defined between the forward-facing flux guide 242 and the permanent magnet 241 , and a second cavity 255 is defined between the rearward-facing flux guide 243 and the permanent magnet 241. The cavities 255 are centred on the movement axis 1 T. By providing the cavities 255, material usage can be reduced and convenient manufacturing processes may be used, e.g. stamping the flux guides 242, 243 out of sheet metal.

[0453] Each attachment recess 254 extends to the respective cavity 255 of the moveable part 240.

[0454] As discussed above, the chassis 200 includes, the forward frame portion 201 and the rearward frame portion 202. The forward frame portion 201 and the rearward frame portion 202 are formed separately. The forward frame portion 201 and the rearward frame portion 202 are directly secured to one another via an adhesive. In other examples, the forward frame portion 201 and the rearward frame portion 202 may be additionally or alternatively directly secured to one another via one or more mechanical fixings, and / or008861056

[0455] 47

[0456] ultrasonic welding. In this example, the forward frame portion 201 and the rearward frame portion 202 are arranged at the forward end and the rearward end of the transducer 10.

[0457] The moveable part 240 of the drive unit 220 is suspended from the forward frame portion 201 by the first suspension element 260, and is suspended from the rearward frame portion 202 by the second suspension element 260. Suitably, the forward frame portion 201 includes the first landing surface 203 where the first suspension element 260 is attached, and the rearward frame portion 202 includes the second landing surface 203 where the second suspension element 260 is attached.

[0458] The forward frame portion 201 is shaped to define a first channel 204 which faces towards the rearward frame portion 202 and extends around the movement axis 11 ’. Likewise, the rearward frame portion 202 is shaped to define a second channel 204 which faces towards the forward frame portion 201 and extends around the movement axis 11 ’. The first end 233 of the tubular yoke 232 is received into the first channel 204 to thereby align the first suspension element 260 relative to the tubular yoke 232, and the second end 234 of the tubular yoke 232 is received into the second channel 204 to thereby align the second suspension element 260 relative to the tubular yoke 232.

[0459] The rearward frame portion 202 includes a first protruding portion 202-1 that is arranged such that a gutter 209 is created between the first protruding portion 202-1 and the tubular yoke 232. The first protruding portion 202-1 protrudes in the forward direction 12’. The forward frame portion 201 includes a second protruding portion 201-1 that is arranged to protrude into the gutter 209. The second protruding portion 201-1 protrudes in the rearward direction 13’. The gutter 209 is at least partly filled by the adhesive to secure the first protruding portion 202-1 and the second protruding portion 201-1 together. The first channel 204 includes a first end surface 204-1 , and the second channel 204 includes a second end surface 204-1. The first and second end surfaces 204-1 extend around the movement axis 11 ’. The first end surface 204-1 faces in the rearward direction 13’, and the second end surface 204-1 faces in the forward direction 12’.

[0460] In some examples, the tubular yoke 232 may be insert moulded into one of the forward frame portion 201 and the rearward frame portion 202.

[0461] In some examples, the first end 233 of the tubular yoke 232 forms an interference fit with the first channel 204, and the second end 234 of the tubular yoke 232 forms an interference fit with the second channel 204. In still further examples, the first channel 204 and the second channel 204 each respectively include one or more press ribs 289 configured to at least partially cause the interference fit between each respective channel 204 and the corresponding end 233, 234 of the tubular yoke 232. The tubular yoke 232 is constrained between the forward frame portion 201 and the rearward frame portion 202. The first end 233 of the tubular yoke 232 abuts the first end surface 204-1 , and the second end 234 of the tubular yoke 232 abuts the second end surface 204-1. The tubular yoke 232 may be attached to the forward frame portion 201 and the rearward frame portion 202. For example, the tubular yoke 232 may be attached using adhesive. Adhesive may be provided in the first channel 204 to attach the tubular yoke 232 and the008861056

[0462] 48

[0463] forward frame portion 201 , and adhesive may be provided in the second channel 204 to attach the tubular yoke and the rearward frame portion 202.

[0464] In other examples, the first end 233 of the tubular yoke 232 may be separated from the first end surface 204-1 by a first tubular yoke clearance space, and the second end 234 of the tubular yoke may be separated from the second end surface 204-1 by a second tubular yoke clearance space.

[0465] The chassis 200 further comprises an overflow passage 215. The overflow passage 215 is connected to the gutter 209 and extends alongside the tubular yoke 232. Adhesive extends from the gutter 209 into the overflow passage 215 to at least partially fill the overflow passage 215.

[0466] The forward frame portion 201 includes a first axis-facing inner surface 206. The first axis-facing inner surface 206 extends around the movement axis 11 ’ and, in particular, around the voice coil former 238 such that a forward end of the voice coil former 238 is radially constrained by the first axis-facing inner surface 206. Similarly, the rearward frame portion 202 includes a second axis-facing inner surface 206. The second axis-facing inner surface 206 extends around the movement axis 11 ’ and around the voice coil former 238 such that a rearward end of the voice coil former 238 is radially constrained by the second axis-facing inner surface 206 of the rearward frame portion 202. The described arrangement of the forward frame portion 201 , the rearward frame portion 202 and the voice coil former 238 aligns the voice coil 235 with respect to the movement axis 11 ’.

[0467] The forward frame portion 201 is shaped to define a first annular surface 216 which faces towards the rearward frame portion 202 and extends around the movement axis 11’. The rearward frame portion 202 is shaped to define a second annular surface 216 which faces towards the forward frame portion 201 and extends around the movement axis 11 ’. The voice coil windings 236, 237 are arranged between the opposing annular surfaces 216.

[0468] The voice coil windings 236, 237 are arranged such that there is a clearance space between each end of the voice coil windings 236, 237 and the chassis 200 in a direction parallel to the movement axis 11 ’. More specifically, the voice coil windings 236, 237 are arranged such that there is a clearance space between each end of the voice coil windings 236, 237 and the respective annular surface 216.

[0469] More particularly, the chassis 200 defines a coil windings space into which the voice coil windings 236, 237 are insertable. The coil windings space extends around the movement axis 11 ’. The coil windings space extends along a direction parallel to the movement axis 11 ’ between the first annular surface 216 and a second annular surface 216. The voice coil windings 236, 237 are positioned within the voice coil windings space such that an axial end 236-1 of the first set of voice coil windings 236 is spaced from the first annular surface 216 along a direction that is parallel to the movement axis 1 T. This spacing may be termed a first clearance space (e.g., a first voice coil clearance space). Additionally or alternatively, the voice coil windings 236, 237 are positioned within the voice coil windings space such that an axial end 236-2 of the second set of voice coil windings 237 is spaced from the second annular surface 216 along a direction that is parallel to the movement axis 11 ’. This spacing may be termed a second clearance space (e.g., a second voice coil clearance space).008861056

[0470] 49

[0471] A possible method for use in manufacturing the transducer 210 shown in Figure 28 includes the following steps:

[0472] 1) Form transducer sub-assembly on a dedicated jig. The transducer sub-assembly includes the permanent magnet 241 , forward-facing flux guide 242 and rearward-facing flux guide 243.

[0473] 2) Fix the first suspension element 260 to the forward-facing flux guide 242 (using a first attachment member 280).

[0474] 3) Insert the voice coil 235 and the tubular yoke 232 in the rearward frame portion 202.

[0475] 4) Optionally, apply glue to a gutter formed between the rearward frame portion 202 and the tubular yoke 232.

[0476] 5) Apply the forward frame portion 201 and allow glue to cure.

[0477] 6) Apply glue to the first suspension attachment surface 268 and install the drive unit 220 with the first suspension element 260. Allow glue to cure.

[0478] 7) Rotate the transducer 210 and apply glue to the second suspension attachment surface 268. 8) Install second suspension element 260 and fixate to rearward-facing flux guide 243.

[0479] 9) Magnetize

[0480] 10) Glue closure element 290 (see Figure 30) in place (if applicable)

[0481] 11) Rotate, glue bottom cover in place (if applicable)

[0482] 12) Solder a voice coil wire and cable to tags. Park cable on stress relief feature and additionally apply glue (if applicable).

[0483] Figure 29 shows a perspective view of the transducer 210.

[0484] As shown in Figure 29, the transducer 210 further comprises a first lead wire 211. The first lead wire 211 extends from the voice coil 235 in an interior space of the transducer 210 enclosed by the chassis 200 and the first and second suspension elements 260, to an exterior space outside of the transducer 210, e.g., to make electrical connection with an externals signal source. The first lead wire 211 extends past the first suspension element 260.

[0485] As discussed above, the voice coil 235 is electrically connectable to a signal source at a location towards the first end of the voice coil 235 and is electrically connectable to the signal source at a location towards the second end of the voice coil 235. The lead wire 211 is provided for conveniently making such an electrical connection.

[0486] The transducer 210 further comprises a first groove 212. The first groove 212 extends past the first suspension element 260 from the interior space to the exterior space. The first groove 212 is formed between a first pair of spacer elements 213. The first pair of spacer elements 213 extend past the first suspension element 260 from the interior space to the exterior space. The first lead wire 211 extends in008861056

[0487] 50

[0488] the first groove 212. The first pair of spacer elements 213 are arranged between the first lead wire 211 and the first suspension element 260.

[0489] In some examples, the pair of spacer elements 213 may be replaced by a single spacer element. A groove through which a lead wire may extend may be cut into the single spacer element.

[0490] The first suspension element 260 includes a first notch 214. More particularly, an outer edge of the first suspension element 260 includes a first notch 214. The first lead wire 211 , the first groove 212, and the first pair of spacer elements 213 extend through the first notch 214 from the interior space to the exterior space.

[0491] The transducer 210 further comprises a second lead wire, a second groove, formed between a second pair of spacer elements, and a second notch formed in the second suspension element 260 (not shown in Figure 29), which mirror the characteristics and arrangement of the first lead wire 211 , first groove 212, first pair of spacer elements 213, and first notch 214, but on the opposite side of the transducer 210 (see Figure 32). More specifically, the second lead wire, the second groove, and / or the second pair of spacer elements extend through the second notch (e.g., formed in the second suspension element 260) from the interior space to the exterior space.

[0492] Conveniently, each and / or the combination of the grooves 212, pairs of spacer elements 213, and notches 214 prevent contact from occurring between the lead wires 211 and the respective suspension elements 260 that each lead wire 211 extends past. An example of a short circuit path that this arrangement prevents is indicated by the arrows in Figure 32.

[0493] Figure 30 shows a second perspective view of the transducer 210. As shown in Figure 30, the transducer 210 further includes a closure element 290 and another closure element 290’. In this example, the closure element 290 is fitted over the forward frame portion 201 and the other closure element 290’ is fitted over the rearward frame portion 202.

[0494] The closure element 290 includes integrated mechanical fasteners 292. The integrated mechanical fasteners 292 are arranged on opposite sides of the transducer 210. The integrated mechanical fasteners 292 may be integrated mounting clicks. The integrated mechanical fasteners 292 are configured to engage with counter mechanical fasteners 295 integrated into an application 294. Conveniently, this allows the transducer 210 to be installed in the application 294, which may be a car seat, so that the installation of the transducer 210 in place can happen without use of glues or external fasteners.

[0495] In some examples, the transducer 210 may have integrated electrical terminals (not shown). The integrated electrical terminals may be electrical pins. The integrated mechanical fasteners 292 may include or be the one or more integrated electrical terminals shown in Figure 1. Conveniently, this would simplify the electrical connection to external power sources, as well as the connections between the application 294 and the transducer 210.

[0496] The closure elements 290, 290’ may be fitted to any of the transducers described above.

[0497] Figure 31 shows a sectional view of a sixth transducer 310.008861056

[0498] 51

[0499] The transducer 310 is broadly similar to the transducer 210. Like reference signs of the elements of transducer 210, incremented by 100, are applied to like elements of the transducer 310.

[0500] Like the transducer 210, the transducer 310 includes a chassis 300 that includes a forward frame portion 301 and a rearward frame portion 302. The transducer 310 further includes a drive unit 320, which includes a stationary part 330 (that is part of the chassis 300) and a moveable part 340 that is moveable relative to the stationary part 330 along a movement axis 11 ”.

[0501] The moveable part 340 of the drive unit 320 includes a permanent magnet 341 to generate magnetic flux, a forward-facing flux guide 342 and a rearward-facing flux guide 343. The moveable part 340 is the same as the moveable part 240 of the transducer 210.

[0502] The stationary part 330 of the drive unit 320 includes a tubular yoke 332, which forms part of the chassis 300. The tubular yoke 332 extends around the movement axis 11 ”.

[0503] The stationary part 330 of the drive unit 320 also includes a voice coil 335. The voice coil 335 includes voice coil windings 336, 337 (a first set of voice coil windings 336 and a second set of voice coil windings 337) arranged on a voice coil former 338. The voice coil former 338 has a generally tubular shape on which the voice coil windings 336, 337 are arranged between a first end and a second end of the voice coil 335.

[0504] The first set of windings 336 and the second set of windings 337 are formed from a single continuous wire, and each of the first set of windings 336 and the second set of windings 337 has an uneven number of winding layers such that the wire extends from the first set of windings 336 in a forward direction 12”, and extends from the second set of windings 337 in a rearward direction 13”. Conveniently, the voice coil 335 is electrically connectable to a signal source at a location towards the first end of the voice coil 335 and is electrically connectable to the signal source at a location towards the second end of the voice coil 335.

[0505] Electrical terminals (like the electrical terminals 139 shown in Figure 1), first and second lead wires (like the first and second lead wires described in relation to Figure 29), or a combination of both may be provided for conveniently making such an electrical connection.

[0506] The transducer 310 further includes a first suspension element 360 and a second suspension element 360 which are respectively configured to deflect along the movement axis 11 ”.

[0507] The first suspension element 360 includes a first suspension attachment surface 368 which is secured to a first landing surface 303 of the chassis 300 (e.g., using adhesive). The second suspension element 360 includes a second suspension attachment surface 368 which is secured to a second landing surface 303 of the chassis 300 (e.g., using adhesive).

[0508] The first suspension element 360 also includes a first suspension attachment formation 370 configured to be attached to the moveable part 340 and the second suspension element 360 includes a second suspension attachment formation 370 configured to be attached to the moveable part 340. The first suspension attachment formation 370 and the second suspension attachment formation 370 are each008861056

[0509] 52

[0510] configured to be attached to a respective attachment formation 350 of the moveable part 340. More particularly, the first suspension attachment formation 370 is configured to be attached to the attachment formation 350 of the forward-facing flux guide 342 by a first attachment member 380, and the second suspension attachment formation 370 is configured to be attached to the attachment formation 350 of the rearward-facing flux guide 343 by a second attachment member 380.

[0511] The attachment of the suspension attachment formations 370 to the moveable part 340 is broadly the same as in the transducer 210, except that the attachment members 380 appear, in Figure 31 , to be pressed further into attachment recesses 354 of the moveable part 340. For the avoidance of doubt however, both the transducer 210, shown in Figure 28, and the transducer 310, shown in Figure 31 , show the assembled state of the respective transducer 210, 310. As such, like in the transducer 210, an axial separation of the first suspension attachment surface 368 and the second suspension attachment surface 368, as measured along the movement axis 11 ”, is equal to an axial separation of the first suspension attachment formation 370 and the second suspension attachment formation 370, as measured along the movement axis 11”.

[0512] On the other hand, unlike the transducer 210, an axial separation of the first suspension attachment surface 368 and the second suspension attachment surface 368, along the movement axis 11 ’, is (substantially) equal to an axial separation of the first landing surface 303 and the second landing surface 303, along the movement axis 11 ”.

[0513] Of course, the transducer 310 may instead be configured like the transducer 210, with the axial separation of the first suspension attachment surface 368 and the second suspension attachment surface 368, along the movement axis 11’, being greater than an axial separation of the first landing surface 303 and the second landing surface 303, along the movement axis 11 ”.

[0514] Returning to the chassis 300, as mentioned previously this includes a forward frame portion 301 and a rearward frame portion 302. The forward frame portion 301 and the rearward frame portion 302 are formed separately.

[0515] The forward frame portion 301 and the rearward frame portion 302 are directly secured to one another via an adhesive. In other examples, the forward frame portion 301 and the rearward frame portion 302 may be additionally or alternatively directly secured to one another via one or more mechanical fixings, and / or ultrasonic welding.

[0516] The moveable part 340 of the drive unit 320 is suspended from the forward frame portion 301 by the first suspension element 360, and is suspended from the rearward frame portion 302 by the second suspension element 360.

[0517] Like in the transducer 210, the forward frame portion 301 is shaped to define a first channel 304 which faces towards the rearward frame portion 302 and extends around the movement axis 11 ”. Likewise, the rearward frame portion 302 is shaped to define a second channel 304 which faces towards the forward frame portion 301 and extends around the movement axis 11”. The first end 333 of the tubular yoke 332 is received into the first channel 304 to thereby align the first suspension element 360 relative to the008861056

[0518] 53

[0519] tubular yoke 332, and the second end 334 of the tubular yoke 332 is received into the second channel 304 to thereby align the second suspension element 360 relative to the tubular yoke 332.

[0520] The rearward frame portion 302 includes a first protruding portion 302-1 that is arranged such that a gutter 309 is created between the first protruding portion 302-1 and the tubular yoke 332. The forward frame portion 301 includes a second protruding portion 301-1 that is arranged to protrude into the gutter 309. The gutter 309 is at least partly filled by the adhesive to secure the first protruding portion 302-1 and the second protruding portion 301-1 together.

[0521] Further like in the transducer 210, the tubular yoke 332 is constrained between the forward frame portion 301 and the rearward frame portion 302. The first end 333 of the tubular yoke 332 forms an interference fit with the first channel 304, and the second end 334 of the tubular yoke 332 forms an interference fit with the second channel 304. In some examples, the first channel 304 and the second channel 304 may each respectively include one or more press ribs 389 configured to at least partially cause the interference fit between each respective channel 304 and the corresponding end 333, 334 of the tubular yoke 332. The first channel 304 includes a first end surface 304-1 , and the second channel 304 includes a second end surface 304-1. The first and second end surfaces 304-1 extend around the movement axis 11 ”. The first end surface 304-1 faces in the rearward direction 13”, and the second end surface 304-1 faces in the forward direction 12”.

[0522] In this example, the first end 333 of the tubular yoke 332 does not abut the first end surface 304-1 , and the second end 334 of the tubular yoke 332 does not abut the second end surface 304-1. The tubular yoke 332 is arranged such that there is a (e.g., tubular yoke) clearance space between one or each end 333, 334 of the tubular yoke 332 and the end of the channel 304-1 in which the or each respective end 333, 334 is inserted along the movement axis 11 ”. More particularly, there is a fist tubular yoke clearance space defined between the first end 333 of the tubular yoke 332 and the first end surface 304-1 along a direction parallel to the movement axis 11”. There is a second tubular yoke clearance space defined between the second end 334 of the tubular yoke 332 and the second end surface 304-1 along a direction parallel to the movement axis 11 ”. Conveniently, the inclusion of one or more tubular yoke clearance spaces allows for better adjustment of the forward frame portion 301 and the second frame portion 302 during assembly of the transducer 310.

[0523] The forward frame portion 301 further includes a first axis-facing inner surface 306. The first axis-facing inner surface 306 extends around the movement axis 11 ” and, in particular, around the voice coil former 338 such that a forward end of the voice coil former 338 is radially constrained by the first axis-facing inner surface 306. Similarly, the rearward frame portion 302 includes a second axis-facing inner surface 306. The second axis-facing inner surface 306 extends around the movement axis 11 ” and around the voice coil former 338 such that a rearward end of the voice coil former 338 is radially constrained by the second axis-facing inner surface 306 of the rearward frame portion 302. The described arrangement of the forward frame portion 301 , the rearward frame portion 302 and the voice coil former 338 aligns the voice coil 335 with respect to the movement axis 11 ”.008861056

[0524] 54

[0525] The forward frame portion 301 is shaped to define a first annular surface 316 which faces towards the rearward frame portion 302 and extends around the movement axis 11”. The rearward frame portion 302 is shaped to define a second annular surface 316 which faces towards the forward frame portion 301 and extends around the movement axis 11 The voice coil windings 336, 337 are arranged between the opposing annular surfaces 316 to thereby axially constrain the voice coil windings 336, 337. In some examples, the voice coil windings 336, 337 are attached to the first annular surface 316 and the second annular surface 316 by adhesive.

[0526] The chassis 200 further comprises an overflow passage 315. The overflow passage 315 is connected to the gutter 309 and extends alongside the tubular yoke 332. Adhesive extends from the gutter 309 into the overflow passage 315 to at least partially fill the overflow passage 315.

[0527] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0528] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0529] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0530] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0531] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0532] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / - 10%.008867056

[0533] 55

[0534] References

[0535] A number of publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below. The entirety of each of these references is incorporated herein.

[0536] PCT / EP2023 / 084674

[0537] US5973422A

[0538] US11341948B2

[0539] EP3597314A1008861056

[0540] 56

[0541] The following clauses, which form part of the description, provide general expressions of the disclosure herein:

[0542] Clause 1. An electromechanical transducer, including:

[0543] a chassis;

[0544] a drive unit which includes a stationary part, which forms part of the chassis, and a moveable part which is moveable relative to the stationary part, wherein the drive unit is operable to cause the moveable part to move along a movement axis relative to the stationary part along a movement axis in a forward direction and a rearward direction;

[0545] a forward frame portion, which forms part of the chassis, wherein the moveable part of the drive unit is suspended from the forward frame portion by a first suspension element configured to deflect along the movement axis;

[0546] a rearward frame portion, which forms part of the chassis, wherein the moveable part of the drive unit is suspended from the rearward frame portion by a second suspension element configured to deflect along the movement axis;

[0547] wherein the forward frame portion is shaped to define a first channel which faces towards the rearward frame portion and extends around the movement axis;

[0548] wherein the rearward frame portion is shaped to define a second channel which faces towards the forward frame portion and extends around the movement axis; a tubular yoke, which forms part of the chassis, having:

[0549] a first end received into the first channel of the forward frame portion to thereby align the first suspension element relative to the tubular yoke, and

[0550] a second end received into the second channel to thereby align the second suspension element relative to the tubular yoke.

[0551] Clause 2. The electromechanical transducer of Clause 1 ,

[0552] further comprising a voice coil, which is included in the stationary part of the drive unit, mounted within the tubular yoke;

[0553] wherein the voice coil includes voice coil windings arranged on a voice coil former; wherein a forward end of the voice coil former is radially constrained by a first axis-facing inner surface of the forward frame portion and a rearward end of the voice coil former is radially constrained by a second axis-facing inner surface of the rearward frame portion to thereby align the voice coil with respect to the movement axis.

[0554] Clause 3. The electromechanical transducer of Clause 2,

[0555] wherein the forward frame portion is shaped to define a first annular surface which faces towards the rearward frame portion and extends around the movement axis and wherein the rearward frame portion is shaped to define a second annular surface which faces towards the forward frame portion and extends around the movement axis;

[0556] wherein the voice coil windings are axially constrained by the first annular surface and the second annular surface.008861056

[0557] 57

[0558] Clause 4. The electromechanical transducer of Clause 3,

[0559] wherein the voice coil windings are glued to the first annular surface and the second annular surface.

[0560] Clause 5. The electromechanical transducer of any one of Clause 2 to 4,

[0561] wherein the voice coil windings are arranged to provide a first set of windings and, spaced therefrom, a second set of windings; and

[0562] wherein the moveable part of the drive unit includes a first flux guide, a second flux guide and a permanent magnet between the flux guides;

[0563] wherein a first air gap is formed between the first flux guide and the tubular yoke and a second air gap is formed between the second flux guide and the tubular yoke.

[0564] Clause 6. The electromechanical transducer of Clause 5,

[0565] wherein the first set of windings and the second set of windings are formed from a single continuous wire.

[0566] Clause 7. The electromechanical transducer of Clause 5 or 6,

[0567] wherein each of the first set of windings and the second set of windings has an uneven number of winding layers; and

[0568] wherein the voice coil is electrically connected to a signal source at a first end of the voice coil and is electrically connected to the signal source at a second end of the voice coil.

[0569] Clause 8. The electromechanical transducer of any preceding Clause,

[0570] wherein the drive unit defines a motor force product BL, where B is the magnetic flux in the air gap and L is the length of windings in the magnetic flux in the air gap;

[0571] wherein B is between 1% and 30% of L, optionally B is between 2% and 10% of L.

[0572] Clause 9. The electromechanical transducer of Clause 8,

[0573] wherein the magnetic flux B in the air gap has a magnitude such that the resulting magnetic attraction between the stationary part and the moveable part causes a radial static deflection of the moveable part relative to the movement axis of no more than 0.1 millimetres.

[0574] Clause 10. The electromechanical transducer of any preceding Clause,

[0575] wherein the forward frame portion has a first end face which faces away from the tubular yoke and the rearward frame portion has a second end face which faces away from the tubular yoke; and wherein a central passage extends between the first end face and the second end face in which the moveable part is moveable along the movement axis.

[0576] Clause 11. The electromechanical transducer of Clause 10,

[0577] wherein a first landing surface is recessed into the first end face and the first suspension element is attached to the first landing surface, wherein a forward clearance space is formed between the first end008861056

[0578] 58

[0579] face and the first landing surface, and the moveable part of the drive unit is moveable into the forward clearance space;

[0580] wherein a second landing surface is recessed into the second end face and the second suspension element is attached to the second landing surface, wherein a rearward clearance space is formed between the second end face and the second landing surface, and the moveable part of the drive unit is moveable into the rearward clearance space.

[0581] Clause 12. The electromechanical transducer of Clause 10 or 11,

[0582] wherein the central passage extends between a first opening in the first end face and a second opening in the second end face; and

[0583] wherein the chassis includes a first closure member attached to the forward frame portion to close the first opening and a second closure member attached to the rearward frame portion to close the second opening.

[0584] Clause 13. The electromechanical transducer of Clause 12,

[0585] wherein the chassis is arranged to provide an airtight seal around the central passage.

[0586] Clause 14. The electromechanical transducer of any preceding Clause,

[0587] wherein the first suspension element is secured to a first landing surface of the chassis and the second suspension element is secured to a second landing surface of the chassis, and

[0588] wherein the first suspension element includes a first suspension attachment formation attached to the moveable part and the second suspension element includes a second suspension attachment formation attached to the moveable part;

[0589] wherein the first suspension attachment formation and the second suspension attachment formation are attached to at least one attachment formation of the moveable part;

[0590] wherein an axial separation of the first landing surface and the second landing surface, as measured along the movement axis, is greater than an axial separation of the first suspension attachment formation and the second suspension attachment formation, as measured along the movement axis, such that the suspension elements are deflected along the movement axis by their attachment to the moveable part when the moveable part is at a rest position.

[0591] Clause 16. A vehicle including the electromechanical transducer of any preceding Clause, wherein the vehicle includes a seat with seat foam therein; and

[0592] wherein the electromechanical transducer is mounted to a recess in the seat foam.

[0593] Clause 17. A method for assembly of an electromechanical transducer, the method including:

[0594] providing a tubular yoke, which forms part of a drive unit, having a first end and a second end; receiving the first end of the tubular yoke into a first annular channel of a forward frame portion; providing a moveable part of the drive unit;

[0595] attaching a first suspension element to the moveable part;

[0596] receiving the moveable part into the tubular yoke;008867056

[0597] 59

[0598] attaching the first suspension element to the forward frame portion to thereby align the first suspension element relative to the tubular yoke and wherein the first suspension element is configured to deflect along a movement axis;

[0599] receiving the second end of the tubular yoke into a second annular channel of a rearward frame portion;

[0600] wherein the first annular channel faces towards the rearward frame portion and the second annular channel faces towards the forward frame portion;

[0601] attaching a second suspension element to the rearward frame portion to thereby align the second suspension element relative to the tubular yoke and wherein the second suspension element is configured to deflect along the movement axis;

[0602] attaching the second suspension element to the moveable part;

[0603] wherein the drive unit is operable to cause the moveable part to move along the movement axis relative to the stationary part in a forward direction and a rearward direction.008861056

[0604] 60

[0605] The following clauses, which form part of the description, provide general expressions of the disclosure herein:

[0606] Clause 1. An electromechanical transducer, including:

[0607] a chassis;

[0608] a drive unit which includes a stationary part, which forms part of the chassis, and a moveable part which is moveable relative to the stationary part, wherein the drive unit is operable to cause the moveable part to move relative to the stationary part along a movement axis in a forward direction and in a rearward direction;

[0609] a first suspension element and a second suspension element which are respectively configured to deflect along the movement axis,

[0610] wherein the first suspension element includes a first suspension attachment surface which is secured to the chassis and the second suspension element includes a second suspension attachment surface which is secured to the chassis, and

[0611] wherein the first suspension element includes a first suspension attachment formation attached to the moveable part and the second suspension element includes a second suspension attachment formation attached to the moveable part;

[0612] wherein the first suspension attachment formation and the second suspension attachment formation are attached to at least one attachment formation of the moveable part;

[0613] Clause 2. The electromechanical transducer of clause 1 , wherein an axial separation of the first suspension attachment surface and the second suspension attachment surface, as measured along the movement axis, is greater than an axial separation of the first suspension attachment formation and the second suspension attachment formation, as measured along the movement axis, such that the suspension elements are deflected along the movement axis by their attachment to the moveable part when the moveable part is at a rest position.

[0614] Clause 3. The electromechanical transducer of clause 1 , wherein an axial separation of the first suspension attachment surface and the second suspension attachment surface, as measured along the movement axis, is equal to an axial separation of the first suspension attachment formation and the second suspension attachment formation, as measured along the movement axis,

[0615] Clause 4. The electromechanical transducer of any one of clauses 1 to 3,

[0616] wherein the first suspension attachment formation and the second suspension attachment formation are mechanically attached to the at least one attachment formation of the moveable part by at least one attachment member.

[0617] Clause 5. The electromechanical transducer of clause 4,

[0618] wherein the at least one attachment formation includes a tapped hole, and

[0619] wherein the at least one attachment member includes a threaded member which makes a threaded connection with the tapped hole.008861056

[0620] 61

[0621] Clause 6. The electromechanical transducer of clause 4 or 5,

[0622] wherein the first suspension attachment formation is mechanically attached to the at least one attachment formation by a first attachment member; and

[0623] wherein the second suspension attachment formation is mechanically attached to the at least one attachment formation by a second attachment member.

[0624] Clause 7. The electromechanical transducer of clause 4 or 5,

[0625] wherein the first suspension attachment formation is mechanically attached to a first attachment formation by a first attachment member; and

[0626] wherein the second suspension attachment formation is mechanically attached to a second attachment formation by a second attachment member.

[0627] Clause 8. The electromechanical transducer of any preceding clause,

[0628] wherein the stationary part of the drive unit includes a voice coil with voice coil windings arranged on a voice coil former; and

[0629] wherein the voice coil windings are arranged to provide a first set of windings and, spaced therefrom, a second set of windings.

[0630] Clause 9. The electromechanical transducer of clause 8,

[0631] wherein the first set of windings and the second set of windings are formed from a single continuous wire.

[0632] Clause 10. The electromechanical transducer of clause 8 or 9,

[0633] wherein each of the first set of windings and the second set of windings has an uneven number of winding layers; and

[0634] wherein the voice coil is electrically connected to a signal source at a first end of the voice coil and is electrically connected to the signal source at a second end of the voice coil.

[0635] Clause 11. The electromechanical transducer of any one of clause 8 to 10, wherein the voice coil former has a first end and a second end, wherein the first end of the voice coil former abuts the first suspension element and the second end of the voice coil former abuts the second suspension element.

[0636] Clause 12. The electromechanical transducer of clause 11 , wherein the chassis includes a first landing surface that the first suspension attachment surface is secured to, and a second landing surface that the second suspension attachment surface is secured to,

[0637] and wherein an axial separation of the first end of the voice coil former and the second end of the voice coil former, along the movement axis, is greater than an axial separation of the first landing surface and the second landing surface, along the movement axis.008861056

[0638] 62

[0639] Clause 13. The electromechanical transducer of clause 12, wherein the first end of the voice coil former, the first suspension attachment surface, and the first landing surface are secured together by a first bead of adhesive; and / or the second end of the voice coil former, the second suspension attachment surface, and the second landing surface are secured together by a second bead of adhesive.

[0640] Clause 14. The electromechanical transducer of any one of clauses 8 to 13, wherein the voice coil windings are arranged such that there is a clearance space between one or each end of the voice coil windings and the chassis along the movement axis.

[0641] Clause 15. The electromechanical transducer of any preceding clause,

[0642] wherein the moveable part of the drive unit includes a first flux guide, a second flux guide and a permanent magnet arranged between the first flux guide and the second flux guide;

[0643] wherein the first suspension attachment formation is attached to a first attachment formation of the first flux guide and the second suspension attachment formation is attached to a second attachment formation of the second flux guide.

[0644] Clause 16. The electromechanical transducer of clause 15,

[0645] wherein the first attachment formation extends in the forward direction towards the first suspension attachment surface and the second attachment formation extends in the rearward direction towards the second suspension attachment surface.

[0646] Clause 17. The electromechanical transducer of any preceding clause,

[0647] wherein the drive unit defines a motor force factor BL, where B is the magnetic flux in the air gap and L is the length of windings in the magnetic flux in the air gap;

[0648] wherein B is between 1% and 30% of L, optionally B is between 2% and 10% of L.

[0649] Clause 18. The electromechanical transducer of clause 17,

[0650] wherein the magnetic flux B in the air gap has a magnitude such that the resulting magnetic attraction between the stationary part and the moveable part causes a radial static deflection of the moveable part relative to the movement axis of no more than 0.1 millimetres.

[0651] Clause 19. The electromechanical transducer of any preceding clause,

[0652] wherein the first suspension element and the second suspension element each include a plurality of bridge arms which extend towards the suspension attachment formation;

[0653] wherein each suspension element has at most three bridge arms.008861056

[0654] 63

[0655] Clause 20. The electromechanical transducer of clause 19,

[0656] wherein each suspension element has two bridge arms.

[0657] Clause 21. The electromechanical transducer of clause 19 or clause 20,

[0658] wherein the suspension elements are formed by stamping to provide the bridge arms and the suspension attachment formation.

[0659] Clause 22. The electromechanical transducer of any preceding clause,

[0660] further comprising:

[0661] a forward frame portion, which forms part of the chassis, wherein the moveable part of the drive unit is suspended from the forward frame portion by the first suspension element; and

[0662] a rearward frame portion, which forms part of the chassis, wherein the moveable part of the drive unit is suspended from the rearward frame portion by the second suspension element.

[0663] Clause 23. The electromechanical transducer of clause 22,

[0664] wherein the forward frame portion is shaped to define a first channel which faces towards the rearward frame portion and extends around the movement axis;

[0665] wherein the rearward frame portion is shaped to define a second channel which faces towards the forward frame portion and extends around the movement axis; and

[0666] wherein the electromechanical transducer further comprises a tubular yoke having:

[0667] a first end received into the first channel of the forward frame portion to thereby align the first suspension element relative to the tubular yoke, and

[0668] a second end received into the second channel to thereby align the second suspension element relative to the tubular yoke.

[0669] Clause 24. The electromechanical transducer of clause 23, wherein the tubular yoke is insert moulded into one of the rearward frame portion and the forward frame portion.

[0670] Clause 25. The electromechanical transducer of clause 23, wherein the first end of the tubular yoke forms an interference fit with the first channel, and the second end of the tubular yoke forms an interference fit with the second channel.

[0671] Clause 26. The electromechanical transducer of clause 25, wherein each of the first channel and the second channel includes one or more press ribs configured to at least partially cause the interference fit between each respective channel and the corresponding end of the tubular yoke.

[0672] Clause 27. The electromechanical transducer of any one of clauses 23 to 26, wherein the tubular yoke is arranged such that there is a clearance space between one or each end of the tubular yoke and the end of the channel in which the or each respective end of the tubular yoke is inserted along the movement axis.008861056

[0673] 64

[0674] Clause 28. The electromechanical transducer of any one of clauses 22 to 27, wherein the forward frame portion and the rearward frame portion are directly secured to one another via: one or more mechanical fixings; ultrasonic welding; and / or an adhesive.

[0675] Clause 29. The electromechanical transducer of clause 28, wherein the forward frame portion and the rearward frame portion are directly secured to one another via at least the adhesive, and wherein: the rearward frame portion includes a first protruding portion that is arranged such that a gutter is created between the first protruding portion and the tubular yoke; and

[0676] the forward frame portion includes a second protruding portion that is arranged to protrude into the gutter,

[0677] wherein the gutter is at least partly filled by the adhesive to secure the first protruding portion and second protruding portion together.

[0678] Clause 30. The electromechanical transducer of clause 29, wherein the chassis further comprises an overflow passage that is connected to the gutter and that extends alongside the tubular yoke, and wherein the adhesive extends from the gutter into the overflow passage to at least partially fill the overflow passage.

[0679] Clause 31. The electromechanical transducer of any preceding clause, further comprising a lead wire, wherein the lead wire extends from an interior space of the electromechanical transducer to an exterior space outside of the electromechanical transducer.

[0680] Clause 32. The electromechanical transducer of clause 31 , wherein an outer edge of the first suspension element or the second suspension element includes a notch through which the lead wire extends from the interior space to the exterior space.

[0681] Clause 33. The electromechanical transducer of clause 31 or clause 32, further comprising a groove, formed between a pair of spacer elements, that extends past the first or second suspension element from the interior space to the exterior space,

[0682] wherein the lead wire extends in the groove, and wherein the pair of spacer elements are arranged between the lead wire and the first or second suspension element.

[0683] Clause 34. The electromechanical transducer of any preceding clause, further comprising an integrated mechanical fastener for fastening the chassis to another structure.

[0684] Clause 35. The electromechanical transducer of clause 34, wherein the mechanical fastener includes one or more integrated electrical terminals.

[0685] Clause 36. A road vehicle including the electromechanical transducer of any preceding clause, wherein the road vehicle includes a seat containing a seat foam; and

[0686] wherein the electromechanical transducer is mounted to a recess in the seat foam.

Claims

00886105665Claims:

1. An electromechanical transducer, including:a chassis;a drive unit which includes a stationary part, which forms part of the chassis, and a moveable part which is moveable relative to the stationary part, wherein the drive unit is operable to cause the moveable part to move relative to the stationary part along a movement axis in a forward direction and in a rearward direction;a first suspension element and a second suspension element which are respectively configured to deflect along the movement axis,wherein the first suspension element is secured to a first landing surface of the chassis and the second suspension element is secured to a second landing surface of the chassis, andwherein the first suspension element includes a first suspension attachment formation attached to the moveable part and the second suspension element includes a second suspension attachment formation attached to the moveable part;wherein the first suspension attachment formation and the second suspension attachment formation are attached to at least one attachment formation of the moveable part;wherein an axial separation of the first landing surface and the second landing surface, as measured along the movement axis, is greater than an axial separation of the first suspension attachment formation and the second suspension attachment formation, as measured along the movement axis, such that the suspension elements are deflected along the movement axis by their attachment to the moveable part when the moveable part is at a rest position.

2. The electromechanical transducer of claim 1 ,wherein the first suspension attachment formation and the second suspension attachment formation are mechanically attached to the at least one attachment formation of the moveable part by at least one an attachment member.

3. The electromechanical transducer of claim 2,wherein the at least one attachment formation includes a tapped hole, andwherein the at least one attachment member includes a threaded member which makes a threaded connection with the tapped hole.

4. The electromechanical transducer of claim 2 or 3,wherein the first suspension attachment formation is mechanically attached to the at least one attachment formation by a first attachment member; andwherein the second suspension attachment formation is mechanically attached to the at least one attachment formation by a second attachment member.008861056665. The electromechanical transducer of claim 2 or 3,wherein the first suspension attachment formation is mechanically attached to a first attachment formation by a first attachment member; andwherein the second suspension attachment formation is mechanically attached a second attachment formation by a second attachment member.

6. The electromechanical transducer of any preceding claim,wherein the stationary part of the drive unit includes a voice coil with voice coil windings arranged on a voice coil former; andwherein the voice coil windings are arranged to provide a first set of windings and, spaced therefrom, a second set of windings.

7. The electromechanical transducer of claim 6,wherein the first set of windings and the second set of windings are formed from a single continuous wire.

8. The electromechanical transducer of claim 6 or 7,wherein each of the first set of windings and the second set of windings has an uneven number of winding layers; andwherein the voice coil is electrically connected to a signal source at a first end of the voice coil and is electrically connected to the signal source at a second end of the voice coil.

9. The electromechanical transducer of any preceding claim,wherein the moveable part of the drive unit includes a first flux guide, a second flux guide and a permanent magnet arranged between the first flux guide and the second flux guide;wherein the first suspension attachment formation is attached to a first attachment formation of the first flux guide and the second suspension attachment formation is attached to a second attachment formation of the second flux guide.

10. The electromechanical transducer of claim 9,wherein the first attachment formation extends in the forward direction towards the first landing surface and the second attachment formation extends in the rearward direction towards the second landing surface.

11. The electromechanical transducer of any preceding claim,wherein the drive unit defines a motor force factor BL, where B is the magnetic flux in the air gap and L is the length of windings in the magnetic flux in the air gap;wherein B is between 1% and 30% of L, optionally B is between 2% and 10% of L.0088610566712. The electromechanical transducer of claim 11 ,wherein the magnetic flux B in the air gap has a magnitude such that the resulting magnetic attraction between the stationary part and the moveable part causes a radial static deflection of the moveable part relative to the movement axis of no more than 0.1 millimetres.

13. The electromechanical transducer of any preceding claim,wherein the first suspension element and the second suspension element each include a plurality of bridge arms which extend towards the suspension attachment formation;wherein each suspension element has at most three bridge arms.

14. The electromechanical transducer of claim 13,wherein each suspension element has two bridge arms.

15. The electromechanical transducer of claim 13 or 14,wherein the suspension elements are formed by stamping to provide the bridge arms and the suspension attachment formation.

16. The electromechanical transducer of any preceding claim,further comprising:a forward frame portion, which forms part of the chassis, wherein the moveable part of the drive unit is suspended from the forward frame portion by the first suspension element;a rearward frame portion, which forms part of the chassis, wherein the moveable part of the drive unit is suspended from the rearward frame portion by the second suspension element;wherein the forward frame portion is shaped to define a first channel which faces towards the rearward frame portion and extends around the movement axis;wherein the rearward frame portion is shaped to define a second channel which faces towards the forward frame portion and extends around the movement axis; and a tubular yoke having:a first end received into the first channel of the forward frame portion to thereby align the first suspension element relative to the tubular yoke, anda second end received into the second channel to thereby align the second suspension element relative to the tubular yoke.

17. A road vehicle including the electromechanical transducer of any preceding claim, wherein the road vehicle includes a seat containing a seat foam; andwherein the electromechanical transducer is mounted to a recess in the seat foam.

Images