Actuator for a heavy vehicle foundation brake

Abstract

An actuator (101) for a heavy vehicle foundation brake, the actuator (101) comprising an output pushrod (160) to interface with the foundation brake; a rotary electric machine (120) arranged to selectively displace the pushrod (160) axially between a retracted position and a deployed position; a rotary to linear gear mechanism to drive linear motion of the pushrod (160) upon rotation of the electric machine (120); and a gear mechanism housing concentrically arranged at least partially within, and configured for rotation with, the rotary electric machine (120); wherein the gear mechanism housing defines a gear mechanism housing cavity; and wherein the pushrod (160) is at least partially received within the gear mechanism housing cavity when the pushrod (160) is in the retracted position.

Description

24-0300 (P607927)ACTUATOR FOR A HEAVY VEHICLE FOUNDATION BRAKETECHNICAL FIELD[OOO1] The present disclosure relates to an actuator for a heavy vehicle foundation brake and a brake assembly including an actuator and a heavy vehicle foundation brake.BACKGROUND

[0002] It is known to provide heavy commercial vehicles such as trucks and buses with disc brake and drum brake actuators operable by compressed air. This requires a system for supplying the compressed air to each wheel-end of a vehicle that requires braking, which is costly due to the need for compressors, air dryers, reservoirs, valves, electronics and pipework such system require.

[0003] As a greater proportion of such heavy vehicles transition to having electrically powered propulsion (either battery electric or hydrogen fuel cell electric) it may become a) more desirable to electrify other systems, such as braking, as electrical power is more readily available on the vehicle and b) to seek to reduce cost of such systems as a way of bringing down the overall purchase cost of electrically powered heavy vehicles to be nearer that of conventional diesel powered heavy vehicles.

[0004] Electromechanical actuation of heavy vehicle foundation brakes is known, but has hitherto required a redesign of the entire actuator and foundation brake combination and / or can no longer fit in the same space envelope as a conventional air actuator and disc or drum foundation brake. Given that electric heavy vehicles are a small proportion of overall heavy vehicles sales, the ground-up redesign, testing of and re-tooling for the series production of new disc brake calipers and drum brakes is not commercially attractive. This is further compounded if the brake and actuator can no longer fit in the usual space envelope and the vehicle itself has to be redesigned to accommodate the actuator and foundation brake.

[0005] The present disclosure seeks to overcome or at least mitigate the problems of the prior art.SUMMARY OF INVENTION

[0006] Aspects and embodiments of the invention provide an actuator and a brake assembly as claimed in the appended claims.

[0007] According to an aspect of the present invention, an actuator for a heavy vehicle foundation brake is provided . The actuator includes : an output pushrod to interface with the foundation brake; a rotary electric machine arranged to selectively displace the pushrod axially between a retracted position and a deployed position; a rotary to linear gear mechanism to drive linear motion of the pushrod upon rotation of the electric24-0300 (P607927) machine; and a gear mechanism housing concentrically arranged at least partially within, and configured for rotation with, the electric machine. The gear mechanism housing defines a gear mechanism housing cavity. The pushrod is at least partially received within the gear mechanism housing cavity when the pushrod is in the retracted position.

[0008] Housing at least part of the pushrod within the gear mechanism housing cavity of the gear mechanism housing provides a more compact actuator. The overall axial length of the actuator is reduced. Advantageously, a compact actuator suitable for use with a pushrod-actuated foundation brake, i.e. a brake that may otherwise be actuated by an air actuator, is provided.

[0009] At least half of the length of the pushrod may be received within the gear mechanism housing cavity when the pushrod is in the retracted position .

[0010] The gear mechanism housing cavity being capable of receiving at least half of the length of the pushrod provides an advantageously compact actuator.

[0011] At least two thirds of the length of the pushrod may be received within the gear mechanism housing cavity when the pushrod is in the retracted position .

[0012] The gear mechanism housing cavity being capable of receiving at least two thirds of the length of the pushrod again provides the advantage of a compact actuator that can be fitted into the desired space envelope.

[0013] The gear mechanism may comprise a lead screw. The pushrod may be connected to the lead screw at a lead screw joint. The lead screw joint may be received within the gear mechanism housing cavity.

[0014] Connection of the pushrod to a lead screw of the gear mechanism enables simple and effective control of the pushrod in a limited space. The lead screw joint being received within the gear mechanism housing cavity allows at least part of the pushrod to likewise be housed within the gear mechanism housing cavity. A compact actuator can thus be provided .

[0015] The lead screw joint may comprise a pushrod connector for connecting the pushrod to the gear mechanism, for transfer of linear motion from the gear mechanism to the pushrod .

[0016] As part of the lead screw joint, the pushrod collector is housed within the gear mechanism housing cavity, providing a compact means of transfer of linear motion from the gear mechanism to the pushrod.

[0017] The pushrod connector may comprise an outboard end secured to the pushrod, and an inboard end secured to the gear mechanism. The inboard end may be secured to the lead screw.24-0300 (P607927)

[0018] Such a pushrod connector provides an effective yet compact means of connection between the pushrod and the lead screw. The transfer of linear motion is enabled in a compact space.

[0019] The inboard end of the pushrod connector may be secured to the lead screw in an interference fit.

[0020] The pushrod connector may be integral to an outboard end of the lead screw.

[0021] Such an arrangement provides an alternative compact means of connection between the pushrod connector and the lead screw.

[0022] The pushrod may be pivotably connected to the gear mechanism.

[0023] Pivotable connection of the pushrod to the gear mechanism creates an articulated connection between the components. As a result, the pushrod has increased freedom of movement with respect to the gear mechanism. An outboard end of the pushrod, i.e. the end at which there is an interface between the pushrod and the foundation brake, can be moved through an arc in the vertical plane. Articulation between the pushrod and the gear mechanism thus allows increased travel of the outboard end of the pushrod - enabling an increased range of travel of an operating shaft of the foundation brake. That is, a full range of travel of the operating shaft can be enabled. The actuator can thus be used with the same interface, e.g . the same operating shaft arrangement, as that of existing air-actuated brakes. Advantageously, no adaptation of the interface between the actuator and the foundation brake is required.

[0024] The pushrod may be pivotably secured to the pushrod connector at a pushrod joint.

[0025] Providing a pivotable connection in such a location enables a compact articulated connection between the pushrod and the lead screw.

[0026] The pushrod connector outboard end may comprise a pushrod connector socket. The pushrod inboard end may be received within the pushrod connector socket. The pushrod inboard end may comprise a ball configured to be received within the pushrod connector socket.

[0027] A ball and socket joint allows a pivotable connection to be formed between the pushrod and the gear mechanism with a minimum of components in a compact space envelope.

[0028] The pushrod joint may be configured such that the pushrod is pivotable about a pushrod pivot axis. The pushrod pivot axis may be transverse to the longitudinal axis of the pushrod.

[0029] The pushrod inboard end may comprise a through bore configured to receive a pin. The pushrod joint may comprise a pin configured to extend through the through24-0300 (P607927) bore so as to pivotably secure the pushrod to the pushrod connector. The pin may extend co-axially with the pushrod pivot axis.

[0030] Such a pin arrangement effectively secures the push rod with relation to the lead screw in a simple arrangement, whilst allowing pivoting of the pushrod with respect to the gear mechanism in the required direction .

[0031] An outboard end of the pushrod may be configured for engagement with the foundation brake.

[0032] The outboard end of the pushrod may be configured for engagement with a brake lever of the foundation brake.

[0033] The outboard end of the pushrod may be rounded, for engagement with a correspondingly shaped brake lever.

[0034] The outboard end of the pushrod being configured in such a way facilitates engagement of the actuator with a foundation brake.

[0035] According to a further aspect of the present invention, an actuator for a heavy vehicle foundation brake is provided. The actuator includes: a rotary electric machine comprising a rotor; and a rotary to linear gear mechanism to drive linear motion upon rotation of the electric machine; and a gear mechanism housing concentrically arranged at least partially within, and configured for rotation with, the electric machine. The gear mechanism housing comprises a tubular body. The tubular body comprises a cylindrical wall. The wall thickness is in the range of 1.8mm to 3mm.

[0036] Such a wall thickness provides low rotational inertia of the gear mechanism housing whilst providing an actuator suitable for use with a pushrod-actuated foundation brake, i.e. a brake that may otherwise be actuated by an air actuator. The gear mechanism housing size allows the actuator to be suitably compact, such that the actuator can fit within the space envelope typically provided for an air actuator. Low rotational inertia advantageously leads to reduced power demand as well as improved brake actuation response time.

[0037] The wall thickness may be in the range of 2 mm to 2.5 mm. The wall thickness may be in the range of 2.2mm to 2.3 mm .

[0038] Again, such a wall thickness provides advantageously low rotational inertia of the gear mechanism housing whilst meeting the strength requirements for a pushrod actuated foundation brake.

[0039] The gear mechanism housing outer diameter may be in the range of 30 mm to 40 mm .

[0040] The gear mechanism housing outer diameter may be in the range of 33 mm to 37 mm .

[0041] Such an outer diameter allows the gear mechanism housing to fit within the desired compact space envelope.24-0300 (P607927)

[0042] The gear mechanism housing inner diameter may be in the range of 25 mm to 35 mm .

[0043] The gear mechanism housing inner diameter may be in the range of 28 mm to 32 mm .

[0044] Such an inner diameter allows a suitable gear mechanism to fit within the gear mechanism housing. That is, such an inner diameter provides a space envelope large enough to house a gear mechanism capable of withstanding sufficient load for the application of a pushrod-actuated foundation brake.

[0045] The gear mechanism housing may be of high tensile alloy steel.

[0046] The gear mechanism housing may be of EN24T steel.

[0047] Such a material is able to provide the required strength whilst meeting the size requirements of the actuator, i.e. fitting the space envelope and facilitating relatively low inertia whilst providing a housing for an appropriate gear mechanism .

[0048] The tubular body may define a gear mechanism housing cavity. The actuator may further comprise an output pushrod to interface with the foundation brake. The pushrod may be at least partially received within the gear mechanism housing cavity.

[0049] Advantageously, the gear mechanism is sized so as to be able to at least partially receive a pushrod, for example when the pushrod is in a retracted position . The actuator can thus be advantageously compact.

[0050] The gear mechanism may comprise an externally threaded lead screw. The gear mechanism housing may comprise an internal thread corresponding to the lead screw external thread.

[0051] The gear mechanism housing comprising an internal thread corresponding to the thread of the lead screw removes the need for an additional component in the form of a nut. The actuator is thus advantageously simplified, and ease of assembly of the actuator is improved.

[0052] According to a further aspect of the present invention, an actuator for a heavy vehicle foundation brake is provided. The actuator includes: an output pushrod to interface with the foundation brake; a rotary electric machine arranged to selectively displace the pushrod axially between a retracted position and a deployed position; and a rotary to linear gear mechanism to drive linear motion of the pushrod upon rotation of the electric machine. The gear mechanism comprises an externally threaded lead screw received within a sleeve assembly. The sleeve assembly comprises an internally threaded sleeve defining a raceway corresponding to the lead screw external thread, and a plurality of ball bearings received within the raceway.

[0053] The inclusion of ball bearings within the gear mechanism provides a low-friction means of translating the rotary motion of the motor to linear motion of the lead screw, and so to axial displacement of the pushrod. Frictional losses are thus minimised,24-0300 (P607927) minimising the impact of the multi-component transfer of motion through the actuator components that makes the actuator suitable for use with a pushrod-actuated foundation brake, i.e. a brake that could be actuated by an air actuator. Power demand on the electric machine is advantageously reduced, leading to optimised brake response time.

[0054] The sleeve assembly may be configured such that a radial load is applied by the internally threaded sleeve to the ball bearings.

[0055] Advantageously, the ball bearings are kept in constant contact with the lead screw, so minimising frictional losses.

[0056] The raceway may comprise a thread corresponding to the lead screw external thread . The raceway may comprise a recirculation path by which the ball bearings are recirculated through the sleeve assembly.

[0057] The actuator may further comprise a gear mechanism housing concentrically arranged at least partially within, and configured for rotation with, the electric machine.

[0058] The sleeve assembly may be connected to the gear mechanism housing such that the sleeve assembly is rotatable with the gear mechanism housing.

[0059] The sleeve assembly may be splined to the gear mechanism housing.

[0060] The pushrod may be connected to the lead screw at a lead screw joint.

[0061] Connection of the pushrod to a lead screw of the gear mechanism enables simple and effective control of the pushrod in a limited space.

[0062] The lead screw joint may comprise a pushrod connector for connecting the pushrod to the gear mechanism, for transfer of linear motion from the gear mechanism to the pushrod .

[0063] The pushrod connector may comprise an outboard end secured to the pushrod, and an inboard end secured to the gear mechanism. The inboard end may be secured to the lead screw.

[0064] Such a pushrod connector provides an effective yet compact means of connection between the pushrod and the lead screw. The transfer of linear motion is enabled in a compact space.

[0065] The inboard end may be secured to the lead screw in an interference fit. Alternatively, the pushrod connector may be integral to an outboard end of the lead screw.

[0066] The pushrod may be pivotably connected to the gear mechanism.

[0067] Pivotable connection of the pushrod to the gear mechanism creates an articulated connection between the components. As a result, the pushrod has increased freedom of movement with respect to the gear mechanism. An outboard end of the pushrod, i.e. the end at which there is an interface between the pushrod and the24-0300 (P607927) foundation brake, can be moved through an arc in the vertical plane. Articulation between the pushrod and the gear mechanism thus allows increased travel of the outboard end of the pushrod - enabling an increased range of travel of an operating shaft of the foundation brake. That is, a full range of travel of the operating shaft can be enabled. The actuator can thus be used with the same interface, e.g . the same operating shaft arrangement, as that of existing air-actuated brakes. Advantageously, no adaptation of the interface between the actuator and the foundation brake is required.

[0068] The pushrod may be pivotably secured to the pushrod connector at a pushrod joint.

[0069] Providing a pivotable connection in such a location enables a compact articulated connection between the pushrod and the lead screw.

[0070] The pushrod connector outboard end may comprise a pushrod connector socket. The pushrod inboard end may be received within the pushrod connector socket. The pushrod inboard end may comprise a ball configured to be received within the pushrod connector socket.

[0071] A ball and socket joint allows a pivotable connection to be formed between the pushrod and the gear mechanism with a minimum of components in a compact space envelope.

[0072] The pushrod joint may be configured such that the pushrod is pivotable about a pushrod pivot axis. The pushrod pivot axis may be transverse to the longitudinal axis of the pushrod.

[0073] An outboard end of the pushrod may be configured for engagement with the foundation brake. The outboard end of the pushrod may be configured for engagement with a brake lever of a foundation brake. The outboard end of the pushrod may be rounded, for engagement with a correspondingly shaped portion of the brake lever.

[0074] A further aspect provides a brake assembly including the actuator of any previous aspect and a foundation brake. The foundation brake may be a disc brake or a drum brake.

[0075] Within the scope of this application, it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and, in particular, the individual features thereof, may be taken independently or in any combination . All embodiments and / or features of any embodiment can be combined in any way and / or combination unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim, although not originally claimed in that manner.24-0300 (P607927)

[0076] Further benefits and advantages of the present invention will become apparent from the following detailed description of at least one exemplary embodiment for carrying out the present invention with reference to the accompanying drawings. Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions, and claims.BRIEF DESCRIPTION OF DRAWINGS

[0077] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which :

[0078] FIG. 1 is a perspective view of an actuator fixed to a foundation brake in the form of a disc brake.

[0079] FIG. 2 is a cross-sectional view of the actuator and foundation brake of FIG. 1, through the plane 2-2, illustrating a pushrod of the actuator in a retracted position .

[0080] FIG. 3 is a cross-sectional view of the actuator and foundation brake of FIG. 1, through the plane 2-2, illustrating a pushrod of the actuator in a deployed position.

[0081] FIG. 4 is a perspective close up view of the actuator from FIG. 1.

[0082] FIG. 5 is a perspective close-up view of an opposite side of the actuator from FIG. 4.

[0083] FIG. 6 is a cross-sectional view of the actuator of FIG. 4, through the plane 6- 6, with an overlay showing the space envelope of a known air actuator.

[0084] FIG. 7 is a cross-sectional view of the actuator of FIG. 4.

[0085] FIG. 8 is an isolated view of FIG. 7, showing just a lead screw assembly of the actuator.

[0086] FIG. 9 is an exploded view of the lead screw assembly of FIG. 8.

[0087] FIG. 10 is a perspective close up view of a connection between a lead screw of the lead screw assembly and the pushrod .

[0088] FIG. 11 has multiple close-up perspective views of components of the lead screw assembly of FIG. 9.DETAILED DESCRIPTIONGeneral structure

[0089] With reference to FIG. 1, a brake assembly 100 having an actuator 101 and a heavy vehicle foundation brake 102 according to an embodiment of the disclosure is indicated generally. The foundation brake 102 is mounted to an axle (not shown) of a heavy vehicle and a brake disc 103 is mounted to a wheel hub (not shown) of a heavy vehicle which is rotatable relative to the axle. Various orientations of the foundation brake 102 are described. In particular, the inboard direction and outboard direction refer to the typical orientation of the foundation brake 102 when fitted to a heavy24-0300 (P607927) vehicle and with reference to the longitudinal centreline of the heavy vehicle. The inboard direction and the outboard direction are shown on Figure 2 as 'I' and 'O' respectively.

[0090] As shown most clearly in FIG. 2 and FIG. 3, the foundation brake 102, in this embodiment, is a disc brake. The function of such a disc brake is well known so will not be described in detail but, briefly, a brake carrier 105 locates friction elements 104 in the form of brake pads to face first and second opposing braking surfaces of the brake disc 103. An actuating arrangement engages the inboard friction element 104 to urge it towards the brake disc 103 and a reaction force slides a caliper housing 106 of the actuating arrangement relative to the brake carrier 105 in order to urge the outboard friction element 104 towards the brake disc 103. When the friction elements 104 contact the braking surfaces of the brake disc 103, friction is generated which acts to retard rotation of the brake disc 103 and therefore the wheel hub and a wheel (not shown) mounted to the wheel hub to slow the heavy vehicle.

[0091] The actuating arrangement comprises, in this embodiment, a brake lever 107, commonly referred to as an operating shaft, arranged to rotate about an axis transverse to a longitudinal axis that passes through the centre of the brake disc 103. Due to an eccentric cam, the brake lever 107 converts a relatively substantial input displacement from the actuator 101 into a smaller displacement, higher force output to a pair of brake tappets 108 (one visible) which in turn urge the inboard friction element 104 into contact with the brake disc 103. To account for the wear of the friction element 104 and maintain a suitable running clearance between the friction elements 104 and the brake disc 103, a wear adjuster mechanism of suitable known type is arranged to automatically extend the brake tappets 108 (which comprise two threadably engaged parts) periodically. A return spring 110 urges the tappets and operating shaft back to their rest positions once a braking operation has ceased, to restore the running clearance. Examples of the disc brakes of this type include the applicant's EX+ and ELSA ranges of disc brakes.

[0092] Disc brakes of the type described require that all the force utilized to generate the friction between the friction elements 104 and the brake disc 103 is provided by the actuator 101. Such brakes do not have a "self-servo" effect whereby initial contact between the friction elements 104 and the brake disc 103 is amplified by wedges / ball and ramp mechanisms etc., to generate more force and therefore more friction from the rotation of the brake disc 103 without additional force being supplied by the actuator 101.

[0093] The upper end of the brake lever 107 is provided with a cup-shaped depression, which is arranged to receive a pushrod 160 (described in more detail below) acting as an output from the actuator 101.24-0300 (P607927)

[0094] Such foundation brakes of this type are typically employed in trucks in the UN / ECE category N3 (maximum mass exceeding 12 tonnes), trailers and semi-trailers in the category 04 (maximum mass exceeding 10 tonnes) and buses in the M3 category (more than eight seats in addition to the driver's seat, and having a maximum mass exceeding 5 tonnes).

[0095] With reference particularly to FIG. 4 and FIG. 5, the actuator 101 of this embodiment is a combined service and park brake actuator 101. The actuator 101 comprises a generally cylindrical actuator housing 111 (with a generally circular crosssection save for features such as the electrical connector) arranged to contain the electromechanical actuating arrangement discussed in more detail below.

[0096] In this embodiment, the actuator housing 111 comprises three main components : an outboard cover 113, an inboard cover 112, and an intermediate cover 114 which are held together by bolts. In this embodiment, the outboard cover 113, the inboard cover 112, and the intermediate cover 114 act, together with the bolts, to react certain axial forces generated within the actuator 101 from actuating operations. The outboard cover 113 and inboard cover 112 aid assembly of the actuator 101, as components of the actuator 101 can be inserted into either open end of the intermediate cover 114 during assembly. It will be appreciated that, in other embodiments, alternative arrangements may be utilized, comprising more or fewer parts held by other fasteners, or other means such as welding, clamping, swaging etc.

[0097] A parking brake mechanism is mounted to an inboard face of the inboard cover 112.

[0098] An electrical connector is also mounted to a radially outer face of the inboard cover in this embodiment, but may be positioned in a variety of other locations in other embodiments, as may be required.

[0099] The actuator housing 111 is configured to be fixable to the foundation brake 102 at the outboard end of the actuator housing 111. As seen in FIG. 5, the outboard cover is provided with a generally hexagonal planar face which is arranged, when assembled to the foundation brake 102, to abut an inboard face of the caliper housing 106. The planar face is arranged, in this embodiment, in terms of its significant contours, to match equivalent faces of known air actuators, thereby enabling the actuator 101 to mount to pre-existing air disc brake caliper housings.

[0100] Similarly, a first stud 115 and a second stud 116 extend axially forward from the outboard planar face of the outboard cover 113 to be received in complementary recesses of the caliper housing 106, using suitable nuts (not shown). In this embodiment, the first stud 115 and the second stud 116 are threaded and have a 16mm diameter and a spacing of 172.7mm centre-to-centre (4.75") to again be able to mount to standard pre-existing heavy vehicle air disc brake calipers.24-0300 (P607927)

[0101] The pushrod 160 extends through an aperture 117 in an outboard wall of the actuator housing 111 to allow the pushrod 160 to actuate in order to interface with the foundation brake 102. In this embodiment, the outboard wall is part of the outboard cover 113. In a retracted position, the pushrod 160 projects beyond the outboard cover 113 by approximately 15mm. A pushrod outboard end 166 of the pushrod 160 is hemispherical in this embodiment to mate with the depression in the brake lever 107. A sealing element 119 may be provided around the perimeter of the aperture 117 to assist in keeping foreign matter out of the interior of either the foundation brake 102 or actuator 101 when the two are assembled together.

[0102] In FIG. 2, the retracted position of the pushrod 160 at the start of its actuation stroke is denoted S. In FIG. 3, the deployed position of the pushrod 160 at the maximum extent of the brake stroke is denoted E. For the caliper housing 106, the axial distance between S and E is at least 40mm, typically more than 50mm. Additionally, the pushrod outboard end 166 of the pushrod 160 follows an arcuate path between S and E due to its contact with the brake lever 107.Actuator

[0103] The actuator 101 includes a torque source for causing the displacement of the pushrod 160. Referring to FIG. 7 in particular, in this embodiment, the actuator 101 is an electric actuator and the torque source is in the form of a rotary electric machine 120 (which may be a motor or a motor generator). The rotary electric machine 120 is arranged to selectively displace the pushrod 160 axially between the retracted position S and fully deployed position E, and positions therebetween. An axis of rotation 122 of the rotary electric machine 120 is substantially aligned with a path of a pushrod inboard end 168 of the pushrod 160 as the pushrod 160 moves from the retracted position to the deployed position .

[0104] The rotary electric machine 120 includes a radially outer stator 123 and a hollow inner rotor 125.

[0105] A rotary to linear gear mechanism (described in more detail below) is provided to drive the linear motion of the pushrod 160 upon rotation of the rotary electric machine 120. In this embodiment, the rotary to linear gear mechanism is located at least partially within the hollow inner rotor 125. This enables the overall length of the actuator 101 to be reduced.

[0106] Further, the pushrod 160 is able to at least partially retract within the hollow inner rotor 125, further enabling the overall length of the actuator 101 to be reduced.

[0107] As described in more detail below, the pushrod 160 is pivotably mounted to an output of the rotary to linear gear mechanism to enable the pushrod outboard end 166 to follow the arcuate path of the brake lever 107.24-0300 (P607927)

[0108] A suitable type of rotary electric machine 120 is chosen that has high power density for the voltage supplied (24V in this embodiment), such that axial forces of the pushrod 160 are comparable or greater than air actuators with a parking brake of comparable size (diameter and length). This may be achieved by a rotary electric machine 120 in which pole pieces of the stator 123 are shaped so that the length of windings 124 may be minimised whilst maintaining the flux handling capacity of the pole pieces and enabling the pole pieces to be space-efficiently arranged in the stator 123. Such rotary electric machines 120 may be able to achieve a power density of in excess of 155kW / m3, and in some embodiments in excess of 200kW / m3.

[0109] An example of a suitable type of rotary electric machine 120 is a Pareta® motor of DG Innovate pic of Caerphilly, UK and as described in W02020208037A1.

[0110] FIG. 6 indicates that the actuator 101 with the rotary electric machine 120 machine of this type is dimensioned to be within the space envelope 118 of a comparable air actuator. The rotary electric machine 120 is able to generate a maximum force of at least 9kN at the pushrod outboard end 166 of the pushrod 160.

[0111] Legislation relating to service brake actuation of foundation brakes for heavy trucks (Regulation No 13 of the Economic Commission for Europe of the United Nations (UN / ECE)) additionally requires that the pushrod be able to apply 75% of its maximum force within a maximum of 0.6 seconds. Such electric machines, when coupled to a suitable rotary to linear gear mechanism are further able to achieve this level of force (6.75kN) within this maximum time.Lead screw assembly

[0112] In this embodiment, the rotary to linear gear mechanism includes a lead screw assembly 126 configured to actuate the output pushrod 160 in order to interface with the foundation brake 102. The lead screw assembly 126 is best shown in FIG. 8 and includes a gear mechanism housing in the form of a lead screw housing 127, and a lead screw 132 configured to translate relative to the lead screw housing 127 along the axis of rotation 122 when the lead screw housing 127 is rotated . The lead screw 132 is configured to actuate the output pushrod 160 as described in more detail below. The lead screw 132 has a lead screw bore 148 extending longitudinally through the lead screw 132.

[0113] The lead screw housing 127 is configured to be selectively rotated by a torque source, the rotary electric machine 120 in this embodiment. The lead screw housing 127 is concentrically arranged at least partially within, and configured for rotation with, the rotary electric machine 120. The lead screw housing 127 is configured for rotation with the rotor 125. In this embodiment, the lead screw housing 127 is shrink-fitted to the rotor 125. For example, the lead screw housing 127 is cooled in liquid nitrogen then pressed into the rotor 125. The subsequent return of the lead screw housing 127 to24-0300 (P607927) ambient temperature rotationally fixes the lead screw housing 127 to the rotor 125. In this embodiment, the lead screw housing 127 is an elongate member including a tubular body 128. At an inboard end of the tubular body 128 of the lead screw housing 127 is a lead screw housing threaded end 129. Adjacent the lead screw housing threaded end 129 in the outboard direction is an external spline 130, best seen on FIG. 9.

[0114] The tubular body 128 includes a cylindrical wall, and the wall thickness (shown on FIG. 8 as "t") is in the range of 1.8mm to 3mm. Such a wall thickness provides low rotational inertia of the lead screw housing 127 whilst providing an actuator suitable for use with a pushrod-actuated foundation brake, i.e. a brake that may otherwise be actuated by an air actuator. The lead screw housing 127 size allows the actuator 101 to be suitably compact, such that the actuator 101 can fit within the space envelope typically provided for an air actuator. Low rotational inertia advantageously leads to reduced power demand as well as improved brake actuation response time. The wall thickness of the tubular body 128 may be in the range of 2 mm to 2.5 mm . In this embodiment, the wall thickness is 2.25mm . Optionally, the wall thickness may be in the range of 2.2mm to 2.3 mm. Again, such a wall thickness provides advantageously low rotational inertia of the lead screw housing 127 whilst meeting the strength requirements for a pushrod actuated foundation brake.

[0115] In this embodiment, the lead screw housing 127 outer diameter is in the range of 30 mm to 40 mm, optionally in the range of 33 mm to 37 mm . In this embodiment, the lead screw housing 127 outer diameter is 35mm. Such an outer diameter allows the gear mechanism housing to fit within the desired compact space envelope. The lead screw housing 127 inner diameter is in the range of 25 mm to 35 mm, optionally in the range of 28 mm to 32 mm . In this embodiment, the lead screw housing 127 inner diameter is 30.5mm . Such an inner diameter allows a suitable gear mechanism to fit within the gear mechanism housing. That is, such an inner diameter provides a space envelope large enough to house a gear mechanism capable of withstanding sufficient load for the application of a pushrod-actuated foundation brake.

[0116] In an alternative embodiment, the lead screw housing outer diameter is in the range of 30mm to 50mm.

[0117] In this embodiment, the lead screw housing 127 is of high tensile alloy steel. For example, EN24T steel could be used . Such a material is able to provide the required strength whilst meeting the size requirements of the actuator, i.e. fitting the space envelope and facilitating relatively low inertia whilst providing a housing for an appropriate gear mechanism . In this embodiment, the inertia is substantially 0.002kgm2.

[0118] In alternative embodiments, the inertia is in the range of 0.0015kgm2and 0.0025kgm2.24-0300 (P607927)

[0119] The tubular body 128 of the lead screw housing 127 defines a lead screw housing cavity 131 extending axially through the lead screw housing 127. The pushrod 160 is at least partially received within the lead screw housing cavity 131. Advantageously, the lead screw housing 127 is sized so as to be able to at least partially receive the pushrod 160, for example when the pushrod 160 is in the retracted position. The actuator 101 can thus be advantageously compact. The lead screw 132 is externally threaded.

[0120] In one embodiment, the lead screw housing 127 includes an internal thread corresponding to the lead screw 132 external thread . The internal thread corresponding to the thread of the lead screw 132 removes the need for an additional component in the form of a nut. The actuator 101 is thus advantageously simplified, and ease of assembly of the actuator 101 is improved.Low friction sleeve

[0121] In the depicted embodiment, as best shown in FIG. 8, the lead screw assembly 126 includes a sleeve assembly 134 that locates on the lead screw 132. The sleeve assembly 134 includes an internally threaded sleeve 135 having a sleeve bore 136 and defining a raceway corresponding to the lead screw 132 external thread, and a plurality of ball bearings (not shown) received within the raceway. The inclusion of ball bearings within the lead screw assembly 126 provides a low-friction means of translating the rotary motion of the rotary electric machine 120 to linear motion of the lead screw 132, and so to axial displacement of the pushrod 160. Frictional losses are thus minimised, minimising the impact of the multi-component transfer of motion through the actuator components that makes the actuator suitable for use with a pushrod-actuated foundation brake, i.e. a brake that could be actuated by an air actuator. Power demand on the electric machine is advantageously reduced, leading to optimised brake response time. In this embodiment, cold-finished ball bearings are used, advantageously increasing the load that can be carried by the lead screw assembly 126. Noise of brake actuation is advantageously reduced by the inclusion of ball bearings.

[0122] A suitable sleeve assembly 134 is provided by Eichenberger Gewinde AG of Burg, Switzerland.

[0123] In this embodiment, the sleeve assembly 134 is located relatively deeply within the lead screw housing cavity 131, due to the length of the pushrod 160. Securing the sleeve assembly 134 in position with respect to the lead screw housing 127 requires modification of the sleeve assembly 134. A bespoke tool (not shown) is required to tighten the sleeve assembly 134 to the lead screw housing 127. A face of the sleeve assembly 134 is modified for engagement with the bespoke tool, so that the lead screw assembly 126 can be assembled.24-0300 (P607927)

[0124] Difficulties can arise during transport of the sleeve assembly 134 prior to assembly of the lead screw assembly 126, in particular in relation to retention of the ball bearings, and in particular due to the modification made to the sleeve assembly 134. In this embodiment, a plug (not shown) is provided in order to secure the ball bearings within the sleeve assembly 134 during modification and transport.

[0125] The sleeve assembly 134 may be configured such that a radial load is applied by the internally threaded sleeve 135 to the ball bearings. Advantageously, the ball bearings are kept in constant contact with the lead screw 132, so minimising frictional losses. "Backlash", where lost motion occurs before application of the disc brake, is minimised by this arrangement, so advantageously minimising actuation response time. The raceway may define a recirculation path by which the ball bearings are recirculated through the sleeve assembly 134. The sleeve assembly 134 is connected to the lead screw housing 127 such that the sleeve assembly 134 is rotatable with the lead screw housing 127. The sleeve assembly 134 is rotationally fixed to the lead screw housing 127. In this embodiment, the sleeve assembly 134 is splined to the lead screw housing 127.Anti-rotation feature

[0126] The lead screw assembly 126 includes a first anti-rotation feature arranged to inhibit relative rotational movement of the lead screw 132 and the actuator housing 111. As the lead screw 132 cannot rotate relative to the actuator housing 111, when the lead screw housing 127 is selectively rotated by the torque source, the lead screw 132 cannot rotate along with the lead screw housing 127. Therefore, the rotational movement of the lead screw housing 127 is converted to linear movement of the lead screw 132 along the axis of rotation 122 in the outboard direction, to actuate the pushrod 160.

[0127] In this embodiment, the first anti-rotation feature is an anti-rotation shaft 139 that locates in a lead screw inboard bore 137 that extends axially through the lead screw 132 from a lead screw inboard end 138 of the lead screw 132. The lead screw inboard bore 137 non-rotationally receives the anti-rotation shaft 139, which is non- rotationally fixed to the actuator housing 111. In this embodiment, as best shown in FIG. 11, the anti-rotation shaft 139 has an elongate anti-rotation shaft body 140 and an anti-rotation shaft head 142 at an inboard end of the anti-rotation shaft body 140. The anti-rotation shaft body 140 locates in the lead screw inboard bore 137. The antirotation shaft head 142 locates in the actuator housing 111.

[0128] In this embodiment, the anti-rotation shaft body 140 has a non-circular cross- sectional profile that corresponds to a non-circular cross-sectional profile of the lead screw inboard bore 137. In this embodiment, the inboard cover 112 of the actuator housing 111 has a blind outboard bore 144. The anti-rotation shaft head 142 has a non-24-0300 (P607927) circular cross-sectional profile that corresponds to a non-circular cross-sectional profile of the outboard bore 144.

[0129] In this embodiment, only a portion of the anti-rotation shaft body 140 has a non-circular cross-sectional profile. Specifically, the anti-rotation shaft body 140 has a part-circular, part linear profile defined by the anti-rotation shaft body 140 having an anti-rotation shaft body flat portion 141.

[0130] Similarly, in this embodiment, only a portion of the anti-rotation shaft head 142 has a non-circular cross-sectional profile. Specifically, the anti-rotation shaft head 142 has a part-circular, part linear profile defined by the anti-rotation shaft head 142 having an anti-rotation shaft head flat portion 143.

[0131] The lead screw inboard bore 137 and the outboard bore 144 of the inboard cover 112 have corresponding profiles such that the anti-rotation shaft body flat portion 141 and the anti-rotation shaft head flat portion 143 inhibit the anti-rotation shaft 139 from rotating relative to the actuator housing 111 and the lead screw 132.

[0132] The inboard cover 112 has a through hole to receive a removable fastening element 145 that engages in an end of the anti-rotation shaft head 142 to locate the anti-rotation shaft 139. This helps to ensure that the anti-rotation shaft 139 can be easily removed during maintenance or if replacement is required. If, for example, the parking brake function is applied but malfunctions and is locked in place, removal of the anti-rotation shaft 139 allows the foundation brake 102 to be released.Anti-eiection feature

[0133] The lead screw 132 further comprises a first anti-ejection feature arranged to limit the maximum relative movement of the lead screw 132 and the lead screw housing 127 in the axial direction . Limiting the maximum relative movement of the lead screw 132 and lead screw housing 127 helps to ensure that the lead screw 132 does not translate so much that it separates from the lead screw housing 127. In addition, the first anti-ejection feature acts as a safety feature as it helps to avoid a potential issue where if the actuator 101 has a control malfunction or a mechanical malfunction, the lead screw 132 could be forcefully ejected from the actuator housing 111.

[0134] In this embodiment, the first anti-ejection feature is axially fixed relative to the lead screw 132 and is configured to interact with a corresponding second anti-ejection feature axially fixed relative to the lead screw housing 127 to limit the maximum relative movement of the lead screw 132 and the lead screw housing 127 in the axial direction . As the first anti-ejection feature moves in the axial direction along with the lead screw 132, and the second anti-ejection feature does not move in the axial direction as it is fixed relative to the lead screw housing 127, after a predetermined amount of travel of the lead screw 132 in the axial direction, the first anti-ejection24-0300 (P607927) feature will come into contact with the second anti-ejection feature, inhibiting any further movement of the lead screw in the axial direction.

[0135] In this embodiment, the first anti-ejection feature projects from the lead screw 132 in a radially outward direction and the second anti-ejection feature projects from the lead screw housing 127 in a radially inward direction . As the lead screw 132 translates within the lead screw housing 127, this helps to ensure that the first antiejection feature comes into contact with the second anti-ejection feature when desired, to limit the maximum relative movement of the lead screw 132 and lead screw housing 127.

[0136] In this embodiment, the sleeve 135 of the sleeve assembly 134 defines the second anti-ejection feature. The sleeve 135 has an inner diameter dimensioned to be greater than an outer diameter of the first anti-ejection feature. This helps to ensure that the sleeve 135 is engaged by the first anti-ejection feature.

[0137] In this embodiment, the first anti-ejection feature is at the lead screw inboard end 138. Specifically, the first anti-ejection feature is a flange 146 at the lead screw inboard end 138. The flange 146 has an outer diameter greater than the outer diameter of the lead screw 132. As the flange 146 is located on the lead screw 132 and has a greater outer diameter, it can interact with the second anti-ejection feature after a predetermined amount of travel of the lead screw 132 in the axial direction . The lead screw housing 127 has an internal diameter that is greater than the outer diameter of the flange 146. This helps to ensure that the lead screw 132 can translate relative to the lead screw housing 127 up to the maximum limit of travel in the axial direction . In this embodiment, the lead screw 132 and the flange 146 are monolithically and integrally formed .

[0138] In other embodiments, the flange 146 could be a separate component such as an annular ring fixed to the lead screw inboard end 138 in any suitable way. For example, the annular ring could be threaded onto the lead screw inboard end 138. This would provide a secure and easy to assemble way of fixing the flange 146 to the lead screw 132.Housing Cavity

[0139] Housing at least part of the pushrod 160 within the lead screw housing cavity 131 advantageously provides a more compact actuator. The overall axial length of the actuator 101 is reduced. Advantageously, a compact actuator suitable for use with a pushrod-actuated foundation brake, i.e. a brake that may otherwise be actuated by an air actuator, is provided.

[0140] At least half of the length of the pushrod 160 is received within the lead screw housing cavity 131 when the pushrod 160 is in the retracted position S. Optionally, at least two thirds of the length of the pushrod is received within the gear mechanism24-0300 (P607927) housing cavity when the pushrod is in the retracted position S. The lead screw housing cavity 131 being capable of receiving at least half of the length of the pushrod 160 provides an advantageously compact actuator 101. In this embodiment, as shown in FIG. 2, substantially the whole of the length of the pushrod 160 is received within the lead screw housing cavity 131 when the pushrod 160 is in the retracted position S.

[0141] The pushrod 160 is connected to the lead screw 132 at a lead screw joint 147. In this embodiment, the lead screw joint 147 is received within the lead screw housing cavity 131. Connection of the pushrod 160 to the lead screw 132 enables simple and effective control of the pushrod 160 in a limited space. The lead screw joint 147 being received within the lead screw housing cavity 131 allows at least part of the pushrod 160 to likewise be housed within the lead screw housing cavity 131. A compact actuator can thus be provided.

[0142] The lead screw joint 147 includes a pushrod connector 163 for connecting the pushrod 160 to the lead screw 132, for transfer of linear motion from the lead screw 132 to the pushrod 160. As part of the lead screw joint 147, the pushrod connector 163 is housed within the lead screw housing cavity 131, providing a compact means of transfer of linear motion from the lead screw 132 to the pushrod 160.

[0143] The push rod connector 163 of this embodiment has a push rod connector outboard end 164 secured to the pushrod 160, and a pushrod connector inboard end 165 secured to the lead screw 132. The pushrod connector inboard end 165 is in this embodiment secured to the lead screw 132 in an interference fit. In alternative embodiments, any suitable alternative form of connection is used. For example, the pushrod connector 163 may be integral to the lead screw 132. Such a push rod connector provides an effective yet compact means of connection between the pushrod 160 and the lead screw 132. The transfer of linear motion is thus enabled in a compact space.Articulated pushrod

[0144] As described briefly above, the pushrod 160 is pivotably connected to the lead screw 132. A pushrod inboard end 168 of the pushrod 160 is pivotably connected to the lead screw 132. Pivotable connection of the pushrod 160 to the lead screw 132 creates an articulated connection between the components. As a result, the pushrod 160 has increased freedom of movement with respect to the lead screw 132. A pushrod outboard end 166 of the pushrod 160, i.e. the end at which there is an interface between the pushrod 160 and the foundation brake 102, can be moved through an arc in the vertical plane. Articulation between the pushrod 160 and the lead screw assembly thus allows increased travel of the pushrod outboard end 166 of the pushrod 160, enabling an increased range of travel of the brake lever 107 of the foundation brake 102. That is, a full range of travel of the brake lever 107 can be enabled. The actuator 101 can thus be used with the same interface, e.g. the same brake lever arrangement, as that of existing24-0300 (P607927) air-actuated brakes. Advantageously, no adaptation of the interface between the actuator 101 and the foundation brake 102 is required.

[0145] In this embodiment, the pushrod 160 is pivotably connected to the lead screw 132 at the lead screw joint 147. The pushrod 160 can be pivotably connected to the lead screw 132 in a simple and effective arrangement in order to provide an articulated connection between the two.

[0146] The pushrod 160 is in this embodiment is pivotably secured to the pushrod connector 163 at a pushrod joint 167. The pushrod connector outboard end 164 includes a pushrod connector socket 162. The pushrod inboard end 168 is received within the pushrod connector socket 162. The pushrod inboard end 168 includes a pushrod ball 161 configured to be received within the pushrod connector socket 162, i.e. in a ball and socket joint. Such a ball and socket joint allows a pivotable connection to be formed between the pushrod 160 and the lead screw 132 with a minimum of components in a compact space envelope.

[0147] The pushrod joint 167 is configured such that the pushrod 160 is pivotable about a pushrod pivot axis 169 (shown on FIG. 8). The pivot axis 169 is transverse to the longitudinal axis of the pushrod 160. In this embodiment, the pushrod inboard end 168 includes a pin retaining feature 159 in the form of a through bore configured to receive a pin 158 so as to pivotably secure the pushrod 160 to the pushrod connector 163. The pin 158 extends co-axially with the pivot axis 169.

[0148] Such a pin arrangement effectively secures the pushrod 160 with relation to the lead screw 132 in a simple arrangement, whilst allowing pivoting of the pushrod 160 with respect to the lead screw assembly in the required direction .

[0149] The pushrod outboard end 166 of the pushrod 160 is configured for engagement with the foundation brake 102, as described above.

[0150] Alignment device

[0151] An alignment device 170 is provided for substantially aligning the pushrod 160 such that a longitudinal axis of the pushrod 160 is substantially aligned with the axis of rotation 122 of the rotary electric machine 120. Locating the pushrod 160 with respect to the rotary electric machine 120, i.e. with respect to the remainder of the actuator 101, enables alignment of the pushrod outboard end 166 of the pushrod 160 at the interface with the foundation brake 102. Ease, and therefore efficiency, of installation of the actuator 101 is thus improved. Damage to components during installation is limited, as the pushrod 160 is less likely to interfere with the brake lever 107 of the foundation brake 102 during installation or re-seating of the actuator 101. The alignment device 170 is particularly advantageous where the pushrod 160 is articulated with respect to a gear mechanism such as the lead screw assembly 126, i.e. where the pushrod outboard end 166 has an increased range of movement with respect to the lead screw assembly 126. In this embodiment, the alignment device 170 is supported by the lead screw24-0300 (P607927) assembly 126. This is an advantageously compact arrangement. The number of components is advantageously minimised by the use of existing components to support the alignment device 170. In this embodiment, the alignment device 170 is at least partially received within the lead screw housing cavity 131. The actuator 101 is thus advantageously compact, with a reduced overall axial length. The actuator 101 can be used with a pushrod-actuated foundation brake, i.e. a brake that may otherwise be actuated by an air actuator.

[0152] More specifically, the alignment device 170 is supported by the pushrod connector 163. A longitudinal axis of the pushrod connector 163 is substantially co-axial with the axis of rotation 122 of the rotary electric machine 120. The alignment device 170 is secured about an outer diameter of the pushrod connector 163. The actuator 101 is advantageously compact, and the number of components is minimised by the alignment device 170 being supported by the pushrod connector 163. The alignment device 170 includes an alignment portion 171 for locating the pushrod 160; and a connection portion 172 by which the alignment device 170 is secured to the lead screw assembly 126. In this embodiment, the alignment portion 171 includes resilient material. The alignment portion 171 is configured to resiliently bias the pushrod 160 such that the longitudinal axis of the pushrod 160 is substantially aligned with the axis of rotation 122 of the rotary electric machine 120. The resilient material of the alignment portion 171 simply and effectively acts to align the pushrod 160 to the desired position . The alignment portion 171 is substantially tubular, including a tubular wall 173. The tubular wall 173 encircles the pushrod 160 so as to substantially align the longitudinal axis of the pushrod 160 with the axis of rotation 122 of the rotary electric machine 120. The tubular formation of the alignment device 170 allows the alignment device 170 to encircle the pushrod 160, and so to move the pushrod 160 towards an aligned position, i.e. where the longitudinal axis of the pushrod 160 is substantially aligned with the axis of rotation 122 of the rotary electric machine 120. The connection portion 172 is substantially tubular. In this embodiment, the connection portion 172 includes elastic material. Such a connection portion 172 can be fitted over a component of the lead screw assembly 126, e.g. the pushrod connector 163, in order to secure the alignment device 170 in position .

[0153] In one embodiment, the connection portion 172 and the alignment portion 171 are of the same elastic and resilient material. In such an embodiment, the alignment device 170 is a single monolithic component.

[0154] In an alternative embodiment (not shown), the alignment portion 171 includes at least two opposing legs extending substantially parallel to the axis of rotation 122 of the rotary electric machine 120. The legs are positioned substantially equidistant to one another about an outer diameter of the alignment device 170. The alignment portion 171 may include a pair of opposing legs, positioned at substantially 180° to one another, or24-0300 (P607927) the alignment portion 171 may include three opposing legs, positioned at substantially 172° to one another. The legs are resiliently biased towards the axis of rotation 122 of the rotary electric machine 120. Such legs simply and effectively act to align the pushrod 160 with the axis of rotation 122 of the rotary electric machine 120.Actuator housing bearing arrangement

[0155] As shown most clearly in FIG. 7, the lead screw assembly 126 is supported in the actuator housing 111 by a first bearing 149 and a second bearing 153. The first bearing 149 supports the lead screw assembly 126 at the outboard end of the actuator housing 111. The actuator housing 111 defines a first bearing chamber 150 to locate the first bearing 149. In this embodiment, the first bearing chamber 150 is defined in the outboard cover 113. The first bearing chamber 150 helps to locate the first bearing 149 in the optimum location at the outboard end of the actuator housing 111. The first bearing 149 includes an inner race fixed relative to the lead screw housing 127 and an outer race fixed relative to the actuator housing 111. This helps the lead screw housing 127 to rotate relative to the actuator housing 111. The first bearing chamber 150 includes a radially outer internal surface. The outer race of the first bearing 149 is fixed relative to the internal surface of the first bearing chamber 150. The first bearing 149 is located adjacent the aperture 117. In other words, the first bearing 149 is located close to the pushrod 160 and brake lever 107 contact point. The reaction force from the brake lever 107 has a load path defined from the foundation brake 102 to the outboard end of the actuator housing 111, and the first bearing 149 is located on the load path . The first bearing 149 helps to direct the reaction force from the foundation brake 102 into the actuator housing 111 after it is engaged by the pushrod 160. This helps to avoid damage to other components of the actuator 101. In this embodiment, the first bearing 149 is a thrust bearing. A thrust bearing helps to better react load from the foundation brake 102 in the axial direction . More specifically, the thrust bearing is an angular contact thrust bearing. An angular contact thrust bearing helps to ensure that the axial load from the foundation brake 102 is directed at an angle to the axis of rotation 122, at least partially in the radial direction and into the actuator housing 111. A first bearing inner race circlip 151 and a first bearing outer race circlip 152 are located either side of the first bearing 149 to help locate and retain the first bearing 149.

[0156] The second bearing 153 is located at an inboard end of the actuator housing 111 to support the lead screw assembly 126 at the inboard end. The second bearing 153 has a smaller outer diameter than an outer diameter of the first bearing 149. This is because the second bearing 153 does not need to react the load from the foundation brake 102 as it is not on the load path. Accordingly, it can be made smaller and lighter to reduce manufacturing costs. The actuator housing 111 defines a second bearing chamber 154. The second bearing chamber 154 is dimensioned to locate the second24-0300 (P607927) bearing 153. The second bearing chamber helps to ensure that the second bearing is located in the correct location to support the lead screw assembly 126 at the inboard end, and allow it to rotate relative to the actuator housing 111. The second bearing chamber 154 has a smaller internal diameter than the first bearing chamber 150 such that the inboard end of the actuator housing 111 is lighter, helping to ensure the centre of gravity 155 of the actuator 101 is closer to the outboard end than the inboard end, to aid mounting to the foundation brake 102. Specifically, the second bearing chamber 154 is in the inboard cover 112. Located inboard of the second bearing 153 on the lead screw housing 127 is an annular engaging collar 156. Located inboard of the engaging collar 156 is a preload nut 157. The preload nut 157 locates on the lead screw housing threaded end 129. As the preload nut 157 is screwed onto the lead screw housing threaded end 129, it applies a force to the engaging collar 156 which is transferred to the second bearing 153 to preload the second bearing 153. At the same time, the whole lead screw housing 127 is moved in the inboard direction. This means that the first bearing inner race circlip 151 also applies a force to the first bearing 149 to preload it.

[0157] Where the word 'or' appears, this is to be construed to mean 'and / or'. This is such that items referred to are not necessarily mutually exclusive and may be used in any appropriate combination .

[0158] The disclosure has been described above with reference to one or more specific embodiments. However, the description is not exhaustive, and the present disclosure is not limited to the embodiments described . Various changes and modifications can be made without departing from the scope of the disclosure as defined in the claims.LISTING OF DRAWING ELEMENTS100 brake assembly101 actuator102 foundation brake103 brake disc104 friction element105 brake carrier106 caliper housing107 brake lever108 brake tappet-0300 (P607927) 0 return spring 1 actuator housing 2 inboard cover 3 outboard cover 4 intermediate cover 5 first stud 6 second stud 7 aperture 8 space envelope 9 sealing element 0 rotary electric machine 2 axis of rotation 3 stator 4 windings 5 rotor 6 lead screw assembly 7 lead screw housing 8 tubular body 9 lead screw housing threaded end0 spline 1 lead screw housing cavity 2 lead screw 3 lead screw outboard end 4 sleeve assembly-0300 (P607927) 5 sleeve 6 sleeve bore 7 lead screw inboard bore 8 lead screw inboard end 9 anti-rotation shaft 0 anti-rotation shaft body 1 anti-rotation shaft body flat portion2 anti-rotation shaft head 3 anti-rotation shaft head flat portion4 outboard bore 5 removable fastening element 6 flange 7 lead screw joint 8 lead screw bore 9 first bearing 0 first bearing chamber 1 first bearing inner race circlip 2 First bearing outer race circlip 3 second bearing 4 second bearing chamber 5 centre of gravity 6 engaging collar 7 preload nut 8 pin-0300 (P607927) 9 pin retaining feature 0 pushrod 1 pushrod ball 2 pushrod connector socket 3 pushrod connector 4 pushrod connector outboard end5 pushrod connector inboard end6 pushrod outboard end 7 pushrod joint 8 pushrod inboard end 9 pivot axis 0 alignment device 1 alignment portion 2 connection portion 3 tubular wall

Claims

24-0300 (P607927)CLAIMS1. An actuator for a heavy vehicle foundation brake, the actuator comprising : an output pushrod to interface with the foundation brake; a rotary electric machine arranged to selectively displace the pushrod axially between a retracted position and a deployed position; a rotary to linear gear mechanism to drive linear motion of the pushrod upon rotation of the electric machine; and a gear mechanism housing concentrically arranged at least partially within, and configured for rotation with, the rotary electric machine; wherein the gear mechanism housing defines a gear mechanism housing cavity; and wherein the pushrod is at least partially received within the gear mechanism housing cavity when the pushrod is in the retracted position .

2. The actuator of claim 1, wherein at least half of the length of the pushrod is received within the gear mechanism housing cavity when the pushrod is in the retracted position.

3. The actuator of claim 2, wherein at least two thirds of the length of the pushrod is received within the gear mechanism housing cavity when the pushrod is in the retracted position.

4. The actuator of any one of claims 1 to 3, wherein the gear mechanism comprises a lead screw, wherein the pushrod is connected to the lead screw at a lead screw joint, and wherein the lead screw joint is received within the gear mechanism housing cavity.

5. The actuator of claim 4, wherein the lead screw joint comprises a pushrod connector for connecting the pushrod to the gear mechanism, for transfer of linear motion from the gear mechanism to the pushrod.

6. The actuator of claim 5, wherein the pushrod connector comprises an outboard end secured to the pushrod, and an inboard end secured to the gear mechanism, optionally wherein the inboard end is secured to the lead screw.

7. The actuator of claim 6, wherein the inboard end of the pushrod connector is secured to the lead screw in an interference fit.

8. The actuator of claim 6, wherein the pushrod connector is integral to an outboard end of the lead screw.

9. The actuator of any one of claims 1 to 8, wherein the pushrod is pivotably connected to the gear mechanism .24-0300 (P607927)10. The actuator of claim 7 or 8, wherein the pushrod is pivotably secured to the pushrod connector at a pushrod joint.

11. The actuator of claim 10, wherein the pushrod connector outboard end comprises a pushrod connector socket, optionally wherein the pushrod inboard end is received within the pushrod connector socket, optionally wherein the pushrod inboard end comprises a ball configured to be received within the pushrod connector socket.

12. The actuator of claim 10 or 11, wherein the pushrod joint is configured such that the pushrod is pivotable about a pushrod pivot axis, and wherein the pushrod pivot axis is transverse to the longitudinal axis of the pushrod.

13. The actuator of claim 12, wherein the pushrod inboard end comprises a through bore configured to receive a pin, and wherein the pushrod joint comprises a pin configured to extend through the through bore so as to pivotably secure the pushrod to the pushrod connector, optionally wherein the pin extends co-axially with the pushrod pivot axis.

14. The actuator of any one of claims 1 to 13, wherein an outboard end of the pushrod is configured for engagement with the foundation brake.

15. The actuator of claim 14, wherein the outboard end of the pushrod is configured for engagement with a brake lever of the foundation brake.

16. The actuator of claim 14 or 15, wherein the outboard end of the pushrod is rounded, for engagement with a correspondingly shaped brake lever.

17. A brake assembly comprising the actuator of any one of claims 1 to 16 and a heavy vehicle foundation brake.

18. The brake assembly of claim 17, wherein the heavy vehicle foundation brake is a disc brake or a drum brake.

19. An actuator for a heavy vehicle foundation brake, the actuator comprising : a rotary electric machine comprising a rotor; and a rotary to linear gear mechanism to drive linear motion upon rotation of the electric machine; and a gear mechanism housing concentrically arranged at least partially within, and configured for rotation with, the rotary electric machine; wherein the gear mechanism housing comprises a tubular body, wherein the body comprises a cylindrical wall, and wherein the wall thickness is in the range of 1.8mm to 3mm.24-0300 (P607927)20. The actuator of claim 19, wherein the wall thickness is in the range of 2 mm to 2.5 mm; optionally when the wall thickness is in the range of 2.2mm to 2.3 mm.

21. The actuator of claim 19 or 20, wherein the gear mechanism housing outer diameter is in the range of 30 mm to 40 mm.

22. The actuator of claim 21, wherein the gear mechanism housing outer diameter is in the range of 33 mm to 37 mm .

23. The actuator of any one of claims 19 to 22, wherein the gear mechanism housing inner diameter is in the range of 25 mm to 35 mm .

24. The actuator of claim 23, wherein the gear mechanism housing inner diameter is in the range of 28 mm to 32 mm .

25. The actuator of any one of claims 19 to 24, wherein the gear mechanism housing is of high tensile alloy steel.

26. The actuator of claim 25, wherein the gear mechanism housing is of EN24T steel.

27. The actuator of any one of claims 19 to 26, wherein the body defines a gear mechanism housing cavity; further comprising an output pushrod to interface with the foundation brake, wherein the pushrod is at least partially received within the gear mechanism housing cavity.

28. The actuator of any one of claims 19 to 27, wherein the gear mechanism comprises an externally threaded lead screw, and wherein the gear mechanism housing comprises an internal thread corresponding to the lead screw external thread.

29. A brake assembly comprising the actuator of any one of claims 19 to 28 and a heavy vehicle foundation brake.

30. The brake assembly of claim 29, wherein the heavy vehicle foundation brake is a disc brake or a drum brake.

31. An actuator for a heavy vehicle foundation brake, the actuator comprising : an output pushrod to interface with the foundation brake; a rotary electric machine arranged to selectively displace the pushrod axially between a retracted position and a deployed position; and a rotary to linear gear mechanism to drive linear motion of the pushrod upon rotation of the electric machine; wherein the gear mechanism comprises an externally threaded lead screw received within a sleeve assembly;24-0300 (P607927) wherein the sleeve assembly comprises an internally threaded sleeve defining a raceway corresponding to the lead screw external thread, and a plurality of ball bearings received within said raceway.

32. The actuator of claim 31, wherein the sleeve assembly is configured such that a radial load is applied by the internally threaded sleeve to the ball bearings.

33. The actuator of claim 31 or 32, wherein the raceway comprises a thread corresponding to the lead screw external thread, and a recirculation path by which the ball bearings are recirculated through the sleeve assembly.

34. The actuator of any one of claims 31 to 33, further comprising a gear mechanism housing concentrically arranged at least partially within, and configured for rotation with, the rotary electric machine.

35. The actuator of claim 34 wherein the sleeve assembly is connected to the gear mechanism housing such that the sleeve assembly is rotatable with the gear mechanism housing.

36. The actuator of claim 35 wherein the sleeve assembly is splined to the gear mechanism housing.

37. The actuator of any one of claims 31 to 36, wherein the pushrod is connected to the lead screw at a lead screw joint.

38. The actuator of claim 37, wherein the lead screw joint comprises a pushrod connector for connecting the pushrod to the gear mechanism, for transfer of linear motion from the gear mechanism to the pushrod .

39. The actuator of claim 38, wherein the pushrod connector comprises an outboard end secured to the pushrod, and an inboard end secured to the gear mechanism; optionally wherein the inboard end is secured to the lead screw.

40. The actuator of claim 39, wherein the inboard end is secured to the lead screw in an interference fit or wherein the pushrod connector is integral to an outboard end of the lead screw.

41. The actuator of any one of claims 31 to 40, wherein the pushrod is pivotably connected to the gear mechanism .

42. The actuator of claim 41, wherein the pushrod is pivotably secured to the pushrod connector at a pushrod joint.2924-0300 (P607927)43. The actuator of claim 42, wherein the pushrod connector outboard end comprises a pushrod connector socket, optionally wherein the pushrod inboard end is received within the pushrod connector socket, optionally wherein the pushrod inboard end comprises a ball configured to be received within the pushrod connector socket.

44. The actuator of claim 43, wherein the pushrod joint is configured such that the pushrod is pivotable about a pushrod pivot axis, and wherein the pushrod pivot axis is transverse to the longitudinal axis of the pushrod .

45. The actuator of any one of claims 31 to 44, wherein an outboard end of the pushrod is configured for engagement with the foundation brake, optionally wherein the outboard end of the pushrod is configured for engagement with a brake lever of a foundation brake, optionally wherein the outboard end of the pushrod is rounded, for engagement with a correspondingly shaped portion of the brake lever.

46. A brake assembly comprising the actuator of any one of claims 31 to 45 and a heavy vehicle foundation brake.

47. The brake assembly of claim 46, wherein the heavy vehicle foundation brake is a disc brake or a drum brake.30

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