An actuator

Abstract

An actuator for a heavy vehicle foundation brake (e.g. disc or drum brake), and a brake assembly, vehicle and method including the actuator. The actuator includes: an (output) pushrod 30, 230a to inte

Description

Technical Field

[0001] The present disclosure relates to an actuator. Aspects of the disclosure relate to an electromechanical actuator for a foundation brake, a foundation brake assembly incorporating an electromechanical actuator, and a method of mounting an actuator to a foundation brake. Background

[0002] It is known to provide heavy commercial vehicles such as trucks and buses with disc 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 Disclosure

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

[0007] According to an aspect of the present disclosure, there is provided an actuator for a heavy vehicle foundation brake. The actuator comprises: 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. An axis of rotation of the electric machine is substantially aligned with a path of an inboard end of the pushrod as the pushrod moves from the retracted position to the deployed position. The actuator may comprise a mounting structure to releasably mount the actuator with respect to the foundation brake.

[0008] Advantageously, this enables the actuator to operate a foundation brake that may otherwise be actuated by an air actuator. This may reduce the cost required to adopt electric actuation of existing heavy vehicle foundation brakes designed for use with air actuators. In addition, the co-axial and concentric configuration of the electric machine and the pushrod enables the actuator to fit with the space envelope of a conventional air actuator, further aiding the installation of the actuator onto heavy vehicles. If the compressed air supply of a heavy vehicle can be reduced in size or omitted by virtue of the adoption of electric actuation, the space this liberates may be utilised on the vehicle for other purposes.

[0009] The actuator may further comprise a rotary to linear gear mechanism to drive the linear motion of the pushrod upon rotation of the electric machine.

[0010] The gear mechanism may be located at least partially concentrically within the electric machine.

[0011] Advantageously, this may enable the axial length of the actuator to be minimised.

[0012] The pushrod may have a stroke between the retracted position and the deployed position of at least 40mm, optionally, at least 50mm, e.g. up to 75 or optionally 65mm.

[0013] Advantageously, a stroke greater than this distance enables the actuator to actuate foundation brakes of heavy vehicles, for example, disc brakes having brake disc diameters of between 400mm and 650mm.

[0014] The actuator may be configured to generate a maximum force of at least 9kN at the end of the pushrod to actuate the foundation brake.

[0015] A force at or in excess of this level is required to effectively brake heavy vehicles of the type described when used with foundation brakes of the type described.

[0016] The actuator may be configured such that the time from a control signal to initiate a braking operation reaching the actuator to the pushrod being able to apply 75% of its maximum force within a maximum of 0.6 seconds, for example, a maximum of 0.4 seconds.

[0017] This speed of application of the actuator to a foundation brake is necessary to meet legislative requirements in certain territories.

[0018] The actuator may further comprise two threaded studs arranged in a spaced parallel relationship to mount the actuator to or relative to a foundation brake, wherein the studs extend generally parallel to the axis of rotation.

[0019] This arrangement is desirable to enable the fitment of the actuator to existing air disc foundation brakes.

[0020] The spacing of the studs may be between 100mm and 150mm, optionally, between 120mm and 121mm (4.75").

[0021] This spacing is typical for mounting apertures of existing air disc foundation brakes.

[0022] An outboard end of the pushrod may be translatable transverse to the axis as it moves between its retracted and deployed positions.

[0023] This enables the pushrod to follow and arcuate path of a lever to enable the pushrod to stay in contact therewith.

[0024] The actuator may further comprise a housing and the pushrod may extend through an aperture of the housing.

[0025] An external face of the housing surrounding the aperture may comprise a seal to seal against a corresponding surface of the foundation brake.

[0026] Advantageously, this assists in inhibiting the entry of foreign matter into the actuator and / or the foundation brake when the two are mounted to each other.

[0027] A sealing element may be provided between the perimeter of the aperture and the pushrod.

[0028] Advantageously, this assists in inhibiting the entry of foreign matter into the actuator when it is not mounted in direct contact with the foundation brake.

[0029] The actuator may further comprise an outer housing of generally circular crosssection.

[0030] This further enables the actuator to fit within an air actuator space envelope, since air actuators are typically of a generally cylindrical shape with a circular cross-section.

[0031] A maximum dimension of the housing transverse to the axis may be 250mm, for example, 200mm.

[0032] Advantageously, limiting the actuator to this dimension assisting in the actuator occupying the same space envelope as a comparable air actuator.

[0033] A maximum dimension thereof along the axis may be 400mm, optionally 300mm, for example 200mm.

[0034] Advantageously, limiting the actuator to this dimension assisting in the actuator occupying the same space envelope as a comparable air actuator. This maximum dimension is measured from the outboard face of the actuator, excluding any mounting arrangements, such as mounting studs.

[0035] The actuator may further comprise a mechanism to selectively hold the pushrod in a selected axial position.

[0036] This enables actuator to operate for both service braking and parking braking.

[0037] The mechanism may be an electromechanical retention mechanism.

[0038] Such a mechanism is able to act as a parking brake with less bulk that a spring park brake chamber.

[0039] The electromechanical retention mechanism may be a pawl and ratchet arrangement.

[0040] Such a mechanism may provide a secure and positive retention of the pushrod in its deployed position.

[0041] The electromechanical retention mechanism may be arranged to selectively inhibit rotation of the rotary electric machine.

[0042] The electromechanical retention mechanism may be mounted at an inboard end of the actuator.

[0043] This location may be advantageous for weight distribution and for service access.

[0044] The actuator may further comprise at least one of control electronics and an inverter incorporated therewith.

[0045] This may beneficially provide a self-contained device that may simplify installation.

[0046] The electric machine may have a power density of at least 155kW / m3, optionally in excess of 200kW / m3 at a supplied voltage of 24V and a supplied current of 250A or less, for example 200A or less, e.g. approximately 200A to 150A.

[0047] An electric machine with this power density enables the actuator to occupy a space envelope that is no larger than an equivalent air actuator, whilst being powered via a standard heavy vehicle electrical supply.

[0048] A further aspect of the present disclosure provides a heavy vehicle foundation brake assembly comprising the actuator of the previous aspect and a heavy vehicle foundation brake.

[0049] The pushrod may interface with a lever of the foundation brake arranged to amplify the force of the pushrod and transmit the force to a friction element to retard rotation of a brake disc or drum.

[0050] The foundation brake may be a disc brake or may be a drum brake.

[0051] The foundation brake may further comprise at least one tappet. The lever may be arranged to axially displace the tappet to advance the friction element towards the brake disc.

[0052] The tappet may be arranged to directly actuate the friction element or indirectly actuate the friction element via a load spreading plate.

[0053] The length of the tappet may be adjustable to account for wear of friction elements thereof.

[0054] In use all the force generating the friction between the friction elements and the brake disc may be provided by the actuator.

[0055] According to a further aspect of the present disclosure there is provided an actuator for applying a heavy vehicle foundation brake. The actuator comprises a pushrod to interface with the foundation brake; an air actuation chamber arranged to displace the pushrod between a retracted position and a deployed position for a service application of the foundation brake; an electric machine arranged to selectively displace the pushrod axially between the retracted position and the deployed position; and an electromechanical retention mechanism arranged to selectively hold the pushrod in a selected axial position to maintain a parking application of the foundation brake.

[0056] Advantageously such a "hybrid" actuator allows for electric parking to be achieved in situations where electric service brake actuation is not possible or practical due to regulatory issues or compatibility requirements. The use of an electric machine in parking brake application reduces the use of air on the vehicle, thereby providing an opportunity to reduce the capacity of the vehicle air supply, saving cost and liberating space on the vehicle. It may also simplify control of the actuator, since coordination is not required between the supply of air to apply the service brake and signalling of the electromechanical mechanism arranged to selectively hold the pushrod to achieve the parking brake application.

[0057] The electric machine may be a rotary electric machine.

[0058] The electric machine may have a power density at least 155kW / m3, optionally in excess of 200kW / m3 at a supplied voltage of 24V and a supplied current of current of 250A or less, for example 200A or less, e.g. approximately 200A to 150A.

[0059] An electric machine with this power density may enable the actuator to occupy a space envelope that is no larger than an equivalent air parking brake actuator.

[0060] The actuator may comprise a rotary to linear gear mechanism to drive the linear motion of the pushrod upon rotation of the electric machine.

[0061] The gear mechanism may be located at least partially concentrically within the electric machine.

[0062] Advantageously, this may enable the axial length of the actuator to be minimised.

[0063] The pushrod may have a stroke between the retracted position and the deployed position of at least 40mm, optionally, at least 50mm, e.g. up to 75mm, optionally 65mm.

[0064] Advantageously, a stroke greater than this distance enables the actuator to actuate foundation brakes of heavy vehicles, for example, disc brakes having brake disc diameters of between 400mm and 650mm.

[0065] The actuator may be configured to generate a maximum force of at least 9kN at the end of the pushrod to actuate the foundation brake.

[0066] A force in excess of this level is required to effectively brake heavy vehicles of the type described when used with foundation brakes of the type described.

[0067] The pushrod may be a first pushrod, and the actuator may further comprise a second pushrod, one of the first and second pushrods arranged to be actuated by the air actuation chamber and the other of the first and second pushrods is arranged to be actuated by the electric machine.

[0068] The first and second pushrods may be arranged in series.

[0069] Advantageously this may enable a simple force transmission arrangement from one to the other.

[0070] The electric machine may actuate the second pushrod and the second pushrod may actuate the first pushrod.

[0071] The electromechanical retention mechanism may be a pawl and ratchet arrangement.

[0072] Such a mechanism may provide a secure and positive retention of the pushrod in its deployed position.

[0073] The electromechanical retention mechanism may be arranged to selectively inhibit rotation of the rotary electric machine.

[0074] The electromechanical retention mechanism may be mounted at an inboard end of the actuator.

[0075] This location may be advantageous for weight distribution and for service access.

[0076] The actuator may further comprise at least one of control electronics and an inverter incorporated therewith.

[0077] This may beneficially provide a self-contained device that may simplify installation.

[0078] A further aspect of the present disclosure provides a heavy vehicle foundation brake assembly, comprising the actuator of the previous aspect and a heavy vehicle foundation brake.

[0079] A further aspect of the present disclosure provides a heavy vehicle comprising a heavy vehicle foundation brake assembly according to the previous aspect.

[0080] The actuator may be a first actuator, and the heavy vehicle may further comprise a second actuator, the second actuator being configured for electromechanical service braking operation and electromechanical parking brake operation.

[0081] The heavy vehicle may comprise a tractor unit and a trailer unit, and the first actuator may be mounted to the trailer unit and the second actuator may be mounted to the tractor unit.

[0082] The heavy vehicle may further comprise a third actuator, the third actuator being configured for electromechanical service braking operation and not configured for electromechanical parking brake operation.

[0083] A further aspect of the present disclosure provides a method for controlling the actuator described above. The method may comprise receiving a braking demand signal; and / or determining if the braking demand signal is a service braking demand signal or a parking braking demand signal in dependence on the identity of the signal received; and / or outputting a signal to drive the electric machine to move the pushrod to a selected axial position corresponding to a parking clamp load if a parking demand signal is determined; and / or outputting a signal to the electromechanical retention mechanism to hold the pushrod at the selected axial position; and / or outputting a signal to a valve to supply compressed air to the actuator if a service braking demand signal is determined.

[0084] A further aspect of the present disclosure provides a controller configured to implement the method of the previous aspect.

[0085] A further aspect of the present disclosure provides computer readable instructions which, when executed by a computer, are arranged to perform a method according to the previous but one aspect.

[0086] 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.

[0087] Further benefits and advantages of the present disclosure will become apparent from the following detailed description of at least one exemplary embodiment for carrying out the present disclosure with reference to the accompanying drawings. Brief Description of Drawings

[0088] One or more embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0089] FIG. 1 is a cross-section through a foundation brake and actuator according to an embodiment of the disclosure in a non-actuated (retracted) condition;

[0090] FIG. 2 is a portion of the foundation brake of FIG. 1 to which the actuator mounts;

[0091] FIG. 3 is a similar cross-section to FIG. 1 but in an actuated (deployed) condition;

[0092] FIG. 4 is a reverse isometric view of the actuator of FIG. 1 and FIG. 2;

[0093] FIG. 5 is a reverse isometric view of the actuator of FIG. 1 and FIG. 2;

[0094] FIG. 6 is a longitudinal cross-section through the actuator of FIG. 4 and FIG. 5 on the plane 6-6, but with an outline of a conventional air actuator superimposed thereon;

[0095] FIG. 7 is a longitudinal cross-section through the actuator of FIG. 4 and FIG. 5 on the plane 7-7, but with an outline of a conventional air actuator superimposed thereon;

[0096] FIG. 8 is a schematic view of foundation brake and actuator of another embodiment;

[0097] FIG. 9 is a schematic view of an actuator according to a further embodiment;

[0098] FIG. 10 is a schematic plan view of a heavy vehicle incorporating foundation brakes and actuators according to an embodiment of the present disclosure; and

[0099] FIG. 11 is a flowchart illustrating a method of operating an actuator according to an embodiment of the present disclosure. Detailed Description

[0100] With reference to FIG. 1, a heavy vehicle foundation brake and actuator according to an embodiment of the disclosure are indicated generally at 2 and 10 respectively, with the foundation brake being mounted to an axle 4 and a brake disc 6 being mounted to a wheel hub 8 which is rotatable relative to the axle 4. Various orientations of the disc brake are described. In particular, the directions inboard I and outboard O refer to the typical orientation of the disc brake when fitted to a vehicle and with reference to the longitudinal centreline of the vehicle.

[0101] The foundation brake, in this embodiment, is a disc brake 2. The function of such a disc brake 2 is well known so will not be described in detail but, briefly, a brake carrier 12 locates friction elements in the form of brake pads 14 to face first and second opposing braking surfaces of the brake disc 6. An actuating arrangement 16 engages the inboard brake pad 14 to urge it towards the brake disc 6 and a reaction force slides a caliper 18 housing the actuating arrangement 16 relative to the brake carrier 12 in order to urge the outboard brake pad 14 towards the brake disc 6. When the brake pads 14 contact the braking surfaces of the brake disc 6, friction is generated which acts to retard rotation of the brake disc 6 and therefore the wheel hub 8 and a wheel (not shown) mounted to the wheel hub to slow the vehicle.

[0102] The actuating arrangement 16 comprises, in this embodiment, a lever 20, commonly referred to as an operating shaft 20, arranged to rotate about an axis transverse to A-A. Due to an eccentric the operating shaft 20 converts a relatively substantial input displacement from the actuator 10 into a smaller displacement, higher force output to a pair of tappets 22 (one visible) which in turn urge the inboard brake pad 14 into contact with the brake disc 6. To account for the wear of the brake pads 14 and maintain a suitable running clearance between the brake pads 14 and the brake disc 6, a wear adjuster mechanism 24 of suitable known type is arranged to automatically extend the tappets 22 (which comprise two threadably engaged parts) periodically. A return spring 26 urges the tappets 22 and operating shaft 20 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.

[0103] Disc brakes 2 of the type described require that all the force utilised to generate the friction between the friction elements 14 and the brake disc 6 is provided by the actuator. Such brakes do not have a "self-servo" effect whereby and initial contact between friction elements 14 and brake disc 6 is amplified by wedges / ball and ramp mechanisms etc. to generate more force and therefore more friction from the rotation of the brake disc without additional force being supplied by the actuator.

[0104] The upper end of the operating shaft 20 is provided with a cup-shaped depression 28, which is arranged to receive a pushrod 30 acting as an output from the actuator 10.

[0105] Such foundation disc 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).

[0106] With reference to FIG. 1 to FIG. 5, the actuator 10 of this embodiment is a combined service and park brake actuator. The actuator 10 comprises a generally cylindrical housing 32 (with a generally circular cross-section save for features such as the electrical connector) arranged to contain the electromechanical actuating mechanism discussed in more detail below.

[0107] In this embodiment the housing 32 comprises three main components, an outboard cover 34a, an inboard cover 34b and an intermediate cover 34c which are held together by bolts 36. In this embodiment, the covers 34a, 34b and 34c act, together with the bolts 36, to react certain axial forces generated within the actuator 10 from actuating operations. It will be appreciated, that in other embodiments alternative arrangements may be utilised, comprising more or fewer parts held by other fasteners, or other means such as welding, clamping, swaging etc.

[0108] A parking brake mechanism 35 is mounted to an inboard face of the inboard cover 34b as described in more detail below.

[0109] An electrical connector 37 is also mounted to a radially outer face of the inboard cover 34b in this embodiment, but may be positioned in a variety of other locations in other embodiments, as may be required.

[0110] As thus seen in FIG. 4, the outboard cover 34a is provided with a generally hexagonal planar face 38 which is arranged, when assembled to the foundation brake 2, to abut an inboard face 40 of the caliper 18. The planar face 38 is arranged, in this embodiment, in terms of its significant contours, to match equivalent faces of known air actuators, thereby enabling the actuator 10 to mount to pre-existing air disc brake calipers whose inboard faces 40 the actuator 10 is arranged to match or interface with.

[0111] Similarly, first and second threaded studs 42 extend axially forward from the outboard planar face 38 to be received in complimentary apertures 44 of the caliper 18, using suitable nuts (not shown). In this embodiment the studs 42 have an 16mm diameter and a spacing of 120.7mm centre-to-centre (4.75") to again be able to mount to standard pre-existing heavy vehicle air disc brake calipers.

[0112] The pushrod 30 extends through an aperture 46 in the outboard cover 34a to engage the lever 20. In the retracted position, pushrod 30 projects beyond the cover 34a by approximately 15mm. The tip of the pushrod 30 is hemispherical in this embodiment to mate with the depression 28 in the lever 20. A seal 48 may be provided around the perimeter of the aperture 46 to assist keeping foreign matter out of the interior of either the foundation brake 2 or actuator 10 when the two are assembled together.

[0113] In FIG. 1 the retracted position of the pushrod 30 at the start of its actuation stroke is denoted S. In FIG. 3, the deployed position of the pushrod 30 at the maximum extent of the brake stroke is denoted E. For the caliper 2 the axial distance between S and E is at least 40mm, typically more than 50mm. An upper limit for this distance (governed by the point at which the operating shaft 20 contacts the housing of the foundation brake) is typically 65mm in current foundation brakes 2. Additionally, the tip of the pushrod 30 follows an arcuate path between S and E due to its contact with the lever 20.

[0114] Referring to FIG. 1 in particular, a rotary electric machine 50 (which may be a motor or a motor generator) is arranged to selectively displace the pushrod 30 axially between the retracted positions S and fully deployed position E, and positions therebetween. An axis X-X of rotation of the electric machine 50 is substantially aligned with a path of an inboard end of the pushrod 30 as the pushrod moves from the retracted position to the deployed position.

[0115] The electric machine 50 comprises a radially outer stator 52 and a hollow inner rotor 54.

[0116] A rotary to linear gear mechanism 56 is provided to drive the linear motion of the pushrod 30 upon rotation of the electric machine 50. In this embodiment the rotary to linear gear mechanism 56 is located at least partially within the hollow inner rotor 54. This enables the overall length of the actuator 10 to be reduced.

[0117] Further, the pushrod 30 is able to at least partially retract within the hollow inner rotor 54, further enabling the overall length of the actuator to be reduced.

[0118] The pushrod 30 is pivotally mounted to an output of the rotary to lineargear mechanism 56 to enable the tip thereof to follow the arcuate path of the lever 20.

[0119] A suitable type of electric machine 50 is chosen that has a suitable power density for the voltage (24V in this embodiment) and peak current (for example less than 250A, e.g. between around 150A and 200A in this embodiment), such that axial forces of the pushrod are comparable or greater than air actuators with a parking brake of comparable size (diameter and length). This may be achieved by an electric machine 50 in which pole pieces of the stator are shaped so that the length of coil windings 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 52. Such motors may be able to achieve a power density of at least 155kW / m3, and in some embodiments in excess of 200kW / m3 at the voltage and current described above, without requiring complex cooling (e.g. just requiring air cooling and not oil cooling, for example).

[0120] An example of a suitable type of electric machine is a Pareta® motor of DG Innovate plc of Caerphilly, UK and as described in WO2020208037A1.

[0121] An electric machine 50 of this type, which is sized to be within the space envelope of a comparable air actuator with a parking brake of similar performance, is able to generate a maximum force of at least 9kN at the end of the pushrod 30. 9kN may be typical for a type 16 / 16 actuator, whereas 15kN may be more typical for a 30 / 30 actuator, for example.

[0122] Legislation relating to service brake actuation of foundation brakes 2 for heavy trucks (Regulation No 13 of the Economic Commission for Europe of the United Nations (UN / ECE)) additionally requires that the pushrod 30 be able to apply 75% of its maximum force within a maximum of 0.6 seconds. Such electric machines 50, when coupled to a suitable rotary to linear gear mechanism 56 are further able to achieve this level of force (6.75kN) within this maximum time.

[0123] With reference to FIG. 1 and FIG. 5 in particular, the parking brake mechanism 35 is now described in more detail. The mechanism is an electromechanical retention mechanism. In this embodiment the mechanism comprises a ratchet gear 60 connected for rotating movement with the rotor 54 and a pawl 62 comprising a pawl tooth 64 arranged to selectively engage and prevent the ratchet gear 60 from rotating in a direction that allows the pushrod 30 to retract (clockwise as depicted in FIG. 5). In this embodiment, the pawl 62 is a two-arm lever that is pivotably mounted to the inboard cover 34b with the pawl tooth 64 at one end and a solenoid actuator 66 at the opposing end. The parking brake is therefore able to be engaged and disengaged upon receipt of a suitable control signal to the solenoid actuator 66 when the pushrod 30 is deployed, to retain the pushrod in this position (and the foundation brake to continue to be applied) without the electric machine 50 being powered.

[0124] As can be seen in FIG. 1, the parking brake mechanism is protected by a parking brake cover 68 on the inboard face of the inboard cover 34b.

[0125] In other embodiments other suitable latching or retention arrangements may be utilised, such as other arrangements of latching pawl and actuator, which in particular provide a failsafe engagement when required. The parking brake mechanism 35 may additionally be provided in other locations of the actuator 10, for example within the housing 32 either outboard or inboard of the electric machine 50. In some embodiments where only service actuation is required, the parking brake mechanism 35 may be omitted (see FIG. 10, actuator 310).

[0126] The housing 32 also contains, in this embodiment, control electronics 72 and one or more inverters 74 for the electric machine 50 and / or solenoid actuator 66. The control electronics 72 and one or more inverters 74 are mounted inboard of the electric machine 50 in a ring configuration on a suitable support with the rotary to linear gear mechanism 56 extending through the centre thereof. This location is beneficially close to the electrical connector 37 and may be advantageous for weight distribution since the control electronics 72 and inverter 74 are typically lighter than the electric machine 50. Thus, positioning them further from the mounting than the electric machine reduces the cantilevered load on the studs 42. Further, this location reduces the amount of copper conductor required to connect to the electric machine 50, reducing costs, and may also reduce the risk of noise / interference occurring.

[0127] The control electronics 72 incorporate a suitable controller 73, such as a microprocessor controller configured to receive instructions from a vehicle electronic control unit (ECU) (90, FIG. 10) indicating a demand for service or park braking and to convert these instructions into appropriate control signals for the electric machine 50 and solenoid actuator 66. Such signals may be received via a CAN bus link from the ECU (91, FIG. 10).

[0128] The invertor(s) 74 may be a DC / DC or DC / AC inverter depending upon the type of electric machine 50 that is used. The inverter(s) 74 may utilise a 24V DC power supply from the heavy vehicle (84, FIG. 10).

[0129] In other embodiments, the positioning may be altered from a ring configuration and / or one or both of the control electronics 72 and inverter(s) may be located in another position on the actuator 10, for example inboard of the cover 34b in place of or adjacent to the parking brake mechanism 35. Alternatively, one or both of the control electronics 72 and inverter(s) may be located away from the actuator 10, for example elsewhere on the vehicle to which the actuator 10 and foundation brake 2 are fitted.

[0130] Referring now to FIG. 6 and FIG. 7, the actuator 10 of FIG. 1 and FIG. 3 to FIG. 5 is depicted superimposed on a conventional air service and parking brake actuator 1000 with equivalent functionality (in this embodiment a 30 / 30 air actuator - the 30 / 30 designation referring to the air of diaphragm acted on by the compressed air in square inches for both the parking brake and service brake). The studs 42 and planar face 38 of both actuators 10, 1000 are aligned. FIG. 6 and FIG. 7 illustrate the more compact size of the actuator 10 compared to the conventional air actuator 1000.

[0131] For example, a maximum length L of a conventional air service and parking brake actuator 1000 parallel to axis X-X is approximately 400mm (excluding the studs 42, pushrod 30, and caging bolt 1010), and it can be seen in this embodiment that the length L' is approximately 80% of L. In some embodiments the length L of the actuator 10 may be reduced to be less than 200mm, for example less than 150mm, so it is comparable to the maximum length of a service brake actuator without a parking brake chamber.

[0132] Further, the maximum transverse width T of the actuator 1000 may be up to 250mm, whereas the maximum transverse width T' of actuator 10 is approximately 80% of that amount. In some embodiments, where the foundation brake is smaller, the transverse width may be 150mm or less.

[0133] It will be appreciated that both the conventional air actuators and electric actuators of the embodiments described herein are generally cylindrical (i.e. have a generally circular outer profile) and therefore the transverse width is generally a diameter. However, the air actuators may comprise non-circular exterior features, such bosses for bolting and tensioning the clamp band, which add to the maximum transverse width and are included in the dimension T above.

[0134] In other embodiments the absolute size of the actuator 10 may vary depending upon the performance required, as may its size relationship to a corresponding air actuator 1000.

[0135] For example, for an actuator 10 with comparable performance to a 30 / 30 air service and parking brake actuator, the motor may have a power output of 3000W to produce a 15kN force at the pushrod at 3000rpm. This motor is approximately 65mm shorter along axis X-X and occupies a 25% smaller space envelope than the 30 / 30 actuator.

[0136] Whilst the actuator has been described in the context of a disc foundation brake 2, as referred to in FIG. 8, similar actuators 110 may be utilised to actuate drum brakes 102. In FIG. 8 similar parts are described by similar reference numerals with the addition of the prefix '1' and only differences are discussed in more detail.

[0137] The primary difference between the actuator 10 and the actuator 110 is that the pushrod 130 is typically longer and terminates in a clevis 130 which is pivotably connected to the lever 120. In the depicted drum brake the lever actuates the friction elements (brake shoes 114) via an actuator arrangement 116 in the form of a cam - typically a so called "s-cam" connected to the lever 20 via a shaft 121. This results in the line of action of the pushrod 130 being transverse to the axis of the axle 104. The actuator uses a suitable mounting arrangement, such as a bracket 142, to be held in a fixed position with respect to the drum brake 102. The bracket 142 may be mounted directly to the drum brake 102, or to the axle 104, for example. As the pushrod 130 is not fully enclosed, a seal 148 may be provided at the aperture where it exits the housing 132 to inhibit foreign matter entering the interior of the actuator 110.

[0138] In other embodiments (not shown) the drum brake may use wedge actuation, where the pushrod terminates in a wedge shape that directly actuates the brake shoes. In such brakes, the line of action of the pushrod is generally parallel to the axis of the axle 104.

[0139] The fact that the actuators 10 and 110 are structurally similar further minimises the costs associated with offering electromechanical actuation across a diverse range of foundation brakes 2, 102. Indeed, heavy vehicles with electric propulsion typically use regenerative braking for most routine braking operations, so there may be a greater adoption of drum brakes 102, as the performance demands for the foundation brakes may be lower, the components are often lower cost and may be inherently better protected from corrosion and contamination that disc brakes.

[0140] Whilst solely electromechanical actuation of parking and service brakes may be possible in some applications. This may not be universally possible whilst a general transition towards electrification of heavy vehicles occurs. This may be due to legislation lagging behind available technology, or the need for cross-compatibility with conventional and electrically powered vehicles.

[0141] In one example, whilst legislation in some territories now permits electric service braking of tractor units of heavy articulated trucks (semi-trucks), corresponding trailer units are permitted to have electric park braking but not electric service braking.

[0142] A further embodiment of the present disclosure is therefore a "hybrid" actuator 210 as depicted schematically in FIG. 9 in partial cutaway. In this embodiment like parts are denoted with the prefix '2' and only differences are discussed in more detail.

[0143] The actuator 210 comprises a mechanism which comprises an air actuated service brake 210a with a pushrod 230a displaceable to the left upon receipt of pressurised air in the interior thereof to the right of a flexible diaphragm via a port 282. When the pressurised air is vented a return spring (not shown) retracts the pushrod 230a.

[0144] A second mechanism is mounted inboard of the first section and comprises a smaller version of the actuator 10 of the first embodiment for use as a parking brake 210b. The pushrod 230b of this section selectively extends into the first section 210a under the influence of the electric machine 250 via the rotary to linear gear mechanism 256. The outboard end of the pushrod 230b is able to engage the inboard end of the pushrod 230a and deploy the pushrod 230a to apply the foundation brake 2. This may happen independent of the supply of air to the first section 230a.

[0145] To initiate a parking application of the associated foundation brake 2 is essentially the same as for the actuators 10 and 110. With reference to FIG. 11, at step S100 when a brake demand signal is received by the controller 90, the controller determines at step S102 if the demand is for parking or service braking. If the demand is for parking, the controller 90 first signals the electric machine 250 to be driven forward at step S104 to apply the foundation brake 2 by advancing the pushrod 230b, which in turn advances the pushrod 230a. At step S106 the controller 90 then signals the solenoid actuator 266 to be actuated to cause the pawl 262 to engage and retain the ratchet 260, thereby preventing rotation of the rotor 254 to retract both pushrods 230a and 230b, thereby holding the foundation brake 2 in the applied condition for parking. Disengagement of the parking brake is essentially the reverse of this process.

[0146] If at step 102 the controller 90 determines a service brake demand is received, at step 208 the controller signals an air control valve to open to supply pressurised air to the air chamber 232a. If the actuator 210 is mounted to a trailer, the air control valve may be a trailer control valve 93 as described below.

[0147] Whilst in this embodiment a central controller 90 is described, it will be appreciated that in some embodiments the role of the controller may be adopted by the controller 73 of one of the actuators 10, acting as a master controller, with the other controllers 73 being slaves. In other embodiments, the system may comprise multiple controllers 73acting as masters, such as one for a front axle and one for a rear axle of a vehicle, with the other actuator on that axle being a slave.

[0148] Regulations applying to the application of the parking brake typically do not set a specific time limit for this to be achieved. Thus, parking brake applications are not required to occur as rapidly as service brake applications. As a consequence, a lower power (and therefore smaller electric machine 250 may be utilised, and the gearing of the of the rotary to linear gear mechanism adjusted to be lower, enabling a suitable force to be applied, but over a longer period. For example, a parking brake application may be acceptable to occur within Is rather than 0.6s.

[0149] Further, the force required for a parking operation may be lower than for an emergency service brake operation, meaning that the electric machine 250 may also be specified to achieve a rated lower maximum force that for an electric service brake, further reducing the required size of machine 250. Typically, the force is determined to be that required to hold the vehicle at its maximum rated mass on an 18% slope. Typically, this equates to a spring force of 6kN. As a result, a motor that is one half, or one third of the size. This may be a reduction solely of length L' with the same transverse width T', just a reduction in T' or a combination of reduction in L' and T'

[0150] FIG. 10 schematically illustrates a heavy vehicle 84 according to an embodiment of the present disclosure. In this embodiment the heavy vehicle 84 is an articulated truck (semi-truck) 84 having a powered tractor unit 85 and an unpowered trailer unit 86. The tractor unit 85 is provided with two front steered wheels 87 and two rear unsteered driven wheels 88. The trailer unit 86 is towed by the tractor unit 85 and has four unsteered, undriven wheels 89. Each wheel is provided with a foundation brake 2 (a disc brake). In other embodiments, the trailer unit's foundation brakes may be drum brakes 102. In other embodiments the numbers and configuration of wheels (driven, undriven / steered, unsteered) may be adjusted in accordance with known tractor and trailer configurations.

[0151] Each foundation brake 2 is actuated by an associated actuator. The drive wheel 88 foundation brakes 2 are provided with actuators 10 as described above. The unpowered trailer wheel 89 foundation brakes 2 are provided with the hybrid actuators 210. The steered wheel 87 foundation brakes 2 are provided with electromechanical service brake only actuators 310. The actuators 310 are adapted actuators 10 which omit the parking brake mechanism 35, but are otherwise functionally the same.

[0152] The tractor unit 85 is further equipped with a controller (ECU 90) to control operation of the actuators 10, 210, 310 on the tractor unit 85 and the trailer unit 86.

[0153] The ECU 90 may comprise a processor and a memory. The processor may be one or more electronic processing devices which operably executes computer-readable instructions. The memory may be one or more memory devices. The memory is electrically coupled to the processor. The memory is configured to store instructions, and the processor is configured to access the memory and execute the instructions stored thereon in response to inputs from operator controls (not shown) in particular a service brake pedal and a parking brake control as are known per se.

[0154] The ECU is able to communicate with each of the actuators 10, 210, 310 via an electrical signal line 91, for example a vehicle CAN bus.

[0155] The tractor unit 85 of this embodiment is also provided with a pressurised air supply 92. The pressurised air supply 92 is not required for the actuators 10 and 310 of the tractor unit itself, but is connected to the air inlet ports 82 of the hybrid actuators 210 of the trailer unit 86 via pressurised air lines 94. A trailer control valve 93 downstream of the pressurised air supply 92 is also connected to the ECU 90 via the electrical signal line 91. The trailer control valve 93 controls the supply of air to the actuators 210, but only for service braking, not parking braking.

[0156] In operation the ECU 90 directly signals the service brake actuation of actuators 10 and 310, and also signals the opening of the trailer control valve 93 to cause pressurised air to flow to the first sections 210a of the actuators 210. When a service brake operation ceases, the ECU 90 further signals the retraction of actuators 10 and 310 and the venting of air from the trailer control valve 93 so the pushrod 330a retracts under the influence of the return spring.

[0157] Further, on receipt of a parking brake demand signal, the ECU 90 directly signals the actuation of actuators 10 (but not 310) as for a service actuation, but also the actuation of actuator 210b directly. Once each of actuators 10, 210b have applied a sufficient force to their respective foundation brakes 2 to hold the vehicle 84, the ECU then signals the actuation of the solenoid actuators 66, 266 to hold that force without the electric machines 50, 250 being energised.

[0158] Typically, steered wheels are not provided with parking brakes due to their additional size, or require differing non-axial mounts to be accommodated in the available space. However, in alternative embodiments the actuators 10 may be sufficiently compact that such actuators may be in line without fouling on surrounding components

[0159] An advantage of this arrangement is that the tractor unit 85 may be specified with a lower output pressurised air supply (e.g. a smaller compressor and reservoir etc), which may reduce costs and mass of the tractor unit, and offer more space for other components of the tractor unit, such as high voltage traction batteries and / or hydrogen storage tanks.

[0160] It will be appreciated that for rigid body heavy vehicles such as buses, coaches and rigid body truck, the configuration of foundation brakes, actuators and controller may be similar to that of the tractor unit 85. However, since there is no trailer requiring a pressurised air supply 92, the air supply 92 (and trailer control valve 93) may however be omitted, or at least reduced in size so as to only supply pressurised air needed for other uses, in particular for air suspension.

[0161] 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.

[0162] 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. For example, whilst a diaphragm air actuator has been described, use of a piston-type actuator could be possible in the hybrid actuator 210. In addition, the parking brake actuator 210b may be located outboard of the service brake actuator 210a. The parking brake may utilise alternative latching or holding arrangements. For example, the linear motion of the pushrod may be restricted instead of the rotary motion of the rotor. This may be achieved with a clamp, linear ratchet, or bayonet-type arrangement for example.

Claims

1. 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; andwherein an axis of rotation of the electric machine is substantially aligned with a path of an inboard end of the pushrod as the pushrod moves from the retracted position to the deployed position; andwherein the actuator comprises a mounting structure to releasably mount the actuator with respect to the foundation brake.

2. The actuator of claim 1, further comprising a rotary to linear gear mechanism to drive the linear motion of the pushrod upon rotation of the electric machine.

3. The actuator of claim 2, wherein the gear mechanism is located at least partially concentrically within the electric machine.

4. The actuator any one of claims 1 to 3, wherein the pushrod has a stroke between the retracted position and the deployed position of at least 40mm, optionally, at least 50mm, e.g. up to 65mm.

5. The actuator of any one of claims 1 to 4, wherein the actuator is configured to generate a maximum force of at least 9kN at the end of the pushrod to actuate the foundation brake.

6. The actuator of any one of claims 1 to 5, configured such that the time from a control signal to initiate a braking operation reaching the actuator to the pushrod being able to apply 75% of its maximum force within a maximum of 0.6 seconds, for example, a maximum of 0.4 seconds.

7. The actuator of any one of claims 1 to 6, further comprising two threaded studs arranged in a spaced parallel relationship to mount the actuator to or relative to a foundation brake, wherein the studs extend generally parallel to the axis of rotation.This arrangement is desirable to enable the fitment of the actuator to existing air disc foundation brakes.

8. The actuator of claim 7, wherein the spacing of the studs is between 100mm and 150mm, optionally, between 120mm and 121mm (4.75").

9. The actuator of any one of claims 1 to 8, wherein an outboard end of the pushrod is translatable transverse to the axis as it moves between its retracted and deployed positions.

10. The actuator of any one of claims 1 to 9, further comprising a housing and the pushrod extends through an aperture of the housing, optionally wherein an external face of the housing surrounding the aperture comprises a seal to seal against a corresponding surface of the foundation brake, optionally wherein a sealing element is provided between the perimeter of the aperture and the pushrod.

11. The actuator of any one of claims 1 to 10, further comprising an outer housing of generally circular cross-section.

12. The actuator of any one of claims 1 to 11, wherein a maximum dimension thereof transverse to the axis is 250mm, for example, 200mm.

13. The actuator of any one of claims 1 to 12, wherein a maximum dimension thereof along the axis is 400mm, optionally 300mm, for example 200mm.

14. The actuator of any one of claims 1 to 13, further comprising a mechanism to selectively hold the pushrod in a selected axial position, optionally wherein the mechanism is an electromechanical retention mechanism.

15. The actuator of claim 14, wherein the electromechanical retention mechanism is a pawl and ratchet arrangement.

16. The actuator of claim 14 or 15, wherein the electromechanical retention mechanism is arranged to selectively inhibit rotation of the rotary electric machine.

17. The actuator of any one of claims 14 to 16, wherein the electromechanical retention mechanism is mounted at an inboard end of the actuator.

18. The actuator of any one of claims 1 to 17, further comprising at least one of control electronics and an inverter incorporated therewith.

19. The actuator of any one of claims 1 to 18, wherein the electric machine has a power density of at least 155kW / m3, optionally in excess of 200kW / m3 at a supplied voltage of 24V and a supplied current of 200A.

20. A heavy vehicle foundation brake assembly comprising the actuator of any one of claims 1 to 19 and a heavy vehicle foundation brake.

21. The foundation brake assembly of claim 20, wherein the pushrod interfaces with a lever of the foundation brake arranged to amplify the force of the pushrod and transmit the force to a friction element to retard rotation of a brake disc or drum.

22. The foundation brake assembly of claim 20 or 21, wherein the foundation brake is a disc brake.

23. The foundation brake assembly of claim 20 or 21, wherein the foundation brake is a drum brake.

24. The foundation brake assembly of claim 22, wherein the foundation brake further comprises at least one tappet and the lever is arranged to axially displace the tappet to advance the friction element towards the brake disc, optionally wherein the tappet is arranged to directly actuate the friction element or indirectly actuate the friction element via a load spreading plate, optionally wherein the length of the tappet is adjustable to account for wear of friction elements thereof.

25. The foundation brake assembly of any one of claims 20 to 24, wherein in use all the force generating the friction between the friction elements and the brake disc is provided by the actuator.

26. A heavy vehicle comprising the brake assembly of any one of claims 20 to 25.

27. An actuator for applying a heavy vehicle foundation brake, the actuator comprising: a pushrod to interface with the foundation brake;an air actuation chamber arranged to displace the pushrod between a retracted position and a deployed position for a service application of the foundation brake;an electric machine arranged to selectively displace the pushrod axially between the retracted position and the deployed position; andan electromechanical retention mechanism arranged to selectively hold the pushrod in a selected axial position to maintain a parking application of the foundation brake.

28. The actuator of claim 27, wherein the electric machine is a rotary electric machine.

29. The actuator of claim 28, wherein the electric machine has a power density at least 155kW / m3, optionally in excess of 200kW / m3 at a supplied voltage of 24V and a supplied current of 200A.

30. The actuator of any one of claims 27 to 29, further comprising a rotary to linear gear mechanism to drive the linear motion of the pushrod upon rotation of the electric machine,optionally wherein the gear mechanism is located at least partially concentrically within the electric machine.

31. The actuator of any one of claims 27 to 30, wherein the pushrod has a stroke between the retracted position and the deployed position of at least 40mm, optionally, at least 50mm, e.g. up to 65mm.

32. The actuator of any one of claims 27 to 31, wherein the actuator is configured to generate a maximum force of at least 9kN at the end of the pushrod to actuate the foundation brake.

33. The actuator of any one of claims 27 to 32, wherein the pushrod is a first pushrod, and the actuator further comprises a second pushrod, one of the first and second pushrods arranged to be actuated by the air actuation chamber and the other of the first and second pushrods is arranged to be actuated by the electric machine, optionally wherein the first and second pushrods are arranged in series.

34. The actuator of claim 33, wherein the electric machine actuates the second pushrod and the second pushrod actuates the first pushrod.

35. The actuator of any one of claims 27 to 34, wherein the electromechanical retention mechanism is a pawl and ratchet arrangement.

36. The actuator of any one of claims 27 to 35, wherein the electromechanical retention mechanism is arranged to selectively inhibit rotation of the rotary electric machine.

37. The actuator of any one of claims 27 to 36, wherein the electromechanical retention mechanism is mounted at an inboard end of the actuator.

38. The actuator of any one of claims 27 to 37, further comprising at least one of control electronics and an inverter incorporated therewith.

39. A heavy vehicle foundation brake assembly, comprising the actuator of any one of claims 27 to 38 and a heavy vehicle foundation brake.

40. A heavy vehicle comprising a heavy vehicle foundation brake assembly according to claim 39, optionally wherein the actuator is a first actuator, and further comprising a second actuator, the second actuator being configured for electromechanical service braking operation and electromechanical parking brake operation, optionally, wherein theheavy vehicle comprises a tractor unit and a trailer unit, and the first actuator is mounted to the trailer unit and the second actuator is mounted to the tractor unit.

41. The heavy vehicle of claim 40, further comprising a third actuator, the third actuator being configured for electromechanical service braking operation and not configured for electromechanical parking brake operation42. A method for controlling the actuator of any one of claims 27 to 38, the method comprising:receiving a braking demand signal;determining if the braking demand signal is a service braking demand signal ora parking braking demand signal in dependence on the identity of the signal received;outputting a signal to drive the electric machine to move the pushrod to a selected axial position corresponding to a parking clamp load if a parking demand signal is determined;outputting a signal to the electromechanical retention mechanism to hold the pushrod at the selected axial position; andoutputting a signal to a valve to supply compressed air to the actuator if a service braking demand signal is determined.

43. A controller configured to implement the method of claim 42.

44. Computer readable instructions which, when executed by a computer, are arranged to perform a method according to claim 42.

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