Friction-assisted claw clutch

Abstract

Coupling arrangement comprising: a piston; one or more pins, the one or more pins being configured to be moved by the piston; one or more friction discs, the one or more friction discs having a number of slots and the one or more pins extending through the slots; and an end plate, the end plate having a number of recesses configured to receive the one or more pins.

Description

TECHNICAL FIELD

[0001] This description relates generally to systems and methods for friction-assisted jaw clutches. BACKGROUND AND SUMMARY

[0002] A vehicle's powertrain may include a transmission that uses the engagement and disengagement of clutches to shift between drive gears or ratios. Such clutches may be wet clutches that synchronize the rotational movement of parts of the transmission. For example, a wet clutch may include a hydraulically pressurized piston that is forced under pressure against the friction plates to synchronize the rotation of the parts.

[0003] However, friction-based wet clutches also have some disadvantages. The torque transmission capacity of such a friction clutch is limited by the number of friction plates included in the clutch. To achieve high torque transmission, a relatively large number of friction plates is required. However, more friction plates require more space, resulting in a larger packaging volume for the friction clutch. Consequently, in some configurations, a friction clutch with enough plates for a high torque load may be too large to fit into the configuration. The greater the number of friction plates, the less efficient the clutch can be.

[0004] Dog clutches, with intermeshing elements such as teeth, claws, and the like, can be used to transmit greater torque than friction clutches because of their more reasonable package size and better efficiency (where efficiency is the power dissipated relative to the torque absorbed during torque transmission). However, dog clutches also have some disadvantages. For example, dog clutches can cause torque shocks in a system, especially if the rotating components are not synchronized before engagement. Adjusting the rotation of the components before engaging a dog clutch to reduce shocks and promote smoother engagement may require additional equipment, such as a synchronizer.

[0005] The problems described above can be at least partially addressed by a friction-assisted dog clutch (FADC) comprising: a piston; a plurality of pins, the plurality of pins being configured to be moved by the piston; one or more friction plates, the friction plates having a number of slots and the plurality of pins passing through the slots; and an end plate, the end plate having a number of recesses configured to receive the plurality of pins. In this way, friction and dog clutch mechanisms are combined, allowing the FADC to synchronize inertia and transmit high torques with greater efficiency than friction clutches. Thus, an FADC can combine the advantages of a friction clutch and a dog clutch in a single arrangement.In addition, in some cases the FADC can be more compact than a friction clutch with enough friction plates to achieve a similar torque transmission capacity and / or than a combination of a dog clutch and a synchronizer with similar characteristics.

[0006] An FADC can be used in the transmissions described above to increase the efficiency of torque transfer. FADCs can be used in transmissions of a wide variety of vehicles, including those with internal combustion engines and / or electric motors. In electric and hybrid vehicles, the range of a traction battery can be extended due to the higher efficiency of FADCs. As another example, an FADC can be advantageous in a power take-off or in disconnect clutches that require relatively high torque transfer. FADCs can also be used in other systems where synchronization of two rotating elements is desired and high torque transfer between the rotating elements is required.

[0007] It should be understood that the above summary is intended to introduce, in simplified form, a selection of concepts that are further explained in the detailed description. It is not intended to identify the most important or essential features of the claimed subject matter, the scope of which is clearly defined by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that address the disadvantages noted above or elsewhere in this disclosure. SHORT DESCRIPTION OF THE CHARACTERS Fig. 1 shows a schematic representation of an exemplary vehicle powertrain that may include one or more friction-assisted dog clutches. Fig. Figure 2 shows a cross-sectional view of a FADC that can be installed in a vehicle such as the one in Fig. 1 shown vehicle may be installed. Fig. 3A shows a first view of a friction disc of the Fig. 2 shown FADC. Fig. 3B shows a second view of the friction disc of Fig. 3A. Fig. 4A shows a first view of an end plate of the Fig. 2 shown FADC. Fig. 4B shows a second view of the end plate of Fig. 4A. Fig. Figure 5 shows a table of the positions of an FADC, such as the FADC of Fig. 2. Fig. Figure 6 shows a second cross-sectional view of the FADC of Fig. 2, with the FADC in a synchronization position. Fig. Figure 7 shows a third cross-sectional view of the FADC of Fig. 2, with the FADC in an engaged position. Fig. Figure 8 shows a flowchart of a method for engaging, disengaging, or maintaining a position of an FADC, such as that shown in Fig. 2 shown FADC. DETAILED DESCRIPTION

[0008] The following description relates to systems and methods for an FADC. The FADC may be included in a vehicle powertrain, an example of which is shown in the schematic diagram of Fig. 1 to facilitate the engagement and disengagement of gears or gear sets, e.g., in a vehicle transmission. The vehicle transmission may, for example, be an automatic transmission in which gear changes are performed by opening and closing FADCs and / or other clutches. The opening and closing of the FADCs may be triggered by hydraulic pressure changes to the FADCs, which may force movement of the FADC pistons. A cross-section of an FADC from Fig. 1 is in Fig. 2, including one or more friction plates (also called discs) and an end plate that interact with the piston and pins of the FADC. A friction plate from the FADC in Fig. 2 is in Fig. 3A-3B, and the end plate is in Fig. 4A-4B. The FADC can be in one of several positions, such as engaged, synchronized, and disengaged, as shown in a table in Fig. 5. Cross-sectional views of the FADC in a synchronization position and an engaged position are shown in Fig. 6 and 7 respectively. The reference axes 260 are shown in the Fig. 2-4 and 6-7, including an x-axis, y-axis, and z-axis, where the x-axis may be parallel to a rotational axis of elements of the FADC and the y-axis and z-axis may be parallel to radial directions. A flowchart of a method for engaging and / or disengaging (e.g., transitioning between disengaged, synchronized, and engaged positions) and / or maintaining a position of the FADC is shown in Fig. 8 shown.

[0009] It should also be understood that the specific arrangements and systems illustrated in the accompanying drawings and described in the following description are exemplary embodiments of the inventive concepts defined herein. For purposes of explanation, the drawings will be described together. Thus, like elements may be referred to by like reference numerals and need not be repeated.

[0010] First of all, Fig. 1 depicts a vehicle 100 having a driveline 101 and a transmission 103. The driveline includes a prime mover 106 and a transmission 108. The prime mover 106 may be, for example, an internal combustion engine and / or an electric motor and is operated to provide rotational power to the transmission 108. The transmission 108 may be of various types, such as a manual transmission, an automatic transmission, or a continuously variable transmission. The transmission 108 receives the rotational power generated by the prime mover 106 as input and outputs the rotational power to the transmission 103 according to a selected gear ratio or setting.

[0011] In one example, the transmission 108 may be a dual-clutch automatic transmission, where a first clutch of the dual-clutch automatic transmission may be closed to engage a first type of gear or gear set, e.g., an odd gear, while a second clutch of the dual-clutch automatic transmission is open and disengaged, where the first and second clutches may each be an FADC. Conversely, the second clutch may be used to engage a second type of gear or gear set, e.g., an even gear, when closed while the first clutch is open and disengaged. The first and second clutches may be configured as a Fig. 1, the clutch 130 may be illustrated, wherein the clutch 130 may be based on the displacement of a piston in accordance with changes in hydraulic pressure and may be arranged in the transmission 108 to enable shifting between gears. It will be appreciated that the clutch 130 in Fig. 1 depicts a general illustration of the position of clutch 130 and is not representative of an actual position within transmission 108. Furthermore, as described above, transmission 108 may include more than one clutch 130. Further details regarding clutch 130 are described below. Furthermore, the dual-clutch automatic transmission described above is a non-limiting example of one or more FADCs integrated into a transmission.

[0012] The prime mover 106 may be powered by energy from an energy storage device 105. In one example, the energy storage device 105 is a battery configured to store electrical energy. An inverter 107 may be disposed between the energy storage device 105 and the prime mover 106 and configured to convert direct current (DC) to alternating current (AC).

[0013] The vehicle 100 may be a commercial vehicle, a light-duty, medium-duty, or heavy-duty vehicle, a passenger vehicle, an off-highway vehicle, and / or a utility vehicle. Additionally or alternatively, the vehicle 100 and / or one or more of its components may be used in industrial, railroad, military, agricultural, and aeronautical applications. In one example, the vehicle 100 is an electric vehicle. In other examples, the vehicle 100 may be a hybrid vehicle, and / or the vehicle 100 may be powered by an internal combustion engine.

[0014] In some examples, such as Fig. 1, the geartrain 103 includes a first axle assembly 102 and a second axle assembly 112. The first axle assembly 102 may be configured to drive a first set of wheels 104, and the second axle assembly 112 may be configured to drive a second set of wheels 114. In one example, the first axle assembly 102 is disposed near a front end 160 of the vehicle 100 and thus includes a front axle, and the second axle assembly 112 is disposed near a rear end 162 of the vehicle 100 and thus includes a rear axle. The geartrain 103 is depicted in an all-wheel drive configuration, although other configurations are possible. For example, the geartrain 103 may be front-wheel drive, rear-wheel drive, or all-wheel drive. Additionally, the geartrain 103 may include one or more tandem axle assemblies.Thus, the powertrain 103 may have other configurations without departing from the scope of this disclosure, and the configurations shown in FIG. Fig. The configuration shown in Figure 1 is provided for illustration, not limitation. Furthermore, the vehicle 100 may include additional wheels that are not coupled to the drivetrain 103.

[0015] In some four-wheel drive configurations, such as the one in Fig. 1, the powertrain 103 includes a transfer case 110 configured to receive rotary power output from the transmission 108. A first input shaft 113 is drivingly connected to a first output 111 of the transfer case 110, while a second input shaft 122 is drivingly coupled to a second output 121 of the transfer case 110. The first input shaft 113 (e.g., a front input shaft) transfers rotary power from the transfer case 110 to a first differential 116 of the first axle assembly 102 to drive the first set of wheels 104, while the second input shaft 122 (e.g., a rear input shaft) transfers rotary power from the transfer case 110 to a second differential 126 of the second axle assembly 112 to drive the second set of wheels 114.For example, the first differential 116 is drivingly coupled to a first set of axle shafts 118 coupled to the first set of wheels 104, and the second differential 126 is drivingly coupled to a second set of axle shafts 128 coupled to the second set of wheels 114.

[0016] In some examples, the vehicle 100 may additionally or alternatively be a hybrid vehicle that includes both an engine and an electric machine, each configured to power one or more of the first axle assembly 102 and the second axle assembly 112. For example, one or both of the first axle assembly 102 and the second axle assembly 112 may be powered by power from the electric machine in a first operating mode in which the electric machine is not operating to provide power (e.g., a motor-only mode), by power from the electric machine in a second operating mode in which the engine is not operating to provide power (e.g., a pure electric mode), and by power from both the engine and the electric machine in a third operating mode (e.g., an electric-assist mode).As another example, one or both of the first axle assembly 102 and the second axle assembly 112 may be an electric axle assembly configured to be driven by an integrated electric machine.

[0017] The vehicle 100 may also include a control system 14. The control system 14 is shown receiving information from a plurality of sensors 16 and sending control signals to a plurality of actuators 18. The sensors 16 may include, for example, at least one clutch sensor 132 for monitoring a position of the clutch 130. Other sensors, such as pressure sensors, temperature sensors, and air / fuel ratio and composition sensors when the prime mover 106 comprises the engine, may be mounted at various locations in the vehicle 100. The plurality of actuators may include valves that control the flow of hydraulic fluid through the clutch 130.The control system 14 may include a controller 12 that can receive input data from the various sensors, process the input data, and trigger the plurality of actuators 18 in response to the processed input data based on instructions or code programmed therein corresponding to one or more routines. More specifically, the controller 12 may be a microcomputer including microprocessor units, input / output ports, an electronic storage medium for executable programs and calibration values, such as a read-only memory chip, random access memory, keep-alive memory, and a data bus.

[0018] As described above, a vehicle's transmission may include at least one clutch that facilitates shifting of the drive wheels on the transmission, and one or more of the transmission's clutches may be FADCs. FADCs may also be used in other applications, such as power take-offs, to name just one example. A cross-section of an exemplary embodiment of an FADC 200 is shown in Fig. 2. In particular, a cross-section of the FADC 200 is shown in a disengaged position 290. The reference axes 260 are also shown and can be used for comparison with the orientations of the Fig. 3A-7. An FADC such as the FADC 200 may be used to synchronize the rotation of two components (e.g., two gears, two shafts, or a gear and a shaft) and to transmit torque between the two components. The FADC 200 may be a wet clutch, with fluid, such as oil, entering the interior 228 of the FADC 200 through the paths indicated by arrows 224 to lubricate the system. Additional fluid, such as oil, may enter a space 229 between a piston 212 and a clutch drum 206 to pressurize the piston 212 to enable the FADC 200 to engage and disengage. For example, a controller may control the pressure applied to the piston via actuators such as valves (e.g., actuators 18 in Fig. 1) applied pressure in response to a pressure sensor (e.g. sensors 16 in Fig. 1) that is in fluid communication with the interior space 228 and / or the gap 229, and / or a clutch sensor (e.g., clutch sensor 132) that detects the position of the FADC 200. The FADC 200 may include a friction synchronization system and a mechanical locking system to synchronize rotation and transfer torque between the components.

[0019] In particular, a clutch gear 208 and a shaft 222 may be coupled to other components (e.g., gears, shafts) of a transmission or other system where controlling the synchronization of the components' inertias is occasionally desired. A bearing 217 may support the clutch gear 208 so that the clutch gear 208 may be indirectly coupled to the shaft 222. Additionally, the bearing 217 may be disposed between the clutch gear 208 and the shaft 222 such that the clutch gear 208 surrounds the bearing 217 and the bearing 217 surrounds the shaft 222. Thus, the clutch gear 208 and the shaft 222 may rotate independently of each other, with little (e.g., negligible) friction between the clutch gear 208 and the shaft 222 impeding rotational movement of either part in the disengaged position 290.

[0020] The FADC 200 may also include the piston 212, the clutch drum 206, an end plate 402, and a friction disc 302. The friction disc 302 may additionally or alternatively be referred to as a disc. The end plate 402 and the piston 212 may both be mechanically connected to the clutch drum 206 via a spline or other suitable connector, and the clutch drum 206 may be mechanically coupled to or integral with the shaft 222. Thus, the end plate 402, the piston 212, and the clutch drum 206 may rotate with the shaft 222 (e.g., at substantially equal angular velocities) about a rotational axis 240. The friction disc 302 may be mechanically coupled to the clutch gear 208 (e.g., by a spline connection) such that the friction disc 302 rotates with the clutch gear 208 (e.g., at substantially the same angular velocities) about the rotational axis 240.

[0021] The FADC 200 may also include a plurality of retaining rings (e.g., retaining rings 216, 218, 220) for securing various components. For example, the retaining ring 216 may hold one end of the piston return spring 214 in a desired position, e.g., along the X-axis. In another example, the retaining rings 218 may fix the bearing 217. Additionally, the retaining ring 220 may be used to hold the end plate 402 in the correct orientation and prevent axial movement of the end plate 402. In other embodiments, additional retaining rings may be attached at additional locations to prevent axial movement of the components. Additionally or alternatively, other Fig. 2 Fasteners not shown can be used to secure the components.

[0022] Additionally, the FADC 200 may include a first sealing ring 226 disposed around the outer diameter of the piston 212 and a second sealing ring 227 disposed around the inner diameter of the piston 212. The first sealing ring 226 and the second sealing ring 227 may each be an O-ring, for example. The first sealing ring 226 and the second sealing ring 227 may prevent fluid from leaking between the piston 226 and the clutch drum 206. For example, the lubricant in the interior space 228 may not move past the first sealing ring 226 or the second sealing ring 227 in the positive x-direction toward the space 229, and the pressure medium in the space 229 may not flow past the first sealing ring 226 or the second sealing ring 227 in the negative x-direction.

[0023] The piston 212 may be mechanically coupled to a first end of a piston return spring 214, and the shaft 222 may be coupled to a second end of the piston return spring 214, with the first end located in a positive x-direction relative to the second end. In some embodiments, there may be a single piston return spring 214 that may circumferentially surround a portion of the shaft 222. In other embodiments, two or more piston return springs 214 may be arranged radially around the shaft 222. In other words, there may be one or more piston return springs 214. When the piston return spring(s) 214 are relative to the Fig. 2, the piston 212 may move in an axial direction indicated by arrow 230 until a surface 248 of the piston contacts (and in some cases pushes against) the friction elements 360 of the friction disc 302. Friction elements 360 may be located on one or more surfaces of the friction disc 302 to create friction between the friction elements 360 and the piston 212 upon contact. Furthermore, the friction disc 302 may move axially (e.g., laterally and parallel to the x-axis) in response to contact with the piston 212 such that the friction elements 360 may also contact a surface 282 of the end plate 402, creating friction between the end plate 402 and the friction disc 302.The friction between the piston 212 and the friction elements 360 of the friction disc 302 (and in some cases the friction between the friction elements 360 and the end plate 402) can result in synchronization of the rotation of the piston 212 and the friction disc 302, thereby synchronizing the rotation of the shaft 222 and the clutch gear 208.

[0024] In some embodiments, more than one friction disc, such as friction disc 302, may be included in an FADC. In such an embodiment, the friction discs may be axially aligned with each other and share a common axis of rotation (e.g., axis of rotation 240). Other discs may also be sandwiched between the friction discs.

[0025] The piston 212 may include a circular bore with a diameter sized to mate with a portion 210 of the clutch gear 208, as well as one or more piston return springs 214 and a shaft 222 extending axially therethrough. The piston may also include modified cylindrical openings 232 with three discrete diameters, forming the cross-section shown, for positioning the pins 202 within the openings 232. In the cross-sectional view of Fig. 2, one opening and one pin are shown, but multiple pins 202 and openings 232 may be arranged radially in the zy-plane, so that multiple pins 202 may be evenly spaced from the rotation axis 240. For example, there may be eight pins. An example configuration of the pins 202 is described below with reference to Fig. 3B and Fig. 4B and described in more detail. As shown in Fig. 2, the pins 202 may include a cylindrical body 238 having a diameter 244 and a cylindrical base 234 having a larger diameter 246. The base 234 of a pin 202 may be mechanically connected to a first end of a pin return spring 204, and an opposing surface 252 (e.g., parallel to the y-axis) of the piston 212 may be mechanically connected to a second end of the pin return spring 204.

[0026] In some examples, each pin 202 may be mechanically coupled to a single pin return spring 204 that circumferentially surrounds the cylindrical body 238. In other examples, multiple pin return springs 204 may be arranged around each pin 202. In other words, there may be one or more pin return springs 204 per pin 202. A single pin return spring per pin may simplify the design, while multiple pin return springs per pin may, for example, provide greater stability.

[0027] When the pin return springs 204 are moved relative to the Fig. 2, the pins 202 can move axially relative to the piston 212 in the direction indicated by arrow 230 until a surface of the base 234 contacts an opposing surface 236 transverse to the y-axis of the opening 232 and / or an end of the pin 202 extends through a slot 304 of the friction disc 302 and at least a portion of a recess 404 of the end plate 402. The friction disc 302 and the end plate 402 are described below with reference to Fig. 3A-3B and 4A-4B are described in more detail.

[0028] In Fig. 3A and Fig. 3B are a first view 300 and a second view 310 of the friction disc 302 with the reference axes 260 for the relationship to the FADC 200 of Fig. 2. As described above, one or more friction discs, such as the friction disc 302, can be used in an FADC, such as the FADC 200 of Fig. 2, be included. On the Fig. 3A-3B and their respective components and features may be referred to collectively herein. Friction disc 302 is an example of such a friction disc, but other embodiments may be incorporated into an FADC without departing from the scope of this disclosure. Friction discs, such as friction disc 302, may also include additional Fig. 3A and Fig. 3B, such as ribs, teeth, and the like for splined connections as described above. Furthermore, friction discs may include further friction elements (e.g., the friction elements 360 of Fig. 2) on one or more surfaces of the friction discs contained in Fig. 3A and Fig. 3B are not shown for reasons of clarity.

[0029] The first view 300 shows the friction disc 302 with a plurality of slots 304. The friction disc 302 may be annular, with an outer edge 306 having an outer diameter 318 and an inner edge 320 having an inner diameter 322, centered about the rotational axis 240, which is parallel to the x-axis. The outer diameter 318 may be sized to fit in an FADC, as shown in Fig. 2. More specifically, the outer diameter 318 may be configured to correspond to the inner diameter of a clutch drum (e.g., the clutch drum 206 in Fig. 2) the FADC to allow for adequate attachment (e.g. via a keyed connection). The inner diameter 422 may be dimensioned to accommodate part of a transmission coupling (e.g. part 210 of Fig. 2), one or more piston return springs (e.g. piston return springs 214 of Fig. 2) and a wave (e.g. wave 222 of Fig. 2) extending axially through it.

[0030] The slots 304 of the friction disc 302 can each be shaped as an elongated ellipse (e.g., a stadium, a curve, a pill shape) and curved such that a radial distance 308 between a slot 304 and the outer edge 306 of the friction disc 302 can be constant across the slots 304. The slot 304 can, for example, have the shape of a kidney or a bean. Likewise, the radial distance 326 between the slots 304 and the inner edge 320 can be constant. In some examples, the distance 308 can be greater than the distance 326, so that the slots 304 are located closer to the inner edge 320 than to the outer edge 306. In other examples, the distance 308 may be less than the distance 326, so that the slots 304 may be located closer to the outer edge 306 than to the inner edge 320.In other examples, the distance 308 may be substantially equal to the distance 326, such that the slots are equidistant from the inner and outer edges 320 and 306, respectively. Additionally, in some examples, the slots 304 may be equidistant from each other, angularly, as shown by arrow 312, and / or radially, as shown by arrow 314.

[0031] The radially arranged slots 304 may be configured as described above to receive a number of pins (e.g., pin 202 of Fig. 2) as in Fig. 3B shown. Fig. Figure 3B shows the second view 310 of the friction disc 302, which includes cross sections of the pins 202. Some dimensions of the Fig. 3A are shown in Fig. 3B for clarity (e.g., distance 308, outer diameter 318, distances by arrow 312 and arrow 314). In one example, each of the slots 304 may be configured to receive two pins, as shown in Fig. 3B. The slots 304 may be configured so that the pins 202 may each contact one end of a slot when the pins 202 extend axially through the slots 304. For example, a first pin 202a may contact a first end 342 of a slot 304, and a second pin 202b may contact a second end 340 of a slot 304. In this way, the first pin 202a and the second pin 202b may each prevent opposite rotational movement of the friction disc 302 relative to the pins 202. More specifically, the first pin 202a may oppose clockwise torque, while the second pin 202b may oppose counterclockwise torque, as shown in Fig. 3B.

[0032] The number of slots of a friction disc (e.g., slots 304 of friction disc 302) may depend on the number of pins (e.g., pin 202 in Fig. 2) in an FADC. For example, an FADC may contain eight pins, and a friction disc contained in the FADC may have four slots arranged as shown in the Fig. 3A and Fig. 3B. As another example, an FADC with more pins may have more slots in the friction plates. In some examples, each slot may be configured to accommodate three or more pins. For example, in other embodiments, the slots may be sized and shaped accordingly. In other embodiments, the slots on a friction plate may be arranged differently to accommodate the pins in an FADC. For example, slots may have a different shape, size, and / or location depending on the number of pins and their arrangement relative to the friction plate in an FADC. Furthermore, in some examples, friction plates may be rectangular, square, elliptical, or other shapes, depending on the geometry of an FADC into which the friction plate is installed.

[0033] Fig. 4A and Fig. 4B show a first view 400 and a second view 410, respectively, of an end plate 402 included in the FADC 200, as described with reference to Fig. 2. The end plate 402 may be in the shape of a ring, with the outer edge 406 having an outer diameter 418 and the inner edge 420 having an inner diameter 422. The inner diameter 422 may be sized to surround a portion of a transmission coupling (e.g., portion 210 of Fig. 2), one or more piston return springs (e.g. the piston return springs 214 of Fig. 2) and a wave (e.g. wave 222 of Fig. 2) extending axially through the end plate 402. The outer diameter 418 may be dimensioned to fit into a clutch drum (e.g., the clutch drum 206 in Fig. 2) and is connected thereto (e.g., via a spline connection). In some examples, the inner diameter 422 may be substantially the same as the inner diameter of the friction disc(s), e.g., the inner diameter 322 of the friction disc 302 ( Fig. 3A) in an FADC. In other examples, the inner diameter 422 may be larger or smaller than the inner diameter of the friction disc(s), e.g., the inner diameter 322 of the friction disc 302. Likewise, in some examples, the outer diameter 418 of the end plate 402 may be substantially the same as the outer diameter of the friction disc(s), e.g., the outer diameter 318 of the friction disc 302 ( Fig. 3A). In other examples, the outer diameter 418 may be larger or smaller than the outer diameter of the friction disc(s), e.g., the outer diameter 318 of the friction disc 302. Furthermore, the rotation axis 240 may extend axially through a center point of the diameter of the end plate 402 (e.g., outer diameter 418 and inner diameter 422). Furthermore, the end plate 402 and the friction disc(s) may have the same rotation axis.

[0034] The end plate 402 may further include a plurality of recesses 404. The number of recesses may correspond to the number of pins (e.g., first pin 202a and second pin 202b in Fig. 3B). For example, an FADC with eight pins can have eight recesses, as in Fig. 4A. The recesses 404 may each be spaced a distance 408 from the outer edge and a distance 426 from the inner edge. In some examples, the distance 408 is substantially the same as the distance 426. In other examples, the distance 408 may be greater or less than the distance 426. In some examples, the distance 408 and the distance 426 may vary such that the recesses are different distances from the outer edge 406 and the inner edge 420. The recesses 404 may also be radially spaced from each other, as in Fig. 3B, so that there may be a first gap 412 between pairs and a second gap 424 between two recesses within a pair. The first gap 412 may be the same as the gap (e.g., the distance shown by arrow 312) between the slots 304 of the friction disc 302, as shown in Fig. 3A and Fig. 3B to allow proper alignment of the pins 202 with the two recesses 404 and the slots 304.

[0035] The recesses 404 can be dimensioned and shaped according to the cross section of the pins. Fig. 3B shows cross-sections of the pins 202 at least partially passing through the recesses 404. In some examples, the pins may have a circular cross-section, and accordingly, the recesses 404 may be cylindrical. In such an example, the recesses 404 may have a diameter at least as large as the diameter of the cross-section of the pin. In some embodiments where the pins have different shapes, the recesses 404 may also have different shapes. The shape of the cross-section of the recesses 404 may be, for example, elliptical, rectangular, triangular, octagonal, square, or a combination thereof, depending on the geometry of the respective pins. Additionally, the recesses 404 may be arranged according to the arrangement of the pins 202. For example, in some embodiments, the first space 412 and the second space 424 may be substantially identical.In other words, the recesses 404 may be radially equidistant from each other if the pins 202 are radially equidistant from each other.

[0036] The Fig. 3A and Fig. 4B are drawn to approximately the same scale, although other relative dimensions may be used if desired.

[0037] Back to Fig. 2: The recesses 404 may extend partially through a thickness (e.g., a dimension parallel to the x-axis) of the end plate 402, with the depth 284 being less than the thickness. In other examples, the recesses 404 may be through-holes and extend through the entire thickness of the end plate 402, such that the depth 284 is equal to the thickness. The recesses 404 may be defined by openings 280 in the surface 282 of the end plate 402. If the depth 284 is less than the thickness of the end plate 402, the openings may also be delimited by the end surfaces 283. For example, if the recesses are cylindrical, the openings 280 and the end surfaces 283 may be circular in the yz-plane. The pins 202 may, for example,by compressing the piston return spring 214 and the pin return springs 204, the pins 202 can be moved through the slots 304 of the friction plate 302 and at least partially into the recesses 404, such that the pins are mechanically locked to the end plate 402. When the pins 202 are locked to the end plate 402, the pins 202 can extend at least partially through the openings 280. In some examples, when the pins 202 are locked to the end plate 402, one end of the cylindrical body 238 can be in surface contact with the end surfaces 283. In this way, a dog clutch can be employed to transmit higher torque than would be possible with an equal number of friction plates alone. Furthermore, the dog clutch mechanism can provide the FADC with greater efficiency than can be achieved with friction plates alone.A clutch without a dog clutch can use a larger number of friction plates to transmit the same maximum torque as a clutch with friction plates and a dog clutch. For example, drag losses in a friction clutch without a dog clutch can be greater due to the larger number of friction plates than in an FADC capable of transmitting a similar torque. Consequently, the FADC can operate with lower drag losses and therefore with greater efficiency than the friction clutch.

[0038] It can be a series of positions of a FADC such as FADC 200 according to the movement of a piston (e.g. piston 212 of Fig. 2) and pins (e.g. pins 202 of Fig. 2) give. Fig. 5 shows a table 500 with the positions of an FADC, including a row 512 with a disengaged position, a row 514 with a synchronization position, and a row 516 with an engaged position. The table 500 includes a column 502 indicating the pressure for each position, a column 504 indicating the compression of the piston return springs (e.g., the piston return springs 214 of Fig. 2) for each position, and a column 506 in which the compression of the pin return springs (e.g. the pin return springs 204 of Fig. 2) is specified for each position. The pressure may be a hydraulic pressure, e.g. generated by oil. There may be a first threshold pressure and a second threshold pressure, the second threshold pressure being greater than the first threshold pressure. The first threshold pressure may correspond to a spring load on the piston return springs such that when the pressure increases above the first threshold pressure, the piston return springs can be compressed to allow the piston to contact the friction disc. The second threshold pressure may correspond to a spring force on the pin return springs such that when the pressure increases above the second threshold pressure, the pin return springs can be compressed to allow the pins to extend through the friction disc and the end plate.As used herein, "extended" may be used in relation to "compressed" to describe springs that may be relatively less compressed, however, "extended" does not indicate whether the springs are extended, at equilibrium, or compressed relative to the balance of the springs. In other words, a spring in an extended position may be under compressive stress, but to a relatively lesser extent than a spring in a compressed position. Because the pressure may be a continuous measure, and springs such as the piston return springs and pin return springs may accordingly be continuously compressed rather than individually, the positions described (e.g., disengaged, engaged, synchronizing) may be ranges encompassing relative positions rather than combinations of exact positions of the individual elements. For example, a synchronizing position may be achieved with a series of springs (e.g.,Piston return springs and pin return springs) that are compressed according to a range of pressures, the lower limit being the first threshold pressure and the upper limit being the second threshold pressure.

[0039] In the disengaged position of the 512 series, the pressure can be lower than the first threshold pressure. This allows the piston return springs and pin return springs to be extended. As in the disengaged position 290 of the FADC 200 in Fig. 2, the piston 212 may be spaced from the friction elements 360 of the friction disc 302, and the base 234 of the pin 202 may be spaced from the piston 212. Because the bearing 217 allows independent rotation of the shaft 222 and the clutch gear 208, and none of the elements rotationally connected to the shaft 222 (e.g., piston 212 and end plate 402 via the clutch drum 206) are in contact with the elements rotationally connected to the clutch gear 208 (e.g., friction disc 302), the shaft 222 and the clutch gear 208 may rotate independently of each other. For example, the shaft 222 and the clutch gear 208 may have different rotational speeds about the rotational axis 240.

[0040] Back to Fig. 5: In the synchronization position of bank 514, the pressure exceeds the first threshold pressure, allowing the piston return springs to compress. However, the pressure is less than the second threshold pressure, allowing the pin return springs to remain substantially extended. An FADC in the synchronization position can be said to be partially engaged.

[0041] Fig. 6 shows a synchronization position 600 of the FADC 200, in which the piston 212 may be in surface contact with at least a portion of the friction elements 360 of the friction disc 302. In some examples, the surface 282 of the end plate 402 may also be in surface contact with the friction elements 360 in the synchronization position. Additionally, the piston return spring 214 may pull the piston 212 against the friction disc 302. Thus, the friction between the piston 212 and the friction disc 302, which have different angular velocities, may synchronize the rotation of the friction disc 302 and the piston 212 to more similar or substantially the same angular velocities, thereby synchronizing the shaft 222 and the clutch gear 208.Similar to the disengaged position, the base 234 of the pin 202 may be spaced from the piston 212 and the pin 202 may be located to the right of the friction disc 302 and the end plate 402 such that the pin 202 does not engage (e.g., extend through or be received by) the slots 304 or recesses 404 of the friction disc 302 or the end plate 402, respectively.

[0042] Back to Fig. 5: In the engaged position of row 516, the pressure is above the first and second threshold pressures, so that the piston return springs and pin return springs are compressed.

[0043] Fig. 7 shows an engagement position 700 of the FADC 200 in which the piston 212 can be in surface contact with the friction elements 360 of the friction disc 302, similar to the synchronization position 600 described above of Fig. 6. In some examples, the surface 282 of the end plate 402 may also be in surface contact with the friction elements 360 in the engaged position. Furthermore, in an engaged position, such as the engaged position 700, one end (e.g., in the negative x-direction) of the cylindrical body 238 of the pin 202 may be to the left of the friction disc 302, such that the pin 202 extends axially through the slot 304 of the friction disc 302. In some examples, the pin 202 may protrude further into the recess 404 of the end plate 402 as pressure continues to increase. Thus, an engaged position may include pins that extend through the friction disc and further into recesses of the end plate.

[0044] Fig. 8 shows a flowchart of a method 800 for engaging, disengaging, or maintaining a position of an FADC, such as the FADC 200 of the Fig. 2 and 6-7. The method 800 may be performed by a controller communicatively coupled to the FADC (e.g., controller 12 of the vehicle 100 in Fig. 1) and controlled by an actuator (e.g. actuators 18 in Fig. 1) according to instructions in a stored memory (e.g. non-volatile memory) of the controller and from the vehicle sensors (e.g. sensors 16 in Fig. 1) received signals. For example, vehicle sensors that detect a change in driving conditions or user inputs may cause the controller to send a signal to a pressure control system, which adjusts the pressure as needed (e.g., increases or decreases) to achieve a desired position (e.g., engaged, disengaged, or synchronized position) of the FADC. In particular, the positions of the pins and piston (e.g., pins 202 and piston 212 of the FADC 200 in Fig. 2, Fig. 6 and Fig. 7) relative to the friction disc(s) and an end plate of an FADC (e.g. friction disc 302 and end plate 402 of the FADC 200 in Fig. 2, Fig. 6 and Fig. 7) by pin return springs and piston return springs, respectively (e.g., pin return spring 204 and piston return spring 214). The piston return springs and pin return springs can be compressed and / or extended by hydraulic pressure corresponding to a first threshold pressure and a second threshold pressure, as shown in Fig. 5 above. In other words, the movement of the piston and pins may be triggered by hydraulic pressure. Thus, the pressure may be increased or decreased by changing the fluid flow (e.g., oil). In some examples, method 800 may be repeated automatically at a regular interval, with the controller programming providing for a timed initiation of method 800. Additionally or alternatively, method 800 may be triggered by a change in vehicle sensor signals.

[0045] Method 800 may begin at 801, where it is determined whether the FADC is requested to be turned on, turned off, or maintained. The controller may evaluate a current position of the FADC compared to the desired position of the FADC to determine whether engagement, disengagement, or maintenance is required. For example, if the current position is engaged and the desired position is engaged, engagement may be requested. Another example: if the current position is engaged and the desired position is disengaged, disengagement may be requested. In some examples, if the current position matches the desired position, neither engagement nor disengagement may be requested. Therefore, maintenance may be requested. In at least some examples, the controller may then request the requested position by sending signals to the actuator.

[0046] If engagement is requested (ENGAGE at 801), method 800 proceeds to 802, which includes moving the piston toward one or more friction plates. As in Fig. 2, the piston 212 may be moved, for example, in the direction shown by arrow 230. The movement of the piston may be initiated by increasing the pressure to overcome the spring force of the piston return spring(s), thereby compressing the piston return spring(s), as shown in Fig. 5. The pressure may only exceed the first threshold pressure when the piston is in surface contact with one of the friction discs.

[0047] Method 800 proceeds to 804 where the rotation is synchronized. More specifically, synchronizing the rotation of a clutch gear and a shaft (e.g., clutch gear 208 and shaft 222 in Fig. 2) by the piston pressing against the friction disc(s). By applying a first pressure between the first threshold pressure and the second threshold pressure, piston return springs can be compressed, forcing the piston against the friction disc(s). The friction generated in the synchronization position can resist unequal rotational speeds of the piston and the friction disc(s), enabling their synchronization.

[0048] Method 800 continues to 805, wherein the pins are optionally engaged with slots of the friction disc(s), such as those shown in the Fig. 2-3B, 6 and 7. In some cases, the pins may be aligned with slots in the friction disk(s) after synchronization at 804. The pins may, for example, be positioned similarly to Fig. 3B are aligned with the slots. Therefore, 805 cannot be completed. If the pins and slots are not aligned, the pins can press on the friction disc(s) with increasing pressure until a torque load causes the friction disc(s) to slide, whereby the slots align with the pin sets and the pins consequently move towards the end plate and can protrude through the friction disc(s) in a subsequent step (806). Thus, an FADC in the synchronization position can transmit up to a first torque between the clutch gear and the shaft, the first torque being the torque load that causes the friction disc(s) to slip. Slots in the friction disc(s) with the reference to Fig. 3A-3B can be compared to a similar shape to the recesses of the end plate as described with reference to Fig. 4A-4B increase the time required for the pins to align with the slots during slippage, thereby preventing misalignment after slippage.

[0049] Next, the method 800 proceeds to 806, where pins (e.g., pins 202 of Fig. 2) be moved by the friction disc(s). For example, movement of the pins by the friction disc(s) may involve compression of the pin return springs due to a further increase in pressure (e.g., applying a second pressure greater than the second threshold pressure). The pins may move in the same direction as the piston at 802. Because the pins may be aligned with the slots (because they become aligned after synchronization at 804 or upon completion of 805), the pins may move through the slots and thus through the friction disc(s).

[0050] Method 800 then proceeds to 808, wherein the pins are locked to the end plate. Specifically, locking the pins to the end plate may include further compressing the pin return springs by increasing the pressure beyond the second pressure such that the pins continue to move toward the end plate (e.g., in the direction indicated by arrow 230 in Fig. 2), whereby the pins are at least partially positioned in the recesses of the end plate (e.g. in the recesses 404 of the end plate 402, as shown in Fig. 2 and 4A-4B). By having the pins at least partially within the recesses of the end plate, the rotation of the pins, piston, end plate, and friction disc is mechanically locked. Thus, method 800 ends in an engaged position in which the rotation of the clutch gear and shaft is synchronized and can transmit up to a second torque therebetween. The second torque may be greater than the first; therefore, locking the pins to the end plate may enable higher torque transmission than can be achieved by the interaction of the piston and pins with the friction disc(s).

[0051] If unlocking is requested (DISENGAGE at 801), method 800 proceeds to 812, where the pins are unlocked with the end plate. For example, unlocking the pins with the end plate may involve moving the pins back (e.g., in a positive x-direction according to the reference axes 260 in the Fig. 2, Fig. 6 and Fig. 7, opposite the direction indicated by arrow 230). According to 812, the pins can still extend through slots in the friction disc(s), but not into recesses in the end plate. Thus, the pressure can be above both the first and second threshold pressure.

[0052] Method 800 continues to 814, where the pins are moved out of the friction disc(s). Moving the pins out of the friction disc(s) may be achieved, for example, by further reducing the pressure (e.g., by applying the second pressure, which is below the second threshold pressure) so that the pin return springs continue to extend and move the springs in the same direction as described in 812 above, at least until the pins no longer protrude through the slots of the friction disc(s). Thus, after 814, the FADC may be in a synchronization position where the pressure is between the first threshold pressure and the second threshold pressure.

[0053] Method 800 proceeds to 816, where the piston is moved away from the friction disc(s). Moving the piston away from the friction disc(s) may include further reducing the pressure to a pressure below the first threshold pressure, allowing the piston return springs to extend in response. The FADC may be in a disengaged position after 816, ending method 800.

[0054] If maintenance is requested (MAINT at 801), method 800 proceeds to 820, maintaining the FADC position. Therefore, a change in position (e.g., engaging or disengaging) is not requested. Maintaining the position may involve maintaining pressure. This allows the piston and pins to remain in the same positions as before method 800 began. Method 800 ends after 820.

[0055] Method 800 is a non-limiting example of a method that may be implemented to engage, disengage, or maintain a position of an FADC. Variations of method 800 may also be performed, including method 800 with additional steps before 801 and / or after a final step before the end (e.g., 808, 816, 820). In some embodiments, method 800 may exclude certain steps. For example, if a clutch sensor determines that the current position of an FADC is synchronized and the desired position is engaged, the method may select engagement (ENGAGE at 801) and skip steps 802 and 804 to further engage the FADC and achieve an engaged position.In some examples, method 800 may end in a synchronization position if the requested torque load is relatively low and the friction disc(s) are suitable for transmitting the requested torque load (e.g., ending after 804 or 806, skipping 808). In this way, method 800 and / or variations thereof may be used to transition between and / or within one of the positions (e.g., engagement, disengagement, synchronization) of an FADC and / or to maintain the current position.

[0056] The technical effect of the FADC disclosed herein is the combination of friction clutch and dog clutch mechanisms in a single clutch with increased efficiency compared to friction clutches with similar torque transmission capability and greater torque transmission capability compared to friction clutches with the same number of friction discs.

[0057] The disclosure also provides a retainer for a clutch assembly comprising: a piston, one or more pins, the one or more pins being movable by the piston, one or more friction plates, the one or more friction plates having a number of slots and the one or more pins passing through the slots, and an end plate, the end plate having a number of recesses adapted to receive the one or more pins. In a first example of the system, the number of slots is less than the number of pins. In a second example of the system, optionally including the first example, the number of recesses corresponds to a number of pins. In a third example of the system, optionally including one or both of the first and second examples, the piston is operable by hydraulic pressure.In a fourth example of the system, optionally including one or more or each of the first to third examples, the one or more friction plates are mechanically coupled to a clutch gear, and the end plate is mechanically coupled to a shaft via a clutch drum. In a fifth example of the system, optionally including one or more or each of the first to fourth examples, the system further comprises: one or more piston return springs, wherein the one or more piston return springs are configured to move the piston toward the end plate when the one or more piston return springs are extended.In a sixth example of the system, optionally including one or more or each of the first to fifth examples, the system further comprises: one or more pin return springs, wherein the one or more pin return springs are configured to move the one or more pins toward the end plate when the one or more pin return springs are extended. In a seventh example of the system, optionally including one or more or each of the first to sixth examples, contact between the piston and the friction plates synchronizes rotation of a clutch gear and a shaft.In an eighth example of the system, optionally comprising one or more or each of the first to seventh examples, the one or more pins extending through the slots and at least partially through the openings of the recesses mechanically lock the rotation of a clutch gear and a shaft such that torque is transmitted between the clutch gear and the shaft.

[0058] The disclosure also provides support for a method comprising: in response to a request to engage a friction-assisted jaw clutch, moving a piston of the friction-assisted jaw clutch toward a friction plate of the friction-assisted jaw clutch, synchronizing rotation of a clutch gear and a shaft of the friction-assisted jaw clutch, moving a pin of the friction-assisted jaw clutch through a slot of the friction plate, unlocking the pin from an end plate of the friction-assisted jaw clutch, and locking the pin to the end plate of the friction-assisted jaw clutch.In a first example of the method, the method further comprises: in response to a request to disengage the friction-assisted jaw clutch, unlocking the pin with the end plate of the friction-assisted jaw clutch, moving the pin out of the slot of the friction disc, and moving the piston away from the friction disc. In a second example of the method, optionally including the first example, moving the piston and moving the pin comprise actuating the movement of the pin and the piston with hydraulic pressure. In a third example of the method, optionally including one or both of the first and second examples, synchronizing the rotation comprises pressing the piston against the friction disc.In a fourth example of the method, optionally comprising one or more or each of the first to third examples, locking the pin to the end plate includes extending the pin at least partially through an opening of a recess of the end plate. In a fifth example of the method, optionally comprising one or more or each of the first to fourth examples, the request to engage the friction-assisted jaw clutch is initiated by a controller communicatively coupled to the friction-assisted jaw clutch in response to a signal from a sensor in fluid communication with an interior of the friction-assisted jaw clutch.

[0059] The disclosure further provides a transmission comprising: a friction-assisted jaw clutch, the friction-assisted jaw clutch comprising a piston coupled to a piston return spring and capable of axially moving a pin, the pin being coupled to a pin return spring, one or more friction plates, each of the one or more friction plates comprising a slot, and an end plate comprising a recess capable of receiving the pin, a controller having instructions stored in non-volatile memory, the instructions executable to: in response to a request to engage the friction-assisted jaw clutch, apply a first pressure to the piston, the first pressure being greater than a first threshold pressure and less than a second threshold pressure, the first pressure being capable of compressing the piston return spring,and apply a second pressure to the piston, wherein the second pressure is greater than the second threshold pressure and is capable of compressing the pin return spring. In a first example of the system, the controller instructions are further executable to: in response to a request to disengage the friction-assisted jaw clutch, apply the second pressure to the piston and apply the first pressure to the piston. In a second example of the system, optionally including the first example, the friction-assisted jaw clutch is a wet clutch. In a third example of the system, optionally including one or both of the first and second examples, the application of the first pressure synchronizes the rotation of the piston and the friction disc such that up to a first torque is transferred therebetween. In a fourth example of the system, optionally including one or more or each of the first through third examples,By applying the second pressure, the piston and the friction disc are locked so that up to a second torque that is higher than the first torque is transmitted between them.

[0060] Fig.1-4B and 6-7 show example configurations with relative positioning of the various components; however, other relative dimensions may be used. When these elements are in direct contact with one another or are directly coupled, they may be referred to as being in direct contact or directly coupled, respectively, at least in one example. Similarly, elements shown side by side or adjacent to one another may be adjacent to one another or adjacent to one another, at least in one example. For example, components that are in surface-to-surface contact with one another may be referred to as being in surface-to-surface contact. As another example, in at least one instance, elements that are separated from one another with only a space between them and that do not have any other components may be referred to as such.In yet another example, elements displayed above / below, on opposite sides, or to the left / right of each other may be referred to as such, relative to each other. Further, in at least one example, as illustrated in the figures, a topmost element or point of an element may be referred to as a "top" of the component, and a bottommost element or point of the element may be referred to as a "bottom" of the component. As used herein, the terms top / bottom, upper / lower, above / below may refer to a vertical axis of the figures and may be used to describe the positioning of elements of the figures relative to each other. Thus, in one example, elements displayed above other elements are arranged vertically above the other elements.As another example, the shapes of the elements depicted in the figures may be referred to as such (e.g., circular, straight, flat, curved, rounded, beveled, angled, and the like). Furthermore, in one example, elements that are coaxial with one another may be referred to as such. Further, in at least one example, the depicted elements that intersect one another may be referred to as intersecting elements or as intersecting elements. Furthermore, an element depicted inside another element or outside another element may be referred to as such. In other examples, elements that are offset from one another may also be referred to as such.

[0061] Features described as axial may be approximately parallel to a datum axis unless otherwise specified. The term "approximately" means plus or minus five percent of the range unless otherwise specified. Features described as reverse may be approximately perpendicular to the datum axis unless otherwise specified. Features described as radial may circumferentially surround or extend outwardly from an axis, such as the datum axis, or a component or feature previously described as radial to a datum axis, unless otherwise specified.

[0062] Features described as longitudinal can be approximately parallel to a long axis. A transverse axis can be perpendicular to a long axis. Features described as lateral can be approximately parallel to the lateral axis. A vertical axis can be perpendicular to both a transverse axis and a long axis. Features described as vertical can be approximately parallel to a vertical axis.

[0063] The following claims particularly point out certain combinations and sub-combinations that are considered novel and non-obvious. These claims may refer to "a" element or "a first" element, or the equivalent thereof. Such claims are to be construed as including the inclusion of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the present claims or by filing new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope than the original claims, are also to be considered included within the subject matter of the present disclosure.

Claims

[1] Coupling arrangement comprising: a piston; one or more pins, the one or more pins being configured to be moved by the piston; one or more friction discs, the one or more friction discs having a number of slots and the one or more pins extending through the slots; and an end plate, the end plate having a number of recesses configured to receive the one or more pins. [2] The clutch assembly of claim 1, wherein the number of slots is less than the number of pins. [3] Coupling arrangement according to one of the preceding claims, wherein the number of recesses corresponds to a number of pins. [4] Clutch arrangement according to one of the preceding claims, wherein the piston is arranged to be actuated by hydraulic pressure. [5] A clutch arrangement according to any one of the preceding claims, wherein the one or more friction discs are mechanically coupled to a clutch gear and the end plate is mechanically coupled to a shaft via a clutch drum. [6] A clutch assembly according to any one of the preceding claims, further comprising one or more piston return springs, wherein the one or more piston return springs are configured to move the piston toward the end plate when the one or more piston return springs are extended. [7] A clutch assembly according to any preceding claim, further comprising one or more pin return springs, wherein the one or more pin return springs are configured to move the one or more pins toward the end plate when the one or more pin return springs are extended. [8] A clutch arrangement according to any one of the preceding claims, wherein the contact between the piston and the friction discs synchronizes the rotation of a clutch gear and a shaft. [9] A clutch assembly according to any preceding claim, wherein the one or more pins extending through the slots and at least partially through openings of the recesses mechanically lock rotation of a clutch gear and a shaft such that torque is transmitted between the clutch gear and the shaft. [10] Transmission, comprising: a friction-assisted jaw clutch, the friction-assisted jaw clutch comprising a piston coupled to a piston return spring and configured to axially move a pin, the pin coupled to a pin return spring, one or more friction discs, each of the one or more friction discs having a slot, and an end plate having a recess configured to receive the pin; a controller having instructions stored in non-volatile memory, the instructions being executable to: Engaging the friction-assisted dog clutch in response to a request; Applying a first pressure to the piston, the first pressure being greater than a first threshold pressure and less than a second threshold pressure, the first pressure being configured to compress the piston return spring; and Applying a second pressure to the piston, the second pressure being greater than the second threshold pressure and configured to compress the pin return spring. [11] The transmission of claim 10, wherein the controller instructions are further executable to: Disengaging the friction-assisted dog clutch in response to a request; Applying the second pressure to the piston; and Applying the first pressure to the piston. [12] A transmission according to claim 10 or 11, wherein the friction-assisted dog clutch is a wet clutch. [13] A transmission according to any one of claims 10 to 12, wherein the application of the first pressure synchronises the rotation of the piston and the friction disc so that up to a first torque is transmitted between them. [14] A transmission according to any one of claims 10 to 13, wherein the application of the second pressure locks the piston and the friction disc so that up to a second torque higher than the first torque is transmitted between them. [15] A transmission according to any one of claims 10 to 14, wherein the request to engage the friction-assisted dog clutch is initiated by the controller in response to a signal from a sensor in fluid communication with the interior of the friction-assisted dog clutch.

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