GB2368376A

GB2368376A - Automatic transmission with hydraulic actuation system having a recuperation valve

Info

Publication number: GB2368376A
Application number: GB0125042A
Authority: GB
Inventors: David Anthony Harries; Andrew David Milsom; John Vivian Comfort
Original assignee: LuK Lamellen und Kupplungsbau Beteiligungs KG; LuK Lamellen und Kupplungsbau GmbH
Current assignee: Schaeffler Buehl Verwaltungs GmbH; LuK Lamellen und Kupplungsbau GmbH
Priority date: 2000-10-25
Filing date: 2001-10-17
Publication date: 2002-05-01
Anticipated expiration: 2021-10-17
Also published as: GB0125042D0; ITMI20012229A1; JP2002168343A; DE10148086A1; GB0026178D0; GB2368376B

Abstract

An automatic transmission is operated by a hydraulic actuation system comprising an electric motor driven pump 223 delivering pressure, via non-return valve 276, to a main control valve 120, gear engagement control valves 144, 146, a clutch actuator 22 and to gear engagement actuators 114, 115. Main control valve 120 selectively connects the clutch actuator 22 to an accumulator 275 or to a reservoir 278 and also controls connection of the gear engagement actuators 114, 115 to the pump 223. A port 326 of recuperation valve 320 is connected to the reservoir 278 via gear engagement control valves 144, 146 so that spring (334, fig 10) urges piston (321) away from valve seat (328) opening inlet (330) and connecting displacement valve 300 and clutch actuator 22 to the reservoir 278 which delivers low pressure fluid to the actuator 22, thereby replenishing fluid, when actuator 22 is not under fluid pressure, required as a result of clutch wear. The gear engagement control valves 144, 146 selectively connect first and second working chambers 118, 119 of actuators 114, 115 to the main control valve 120 or to the reservoir 278. A pressure sensor 282 may be used, in a closed loop feedback control system, to control the pressure produced by the pump 223. Potentiometers 226, 227 may also be used in a closed loop control system to control valves 144, 146.

Description

HYDRAULIC ACTUATION SYSTEMS

This invention relates to hydraulic actuation systems and in particular hydraulic actuation systems for automated transmission systems.

In automated transmission systems of, for example, the type disclosed in W097/05410 or W097/40300, whose content is expressly incorporated in the disclosure content of the present application, fluid pressure actuators are used to control actuation of a clutch actuator mechanism and/or a gear engaging mechanism. In accordance with W097/05410, separate control valves are used to control the clutch actuator mechanism and the gear engaging mechanism.

W097/40300 discloses a hydraulic actuation system in which a main control valve controls both the clutch actuation mechanism and, together with secondary valves, shift and select actuators of a gear engaging mechanism.

The use of a single main control valve in this manner reduces the number of components, providing savings in the overall size and cost of the system.

The design of the master control valve is however significantly more complicated, which reduces the cost savings.

With hydraulic actuation systems of this type, position sensing means must be associated with the clutch actuator in order to provide feedback of the clutch position which may be used to control actuation of the clutch. It is not always possible to locate such position sensing means on the clutch actuator itself due to packaging restraints. In accordance with EP0702760 whose content is expressly incorporated in the disclosure content of the present application, a displacement valve may be interposed between the source of hydraulic fluid under pressure and the clutch actuator so that displacement of the displacement valve will cause displacement of fluid causing a corresponding displacement of the clutch actuator. The position

sensing means may thus be provided on the displacement valve, which may be located remote from the clutch actuating mechanism.

In order to accommodate wear in the system, means must be provided to replenish fluid in the system between the displacement valve and clutch actuator. This has been achieved in EP0702760 by providing a valve in the displacement valve which is open when pressure is not applied to the displacement valve, thereby allowing fluid to flow to the clutch actuator.

The valve however closes upon application of pressure to the displacement valve, so that the pressure is transmitted to the clutch actuator.

Due to difficulties in manufacturing the displacement valve and resulting costs involved it is desirable to have a recuperation valve which is separate from the displacement valve and is arranged to close on or prior to application of pressure to the displacement valve.

According to one aspect of the present a hydraulic actuation system for an automated transmission system comprises: a hydraulic clutch actuator for controlling engagement of a clutch ; a source of hydraulic fluid under pressure; a hydraulic fluid reservoir; a main control valve for selectively applying fluid under pressure to the hydraulic clutch actuator; a displacement valve located between the main control valve and the clutch actuator said displacement valve including a piston slidably mounted in a cylinder, a first side of the piston connected to the main control valve and a second side of the piston connected to the clutch actuator, an inlet opening to the cylinder of the displacement valve on said second side of the piston, the inlet being connected to the reservoir via a recuperation valve ; the recuperation valve comprising a valve member urged by a first spring means towards a valve seat, said valve member being mounted for limited movement on a piston which is biased away from the valve seat by a

second spring means, the piston being sealingly located in a bore, the side of the piston remote from the valve seat being connected, via the main control valve to the source of fluid under pressure so that while clutch actuator is connected to the source of fluid under pressure, pressure will be applied to the piston of the recuperation valve to displace the piston against the load applied by the second spring means and to urge the valve member into sealing engagement with the valve seat, the valve seat providing an inlet from the reservoir and an outlet being provided from the bore of the recuperation valve on the side of the piston adjacent the valve seat, the outlet being connected to the inlet of the displacement valve.

In accordance with a preferred embodiment of the present invention the main control valve connects the side of the piston of the recuperation valve remote from the valve seat, to the source of fluid under pressure prior to connecting the displacement valve to the source of fluid under pressure, the side of the piston of the recuperation valve remote from the valve seat remaining connected to the source of fluid under pressure, while the displacement valve is connected thereto.

According to a further embodiment, the main control valve also selectively connects a gear engagement actuator to the source of fluid under pressure, the main control valve moving between; in a first position in which the clutch actuator and the gear engagement actuator are isolated from the source of fluid under pressure; in a second position in which the clutch actuator is isolated from the source of fluid under pressure and the gear engagement actuator is connected to the source of fluid under pressure ; and in a third position in which the clutch actuator and the gear engagement actuator are connected to the source of fluid under pressure; the side of the piston of the recuperation valve remote from the valve seat being connected to the gear engagement actuator.

In the hydraulic system disclosed above, when the main control valve is in its first (rest) position the recuperation valve will be held open, the second spring means urging the piston away from the valve seat so that the valve member is clear of the seat. In this position one side of the displacement valve and the clutch actuator are connected to the reservoir via the recuperation valve and the opposite side of the displacement valve is connected to reservoir via the main control valve. Non-pressurised fluid may consequently be delivered from the reservoir to the displacement valve and clutch actuator to accommodate any wear in the clutch actuation system.

Upon initiation of a gear change the main control valve is moved to its second position, connecting the gear engagement actuator to the source of fluid under pressure. The application of this fluid pressure to the piston of the recuperation valve opposes the load applied to the piston by the second spring means and causes the piston to move towards the valve seat bringing the valve member into sealing engagement with the valve seat. The valve seat is closed by the valve member under the load applied by the first spring means. The clutch actuator and displacement valve are thereby isolated from the reservoir by the recuperation valve.

Now upon movement of the main control valve to the third position and connection of the displacement valve to the source of fluid under pressure, the displacement valve will move, displacing fluid to the clutch actuator in order to actuate the clutch.

The recuperation valve remains closed while the gear engagement actuator is connected to the source of fluid under pressure. The clutch may however be released by returning the main control valve to the second position, thereby permitting fluid to drain from the displacement valve and the clutch actuator to displace fluid back into the displacement valve.

If during this process a vacuum is created in the clutch actuator/displacement valve due, for example, to the slow return of the clutch actuator piston, the fluid pressure differential will force the valve member of the recuperation valve to open against the load applied by the first spring means, allowing fluid to be delivered from the reservoir and preventing air ingress into the system.

The invention is now described by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows diagrammatically a semi-automated transmission system utilising a hydraulic actuation system in accordance with the present invention; Figure 2 shows a gear selector mechanism and associated selector gate of the transmission system illustrated in Fig. 1; Figure 3 illustrates diagrammatically the hydraulic actuation system of the transmission system illustrated in Fig. 1; Figure 4 shows a sectional diagrammatic illustration of the main control valve of the hydraulic actuation system illustrated in Fig. 3, in an energised second position; Figure 5 shows a view similar to Fig. 4 of the main control valve in an energised third position; Figure 6 shows a view similar to Fig. 4 of the main control valve in an energised fourth position;

Figure 7 shows a sectional diagrammatic illustration of the gear shift control valve of the hydraulic actuation system illustrated in Fig. 3, in an energised null position; Figure 8 shows a view similar to Fig. 7 with the gear shift control valve in an energised third position; Figure 9 shows a view similar to Fig. 7 of the gear shift control valve in an energised fourth position; Figure 10 shows a view of the recuperation valve of the system illustrated in Fig. 3, in a closed position.

Fig. 1 of the accompanying drawings shows an engine 10 with a starter and associated starter circuit 1 osa which is coupled through the main drive friction clutch 14 to a multi-speed synchromeshed lay shaft-type gearbox 12, via a gearbox input shaft 15. Fuel is supplied to the engine by a throttle 16 which includes a throttle valve 18, operated by accelerator pedal 19. The invention is equally applicable to electronic or mechanical fuel injection petrol or diesel engine.

The clutch 14 is actuated by a release fork 20 which is operated by a hydraulic slave cylinder 22, under the control of a clutch actuator control means 38.

A gear selector lever 24 operates in a gate 50 having two limbs 51 and 52 joined by a cross track 53 extending between the end of limb 52 and intermediate of the ends of limb 51. The gate 50 defines five positions;"R" at the end of limb 52;"N"intermediate of the ends of the cross track 53; "S"at the junction of limb 51 with the cross track 53; and"+"and"-"at the extremities of limb 51. In limb 51 the lever 24 is biased to the central "S"position. The"N"position of the selector lever 24 corresponds to

neutral ;"R"corresponds to selection of reverse gear ;"S"corresponds to selection of a forward drive mode ; momentary movement of the lever to the "+"position provides a command to cause the gearbox to shift up one gear ratio; and momentary movement of the gear lever 24 to the"-"position provides a command to cause the gearbox to shift down one gear ratio.

The positions of the lever 24 are sensed by a series of sensors, for example micro switches or optical sensors, positioned around the gate 50. Signals from the sensors are fed to an electronic control unit 36. An output from the control unit 36 controls a gear engaging mechanism 25, which engages the gear ratios of the gearbox 12, in accordance with movement of the selector lever 24 by the vehicle operator.

In addition to signals from the gear selector lever 24, the control unit 36 receives signals from: sensor 19a indicative of the degree of depression of the accelerator pedal 19; sensor 30 indicative of the degree of opening of the throttle control valve 18; sensor 26 indicative of the engine speed; sensor 42 indicative of the speed of the clutch driven plate ; and sensor 34 indicative of the clutch slave cylinder position.

The control unit 36 utilises the signals from these sensors to control actuation of the clutch 14 during take-up from rest and gear changes, for example as described in patent specifications EP0038113, EP0043660, EP0059035, EP0101220 and W092/13208 whose content is expressly incorporated in the disclosure content of the present application.

In addition to the above mentioned sensors, control unit 36 also receives signals from a vehicle speed sensor 57, ignition switch 54 and brake switch

56 associated with the main braking system, for example the footbrake 58 of the vehicle.

A buzzer 55 is connected to the control unit 36 to warn/indicate to the vehicle operator as certain operating conditions occur. In addition or in place of the buzzer 55 a flashing warning light or other indicating means may be used. A gear indicator 60 is also provided to indicate the gear ratio selected.

As illustrated in Fig. 2, the gear engagement mechanism 25 comprises three shift rails 111, 112, 113 mounted parallel to one another for movement in an axial direction. Each shift rail 111, 112, 113 is associated with two of the gear ratios of the gearbox 12, via a selector fork and synchromesh unit in conventional manner, so that movement of the shift rails 111, 112, 113 in one axial direction will cause engagement of one of the associated gear ratios and axial movement of the shift rail 111, 112, 113 in the opposite axial direction will cause engagement of the other associated gear ratio.

Typically ; first and second gear ratios are associated with shift rail 111, so that axial movement of the shift rail 111 in a first direction will engage first gear or axial movement of shift rail 111 in a second direction will engage second gear; third and fourth gear ratios are associated with shift rail 112, so that axial movement of shift rail 112 in the first direction will engage third gear or axial movement of shift 112 in a second direction will engage fourth gear; and fifth and reverse gear ratios are associated with shift rail 113, so that axial movement of shift rail 113 in the first direction will engage fifth gear while axial movement of shift rail 113 in the second direction will engage reverse gear.

A selector member 110 is mounted for movement in a select direction X transverse to the axes of the shift rails 111, 112, 113 and in a shift direction Y, for movement axially of the shift rails 111, 112 and 113. The selector member 110 may thus be moved in direction X along a neutral plane A-B, so

that it may be indexed with and engaged a selected one of the shift rails 111, 112 and 113. The selector member 110 may then be moved in direction Y to move the engaged shift rail 111, 112, 113 axially in either direction to engage one of the gear ratios associated therewith.

As illustrated in Fig. 3, selector member 110 is movable in the select direction X by means of a fluid pressure operated select actuator 114, along the neutral plane A-B of the gate illustrated in Fig. 2, to align the select member 110 with one of the shift rails 111,112, 113, and thereby select a pair of gears associated with that shift rail. The selector member 110 may then be moved in the shift direction Y by means of a fluid pressure operated shift actuator 115, to move the shift rail 111, 112, 113 axially in either direction to engage one of the gear ratios associated therewith.

The actuators 114 and 115 each comprise a double-acting ram having pistons 116,117 respectively, which divide the actuators 114,115 into two working chambers 118,119, the working chambers 118,119 being disposed on opposite sides of each of the pistons 116,117. Operating rods 114a, 115a extend from one side of the pistons 116,117 respectively and are operatively connected with the selector member 110 for movement thereof in the select and shift directions X and Y respectively. As a consequence of the connection of operating rods 114a, 115a to the pistons 116,117, the working area of pistons 116,117 exposed to working chamber 118 is smaller than the working area of pistons 116, 117 exposed to working chamber 119.

A solenoid operated main control valve 120 comprises a housing 122, defining a bore 124. A spool 126 is slideably located in the bore 124, the spool 126 having three axially spaced circumferential lands 128,130, 132 which sealingly engage the bore 124. A solenoid 134 acts on one end of the spool 126, so that upon energisation of the solenoid 134, the spool 126

is moved axially of the bore 124 against a load applied by a compression spring 136, acting on the opposite end of the spool 126.

Inlets 138 and 139 to the bore 124 of valve 120 are connected to a spring accumulator 275. The spring accumulator 275 comprises a piston 285 which is slidably sealed in a cylinder 286. A spring 287 acts on one side of the piston 285 biasing it to one end of the cylinder 286. An electricallydriven pump 223 is provided to charge the accumulator 275 via a non-return valve 276, delivering fluid to the side of the piston 285 remote from the spring 287, thereby compressing the spring 287 and pressurising the fluid.

The side of the piston 285 from which the spring 287 acts, is vented and serves as a fluid reservoir 278 for the system. A pressure transducer 282 is provided between the spring accumulator 275 and inlets 138,139 of the main control valve 120 to measure the accumulator pressure and send signals corresponding thereto to the control unit 36.

An outlet 140 from the bore 124 of main control valve 120 is connected to the reservoir 278. A first port 142 from bore 124 is connected to working chambers 118 of the select and shift actuators 114,115 and selectively to working chambers 119 via select and shift valves 144,146 and a second port 148 is connected to the clutch slave cylinder 22. A pressure relief valve 280 is provided between the outlet of the pump 223 and the reservoir 278, to ensure that the pressure supplied by the pump 223 does not exceed a maximum predetermined value.

The shift and select valves 144,146 are both solenoid operated valves having a housing 150 defining a bore 151 with a spool 152 slideably mounted in the bore 151. The spool 152 has three axially spaced circumferential lands 154,156, 158, the lands sealingly engaging the bore 151. An axial bore 160 opens to end 162 of the spool 152 and connects to a cross-bore 164, the cross-bore 164 opening between lands 154 and 156 of the spool 152. A solenoid 166 acts on end 168 of spool 152 remote

from the end 162, so that upon energisation of the solenoid 166, the spool 152 will move axially of the bore 151 against a load applied by a compression spring 170 acting on end 162 of the spool 152.

An inlet 172 to the bore 151 is connected to port 142 of the main control valve 120. An outlet 174 from the bore 151 is connected to the reservoir 278. Port 178 of the select valve 144 is connected to the second working chamber 119 of the select actuator 114 and port 178 of shift valve 146 is connected to the second working chamber 119 of shift actuator 115.

The construction and operation of the valves 144 and 146 and actuators 114 and 115 are identical as illustrated in figures 7 to 9.

Port 148 of the main control valve 120 is connected to the clutch slave cylinder 22 via a displacement valve 300. The displacement valve 300 comprises a piston 302 slidably mounted within a bore 304 the piston 302 sealingly engaging the cylindrical surface of the bore 304. The bore 304 is connected to port 148 of the main control valve 120, on a first side of the piston 302 by a port 306 and to the slave cylinder 22 on the second side of the piston 302 by a port 308. An inlet 310 is provided to the bore 304 on the second side of the piston 302. A rod 312 extends to one side of the piston 302 coaxially of the bore 304 and position sensing means 314, for example a linear rheostat is associated with the rod 312 to provide an indication of the position of the piston 302.

Inlet 310 of the displacement valve 300 is connected to the reservoir 278 via a recuperation valve 320. The recuperation valve 320 has a stepped bore 324, a correspondingly stepped piston 321 being slidingly located in the bore 324, a larger diameter portion 322 of the piston 321 being sealed with respect to a larger diameter portion of the bore 324 and a smaller diameter portion 323 of piston 321 being sealed with respect to a smaller diameter portion of the bore 324. The bore 324 on the larger diameter side

of the piston 321 is connected to the port 142 of the main control valve 120, via a port 326. A valve seat formation 328 coaxial of the bore 324 is provided at the end of the bore 324 remote from the port 326, the valve seat formation 328 surrounding an inlet 330 to the bore 324. The inlet 330 is connected to the reservoir 278. An outlet 332 is provided from the bore 324 adjacent valve seat formation 328, the outlet 332 being connected to inlet 310 of the displacement valve 300.

The piston 322 is biased away from the valve seat formation 328 by means of a helical compression spring 334 which acts between the shoulder 325 of the bore 324 and the shoulder between portions 322 and 323 of the piston 321. The portion of the bore324 in which spring 334 is located is vented to the reservoir 278 via port 335, so that fluid leaking past the seals between the piston 321 and the wall of the bore 324 will be returned to the reservoir 278. The piston 321 has a closed bore 336 which opens to the end adjacent the valve seat formation 328. A valve member 338 is mounted for axial movement in the bore 336, a radial flange 340 on the valve member 338 being arranged to engage in inwardly directed radial flange 342 at the open end of the bore 336 to retain the valve member 338 within the bore 336. A helical compression spring 344 urges the valve member 338 towards the open end of bore 336. An annular sealing element 346 is provided on the valve member 338, the annular sealing element 346 being coaxial of the inlet 330, so that engagement of the sealing element 346 and the valve seat 328 will close the inlet 330. The end of the piston 322 adjacent the valve seat formation 328 is provided with abutment means 348 so that the end will be held clear of the valve seat formation 328 and a clearance is provided between the valve member 338 and the cylindrical surface of the bore 336, so that the bore 336 will be open to pressure of fluid at the outlet 332, and fluid will be able to flow from the inlet 330 to the outlet 332 when the valve member 338 is open. Alternatively, apertures may be provided in the cylindrical wall of the bore 336 to provide a passageway to the outlet 332.

When the transmission is in gear and the clutch 14 engaged, the solenoids 134 and 166 will be de-energised and valves 120, 144 and 146 will be in the rest positions illustrated in Fig. 3. In this position, the port 306 of the displacement valve 300 is connected via port 148 and outlet 140 of the main control valve 120 to the reservoir 278; the port 142 is isolated from the inlet 139 by land 130; the working chambers 118 of the select and shift actuators 114, 115 will be connected to the reservoir 278 via inlet 172, passageways 164,160 and outlet 174 of the select and shift valves 144,146 ; and working chambers 119 of the select and shift actuators 114,115 will be connected to the reservoir 278 via port 178 and outlet 174 of the select and shift valves 144,146. There will consequently be no movement of the clutch slave cylinder 22 or the select and shift actuators 114,115.

Moreover, the port 326 of the recuperation valve 320 will be connected to the reservoir 278 via the shift and select valves 144,146. Spring 334 will consequently urge the piston 321 away from the valve seat formation 328, unseating the valve member 328, opening the inlet 330 and connecting the displacement valve 300 and the clutch slave cylinder 22 to the reservoir 278. Fluid may consequently be delivered from the reservoir 278 to the displacement valve 300 and the clutch slave cylinder 22 to replenish fluid therein which may be required as a result of wear of the clutch 14 and clutch actuation components.

When a gear change is initiated by, for example, the driver of the vehicle moving the gear selector lever 24 momentarily to the'+'position, or by automatic initiation, solenoid 134 is energised to move the spool 126 of main control valve 120 to a second position, as illustrated in Figure 4. In this second position the working chambers 118 of both the select and shift actuators 114, 115, and inlets 172 of the select and shift valves 144,146 are connected to the spring accumulator 275, via port 142 and inlet 138. In

this second position, port 306 of the displacement valve 300 remains connected to the reservoir 278. Connection of port 142 of the main control valve 120 to the accumulator 275 will apply pressure to port 326 of recuperation valve 320 causing piston 321 to move downwardly against the load applied by spring 334 until the piston 321 abuts the end of bore 324 and the valve member 338 sealingly engages the valve seat 328 to close inlet 330.

Simultaneously, with energisation of solenoid 134 to move the main control valve 120 to the second position illustrated in Fig. 4, solenoids 166 of the select and shift control valves 144,146 are energised to move the spool 152 to a null position as illustrated in Fig. 7. In this position, the land 158 of spool 152 closes port 178 thereby closing working chamber 119 and creating a hydraulic lock preventing movement of the select and shift actuators 114 and 115, even though working chambers 118 thereof are connected to the spring accumulator 275 by the main control valve 120. The connection of port 172 to the outlet 174 via bores 160 and 164 is also closed.

Further energisation of the solenoid 134 to the third position illustrated in Fig. 5 will then close the connection between the port 306 of the displacement valve 300 and the reservoir 271 and open the connection between port 306 and the spring accumulator 275. The application of fluid under pressure to piston 302 of the displacement valve 300 will cause the piston 302 to be displaced to the left (as illustrated in figure 3), displacing fluid from that side of the piston 302 to the clutch slave cylinder 22, thereby actuating the release fork 20 to disengage the clutch 14. Movement of the clutch slave cylinder 22 and thus shift fork 20 will correspond to movement of the piston 302 of displacement valve 300 and consequently the position sensing means 314 will provide an indication of the position of the clutch 14 which may be used in a closed loop feedback circuit to control actuation of the clutch in known manner.

Due to the differential areas of piston 321 the pressure of fluid acting on the larger diameter portion 323 will out-balance that of pressure acting on the smaller diameter portion 324 and the load applied by spring 334 thereby maintaining the valve member 338 closed. The pressure of fluid acting on the valve member 338 will furthermore reinforce the load applied by spring 344.

Upon disengagement of the clutch 14, solenoid 134 of the main control valve 120 may be energised to move the main control valve back to a fourth position, as illustrated in figure 6. In this fourth position, the port 148 is isolated from the inlet 138 and the outlet 140, so that the clutch 14 will be clamped in the disengaged position. The solenoids 166 of the select and shift valves 144,146 may then be selectively energised, moving the select and shift valves 144,146 between third and fourth positions, in order to disengage the currently selected gear and engage a new gear.

Energisation of solenoid 166 to move the select or shift valve 144,146 to the third position illustrated in Fig. 8, in which working chamber 119 is connected to reservoir 278, while working chamber 118 is connected to the accumulator 275, will create a pressure differential across the pistons 116 and 117, causing the operating rod 114a, 115a to extend. Energisation of solenoid 166 to move the select or shift valve 144,146 to the fourth position illustrated in Fig. 9, in which both working chambers 118 and 119 are connected to the accumulator 275, will cause the operating rods 114a, 115a to retract, due to the differential working areas of the pistons 116 and 117.

Consequently, by appropriate control solenoids 166 of the select and shift valves 144,146, the selector member 110 may be moved to engage the desired gear.

Potentiometers 226 and 227 are connected to the operating rods 114a, 115a respectively, to provide signals indicative of the position of the associated operating rods. Signals from the potentiometers 226,227 are fed to the

control unit 36 to provide an indication of the position of the operating rods 114a, 115a, for each of the gear ratios of the gear box 12 and also to indicate the position of the operating rod 115a, when the select member 110 is in the neutral plane A-B of Fig. 2. The transmission system may thus be calibrated, so that predetermined position signals from the potentiometers 226 and 227 correspond to engagement of each of the gear ratios of the gear box 12.

Measurements from the potentiometers 226 and 227 may thus be used by a closed loop control system to control valves 144 and 146, to move the operating rods 114a and 115a, to the predetermined positions to engage the desired gear ratio.

When the desired gear ratio has been engaged, the solenoids 166 of the select and shift valves 144,146 are energised to move the valves 144,146 back to their null positions, closing the ports 178 and creating a hydraulic lock preventing movement of the actuators 114,115.

Solenoid 134 of the main control valve 120 may then be energised to move the main control valve 120 from its fourth to its second position, thereby allowing fluid from the displacement valve 300 to be returned to the reservoir 278. The pressure of fluid in the clutch slave cylinder 22 displaces the displacement valve 30, permitting re-engagement of the clutch 14. The main control valve 120 may be switched between the third and second positions, so that the clutch 14 is re-engaged in controlled manner, for example as disclosed in EP0038113 ; EP0043660 ; EP0059035 ; EP0101220 or WO92/13208.

If during this phase a vacuum is created in the displacement valve 300/clutch slave cylinder 22, due for example to the slow return of the clutch actuator piston, the reduced pressure in the recuperation valve 320 will cause the valve member 338 to open against spring 344, permitting fluid to be

delivered to the displacement valve 300 from the reservoir 278. This will avoid the tendency for air to be sucked into the system under such circumstances.

When the clutch 14 has been re-engaged, solenoid 134 of the master control valve 120 may be de-energised, so that it returns to the rest position illustrated in Fig. 3. Similarly the solenoids 166 of the shift and select valves 144,146 may be de-energised. Movement of the select and shift valves 144,146 to the rest position illustrated in Fig. 3 will open working chamber 119 to reservoir 278, thereby releasing pressure therein.

Release of pressure to the larger diameter portion 322 of piston 321 will allow the piston 321 to move under the load applied thereto by spring 334 causing the recuperation valve 320 to open, permitting free flow of fluid from the reservoir 78 to the displacement valve 300/clutch slave cylinder 22.

According to a preferred embodiment of the invention, the cylinder 286 of the accumulator, the bore 124 of the main control valve 120, the bores 151 of the select and shift valves 144,146, the cylinders of the select and shift actuators 114, 115, the bore 304 of the displacement valve 300 and/or the bore 324 of the recuperation valve 320, may be defined by a common housing, the bores/cylinders of the various components being appropriately inter-connected by passages through the common housing. The valve/actuator pack so formed would be mounted on or adjacent the gearbox 12.

The electrically driven pump 223, and control unit 36 may also be mounted with the valve/actuator pack or may be mounted remotely thereof and interconnected thereto by, for example, elastomeric pressure hoses.

Various modifications may be made without departing from the invention. For example, while in the above embodiment the hydraulic circuit has been described with reference to a semi-automated transmission system, the invention is equally applicable to fully-automated transmission systems or to automated manual transmission systems.

Furthermore although in the above embodiment the side of the piston of the recuperation valve remote from the valve seat is connected to the source of fluid under pressure via the connection of the main control valve to the gear engagement actuator, a separate port may be provided on the main control valve for connection of the side of the piston of the recuperation valve remote from the valve seat to the source of fluid under pressure.

The patent claims submitted with the application are proposed formulations without prejudice to the achievement of further patent protection. The applicant reserves the right to submit claims for further combinations of characteristics, previously only disclosed in the description and/or drawings.

References back used in sub-claims refer to the further development of the subject of the main claim by the characteristics of the respective sub-claim ; they are not to be understood as a waiver with regard to achieving independent item protection for the combination of characteristics in the related sub-claims.

Since the subject of the sub-claims can form separate and independent inventions with reference to the prior art on the priority date, the applicant reserves the right to make them the subject of independent claims or of division declarations. Furthermore, they may also contain independent inventions which demonstrate a design which is independent of one of the objects of the preceding sub-claims.

The embodiments are not to be considered a restriction of the invention. Rather, a wide range of amendments and modifications is possible within the scope of the current disclosure, especially those variations, elements and combinations and/or materials which, for example, the expert can learn by combining individual ones together with those in the general description and embodiments in addition to characteristics and/or elements or process stages described in the claims and contained in the drawings with the aim of solving a task thus leading to a new object or new process stages or sequences of process stages via combinable characteristics, even where they concern manufacturing, testing and work processes.

Claims

1. A hydraulic actuation system for an automated transmission system comprising: a hydraulic clutch actuator for controlling engagement of a clutch ; a source of hydraulic fluid under pressure; a hydraulic fluid reservoir; a main control valve for selectively applying fluid under pressure to the hydraulic clutch actuator; a displacement valve located between the main control valve and the clutch actuator said displacement valve including a piston slidably mounted in a cylinder, a first side of the piston connected to the main control valve and a second side of the piston connected to the clutch actuator, an inlet opening to the cylinder of the displacement valve on said second side of the piston, the inlet being connected to the reservoir via a recuperation valve ; the recuperation valve comprising a valve member urged by a first spring means towards a valve seat, said valve member being mounted for limited movement on a piston which is biased away from the valve seat by a second spring means, the piston being sealingly located in a bore, the side of the piston remote from the valve seat being connected, via the main control valve to the source of fluid under pressure so that while clutch actuator is connected to the source of fluid under pressure, pressure will be applied to the piston of the recuperation valve to displace the piston against the load applied by the second spring means and to urge the valve member into sealing engagement with the valve seat, the valve seat providing an inlet from the reservoir and an outlet being provided from the bore of the recuperation valve on the side of the piston adjacent the valve seat, the outlet being connected to the inlet of the displacement valve.

2. A hydraulic actuation system according to claim 1 in which the main control valve connects the side of the piston of the recuperation valve remote from the valve seat, to the source of fluid under pressure prior to

connecting the clutch actuator to the source of fluid under pressure, the side of the piston of the recuperation valve remote from the valve seat remaining connected to the source of fluid under pressure, while the clutch actuator is connected thereto.

3. A hydraulic actuation system according to claim 1 or 2 in which the main control valve further selectively connects a gear engagement actuator to the source of fluid under pressure, the side of the piston of the recuperation valve remote from the valve seat being connected to the gear engagement actuator.

4. A hydraulic actuation system according to claim 3 in which the main control valve is moveable between; a first position in which the clutch actuator and the gear engagement actuator are isolated from the source of fluid under pressure; a second position in which the clutch actuator is isolated from the source of fluid under pressure and the gear engagement actuator is connected to the source of fluid under pressure; and a third position in which the clutch actuator and the gear engagement actuator are connected to the source of fluid under pressure.

5. A hydraulic actuation system according to claim 4 in which the main control valve is movable to a fourth position in which the clutch actuator is isolated from both the accumulator and the reservoir, and the gear engagement actuator is connected to the accumulator.

6. A hydraulic actuation system according to any one of claims 3 to 5 in which the gear engagement actuator is selectively connected to the main control valve or to the reservoir by means of a gear engagement control valve.

7. A hydraulic actuation system according to claim 6 in which the gear

engagement control valve is movable between : a) a rest position in which a first and a second working chamber of the gear engagement actuator and the connection to the main control valve are all connected to the reservoir; b) a null position in which the first working chamber of the gear engagement actuator is connected to the main control valve and the second chamber of the gear engagement actuator closed ; c) a third position in which the first and second working chambers of the gear engagement actuator are connected to the main control valve and isolated from reservoir; and d) a fourth position in which first working chamber of the gear engagement actuator is connected to the main control valve and the second working chamber is connected to the reservoir.

8. A hydraulic actuation system according to any one of the preceding claims in which the gear engagement mechanism includes two gear engagement actuators, a select actuator for moving a select member in a first direction and a shift actuator for moving a select member in a second direction, the select and shift actuators having independent select and shift control valves, the select and shift control valves selectively connecting the select actuator and shift actuator respectively, to the main control valve or to the reservoir.

9. A hydraulic actuation system according to any one of the preceding claims in which the main control valve comprises a spool slidably mounted in a bore, the spool having three circumferential lands which sealingly engage the bore, an inlet being provided to the bore for connection to the source of hydraulic fluid under pressure, an outlet from the bore being connected to the reservoir; a first port opening to the bore, the first port being connected to the gear engagement control valve and a second port opening to the bore, the second port being connected to the clutch actuator:

in a first position of the spool, the first port being isolated from the inlet and outlet and the second port being connected to the outlet ; in a second position of the spool, the first port being connected to the inlet and the second port being connected to the outlet ; in a third position of the spool, the first and second ports being connected to the inlet ; and in a fourth position of the spool, the first port is connected to the inlet and the second port is isolated from both the inlet and the outlet.

10. A hydraulic actuation system according to any one of the preceding claims in which the gear engagement control valve comprises a spool slideably mounted in a bore, the spool having three circumferential lands which sealingly engage the bore, an inlet being provided to the bore for connection to the main control valve ; an outlet being provided from the bore for connection to the reservoir; and a first port opening to the bore, the first port being connected to a first working chamber of the gear engagement actuator; the spool having an axial bore opening to one end of the spool, the axial bore connecting with a cross-bore opening between first and second lands of the spool : in a rest position of the spool, the inlet being connected to the outlet via the cross-bore and axial bore and the first port being connected to the outlet ; in a null position of the spool, the first port being closed and the inlet being isolated from the outlet ; in a third position of the spool, the first port being connected to the inlet and isolated from the outlet ; and in a fourth position of the spool, the first port connected to the outlet, the inlet being isolated from the first port and the outlet.

11. A hydraulic actuation system according to claim 10 in which the gear engagement actuator comprises a double-acting ram having a piston, the

working area on one side of the piston being greater than that of the other side of the piston, the first port of the gear engagement valve being connected to the side of the piston with the larger working area, the side of the piston with the smaller working area being connected directly to the main control valve.

12 A hydraulic actuation system according to any one of the preceding claims in which the recuperation valve has a stepped piston, the end of the piston remote from the valve seat being greater than the end adjacent the valve seat, so that when both the recuperation valve and the displacement valve are connected to the source of fluid under pressure, the area differential will produce a load greater than the load applied to the piston by the first and second spring means, thereby maintaining the valve member of the recuperation valve in sealing engagement with the valve seat.

13. A hydraulic actuation system according to any one of the preceding claims in which the valve member of the recuperation valve is slidingly located in a closed bore of the piston, the closed bore being open to the outlet from the recuperation valve, when the valve member sealingly engages the valve seat.

14. A hydraulic actuation system according to any one of the preceding claims in which a position sensor is provided on the displacement valve, the position sensor being used in a closed loop control system to control the position of the clutch.

15. A hydraulic actuation system according to any one of the preceding claims in which a plurality of the components are defined by a common housing, the components being interconnected with one another in appropriate manner by passageways formed in the common housing.

16. A hydraulic actuation system substantially as described herein with reference to and as shown in Figs. 1 to 11 of the accompanying drawings.

17. An automated transmission system including a hydraulic actuation system as claimed in any one of claims 1 to 16.