ITMI20012229A1 - HYDRAULIC DRIVE SYSTEMS, PARTICULARLY FOR TRANSMISSION SYSTEMS OR AUTOMATIC GEARBOXES - Google Patents

Description

DESCRIPTION

The present invention relates to hydraulic drive systems and, in particular, hydraulic drive systems for automatic transmission or gearbox systems.

In automatic gearbox systems, for example of the type described in international patent application WO97 / 05410 or W097 / 40300, the content of which is expressly incorporated in the description of the present application, pressurized fluid actuators are used to control the operation of an actuator mechanism clutch and / or gear engagement mechanism. In accordance with W097 / 05410, separate control valves are employed to control the clutch actuating mechanism and the gear engagement mechanism.

WO97 / 40300 discloses an actuation system in which a master control valve both controls the clutch actuation mechanism and, together with secondary valves, moves and selects actuators of a gear engagement mechanism. Using a single main control valve in this way reduces the number of components, providing savings in overall system size and cost. The structure of the main control valve is however significantly more complicated, which reduces the cost savings.

With hydraulic drive systems of this type, position sensing means must be associated with the clutch actuator to provide clutch position traction which can be employed to control clutch actuation. It is not always possible to position said position sensor means on the clutch actuator itself due to space constraints. According to European patent application EP 0702 760, the content of which is expressly included in the description of the present application, a displacement valve can be placed between the source of pressurized hydraulic fluid and the clutch actuator in such a way that displacement of the displacement will cause fluid displacement resulting in a corresponding displacement of the clutch actuator. The position sensing means can thus be provided on the displacement valve, which can be positioned distant from the clutch actuation mechanism.

In order to compensate for wear in the system, means must be provided for integrating fluid into the system between the displacement valve and the clutch actuator. This was achieved in EP 0702 760 by providing a valve in the displacement valve which is opened when pressure is not applied to the displacement valve thereby allowing fluid to flow to the clutch actuator. However, this valve closes upon application of pressure to the displacement valve, whereby the pressure is transmitted to the clutch actuator.

Because of the difficulty in manufacturing the displacement valve and the consequent costs involved therein, it is desirable to have a recovery valve which is separate from the displacement valve and is adapted to close at or prior to the application of pressure to the displacement valve. shift.

According to an aspect of the present invention, a hydraulic drive system for an automatic shifting system comprises:

a hydraulic clutch actuator for controlling engagement of a clutch;

a source of hydraulic fluid under pressure;

a reservoir of hydraulic fluid;

a master control valve for selectively applying fluid under pressure to the hydraulic clutch actuator;

a displacement valve positioned 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 being connected to the main control valve of a second side of the piston being connected to the clutch actuator, an inlet port to the displacement valve cylinder on said second side of the piston, the inlet being connected to the reservoir via a recovery valve;

the recovery valve comprising a valve element urged by first spring means towards a valve seat, said valve element being mounted to perform limited movement on a piston which is stressed loosely from the valve seat by second spring means, the piston being positioned at seal in a bore, the side of the piston is distant, from the valve seat being connected, via the main control valve to the source of fluid under pressure such that while the clutch actuator is connected to the source of fluid under pressure, pressure will be applied to the piston of the recovery valve to move 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 by the recovery valve hole on the side of the piston adjacent to the valve seat, the ex ita being connected to the displacement valve inlet.

According to a preferred embodiment of the present invention, the main control valve connects the piston side of the recovery valve remote from the valve seat to the pressurized fluid source before connecting the displacement valve to the pressurized fluid source, the side of the recovery valve piston away from the valve seat remaining connected to the source of fluid under pressure, while the displacement valve is connected to it.

According to a further embodiment, the main control valve also selectively connects a gear engaging actuator to the source of fluid under pressure, the main control valve moving 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 pressurized fluid source and the gear engagement actuator is connected to the pressurized fluid source; And

a third position in which the clutch actuator and the gear engaging actuator are connected to the source of fluid under pressure;

the piston side of the recovery valve remote from the valve seat being connected to the gear engagement actuator.

In the previously described hydraulic system, when the main control valve is in its first (rest) position, the recovery valve will be held open, and according to the spring means by biasing the piston loosening from the valve seat so that the the valve element is separated from the seat. In this position, one side of the displacement valve and the clutch actuator are connected to the reservoir via the recovery valve and the opposite side of the displacement valve and connected to the reservoir via the main control valve. Non-pressurized fluid can subsequently be delivered from the reservoir to the displacement valve and clutch actuator to compensate for any wear in the clutch actuation system.

Upon initiation of a gear shift, 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 on the piston of the recovery valve opposes the load applied to the piston of the second spring means and causes the piston to move towards the valve seat bringing the valve element into sealing engagement with the valve. valve seat. The valve seat closed by the valve element under the load applied by the first spring means. The clutch actuator and displacement valve are thus isolated from the reservoir by the recovery valve. At this point, upon movement of the main control valve the third position is to connect the displacement valve to the source of fluid under pressure, the displacement valve will move, moving fluid to the clutch actuator to operate the clutch.

The recovery valve remains closed while the gear engagement actuator is connected to the source of fluid under pressure, the clutch can however be released by returning the main control valve to the second position, thus allowing fluid to drain from the displacement valve and clutch actuator to move fluids back into the shift valve.

If, during this process, a vacuum is created in the clutch actuator / displacement valve due to e.g. slow return of the clutch actuator piston, the fluid pressure differential will force the valve element of the recovery valve to open against the load applied by the first spring means, allowing the fluid to be dispensed from the tank and preventing the entry of air into the system.

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure -1-, schematically illustrates a semi-automatic transmission or gearbox system using a hydraulic drive system according to the present invention;

FIG. 2 illustrates a gear selector mechanism and established selection gate of the transmission-shift system illustrated in FIG. 1;

Figure 3 schematically illustrates the hydraulic actuation system of the transmission system illustrated in Figure 1;

Figure 4 illustrates a schematic sectional representation of the main control valve of the hydraulic actuation system illustrated in Figure 3, in a second mentioned position;

Figure 5 illustrates a view similar to Figure 4 of the main control valve in a third energized position;

Figure 6 illustrates a view similar to Figure 4 of the main control valve in a fourth energized position;

Figure 7 illustrates a schematic sectional representation of the shift control valve of the hydraulic drive system illustrated in Figure 3, in an energized neutral position;

Figure 8 illustrates a view similar to Figure 7, with the shift control valve in a third energized position;

Figure 9 illustrates a view similar to Figure 7 of the shift control valve in an energized fourth position;

Figure 10 illustrates a view of the recovery valve of the system illustrated in Figure 3, in a closed position.

Figure 1 of the accompanying drawings illustrates an internal combustion engine with a starter and an associated starter circuit 10a which is connected via the main drive friction clutch 14 to an available shaft-type gearbox or gearbox 12. with multi-speed or multi-speed synchro-meshing, through an input shaft 15 of the gearbox. Fuel is supplied to the engine by a carburetor 16 which includes a throttle valve 18 operated by the accelerator pedal 19. The invention is also applicable to a gasoline engine or a mechanical electronic fuel injection diesel engine.

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

A gear selection lever 24 operates in a guided passage 50 having two flaps 51 and 52 joined by a cross track 53 extending between the end of the flap 52 and in an intermediate position at the ends of the flap 51. The gate passage 50 defines five positions; "R" at the ends of the flap 52; "N" in an intermediate position at the ends of the cross track 53; "S" at the junction of the flap 51 with the cross track 53, and "+" and at the ends of the flap 51. In the flap 51, the lever 24 is urged to the central position "S". The "N" position of the selector lever 24 corresponding to neutral; "R" corresponds to selection of reverse gear; "S" corresponds to selection of the forward travel mode; momentary movement of the lever to the " + " position provides a command for causing the shift to cause shifting up a gear ratio; and momentary movement of the shift lever 24 to the position provides a command for determining shift shifting of a gear ratio.

The positions of the lever 24 are detected by means of a series of sensors, for example microswitches or optical sensors, positioned around the gate passage 50. Signals from the sensors are fed to an electronic control unit 36. An output from the control unit 36 controls a gear engagement mechanism 25, which engages the transmission-to-gear ratios of the gearbox 12 in accordance with the movement of the selector lever 24 by the driver of the vehicle.

In addition to signals from the gear selector or shift lever 24, the control unit 36 receives signals from:

sensor 19a indicative of the degree of lowering of the accelerator pedal 19;

sensor 30 indicative of the degree of opening of the butterfly control valve 18;

sensor 26 indicative of the engine speed;

sensor 42 indicative of the speed of the clutch operated disc;

sensor 34 indicating the position of the slave cylinder of the clutch.

The control unit 36 uses the signals from this sensor to control actuation of the clutch 14 during starting from rest or stationary state and gear changes, for example as described in the patent descriptions EP 0038 113, EP 0043 660, EP 0059 035, EP 0101 220, and W092 / 132O8 whose content is expressly incorporated in the description of the present application.

In addition to the aforementioned sensors, the control unit 36 also receives signals from a vehicle speed sensor 55, ignition switch 54 and brake switch 56 associated with the main brake system, e.g., the vehicle foot brake 58. .

A buzzer 57 is connected to the control unit 36 to alert / indicate to the driver of the vehicle the occurrence of certain operating conditions. In addition to or in place of the buzzer 57, a selection lamp or other indicator means may be employed. A gear indicator 60 is also provided to indicate the selected gear.

As illustrated in FIG. 2, the gear engagement mechanism 25 includes three gear change rails 111, 112, 113 mounted parallel to each other to move in an axial direction. Each shift rail 111, 112, 113 is associated with two of the gear ratios of the gearboxes 12, via a synchro-gear selector fork unit in a conventional manner, such that movement of the shift rails 111, 112, 113 in one axial direction will cause engagement of one of the associated gear ratios or gears while axial movement of the shift rail 111, 112, 113 in the opposite axial direction will result in engagement of the other associated gear ratio or gear.

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

A selector element 110 is mounted to move in a selection direction X transversely to the axes of the shift rails 111, 112, 113 and in a shift direction X to move axially to the shift rails 111, 112, 113. The selector element 110 can thus be moved in the X direction along a neutral plane Ά-Β whereby it can be registered and engaged with a selection of the gear change rails 111, 112 and 113. The selector element 110 can then being moved in the Y direction 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 Figure 3, the selector element 110 is movable in the selection direction X by means of a selection actuator 114 operated by pressurized fluid, along the neutral plane A-B of the gate passage illustrated in Figure 2, to align the selecting 110 with one of the shifting rails 111, 112, 113 and thereby selecting a pair of gears associated with that shifting rail. The selector element 110 can then be moved in the shift direction ΐ by a pressurized fluid actuator 115 to move the shift rail 111, 112, 113 axially in either direction. to engage one of the gear ratios associated with it.

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

A solenoid operated main control valve 120 includes a housing 112 defining a hole 124. A spool 126 is slidably positioned in the hole 124, the spool 126 having three circumferentially axially spaced ribs 128, 130, 132 which sealingly engage the hole 124. A solenoid 134 acts on one end of the spool 126 whereby, upon energization of the solenoid 134, the spool 126 is displaced axially to the hole 124 against a load applied by a compression spring 136 acting on the opposite end of the spool 126.

Inlets 138 and 139 to bore 124 of valve 120 are connected to a spring accumulator 275. The spring accumulator 275 includes a piston 285 which is slidably sealingly engaged in a cylinder 286. A spring 287 acts on one side of the piston 285 urging it to one end of the cylinder 286. An electrically operated pump 223 is provided to charge the accumulator 275 through a non-return valve 276, delivering fluid to the side of the piston 285 distant from the spring 287, thereby compressing the spring 287 and pressurizing the fluid. The side of the piston 285 from which the spring 287 acts is vented and serves as a reservoir 278 of fluid for the system. A pressure transducer 282 is provided between the spring accumulator 275 and inlets 138, 139 of the main control valve 120 for measuring the pressure of the accumulator and transmitting corresponding signals thereto to the control unit 36.

An outlet 140 from port 124 of main control valve 120 is connected to reservoir 278. A first port 142 from port 124 is connected to work chambers and 118 of the shift and shift actuators 114, 115 and selectively to the shift chambers work 119 by means of gear selection and change valves 114, 146 and a second port 148 connected to the slave cylinder 22 of the clutch. A pressure release valve 280 is disposed between the pump 223 outlet of the reservoir 278 to ensure that the pressure supplied by the pump 223 does not exceed a predetermined maximum 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 slidably mounted in the hole 151. The spool 152 has three axially spaced circumferential ribs 154, 156, 158, which seal the hole 151. An axial hole 160 opens towards the end 162 of the spool 152 and connects to a transverse or cross hole 164, the transverse hole 164 opening between the ribs 154 and 156 of the spool 152. A solenoid 166 acts on the end 1698 of the spool 152 distant from the end 162, so that upon energization of the solenoid 166, the spool 152 will move axially to the hole 151 against a load applied by a compression spring 170 acting on the end 162 of the spool 152 .

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

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

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

The inlet 310 of the displacement valve 300 is connected to the tank 278 by means of a recovery valve 320. The recovery valve 320 has a stepped hole 324, a correspondingly stepped piston 321 being slidably positioned in the hole 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 the piston 321 being sealed with respect to a smaller diameter portion of the bore 324. The bore 324 on the side of larger diameter of piston 321 is connected to port 142 of main control valve 120 through port 326. A valve seat formation 328 coaxial with port 324 is provided at the end of port 324 remote from port 326, in a seat formation valve 328 surrounding an inlet 330 at port 324. Inlet 330 is connected to reservoir 278. An outlet 332 is provided by port 324 adjacent to valve seat formation 328, outlet 332 being connected to inlet 310 of the valve displacement 300.

The piston 322 is biased in loosening from the valve seat formation 328 by a helical compression spring 334 which acts between the shoulder 325 of the bore 324 and the shoulder between the portions 322 and 323 of the piston 321. The portion of the bore 324 in which it is when positioned, the spring 334 is vented to the reservoir 278 through the port 335, whereby fluid seeping from the seals between the piston 321 and the wall of the hole 324 will be returned to the reservoir 278. The piston 321 has a closed hole 336 which opens at the end adjacent to the valve seat formation 328. A valve element 338 is mounted to perform axial movement in the bore 336, a radial flange 340 on the valve element 338 being adapted to engage in an inwardly directed radial flange 342 at the open end of bore 336 for holding valve member 338 within bore 336. A helical compression spring 344 urges valve member 338 toward the a perta of the hole 336. An annular sealing element 346 is provided on the valve element 338, the annular sealing element 346 being coaxial with the inlet 330, whereby 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 such that the end will be kept spaced from the valve seat formation 328 and a clearance thus being provided between the valve element 338 and the cylindrical surface of the hole 336 whereby the hole or chamber 336 will be open to the pressure of the fluid at the outlet 332 and the fluid will flow from the inlet 330 to the outlet 332 when the valve element 338 is open. Alternatively; openings may be provided in the cylindrical wall of hole 336 to provide passage to outlet 332.

When the gearbox is in gear and the clutch 14 is engaged, the solenoids 134 and 166 will be de-energized and the valves 120, 144 and 146 will be in the rest positions shown in Figure 3. In this position, the port 306 of the valve displacement 300 is connected via port 148 and output 140 of main control valve 120 to tank 278; the port 142 is isolated from the inlet 139 by the rib 130; the working chambers 118 of the gear selection and shifting actuators 114, 115 will be connected to the reservoir 278 through the inlet 172, the passages 164, 160 and the output 174 of the gear selection and shifting valves 144, 146; and the working chambers 119 of the shifting and shifting actuators 114, 115 will be connected to the reservoir 278 through the port 178 and the output 174 of the shifting and shifting valves 144, 146. Consequently, there will be no movement of the slave cylinder 22 of the clutch or of the gear selection and shifting actuators 114, 115.

In addition, the port 326 of the recovery valve 320 will be connected to the reservoir 278 through the shift and select valves 144, 146. The spring 334 will consequently urge the piston 321 away from the valve seat formation 328, disengaging the valve element 328, opening the inlet 330 and connecting the displacement valve 300 and the slave cylinder 22 of the clutch to the reservoir 278. Fluid can consequently be delivered from the reservoir 278 to the displacement valve 300 and the slave cylinder 22 of the clutch to top up fluid therein which may be required as a result of wear of the clutch 14 and of the clutch actuation components.

When a gear shift is initiated for example by the driver of the vehicle moving the shift lever 24 momentarily to the position or by automatic starting, the solenoid 134 is energized to move the spool 126 of the main control valve 120 to a second position, as is shown in Figure 4. In this second position, the working chambers 118 of both the gear selector and shift actuators 114, 115, and the inputs 172 of the gear selector and shift valves 114, 146 are connected to the accumulator a spring 275 through port 142 and inlet 138. In this second position, port 306 of displacement valve 330 remains connected to reservoir 278. Connection of port 142 of main control valve 120 to accumulator 275 will apply pressure to port 326 of the recovery valve 320 causing the piston 321 to move downwards against the load applied by the spring 334 aff in that the piston 321 will not abut the end of the bore 324 and the valve element 338 will sealingly engage the valve seat 328 to close the inlet 330.

Simultaneously with the energization of the solenoid 134 to move the main control valve 120 to the second position illustrated in FIG. 4, the solenoids 166 of the shift and shift control valves 144, 146 are energized to move the spool 152 to a position. in this position, the rib 158 of the spool 152 closes the opening 178 so as to close the working chamber 119 and create a hydraulic lock preventing movement of the selection and gear change actuators 114 and 115, also if the working chambers 118 thereof are connected to the spring accumulator 275 by the main control valve 120. The connection of the port 172 to the outlet 174 through the holes 160 and 164 is also closed.

Further energizing 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 the port 306 and the spring accumulator 275. The application of fluid under pressure to the piston 302 of the displacement valve 300 will cause the piston 302 to be moved to the left (as illustrated in Figure 3), displacing fluid from that side of the piston 302 to the slave cylinder 22 of the clutch thereby operating the release 20 to disengage the clutch 14. Movement of the slave cylinder 22 of the clutch and therefore of the shift fork 20 will correspond to movement of the piston 302 of the displacement valve 300 and consequently the position sensing means 314 will provide an indication of the position of the clutch 14 which can be used in a closed loop feedback circuit to control the drive d of the clutch in the known way.

Due to the differential areas of the piston 321, the pressure of the fluid acting on the larger diameter portion 323 will be out of balance with respect to the pressure acting on the smaller diameter portion 324 and the load applied by the spring 334 thus keeping the valve element 338 closed. The pressure of the fluid acting on the valve element 338 will also reinforce the load applied by the spring 344.

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

Energizing the solenoid 166 to move the shift selector valve 144, 146 to the third position illustrated in Figure 8, where the working chamber 119 is connected to the reservoir 278, while the working chamber 118 is connected to the accumulator 275 , will create a pressure differential across the pistons 116 and 117, causing the operating stem 114a, 115a to extend. Energizing the solenoid 166 to move the shift or shift valve 144, 146 to the fourth position shown in Figure 9, where both working chambers 118 and 119 are connected to accumulator 275, will cause the operating stems to retract 114a, 115a due to the differential working areas of the pistons 116 and 117. Consequently, by appropriate control solenoids 166 of the shift and shift valves 144, 146, the selector element 110 can be moved to engage the desired gear. .

Potentiometers 226 and 227 are connected to the actuation rods 114a, 115a respectively to provide signals indicative of the position of the associated operating actuation rods. Signals of the potentiometers 226, 227 are fed to the control unit 36 to provide an indication of the position of the operating or driving rods 114a, 115a for each of the transmission ratios of the gearbox 12 and to also indicate the position of the operating rod 115a when the selection element 110 is located in the neutral plane A-B of Figure 2. The gear-shift system can thus be calibrated in such a way that predetermined position signals from the potentiometers 226 and 227 correspond to the engagement of each of the transmission ratios of the gearbox or gearbox 12

Measurements from potentiometers 226 and 227 can thus be employed by a closed loop control system to control valves 144 and 146, to move the operating stems 114a and 115a, to predetermined positions to engage the desired transmission-to-gear ratio.

When the desired gear ratio has been engaged, the solenoid 166 of the shift and shift valves 144, 146 are energized 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.

The solenoid 134 of the main control valve 120 can then be energized to move the main control valve 120 to its fourth to its second position thereby allowing fluid from the shift valve 300 to be returned to the reservoir 278. The fluid pressure in the cylinder slave 22 of the clutch moves the displacement valve 30, allowing re-engagement of the clutch 14. The main control valve 120 can be switched between the third and second positions whereby the clutch 14 is re-engaged in a controlled manner for example as described in EΡ 0043 660; EP 0059 035; EP 0101 220 or WO92 / 13208.

If, during this phase, a vacuum is created in the displacement valve 300 / in the clutch slave cylinder 22, for example due to the slow return of the clutch actuator piston, the reduced pressure in the recovery valve 320 will cause the The valve member 338 opens against the spring 334, allowing fluid to be delivered to the displacement valve 300 from the reservoir 278. This will avoid tendency for air to be drawn into the system under these circumstances.

When the clutch 14 has been re-engaged, the solenoid 134 of the main control valve 120 may be deenergized, whereby it will return to the rest position illustrated in FIG. 3. Similarly, the solenoid 166 of the shift and shift and select valves 144, 146 can be de-energized. Movement of the gear selector and shift valves 144, 146 to the rest position illustrated in FIG. 3 will open the working chamber 119 to the reservoir 278, thereby releasing the pressure therein.

Releasing the pressure at the larger diameter portion 322 of the piston 321 will allow the piston 321 to move under load applied to it by the spring 334 causing the recovery valve 320 to open, allowing fluid flow from the reservoir 78 to the displacement valve 300 / to the slave cylinder 22 of the clutch.

According to a preferred embodiment of the invention, the accumulator cylinder 286, the port 124 of the main control valve 120, the ports 151 of the selection and gear shift valves 144, 146, the cylinders of the selection actuators and gear shift 114, 115, the port 304 of the displacement valve 300 / the port 324 of the recovery valve 320 can be defined by a common housing, the holes / cylinders of the various components being appropriately interconnected by passing through the common housing . The valve / actuator package thus formed would be mounted on or adjacent to the gearbox or gearbox 12.

The electrically operated pump 223, and the control unit 36 may also be mounted with the valve / actuator package or may be remotely mounted therefrom and interconnected thereto, for example by elastomeric pressure pipes.

Various modifications can be made without departing from the scope of the invention. For example, although in the previous embodiment the hydraulic circuit has been described with reference to a semi-automatic gearbox system, the invention is equally applicable to fully automatic gearbox systems or to automatic-manual gearbox systems.

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

The patent claims submitted with this application constitute proposed formulations without prejudice to obtaining further patent protection. The Applicant reserves the right to submit claims for further combinations of characteristics, preferably only mentioned in the description and / or in the drawings.

References used in the sub-claims relate to further developing the subject matter of the main claim by the features of the respective sub-claim. They are not to be regarded as a waiver relating to obtaining protection for independent elements for the combination of features in the related sub-claims.

Since the subject of the sub-claims can constitute separate and independent inventions with reference to the prior art at the priority date, the Applicant reserves the right to make them the subject of independent claims or divisional claims. Furthermore, they also contain independent inventions, revealing a structure independent of one of the objects of the preceding sub-claims.

The embodiments are not to be regarded as a limitation of the invention. Rather, a wide range of amendments and modifications are possible within the scope of the present description, particularly those variations, those elements and / or those combinations and / or materials which, for example, the skilled person can learn by combining some individual together with those of the general description and of the embodiments in addition to features and / or elements or process stages described in the claims and contained in the drawings, in order to solve a task leading thus to a new object or to new process stages or sequences of process steps through combinable characteristics, even when they involve manufacturing, testing and work processes.

Claims (16)

CLAIMS 1. Hydraulic drive system for an automatic shifting system comprising: a hydraulic clutch actuator for controlling engagement of a clutch; a source of hydraulic fluid under pressure; a reservoir of hydraulic fluid; a master control valve for selectively applying fluid under pressure to the hydraulic clutch actuator; a displacement valve positioned 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 being connected to the main control valve and a second side of the piston being connected to the clutch actuator, an inlet opening to the displacement valve cylinder on said second side of the piston, the inlet being connected to the reservoir via a recovery valve; the recovery valve comprising a valve element urged by first spring means towards a valve seat, said valve element being mounted to perform limited movement on a piston which is stressed loosely from the valve seat by second spring means, the piston being positioned at seal 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 the clutch actuator is connected to the source of fluid under pressure, pressure will be applied to the piston of the recovery valve to move 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 by the bore of the recovery valve on the side of the piston adjacent to the valve seat, the output ess endo connected to the displacement valve inlet. The hydraulic actuation system of claim 1, wherein the main control valve connects the piston side of the recovery valve remote from the valve seat to the source of pressurized fluid prior to connecting the clutch actuator to the fluid source under pressure, the piston side of the recovery valve away from the valve seat remaining connected to the source of fluid under pressure, while the clutch actuator is connected to it. 3. The hydraulic actuation system of claim 2, wherein the main control valve further selectively connects a gear engaging actuator to the source of fluid under pressure, the piston side of the recovery valve remote from the valve seat being connected to the gear engagement actuator. The hydraulic drive system according to claim 3, wherein the main control valve is movable 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 pressurized fluid source and the gear engagement actuator is connected to the pressurized fluid source; And a third position in which the clutch actuator and the gear engagement actuator are connected to the source of fluid under pressure. The hydraulic actuation system of claim 4, wherein 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 clutch engagement actuator is connected to the accumulator. A hydraulic drive system according to any one of claims 3 to 5, wherein the gear engaging actuator is selectively connected to the main control valve or reservoir by means of a gear engaging control valve. The hydraulic drive system of claim 6, wherein the gear engagement control valve is movable between: a) a rest position in which first and second working chambers of the gear engagement actuator and the connection to the main control valve are all connected to the reservoir; b) a neutral or zero 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 is 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 the reservoir; And d) a fourth position where the second working chamber of the gear engagement actuator is connected to the main control valve and the first working chamber is connected to the reservoir. 8. A hydraulic drive system according to any one of the preceding claims, wherein the gear engaging mechanism includes two gear engaging actuators, a selection actuator for moving a selection element in a first direction and a gear shift actuator for moving a selection element in a second direction, the shift and shift actuators having independent shift and shift control valves, the shift and shift control valves selectively connecting the shift actuator and the actuator gear shift to the main control valve or tank respectively. 9. Hydraulic actuation system according to any one of the preceding claims, wherein the main control valve comprises a spool slidably mounted in a bore, the bore having three circumferential ribs which sealingly engage the bore, an inlet being associated with the bore for connection to the bore. source of hydraulic fluid under pressure, an outlet from the bore being connected to the reservoir; a first port opening towards the hole, the first port being connected to the gear engagement control valve and a second port opening towards the hole, 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 the 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 being connected to the inlet and the second port being isolated from both the inlet and the outlet. A hydraulic drive system according to any one of the preceding claims, wherein the gear engagement control valve comprises a spool slidably mounted in a bore, the spool having three circumferential ridges or solids that sealingly engage the bore, an inlet being associated with the hole for connection to the main control valve; an outlet being provided by the hole for connection to the tank, and a first port opening towards the hole, the first port being connected to a first working chamber of the gear engagement actuator; the spool having an axial hole opening towards one end of the spool, the axial hole connecting with a transverse hole opening between the first and second ribs of the spool: in a rest position of the spool, the inlet being connected to the outlet through the transverse hole and the axial hole and the first port being connected to the outlet between adjacent ribs on the spool; in a neutral or 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 being connected to the outlet, the inlet being isolated from the first and the outlet. 11. The hydraulic drive system of claim 10, wherein the gear engagement actuator comprises a double acting piston or ram having a piston element, the working area on one side of the piston element being greater than that of the other side of the piston element, the first port of the gear engagement valve being connected to the side of the piston element with the largest working area, the side of the piston element with the working area minor being connected directly to the main control valve. Hydraulic actuation system according to any one of the preceding claims, wherein the recovery valve has a stepped piston, the end of the piston distant from the valve seat being greater than the end adjacent to the valve seat so that when it is the recovery valve that 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 recovery valve in sealing engagement with the valve seat. 13. Hydraulic actuation system according to any one of the preceding claims, wherein the valve member of the recovery valve is slidably positioned in a closed bore of the piston, the closed bore being open towards the outlet from the recovery valve, when the valve element sealingly engages the valve seat. Hydraulic actuation system according to any one of the preceding claims, wherein a position sensor is provided on the displacement valve, the position sensor being employed in a closed loop control system to control the position of the clutch. Hydraulic drive system according to any one of the preceding claims, wherein a plurality of the components are defined by a common housing, the components being interconnected to each other in an appropriate manner by passages formed in the common housing. Automatic shifting system including a hydraulic drive system according to any one of claims 1 to 16.