GB2336884A

GB2336884A - A hydraulic actuation system with reduced energy consumption

Info

Publication number: GB2336884A
Application number: GB9809496A
Authority: GB
Inventors: David Anthony Harries
Original assignee: Kongsberg Techmatic UK Ltd
Current assignee: LuK Leamington Ltd
Priority date: 1998-05-02
Filing date: 1998-05-02
Publication date: 1999-11-03
Anticipated expiration: 2018-05-02
Also published as: GB2336884B; KR19990087979A; JPH11344055A; FR2778212A1; ITMI990930A1; DE19918788A1; BR9902061A; IT1312275B1; GB9809496D0; FR2778212B1

Abstract

A hydraulic actuation system, eg for a clutch, includes a pressure accumulator 12, a pump 16 being connected between the pressure accumulator 12 and a reservoir 14, the pump 16 pumping fluid from the reservoir 14 to the pressure accumulator 12. Non-return valves 18, 36 being located between the accumulator 12 and pump 16 and between the pump 16 and reservoir 14 to prevent flow of fluid from the accumulator 12 to the pump 16 and from the pump 16 to the reservoir 14 respectively. A solenoid control valve 20, in a first position, connecting the accumulator 12 to a slave cylinder 34 and, in a second position, connecting the slave cylinder 34 to a point between the pump 16 and the non-return valve 36, so that fluid under pressure may be pumped from the slave cylinder 34 directly to the accumulator, thereby reducing the energy consumption of the pump.

Description

2336884 HYDRAULIC ACTUATION SYSTEMS The present invention relates to

hydraulic actuation systems and in particular, though not exclusively, to hydraulic actuation systems used in automatic and semi-automatic transmissions for motor vehicles, of the type disclosed, for example, in the applicant's earlier European Patent Nos. 0038113, 0043660, 0059035 and 0101220.

In such transmission systems, the engagement and disengagement of a clutch is controlled by an electronic unit in response to operation of a throttle and a gear selector lever, by the vehicle driver. Typically clutch engagement is monitored by sensing the position of a clutch release lever which operates the release bearing of the clutch. This is normally achieved by using a slave cylinder to operate the clutch release lever, the slave cylinder also including a cylinder travel sensor.

The hydraulic actuating system comprises a pressure accumulator and pump means by which the pressure accumulator may be charged from a hydraulic fluid reservoir. The hydraulic actuation system is connected to the slave cylinder of the clutch actuation system by a control valve, which selectively connects the slave cylinder to the pressure accumulator to disengage the clutch; or to drain to the reservoir, to allow the clutch to reengage.

Hitherto, with hydraulic systems of this type, when the clutch is engaged by connection of the slave cylinder to reservoir, the pressure of fluid in the slave cylinder is allowed to drop to the pressure of fluid in the reservoir. The pump must then be actuated to pump fluid from the reservoir to recharge the pressure accumulator.

However, in order to enable the clutch to re-engage, the pressure in the 1 slave cylinder need only be reduced to an extent sufficient to allow the clutch spring to re-engage the clutch. Typically, the hydraulic pressure required to release a clutch may be of the order of 40 bar. Reduction of this pressure to the order of 25 bar will then allow the clutch to reengage, while the pressure of fluid in the reservoir would normally be at atmospheric pressure.

In accordance with the present invention, a hydraulic actuating system comprises; a pressure accumulator; a pump connected between the pressure accumulator and a reservoir, said pump being adapted to pump fluid from the reservoir to the pressure accumulator; a first non-return valve located between the accumulator and the pump to prevent flow of fluid from the accumulator to the pump; a second non-return valve located between the pump and the reservoir to prevent flow of fluid from the pump to the reservoir; and a solenoid control valve, the solenoid control valve; in a first position connecting the pressure accumulator to a slave cylinder; and in a second position connecting the slave cylinder to a point between the pump and the second non-return valve.

With the hydraulic actuating system disclosed above, when in the first position, the control valve will connect the slave cylinder to the pressure accumulator, thereby introducing fluid under pressure into the slave cylinder which will act, for example, to disengage a clutch. When the control valve is moved to it's second position, the pump may then be energised to pump fluid out of the slave cylinder thus reducing pressure in the slave cylinder and allowing re-engagement of the clutch. The fluid is pumped from the slave cylinder to the pressure accumulator, to recharge the pressure accumulator. In this manner, the pressure drop across the pump is significantly reduced, so that energy consumption of the pump will be reduced correspondingly.

According to the preferred embodiment of the invention, in a third position of the control valve, the slave cylinder may be connected to the reservoir as well as between the pump and the second non-return valve, by a restricted flow path. If the rate of fall of pressure to the slave cylinder due to the action of the pump is insufficient, the control valve may then be switched to the third position, so that additional fluid may then be bled off to the reservoir. Preferably the control valve is a solenoid operated proportional flow control valve in which the position of the valve is controlled by the current applied across the solenoid.

An embodiment of the invention is now described, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 is a diagrammatic illustration of a hydraulic actuation system in accordance with the present inventions, showing valve means in a first position; Figure 2 is an illustration similar to Figure 1 showing the valve means in a second position; and Figure 3 is a view similar to Figure 1 showing the valve means in a third position.

As illustrated in Figure 1, a hydraulic actuation system 10 includes a pressure accumulator 12. The pressure accumulator 12 is connected to a hydraulic fluid reservoir 14 via a pump 16, by which hydraulic fluid may be pumped from the reservoir 14 to charge the pressure accumulator 12. A non-return valve 18 is located between the pressure accumulator 12 and the pump 16 to prevent flow of fluid from the pressure accumulator 12 to the pump 16.

A solenoid operated proportional flow control valve 20 comprises a housing 22 defining a bore 24. The housing defines four axially separated ports 26, 28, 30 and 32; port 26 connecting the bore 24 to the pressure accumulator 12; port 28 connecting the bore 24 to the connection between the reservoir 14 and pump 16; port 30 connecting the bore 24 to the reservoir 14; and port 32 connecting the bore 24 to a slave cylinder 34 of, for example, a clutch actuating mechanism. An annular groove 38 is provided in the bore 24 between ports 28 and 30.

A non-return valve 36 is located in the connection between the reservoir 14 and pump 16, between the connection thereto from port 28 and the reservoir 14. The non-return valve 36 prevents flow of fluid from the pump 16 and slave cylinder 34 to the reservoir 14.

A spool 40 is slidingly located in the bore 34, the spool 40 having three axially spaced lands, 42, 44 and 46, the lands 42, 44 and 46 sealingly engaging the surface of the bore 34. Land 46 which is adjacent to the end of bore 34 connected to the reservoir 14 via port 30, has one or more angularly spaced grooves 48 extending axially from the end adjacent port part way along the length of the land 46, the or each groove 48 opening into a circumferential groove 64 in the land 46.

The spool 40 is biased axially of the bore 34, away from the end thereof adjacent port 30, by spring means 65. A solenoid actuator 50 engages the end of spool 40 remote from spring means 65, so that upon energisation the solenoid acutuator will oppose the biasing load of spring means 65 and move the spool 40 axially of bore 34 towards the end thereof adjacent port 30. The degree of movement of the spool 40 will depend on the current applied across the solenoid actuator 50.

In this manner, the position of spool 40 may be controlled so that; In a first position illustrated in Figure 1, the ports 26 and 32 are located between lands 42 and 44 of the spool 40, so that the slave cylinder 34 will be connected to the pressure accumulator 12; In a second position illustrated in Figure 2, ports 26 and 32 will be separated by land 44 and port 32 will be connected to port 28, between lands 44 and 46, the slave cylinder 34 thereby being connected to the pump 16, in this position, the annular groove or grooves 48 in land 46 are not exposed to the axial groove 38 of bore 34; In a third position as illustrated in Figure 3, ports 28 and 32 are inter- connected between lands 44 and 46, while the circumferential groove 64 is exposed the annular groove 38, providing a restricted flow path between the slave cylinder 34 and reservoir 14 along the groove or grooves 48.

With the system described above, when the system is de-engerised, the solenoid valve 20 will be in the position illustrated in Figure 3, so that the slave cylinder 34 is connected to the hydraulic fluid reservoir 14 via port 30 and groove or grooves 48, permitting fluid to be fed to the slave cylinder 34, to accommodate wear in the clutch actuation system.

Upon energisation of the system, the pump 16 is energised to charge the pressure accumulator 12, means being provided to de-energise the pump once the pressure accumulator 12 reaches the required pressure.

To disengage the clutch, the solenoid actuator 50 is energised to move the spool 40 to the position illustrated in Figure 1, thereby connecting the pressure accumulator 12 to the slave cylinder 34, so that pressure is applied to the slave cylinder 34 to disengage the clutch.

To re-engage the clutch, the solenoid actuator 50 is energised to move spool 40 to the position illustrated in Figure 2, in which the slave cylinder 34 is connected to the pump 16. The pump 16 is then energised to pump fluid out of the slave cyliner 34 and back into the pressure accumulator 12, thereby permitting movement of the slave cylinder 34 to allow the clutch to re-engage. Only if the rate of reduction of pressure in the slave cylinder 34 is too slow, is the solenoid actuator 50 energised to return the spool 40 to the position illustrated in Figure 3, when pressure will be bled off from the slave cylinder 34 through the groove or grooves 48 into the reservoir 14.

In this manner, the pressure on the inlet side of the pump 16 may be kept relatively high thereby reducing the time taken and energy used to recharge the pressure accumulator 12.

When the pressure accumulator 12 has been charged to the required pressure, the pump 16 and solenoid actuator 50 are de-energised allowing the spool 40 to return to the position illustrated in Figure 3, in which the slave cylinder 34 is connected to reservoir 14 via the groove of grooves 48.

With the arrangement described above, when the clutch is being reengaged, the solenoid actuator 50 may be pulsed so that the spool 40 will oscillate between the positions illustrated in Figures 2 and 3. In this manner the rate of re-engagement of the clutch may be controlled accurately for the particular driving conditions. Moreover the energising current may be varied using pulse width modulation to vary the average current applied across the solenoid actuator 50.

Various modifications may be made without departing from the invention. For example while in the above embodiment, one or more axial grooves 48 in land 46 provide a restricted connection between the slave cylinder 34 and reservoir 14 when the valve is in the third position, other suitable means, for example a restricted bore may be used for this purpose

Claims

1. A hydraulic actuating system comprising; a pressure accumulator; a pump connected between the pressure accumulator and a reservoir, said pump being adapted to pump fluid from the reservoir to the pressure accumulator; a first non-return valve located between the accumulator and the pump to prevent flow of fluid from the accumulator to the pump; a second non-return valve located between the pump and the reservoir to prevent flow of fluid from the pump to the reservoir; and a solenoid control valve, the solenoid control valve; in a first position connecting the pressure accumulator to a slave cylinder; and in a second position connecting the slave cylinder to a point between the pump and the second non-return valve.

2. A hydraulic actuating system according to Claim 1 in which the solenoid control valve in a third position connects the slave cylinder to the reservoir, by a restricted flow path.

3. A hydraulic actuating system according to Claim 2 in which the control valve is a solenoid operated proportional flow control valve.

4. A hydraulic actuating system according to Claim 3 in which the control valve may be energised to oscillate the control valve between the second and third positions.

5. A hydraulic actuating system according to any one of the preceding claims in which the control valve comprises a bore with four axially separated ports; a first port connected to the pressure accumulator; a second port connected between the pump and the second non- return valve; a third port connected to the reservoir; and a fourth port connected to the slave cylinder; a spoof being slidingly located in the bore, the spool comprising three axially separated lands which sealingly engage the wall of the bore; the lands being located such that; in a first position of the spool, the first and fourth ports will be interconnected between a first and second lands of the spool, the second port being located between the second land and a third land, the third land being located between the second and third ports; in a second position the first port is separated from the fourth port by the second land, the second port being interconnected to the fourth port between the second and third lands and the third port and fourth port being separated by the third land; and in a third position of the spool, the fourth port is interconnected to the second and third ports.

6. A hydraulic actuating system according to Claim 5 in which one or more grooves are provided in the third land, the or each groove extending axially of the third land from the end thereof remote from the first and second lands, said grooves extending part way along the third land and being opened to the bore when the spool is in the third position, to provide a restricted flow path between the fourth port and the third port.

7. A hydraulic actuating system substantially as described herein with reference to and as shown in Figures 1 to 3 of the accompanying drawings.