GB2314136A

GB2314136A - Hydraulic clutch actuator with a reservoir connected between master and slave cylinders

Info

Publication number: GB2314136A
Application number: GB9712060A
Authority: GB
Inventors: Christian Hoffmann; Bernard Stragier; Eric Arquisch
Original assignee: Valeo SE
Current assignee: Valeo SE
Priority date: 1996-06-10
Filing date: 1997-06-10
Publication date: 1997-12-17
Anticipated expiration: 2017-06-10
Also published as: GB2314136B; KR100470620B1; KR980001152A; FR2749544A1; FR2749544B1; GB9712060D0

Abstract

A hydraulic clutch actuator has a pressure chamber 34 that comprises a master cylinder 12 and a slave cylinder 24 connected by a pipe 18 having therein an expansion duct which is joined to a reservoir 38 of a re-supply device 36. A valve 42, eg a normally open solenoid valve, is controlled by, for example, a computer and isolates the reservoir 38 with respect to the pressure chamber 34 when a declutching phase is initiated. When the clutch is not operated a normally open valve 42 allows an automatic re-supply of fluid and, in the event of a temperature rise, the fluid may back up inside the reservoir 38. Flow limiter 44 provides progressive clutch engagement if a failure occurs. Normally open valve 42 allows, in the event of a failure, the piston 22 in cylinder 24 to return to its idle position, thereby engaging the clutch 11. Clutch control may either be automatic, eg an electric motor operated by a computer, or via a pedal 26 having a sensor which operates the valve 42. The actuator may also be used with vacuum or hydraulic amplification devices of the type used in brake systems.

Description

IMPROVED DEVICE FOR THE HYDRAULIC CONTROL OF A MOTOR VEHICLE CLUTCH The invention concerns an improved device for the hydraulic control of a motor vehicle clutch.

In a device for controlling a motor vehicle clutch, of the type in which the hydraulic chambers of two cylinders, sending and receiving, are connected by a pipe and form with the latter a pressure chamber filled with a liquid designed to transmit the movement of a piston in the sending cylinder to a piston in the receiving cylinder in order to bring about declutching, of the type in which a re-supply device is provided which has a reservoir of fluid and which keeps the pressure chamber constantly filled with fluid, and of the type in which the resupply device is isolated from the pressure chamber when the piston in the sending cylinder is moved from an idle position to a position in which it brings about declutching, and in which the piston associated with the sending cylinder is connected to an actuator which controls its movements, whilst the piston associated with the receiving cylinder is connected to a mechanism which acts on the clutch.

Clutch hydraulic control devices exist, and these allow reduction of the force which has to be supplied by the driver in order to bring about declutching. This is because, and unlike a cable control device, it is possible, according to the diameters of the sending and receiving cylinders, to obtain a demultiplication of the force required without for all that increasing the travel of the control pedal to an immoderate extent.

It is also easy to interpose, in the hydraulic circuit, vacuum or hydraulic amplification devices, of the type used for braking systems, in order to assist the driver during the declutching phase.

Hydraulic control devices have the additional advantage of being particularly well suited to the design of controlled clutches in which the declutching is controlled not directly by the driver but by a computer which brings about declutching, for example when a movement of the gear lever is detected. The computer receives information coming notably from different sensors such as those associated with the gear change lever, the input shaft and the output shaft.

The computer then brings about the declutching and then the reengagement of the clutch in accordance with various parameters such as the speed of rotation of the engine. For this purpose it acts for example on an electric motor which, by means of a transmission, acts on the piston of the sending cylinder.

In the context of such a type of clutch control, it is particularly advantageous to be able to know, at any time, the position of each of the pistons in the two cylinders in order to be able to correctly control notably the clutch slipping phase in order not to cause jerks.

A problem is then posed since the re-supply device is obtained only after a dead travel of the piston associated with the sending cylinder. It is therefore important to avoid this dead travel.

According to the present invention there is provided a device for controlling a motor vehicle clutch, in which the hydraulic chambers of two cylinders, sending and receiving, are connected by a pipe and form with the latter a pressure chamber filled with a liquid designed to transmit the movement of a piston in the sending cylinder to the piston in the receiving cylinder in order to bring about declutching, in which a re-supply device is provided which has a reservoir of fluid and which maintains a constant filling of the pressure chamber, and in which the piston in the sending cylinder is connected to an actuator which controls its movements and the pistons in the redeiving cylinder acts on the clutch, whilst the re-supply device is isolated from the pressure chamber when the piston in the sending cylinder is moved from an idle position to a position in which it brings about declutching, wherein the re-supply device has a controlled valve which is interposed in a duct which is connected at one end to the reservoir and which opens out through its other end into the pipe connecting the two cylinders, and in that the valve is closed when the piston in the sending cylinder is moved from its idle position in a direction tending to bring about declutching.

By virtue of the invention, the control device is of simple form, and without dead travel.

It need not use a pump and accumulator as described in the document GB-A-2 101 256.

According to other characteristics of the invention: Preferably the valve is normally open; Advantageously closure of the valve is controlled by a computer; Conveniently a flow limiter is provided which is interposed between the fluid~reservoir and the pressure chamber; Preferably the flow limiter is interposed in the duct, between the reservoir and the valve; Conveniently the flow limiter is formed by a restriction of the duct passage diameter.

Other characteristics and advantages of the invention will emerge from a reading of the detailed description which follows, for an understanding of which reference will be made to the accompanying drawings in which: - Figures 1 to 3 depict a device for the hydraulic control of a motor vehicle clutch designed according to the state of the art, and respectively depicted in the clutch engagement position, in the intermediate position and in the declutching position; - Figures 4 to 6 are views similar to those in Figures 1 to 3 depicting a control device of the invention.

Figure 1 depicts a device 10 for the hydraulic control of a clutch 11 which is designed in accordance with the state of the art. The control fluid can for example be oil.

The control device 10 has essentially a sender with a sending cylinder 12 inside which an axially movable piston 14 delimits, with the cylinder 12, a variable-volume hydraulic chamber 16 which is connected by a pipe 18 to a hydraulic chamber 20, which is delimited by the receiving cylinder 24 of a receiver and the piston 22 of the receiving cylinder 24. The pistons 14, 22 are axially movable inside the cylinders 12, 24.

The piston 14 of the sending cylinder 12 is connected to an actuator 26 which controls its movements.

The actuator 26 can be either a conventional clutch pedal or an automatic or hydraulic ram, for example in the case of a controlled clutch.

The automatic ram can include, in a known fashion, an electric motor which acts on a mechanical transmission connected to the piston. The electric motor is controlled by the aforementioned computer. For more information reference should be made for example to the document FR-A-2 721 264.

The piston 22 of the receiving cylinder 24 is connected to a mechanism 28 which acts directly on the clutch 11. In a known fashion, the clutch 11 has notably a control fork which is associated with a clutch release bearing in order to move a thrust plate axially with respect to a reaction plate 32, in order to clamp and release the friction linings of a friction disc 30 between the said thrust and reaction plates 32. For this purpose the bearing usually acts on the inner ends of the fingers of a diaphragm bearing on a cover fixed to the reaction plate 32 in order to act on the thrust plate integral in rotation - with axial mobility - with the cover.

The friction disc 30 is fixed with respect to rotation to the input shaft of the gearbox, whilst the reaction plate 32 is integral with the primary shaft. For simplicity only the reaction plate 32 and friction disc 30, together with the diaphragm, have been depicted in the figures.

The hydraulic chambers 16, 20 of each of the cylinders 12, 24 and the pipe 18 which connects them form a pressure chamber 34 filled with a non-compressible fluid which makes it possible to transfer any movement of one of the pistons to the other piston.

In fact, in an idle position of the device (clutch 11 in the engaged position), the piston 14 is in a position such that the volume of the hydraulic chamber 16 of the sending cylinder 12 is at its maximum whilst the piston 22 in the receiving cylinder 24 is in a position such that the volume of the corresponding chamber 20 is at its minimum.

In this way, if the piston 14 of the sending cylinder 12 is moved by the actuator 26 in a direction which reduces the volume of the hydraulic chamber 16, a volume of fluid corresponding to this movement is transferred through the pipe 18 to the chamber 20 of the receiving cylinder 24, which causes a corresponding movement of the piston 22.

In a known fashion, it is necessary to provide a device 36 for re-supplying the pressure chamber 34 which makes it possible to compensate for any fluid leaks and which also makes it possible to take up the progressive wear on the linings of the friction disc 30, the said linings being designed to be gripped between the thrust and reaction plates under the action of the diaphragm.

In addition, the re-supply device 36 also fulfils the role of an expansion tank which prevents the expansion of the fluid contained in the pressure chamber 34 from causing a movement of the piston 22 in the receiving cylinder 24 which might cause an initiation of declutching, and thus cause the clutch 11 to slip.

For this purpose, a reservoir of liquid 38 for the re-supply device 36 has an expansion duct 40 which opens out in the hydraulic chamber 16 of the sending cylinder 12 when the piston 14 thereof is in the idle position depicted in Figure 1.

This arrangement enables the piston 14 to close off the inlet of this expansion duct as soon as it has progressed axially as far as an intermediate position depicted in Figure 2.

From this intermediate position, the pressure chamber 34 is completely isolated from the re-supply device 36, and when the piston 14 progresses towards its declutching position (linings of the disc 30 released) the fluid is driven towards the receiving cylinder 24 in order to cause the movement of the piston 22 in the receiving cylinder 24, which is shown diagrammatically in Figure 3.

As can be seen, this known device of the state of the art has the drawback of the existence of a dead travel of the piston 14, which therefore corresponds to a travel of the pedal or actuator 26 during which the piston 22 in the receiving cylinder 24 remains immobile.

In addition, the exact position of the piston 14, from which the transmission of the movement is effectively provided, is difficult to know and, moreover, experience proves that the change from dead travel to active travel does not always take place very precisely.

This lack of precision is particularly detrimental, notably in the case of a controlled clutch, since it occurs essentially at the delicate time of the clutch control phase which corresponds to the slipping of the clutch.

It therefore appears advantageous to propose a device for the hydraulic control of a clutch will eliminates the initial dead travel of the piston 14 in the receiving cylinder 24.

A control device 10 of the invention is depicted in Figures 4 to 6, in which elements which are identical or similar to those depicted in Figures 1 to 3 will be designated by the same reference figures.

In this embodiment, the expansion duct 40, which is connected to the reservoir 38 of the re-supply device 36, opens out not in the hydraulic chamber 16 of the sending cylinder 12 but directly into the pipe 18 which connects two hydraulic chambers 16, 20 of the two cylinders 12, 24.

In order to isolate the pressure chamber 34 with respect to the reservoir 38, a valve 42 is interposed in the expansion duct 40.

This valve 42 is controlled by the computer.

The valve 42 is a solenoid valve of the normally open type and its closure is controlled, for example, by a computer (not shown) which, in the case of a controlled clutch, is responsible for controlling the clutch engagement manoeuvre by activating the actuator 26.

Thus, the valve 42 being normally open, in the idle position of the device, the re-supply of the pressure chamber with fluid takes place automatically and, in the event of a rise in temperature of the fluid, the latter is able to back up inside the reservoir 38.

On the other hand, at the start of the declutching phase, the computer controls the closure of the valve 42 in order to isolate the pressure chamber 34 with respect to the re-supply device 36, as shown diagrammatically in Figures 5 and 6.

Where the actuator 26 is a conventional pedal, it is possible to determine the start of the declutching phase by virtue of a force sensor arranged at the pedal. If the clutch is of the controlled type, it will even be possible to bring about the closure of the valve 42 by means of the computer before the actuator 26 is started up.

The choice of a normally open valve 42 is particularly advantageous in the event of a failure of the device. This is because, if the device controlling the valve 42 fails, the latter returns to its normally open position, which brings about the leakage of the liquid contained in the pressure chamber 34 to the reservoir 38. As a result the piston 22 in the cylinder 24 returns to its idle position, which ensures the return of the clutch to its engaged position (with the linings of the friction disc 30 gripped between the thrust and reaction plates 32), thus enabling the engine to drive the driving wheels of the vehicle so that the driver can reach the nearest garage.

If the failure arises when the clutch is declutched, it is desirable for the return to the engaged position not to take place too abruptly, otherwise the entire transmission chain of the vehicle may be stressed abruptly.

A flow limiter 44, which provides a certain degree of progressiveness of the return to the clutch-engaged position, in the event of failure, has therefore been provided in the expansion duct 40.

In the example embodiment which is depicted in Figures 4 to 6, the flow limiter is produced by means of a restriction 44 in the diameter of the expansion duct 40 which is arranged between the reservoir 38 and the valve 42.

The control device of the invention therefore affords a more precise control of the declutching and re-engagement but also makes it possible to use a sending cylinder of simple design, unlike the state of the art, which requires the use of a sending cylinder piston having a re-supply chamber which is connected to the pressure chamber by non-return valve devices. Likewise, the idle position of the piston in the sending cylinder is no longer decisive for both ensuring re-supply and allowing expansion of the liquid.

It will be noted, in a known fashion, that the piston in the receiving cylinder is subjected to the action of a return spring, not marked in the figures.

As a variant a position sensor is associated with the actuator 26 or piston 14 in the sending cylinder 12. Likewise a position sensor is associated with the piston 22 in the receiving cylinder 24 or preferably with the clutch release bearing.

The computer contains a program which associates, with each position of the actuator 26 or of the piston 14, a corresponding position of the piston 22 or of the clutch release bearing.

By virtue of the aforementioned position sensors, the positions read are compared with the theoretical positions. Thus, in the event of abnormal expansion of the control fluid, caused for example by an excessive temperature underneath the bonnet, or an excessive temperature of the clutch, the solenoid valve 22 is opened, during the declutching phase, by means of the computer receiving the information from the aforementioned sensors. By virtue of the restriction 44, it is then possible to control leakages in order to take up expansion in order to return to the theoretical conditions.

Claims

1. A device for controlling a motor vehicle clutch, in which the hydraulic chambers of two cylinders, sending and receiving, are connected by a pipe and form with the latter a pressure chamber filled with a liquid designed to transmit the movement of a piston in the sending cylinder to the piston in the receiving cylinder in order to bring about declutching, in which a resupply device is provided which has a reservoir of fluid and which maintains a constant filling of the pressure chamber, and in which the piston in the sending cylinder is connected to an actuator which controls its movements and the piston in the receiving cylinder acts on the clutch, whilst the re-supply device is isolated from the pressure chamber when the piston in the sending cylinder is moved from an idle position to a position in which it brings about declutching, wherein the re-supply device has a controlled valve which is interposed in a duct which is connected at one end to the reservoir and which opens out through its other end into the pipe connecting the two cylinders, and the valve is closed when the piston in the sending cylinder is moved from its idle position in a direction tending to bring about declutching.

2. A device according to Claim 1, wherein the valve is normally open.

3. A device according to Claim 2, wherein the closure of the valve is controlled by a computer.

4. A device according to Claim 3, wherein the closure of the solenoid valve is brought about before the actuator is started up.

5. A device according to Claim 3 or 4, wherein the opening of the solenoid valve is controlled by a computer in the event of abnormal expansion of the control fluid.

6. A device according to any one of the preceding claims, wherein a flow limiter is provided which is interposed between the fluid reservoir and the pressure chamber.

7. A device according to Claim 6, wherein the flow limiter is interposed in the duct, between the reservoir and the valve.

8. A device according to Claim 7, wherein the flow limiter is formed by a restriction in the passage diameter of the duct.

9. A device for controlling a motor vehicle clutch constructed and arranged substantially as herein described, with reference to, and as illustrated in Figures 4 to 6 of the accompanying drawings.