GB2279124A

GB2279124A - Actuating means for a motor vehicle friction clutch comprises master cylinder operated by electric motor via screw and nut drive

Info

Publication number: GB2279124A
Application number: GB9412175A
Authority: GB
Inventors: Michael Pfeuffer
Original assignee: Fichtel and Sachs AG
Current assignee: ZF Sachs AG
Priority date: 1993-06-18
Filing date: 1994-06-17
Publication date: 1994-12-21
Anticipated expiration: 2014-06-17
Also published as: GB2279124B; DE4320204A1; FR2706552A1; FR2706552B1; GB9412175D0

Description

2279124 1 ACTUATING MEANS FOR A MOTOR VEHICLE FRICTION CLUTCH This

invention relates to an actuating means for an hydraulically actuated friction clutch of a motor vehicle of the kind comprising an hydraulic master cylinder adapted to actuate an hydraulic slave clutch cylinder and having a piston movable axially in the cylinder, an electric motor connected to the master cylinder to form a subassembly and having a spindle rotating about an axis, and drive means coupling the motor spindle to the piston and converting the rotational movement of the spindle into an axial movement.

Actuating means of the kind set forth are known (DE-A-39 35 438 and DE-A39 35 439), and are used instead of a clutch pedal to engage and disengage an orthodox motor vehicle clutch. The actuating means is controlled by an electronic control system which in its turn, with the aid of sensors, responds to operating parameters of the vehicle, for example engine speed, gearbox input shaft speed and throttle pedal position. The control system engages the -clutch automatically on starting and on gear changes in a gearbox of the vehicle and disengages the clutch when the vehicle comes to a halt and at the start of the gear- changing sequence.

slightly vibrations in It is furthermore known from DE-A-33 30 332, DE-A34 38 594 and DE-A-36 24 755 to disengage the clutch in order to reduce rotational the drive train. The clutch then transmits the driving torque with a slight slip which eliminates the rotational vibrations superimposed on the driving torque. The rotational vibrations are detected and tuned out by a slip-control circuit 2 controlling the actuating means. In this case the actuating means may only control the slip, but it can also handle this function in addition to that of automatic actuation of the clutch.

Whereas clutch disengagement must take place comparatively rapidly, a relatively long time is needed f or engaging the clutch, in order to prevent as f ar as possible any thump on engagement. on disengagement, the actuating means works against the force of the main clutch spring, and therefore requires a relatively large motor torque and accordingly a relatively large motor.

It is known from DE-A-37 06 849 to actuate the hydraulic master cylinder of an hydraulic clutch actuating means by an eccentric crank, of which the crank wheel is in the form of a worm wheel meshing with a worm mounted on the spindle of an electric motor. A compensating spring bears on the crank wheel and is tensioned by the electric motor as the clutch engages, and then on disengagement it assists the electric motor in working against the force of the clutch spring. However this actuating means takes up a relatively large amount of space and involves a relatively large number of individual components, which makes assembly expensive.

According to the present invention, in an actuating means of the kind set forth the motor spindle and the master cylinder are arranged co-axially, and the drive means comprises a screw drive co-axial with the motor spindle, having a threaded spindle onto which a nut is screwed, the threaded spindle being connected to the motor spindle f or rotation with it and the nut being connected to the piston and bein g prevented from 3 rotation relative to the master cylinder but being axially movable, and the piston has, in its end adjacent the motor, a recess for axially receiving the threaded spindle.

The actuating means has a simple construction with only a few components and requires only relatively little space, as the piston of the master cylinder is employed for accommodating the threaded spindle. As the master cylinder, the electric motor and the threaded spindle are arranged on a common axis, transverse loads on the piston which would load its seals are avoided.

The nut may engage the piston loosely in the actuating direction of the piston, as long as it is ensured, by return springs or the like, that the piston can be moved in the return direction as well. Preferably the piston and the nut are rigidly connected together, in particular made in one piece, in order to allow the piston to be positively driven by the electric motor in both directions. This variant takes a particularly simple form when the nut is in the form of an internal thread in a central bore in the piston.

The threaded spindle can take the form of a component manufactured separately from the motor spindle and fixed to it or secured to it for rotation. The cost of assembly is reduced if the threaded spindle takes the form of an integral extension of the motor spindle.

The electric motor and the master cylinder may comprise components which are independently secured to a housing for the drive means. This has the advantage that they can be manufactured from a material which 4 best serves the required purpose, so that for example the master cylinder may be of a material resistant to corrosion by hydraulic fluid. However, this increases the cost of construction and assembly. In a preferred embodiment therefore the electric motor is mounted on a housing having an integrally formed cylinder bore for the piston. Such a housing is particularly economical in space and reduces the assembly cost of the actuating means.

In a preferred embodiment a compensating spring is arranged round the threaded spindle and axially between the piston and a stop face fixed relative to the master cylinder, this spring acting to urge the piston in a clutch-disengaging direction. The compensating spring is preferably a helical coil compression spring, and the stop face comprises an abutment face formed by the electric motor. The spring can in this way be mounted in a particularly space-saving manner.

There is usually associated with the actuating means a travel sensing device which produces a signal representing the disengaged position of the clutch for the purpose of controlling the actuating means. In a preferred embodiment there is provided for this purpose a position sensor connected to the master cylinder and of which the moving element is connected to the piston.

In particular where a compensating spring is employed, at least one braking device, which acts to hold the piston in the clutch-engaged position and preferably also in the disengaged position is associated with the screw drive. The braking device ensures that the actuating means is positively held at least at its end, that is, engaged and disengaged positions. The braking device can take the form of an electromagnetically actuated, and electromagnetically released, brake.

resilient detent devices, such spring-loaded ball detents, which yieldingly hold the piston in in particular Also suitable are as for example resiliently and the clutch-engaged position and/or the disengaged position relative to the housing of the master cylinder.

An embodiment of the invention by way of example is shown in the accompanying drawing, the single figure of which shows diagrammatically a clutch-actuating means with an electric motor, seen in a partial axial longitudinal section.

The vehicle friction clutch I illustrated in the drawing is of a known form and comprises a clutch plate 5 secured for rotation with a gearbox input shaft 3 and urged by a main clutch spring, for example a diaphragm spring 7, into an engaged position in which it is clamped frictionally between a pressure plate 9 and an opposing plate in the form of a flywheel 13 connected to a crankshaft 11 of the engine of the vehicle. The clutch 1 can be disengaged by means of a withdrawal mechanism 15 acting against the force of the spring 7.

An electric motor actuating means 17 is provided to actuate the withdrawal mechanism. The means 17 comprises an electric motor 19, for example a direct current commutator motor, which is connected to a hydraulic master cylinder 21 to form a sub-assembly. The master cylinder 21 is connected through an hydraulic pipe 23 to an orthodox hydraulic slave cylinder 25 acting on the withdrawal mechanism 15 in 6 order to actuate the latter. A drive means in the form of a screw drive indicated generally at 27 converts the rotation of a spindle 31 of the motor 19 about an axis 29 into an axial displacement of a piston 37 of the master cylinder 21 sliding in and sealed in a cylinder bore 33 in a housing 35. The screw drive 27 has a screw-threaded spindle 39 arranged coaxially with the cylinder bore 33 and with the motor spindle 31, and a nut 41 screwed axially on the threaded spindle 39 and connected to the piston 37.

The threaded spindle 39 is formed as an integral extension of the motor spindle 31 and extends into a central bore 43 in the piston 37. The nut 41 is formed integrally with the piston 37 as an internal screw thread in the bore 43. Means 45 guide the piston 37 and thereby the nut 41 in a way that prevents rotation but allows axial movement in relation to the housing 35, in response to rotation of the spindles 31 and 39 by the motor 19.

A compensating spring 51 in the f orm of a helical coil compression spring is provided in a chamber 47 of the housing 35, rearwardly of the cylinder bore 33. The spring 51 is placed round the threaded spindle 39, between the piston 37 and an abutment face formed by a flange 49 on the electric motor 19 secured to the housing 35. The force which the spring 51 exerts on the piston 37 acts to oppose the force exerted by the diaphragm spring 7 on the piston 37 through the hydraulic fluid.

The electric motor 19 and the friction clutch 1 are controlled by a control system 53. When the nut 41 and thus the piston 37 are driven in a forward direction,, that is towards a pressure space 55 of the 7 master cylinder 21, the friction clutch 1 is disengaged. The drawing shows the piston 37 in the disengaged position. In its movement into the disengaged position the motor 19, assisted by the compensating spring 51, works against the force of the diaphragm spring 7. on clutch engagement the diaphragm spring 7 drives the piston 37 in the opposite direction, compressing the spring 51. In both directions of movement the motor 19 is in action and it determines the actuating speed under the control of the control system 53. The control system 53 takes the form of an orthodox electronic automatic clutch-engaging and disengaging clutch control system responsive to operating parameters of the vehicle and The control system can the in particular of the engine. also serve other functions, deliberate introduction of a in particular slight slip in the transmission of the driving torque in order to eliminate or at least reduce variations in rotational speed in the drive train. Suitable control systems are described for example in the previously mentioned patent applications DE-33 30 332, DE-34 38 594, DE- 36 24 755, DE-39 35 438 and DE-39 35 439.

The control system 53 responds to a number of sensors, not shown, for example speed sensors which record the engine speed, the gearbox input shaft speed, the gear lever position and the vehicle speed. In order to be able to position exactly the withdrawal mechanism 15 of the clutch 1, the control system 53 operates as a position regulator, to which is supplied an actual position signal from the clutch actuating means 17. For this purpose the means 17 includes a linear position sensor 57, in the form of a linear potentiometer, of which the slider 59 is connected directly to the piston 37.An incremental sensor, not 8 shown, can be connected to the motor spindle 31 in increase the accuracy with which the actual position is ascertained. The position sensor 57 is mounted in the chamber 47 of the housing 35. The housing 35 also contains at least part of the electronic components of the control system 53, for example the electronic drive circuit for the motor 19.

In order to prevent the diaphragm spring 7 andlor the compensating spring 51 being able to move the piston 37 when the motor 19 is not energised, a braking device in the form of a spring-loaded ball detent 61 is provided on the housing 35, acting to hold the piston 37 or the nut 41 associated with it in the clutch-engaged position. A further detent 61 is shown in dotted lines, and this acts to hold the piston 37 in the disengaged position. The residual forces of the detents 61 are of such a size that they cannot be overcome by the springs 7,15 alone. It will be understood that instead of resilient detents other braking devices could equally well be used. For example electromagnetic brake devices, preloaded resiliently into their braking position, could be provided, of which the electromagnet releases the brake when it is energised.

A recuperation port 63 connected to a hydraulic fluid reservoir (not shown) opens into the bore 33 of the master cylinder 21 and is uncovered when the piston 37 is in the position associated with the fully engaged position of the clutch 1, the port being closed off by the piston 37 after a certain degree of lost-motion has been taken up. In the fully engaged position of the clutch hydraulic fluid from the reservoir can flow in, to take up clearances which 9 arise as a result of wear, in particular of the friction linings of the clutch plate 5.

The end of the motor spindle 31 remote from the master cylinder 21 is accessible from outside the housing 35 and is provided with keying faces 65 which can be connected to a crank handle 67 or the like for emergency operation. The screw drive 27 can therefore also be operated by hand, for example in the event of failure of the control system 53.

In the embodiment described above the master cylinder 21 is an integral part of the housing 35. Alternatively, in a modification (not shown), the cylinder bore 33 could be provided in a separate cylinder housing connected to the housing 35. In further modifications (not shown) the screw drive 27, of which the threaded spindle 39 is connected integrally to the spindle 31 of the motor, and of which the nut 41 is an integral part of the piston 37, could if desired also be made as separate components.

Claims

Actuating means for an hydraulically actuated motor vehicle friction clutch of the kind set forth, in which the motor spindle and the master cylinder are arranged co-axially, the drive means comprises a screw drive coaxial with the motor spindle, and having a threaded spindle onto which a nut is screwed, the threaded spindle being connected to the motor spindle for rotation with it, and the nut being connected to the piston and being prevented from rotating relative to the master cylinder but being axially movable, and the piston has, in its end adjacent the motor, a recess for axially receiving the threaded spindle.
2. Actuating means as claimed in claim 1, in which the nut engages the piston loosely in the actuating direction of the piston.
3. Actuating means as claimed in claim 1, in which the piston and the nut are rigidly connected together.
4. Actuating means as claimed in claim 3, in which the piston and nut are made in one piece.
5. Actuating means as claimed in claim 3 or claim 4, in which the nut is f ormed as an internal thread in a central bore in the piston.
6. Actuating means as claimed in any preceding claim, in which the threaded spindle is separate from the motor spindle, and secured to it for rotation.

4 11
7. Actuating means as claimed in any of claims 1 to 5, in which the threaded spindle is formed as an integral extension of the motor spindle.
8. Actuating means as claimed in any preceding claim, in which the electric motor and the master cylinder comprise components which are independently secured to a housing for the drive means.
9. Actuating means as claimed in any of claims 1 to 7, in which the motor is mounted on a housing having an integrally formed cylinder bore for the piston.
10. Actuating means as claimed in any preceding claim, in which a compensating spring is arranged round the threaded spindle and axially between the piston and a stop face fixed relative to the master cylinder, and acts to urge the piston in a clutch-disengaging direction.
11. Actuating means as claimed in claim 10, in which the compensating spring abuts against a stop face formed by the motor.
12. Actuating means as claimed in claim 10 or claim 11, in which the compensating spring comprises a helical coil compression spring.
13. Actuating means as claimed in any preceding claim, in which the piston is connected to a linearly movable slider element of a position sensor connected to the master cylinder.
14. Actuating means as claimed in any preceding claim, in which a braking device is provided in association 12 with the screw drive, the device acting to hold the piston in the clutch- engaged position.
15. Actuating means as claimed in claim 14, in which a further braking device is provided to hold the piston in the clutch-disengaged position.
16. Actuating means as claimed in claim 14 or claim 15, in which the or each braking device comprises a detent device, for resiliently and yieldingly holding the piston relative to the housing of the master cylinder.
17. Actuating means as claimed in claim 16, in which the detent device comprises a spring-loaded ball detent.
18. Actuating means of the kind set forth substantially as described herein with reference to and as illustrated in the accompanying drawings.