GB2205377A

GB2205377A - Clutch actuation device

Info

Publication number: GB2205377A
Application number: GB08806414A
Authority: GB
Inventors: Georg Bestler; Helmut Mrosek; Michel Claire
Original assignee: Knorr Bremse AG
Current assignee: Knorr Bremse AG
Priority date: 1987-03-20
Filing date: 1988-03-18
Publication date: 1988-12-07
Anticipated expiration: 2008-03-18
Also published as: FR2612464A1; GB2205377B; DE3709166C1; FR2612464B1; GB8806414D0

Abstract

A clutch actuation device, particularly a clutch amplifier which operates hydro-pneumatically, comprises a hydraulic working piston (17) and a pneumatic working piston (25) provided in a common casing (13, 15) and structurally separate but associated with each other functionally, so that either purely pneumatic or hydraulic-pneumatic actuation can optionally be effected. For this purpose, a control valve (1) is preferably integrated into the casing (13, 15) and can be activated by the clutch pedal via a master cylinder (5) for hydraulic-pneumatic actuation, or can be controlled by means of a solenoid valve (11) activated by electronic control processes in order to provide, in this case, a purely pneumatic activation of the device, i.e. of the pneumatic working piston for the purpose of disengaging the clutch which is connected to the device. The device also preferably incorporates a variable volume hydraulic chamber (65) to provide wear adjustment. <IMAGE>

Description

HYDROPNEUMATIC CLUTCH ACTUATOR The invention concerns a hydropneumatic clutch actuator, particularly an amplifier actuator.

The great majority of commercial vehicles are equipped with mechanical gears. One of the many reasons for this is the high efficiency of these gears.

In order to improve driving performance and vehicle efficiency the gears of commercial vehicles are equipped with a large number of gear ratios, which places considerable physical and also mental demands on the driver when changing gear. Gear changing operations can be automated and optimised by modern computers suitable for vehicles.

In the great majority of vehicles, the clutch between engine and gears, as required for driving, manoeuvering and usually also for changing gear, is designed as a friction clutch subject to wear; this clutch is operated by a foot pedal. In larger vehicles, operation is mostly achieved hydraulically, and with very powerful engines, pneumatic auxiliary force (clutch amplifier) is used.

In known clutch amplifier (DE OS 2 124 948), a hydraulic working piston and a pneumatic working or servo piston operate inside a casing unit. Both pistons are coupled together, i.e. are constrained to move together, a cylinder chamber filled with hydraulic medium being located inside the piston rod arranged common to both pistons. The push rod, which extends from the piston rod arrangement and activates the clutch, rests on the hydraulic medium in the cylinder chamber via a support piston. In addition, means are provided which, in a predetermined operational position, connect the actual hydraulic pressure chamber of the clutch actuation mechanism to the cylinder chamber in the piston rod in such a way that adjusting movements of the support piston relative to the piston rod arrangement are possible.

Embodiments of the invention may provide a hydropneumatic clutch amplifier of the type described and allowing partially automatic clutch operation, using modern electronic means, which assist the manual clutch in some operating regions. The actuation mechanism may preferably be equipped with substantially conventional components, i.e. it should be possible to operate with the option of manual actuation with a conventional transmission cylinder and a conventional push rod actuation on the clutch. In particular, emergency actuation of the clutch should be ensured in the case of electronics failure.

According to the present invention there is provided a hydropneumatic clutch amplifier for motor vehicles, with hydraulic and pneumatic working pistons arranged in a casing in a tandem arrangement, controlled by a control valve connected to a hydraulic transmission cylinder and capable of acting on a common connecting rod which actuates the clutch, wherein a hydraulically operating adjusting mechanism automatically adjusts the stroke of the clutch amplifier, wherein the pneumatic working piston and the hydraulic working piston are structurally separate from each other and operate in tandem so that, for hydropneumatic actuation, they can both be activated together and, for purely pneumatic actuation, the pneumatic working piston can be activated alone.

Conveniently, the actuator may include a hydraulically operated adjusting mechanism which automatically adjusts the stroke of the clutch.

By separating the hydraulic wdrking piston from the pneumatic working piston, while maintaining their structural arrangement in one device, it is possible to operate the actuation mechanism either purely pneumatically or hydraulically and pneumatically. For purely pneumatic operation, the control valve, which is likewise integrated structurally into the device, can be activated separately from the hydraulic valve system, so that it can activate the pneumatic working piston when the hydraulic working piston is in the rest position. In this arrangement the control valve can be controlled by a solenoid valve, which lends itself to modern electronic control. In this way, automated clutch actuation for specified operating conditions is made possible.

A further substantial advantage of the actuation mechanism may be achieved by having continuous hydraulic adjustment in tension and compression directions present as an isolated system in the pneumatic working piston, the compensating volume chamber used for this purpose having a permanent charge and being without any connection to the hydraulic operating medium in the pressure chamber of the hydraulic working piston. In this way, problems of bubble formation and ventilation of the hydraulic medium in the adjusting or compensating volume chamber are completely excluded. Over and above this, it is also possible to use different hydraulic media for both the actuation of the hydraulic working piston and the continuous adjusting process.

The separation of hydraulic piston and pneumatic piston is particularly advantageous for the solenoid-valve-controlled actuation process because the hydraulic piston does not have to follow up the pneumatic piston, and hence no unnecessary filling up of the hydraulic operating chamber, i.e. the pressure chamber of the hydraulic working piston, is required.

One embodiment of the invention will now be described with reference to the attached Figure, which shows a longitudinal view of the clutch amplifier.

The drawing shows a hydropneumatic clutch amplifier into which is integrated a control valve 1 which operates as described below. The control valve 1 is connected to a hydraulic transmission cylinder 5 by means of a duct 3 which conducts a hydraulic medium.

The transmission cylinder can be actuated in the conventionally known manner by means of a clutch pedal 7. A solenoid valve 11 is additionally connected to the control valve 1 via a duct 9; the solenoid valve can be actuated by means of a control mechanism (not shown) in order to introduce compressed air into the control valve 11 through the duct 9.

The clutch amplifier is formed as one structural unit comprising two casings 13 and 15. A hydraulic working piston 17 is mounted inside the casing 13, and can be activated by the introduction of hydraulic medium into a cylinder chamber 19, so that, when pressure is applied, it carries out a movement directed towards the right in the drawing. As seen in the Figure, the working piston 17 penetrates the connecting region between the two casings 13 and 15 by means of a push rod 21 located on it and bears against a dish-shaped depression 23, which is constructed in the facing surface of a pneumatic working piston 25.

The working piston 25 can be activated in the manner described below by the introduction of compressed air into the chamber 27, so that it carries out a movement directed towards the right in the drawing. The working piston 25, whose outer contour is guided, preferably by means of a guide ring 29 and a seal 31, in relation to the inside wall of the casing 15, has an axially aligned extension 33 in the form of a shell, inside which a co-axially aligned compensating piston 35 is arranged displaceably under seal. The outer surface of the compensating piston 35 is guided under seal with respect to the extension 33, and its inner surface rests with a seal on the outer contour of a piston rod 37.The compensating piston is continuously biased by a spring 39 in the direction of the pneumatic working piston 25, the spring 39 being supported as shown on a stop bracket 41 fixed on the inside of the extension 33. A further spring 43, supported on the stop bracket 41, acts on a step on the outer contour of the piston rod 37 and constantly biases the latter in the direction of the pneumatic working piston 25. A third spring 45 is supported on the stop bracket 41 on the opposite side to springs 39 and 43, and extends to an inserted part 47 in the base 49 of the casing 15. The spring 45 operates directly against the working piston 25 and tends to displace the latter into its starting position shown in the drawing.

On the outer contour of the piston rod 37 there are two axially spaced stops, a stop disc 51 and a stop ring 53. The radially inner end of the inserted part 47 is constructed as a stationary stop 55, a stop disc 57 being held between the stop 55 and the base 49 of the casing 15. The stop disc 57 serves as an end stop for the stop ring 53 when the latter, together with the piston rod 37, completes a.movement directed towards the left, while the stop disc 51 comes to rest against the stop 55 when the piston rod 37 completes a movement directed towards the right.

The compensating piston 35 mentioned above and the pneumatic working piston 25 define an inner chamber 59 which serves to contain a hydraulic pressure medium.

The hydraulic pressure medium can be introduced into the chamber 59 before the assembly of the amplifier unit after removing a fill plug 61 located in the working piston 25. The chamber 59 extends in free connection into the region of a regulating valve 63, which in closed position (corresponding to the drawing) separates the chamber 59 from a further chamber 65 for the hydraulic pressure medium. The regulating valve 63 comprises a valve ball 69 which is biased by a spring 67 and can make a seal with a valve seat 71. The abutment of the pneumatic working piston 25 on the valve ball 69 holds the latter in its sealing position on the valve seat, so that the valve ball 69 opens under the force of the spring 67 when relative axial motion occurs in the sense of mutual separation of the piston rod 37 and the working piston 25.A perforated or segmented guide ring 73, extending axially from the working piston 25, is provided inside the chamber 59 and acts as a guide for the piston rod 37, so that transverse forces acting on the piston rod 37 are taken up by the working piston 25 and braced by the guide ring 29 against the casing 15.

On introduction of a hydraulic pressure medium into the cylinder chamber 19 the working piston 17 operates against the pneumatic working piston 25 and moves with it towards the right in the manner described below, an amplifying effect being initiated by the introduction of compressed air into the chamber 27. As a result of the separation of the working piston 25 from the working piston 17, a purely pneumatic activation of the working piston 25 can also be effected, without simultaneous activation of the hydraulic working piston 17 being necessary.

During purely pneumatic activation, controlled by the introduction of compressed air into the chamber 27 by means of the control valve 1, the pneumatic working piston 25 moves in the sense of releasing or disengaging the clutch, the working piston 17 remaining in its depicted starting position, the cylinder chamber 19 not being pressurised. Thus it is not necessary to top up the hydraulic medium in the cylinder chamber 19.

The depicted starting position of the working piston 17, which is guided and sealed on the inside wall of the cylinder chamber 19, is set by a stop disc 75 placed on the push rod 21. The stop disc 75 is fixed in its turn by a securing ring 77.

The clutch amplifier operates in the following way: If the control valve 1 is activated in the conventional manner, by actuation of the transmission cylinder 5 by means of the clutch pedal 7, hydraulic pressure medium enters the chamber 79 of the control valve via the duct 3 and from it reaches the cylinder chamber 19 via a channel 82, so that the working piston 17 is hydraulically activated, i.e. is displaced towards the right. The pressure in the chamber 79 simultaneously activates the two-component control piston 81, 83, which is displaced towards the right in the drawing against the force of the spring 85 until it causes a valve plate 87 to be raised from its seat and a chamber 89, joined by means not shown to a pneumatic reservoir, to be connected thereby to the chamber 91 and via it to the chamber 27 by a further connection (not shown).When this connection is made, the servo effect of the clutch amplifier begins, the working piston 25 and the hydraulically activated piston 17 applying the actuation force. The force is transferred from the pneumatic working piston 25 to the push rod piston 93 via the valve ball 89, the sealed valve seat 71 and the hydraulic volume in the chamber 65, the working travel being determined by the specified transmission volume at the clutch pedal 7. Any rotational movements occurring are allowed for by the working piston 25 via the guide ring 29. The push rod piston 93 acts on the clutch by means of the connecting rod 95, so that the clutch is released i.e. disengaged, when the working piston is actuated in the direction of the arrow A.

If actuation takes place using the solenoid valve 11, actuated by means of a control unit, the chamber 97, connected with the duct 9, is pneumatically activated, causing the individual piston 83 to lift the valve plate 87 from its intake seat against the spring 85 and thereby connect the chamber 91 with the chamber 27 as described above. The working piston 25 is pneumatically activated without simultaneous hydraulic activation of the working piston 17; the working piston 17 remains in place as described above, so that supply of a hydraulic pressure medium to the cylinder chamber 19 is rendered unnecessary.

When the pneumatic working piston 25 is driven, as a result either of actuating the clutch pedal 7 or of activating,the solenoid valve 11, the stop disc 51 and the stop 55 determine the maximum extent of the stroke. The normal position of the push rod piston 93 in relation to the piston rod 37 is set by a securing ring 101 as shown in the diagram. When the working piston 25 moves back, the stop 53 comes up against the stop disc 57, simultaneously fixing the normal stop position of the valve ball 69 on the working piston 25.

The return of the clutch amplifier, causing re-engagement of the clutch, is achieved by reducing the pressure in the chamber 79 (in the case of operation by the clutch pedal 7) or by reducing the pressure in the chamber 91 (in the case of control by the solenoid valve 11), with the result that the chamber 27 is ventilated via a connection (not shown) and the control valve 1. In the former case, where the cylinder chamber 19 had been pressurised, it is then de-pressurised. The return of the pneumatic working piston 5 with, in the case of pedal actuation, concomitant return of the working piston 17, occurs under the action of return forces on the clutch via the push rod piston 93 and by the spring 45.Furthermore, after the stop 53 comes to rest on the stop disc 57 and the stop 55, the ball seat between the valve ball 69 and the valve seat 71 is opened by means of spring 67; this opens the connection from the chamber 65 to the chamber 59. This process enables the push rod piston 93 to move in direction A and direction B. In the case of movement in direction B, wear of the clutch lining is correspondingly compensated or further wear reduced.

The volume displaced from the chamber 65 when the tappet piston moves in direction A or B is taken up into the chamber 59, which operates as a compensating volume, the volume in the chamber 59 being alterable by the compensating piston 35 under the effect of the spring 39. According to the setting of this spring, a defined pressure can prevail in the chambers 59 and 65 with the apparatus ventilated; the pressure constantly retains the push rod piston 93 in position on the clutch lever. The setting of the spring 43 will depend on this pressure, this spring 43 guaranteeing closure of the ball seat when the mechanism is actuated in accordance with the resultant ring area between the diameter of the tappet piston 93 and the internal diameter of the compensating piston 35.

As mentioned above, the chambers 59 and 65 are filled with hydraulic medium via the bore sealed by the fill plug 61. The air inside the chamber 103 is in contact with the external air via a ventilation valve (not shown), i.e. volume changes are easily possible in the chamber 103 without the occurrence of excess or reduced pressure.

Claims

CLAIMS:

1. Hydropneumatic clutch amplifier for motor vehicles, with hydraulic and pneumatic working pistons arranged in a casing in a tandem arrangement, controlled by a control valve connected to a hydraulic transmission cylinder and capable of acting on a common connecting rod which actuates the clutch, wherein the pneumatic working piston and the hydraulic working piston are structurally separate from each other and operate in tandem so that, for hydropneumatic actuation, they can both be activated together and, for purely pneumatic actuation, the pneumatic working piston can be activated alone.

2. Clutch actuator according to claim 1, in which there is a hydraulically operated adjusting mechanism which automatically adjusts the stroke of the clutch.

3. Clutch actuator according to claim 2, characterised in that the hydraulic adjusting mechanism is arranged in the pneumatic working piston and can travel with it.

4. Clutch actuator according to claim 3, wherein two chambers, which are filled with hydraulic medium and can be separated from each other or connected together by means of a valve mechanism, are arranged on the opposite side of the pneumatic working piston from the pressure medium, the first chamber being located inside the piston rod and delimited by a push rod piston which can slide inside the piston rod and is connected to the connecting rod of the clutch actuator, so that, when the valve arrangement is open, relative displacements of the push rod piston cause volume redistribution between the two chambers.

5. Clutch actuator according to claim 4, wherein the second chamber is delimited by a spring-biased adjustable piston for volume compensation, and the valve mechanism is located on the end of the piston rod facing the pneumatic working piston.

6. Clutch actuator according to claim 5, wherein the piston rod is capable of limited travel relative to the pneumatic working piston, so that when pneumatic pressure is applied to the working piston and the working piston and piston rod approach each other, the valve mechanism can be closed by the working piston.

7. Clutch actuator according to any preceding claim, wherein the hydraulic working piston bears against a depression in the pneumatic working piston by means of a push rod extending axially from it, the hydraulic working piston extending under seal through a partition between the casings of the working pistons.

8. Clutch actuator according to any preceding claim, wherein the control valve can be controlled both hydraulically by the transmission cylinder and pneumatically by a solenoid valve.

9. Clutch actuator according to claim 8, wherein the hydraulically controlled control piston of the control valve comprises two individual pistons, the hydraulic control acting upon both pistons and the pneumatic control acting on only one of the pistons by means of the solenoid valve, so that in the case of hydraulic control, both the hydraulic working piston and the pneumatic working piston are activated, while in the case of pneumatic control only the pneumatic working piston is activated, the hydraulic working piston remaining in the rest position.

10. A Clutch actuator according to any preceding claim, adapted to operate as an amplifier actuator.

11. A Clutch actuator substantially as specifically described herein as illustrated in the drawing.