GB2189001A - Hydraulically controlled clutch actuating device for automotive vehicles - Google Patents

Abstract

A hydraulically controlled clutch actuating device, for automotive vehicles, comprises a clutch-pedal operated master cylinder and an auxiliarly spring-loaded master cylinder 1 with a power booster 110 supplying to a slave cylinder actuating a clutch release yoke. In the auxiliary cylinder 1 booster unit, an axially displaceable control piston 3 is coaxially arranged in both a working piston 4, and a pneumatic vacuum power booster which acts upon the working piston 4. The booster comprises a rolling diaphragm 22 and a control valve device controllable by the control piston, with the movement of the diaphragm caused by a pressure difference which acts thereon, being transmitted to the working piston 4 whereby a reaction force proportional to the output pressure acts on the control piston. Upon actuation of the vacuum booster 2, the movements of the working piston 4 and of the control piston 3 occur in opposite directions, with the reaction force being generated by an elastic reaction element 7, concentrally arranged around the control piston 3 between the control piston 3 and the diaphragm 22. <IMAGE>

Description

SPECIFICATION Hydraulically controlled clutch actuating device for automotive vehicles This invention relates to a hydraulically controlled clutch actuating device for automotive vehicles, comprising an auxiliary master cylinder having a clutch-pedal-operable, springloaded working piston by means of which pressure medium is supplied to a slave cylinder actuating a clutch release yoke, an axially displaceable control piston being arranged coaxially within the working piston, a pneumatic vacuum power booster having a chamber of constant pressure, a chamber of variable pressure, a movable wall as well as a control valve device controllable by the control piston, movement of the movable wall caused by a pressure difference acting thereon being transmitted to the working piston whereby a reaction force proportional to the output pressure acts on the control piston.

Such a clutch actuating device is known from West German Examined and Printed Patent Application (DE-AS) No. 16 30 311. The device disclosed therein has an auxiliary piston which is connected with a compensating piston rod, which is axially displaceably guided within an auxiliary cylinder connected to the pressure line proceeding from the master cylinder, and which is pressurisable by the pressure medium on a piston surface exceeding the size of the piston surface of a compensating piston connected with the compensating piston rod.The compensating piston biassed by a compression spring and coaxially arranged with the working piston of the arrangement actuates the control valve device of a pneumatic compressed-air-assisted power booster, said control valve device allowing an air pressure difference to act on the movable wall of the power booster, which generates a boosting force acting on the working piston.

The pressure medium volume enclosed in the servo cylinder and having direct contact with the piston surface of the comnpensating piston serves as a reaction element for the transmission of the reaction force proportional to the output pressure.

However, the complicated design of the known clutch actuating device is to be considered disadvantageous, said design inevitably involving a high amount of working efforts and cost. Disadvantageous is also the necessity of sealing a plurality of moving parts relative to one another which implies unfavourable friction conditions in the overall system. Adjusting the desired gradient of the functional characteristic of said known clutch actuating device is also relatively complicated. Additional costs are also involved by the necessity of using a compressed-air reservoir fed by a compressor.

It is therefore an object of the present invention to provide a hydraulically controlled clutch actuating device of the type referred to above where the above-mentioned disadvantages will largely be avoided and which will permit a simpler design while maintaining the high-degree operational reliability.

According to the present invention there is provided a hydraulically controlled clutch actuating device, for automotive vehicles, comprising an auxiliary master cylinder having a clutch-pedal-operable, spring-loaded working piston by means of which pressure medium is supplied to a slave cylinder actuating a clutch release yoke, an axially displaceable control piston being arranged coaxially within the working piston, a pneumatic vacuum power booster having a chamber of constant pressure, a chamber of variable pressure, a movable wall as well as a control valve device controllable by the control piston, movement of the movable wall caused by a pressure difference acting thereon being transmitted to the working piston whereby a reaction force proportional to the output pressure acts on the control piston, characterised in that, upon the actuation of the vacuum power booster, the movements of the working piston and of the control piston occur in opposite directions and in that the reaction force is generated by an elastic reaction element concentrically arranged around the control piston between the control piston and the movable wall.

Thus, a hydraulically controlled clutch actuating device is provided which, due to the use of a vacuum power booster, provides for a considerable saving in cost as the energy source required for the boosting power is formed by a suction pipe connection of an Otto engine which is provided anyhow, or by the vacuum pump of a diesel engine. Thus, no special energy source (such as a compressorsupplied pressure reservoir) is needed. Further, the use of a well-proved control principle (poppet valve) guarantees a long life of the inventive clutch actuting device.

A particularly advantageous embodiment of this invention provides that the elastic reaction element is formed by a reaction disc having a central opening and co-operating with an annular shoulder of the control piston, in the rest position of the clutch actuating device said shoulder being arranged at a predetermined distance in respect thereof, as well as the reaction disc co-operating with a transmission member axially supporting itself at the working piston. This embodiment permits a precise and simple adjustment of both the desired transmission ratio (gradient of the functional characteristic) and the position of the actuating point by changing the ratio between the surface of the annular shoulder of the piston and the transmission member's surface having contact with the reaction disc.A further advantage of said embodiment consists in the possibility of influencing the response behaviour of the vacuum power booster by the coordination of the distance between the shoulder and the reaction disc, on the one hand, and of the opening distance of the poppet valve, on the other hand.

A further development of the inventive subject matter provides that, between the surface of the control piston and the reaction disc, a sleeve-like extension of the control valve housing is provided wherein the control piston is guided in an axially sliding manner. By means of these measures the operational reliability of the device is considerably increased as otherwise a strong deformation of the reaction disc, especially resulting in cases of high reaction forces, could lead to jamming of the control piston.

A particularly simple embodiment of the inventive hydraulically controlled clutch actuating device is achieved in that the elastic reaction element is formed by a rolling diaphragm whose outside edge is fastened at the movable wall, its inside edge being fastened at the control piston. Said rolling diaphragm is arranged in a cylindrical chamber within the control valve housing, which communicates with respectively the vacuum chamber comprising the chamber of constant pressure and the working chamber comprising the chamber of variable pressure via axial channels.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 schematically shows a clutch actuating device with a hydraulically actuated pneumatic power booster; Figure 2 is an axial section of an example of an embodiment of the power booster according to this invention; and Figure 3 is a partial section of the pneumatic power booster with another embodiment of the reaction device.

In Figure 1, reference numeral 100 denominates a clutch pedal whose lever 101 is supported in a pivotal manner at a bolt 102 and, by means of a piston rod 111, is connected with a piston 104 arranged in a master cylinder 103. An essential part of this invention is formed by a hydraulically actuated booster device 110 consisting of an auxiliary master cylinder 1 as well as of a pneumatic power booster 2. On the one hand, the booster device 110 is connected with the master cylinder 103 via a hydraulic line 105. On the other hand, it is connected with a clutch slave cylinder 107 via a hydraulic line 106. A piston rod 109 connects the piston 108 of the clutch slave cylinder 107 with a release yoke of the clutch, said release yoke not being illustrated in the drawing.

The design of the booster device 110 schematically represented in Figure 1 will now be explained in more detail, reference being made to an embodiment illustrated in Figure 2. As already mentioned above, the booster device consists of a vacuum power booster 2 as well as of an auxiliary master cylinder 1 flanged thereto and fastened at the booster housing 21 by means of fastening bolts 44 and lock nuts 43. The joint between the booster housing 21 and the auxiliary master cylinder 1 is sealed by means of a sealing ring 42. A working piston 4 is slidingly guided in a cylindrical bore 10 of the auxiliary master cylinder 1. Referring to the drawing, the right-hand end of said working piston 4 protrudes into the interior of booster housing 21. At its end averted from the power booster 2, the working piston 4 has a cylindrical recess 12.A compression spring 13 supports itself at the end wall of said recess 12. In the rest position, said compression spring 13 prestresses the working piston 4 in the direction of the vacuum, booster 2. In the recess 12, there is a central valve 8 formed by a valve body 35, a compression spring 34 prestressing the valve body 35 in the closing direction, as well as a spring holder 33. The valve body 35 co-operating with a seat 36 formed at the working piston 4 is fastened to a valve pin 32 guided in an axial bore 37 of the working piston 4.

The function of said pin 32 will be explained in more detail in connection with the function of the clutch actuating device. Referring to the drawing, the auxiliary master cylinder 1 has a threaded bore 14 at its left end. Said threaded bore 14 serves to connect the hydraulic line 106 shown in Figure 1.

The working piston 4 which, together with the end wall of the bore 10, confines a pressure chamber 49 sealed relative to the bore 10 by means of a gasket 38 arranged in an annular groove at the surface of the working piston 4. In the middle part of the working piston 4, the axial bore 37 receiving the valve pin 32 passes over into an expanded stepped axial bore 15 communicating with an annular chamber 11 of the auxiliary master cylinder 1 by means of radial channels 16. Via a radial threaded bore 17, said chamber 11 communicates with the clutch master cylinder 103 by means of the hydraulic line 105 shown in Figure 1.

Referring to the drawing, at the right-hand end of the auxiliary master cylinder 1, the working piston 4 supports itself with its radial annular collar 18 at a stop disc 41 held in position by a bushing 48 secured in a larger diameter section 19 of the bore 10 by means of a retaining ring 59 and sealed relative to section 19 by means of an 0-ring 25. The bushing 48 simultaneously serves to axially guide the working piston 4 and is sealed relative to the same by means of a gasket 31 arranged in a radial recess of the bushing 48.

A control piston 3 is arranged in a coaxially displaceable manner in the stepped bore 15 of the working piston 4 and is sealed by means of a groove ring 20. In the rest position of the arrangement, the control piston 3, whose function will be explained in more detail fur ther below, inter alia keeps the central valve 8 open by means of its left end in the drawing while supporting itself at the edge of its front face at a step 64 of the stepped bore 15.

The booster housing 21 of the vacuum power booster 2 co-operating with the auxiliary master cylinder 1 is sub-divided by an axially movable wall 22 into a vacuum chamber 23 and a working chamber 24. The axially movable wall 22 consists of a diaphragm disc 26 as well as of a flexible diaphragm 27 resting on the diaphragm disc 26, said diaphragm 27 forming a rolling diaphragm 27' for a seal in the area between the outside circumference of the diaphragm disc 26 and the booster housing 21. The vacuum chamber 23 communicates with a suitable vacuum source, e.g., the suction pipe of an Otto engine or a vacuum pump, via a non-illustrated non-return valve. The diaphragm disc 26 of this embodiment is designed in one piece with a control valve housing 6 sealed relative to the booster housing 21 by means of a sealing ring 70 provided with a guideway.Together with a radially inside sealing seat 28, a radially outside sealing seat 29, as well as with a poppet valve body 30, said control valve housing 6 forms a control valve device of the vacuum power booster 2. In the rest position of the arrangement, the sealing surface of the poppet valve body 30 lies at the radially outside sealing seat 29 and is prestressed in the direction of this sealing seat 29 by means of a compression spring 40 supporting itself with its other end at a closure member 39 inserted into the control valve housing 6 and having both an air intake opening 45 and several channels 46, 47 extending both radially and axially.

At the vacuum chamber side end, the control valve housing 6 has a cylindrical recess 9 receiving a rubber-elastic reaction disc 7 as well as a cylindrical transmission member 5.

Referring to the drawing, the transmission member 5 supports itself at the right-hand end of the working piston 4 and has several axially extending vacuum channels 50 communicating with a central axial bore 52 of the control piston 3 via a radial bore 51 in the control piston 3. Said axial bore 52 ends in a cylindrical recess 53 at the right-hand end of the control piston 3. At the bottom of the cylindrical recess 53 a compression spring 54 supports itself which, on the one hand, keeps the poppet valve body 30 on the closure member 39 and which, on the other hand, prestreses the control piston 3 in the direction of the central valve 8, with the annular cylindrical outside wall of the recess 53 forming the radially inside sealing seat 28.

Near the radial bore 51, the control piston 3 is provided with an annular shoulder 55. In the rest position of the clutch actuating device, said annular shoulder 55 is arranged at an axial distance in respect of the reaction disc 7, the reaction disc 7 sitting on a cylindrical extension 56 of the control valve housing 6 wherein the right-hand end of the control piston 3, sealed by means of an 0-ring 57, is slidingly guided.

The control valve housing 6 finally has radially extending channels 58 forming a common vacuum-and-atmospheric-air channel section.

Figure 3 shows a partial section of the vacuum power booster with another embodiment of the used reaction element, with the parts which correspond to Figure 2 having been assigned like reference numerals. In this embodiment, the elastic reaction element is formed by a small rolling diaphragm 60 arranged in a cylindrical chamber 61 and fastened at its respective outside and inside edges at the control valve housing 6 and at the control piston 3, respectively. On the side of the vacuum chamber, the chamber 61 is closed by the transmission member 5 mentioned in connection with Figure 2, whose axial extension 63 secures the outside edge of the rolling diaphragm 60 in the respective recess of the control valve housing 6.Axial displacement of the transmission member 5 relative to the control valve housing 6 is prevented by a retaining ring 62 supported in a surrounding groove in the control valve housing 6.

So as to pressurise the rolling diaphragm 60 with the pressure difference acting on the movable wall 22, the chamber 61, on the one hand, communicates with the vacuum chamber 23 via the vacuum channels 50 in the transmission member 5 and, on the other hand, with the working chamber 24 via axial channels 65 designed in the control valve housing 6.

The mode of operation of the clutch actuating device will be explained in more detail in the following, in particular in connection with Figures 1 and 2, with the explanation starting from the rest position of the arrangement illustrated in Figure 2.

As already mentioned above, the vacuum chamber 23 of the vacuum power booster 2 is connected with a suitable vacuum source.

In the illustrated rest position, the vacuum generated by said vacuum source propagates into the working chamber 24 via the vacuum channels 50 in the transmission member 5, the radial bore 51, the axial bore 52 in the control piston 3, the open radially inside sealing seat 28, and the channels 58 in the control valve housing 6, thus-in the rest position-a vacuum prevailing in both chambers 23, 24.

Upon an actuation of the arrangement by pressing down the clutch pedal 100 (Figure 1) a hydraulic pressure will be generated in the clutch master cylinder 103 which will be able to propagate in the direction of the clutch slave cylinder 107 via the line 105 connected to the threaded bore 17, via the annular chamber 11, and via the open central valve 8.

Upon a further increase of the hydraulic pressure the force of the compression spring 54 will be overcome and the control piston 3 in Figure 2 will be displaced to the right.

Thereby the radially inside sealing seat 28 at the right-hand end of the control piston 3 at first will come to abut on the poppet valve body 30 whereby communication between the two chambers 23, 24 will be interrupted. At the same time, the action of the compression spring 34 will cause the central valve 8 to close and the annular chamber 11 will be separated from pressure chamber 49. A further pressure increase in the annular chamber 11 will be followed by a further movement of the control piston 3 to the right. Thereupon, the poppet valve body 30 will be lifted off the radially outside sealing seat 29 at the control valve housing 6 against the action of the force of the compression spring 40, whereby the working chamber 24 will be connected with the atmosphere via the radial channels 58, the air intake channels 46, 47 and the air intake opening 45 of the closure member 39.

The actuating force applied via the hydraulic line 105 and the boosting force acting on the movable wall 22 due to the pressure difference between the vacuum and working chambers 23, 24 will cause the working piston 4 to move to the left and will generate an increased pressure in the pressure chamber 49 of the auxiliary master cylinder 1, the piston 108 of the clutch slave cylinder 107 being pressurised by said increased pressure. This operation will continue as long as the actuating force acting on the control piston 3 exceeds the reaction force generated by the reaction disc 7 during transmitting the boosting force of the movable wall, said reaction force attempting to move the control piston 3 back to the left.As soon as the reaction force prevails due to the progressing pressure increase in the working chamber 24, the control piston 3 will be displaced to the left relative to the control valve housing 6 until the poppet valve body 30 will abut on the radially outside sealing seat 29. Thereby, any further supply of atmospheric air will be interrupted, thus a further pressure increase in the working chamber 24 not coming about and the vacuum power booster 2 remaining in its actuating position.Upon a reduction of the actuating force at the clutch pedal 100, the reaction force of the reaction disc 7 will move the control piston 3 further to the left, thereby the radially inside sealing seat 28 lifting off the poppet valve body 30 and a pressure reduction being effected from the working chamber 24 towards the vacuum chamber 23 so that the actuation of the auxiliary master cylinder 1 will lessen or be terminated in case of a complete reduction of the actuating force.

As is evident from the description of the hydraulically controlled clutch actuating device, control is effected exclusively by means of the boosting force active at the control valve housing, the magnitude of said boosting force determining the magnitude of the actuating force to be generated at the clutch pedal in the ratio of the transmission formed by the surfaces of the transmission member and of the annular shoulder of the control piston.

Thus, by means of the inventive vacuum power booster, it is easily possible to achieve different boosting ratios by varying the surface ratio without thereby changing the size and loading of the control valve housing and of the control components.

Claims (10)

1. A hydraulically controlled clutch actuating device, for automotive vehicles, comprising an auxiliary master cylinder having a clutch-pedaloperable, spring-loaded working piston by means of which pressure medium is supplied to a slave cylinder actuating a clutch release yoke, an axially displaceable control piston being arranged coaxially within the working piston, a pneumatic vacuum power booster having a chamber of constant pressure, a chamber of variable pressure, a movable wall as well as a control valve device controllable by the control piston, movement of the movable wall caused by a pressure difference acting thereon being transmitted to the working piston whereby a reaction force proportional to the output pressure acts on the control piston, characterised in that, upon the actuation of the vacuum power booster, the movements of the working piston (4) and of the control piston (3) occur in opposite directions and in that the reaction force is generated by an elastic reaction element (7, 60? concentrically arranged around the control piston (3) between the control piston (3) and the movable wall (22).

2. A hydraulically controlled clutch actuating device as claimed in claim 1, characterised in that the elastic reaction element (7, 60) is formed by a reaction disc (7) having a central opening.

3. A hydraulically controlled clutch actuating device as claimed in claim 2, characterised in that the reaction disc (7) co-operates with an annular shoulder (55) of the control piston (3), in the rest position of the clutch actuating device said shoulder (55) being arranged at a predetermined distance in respect thereof, as well as the reaction disc co-operating with a transmission member (5) axially supporting itself at the working piston (4).

4. A hydraulically controlled clutch actuating device as claimed in claim 2 or claim 3, characterised in that, between the surface of the control piston (3) and the reaction disc (7), a sleeve-like extension (56) of the control valve housing (6) is provided wherein the control piston (3) is guided in an axially sliding manner.

5. A hydraulically controlled clutch actuating device as claimed in claim 3, characterised in that the transmission member (5) is provided with axial bores (50) ending in a vacuum chamber (23) comprising the chamber of constant pressure and communicating with an axial bore (52) within the control piston (3), with the axial bores (50, 52) forming a partial section of a vacuum channel connecting the vacuum chamber (23) with a working chamber (24) of the vacuum power booster comprising the chamber of variable pressure.

6. A hydraulically controlled clutch actuating device as claimed in claim 1, characterised in that the elastic reaction element (7, 60) is formed by a rolling diaphragm (60) whose outside edge is fastened at the movable wall (22), its inside edge being fastened at the control piston (3).

7. A hydraulically controlled clutch actuating device as claimed in claim 6, characterised in that the rolling diaphragm (60) is arranged in a cylindrical chamber (61) within the control valve housing (6), which chamber (61) communicates with respectively a vacuum chamber (23) comprising the chamber of constant pressure and a working chamber (24) comprising the chamber of variable pressure via axial channels (respectively 50 and 65).

8. A hydraulically controlled clutch actuating device as claimed in any of the preceding claims, characterised in that, within the working piston (4), a stop (64) is provided which determines the relative position of the control piston (3) in respect of the working piston (4) and whereat the control piston (3) is axially supporting itself in the rest position of the clutch actuating device.

9. A hydraulically controlled clutch actuating device as claimed in any of the preceding claims, characterised in that the control valve device is formed by two concentrically arranged sealing seats (28, 29) and by a poppet valve body (30), with the radially inner sealing seat (28) forming a vacuum valve with the poppet valve body (30) and the radially outer sealing seat (29) forming the atmospheric air valve with the poppet valve body (30).

10. A hydraulically controlled clutch actuating device, for automotive vehicles, substantially as herein described with reference to Figures 1 and 2 with or without reference to Figure 3 of the accompanying drawings.