GB2203812A

GB2203812A - Hydraulically driven boosted actuating device for an automotive vehicle clutch or brake

Info

Publication number: GB2203812A
Application number: GB08802985A
Authority: GB
Inventors: Wilfried Wagner; Lothar Schiel
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1987-02-11
Filing date: 1988-02-10
Publication date: 1988-10-26
Anticipated expiration: 2008-02-10
Also published as: GB8802985D0; GB2203812B; FR2610676A1; DE3704133A1; JPS63203459A

Abstract

An auxiliary generating cylinder has a pedal-operated piston by means of which pressure medium is supplied to a slave cylinder actuating a brake member and/or a clutch release yoke. Between the auxiliary generating cylinder and the slave cylinder is connected a pneumatic vacuum boosting device (110). The latter comprises an axially displaceable control piston (3) arranged coaxially in relation to a working piston (4), as well as a pneumatic vacuum power booster comprising in a booster housing (21) a vacuum chamber (23) of constant pressure, a working chamber (24) of variable pressure and a movable wall (22) cooperating with the working piston. A control valve device, which is controllable by the control piston (3) includes a control valve housing (6), a first (28) and a second valve seat (29) as well as a poppet valve (30) coacting with both seats. Movement of the movable wall, caused by a pressure difference which acts on opposite sides thereof is transmitted onto the working piston to which is coupled directly. The control valve housing (6) is arranged stationarily in the booster housing (21) separately from the movable wall (22). The control piston (3) is of tube-shaped configuration and guided on the working piston (4) in sealed relationship thereto. The supply of the hydraulic pressure medium required for driving the actuating device takes place along its longitudinal axis. <IMAGE>

Description

HYDRAULICALLY DRIVEN ACTUATING DEVICE FOR AN AUTOMOTIVE VEHICLE This invention relates to a hydraulically driven actuating device for an automotive vehicle, in particular for the actuation of a hydraulic brake system and/or a hydraulic clutch, of the kind having a hydraulic inlet port, an auxiliary generating cyLinder by means of whose actuating-pedal-operabLe working piston pressure medium is supplied to a slave cylinder actuating a brake member and/or a cLutch release yoke, an axially displaceable control piston arranged coaxia ily in relation to the working piston, as well as a pneumatic vacuum power booster comprising in a booster housing a vacuum chamber of constant pressure, a working chamber of variable pressure and a movable wall cooperating with the working piston, and a controL valve device which is controllable by the control piston and which is formed by a control valve housing, a first and a second valve seat as well as a poppet valve coacting with the two valve seats, the movement of the movable wall, caused by a pressure difference which acts thereon, being transmitted onto the working piston.

Such a hydraulically-driven actuating device is known from the applicant's earlier application P3608699. The subject matter of the invention described therein comprises a working piston displaceably guided in the movable wall as well as a control piston sliding in the working piston and carrying a vacuum valve seat on its end close to the poppet valve. This arrangement is preferabLy so chosen that the movement of the working piston and the control piston takes place in opposing directions upon the actuation of the vacuum power booster, and that the reaction force proportional to the hydraulic output pressure is generated by an elastic reaction element concentrically arranged around the control piston between the control piston and the movable wall.

However, what has to be regarded as less advantageous in the known actuating device is its complicated structure which inevitably involves a large amount of working effort and costs. Another drawback is the necessity of sealing a plurality of movable parts in relation to one another, unfavourable friction conditions in the entire system ensuing therefrom. Likewise the adjustment of the desired gradient of the functional characteristics is rather complicated. Other shortcomings are the comparatively slow release action of the known actuating device which is particularly inexpedient in the event of the device being used as a clutch actuating device, and the blind-end bore confined in the working piston by the control piston, which causes considerable difficulties when bleeding the hydraulic system.

Therefore, it is an object of the instant invention to devise a hydraulically driven actuating device of the kind referred to, wherein the abovementioned shortcomings are largely avoided and the design of which can be simplified, while a highdegree reliability of operation is maintained.

According to the invention, there is provided a hydraulically driven actuating device for an automotive vehicle, in particular for the actuation of a hydraulic brake system and/or a hydraulic clutch, of the kind having a hydraulic inlet port, an auxiliary generating cylinder by means of whose actuating-pedal-operable working piston pressure medium is supplied to a slave cylinder actuating a brake member andlor a clutch release yoke, an axially displaceable control piston arranged coaxially in relation to the working piston, as well as a pneumatic vacuum power booster comprising in a booster housing a vacuum chamber of constant pressure, a working chamber of variable pressure and a movable wall cooperating with the working piston, and a control valve device which is controllable by the control piston and which is formed by a control valve housing, a first and a second valve seat as well as a poppet valve coacting with the two valve seats, the movement of the movable wall, caused by a pressure difference which acts thereon, being transmitted onto the working piston, characterised in that the movable wall is coupled directly with the working piston, in that the control valve housing is arranged stationarily in the booster housing separately from the movable wall, with the control piston being of tube-shaped configuration and being guided on the working piston in sealed relationship thereto, and in that the supply of the pressure medium required for driving the actuating device takes place in the longitudinal axis of the device.

Hence, there is attained a hydraulically-driven actuating device for an automotive vehicle wherein a considerable improvement of the response and reLease behaviour of the vacuum power booster is accomplished. Since, after the response of the vacuum power booster, contact between the control piston and the poppet valve is not maintained, there will not be any force component resulting from the pressure difference that acts upon the poppet valve, so that a more pleasant pedal feeling is imparted to the driver. Moreover, quicker reduction of the pressure prevailing in the auxiliary generating cylinder is permitted, since the working piston is entrained by the movable wall to assume its rest position when the vacuum power booster is released.

By arranging the supply of the hydraulic pressure medium in the longitudinal axis of the device, the latter's bleeding ability is markedly improved.

An improvement of the subject matter of this invention provides that the control valve housing is integrated in the booster housing half remote from the auxiliary generating cylinder. This results in a particularly compact structure.

According to another feature of this invention, the connection between the vacuum chamber and the working chamber is established via a plurality of vacuum channels which are arranged in a symmetrically distributed fashion in the booster housing half remote from the auxiliary generating cylinder as well as via an atmosphere passage contained in the control valve housing. Thereby, still further simplification of the inventive subject matter is achieved.

The present invention is of special significance for the actuation of a hydraulic clutch which requires low pedal forces, whilst at the same time upon decline of the actuating force an amount of pedal resetting force as high as possible is needed to be produced. This demand is met by the invention in an excellent fashion in that the control of the hydraulic pressure which is to be developed in the auxiliary generating cylinder will be performed on attainment of the operating point of the vacuum power booster, the actuating force remaining the same, exclusively in dependence upon the stroke covered by the working piston and/or the volume of pressure medium required for the actuation of the vacuum power booster.

In order to transmit the reaction force proportional to the hydraulic output pressure onto the brake pedal when using the subject matter of this invention for the actuation of a hydraulic brake system, the present invention may provide that the control piston comprises an axial extension to which a plate is secured, the plate together with a diaphragm abutting on it sealingly bounding a vacuum chamber designed at the control valve housing and communicating with the vacuum channels. This measure serves to regulate precisely the brake force when the brake pedal is depressed. Moreover, the variation of the plate's surface permits variation of the transmission ratio (gradient of the characteristic curve) of the device in an advantageously simple manner.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, wherein corresponding parts have been assigned like reference numerals.

In the drawings, Figure 1 is a schematic view of an actuating device for the actuation of a hydraulic clutch with a hydraulically driven vacuum power booster; Figure 2 is an embodiment of the vacuum power booster according to the invention in axial cross section; Figure 3 is a partial cross-section of another embodiment of a vacuum power booster suitable for actuation of a hydraulic brake system, and Figure 4 is a graph representing the dependency of the outlet pressure of the actuating device on its inlet pressure that is proportional to the actuating force.

In Figure 1, reference numeral 100 designates a clutch pedal, whose lever 101 is pivotably supported on a bolt 102 and is coupled by means of a piston rod 111 with a piston 104 arranged in a generating cylinder 103. An essential part of the invention is formed by a hydraulically driven boosting device 110 which is composed of an auxiliary generating cylinder 1 as well as a pneumatic vacuum power booster 2. The boosting device 110 communicates via a hydraulic line 105 with the generating cylinder 103, on the one hand, and via a hydraulic line 106 with a clutch slave cylinder 107, on the other hand.

The latter has a piston 108 which by means of a piston rod 109 is in connection with a release fork of the clutch which is not illustrated in the drawing.

The structure of the boosting device 110 schematically shown in Figure 1 is explained in greater detail in a first embodiment which is shown in Figure 2. As has already been mentioned, the boosting device is composed of a vacuum power booster 2 as well as an auxiliary generating cylinder 1 which is flanged thereto and which, by means of setbolts 44 and locknuts 43, is fastened to a booster housing 21 comprising two booster housing halves 21a,b.

In a cylindrical bore 10 of the auxiliary generating cylinder 1, a working piston 4 is slidably guided whose right-hand end shown in the drawing projects into the interior of the booster housing 21. At its end remote from power booster 2, working piston 4 has an annular surface on which a compression spring 13 is supported which biasses working piston 4 in the inactive position in the direction of vacuum power booster 2. Working piston 4 is provided with a central valve 8 which is formed by a valve member 35, a compression spring 34 biassing valve member 35 in the closing direction as well as a holder 33.Valve member 35 which cooperates with a seat 36 designed on working piston 4 is secured to a valve pin 32 which extends through an axial bore 37 of working piston 4 and the purpose of which will be explained more closely in connection with the function of the clutch-actuating device. At its left-hand end, as seen in the drawing, the auxiliary generating cylinder 1 contains a threaded bore 14 which serves to receive a connection from the hydraulic line 106 shown in Figure 1.

Working piston 4 which, together with the end wall of bore 10, confines a pressure chamber 49 is sealed relative to bore 10 by means of a sealing sleeve 38 which is arranged in an annular groove on the surface of the piston 4. Axial bore 37 accommodating valve pin 32 is succeeded in the midportion of working piston 4 by another axial bore 15 which, via radial channels 16, communicates with an annular chamber 11 of auxiliary generating cylinder 1 which latter is in communication with the hydraulic line 105 shown in Figure 1 as well as with the generating cylinder 103.

Annular chamber 11 houses a retaining ring 18 which is slid onto working piston 4 and cooperates with a cross pin 12 fixed to the valve pin 32 and thereby actuating central valve 8.

At the right-hand end of the auxiliary generating cylinder 1, as seen in the drawing, working piston 4 bears with a radial annular collar against a stop washer 41 which latter is secured in position by a bushing 48 which is secured by a guard ring 59 in a larger-diameter portion 55 of bore 10 and which is sealed relative to portion 55 by means of an O-ring 25. Simultaneously, bushing 48 serves to guide working piston 4 axially and is sealed relative thereto by means of a sealing sleeve 31 which is arranged in a radial recess of bushing 48.

At the right-hand end of working piston 4, a control piston 3 is coaxially slidably arranged on the outside surface of piston 4 and is sealed relative thereto by a groove ring 20. In this arrangement, control piston 3 forms part of a control valve device, the purpose of which will be explained hereinbelow.

Booster housing 21 of the vacuum power booster 2 coacting with the auxiliary generating cylinder 1 is subdivided into a vacuum chamber 23 and a working chamber 24 by an axially movable wall 22. The axially movable wall 22 is composed of a diaphragm plate 26 as well as of a flexible rolling diaphragm 27 which is buttoned into diaphragm plate 26 and which provides for sealing in the area between the outer periphery of diaphragm plate 26 and booster housing 21. Vacuum chamber 23 is in communication with an appropriate vacuum source, e.g. the intake pipe of an internal-combustion engine or a vacuum pump, via a non-illustrated non-return valve.In this embodiment, diaphragm plate 26 is fastened directly to working piston 4 and is fixed in position by means of a guard ring 9, the pneumatic sealing of the two chambers 23,24 in relation to each other being effected by a ring seal 7 at the point the diaphragm plate 26 is fastened. In order to control the pressure difference prevailing at movable wall 22, there is provided the abovementioned control valve device which is accommodated in a control valve housing 6, the latter being integrated in the booster housing half 21b remote from the auxiliary generating cylinder 1 separately of movable wall 22. The control valve device of vacuum booster 2 comprises a radially outwardly disposed sealing seat 29 designed on control valve housing 6, a radially inwardly disposed sealing seat 28 designed on control piston 3 as well as a poppet valve 30.In the arrangement's inactive position, the sealing surface of poppet valve 30 abuts on the radially inwardly disposed sealing seat 28 and is biassed in the direction of this sealing seat 28 by a compression spring 40 which, with its other end, is supported on a pressure member 5 closing control valve housing 6. The connection between vacuum chamber 23 and working chamber 24 is effected by means of a plurality of vacuum channels 50 which are designed in the booster housing half 21b remote from the auxiliary generating cylinder 1 and which communicate with an atmosphere passage 51 contained in control valve housing 6. This passage, in the arrangement's inactive position, permits the vacuum prevailing in vacuum chamber 23 to propagate into working chamber 24. Moreover, control valve housing 6 contains at its end close to the working chamber a cylinder-shaped recess 52 which is in communication with working chamber 24, on the one hand, and which, on the other hand, receives a compression spring 54 that biasses control piston 3 in the direction of poppet valve 30.

As has already been mentioned, control valve housing 6 is closed to the outside by closure member 5. At the same time, the closure member 5 has formed therein a hydraulic inlet port 17 which continues into a pressure medium channel 63 which extends axially in an extension 62 of closure member 5. The extension 62 forms an additional guiding surface for control piston 3 and is sealed in relation thereto by means of an annular seal 56. A poppet valve guide 53 is supoported on the left-hand end surface of closure member 5, as seen in the drawing. Additionally the closure member 5 carries an air filter 19 which is held on the surface of closure member 5 by means of a holding cap 61.The holding cap 61 is furnished with several air intake openings 46 which, together with an intake channel 42 provided in closure member 5, permits atmospheric air to enter into the interior of control valve housing 6.

Figure 3 shows a partial cross-section of a vacuum power booster which can be used in another embodiment of an actuating device for the actuation of a hydraulic brake system, wherein all parts corresponding to those of Figure 2 have have been assigned like reference numerals. In this embodiment, control piston 3 comprises an axial extension 45 on which a plate 47 is fastened. The plate 47 confines together with a diaphragm 39 abutting on it a vacuum chamber 58 which is designed at control housing 6 and which is in communication with one of the vacuum channels 50 via a vacuum channel 60. The interior of control valve housing 6 is sealed relative to vacuum chamber 58 by means of an O-ring 57 and communicates with working chamber 24 through a radial channel 51a.As a result, plate 47 can be subjected to the pressure difference prevailing at the movable wall 22, a transmission mechanism being formed thereby which serves to effect hydraulic feedback.

The mode of function of a hydraulically driven actuating device according to the invention will now be explained in connection with Figures 1,2 and 4 in particular. In doing so, the arrangement's inactive position is first considered as shown in Figure 2.

As has already been mentioned, vacuum chamber 23 of vacuum power booster 2 is connected to a suitable vacuum source. The vacuum generated by this vacuum source propagates in the inactive position shown via the vacuum channels 50 in the rear booster housing half 21b, via the open radially outwardly disposed sealing seat 29, via cylindrical recess 52 and atmosphere passage 51 in control valve housing 6 into the working chamber 24 so that vacuum is prevailing in both chambers 23,24 in the inactive position.

Upon actuation of the device by depressing the clutch pedal 100 (Figure 1), hydraulic pressure is generated in the generating cylinder 103 which can propagate through line 105 connected to inlet port 17, through pressure medium channel 63, axial bores 15 and 37 in working piston 4 and through the open central valve 8 in the direction of clutch slave cylinder 107. Upon further increase of the hydraulic pressure, the force of compression spring 54 is overcome, and control piston 3 in Figure 2 is displaced to the left. As a result, poppet valve 30 will first move into abutment on the radially outwardly disposed sealing seat 29, the connection between the two chambers 23,24 being thereby interrupted. Further pressure increase in the interior of control piston 3 is followed by further movement of the latter to the left.Subsequently, sealing seat 28 on control piston 3 is lifted by poppet valve 30 in opposition to the effect of the spring force of compression spring 54, in consequence whereof working chamber 24 becomes connected to the atmosphere through the atmosphere passage 51, the interior of control valve housing 6, atmosphere intake channel 42 in closure member 5 as well as air filter 19 and air intake openings 46 in holding cap 61 (operating point A of the vacuum power booster 2, see Figure 4).

Working piston 4 is moved to the left by the actuating force introduced through hydraulic line 105 and by the auxiliary force acting upon the movable wall 22 due to the pressure difference between the vacuum and working chambers 23,24. In consequence thereof, central valve 8 closes under the effect of compression spring 34, and axial bore 37 is isolated from pressure chamber 49.

Simultaneously, boosted pressure is generated in pressure chamber 49 of auxiliary generating cylinder 1 which pressure is applied to piston 108 of clutch slave cylinder 107. The movement of working piston 4 to the left causes expansion of the interior of control piston 3 so that the hydraulic pressure prevailing therein is decreased. This also causes decline of the force acting upon control piston 3 so that the sealing seat 28 on control piston 3 closes under the effect of the spring force of compression spring 54.

This interrupts further supply of atmospheric air into working c-hamber 24 so that further pressure rise in the auxiliary generating cylinder 1 is prevented and the vacuum power booster 2 persists in its actuating position. Further delivery of atmospheric air into working chamber 24 is effected in that pressure medium is replenished through line 105 until the inlet pressure corresponding to the operating point A (Figure 4) has been reached again.

Thus, the device becomes controllable exclusively by the metered inlet volume (pedal travel), while its operating ability will be exhausted at the moment the full atmospheric pressure is reached in working chamber 24 (point of maximum boosting B in Figure 4).

During the release action (reduction of the actuating force), control piston 3 will be displaced to the left under the effect of compression spring 54 as soon as the hydraulic pressure prevailing in its interior has attained the value corresponding to point C (Figure 4), in consequence whereof poppet valve 30 will lift off sealing seat 29.

Accordingly, the pressure in the interior of control piston 3 will likewise decrease by virtue of the pedal resetting movement corresponding to the distance C-D (Figure 4). In point D, central valve 8 will open (working piston 4 moves into abutment on stop washer 41) so that further decrease of the hydraulic pressure takes place in the ratio 1 : 1.

As can be taken from the description of a hydraulically controlled clutch actuating device according to the invention, the control is performed exclusively in dependence on the distance covered by the actuating pedal, the dependence between the actuating device's outlet pressure and its inlet pressure being solely variable by variation of the spring force of compression spring 54 biassing control piston 3.

Claims

CLAIMS:

1. A hydraulically driven actuating device for an automotive vehicle, in particular for the actuation of a hydraulic brake system and/or a hydraulic clutch, of the kind having a hydraulic inlet port, an auxiliary generating cylinder by means of whose actuating-pedal-operable working piston pressure medium is supplied to a slave cylinder actuating a brake member and/or a clutch release yoke, an axially displaceable control piston arranged coaxially in relation to the working piston, as well as a pneumatic vacuum power booster comprising in a booster housing a vacuum chamber of constant pressure, a working chamber of variable pressure and a movable wall cooperating with the working piston, and a control valve device which is controllable by the control piston and which is formed by a control valve housing, a first and a second valve seat as well as a poppet valve coacting with the two valve seats, the movement of the movable wall, caused by a pressure difference which acts thereon, being transmitted onto the working piston, characterised in that the movable wall (22) is coupled directly with the working piston (4), in that the control valve housing (6) is arranged stationarily in the booster housing (21) separately from the movable wall (22), with the control piston (3) being of tube-shaped configuration and being guided on the working piston (4) in sealed relationship thereto, and in that the supply of the pressure medium required for driving the actuating device takes place in the longitudinal axis of the device.

2. A hydraulically driven actuating device as claimed in claim 1, characterised in that the control valve housing (6) is integrated in the booster housing half (21b) remote from the auxiliary generating cylinder (1).

3. A hydraulically driven actuating device as claimed in claim 1, characterised in that, at its edge remote from the sealing surface, the poppet valve (30) is clamped in between the booster housing half (21b) remote from the auxiliary generating cylinder (1) and a closure member (5) closing the control valve housing (6) towards the outside.

4. A hydraulically driven actuating device as claimed in any one of claims 1 to 3, characterised in that a hydraulic inlet port (17) is provided in the closure member (5) and continues into a pressure-medium channel (63) which extends axially in a cylinder-shaped extension (62) of the closure member (5), the control piston (3) being additionally guided on the surface of the extension (62) in sealed relationship thereto.

5. A hydraulically driven actuating device as claimed in any one of claims 1 to 4, characterised in that the connection between the vacuum chamber (23) and the working chamber (24) is established via a plurality of vacuum channels (50) which are arranged in a symmetrically distributed fashion in the booster housing half (21b) remote from the auxiliary generating cylinder (1) as well as via an atmosphere passage (51) contained in the control valve housing (6).

6. A hydraulically driven actuating device as claimed in any one of claims 1 to 5, for the actuation of a hydraulic clutch, characterised in that the control of the hydraulic pressure which is to be developed in the auxiliary generating cylinder (1) will be performed on attainment of the operating point of the vacuum power booster (2), the actuating force remaining the same, exclusively in dependence upon the stroke covered by the working piston (4) and/or the volume of pressure medium required for the actuation of the vacuum power booster (2).

7. A hydraulically driven actuating device as claimed in any one of claims 1 to 5, for the actuation of a hydraulic brake system, characterised in that the control piston (3) comprises an axial extension (45) to which a plate (47) is secured, the plate together with a diaphragm (39) abutting on it sealingly bounding a vacuum chamber (58) at the control valve housing (6) and communicating with the vacuum channels (50).

8. A hydraulically driven actuating device as claimed in claim 7, characterised in that the control piston (3) is guided in the control valve housing (6) and sealed by means of an annular seaL (56).

9. A hydraulically driven actuating device as claimed in any one of claims 1 to 8, characterised in that the poppet valve (30) in the inactive position abuts with its sealing surface on the second valve seat (28) formed on the control piston (3) and is biassed in the actuating direction of the control piston (3).

10. A hydraulically driven actuating device as claimed in any one of the preceding claims, characterised in that arranged at the closure member (5) is an air filter (19) which is held by means of a holding cap (61) containing air intake openings (46).

11. A hydraulically driven actuating device as claimed in any one of the preceding claims, characterised in that there is provided a poppet valve guide (53) which is supproted on the end surface of the closure member (5) facing the poppet valve (30).

12. A hydraulically driven actuating device for an automotive vehicle substantially as described with reference to the accompanying drawings.