GB2202295A

GB2202295A - Pneumatic vacuum power booster for vehicle clutch or brake hydraulic systems

Info

Publication number: GB2202295A
Application number: GB08800682A
Authority: GB
Inventors: Wilfried Wagner; Lothar Schiel
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1987-01-15
Filing date: 1988-01-13
Publication date: 1988-09-21
Anticipated expiration: 2008-01-13
Also published as: DE3700979C2; FR2609675A1; JPS63180554A; FR2609675B1; GB2202295B; DE3700979A1; JP2661695B2; GB8800682D0

Abstract

A pneumatic vacuum power booster (2) has in its booster housing a vacuum chamber (23) of constant pressure, a working chamber (24) of variable pressure and a movable wall (22) cooperating with a working piston (4), a control valve device which is controllable by a control piston (3) and is formed by a first (29) and a second (28) valve seat as well as a poppet valve (30) coacting with the two valve seats. Movement of the movable wall (22), caused by a pressure difference which acts thereon, is transmitted onto the working piston (4). Movements of the working piston and of the control piston take place in opposite directions upon actuation of the vacuum power booster. The booster housing (21) incorporates a chamber (7) which is in permanent communication with the atmosphere and which is connectible with the working chamber (24). The poppet valve (30) in its inactive position abuts with its sealing surtace on the second valve seat (28) on the control piston (3) and is biassed in the actuating direction of control piston (3). The working piston (4) is rigidly coupled to the movable wall (22), with the control valve housing (6) being arranged within the booster housing (21). <IMAGE>

Description

HYDRAULICALLY DRIVEN ACTUATING DEVICE FOR AN AUTOMOTIVE VEHICLE The present 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 comprising an auxiliary generating cylinder by means of whose actuating-pedal-operable working piston pressure medium is supplied to a slave cylinder actuating brake members and/or a clutch release yoke, an axially displaceable control piston arranged coaxially in relation to the working piston, 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 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, and the movements of the working piston and of the control piston taking place in opposite directions upon actuation of the vacuum power booster.

Such a hydraulically driven actuating device is

known from the applicant's earlier application

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 movements of the working piston and the control piston take place in opposite directions upon 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. Another shortcoming can be seen in the comparitively 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.

Therefore, it is an object of the present invention to produce a hydraulically driven actuating device of the kind referred to, wherein the above-mentioned shortcomings are largely avoided and the design of which can be simplified, while a high degree of reliability of operation is maintained.

According to the invention in its broadest aspect 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 comprising an auxiliary generating cylinder by means of whose actuating-pedal-operable working piston pressure medium is supplied to a slave cylinder actuating brake members and/or a clutch release yoke, an axially displaceable control piston arranged coaxially in relation to the working piston, 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 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, and the movements of the working piston and of the control piston taking place in opposite directions upon actuation of the vacuum power booster, characterised in that the booster housing incorporates a chamber which is in permanent communication with the atmosphere and which is connectible with the working chamber, in that the poppet valve in its inactive position abuts with its sealing surface on the second valve seat formed on the control piston and is biassed in the actuating direction of control piston, and in that the working piston is rigidly coupled to the movable wall, with the control valve housing being arranged within the booster housing.

Hence, there is attained a hydraulically driven actuating device for an automotive vehicle wherein a considerable improvement of the release behaviour of the vacuum power booster is accomplished. Since, after 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 through the movable wall to assume its rest position when the vacuum power booster is released.

A favourable improvement of the subject matter of this invention provides that the chamber in the booster housing which is in permanent communication with the atmosphere is confined by a pleated bellows which is clamped between a booster housing half and the movable wall.

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 in an excellent fashion according to a feature - of the invention in that the control of the hydraulic pressure which is to develop in the auxiliary generating cylinder will be performed on attainment of the operating point of the vacuum power booster, with 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 an embodiment of this invention for the actuation of a hydraulic brake system, it is provided that the control piston comprises an axial extension which is sealedly guided in the movable wall and to which a plate is secured, the said plate together with a diaphragm abutting on it sealingly bounding a vacuum chamber configured in the movable wall. This measure serves to regulate precisely the brake force when the brake pedal is depressed. Moreover, the variation of the piate's surface allows the transmission ratio (gradient of the characteristic curve) of the device to be varied in an advantageously simple manner.

A particularly simple design of the reaction mechanism in accordance with an embodiment of this invention resides in that the diaphragm is designed integrally with the rolling diaphragm of the movable wall.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: 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 crosssection.

Figure 3 is a partial cross-section of a vacuum power booster suitable for actuation of a hydraulic brake system, and Figure 4 is a diagram view showing the dependence of the outlet pressure of an actuating device according to the invention 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 at 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 present invention is 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 a piston 108 in the cylinder 107 is connected by means of a piston rod 109 to 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 relation to 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 is slidably guided a working piston 4 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 and a holder 33. Valve member 35 which cooperates with a seat 36 formed on working piston 4 is secured to a valve pin 32 which extends through an axial bore 37 of working piston 4 and whose purpose will be explained more fully 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 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 on the surface of the piston. 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, via a radial threaded bore 17, is in communication, through the hydraulic line 105 shown in Figure 1, 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 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 located by a retaining ring 59 in a iarger diameter portion 55 of bore 10 and which is sealed relative to portion 55 by means of an 0-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.

In a larger-diameter portion 19 of bore 15 of working piston 4, a control piston 3 is coaxially slidably arranged and sealed by means of 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 latter is composed of a diaphragm plate 26 as well as of a flexible rolling diaphragm 27 which is attached to 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 source, via a nonreturn valve (not shown). In this embodiment, diaphragm plate 26 is formed integrally with a control valve housing 6 which is arranged within booster housing 21 and which forms a control valve device of the vacuum power booster 2 in conjunction with control piston 3, a radially inwardly disposed sealing seat 28 formed thereon, a radially outwardly disposed sealing seat 29, and a poppet valve 30.In the inactive position of the apparatus, 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 that is inserted into control valve housing 6 and, by virtue of which, rigid coupling of working piston 4 and movable wall 22 is effected.

The interior of booster housing 21 houses a chamber 7 which is connectible to working chamber 24 and is bounded by a pleated bellows 9 clamped in between the booster housing half 21a on the left (in the drawing) and movable wall 22. Chamber 7 which is in permanent communication with the surrounding atmosphere through an atmosphere intake channel 42 communicates at the same time with the annular chamber confined by poppet valve 30 through an axially extending channel 50 in pressure member 5.

At its end close to the working chamber, control valve housing 6 contains a cylinder-shaped recess 52 which, on the one hand, communicates with vacuum chamber 23 via several radial bores 51, whilst, on the other hand, it is in connection with working chamber 24 via air ducts 46 contained in the end wall 56 which closes control valve housing 6. A compression spring 54 is supported on end wall 56, on the one hand, and in a recess 53 on control piston 3, on the other hand.

Figure 3 shows a partial cross-section of a vacuum power booster which can be used in an actuating device for the actuation of a hydraulic brake system according to another embodiment of the invention, wherein all parts corresponding to those of Figure 2 have been assigned like reference numerals. In this embodiment, control piston 3 has an axial extension 45 on which a plate 47 is fastened. Plate 47 confines together with a diaphragm 39 abutting on it a vacuum chamber 58 which is designed in diaphragm plate 26 and which is in communication with vacuum chamber 23 via a vacuum channel 60. The interior of control valve housing 6 is sealed relative to vacuum chamber 58 by means of an 0-ring 57 and communicates with working chamber 24 through a radial channel 61.As a result, plate 47 can be influenced by the pressure difference prevailing at the movable wall formed by diaphragm plate 26 and diaphragm 27, a transmission mechanism being thereby formed which assists in effecting hydraulic feedback.

The mode of function of a hydraulically driven actuating device according to the invention will be explained hereinbelow in connection with Figures 1,2 and 4 in particular. In doing so, reference will be made to the inactive position of the apparatus which is 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 bores 51 in diaphragm plate 26, the open radially outwardly disposed sealing seat 29, cylindrical recess 52 and air ducts 46 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 depression of the clutch pedal 100 (Figure 1), hydraulic pressure is generated in the generating cylinder 103 which can propagate through line 105 connected to threaded bore 17, through annular chamber 11 and 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 right. 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 thus interrupted. Further pressure increase in annular chamber 11 is followed by a further movement of control piston 3 to the right.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 is connected through the axial air ducts 46, chamber 7 and atmosphere intake channel 42 with the atmosphere (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 vacuum and working chambers 23,24. In consequence thereof, central valve 8 closes under the effect of compression spring 34 and annular chamber 11 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 annular chamber 11 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 chamber 24 so that further pressure rise in the auxiliary generating cylinder 1 is prevented and the vacuum power booster 2 remains in its actuating position.

Further delivery of atmospheric air into working chamber 24 is effected in that pressure fluid 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 annular chamber 11 has attained the value corresponding to point C (Figure 4), in consequence whereof poppet valve 30 closing sealing seat 29 will lift from the latter.

Accordingly, the pressure in annular chamber 11 will likewise decrease by virtue of the pedal resetting movement corresponding to the distance C-D (Figure 4).

At 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 comprising an auxiliary generating cylinder by means of whose actuating-pedal-operable working piston pressure medium is supplied to a slave cylinder actuating brake members and/or a clutch release yoke, an axially displaceable control piston arranged coaxially in relation to the working piston, 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 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, and the movements of the working piston and of the control piston taking place in opposite directions upon actuation of the vacuum power booster, characterised in that the booster housing (21) incorporates a chamber (7) which is in permanent communication with the atmosphere and which is connectible with the working chamber (24), in that the poppet valve (30) in its 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 control piston (3), and in that the working piston (4) is rigidly coupled to the movable wall (22), with the control valve housing (6) being arranged within the booster housing (21).

2. A hydraulically driven actuating device as claimed in claim 1, characterised in that the chamber (7) in the booster housing (21) which is in permanent communication with the atmosphere is confined by a pleated bellows (9) which is clamped between a booster housing half (21a) and the movable wall (22).

3. A hydraulically driven actuating device as claimed in claim 1, characterised in that the rigid coupling between the working piston (4) and the movable wall (22) is effected by means of a pressure member (5).

4. A hydraulically driven actuating device as claimed in claim 3, characterised in that the pressure member (5) is provided with at least one axially extending channel (50) which, upon actuation of the vacuum power booster (2), connects the chamber (7) in the booster housing (21) with the working chamber (24) via several air ducts (46) axially extending in the movable wall (22).

5. A hydraulically driven actuating device as claimed in claim 3 or 4, characterised in that, at its edge remote from the sealing surface, the poppet valve (30) is clamped between the movable wall (22) and pressure member (5).

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 develop in the auxiliary generating cylinder (1) will be performed on attainment of the operating point of the vacuum power booster (2), with 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) which is sealedly guided in the movable wall (22) and to which a plate (47) is secured, the said plate together with a diaphragm (39) abutting on it sealingly bounding a vacuum chamber (58) configured in the movable wall (22).

8. An actuating device as claimed in claim 7, characterised in that the diaphragm (39) is designed integrally with the rolling diaphragm (27) of the movable wall (22).

9. An actuating device as claimed in claim 8, characterised in that the integrally designed diaphragm (39,27) contains apertures in the area of the channels (61).

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