GB2213891A

GB2213891A - Hydraulic brake system

Info

Publication number: GB2213891A
Application number: GB8900451A
Authority: GB
Inventors: Juergen Schonlau; Alfred Birkenbach
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co OHG
Priority date: 1988-01-12
Filing date: 1989-01-10
Publication date: 1989-08-23
Anticipated expiration: 2009-01-10
Also published as: GB8900451D0; GB2213891B; DE3800552A1

Description

i.Schonlau 51-22 r 1 1 1 213 891 HYDRAULIC BRAKE SYSTEM The present

invention relates to a hydraulic brake system for an automotive vehicle with pneumatic brake force boosting, with at least one master cylinder, wheel cylinders and an anti-lock control system (ABS).

The prior art includes pneumatic brake power boosters operating on the basis of pressure in excess of or below atmospheric pressure. More particularly, low-pressure brake power boosters, also termed vacuum brake power boosters, have become known which are used especially in passenger vehicles. See in this regard e.g. 'Brake Handbook of

Alfred Teves GmbH, eighth edition, Bartsch publishing house, Ottobrunn near Munich, page 88 to page 107.1 Distinctions are made between vacuum brake power boosters which are actuated mechanically, for instance by pedal force, and hydraulically actuated vacuum brake power boosters.

Vacuum brake power boosters for automotive vehicles utilise the pressure gradient between the vacuum prevailing in the intake manifold of a fourstroke engine and the atmospheric outside pressure as a power source for boosting the hydraulic pressure that is generated in the master cylinder by the driver's pedal force. In two-stroke engines or in Diesel engines, a vacuum pump driven by the engine is used which supplies the necessary vacuum 2 of e.g. 0.7 up to 0.8 bar.

It is also known from the prior art that the above-described pneumatic brake power boosters can be used in anti-lock systems (ABS).

German patent application P3728298.0 is referred to, for example.

In that application there is described a braking pressure control device, more particularly, an anti-lock control device, for a hydraulic brake system for an automotive vehicle, comprising a master cylinder with a central regulating valve interposed between the pressure chamber of the master cylinder and the filling chamber of a fastfill device, comprising several wheel cylinders, a boosting apparatus for the master cylinder, sensors for determining the wheel rotational speeds, an electronic regulator for processing the sensor signals, a modulator device for the pressure modulation in the wheel cylinders, at least one motor-driven hydraulic pump and a pressure-limiting valve for the filling chamber.

The special characteristic of the braking pressure regulating device resides in that there is provision of a by-pass line with a valve member which, by circumvention of the pressure-limiting valve, connects the filling chamber to an unpressurised chamber, preferably the supply reservoir of the brake system.

The brake power booster described in the above- mentioned German patent application is a pneumatic booster of the type described hereinabove.

Aggregates composed of a vacuum brake power booster and a master cylinder, in particular when they are combined with further components of an anti-lock system, are relatively large and bulky.

1 3 This causes problems when they are mounted into automotive vehicles. Frequently, the mounting space available for a vacuum brake power booster with tandem master cylinder and anti-lock components does not suffice. Particularly serious problems will result where there is no possibility in vehicles of directly actuating the booster by means of piston rod and brake pedal.

The following objects are to be achieved by the present invention:

The stated disadvantages of the state of the art are to be avoided. It is desired to attain increased flexibility in mounting the brake power boosters, the master cylinders and the components of anti-lock systems. Deflection of the pedal force to any other place in the engine compartment is to be rendered possible. Lost travels during actuation of the brake system are to be avoided. The individual components of the system should not cause disturbing noise during driving. The brake system should have an only small hysteresis. The location of mounting the brake power booster should be at one's choice.

Another object to be achieved lies in that comprehensive dual-circuit operation of the entire brake system is to be accomplished. That means that dual-circuit operation does not only exist in the area between the master cylinder and the wheel cylinders, but also in the area between brake pedal and, respectively, booster, on the one hand, and the master cylinder, on the other hand.

moreover, it is an object of this invention to improve the pedal feeling. A reaction force at the brake pedal during the braking operation is to furnish the driver with information about the braking operation.

4 is This invention is to enable the accomplishment of a very slim design of the master cylinder, that is to say in particular of a master cylinder into which a hydraulic booster is integrated, see in this respect the embodiment according to Figure 3 which will be described further below.

The brake system is desired to lend itself to ease of mounting into vehciles both with left-hand steering and with right-hand steering.

The position of the master cylinder in relation to the splashboard shall be at one's will. Mounting the master cylinder transversely in relation to the driving direction shall be possible as well.

According to the invention there is provided a hydraulic brake system for an automotive vehicle with pneumatic brake force boosting, with at least one master cylinder, wheel cylinders and an antilock control system (ABS), characterised in that there is provided 4 master cylinder, and a pneumatic control unit actuated by the hydraulic pressure of the master cylinder, in particular a vacuum control unit which generates a controlled pneumatic pressure, in that a pneumatic booster acted upon by the controlled pneumatic pressure, in particular a vacuum booster, is disposed which actuates a device intended for the hydraulic pressurisation of the wheel cylinders that is effected by means of an anti-lock pressure modulator, and in that pedal master cylinder, control unit and booster are arranged at separate locations.

This basic idea of the invention can be supplemented by adding to the device for pressurisation of the wheel cylinders a device which serves to generate a reaction force at the brake f 1 pedal.

The device for generating a reaction force can be actuated pneumatically. In an alternative embodiment, the device for generating a reaction force can be actuated hydraulically.

one embodiment of this invention can be devised such that the actuation of the master cylinder is performed by a translatory force generated by the booster.

As an alternative to this, it is further suggested that the actuation of the auxiliary master cylinder be effected by a hydraulic pressure generated by the booster.

In order to be able to use a hydraulic brake power booster in carrying out the invention, it is proposed that there is provision of a pneumatic booster to which the controlled pneumatic pressure is applied, more particularly a vacuum booster, which generates hydraulic pressure for a hydraulic brake power booster that is preferably disposed in the pedal master cylinder.

Another embodiment of this invention suggests that a pedal master cylinder is provided which comprises a first and a second hydraulic pressure chamber and at least one working chamber for pressurising the wheel cylinders, that the first pressure chamber is pressurisable by the pedal force applied on the brake pedal, that a control unit is arranged for which is actuatable by the hydraulic pressure in the first pressure chamber and generates a controlled pneumatic pressure, that a booster is provided which, in dependence upon the controlled pneumatic pressure, generates a controlled hydraulic pressure which latter is applied to the second hydraulic pressure chamber, that the second 1 Z 6 hydraulic pressure chamber is designed as a boosting pressure chamber which is confined by the effective cross-section of a converter piston which converts the controlled hydraulic pressure into a translatory force and indirectly or directly transmits it to at least one working piston of the master cylinder.

It is proposed in another embodiment that there is provision of a pedal master cylinder with a first and a second pressure chamber, a hydraulic pressure dependent upon the pedal force being generated in the first pressure chamber during the braking operation, while a reference pressure is prevailing in the second pressure chamber which, during the braking operation, will generate at the brake pedal a reaction force which can be felt by the driver, that a control unit is disposed which generates a controlled pneumatic pressure in dependence upon the pressure level in the first pressure chamber, that a booster is provided which is acted upon by the controlled pneumatic pressure and generates a translatory force which is transmitted onto at least one working piston of an auxiliary master cylinder by means of a push-rod element, that the auxiliary master cylinder includes at least one working chamber for generating a hydraulic pressure for application to the wheel cylinders and a pressure chamber for the reference pressure (reference pressure chamber), the reaction force at the brake pedal being dictated by the latter pressure, and that the reference pressure chamber and the second pressure chamber of the pedal master cylinder are interconnected hydraulically.

A compact design of the subject matter of this invention results from the fact that the control unit and the booster are integrated to form a 7 construction unit, that the construction unit incorporates a sensing piston element to which the controlled pneumatic pressure is applicable which indirectly or directly generates a hydraulic reference pressure which will produce during the braking operation a reaction force at the brake pedal which can be felt by the driver.

Developing this construction principle further, it can be arranged that the sensing piston comprises an especially plate-shaped end to which is applicable the controlled pneumatic pressure, preferably via a diaphragm.

This invention allows the attaining of the following advantages:

The brake system designed according to this invention can be fitted easily into the various types of cars, in particular together with components of an anti-lock system, and both in lefthand and right-hand steered vehicles. Complete dual-circuit operation starting from the brake pedal up to the wheel cylinder is accomplished.

The brake feeling, that means the reaction force at the pedal, is improved. Moreover, the initially described shortcomings of the state of the art are avoided. The advantages accomplished by this invention can be utilised both in brake systems with as well as without anti-lock control.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which:- Figures 1 and 2 show in a block diagram view two embodiments of this invention.

Figure 3 shows another embodiment with an antilock system (ABS).

Figure 4 shows a detail of -the embodiment- k 8 according to Figure 3.

Figure 5 shows a schematic view of another embodiment of this invention.

Figure 6 shows an embodiment representing a variant of the embodiment according to Figure 5.

Figure 7 shows a detail of the embodiment according to Figure 6.

Hereinbelow, the structural elements and processes necessary for the design and the mode of operation of the embodiments will be described. Further details, in particular in respect of the design and the mode of effect of vacuum brake power booster, pertinent pneumatic control units and antilock systems can be taken from the initially cited prior art.

In Figure 1, reference numeral 1 designates the brake pedal. 2 refers to the push rod which acts upon the working pistons of the master cylinder 3. 4 designates a hydraulic line which supplies the pressure generated in the master cylinder further to a pneumatic control unit 5. Line 6 is a line for the pneumatic auxliary energy, in particular for the vacuum. The pneumatic control unit generates a controlled pneumatic pressure as a function of the hydraulic pressure supplied by the pedal master cylinder. This controlled pneumatic pressure is prevailing in line 7.

Reference numeral 8 is assigned to a pneumatic booster, in particular a vacuum brake power booster or low-pressure brake power booster. The pneumatic auxiliary energy, in particular the vacuum, is delivered to pneumatic booster 8 via line 9. The pneumatic booster converts the controlled pneumatic pressure, into a translatory mechanical force at a push rod or into a controlled hydraulic pressure.

c 1 9 The line 10 illustrates both alternative effects.

Reference numeral 11 designates a device for pressurising the wheel cylinders. Predominantly, a master cylinder with working pistons and working chambers is concerned.

Reference numeral 12 designates a hydraulic line leading to the anti-lock pressure modulator 13. This anti-lock pressure modulator has a pressurefluid supply of its own whicl is assigned reference numeral 14. 16 stands for the pressure-fluid supply line.

The electronic regulator of the anti-lock system carries reference numeral 15. 17 is the electrical signal lines which lead from the electronic regulator to pressure modulator 13.

The electrical lines 17 serve to deliver output signals from the electronic regulator to solenoid valves of the pressure modulator.

Reference numeral 18 designates the entirety of all hydraulic lines leading to the wheel cylinders of the wheel brakes. One of the wheel brakes is illustrated in Figure 1, it carries reference numeral 19.

Figure 2 shows an extension of the embodiment according to Figure 1:

Beside the device 11 for pressurising the wheel cylinders, a device 20 for generating a reaction force at the brake pedal is connected after the pneumatic booster 8 in terms of effect, see line of effect 21. on the one hand, this line 21 can designate a mechanical force, see in this regard for instance the embodiment according to Figure 6. Alternatively, 21 designates a hydraulic line through which the device for generating a reaction force at the brake pedal is actuated.

Reference numeral 22 refers to the line of effect for the reaction force leading to the brake pedal.

In Figure 3, reference numeral 23 designates the brake pedal. The brake pedal operates the piston 24 in the master cylinder 25.

The right-hand portion of the master cylinder comprises a converter piston 26, a first pressure chamber (pressure chamber 27) and a second pressure chamber (booster pressure chamber 28). The left hand portion of the master cylinder 25 in Figure 3 is of conventional design. It includes a push-rod piston 29 and a floating piston 30 as well as two working chambers 31,32.

Reference numeral 33 designates the entirety of a pneumatic booster. The housing is designated by 34. The sheet-metal piston of the booster carries reference numeral 35. The piston is sealed relative to the housing by a rolling diaphragm 36.

The piston of the booster is coupled with a push rod 37. The latter actuates a working piston 38 which, upon operation of the booster, generates hydraulic pressure in working chamber 39 of the auxiliary master cylinder 40.

Reference numeral 41 designates the entirety of a pneumatic control unit. The basic component parts of this control unit are depicted schematically in Figure 4 for better illustration.

Reference numeral 42 (Figure 3) designates the entirety of the anti-lock pressure modulator. This pressure modulator comprises a number of opening and closing valves designed as solenoid valves. One of these solenoid valves is furnished with reference numeral 77. The solenoid valves are actuated by the output signals of an electronic regulator not shown.

z f i 11 This actuation serves to produce the pressure phases in the wheel cylinders of the wheel brakes which are essential for anti-lock control. These phases concern the pressure decrease, the maintaining constant of the pressure and the reincrease of the pressure.

Design and mode of operation of the anti-lock pressure modulator are discernible for instance from the prior German patent application P3728298.0 referred to hereinabove.

VL, HR, VR, HL refer to the wheel brakes front left, rear right, front right, rear left.

The supply of the anti-lock pressure modulator with pressure fluid is performed by the two pumps 43, 44 which are driven by an electric motor 45.

This electric motor is energised in the anti-lock control mode by an output signal from the electronic regulator.

Reference numerals 46,47 designate two reservoirs for pressure fluid. 48,49 are the suction lines of the pumps, 50,51 are the pressure lines of the pumps. 52,53 designate the pressure lines leading from the working chambers 31,32 of the master cylinder to the antilock pressure modulator. 54 refers to the line leading from the pressure modulator to the supply reservoirs.

Reference numerals 55,56,57 designate lines which establish a connection between the supply reservoir and the master cylinder. Line 57 constitutes a connection between the first pressure chamber 27 and the supply reservoir 47.

Reference numeral 58 refers to a vacuum line which communicates with the intake manifold of the vehicle's combustion engine. 59 is a pneumatic line containing a controlled pneumatic pressure.

i 12 The embodiment displayed in Figure 3 operates as follows:

Upon depression of the pedal, hydraulic pressure is generated in the first pressure chamber 27. Pressure fluid propagates through a line 60 into a channel 61 of the pneumatic control housing, see in this respect also Figure 4.

As can be taken from Figure 4, this -causes pressure to develop in a control cylinder 62 of control unit 41. Control piston 63 moves to the left. The shaped metal part 64 coupled to control piston 63 is pressed onto the plate-shaped seat 65. Hence the vaccum prevailing in a vacuum chamber 66 is shut off relative to a second chamber 67. 68 designates a sealing rolling diaphragm. The vacuum line 58 of Figure 3 is shown in Figure 4 as having its port in vacuum chamber 66.

Upon further movement of control piston 63 to the left. a valve member 69 of the atmospheric-air valve will lift from valve seat 70 of the atmospheric-air valve. The arrow 71 designates the intake of the atmospheric air subjected to atmospheric pressure. 72 is a filter for the atmospheric air.

A control action takes place in the area of valve member 69 and valve seat 70.

Air under atmospheric pressure flowing in from the outside is caused to assume a predetermined pressure level (vacuum level) which prevails in chamber 67.

This controlled pneumatic pressure propagates via line 59 into chamber 73 of the booster (Figure 3). Since the vacuum of the engine's intake manifold is prevailing in chamber 74 of the booster, the sheet-metal piston 45 is moved to the left.

0.

13 1 Hydraulic pressure develops in the working cylinder 39.

Pressure fluid flows via a line 75 into the booster pressure chamber 28 of the master cylinder 25. Via a push rod 76, push-rod piston 29 of the tandem master cylinder is moved to the left. In a manner known per se, pressure is built up in working chamber 32 and in working chamber 31 and is supplied through line 52,53 to the anti-lock pressure modulator 42 in the embodiment according to Figure 3.

Figure 5 shows a master cylinder 78, an auxiliary master cylinder 79 as well as a control unit 80 and a pneumatic booster 81.

The master cylinder 78 comprises a first and a second pressure chamber 82, 83. The auxiliary master cylinder 79 is of conventional construction. it comprises a push-rod piston 84 and a floating piston 85. 86,87 designate the working chambers of the auxiliary master cylinder.

When brake pedal 88 is depressed, hydraulic pressure is developed in the first pressure chamber 82. Hydraulic pressure fluid is supplied to the pneumatic control unit 80 through a line 89. This control unit generates a controlled pneumatic pressure, as has been described already in connection with the preceding embodiments. The line for this penumatic pressure is referred to by 90.

Reference numerals 91 and 92 designate vacuum lines which contain the vacuum prevailing at the intake manifold of the combustion engine. In the present case, the vacuum chamber 93 of booster 81 is connected upstream of the pneumatic control unit 80, insofar as the vacuum line is concerned.

Controlled pneumatic pressure is prevailing in 9 k 14 is a chamber 94 of the pneumatic booster. As shown. the vacuum of the intake manifold is prevailing in vacuum chamber 93. As a result of the difference in pressure, a sheet-metal piston 95 is moved to the left. Via a push rod 96, the push-rod piston 84 is moved to the left. and pressure is developed in working chambers 86,87 in a manner known per se, which pressure is supplied further to the wheel brakes 99,100 via the lines 97, 98.

Upon further depression of the pedal, pressure fluid out of the second pressure chamber 83 is delivered via a line 101 into a chamber 102 of the auxiliary master cylinder. The size of this chamber is dictated by the amount the push-rod piston 84 is displaced. Consequently, the volume of chamber 102 and, respectively, the pressure in chamber 102 represents a reference value for the continuation of braking. Because of the hydraulic connecting line 101, the same pressure as in chamber 102 is prevailing in the second pressure chamber 83 of the pedal master cylinder 78. This pressure acts upon pistons 103,104 of the pedal master cylinder and thus upon piston rod 105 and the brake pedal 88. In this way, a reaction force is exerted on the brake pedal which the driver can feel and which informs him about the progress of the braking operation.

The component parts which are designed and arranged as individual aggregates in the embodiment according to Figure 5, i.e. pneumatic booster and pneumatic control unit, are united to form one aggregate in Figure 6.

The embodiment according to Figure 6 includes in addition a device for generating a reaction force at the brake pedal which is applied directly by the controlled pneumatic pressure. This reaction force W 4 g is dependent upon the controlled pneumatic pressure in a chamber 106 of Figure 6.

A description of the control of the pneumatic pressure will follow:

Hydraulic pressure is generated by a pedal master cylinder not shown in Figure 6, which corresponds to the pedal master cylinder of Figure 5. This pressure is led via a line 107 into a pressure chamber 108. A piston 109 is moved to the left.

As can be taken from Figurs 6 and 7, the component part 110 moves to sit on the component part 111 designed as a valve seat. Thus, the vacuum of the intake manifold prevailing in a chamber 112, in a hose 113, in a channel 114, a chamber 127 and in a chamber 115 is isolated from chamber 106. Reference numeral 130 designates the vacuum line which connects vacuum chamber 112 with the intake manifold of the engine.

Hose 113 serves to connect chamber 112 under vacuum with channel 114 and thus with all chambers which are in communication with channel 114.

When piston 109 moves further to the left and after component part 110 has come to abut on edge 128, component part 111 will lift from component part 110, see Figures 6 and 7.

Now, air under atmospheric pressure propagates through a line 129, filter 116, chamber 117, the valve composed of component parts 110, 111, a chamber 131 and a channel 118 into chamber 106.

Control of the atmospheric air pressure takes place between the component parts 110,111. Therefore, controlled pneumatic pressure is prevailing in chamber 106.

owing to the difference of pressures in the 1 k 16 chambers 112 and 106, the sheet-metal piston 119 of booster 120 of the embodiment according to Figure 6 is moved to the left. The sheet-metal piston is connected to housing 126 by a rolling diaphragm 125.

Displacement of the sheet-metal piston to the left also causes push rod 121 to move to the left.

It acts upon the pistons of an auxiliary master cylinder not shown in Figure 6.

Upon brake application, as is shown, controlled pneumatic pressure is prevailing in chamber 106, whilst vacuum is prevailing in chamber 115. The consequence thereof is that a force directed to the right is exerted on a plate-shaped or mushroom-shaped sensing piston 122, which force gen6rates a pressure in hydraulic line 107. In turn, this pressure can be felt as a reaction force at the brake pedal.

Sensing piston 122 is sealed in relation to housing 123 by a rolling diaphragm 124.

The instant invention is not restricted to the described embodiments. Further connections are possible in order to achieve great flexibility in mounting the brake systems on vehicles of various types, and by exploiting the idea of this invention and its embodiments.

A A 1 17

Claims

CLAIMS:

1. A hydraulic brake system for an automotive vehicle with pneumatic brake force boosting, with at least one master cylinder. wheel cylinders and an anti-lock control system (ABS), characterised in that there is provided a master cylinder (3), and a pneumatic control unit (control unit) (5) actuated by the hydraulic pressure of the master cylinder, in particular a vacuum control unit which generates a controlled pneumatic pressure, in that a pneumatic booster (booster) (8) acted upon by the controlled pneumatic pressure, in particular a vacuum booster, is disposed which actuates a device (11) intended for the hydraulic pressurisation of the wheel cylinders that is effected by means of an antilock pressure modulator (13), and in that pedal master cylinder (3), control unit (5) and booster (8) are arranged at separate locations. (Figure 1)

2. A hydraulic brake system as claimed in claim 1, characterised in that there is provided a master cylinder (3), and a pneumatic control unit (control unit) actuated by the hydraulic pressure of the master cylinder, in particular a vacuum control unit (5) which generates a controlled pneumatic pressure, in that a pneumatic booster (booster) acted upon by the controlled pneumatic pressure, in particular a vacuum booster (8), is disposed which actuates a device (11) intended for the hydraulic pressurisation of the wheel cylinders that is effected by means of an anti-lock pressure modulator (13), and actuates a device (20) intended for generating a reaction force at the brake pedal (1). (Figure 2).

3. A hydraulic brake system as claimed in claim 1 or 2, characterised in that the device for 18 generating a reaction force is actuated pneumatically. (Figure 6).

4. A hydraulic brake system as claimed in claim 1 or 2, characterised in that the device for generating a reaction force is actuated hydraulically. (Figure 5)

5. A hydraulic brake system as claimed in claim 1 or 2, characterised in that the actuation of the device designed as an auxiliary master cylinder for pressurising the wheel cylinders is performed by a translatory force generated by the booster. (Figure 6)

6. A hydraulic brake system as claimed in claims 1 or 2, characterised in that the actuation of the device designed as an auxiliary master cylinder and meant for pressurising the wheel cylinders is performed by hydraulic pressure generated by the booster.

7. A hydraulic brake system as claimed in claim 1, characterised in that there is provided a master cylinder (25), and a pneumatic control unit (control unit) actuated by the hydraulic pressure of the master cylinder, in particular a vacuum control unit (41) which generates a controlled pneumatic pressure, and in that there is provided a pneumatic booster to which is applied the controlled pneumatic pressure, more particularly a vacuum booster (33), which generates hydraulic pressure for a hydraulic brake power booster (28,26) which is disposed in the pedal master cylinder (25).

8. A hydraulic brake system as claimed in any one of the preceding claims, characterised in that a pedal master cylinder (25) is provided which comprises a first and a second hydraulic pressure chamber and at least one working chamber for A 19 pressurising the wheel cylinders, in that the first pressure chamber (27) is pressurisable by the pedal force applied on the brake pedal, in that a control unit (41) is arranged which is actuatable by the hydraulic pressure in the first pressure chamber and which generates a controlled pneumatic pressure, in that a booster (33) is provided which, in dependence upon the controlled pneumatic pressure, generates controlled hydraulic pressure which latter is applied to the second hydraulic pressure chamber, and in that the second hydraulic pressure chamber is designed as a boosting pressure chamber (28) that is confined by the effective cross-section of a converter piston (26) which converts the controlled hydraulic pressure into a translatory force and indirectly or directly transmits it to at least one working piston (29) of the master cylinder. (Figure 3).

9. A hydraulic brake system as claimed in any one of the preceding claims, characterised in that there is provided a pedal master cylinder (78) with a first and a second pressure chamber, a hydraulic pressure dependent upon the pedal force being generated in the first pressure chamber (82) during the braking operation, while a reference pressure is prevailing in the second pressure chamber (83) which, during the braking operation, will produce at the brake pedal (88) a reaction force which can be felt by the driver, in that a control unit (80) is provided which generates a controlled pneumatic pressure in dependence upon the pressure level in the first pressure chamber (82), in that a booster (81) is provided which is acted upon by the controlled pneumatic pressure and generates a translatory force that is transmitted onto at least one working piston (84) of an auxiliary master cylinder (79) by means of a push-rod element (96), in that the auxiliary master cylinder includes at least one working chamber (86,87) for generating a hydraulic pressure for application to the wheel cylinders and a pressure chamber for the reference pressure (reference pressure chamber), the reaction force at the brake pedal being dictated by the latter pressure, and in that the reference pressure chamber (102) of the auxiliary master cylinder and the second pressure chamber (83) of the pedal master cylinder are interconnected hydraulically. (Figure 5).

10. A hydraulic brake system as claimed in any is one of the preceding claims, characterised in that the control unit and the booster are integrated to form a construction unit, in that the construction unit incorporates a sensing piston element (122) to which is applicable the controlled pneumatic pressure which indirectly or directly generates a hydraulic reference pressure that will produce during the braking operation a reaction force at the brake pedal which can be felt by the driver. (Figure 6).

11. A hydraulic brake system as claimed in claim 10, characterised in that the sensing piston (122) comprises an especially plate-shaped end to which is applicable the controlled pneumatic pressure, preferably via a diaphragm (124).

12. A hydraulic brake system substantially as described with reference to the accompanying drawings.

Publ,,d 1988 at The Patent Office. State 1-jouse. 66'71 High Holborn. London WCIR 4TP_ Further copies maybe obtained from The Patent office.

Sales Branch, St Mary Cray. Orpington, Kent BP_9 3RD Printed by Multiplex techniques Rd. St Mary Cray, Kent. Con. 1'87 tr