GB2213892A - Hydraulic brake system - Google Patents

Abstract

A hydraulic brake system for an automotive vehicle comprises a master cylinder (37), wheel cylinders, a vacuum brake power booster (2) and a control unit for generating a controlled pneumatic pressure for the vacuum brake power booster (2). The vacuum brake power booster (2) generates a controlled hydraulic pressure which serves to generate in the master cylinder (37) an operating pressure for actuating the wheel cylinders of the brake system. This operating pressure acts via a duct (35) upon a sensing piston (44) which, in turn, converts the operating pressure into a reaction force which can be felt at the brake pedal. The master cylinder and the pheumatic control unit are combined to form a construction unit and are arranged at a location separated from that & the pneumatic brake power booster. <IMAGE>

Description

HYDRAULIC BRAKE SYSTEM The present invention relates to a hydraulic brake system for an automotive vehicle with a master cylinder, wheel cylinders, a pneumatic brake power booster, a control unit for generating a controlled pneumatic pressure (pneumatic control unit) for the pneumatic brake power booster and preferably an anti-lock control system (ABS).

Pneumatic brake power boosters operating on the basis of pressure in excess of or below atmospheric pressure are known from the prior art. 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 up to page 107.' 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 the four-stroke engine and the atmospheric outside pressure as a power source for boosting the hydraulic pressure that is generated in the master cylinder by the drivers'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 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.O is referred to, for instance.

That application describes 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 fast-fill 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 this 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 abovementioned German patent application is a pneumatic booster of the type described hereinabove.

Aggregates composed of a vacuum 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. 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 in cases where there is no possibility 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 described shortcomings of the prior art are to be avoided.

A considerably smaller hysteresis of the system is to be attained. The number of the seals is to be reduced. A system is to be found which curtails manufacturing costs. In particular, the complicated vacuum brake power booster as well as the control housing for the vacuum brake power booster of the prior art are to be rendered simpler and cheaper.

It is desired to ensure that the vacuum brake power booster housing receives only its inherent compressive forces. It is the inevitable property of brake power housings that they expand in a very detrimental way upon brake application.

It is one of the objects of this invention to minimise the effect of this detrimental housing expansion on the system's functioning. Moreover, the housing for the vacuum brake power booster is to be of lighter weight and is to allow a smaller design in respect of its volume.

It is desired to achieve that the vacuum brake power booster is designed; such as to require the introduction of considerably less air in order to obtain the boosting effect. Besides, the noises in the vacuum brake power booster caused by air are to be reduced. The response time of the vacuum brake power booster is to be improved.

The objects to be achieved by this invention also cover the following: Increased flexibility in mounting the brake power boosters, the master cylinders and the components of anti-lock systems is to be attained.

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.

This invention is to enable the accomplishment of a very slim master cylinder design, and that is to say in particular of a master cylinder into which a hydraulic booster and a pneumatic control unit are integrated.

The brake system is desired to lend itself to ease of mounting into vehicles 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 one aspect of the invention there is provided a hydraulic brake system for an automotive vehicle with a master cylinder, wheel cylinders, a pneumatic brake power booster, a control unit for generating a controlled pneumatic pressure (pneumatic control unit) for the pneumatic brake power booster and preferably an anti-lock control system (ABS), characterised in that there is provision of a device which generates a reaction force by utilising the hydraulic pressure in at least one working chamber of the master cylinder, which reaction force can be felt at the brake pedal by the driver during the braking operation, in that the master cylinder, the device for generating the reaction force and the pneumatic control unit are combined to form a construction unit and are arranged at a location separated from that of the pneumatic brake power booster.

According to a further aspect of the invention there is provided a hydraulic brake system for an automotive vehicle with a master cylinder, wheel cylinders, a pneumatic brake power booster, a control unit for generating a controlled pneumatic pressure for the pneumatic brake power booster and preferably an anti-lock control system (ABS), characterised in that, in addition to the pneumatic brake power booster, a hydraulic brake power booster is provided which includes a boosting pressure chamber which, upon brake application, is subject to hydraulic boosting pressure medium that is subjected to the hydraulic pressure generated by the pneumatic brake power booster, in that the hydraulic brake power booster comprises a booster piston whose effective boosting cross-section confines the boosting pressure chamber, in that there is provision of a device (reaction force device) for generating a reaction force which can be felt at the brake pedal by the driver during braking, in that the reaction force device is a particularly pistonlike designed component part (reaction-force transmitting element) for the transmission of a translatory force which forms part of the wall of the boosting pressure chamber and which, upon brake application, is subject to hydraulic boosting pressure medium and in that the master cylinder, the hydraulic brake power booster, the device for generating the reaction force and the control unit form a construction unit which is arranged at a location different from that of the pneumatic brake power booster.

To render this basic idea of the invention more concrete, it is suggested that the master cylinder, more particularly tandem master cylinder, comprise at least one piston incorporating an internal duct whose first opening terminates into at least one working chamber of the master cylinder, that a guidance means is disposed in the area of the second opening of the duct in which a piston is sealingly guided which pertains to a device for generating a reaction force sensible at the brake pedal by the driver during braking, the piston having applied to it the pressure medium of the working chamber of the master cylinder and serving as a force simulator and/or travel simulator.

In a preffered embodiment, the internal duct of the piston accommodated in the master cylinder and the piston are furnished with a special design consisting in that the piston sealingly guided in the area of the second opening of the duct is formed and arranged such that it senses the hydraulic pressure in the working chamber of the master cylinder and, in its capacity of a sensing piston, converts it into a reaction force and indirectly or directly, especially via a piston rod, transmits it to the brake pedal during the braking operation.

A compact structure is achieved by an embodiment which arranges for the construction unit composed of master cylinder, device for generating a reaction force and pneumatic control unit also to include a hydraulic brake power booster.

A very cost-efficient embodiment of this invention is attained in that a piston is furnished in the master cylinder which fulfills the function of a booster piston and of a working piston, in that the piston comprises two effective cross-sections to which pressure medium can be applied, the first cross-section thereof being subject to hydraulic boosting pressure medium and the second crosssection being subject to the hydraulic pressure medium of the working chamber of the master cylinder.

The entire construction unit is particularly apt for being fitted on vehicles of various types owing to the fact that the master cylinder, the hydraulic booster, the device for generating a reaction force and the pneumatic control unit are arranged coaxially in relation to each other.

The object to be achieved, i.e. to obtain a design of the entire aggregate as compact as possible, is achieved among others in that the pneumatic control valve of the control unit for generating a pneumatic pressure difference for the pneumatic brake power booster is accommodated in a control housing that is located in an outside housing coupled to the master cylinder (outside housing).

In order to avoid special hose lines for delivering the controlled pneumatic pressure, it is suggested in an embodiment that at least one duct for conveying the controlled pneumatic pressure is furnished in the outside housing.

For the same reason, it is further proposed that the master cylinder and the outside housing are interconnected by flanges in such a fashion that the sealing surfaces of the flanges are designed so as to form at least one duct for the controlled pneumatic pressure.

In order to obtain a reaction force at the brake pedal which is dependent upon the pressure in the booster chamber of the hydraulic brake power booster, it is suggested as a suitable arrangement that part of the reaction-force transmitting element senses the hydraulic pressure in the boosting pressure chamber. This sensing action will then be decisive for the reaction force.

To improve the brake pedal feeling, the regulation of the brake force and of the reaction force which can be felt at the brake pedal, it is suggested further to provide for a semirigid member, in particular a rubber disc, which is inserted between the reaction-force transmitting element and one or more component parts acting directly or indirectly upon the brake pedal.

A particularly space-saving solution is achieved in that the master cylinder, the hydraulic brake power booser, the device for generating the reaction force and the control unit are located coaxially.

In developing this idea further, it can be arranged that the master cylinder incorporates the hydraulic booster as an integral component part.

It is further suggested that the booster piston and a working piston of the master cylinder form one component part.

A spatially compact embodiment is accomplished in that the master cylinder housing comprises an additional, cylindrical chamber, in that the booster piston extends in this cylindrical chamber in a sealing fashion, and in that the end member of the reaction-force transmitting element is sealingly guided in the wall of the cylindrical chamber, the said end member being of plunger-piston-type configuration.

This invention affords the following advantages: The pneumatic brake power booster housing receives but inherent compressive forces, since the vacuum brake power booster is located spatially isolated from the other components of the system.

Therefore, the expansion of the booster housing is no more of significance for the functioning of the entire system.

The booster housing can be of a very lightweight design. The volume of the housing is extremely diminished. In turn, this has as a result that only very little air must be introduced, that noises caused by air are decreased and that the response times are improved.

The pneumatic brake power boosters and control units of the state of the art necessitate a number of seals. Moreover, many types of known vacuum brake power boosters incorporate so-called rubber reaction discs. The seals and the rubber reaction disc cause an undesirable, relatively large hysteresis. Only a very small number of seals is still necessary in carrying out the present invention. Besides, one embodiment of this invention does not require a rubber reaction disc, which has as a consequence that the hysteresis of the entire system has become substantially smaller.

Yet a small hysterises affords an improved mode of function of the complete brake system.

Further, very simple types of construction for the vacuum boosters and control units have been found which are very complicated in accordance with the prior art.

The brake system according to this invention can be fitted easily into types of cars, in particular together with components of an anti-lock system, and both in left-hand 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.

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 by way of example with reference to the accompanying drawings, in which: Figure 1 shows the arrangement of the individual components of a first embodiment in relation to each other as well as details of said component, Figure 2 shows, the arrangement of the individual aggregates of a second embodiment as well as details of the individual aggregates.

Figure 3 shows a detail of Figure 2.

Hereinbelow, the structural elements and processes necessary for the design and mode of operation of the embodiment will be described.

Further details in respect of the design and the mode of effect can be taken from the initially cited prior art.

In Figure 1 is an aggregate which, in its entirety, is designated by reference numeral 1, and a schematically illustrated pneumatic brake power booster 2 which, in the present embodiment, is designed as a vacuum brake power booster or lowpressure brake power booster.

Reference numeral 3 designates a vacuum line which supplies vacuum from the intake manifold of the combustion engine of the vehicle to the pneumatic brake power booster 2 and to the aggregate 1 which will be described in greater detail hereinbelow.

Reference numeral 4 stands for the line for the controlled pneumatic pressure. Line 5 conveys controlled hydraulic boosting pressure. Lines 6,7 refer to the hydraulic pressure lines to the wheel cylinders.

When the system according to the invention is used in connection with an anti-lock device, the pressure lines 6,7 lead to a pressure modulator which is not shown in the drawing.

This pressure modulator modulates the pressure in the wheel cylinders of the anti-lock apparatus in order to perform the pressure phases necessary for anti-lock control such as pressure decrease, maintaining the pressure constant and pressure reincrease.

Reference numerals 8,9 designate lines for the pressure medium which lead to the supply reservoir.

The mode of operation of the pneumatic control unit will be described hereinbelow.

Upon depression of the brake pedal, a piston rod 10 moves to the left. As can be gathered from the Figure, a compression spring 11 is provided which is supported on a step 12 of piston rod 10, on the one hand, and on a valve member 13, on the other hand. Valve member 13 moves to seat on a valve seat 14. Thus, the vacuum of the intake manifold prevailing in a chamber 15, a duct 16 and an annular chamber 17 is isolated from a chamber 18.

Upon further movement of piston rod 10 to the left and after component part 13 has moved into abutment on an edge 19, valve seat 14 will lift from valve member 13.

Consequently, control of the air pressure is performed between the component parts 13 and 14 of a so-called "vacuum control valve".

Air under controlled pressure can now propogate into chamer 18, chamber 18 together with a duct 23, a duct 24, a duct 25 and line 4 convey controlled pneumatic pressure.

The pneumatic brake power booster's mode of operation is described as follows: A vacuum brake power booster of conventional type of construction is involved which lacks the mechanical or hydraulical actuating member and which is equipped with an auxiliary master cylinder 28.

Caused by the difference of the pressures in chambers 26 and 27, a force directed to the left is exerted on the sheet-metal piston 29. The latter is displaced to the left.

Displacement of the sheet-metal piston to the left causes a push rod 30 likewise to move to the left. It acts upon a piston 31 of the auxiliary master cylinder 28.

It will be apparent from the actions described above that hydraulic pressure is built up in a working chamer 32 of the auxiliary master cylinder 28 which is a function of the difference of the pressures in chambers 27,26 of the pneumatic booster.

The mode of operation of the hydraulic booster will now be described.

The essential component parts of the booster are a boosting pressure chamber 33 and a booster piston 34 which latter is the right-hand part of a piston 62.

As is shown, there is a hydraulic connection between working chamber 32 of the auxiliary master cylinder 28 and pressure chamber 33 of the booster, namely, via pressure line 5.

With the hydraulic boosting pressure increasing booster piston 62 and booster piston 34 will be displaced to the left. Piston 62 contains an internal duct 35. The left-hand portion of piston 62 is designed as a working piston 36 of the master cylinder which latter is assigned reference numeral 37 in its entirety.

Reference numeral 38 designates a step or an annular surface which represents the hydraulically effective cross-section of booster piston 34.

When controlled hydraulic boosting pressure enters booster chamber 33 via line 5 and ducts 39, 40, the annular surface and the effective cross section 38 of the booster piston is acted on by hydraulic boosting pressure piston 62 and, respectively, booster piston 34 is displaced to the left.

Hereinbelow follows the description of the mode of operation of the master cylinder.

As is apparent from the Figure, the master cylinder's structure differs from the conventional structure of a master cylinder.

In the present case brake fluid is suppled out of the non-illustrated supply reservoir into a working chamber 49 via line 8 and ducts 46,47 and the central valve which, as a whole, is referred to as 48. This is the situation prevailing when the brake is not applied.

When the brake is applied, the central valve closes the connection to the supply reservoir, thereby allowing pressure to develop in working chamber 49.

A central valve 50 operates in the floating working piston 55 in a corresponding manner. When the brake is not applied, brake fluid flows out of the supply reservoir via line 9, via a duct 52, an annular chamber 53 and via ducts 51,54, through central valve 50 into working chamber 41. Central valve 50 will be closed upon brake application so that pressure may develop in working chamber 41.

Upon depression of the brake pedal, piston rod 21 is displaced to the left, and the pneumatic control unit performs its function. The pneumatic brake power booster generates a controlled hydraulic pressure which is delivered into boosting pressure chamber 33. The combined booster piston/working piston 34,36 is shifted to the left due to the effect of the hydraulic boosting pressure in the boosting pressure chamber. Working piston 36 has a hydraulically effective cross-section 61, that means, pressure in dependence upon the pressure level in booster chamber 33 is built up in working chamber 41. An intermediate piston 55 is displaced to the left due to the pressure build-up in working chamber 41. Pressure develops likewise in working chamber 49. The wheel cylinders are subjected to pressure via pressure lines 6,7.

Hereinafter follows the description of the mode of operation of the device for generating a reaction force which is sensible at the brake pedal by the driver during the braking operation: The extreme right-hand part of extension 43 of booster piston 34 is designed as a cylinder 42 for a sensing piston 44.

That is to say, cylinder 42 and sensing piston 44 form a cylinder-and-piston assembly which senses the pressure prevailing in duct 35 and converts it into a translatory force directed to the right which occurs at sensing piston 44.

Prevailing in duct 35 is the pressure of working chamber 41, since duct 35 and working chamber 41 are in hydraulic communication through bore 45.

The pressure in cylinder 42 which is identical with the pressure in working chamber 41 is an indication that braking is being continued. As is described, this pressure is converted by the sensing piston 44 movably arranged in cylindrical guidance means 60 into a force which acts in the direction to the right, that it to say, upon piston rod 10. The latter transmits this force as a reaction force onto the brake pedal. The effect of the force at the brake pedal resulting therefrom furnishes the driver with information about the braking operation. Thus, the sensing piston performs the function of a force simulator or travel simulator.

As can be seen from the Figure, the basic idea of this invention provides a very compact type of construction of aggregate 1.

This is achieved owing to the constructive arrangement described in the following: The left hand part of the aggregate comprises the entire master cylinder. The function of the hydraulic booster is performed by single components which are located in the master cylinder and which are parts of the master cylinder, whereby space is economised. Coupled to the master cylinder via flanges 56,57 is an outside housing 58 which, in turn, accommodates a control housing 59 with the individual component parts of the pneumatic control unit and the device for generating a reaction force.

Flange 57 includes a recess which, together with flange 56, forms a duct 25 for the controlled pneumatic pressure. Hence it follows that no separate structural element and no separate space is required for this duct.

In Figure 2, reference numeral 101 designates an aggregate which is composed of a master cylinder 118, a device for generating a reaction force which can be felt at the brake pedal by the driver during braking, as well as a control unit.

Reference numeral 102 designates a pneumatic brake power booster consisting of a sheet-metal housing 103 and a hydraulic piston-and-cylinder assembly 104 which is also termed as 'auxiliary master cylinder'. 105 is a supply reservoir for pressure fluid.

By means of a control unit which, in its entirety, is referred to by 106, a controlled pressure below atmospheric pressure is generated which is delivered via a line 107 into a chamber 108 of the pneumatic booster. 109 and 110 designate the lines for this pressure below atmospheric pressure which is referred to as "vacuum" in the language of brake experts.

It can be gathered from Figure 2 that the port, i.e. line 110, for the vacuum, vacuum chamber 111 of the pneumatic booster, vacuum line 109 as well as chamber 112 of control unit 106, which chamber is subject to vacuum, are inserted in series in terms of connection schemes. That is to say, different pneumatic pressure levels exist in the chambers 111 and 108 of the pneumatic booster 102.

Reference numeral 113 is assigned to a hydraulic pressure line which connects the pressure chamber 114 of the auxiliary master cylinder 104 to the booster chamber 115 of the master cylinder.

Controlled hydraulic boosting pressure is prevailing in chambers 114 and 115. The magnitude of the hydraulic pressure is a function of the difference between the pneumatic pressures in chambers 111, 108 of the pneumatic booster 102.

Supply reservoir 105 connects to the master cylinder 118 through lines 116,117. Line 119 establishes a connection between supply reservoir 105 and piston-and-cylinder assembly 104.

Reference numerals 120,121 designate pressure lines which provide communication between the working chambers 122, 123 of master cylinder 118 and the non-illustrated wheel cylinders of the vehicle.

If the brake system is equipped with an antilock device, the pressure lines 120,121 lead to a pressure modulator of the anti-lock system. This pressure modulator modulates in the anti-lock control mode the pressure in the wheel cylinders, see in this respect the initially mentioned German patent application 3728298.0 pertaining to the state of the art.

The mode of operation of the control unit will be described hereinbelow.

Upon depression of brake pedal 124, piston rod 125 moves to the left. As can be gathered from Figures 2 and 3, a compression spring 126 is provided which is supported on a step 127 of piston rod 125, on the one hand, and on a valve member 128, on the other hand, see especially Figure 3. As is discernible from Figures 2 and 3, more particularly from Figure 3, valve member 128 moves t sit on a valve seat 129. Thus, the vacuum of the intake manifold prevailing in chamber 112 is isolated from chamber 130. Chambers 112 and 130 are separated from each other by a rolling diaphragm 151.

Upon further movement of piston 125 to the left and after valve member 128 has moved into abutment on an edge 131, valve seat 129 will lift from valve member 128.

Now air under atmospheric pressure can propogate via the line which is illustrated as arrow 132 in Figure 2, via a filter 133, a chamber 134, the valve composed of the component parts 128,129 (see Figure 3), a chamber 135, channel 136 and line 107 into chamber 108 of the vacuum brake power booster 102. That is to say, line 107 contains controlled pneumatic pressure.

Consequently, control of the air pressure is perfomed between the component parts 128 and 129 of a so-called "vacuum control valve". Controlled pneumatic pressure is prevailing in chamber 108 of the vacuum brake power booster.

The pneumatic brake power booster is described as follows: Due to the difference of the pressures in chambers 108 and 111, a force directed to the left is exerted on diaphragm plate 137. The latter is displaced to the left. Diaphragm plate 137 is coupled to housing 103 by means of rolling diaphragm 138.

Displacement of the diaphragm plate to the left causes a push rod 139 likewise to move to the left.

It acts upon a piston 140 of the auxiliary master cylinder 104.

It becomes apparent from the actions described hereinabove that hydraulic pressure is built up in working chamber 114 of the auxiliary master cylinder 104 which is a function of the difference of the pressures in chambers 111, 108 of the pneumatic booster.

Description of the mode of operation of the hydraulic booster follows hereinbelow.

The essential component parts of the booster are a boosting pressure chamber 115 and a booster piston 141.

As is depicted, there is a hydraulic connection between working chamber 114 of the auxiliary master cylinder 104 and pressure chamber 115 of the booster, namely, via pressure line 109.

With the boosting pressure increasing, booster piston 141 will be displaced to the left. At the same time, a force is exerted on the effective cross-section of end portion 142 of the reactionforce transmitting element 143 which force is dependent upon the pressure level in booster chamber 115. The end 142 of the reaction-force transmitting element, which end is close to the master cylinder, can be designed as a plunger piston and would then extend into booster chamber 115 and act as a plunger piston. The piston-like end portion 142 is sealedly guided in the bottom of the master cylinder housing.

The seal is referred to by 145.

The device for generating a reaction force will be described in the following: The hydraulic pressure in the boosting pressure chamber 115 which acts upon the piston-shaped end portion 142 of the reaction-force transmitting element 143 is converted into a force component directed to the right which becomes effective at the right-hand end of the reaction-force transmitting element which is designed like a plate.

This reaction force acts upon a rubber disc 146.

Upon depression of the brake pedal, a piston 147 is moved to the left by piston rod 125. The pedal force is applied onto rubber disc 146 via an intermediate member 148.

Simultaneously, the above-described reaction force acts upon the rubber disc from the left to the right. The driver senses this reaction force during braking. It represents for him a sensible information about the braking operation.

The left-hand part of the aggregate 101 displayed below in Figure 2 comprises a tandem master cylinder 118. The mode of function of this tandem master cylinder is of conventional type: The tandem master cylinder has two working pistons 149,150 as well as two pressure chambers 122, 123.

The working piston 150 arranged on the brake pedal side forms together with booster piston 141 one joint component part. When boosting pressure develops in boosting pressure chamber 115, the combined booster piston/working piston 150, 141 is displaced to the left. Pressure develops in working chamber 123. A floatingly-arranged piston 149 moves to the left due to th pressure in working chamber 123. Pressure is built up in pressure chamber 122.

The pressures in the working chambers 122, 123 are supplied via pressure lines 120, 121 to the wheel cylinders.

Two embodiments of this invention were described hereinabove. However, the invention is not restricted to these embodiments. It can be represented by further embodiments.

For example: Separating the pressure-medium circuit for the hydraulic brake force boosting from the pressure-medium circuit for the actual brake application enables the use of two types of pressure media which is suitable under certain conditions of application. Thus, for instance, the booster circuit (auxiliary-master-cylinder pressure chamber 32 and boosting pressure chamber 33) can operate with normal hydraulic pressure medium, while brake fluid can be used for the working chambers of the master cylinder and the wheel cylinders.

It may also be arranged for instance that, instead of a vacuum brake power booster, a booster with compressed air is used. Besides, it is possible within the scope of this invention, in particular in its second embodiment, to utilise two hydraulic pressure media. The first pressure medium serves for the hydraulic brake force boosting. The auxiliary master cylinder and the hydraulic booster work with this first pressure medium. The second pressure medium can be brake fluid. This second pressure medium is utilised by the master cylinder and the aggregates hydraulically connected after it, such as anti-lock pressure modulator and wheel cylinders.

Claims (17)

CLAIMS:

1. A hydraulic brake system for an automotive vehicle with a master cylinder, wheel cylinders, a pneumatic brake power booster, a control unit for generating a controlled pneumatic pressure (pneumatic control unit) for the pneumatic brake power booster and preferably an anti-lock control system (ABS), characterised in that there is provision of a device which generates a reaction force by utilising the hydraulic pressure in at least one working chamber of the master cylinder, which reaction force can be felt at the brake pedal by the driver during the braking operation, in that the master cylinder, the device for generating the reaction force and the pneumatic control unit are combined to form a construction unit and are arranged at a location separated from that of the pneumatic brake power booster.

2. A hydraulic brake system as claimed in claim 1, characterised in that the master cylinder (37), more particularly a tandem master cylinder, comprises at least one piston (34,36) incorporating an internal duct (35) whose first opening terminates into at least one working chamber (41) of the master cylinder, in that a guidance means (60) is disposed in the area of the second opening of the duct (35) in which a piston (44) is sealingly guided which pertains to a device for generating a reaction force sensible at the brake pedal by the driver during braking, the said piston being subject to the pressure medium of the working chamber (41) of the master cylinder and serving as a force simulator and/or travel simulator.

3. A hydraulic brake system as claimed in claim 1, characterised in that the piston (44) sealingly guided in the area of the second opening of the duct (35) is designed and arranged such that it senses the hydraulic pressure in the working chamber (41) of the master cylinder and, in its capacity as a sensing piston, converts it into a reaction force and indirectly or directly, especially via a piston rod, transmits it onto the brake pedal during the braking operation.

4. A hydraulic brake system as claimed in claim 1 or 3, characterised in that the construction unit composed of master cylinder (37), device for generating a reaction force (42,44) and pneumatic control unit includes a hydraulic brake power booster (33,34).

5. A hydraulic brake system as claimed in any one of claims 1 to 4, characterised in that a piston is provided in the master cylinder (37) which fulfils the function of a booster piston (34) and a working piston (36), in that the piston (34,36) comprises two effective cross-sections (61,62) subject to pressure medium, the first cross-section (62) thereof being subject to hydraulic boosting pressure medium and the second cross-section (61) being subject to the hydraulic pressure medium of the working chamber (41) of the master cylinder (37).

6. A hydraulic brake system as claimed in any one of the preceding claims, characterised in that the master cylinder (37), the hydraulic brake power booster (33,34), the device for generating a reaction force (42,44) and the pneumatic control unit are arranged coaxially in relation to each other.

7. A hydraulic brake system as claimed in any one of the preceding claims, characterised in that the pneumatic control valve (20,13) of the control unit for generating a pneumatic pressure difference for the pneumatic brake power booster (2) is accommodated in a control housing (59) that is located in an outside housing coupled to the master cylinder (outside housing) (58).

8. A hydraulic brake system as claimed in any one of the preceding claims, characterised in that at least one duct (24) for conveying the controlled pneumatic pressure is furnished in the outside housing (58).

9. A hydraulic brake system as claimed in any one of the preceding claims, characterised in that the master cylinder (35) and the outside housing (58) are interconnected by flanges (56,57), and in that the sealing surfaces of the flanges are so designed as to form at least one duct (25) for the controlled pneumatic pressure.

10. A hydraulic brake system for an automotive vehicle with a master cylinder, wheel cylinders, a pneumatic brake power booster, a control unit for generating a controlled pneumatic pressure for the pneumatic brake power booster and preferably an anti-lock control system (ABS), characterised in that, in addition to the pneumatic brake power booster, a hydraulic brake power booster is provided which includes a boosting pressure chamber which, upon brake application, is subject to hydraulic boosting pressure medium that is subjected to the hydraulic pressure generated by the pneumatic brake power booster, in that the hydraulic brake power booster comprises a booster piston whose effective boosting cross-section confines the boosting pressure chamber, in that there is provision of a device (reaction force device) for generating a reaction force which can be felt at the brake pedal by the driver during braking, in that the reaction force device is a particularly piston-like designed component part (reaction-force transmitting element) for the transmission of a translatory force which forms part of the wall of the boosting pressure chamber and which, upon brake application, is subject to hydraulic boosting pressure medium and in that the master cylinder, the hydraulic brake power booster, the device for generating the reaction force and the control unit form a construction unit which is arranged at a location different from that of the pneumatic brake power booster.

11. A hydraulic brake system as claimed in claim 10, characterised in that the reaction-force transmitting element (43) is equipped with a device, in particular a piston (42), which senses the hydraulic pressure in the boosting pressure chamber (15) and converts it into a reaction force.

12. A hydraulic brake system as claimed in claim 10 or 11, characterised in that a semirigid member, in particular a rubber disc (46), is provided which is inserted between the reactionforce transmitting element (43) and one or more component parts acting directly or indirectly upon the brake pedal (24).

13. A hydraulic brake system as claimed in claims 10 to 12, characterised in that the master cylinder, the hydraulic brake power booster, the device for generating the reaction force and the control unit are located coaxially.

14. A hydraulic brake system as claimed in any one of claims 10 to 13, characterised in that the master cylinder incorporates the hydraulic booster as an integral component part.

15. A hydraulic brake system as claimed in any one of claims 10 to 14, characterised in that the booster piston (41) and a working piston (50) of the master cylinder (18) form one component part.

16. A hydraulic brake system as claimed in any one of claims 10 to 15, characterised in that the master cylinder housing (44) comprises a cylindrical chamber (15), in that the booster piston (41) extends in said cylindrical chamber (15) in a sealing fashion, and in that the end member (42) of the reaction-force transmitting element (43) is sealingly guided in the wall of the cylindrical chamber, the said end member being of plungerpiston-type configuration.

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