DE4312118C2 - Hydraulic brake system for vehicles - Google Patents

Description

The invention relates to hydraulic brake systems for vehicles with the application of the brakes on all wheels of a drive master control master cylinder, the a primary pressure chamber and has a secondary pressure chamber, both normally from a brake fluid reservoir via a primary or a secondary backflow valve are fed, which close, when the master cylinder is operated by a pedal, the primary pressure chamber being attached to primary wheel brake actuators is closed with which it forms a primary brake circuit, and the secondary pressure chamber is connected to secondary wheel brake actuators sen with whom it forms a secondary brake circuit.

The brakes of a moving vehicle must be automatic be operated when the vehicle with an intelligent Travel control is equipped to make it another driving stuff automatically in a substantially constant time interval can follow. If the vehicle in front is his Speed increases, the distance between increases the two vehicles automatically. The size is also reduced Intermediate distance when the vehicle in front is driving slowed down.  

To be able to brake automatically, the vehicle must be equipped with the Travel control have a device that the brakes automatically supplied with pressure. This can be done with a special Vacuum booster happen, such as from EP-A-0 303 470 is known. This ensures that all brakes are applied with approximately the same pressure. This is achieved in that a Force is applied, he a pressure in the primary pressure chamber testifies, which in turn acts on the secondary piston and a substantially equal pressure in the secondary pressure space generated. Vacuum booster from EP-A-0 303 470 known type can, however, undesirable pedal operation cause movements.

According to the invention is in a hydraulic brake system for a vehicle with an intelligent journey control and an electronic control module for sub separate from travel control signals and to provide electrical A hydraulic pressure device flows depending on Travel control signals actuated to the primary pressure space of the To put the master cylinder under pressure so that the brakes be applied to all wheels by the primary wheel brake actuators directly and the secondary wheel brake actuators indirectly be put into operation after a shut-off valve in a Return flow line from the primary pressure chamber of the master brake cylinder closed to the brake fluid reservoir.

As a result, the brakes are automatically based on such Signals applied, whereby at a given vehicle speed a desired braking distance between the Vehicle and the preceding vehicle is observed.

The shut-off valve can be an electromagnetic valve or have that in the return line to the brake fluid container is arranged. So if the printing device due to an electrical output from the control module Electricity is active, then the electromagnetic valve through the  electric current is closed and prevents braking fluid from the primary pressure chamber in the brake fluid flows back.

The hydraulic pressure device can be a hydraulic pump comprise, which are created by applying a control module electrical current is started. With one Arrangement prevents the closing of the solenoid valve Brake fluid on it, through the return line in the Brake fluid reservoir to flow back to the extent that Brake fluid through the pump from the brake fluid reservoir is withdrawn through a supply line.

Alternatively, the hydraulic pressure device can be hydraulic have pressure accumulator. With such an arrangement is a normally closed second electromagnetic actuated feed valve in a leading to the primary pressure chamber Line arranged and following the normally open Shut-off valve can be operated.

The fluid for the printing device can through the feed valve be fed directly into the primary pressure chamber. age natively it can be a chamber in front of or behind the primary pressure chamber are fed through this chamber and through the primary pressure chamber a primary backflow valve in the primary piston under pressure set which remains open because the primary piston in its retracted position remains.

That is why all brakes are released simultaneously and from the pedal pending actuated.

The pedal is operated by an electrical switch detected that the pump and the electromagnetically operated Shut-off valve de-energized and thus the hydraulic pressure makes the facility ineffective. Has an operation of the pedal thus takes precedence over automatic application of the brakes the hydraulic pressure device.  

The response time for the automatic application of the brakes is extremely short, so applying and releasing the brakes takes place almost immediately after receiving a corresponding signal instead of. Since the primary pressure chamber of the master brake cylinder under Pressure is applied to activate the main brake cylinder triggering it yourself is the same as secondary or floating piston of the master brake cylinder the pressures in the primary and Secondary brake circuit on each other, as in one Pedal actuation of the master brake cylinder happens. The one from the hydraulic pressure device on the primary as well as on the Secondary circuit pressure can be up to an amount increase by the (desired) vehicle deceleration is determined. This amount is directly from a sensor measured, which measures the (negative) vehicle acceleration. Alternatively, the amount is indirectly derived from information about derived the wheel speed.

The invention enables the brakes to always be automatic then be created if the time interval between the preceding and the following vehicle predetermined limit falls below values.

If the vehicle brake system has an anti-lock braking system (ABS) has, the pump device, the pump for automa table application of the brakes based on a travel control signal include. In such a system, it becomes the return line controlling solenoid valve always closed when the Brakes on the front wheels of the vehicle can be controlled. This will remove excess fluid from the front brakes in the. Master cylinder and pumped into the rear brakes to do that To increase the pressure level so that in the annulus behind the primary piston of the master cylinder also trapped fluid gets under higher pressure and prevents the foot of the Driver an opposite reaction force of the brake pedal acts.  

The automatic brake system according to the invention works with increased pressure level in both primary and secondary brakes circle to an unwanted braking in an anti-lock system to prevent the affected wheel brakes speaking anti-lock signals from sensors to the be hitting wheels are sent out by the pressure supply separates or connects to these.

The electromagnetically operated shut-off valve is preferred wise under a spring preload to the greatest possible Ensure pressure generation in the primary brake circuit. The elec tromagnetically operated shut-off valve is therefore due of a signal triggered by the brake pedal is always closed sen when a brake application directly to an auto matically braking. Similarly, it will Electromagnetically operated shut-off valve in response to a signal open, indicating that an arbitrary actuation of the Brake is finished by the pedal.

The brake system according to the invention can be further developed that they always have the brakes, or at least some of them then moored when the vehicle is parked uphill should. If the traction force exceeds the holding force, the brakes released so that the vehicle can start.

With anti-lock control, excess brake fluid from the front brakes directly or indirectly from the engine driven pump used to the on the rear brakes to increase applied pressure.

Exemplary embodiments of the invention are described below Described schematic drawings with further details ben. Show it:

Figure 1 is a block diagram of an X-split hydraulic brake system for a vehicle.

Fig. 2 shows a modification of Fig. 1;

Fig. 3 shows a further modification of Fig. 1;

Figure 4 is a block diagram of an anti-lock hydraulic brake system for a four-wheel vehicle.

Fig. 5 is an enlarged section through an electromagnetic valve shown in Fig. 4;

Fig. 6 is a similar of Figure 1 block diagram of a braking system, but with division into a front and a rear brake circuit.

FIG. 7 shows a block diagram similar to FIG. 4, but with a four-channel anti-lock braking system;

Fig. 8 shows part of a system similar to Fig. 4 with a modification;

Fig. 9 shows a modification of Fig. 8; and

Fig. 10 shows a part of another brake system.

The brake system shown in Fig. 1 in the X-pitch has a master cylinder 1, the casing 2 has a longitudinal bore 3. In this work a primary piston 4 , which is actuated by a pedal 5 , and a secondary or floating piston 6 , which is between the inner, with respect to the vehicle in front of, the end of the primary piston 4 and a closure or end wall 7 on Pedal 5 is arranged distal end of the bore 3 . A primary pressure chamber 8 is formed in the bore 3 between the two pistons 4 and 5 , and a secondary pressure chamber 9 is formed between the secondary piston 6 and the end wall 7 . The primary pressure chamber 8 is in the unactuated or idle position of the brake with a brake fluid container 10 via a normally open return valve 11 and a return line 12 ; the secondary pressure chamber 9 is connected to the brake fluid container 10 through a normally open return valve 13 .

The primary pressure chamber 8 is connected to an actuator 15 , for. B. wheel brake cylinder, a brake on a front wheel 16 of the vehicle and with an actuator 17 , z. B. wheel brake cylinder for a brake connected to the diagonally opposite rear wheel 18 of the vehicle. The primary pressure chamber 8 and these two brakes form a primary brake circuit.

The secondary pressure chamber 9 is with an actuator 19 , for. B. wheel brake cylinder, a brake on the other front wheel 20 of the vehicle and with an actuator 21 , z. B. wheel brake cylinder, a brake on the diagonally opposite rear wheel 22 of the vehicle. The secondary pressure chamber 9 and the two actuators 19 and 21 form a secondary brake circuit.

The brake system includes an intelligent control system with a radar device 23 for determining the distance and the speed of a preceding vehicle, as well as an acceleration / deceleration sensor 27 . Signals from the radar device 23 and the sensor 27 are fed to an electronic control module 24 , which is able to emit electrical working currents in accordance with the signals received by the radar device 23 and the sensor 27 .

The brake system also includes a hydraulic pump 25 , which is driven by an electric motor 26 on the basis of the current supplied by the electronic control module 24 in order to withdraw brake fluid from the brake fluid reservoir 10 and to pump it into the primary brake circuit with the primary pressure chamber 8 .

The return line 12 includes a shut-off valve, in the example presented Darge a solenoid valve 28 to break the connection of the primary pressure chamber 8 with the brake fluid reservoir 10 via the normally open backflow valve 11 when the motor 26 is under voltage.

An electrical monitoring switch 29 is assigned to the pedal 5 .

During normal service braking, the primary piston 4 is first pushed so far by actuating the pedal 5 in the cylinder bore 3 that the backflow valve 11 is closed and the primary pressure chamber 8 is thereby separated from the brake fluid container 10 . Further forward movement of the primary piston 4 causes the secondary piston 6 to be advanced in the cylinder bore 3 , thereby closing the backflow valve 13 in order to separate the secondary pressure chamber 9 from the brake fluid container 10 . Then the brakes in the primary and secondary brake circuit are operated simultaneously and with the same pressure, since a compensating movement of the secondary piston 6 in the cylinder bore 3 ensures pressure compensation.

When the pedal 5 is released, the pistons 4 and 6 return to their original operating positions under the action of return springs, and the backflow valves 11 and 13 release the flow paths to the brake fluid reservoir 10 again.

During normal actuation of the master cylinder 1 , a signal emitted by the switch 29 prevents the electronic control module 24 from acting, regardless of whether it receives signals from the radar device 23 and whether the driver has selected automatic driving mode. As a result, the shut-off valve 28 remains de-energized and is held in an open position by a return spring, so that a free connec tion from the primary pressure chamber 8 via the return line 12 to the brake fluid container 10 is made.

When the vehicle is traveling on a road behind a preceding vehicle and the driver has opted for automatic following, the radar 23 monitors the relative speed with respect to the preceding vehicle and the distance between this and the following vehicle and gives a signal to the electronic Control module 24 . If this determines that the signal is such that corrective action is required to maintain the relative speed and the distance between the two vehicles within predetermined limits, then the motor 26 is energized with an electrical current delivered by the electronic control module set and the solenoid valve 28 brought to close. The pump 25 draws the brake fluid liquid keitsbehälter 10 and pumps it into the primary brake circuit, so that the pressure rises there, since the return line 12 is closed to fluid reservoir 10 through the solenoid valve 28th In particular, brake fluid is pumped to the actuators 15 and 17 and also reaches the primary pressure chamber 8 through the outlet opening connected to them. The pressure increase in the primary pressure chamber 8 is transferred to the floating secondary piston 6, which in turn, as above, be written is shifted in the cylinder bore 3 to the front to close the relief valve 13 and the fluid in the seconding därdruckraum 9 and set in the secondary brake circuit under pressure , Because of the described compensating effect of the secondary piston 6 , the brakes are applied to all four wheels simultaneously and with the same pressure. The pressure prevailing in the primary pressure chamber 8 acts on the primary piston 4 and holds it in contact with a rear stop, so that no reaction force is transmitted to the pedal 5 .

When the pump 25 has generated sufficient pressure, its motor 26 stops.

Once the brakes have been applied long enough to increase the distance between the vehicle and the preceding vehicle to the required extent, the electronic control module 24 de-energizes the motor 26 . The brake actuating pressure of the pump 25 is not maintained and the brakes are relieved via the pressure chambers 8 and 9 to the brake fluid container 10 because the valve 28 pul siert or opens to release the return line 12 .

With automatic actuation of the brakes on the basis of a signal from the radar device 23 , the acceleration / deceleration sensor 27 limits the achievable deceleration.

In the brake system shown in Fig. 2 is also dependent on signals from the control module 24 second solenoid valve 30 in a feed line 21 between the brake fluid container 10 and the suction side of the pump 25 is arranged. This solenoid valve 30 is normally open so that brake fluid from the container 10 can be pumped into the primary brake circuit to automatically apply the brakes. However, as soon as the pressure in the primary brake circuit has been increased by the pump 25 to a predetermined maximum value, the electronic control module 24 causes the solenoid valve 30 to be closed. As a result, the brake fluid reservoir 10 is separated from the pump so that it is no longer supplied with liquid.

The design and mode of operation of the brake system shown in FIG. 2 are otherwise the same as in FIG. 1.

In the brake system shown in Fig. 3, an electromagnetic solenoid valve 32 is arranged between the pressure side of the pump 25 and the primary brake circuit; further, a relief valve 33 is provided between the pressure side of the pump and the brake fluid container 10 . When the fluid in the primary brake circuit reaches a certain pressure during operation, the solenoid valve 32 is closed by the electronic control module 24 , and the fluid from the pressure side of the pump 25 flows in a closed circuit back into the brake fluid reservoir 10 via the opening relief valve 33 .

Otherwise, the construction and mode of operation of the system shown in FIG. 3 are the same as in FIG. 1.

Shown to the one in Fig. 4, X-split braking system is part of an anti-lock (ABS) modulator 40 of a known four-channel construction. As shown, the modulator 40 for regulating the actuation of the brakes on each wheel 20 , 16 , 18 , 22 each has an electromagnetically actuated inlet valve 41 , 42 , 43 , 44 and an electromagnetically actuated outlet valve 41 a, 42 a, 43 a and 44 a and an expansion chamber 45 , to which each brake, in order to be relieved, can deliver brake fluid, and a pump 46 , which is driven by an electric motor 47 , to draw off liquid from the expansion chamber 45 and to pump it back in order to reapply a wheel brake, when the behavior of this wheel has been corrected.

A wheel speed sensor 50 , 51 , 52 and 53 is assigned to each of the wheels 20 , 16 , 18 , 21 .

As in the system shown in Fig. 2, the electromagnetically operated shut-off valve 28 in the return flow line 12 , and the second electromagnetically operated valve 30 between the brake fluid reservoir 10 and the suction side of the pump 46 is arranged according to FIG. 4.

The electromagnetically operated shut-off valve 28 is shown in an individual in FIG. 5. It has a valve body 60 which is relatively movably connected to a magnet armature 61 . This is normally held at a distance from a valve seat 62 leading to the primary pressure chamber 8 when an electromagnet 63 surrounding the armature is dead. When the electromagnet 63 is de-energized, the valve 28 is therefore open. When the electromagnet 63 is energized, the armature 61 moves in the direction of the valve seat 62 in order to press the valve body 60 against the valve seat 62 and thereby separate the pressure chamber 8 from the brake fluid container 10 . Any excess movement of the armature 61 in the direction of the valve seat 62 is compensated for by a relative movement between the armature 61 and the valve body 40 , a lost motion spring 64 being compressed.

With normal operation of the brake system shown in Fig. 4, the solenoid valves 28 , 30 and 41-44 remain de -energized, so that an unrestricted connection between the pressure spaces 8 and 9 and the brakes on the four wheels of the vehicle.

However, if one of the sensors, for example sensor 52 , detects an impending risk of locking on the associated wheel, it emits a signal which causes electronic control module 24 to emit an energy flow. This actuates the valve 43 to disconnect the brake actuator 17 from the master cylinder 1, and the solenoid valve 43 a, so that flowing out of the respective brake to the respective brake actuators to the expansion chamber 45 to be connected in this liquid. The pump 46 draws brake fluid from the expansion chamber 45 and compensates for the volume of fluid discharged from the brake as soon as the solenoid valve 43 has switched after the end of the anti-lock signal in order to reconnect the actuator 17 to the master brake cylinder 1 .

If a driven wheel assigned to the secondary pressure chamber 9 , for example the wheel 20 , tends to spin, a signal emitted by the speed sensor 50 causes the electronic control module 24 to close the electromagnetic valves 42 , 43 and 44 , so that pressure from the master brake cylinder 1 to the brake actuator 19 arrives and the brake on the wheel 20 only operated to regulate the traction. After this traction control, the actuator 19 delivers liquid to a secondary pressure chamber, not shown, and a secondary pump, also not shown, delivers liquid back to the pressure chamber 9 . When the front wheel 16 spins, fluid is pumped from the brake fluid reservoir 10 into the primary pressure chamber 8 . Since the primary backflow valve 11 remains open, no damage occurs when the first solenoid-operated shut-off valve 28 opens to relieve the primary brake circuit when the wheel 16 is back under control.

If an intervention directed against spinning a wheel is immediately followed by brake actuation while the expansion chamber 25 is still filled with brake fluid, there is still an overpressure in the primary pressure chamber 8 when the brakes are released. In order to avoid damage to the primary backflow valve 11 , the first electromagnetically operated shut-off valve 28 is closed again when a brake application immediately follows a correction of a wheel spin. The signal required for this is emitted by switch 29 , which is also a brake light switch. When the brake is released, brake fluid, which was enclosed in an annular space 55 between the electromagnetically controlled shut-off valve 28 and the backflow valve 11 , flows out via the backflow valve 11 until the brake light is switched off. At this point in time, the primary backflow valve 11 is open and the first electromagnetically controlled shut-off valve 28 provided with a metal seat can now be opened in order to release pressure. This Aufeinan consequently makes it possible to use a conventional return valve provided with a rubber seat for the primary pressure chamber 8 . Accordingly, both the primary and the secondary brake circuit can each have a rubber-coated backflow valve 11 or 13 .

In a conventional brake system, the brakes are dimensioned such that the front wheels tend to lock in front of the rear wheels, so that skidding is avoided in the event of ABS failure. Because of this requirement, the potential contribution of the brakes on the rear wheels 18 and 22 to braking is not fully exploited, especially when an average driver stops the pedal from vibrating due to ABS control of the brakes 20 and 16 on the front wheels press harder to increase the rear wheel brake pressure. With such an ABS control, the brake fluid enclosed in the annular space 55 can be used:
If the front brakes of the ABS are regulated during emergency braking, the first electromagnetically operated shut-off valve 28 closes, so that liquid is trapped in the annular space 55 . The motor-driven pump 46 is energized, so that liquid that has flowed out into the respective expander chambers is pumped back into the master brake cylinder 1 . At the same time, brake fluid is released to re-apply the brakes on the front wheels 20 and 16 , and excess brake fluid increases the pressure in the brake cylinder 1 and the rear wheel brakes. Brake fluid enclosed in the annular space 55 is thus pressurized. The annular space 55 acts like a buffer chamber between the master cylinder 1 and the driver, so that the pedal feel is significantly improved. In addition, the rear brakes act like an accumulator to smooth the cyclical pulsations of the pump 46 .

The relationship between the master cylinder pressure and the pressure in the annular space 55 is shown below, assuming that there is a pressure of 15 bar in the front wheel brakes when there is a risk of locking, and an actuating force of 40 N causes a pressure of 20 bar to be applied:

The area ratio between master cylinder 1 and annular space 55 is 2: 1 in this example. The master cylinder pressure and the pressure acting on the rear brakes can rise from 20 to a maximum value of 40 bar without any increase in the actuating force. The front brakes are regulated by the ABS at 15 bar. The automatic increase in the rear wheel brake pressure when regulating the front wheel brakes is advantageous because the available traction is better used and a larger part of the vehicle weight is shifted to the more strongly braked front wheels.

To hold a vehicle parked uphill, the brakes, or those on an axle, are automatically applied using the intelligent travel control described above. The driver can now release the brake pedal 5 to start off. When the forward traction exceeds the brake holding force, the first solenoid-operated shut-off valve 28 opens to release the brake pressure.

The construction and mode of operation of the embodiment shown in FIG. 4 are otherwise the same as in FIG. 2.

In the brake system shown in FIG. 6, divided into a front wheel and a rear wheel brake circuit, the brakes on the rear wheels 18 and 22 are actuated from the primary pressure chamber 8 , with which they form the primary brake circuit, and the brakes on the rear wheels 20 and 16 actuated from the secondary pressure chamber 9 with which they form the secondary brake circuit. As in the embodiment of Figure 1, the primary brake circuit can be pressurized to achieve an immediate automatic vehicle deceleration. the brakes on the front wheels 20 and 16 are actuated indirectly by the secondary pressure chamber 9 .

Otherwise, the construction and mode of operation of the brake system according to FIG. 6 are the same as in FIG. 1.

The brake system according to FIG. 7 is similar to that shown in FIG. 6, with the exception that it comprises an anti-slip modulation device 80 similar to the modulator 40 shown in FIG. 4 and also has the second electromagnetic valve 30 . This system allows the pressure applied to the brakes on the rear wheels 18 and 22 to be increased when the front wheels 20 and 16 are subject to anti-slip control.

In a modification in which the brakes of the front wheels 20 and 16 are connected to the primary brake circuit, the pressure in the brakes of the rear wheels 18 and 22 is increased as described above. However, when the brakes of the front wheels 20 and 16 are connected to the secondary pressure chamber 9 as shown, excess brake fluid is pumped from these brakes into the secondary pressure chamber 9 , and the floating secondary piston 6 moves back towards the pedal 5 to the brakes the rear wheels 18 and 22 to apply pressure. The above-described action on the brakes is possible with single drive of the front or rear axle as well as with joint drive of the front and rear axle with four-wheel drive.

The construction and mode of operation of the brake system shown in FIG. 7 are otherwise the same as in FIG. 4.

In Fig. 8, a hydraulic master brake cylinder is shown, which can replace that of the brake system shown in FIG. 4 and the associated control valves. In the brake system shown in FIG. 8, the shut-off valve 28 is arranged in a line between the brake fluid reservoir 10 and a normal sniffer bore 81 , through which the primary pressure chamber 8 is supplied with brake fluid from the brake fluid reservoir 10 via the backflow valve 11 when it is open. Another electromagnetically controlled accumulator valve 82 is arranged in a line between a hydraulic accumulator or pressure accumulator, not shown, and the sniffer bore 81 . For normal brake application, valve 28 is open and valve 82 is closed.

When the brakes are to be operated independently of a pedal actuation of the master brake cylinder in order to establish and maintain a certain distance from a vehicle in front, the valve 28 is energized so that it closes and the solenoid of the valve 82 is pulsed so that the primary circuit, which includes the actuators 17 and 21 , through the open backflow valve 11 and a primary feed port 83 brake fluid is supplied. At the same time, the secondary piston 6 moves forward in the cylinder bore 3 and actuates the secondary brake circuit, which includes the actuators 19 and 15 , through a secondary outlet 24 . Again, the secondary piston 6 ensures that the pressures prevailing in the two brake circuits are essentially the same.

As soon as the correct distance to the vehicle in front has been established, the valve 82 is closed and the valve 28 is opened or pulsed so that the braking force is eliminated.

Should the driver apply the brakes during automatic braking, the accumulator valve 82 is closed and the shutoff valve 28 assigned to the brake fluid container 10 is opened. The master cylinder generates brake pressure when the relief valve 11 relative to the seconding därkolben 6 closes. As a result, most of the excess brake fluid (ie, that which is not conveyed by the master brake cylinder) can flow back into the brake fluid reservoir. The secondary piston 6 supplies its own brake fluid to the secondary brake circuit so that it does not receive any excess brake fluid.

In known hydraulically actuated brake systems, both master cylinder pistons 8 and 6 stop when the excess brake fluid is introduced, so that in arbitrary braking by pedal actuation of the master cylinder, an initial movement of the master cylinder pistons 8 and 6 closes the backflow valves 11 and 13 . The excess brake fluid in both brake circuits does not have enough time to flow out. When the ABS subsequently takes effect, liquid can therefore be pushed back into the master brake cylinder and it may therefore be necessary for the return flow tiles 11 and 13 to open against the prevailing pressure in order to allow all or part of the excess brake fluid to flow off. Under these conditions, the backflow valves can be damaged in known brake systems.

Erfinungsgemäß the secondary piston moves during automatic brake 6 from the primary return valve 11 off, so that the primary pressure chamber 8 and the fluid reservoir are connected to each other. Thus, the backflow valve 11 remains open so that it cannot be damaged.

When one of the driven wheels begins to slip because the vehicle is on a different friction roadway under the driven wheels, the solenoids of valves 28 and 82 are energized so that both brake circuits are pressurized. In this case, the ABS modulator 40 separates the non-driven and the non-spinning wheels and applies pressure to the brake of the wheel that has started to spin. As a result, usable torque is given to the wheel on a better surface so that the vehicle can start.

The connection of the solenoid valves 28 and 82 to the inlet 81 fed by the brake fluid reservoir has the advantage that these two valves are separated from the hydrostatic brake system when the brakes are operated normally; as a result, a risk of damage is avoided. Another advantage is that the primary piston 8 is held firmly against its rear stop, so that no movement takes place on the brake pedal.

In the brake system shown in FIG. 9, a separate inlet opening 85 is provided, which leads directly from the valve 82 to the primary pressure chamber 8 . In this brake system, pressure fluid is supplied to the outlet 83 directly from the pressure chamber 8 , and an equal pressure acts on the secondary piston 6 via the open backflow valve 11 . This arrangement has the disadvantage that the accumulator valve 82 is not separated from the primary brake circuit when the brakes are operated normally.

Otherwise, the construction and mode of operation of the brake system shown in FIG. 9 are the same as in FIG. 8.

The system shown in FIG. 10 is an example of a master brake cylinder without an integrated power source, as is present in the form of the accumulator in the system shown in FIG. 9. Referring to FIG. 10 of the normal, keitsbehälter from the brake liquid leading to the return valve 11 the inlet 87 is not connected to the pressure chamber 8 via the return valve 11, but to a separate motor-driven power source having a pump 88. In addition, a single solenoid valve 89 is arranged between the brake fluid reservoir and a normal inlet 90 to the primary pressure chamber 8 .

For automatic braking, the solenoid valve 89 is closed and the pump 88 is started so that it supplies liquid to the primary brake circuit. At the same time, the secondary piston 6 moves to actuate the secondary circuit. At the desired vehicle deceleration, the motor-driven pump 88 is switched off. When the driver operates the brakes normally, the solenoid valve 89 opens and connects the primary inlet 87 to the brake fluid container. Otherwise, the construction and mode of operation of the system shown in FIG. 10 are the same as in FIG. 8.

Claims (12)

1. Hydraulic brake system for vehicles with a brake application to all wheels ( 16 , 20 , 18 , 22 ) of a vehicle controlling master brake cylinder ( 1 ), which has a primary pressure chamber ( 8 ) and a secondary pressure chamber ( 9 ), both of which normally are fed by a brake fluid reservoir ( 10 ) via a primary or a secondary backflow valve ( 11 , 13 ), which close when the master brake cylinder ( 1 ) is actuated by a pedal ( 5 ), the primary pressure chamber ( 8 ) being sent to primary wheel brake actuators ( 15 , 19 ) is connected, with which it forms a primary brake circuit, and the secondary pressure chamber ( 9 ) is connected to secondary wheel brake actuators ( 19 , 21 ) with which it forms a secondary brake circuit, and wherein the vehicle with intelligent travel control ( 23 ) and an electronic control module ( 24 ) for distinguishing travel control signals and for supplying electrical currents, dadurc h characterized in that a hydraulic pressure device ( 25 ) can be actuated as a function of travel control signals in order to pressurize the primary pressure chamber ( 8 ) of the master brake cylinder ( 1 ) so that the brakes are applied to all wheels ( 16 , 20 , 18 , 22 ) are put into operation by the primary wheel brake actuators ( 15 , 17 ) directly and the secondary wheel brake actuators ( 19 , 21 ) indirectly after a shut-off valve ( 28 ) in a return line ( 12 ) from the primary pressure chamber ( 8 ) of the master brake cylinder to the brake fluid reservoir ( 10 ) has closed. 2. Brake system according to claim 1, characterized in that the shut-off valve ( 28 ) is a normally open solenoid valve which is closed by a signal from the control module ( 24 ) when the hydraulic pressure device ( 25 ), also by a signal from the control module ( 24 ), is actuated, the closing of the shut-off valve ( 28 ) preventing backflow of brake fluid into the brake fluid reservoir ( 10 ) from the primary pressure chamber ( 8 ) of the master brake cylinder ( 1 ). 3. Brake system according to claim 2, characterized in that the hydraulic pressure device comprises a hydraulic pump ( 25 ) which can be actuated by energizing an electric motor ( 26 ) with an electrical current output by the control module ( 24 ), with a closing of the electromagnetic valve ( 28 ) backflow of brake fluid to the brake fluid reservoir ( 10 ) is prevented by a return flow line ( 12 ), while brake fluid is drawn off by the pump ( 25 ) via a feed line from the brake fluid reservoir ( 10 ). 4. Brake system according to claim 2, characterized in that the hydraulic pressure device ( 25 ) has a hydraulic accumulator, wherein a normally closed second electromagnetically actuated feed valve ( 82 ) arranged in a line leading to the primary pressure chamber ( 8 ) and subsequent to the normally open Shut-off valve ( 28 ) can be actuated. 5. Brake system according to claim 4, characterized in that liquid for the pressure device ( 25 ) through the feed valve ( 82 ) is fed directly into the primary pressure chamber ( 8 ). 6. Brake system according to one of claims 1 to 4, characterized in that brake fluid is supplied from the pressure device ( 25 ) to a chamber adjacent to the primary pressure chamber ( 8 ), around this and also the primary pressure chamber ( 8 ) through a primary backflow valve ( 11 ) in the primary piston ( 14 ) under pressure. 7. Brake system according to one of claims 1 to 6, in which an arbitrary actuation of the master cylinder ( 1 ) via the pedal ( 5 ) is monitored by an electrical switch ter ( 29 ), characterized in that an actuation of the switch ( 29 ) the shut-off valve ( 28 ) is de-energized and the hydraulic pressure device ( 25 ) is ineffective. 8. Brake system according to one of claims 1 to 7, characterized in that the primary and the secondary brake circuit from the hydraulic pressure device ( 25 ) supplied pressure can be increased to an amount determined by the vehicle deceleration. 9. Brake system according to one of claims 1 to 8, characterized in that it has an anti-lock braking system (ABS), the slip-preventing pump is also provided as a pump for automatically applying the brakes due to travel control signals, the electromagnetically operated shut-off valve ( 28 ) in the return line ( 12 ) is always closed when the brakes on the front wheels ( 16 , 20 ) of the vehicle are activated. 10. Brake system according to one of claims 1 to 9, characterized in that the pressure level in the primary brake circuit and in the secondary brake circuit is increased to affect the brakes at a Anti-lock braking system to prevent which wheels are affected Compliance with sensors emitted on these wheels Anti-lock signals switched on or off. 11. Brake system according to one of claims 1 to 10, characterized in that the electromagnetically operated shut-off valve ( 28 ) is biased by an spring into an open position. 12. Brake system according to one of claims 1 to 11, characterized in that at least one of their brakes can be applied when the vehicle is parked uphill, this brake is released when the Traction force exceeds the holding force, causing the vehicle can start.