DE3403236A1 - Brake system for motor vehicles - Google Patents

Abstract

A brake system for motor vehicles according to the patent ... (Patent Application P 3323402.7) has a dual circuit hydraulic brake pressure sensor (3), which essentially comprises a brake booster (4) and a master cylinder (5). A front wheel (VR or VL) is directly connected and a rear wheel (HL or HR) by way of a brake pressure modulator (6, 7) to the two brake circuits (1, 2) respectively. In addition a pressure medium line, into which a separating valve (18) is inserted, runs from the rear wheel brakes (14, 15) to a pressure balancing tank (11) for reducing the pressure. The auxiliary power supply system has a pressure medium pump (8), the pressure side of which can be "short-circuited" with the intake side by way of a valve (19) in order to reduce the auxiliary power transmitted to the brake pressure sensor and thereby to reduce the brake pressure on the front wheel brakes (12, 13). The brake system is suitable both for open-loop control of the brake pressure distribution and for closed-loop control of the brake slip. For balancing of pressure differences between the front wheel brakes (12, 13) the two hydraulically separated brake circuits (1, 2) are connected by a control element (20, 34), the piston (23, 36) of which is coupled to a separating valve (21). For influencing the pressure behaviour should the booster brake circuit (2) fail, hydraulically actuated control valves (29, 33, 38, 40) ... Original abstract incomplete. <IMAGE>

Description

Brake system for motor vehicles

(Addition to patent application P 33 23 402.7)) The invention relates on a braking system intended for motor vehicles with a two-circuit hydraulic, pedal-operated brake pressure transducer with an auxiliary energy source is connected and on whose two brake circuits each have a front wheel and a rear wheel are connected, with brake pressure modulators in the ones leading to the rear wheels Pressure medium lines as well as from the rear wheel brakes to a pressure compensation tank leading pressure medium lines, inserted into the isolating valves that can be switched to passage are, with switchable valves to reduce the gain by reducing the auxiliary energy transmitted to the brake pressure transducer, furthermore with sensors and with electrical circuits for determining and evaluating the wheel rotation behavior as well as to generate control signals with which the brake pressure distribution to the front wheels and the rear wheels and the brake pressure curve when locking tendencies occur can be influenced, according to patent ... (patent application P 33 23 402.7).

Brake systems with slip control are known in numerous variants. With sensors, e.g. inductive transducers, will be in such Systems, the turning behavior of wheels is measured directly or indirectly, and it is recorded in the brake pressure curve intervened when the measured values or

the changes over time indicate a risk of blocking. With The help of modulators, which can also be designed as switchable valves, the tendency to lock is counteracted by working on the affected wheel or jointly Regulated wheel groups, the brake pressure is reduced according to specified rules, constant is held and, if necessary, increased again, with the aim of reducing the wheel brake slip one for braking, driving stability and steering ability of the vehicle favorable value to regulate.

Since the grip of the wheels on the road as well as the braking on the The forces occurring in the wheel depend on numerous parameters, the most important of which vary within very wide limits, such brake slip control systems are expensive. Simplifying the plants and reducing the manufacturing effort with none or only a slight loss in control accuracy is therefore a central task in the development of brake slip control systems.

A braking system with an auxiliary energy source is already in the German Offenlegungsschriften DE-OS 30 40 561 and DE-OS 30 40 562 described. The brake pressure transducer this system contains a brake pressure control valve controlled by the brake pedal, to which a brake circuit is connected. Via a single or tandem main cylinder, which is structurally combined with the brake pressure control valve and which is also from the through the auxiliary power increased brake pedal force applied one or two additional brake circuits are connected. For brake slip control are electromagnetic switching valves inserted in the hydraulic brake circuits controlled, which block the flow of hydraulic medium to the wheel brake and thereby can prevent a further increase in brake pressure. By opening an outlet towards the pressure equalization tank, the brake pressure is increased to the desired pressure level reduced. The working spaces of the master cylinder can be accessed via further switching valves feed dynamic pressure from the auxiliary energy source, thereby preventing the outflow of Hydraulic medium balanced in the expansion tank and thereby emptying the Working spaces is prevented by repeated pressure reduction. The effort required of hydraulic resources is quite high in such systems.

There are already systems with circulating throttle amplifiers (Offenlegungsschriften DE-OS 30 40 548 and DE-OS 30 40 540) known, in which the pressure medium path of the A throttle valve is inserted into the auxiliary energy-feeding pump, which is only activated when the brake is actuated closes, thereby initiating the pressure build-up in the auxiliary energy source and for the Brake booster ensures. In addition, the structure of the is again made up of a brake valve and a master cylinder existing hydraulic unit and the arrangement of the usually switched solenoid valves similar to the one previously described System.

Another problem in the design of braking systems poses the Adaptation of the braking force distribution to the static and dynamic loads the vehicle axles The usual brake force distributors limit on a fixed pressure-dependent control. Load-dependent or delay-dependent Brake force regulators are also known in different designs.

With all devices, only a relatively rough adjustment to the achieve actual axle load distribution.

It is also already known a brake force distributor in which the static Axle load distribution measured with sensors when the vehicle is stationary and entered into a microcomputer is fed in, taking into account these measured values and the measured Brake pressure according to a stored mathematical relationship, the braking force distribution controls on the front axle and the rear axle (European patent application EP-A1 062246). Such a brake force distributor also has the disadvantage that only one calculated, but not the adhesion value actually given at the time of the braking process is decisive for the braking force distribution. Therefore, the braking system has to avoid the dangerous Avoid overbraking the rear axle with certainty, designed in such a way that in most cases the contribution of the rear axle to the braking is less than this would be physically possible. It should also be taken into account that the actual values in practice, they usually deviate significantly from the calculated target values.

The ones in the design of the braking force distribution and the stored brake characteristic values assumed to be constant are subject to a mathematical relationship considerable as a result of manufacturing tolerances, temperature changes, wear and tear, etc. Changes. That’s why it’s already suggested the brake slip on the front and rear wheels with the help of wheel and vehicle sensors as well as logical ones To determine logic circuits and the brake slip on the rear axle in Control depending on the brake slip of the front axle in such a way that at approximately the same frictional connection effort with each braking process on the rear wheels as set on the front wheels (German patent application P 33 01 948.7).

However, there remains the disadvantage that even with such a brake force distributor can only achieve that in most cases when overbraking, i.e. too strong Brake actuation first of all on the front wheels and only when the pressure is even higher the rear wheels To block. This is important because the locking of the rear wheels with a high There is a risk of skidding, while the loss of steering ability due to blocking Front wheels are the lesser evil in comparison. If the brakes are applied too hard, which is given by a relatively low brake pedal pressure on a slippery road surface is, can not be prevented with all the brake force distributors described Block both the front and rear wheels and thereby the vehicle loses its steering ability and driving stability.

It has therefore already been proposed a braking system that both - with every braking process - the braking force distribution to the front and rear axles controls than also prevents the wheels from locking. The for this necessary hydraulic units and the brake pressure modulators are thereby used Control of the brake force distribution and also used for brake slip regulation, so that the manufacturing cost for the brake system is relatively low overall. The aforementioned and in the main patent ... (patent application P 33 23 402.7) Brake system described is characterized by particularly low effort and is still able to optimally apply the braking force to the front wheels with every braking process and rear wheels, which results in an even utilization of the adhesive strength at the front and rear axle, and also to prevent the wheels from locking, whereby even when panic braking on black ice, etc. the driving stability and steering ability of the vehicle is retained.

However, the pressure curve at the front wheel brakes is in the brake system according to the main patent, if the brake pressure transducer consists of a master cylinder combined circulation throttle amplifier exists, on whose throttle valve one of the is directly connected to both brake circuits when the brake pressure is reduced in a controlled manner not completely even on the front axle. The reason for this is that too when switching off or short-circuiting the auxiliary power source, the pedal force continues in the master cylinder circuit, but not in the one connected to the throttle valve Circle works. As a result, a certain residual pressure is retained in the master cylinder circuit.

The invention is therefore based on the object without or at most the brake pressure curve at the front wheel brakes with little additional expenditure on components, especially when lowering the brake pressure, to improve or the ideal course to be adjusted even more closely. In addition, the behavior in the event of a pressure failure in a front wheel brake circuit in the desired way - depending on the design and the special requirements - be influenced.

It has now been found that this task is accomplished by a Further development of a brake system of the type mentioned can solve the therein consists that the two hydraulically separate brake circuits between the brake pressure transducer and the front brakes together by a hydraulically operated actuator are connected, the brake pressure differences at the two front brakes largely or completely compensates.

According to the invention is thus with a simple additional component achieves that in all braking phases, i.e. both with normal brake application and Even with the brake slip control, the same brake pressure in both front wheel brakes is available. A complete pressure reduction is also made possible, which above all is important in the case of low adhesion or braking force coefficient.

Brake pressure transducers can thus also be used for the brake system according to the invention which are not able to operate in both brake circuits by actuating the the amplification reducing valve to completely reduce the brake pressure. this applies e.g. when training the brake force transducer in the form of one with one Single master cylinder combined circulation throttle booster, which has a throttle valve owns, to which one of the two brake circuits is directly connected, with as Auxiliary energy source, a pressure medium pump is provided, the pressure side of which has a Valve that can be switched to flow to reduce the gain or decrease the auxiliary power transferred to the brake force generator temporarily to the pressure compensation tank can be connected.

The actuator is according to a further advantageous embodiment of the invention in the form of a piston displaceably arranged in a cylinder formed, the two end faces of which each delimit a chamber, each on one of the two brake circuits are connected.

Furthermore, according to one embodiment of the invention, it is possible the piston of the actuator with one in the pressure medium line of the master cylinder circuit Mechanical isolating valve inserted between the brake pressure transducer and the actuator to couple that when the pressure is equal or higher In the second, e.g. in the The brake circuit connected to the throttle valve is open.

Some additional switching elements that can be inserted into the brake circuits Influencing the pressure curve, especially in the event of a pressure failure in one of the two Front wheel brake circuits, and various options for generating the control variables for these components are described in the subclaims.

Further features, advantages and possible uses of the invention proceed from the following description of exemplary embodiments of the invention the attached illustrations.

It shows in a schematic simplification Fig. 1 the hydraulic and electrical circuit diagram of a brake system of the type according to the invention, FIG. 2 in the same way Representation like FIG. 1, an extension according to an embodiment of the invention, 3 shows an alternative embodiment to the example in the same manner of representation according to Fig. 2, Fig. 4 in the same way of representation an addition to the embodiment According to FIG. 1, FIG. 5 an alternative to the exemplary embodiment according to FIG. 4 and FIG. 6 a further embodiment example to supplement the embodiment according to FIG. 1 A particularly simple braking system that is able to both distribute the braking force to control the front axle and the rear axle, as well as the brake slip for To regulate the avoidance of locking wheels, Fig. 1 shows.

It is a hydraulic brake system with two brake circuits 1 and 2, each with the wheel brakes connected by a diagonal are. Brake circuit 1 acts directly, apart from what is described below, normally open isolating valve, on the left front wheel VL and via a brake pressure modulator 6 on the right rear wheel HR. Brake circuit 2 is directly on the right front wheel VR and connected to the right rear wheel HR via a brake pressure modulator 6. The brake circuit 2 is directly connected to the right front wheel VR and via a brake pressure modulator 7 connected to the left rear wheel HL.

A hydraulic brake pressure transducer to supply the two brake circuits 1.2 is denoted by 3 in its entirety. The brake pressure transducer 3 sits down composed of a brake booster 4 and a single master cylinder 5. the The pedal force acting on the brake pressure transducer is symbolized by an F.

The brake booster 4 is, for example, a circulation throttle booster suitable, on its (not shown) throttle valve in a known manner the brake circuit 2 is connected directly.

The auxiliary energy source contains a pressure medium pump 8, which is mechanically is coupled to an electric motor drive 9. The pressure side of the pump 8 opens into the circulation throttle booster 4, the suction side of the pump leads to a Pressure equalization tank 11. A pressure relief valve 10, which connects the suction side with the pressure side the pressure medium pump 8 connects, is used to limit the pressure.

The rear brakes 14 and 15 are also via check valves 16,17, which hydraulically decouple the rear wheel brake circuits, and initially via a still locked 2/2-way valve 18 with the expansion tank 11 in connection. Above This way, as will be described later here, a pressure reduction at the rear wheel brakes can be achieved 14.15 force.

In parallel with the input and output of the circulating throttle amplifier 4 A valve 19 is connected in the auxiliary power supply circuit, which in the idle state Is blocked.

This 2/2-way valve 19 is used to reduce the gain or the auxiliary energy transferred to the brake pressure transducer 3 and thereby to reduce the Brake pressure in the front wheel brakes 12, 13.

An actuator 20 coupled to a separating valve 21 connects the two hydraulically separated brake circuits 1 and 2. The actuator consists of one Cylinder 22 in which a piston 23 is slidably arranged. The end faces of the piston delimit chambers 24,25, each of which is connected to one of the two brake circuits 1,2 are connected.

In the master cylinder brake circuit 1 is in the pressure medium path of the valve 21 is inserted into the master cylinder 5 to the actuator 20, which is open, as long as there is pressure equality in the chambers 24, 25 or the pressure in the chamber 25 outweighs.

To determine the wheel rotation behavior, all wheels are equipped with sensors Sl to S4 equipped, the information about the wheel rotation behavior in the form of electrical Signals the electronic linkage and evaluation circuit 26 feed. In this electronics 26, the electrical signals are then used for the control the brake pressure modulators 6,7 and the valves 18,19 generated. It is here both in the modulators 6,7 and in the valves 18 and 19 to electromagnetically 2/2-way valves which can be actuated and blocked in the basic position, i.e. in the non-energized state.

The brake system according to FIG. 1 works as follows: When the brake is actuated by exerting a pedal force, symbolized by the arrow F, is immediately in the two brake circuits 1,2 pressure built up, which is dependent on the foot force F. and is amplified by the auxiliary hydraulic energy applied by the pump 8. By throttling the delivery flow of the pump 8 in the throttle point, not shown hydraulic pressure is built up within the booster 4, which is directly acts on the brake circuit 2 and supports the force on the piston in the master cylinder 5.

Via the pressure medium lines leading to the rear wheel brakes 14,15 27.28 is only activated after actuation or switching over of the 2/2-way valves 6.7 Transfer pressure. The appropriate design of the electronics 26 ensures that that the brake pressure at the rear wheels corresponds to the brake pressure at the front wheel brakes 12,13 follows delayed and as a function of the determined with the help of the sensors S1 to S4 Wheel slip is metered. The wheel slip on the rear wheels should be smaller than on the front wheels or at most the same as the front wheel slip.

If the risk of blocking is sensed on the front or rear wheels, sets the brake slip control. To prevent a further increase in brake pressure on the rear axle, it is sufficient to switch the valves 6, 7 back to the blocking position. If a pressure reduction on the rear axle is required, the valve 18 is energized, see above that now via the check valves 16, 17 pressure to the pressure compensation tank 11 is reduced towards, the desired lower pressure level by controlling the Switching times of the valve 18 is specified by the electronics 26.

The valve 19 is energized to reduce the pressure on the front axle. Through this become, so to speak, the input and output of the auxiliary power connection of the brake pressure transducer 3 shorted out, reducing the hydraulic pressure in the one to the throttle booster 4 connected brake circuit completely and in the one connected to the master cylinder 5 Brake circuit 2 can be lowered to a residual value proportional to the pedal force F. can. Due to the hydraulic imbalance that occurs in the actuator 20 the piston is moved to the right - based on Fig. 1 - and thereby the isolating valve 21 closed. This has a separation of the master cylinder 5 from the front wheel brake 12 result, so that a lowering below the residual pressure in the master cylinder 5 becomes possible.

Another advantage of the actuator 20 in conjunction with the isolation valve 21 consists in the fact that the pressure drop on the front axle does not affect the master cylinder piston transmits. This prevents the brake pedal from pulsing.

If the master cylinder circuit 1 fails, the booster brake circuit remains 2 fully effective.

In order to transfer pressure to the even if the brake circuit 2 fails To ensure wheel brake 12 of the left front wheel VL was implemented in the according to Fig. 2, the actuator 20 via a hydraulically operated switching valve 29, the a check valve 30 is parallel, hydraulically connected. In the rest position, i.e. as long as there is no control pressure at ports P1> P2, the hydraulic Connection blocked through valve 29. The control pressure for actuating the Valve 29 is controlled by throttling points inserted in the auxiliary power supply system 31 or 32 generated. The throttle point arranged in the main flow of the pressure medium pump 8 31 delivers with every braking, i.e. always when the pump 8 is delivering, one of the pressure difference tp dependent signal to the control inputs Pl, P2 of the valve 29 whereby this is switched to flow. When the pump 8 does not deliver or the aperture 31 is not traversed, this leads to locking, so to speak of the actuator 20, because a displacement of the piston 23 when the valve 29 is closed not possible.

The isolating valve 21 thereby forcibly remains open. So it is ensures that if the auxiliary power supply fails, the passage from the master cylinder 5 remains open via the brake circuit 1 to the front wheel brake 12.

The hydraulic path via the check valve 30 is in any case sure that the piston 23 of the actuator 20 when you let go of the brake pedal can slide back into the starting position in which the isolating valve 21 is open.

Instead of the throttle point 31, the throttle point 32 use according to FIG. 2 to generate the controlling differential pressure Ap '. At this Throttle point only then falls a differential pressure ap 'switching valve 29 on if during the brake slip control, because the brake pressure on the front axle is too high prevails, the valve 19 is energized. If the auxiliary power supply fails and so that the brake circuit 2, no control pressure can arise at the throttle point 32 either.

Instead of the valve 29 according to FIG. 2, it can also be used in the brake circuit 1, which connects the master cylinder 5 to the front brake 12, a hydraulic one operated valve 33 can be used, but in the rest position, i. as long as there is no control pressure, it must be switched to continuity. Fig. 3 shows this embodiment of the invention. The valve 33 is located in this embodiment parallel to the pressure medium path given by the isolating valve 21 and the actuator 20 and connects the front wheel brake 12 to the output of the master cylinder 5.

The differential pressure ap for controlling this valve can be equal Way as in the embodiment according to FIG. 2 by a throttle point 31 in the main flow the pump 8 or through a throttle 32 in series to which the auxiliary energy source short-circuiting valve 19 win.

Another possibility for keeping the brake circuit 1 open in the event of a failure of the brake circuit 2 or the auxiliary power supply system is shown in FIG. 4. In this The embodiment is an actuator 34 that is in the same place as the actuator 20 is arranged and is also mechanically coupled to the isolating valve 21, equipped with a spring-loaded detent 35, which the piston 36 of the actuator holds in the basic position as long as the in turn generated by a throttle point 31 Dynamic pressure PB is below a value dependent on the spring 37 of the detent 35. Consequently is the function of the actuator whenever the pump 8 is working properly 34 ensured. If the auxiliary power fails, it occurs at the throttle point 31 no back pressure and the locking mechanism prevents the piston 36 from moving.

In the embodiment of the invention according to FIG. 5, the brake circuit is 2 via a switching element 38 designed as a hydraulic slide with the dem Isolation valve 21 opposite chamber 25 of the actuator 20 connected. The switching element 38 consists essentially of a cylinder with a displaceably arranged therein Piston 39. This switching element is traversed by the delivery flow of the hydraulic pump 8, as indicated by the connections C> D and the arrows, and acts like a 2/2 way valve. In the rest position, the flow is from input A of the switching element 38 to output B and thus to chamber 25 of actuator 20 is interrupted.

Promotes the pump 8, then it is put in by the in a throttle Piston 39 resulting back pressure of the piston 39 against the pressure of a return spring 41 shifted axially and opens the way from the brake circuit 2 in the actuator chamber 25. Otherwise, the mode of operation is the same as that of the exemplary embodiment according to FIG. 2 comparable.

Finally, according to the invention, that shown in FIG. 6 is also shown Variant provided. In this embodiment, the hydraulic connection of the actuator 20 to the right front wheel brake VR or to the booster brake circuit 2 a hydraulically releasable check valve 40 inserted, which the pressure medium flow only opens when the pressure in brake circuit 2 exceeds a certain minimum pressure of e.g. 1 bar increases.

If brake circuit 2 fails, e.g. because the auxiliary energy source fails, closes the check valve 14 and thereby locks the piston 23 of the actuator 20, so that the isolating valve 21 in the brake circuit 1 remains open.

The connection between the front wheel brake 12 and the master cylinder 5 remains So behave so that the front wheel VL is braked despite the failure of the auxiliary power source can be, albeit without brake booster.

The arrangement last described is characterized by particularly low levels Component costs.

Claims (15)

Claims f brake system for motor vehicles, in particular for Road vehicles, with a two-circuit, essentially consisting of a brake booster as well as a master cylinder existing hydraulic, pedal-operated brake pressure transducer, which is connected to an auxiliary energy source and its two brake circuits respectively a front wheel and a rear wheel are connected, with brake pressure modulators in the pressure medium lines leading to the rear wheels as well as from the rear wheel brakes to a pressure compensation tank leading pressure medium lines, in which on passage Switchable isolation valves are used, with switchable valves for reduction the gain by reducing the auxiliary energy transferred to the brake pressure transducer, furthermore with sensors and with electrical circuits for determination and evaluation of the wheel rotation behavior as well as for the generation of control signals with which the brake pressure distribution on the front wheels and the rear wheels and the brake pressure curve when it occurs can be influenced by blocking tendencies, according to patent ... (patent application P 33 23 402.7), that the two hydraulic separate brake circuits (1,2) between the brake pressure transducer (3) and the front wheel brakes (12.13) are connected to one another by a hydraulically operated actuator (20, 34), the brake pressure differences at the two front wheel brakes (12, 13) largely or completely compensates. 2. Brake system according to claim 1, d a d u r c h g e -k e n n z e i c h n e t that by actuating the gain reducing valve (19) of the Brake pressure in one of the two brake circuits connected to the brake pressure transducer (3) (1,2) completely, in the other only except for one of the brake pedal force (F) dependent residual pressure can be reduced. 3. Brake system according to claim 2, d a d u r c h g e -k e n n z e i c h n e t that the brake pressure transducer (3) is in the form of a single master cylinder combined circulation throttle amplifier is formed and has a throttle valve, to which one of the two brake circuits (2) is directly connected and that as an auxiliary energy source a pressure medium pump (8) is provided, the pressure side of which has a flow through switchable valve (19) can be connected to the expansion tank (11). 4. Brake system according to one of claims 1 to 3, d a -d u r c h g It is not shown that the actuator (20, 34) is in the form of a cylinder (22) displaceably arranged piston (23,36) is formed, the two end faces of which limit one chamber (24,25) each, each of which is connected to one of the two brake circuits (1,2) are connected. 5. Brake system according to claim 4, d a d u r c h g e -k e n n z e i c h n e t that the piston (23,36) of the actuator (20,34) with one in the pressure medium line one of the two brake circuits (1) functionally between the brake pressure transducer (3) and the isolating valve (21) inserted into the actuator (20, 34) is mechanically coupled, this when the pressure on the two front wheel brakes is equal (12> 13) and at higher Pressure in the other, i.e. in the one directly from the brake pressure transducer (3) to the front brake (13) leading brake circuit (2) is open. 6. Brake system according to claim 5, d a d u r c h g e -k e n n z e i c h n e t that the brake pressure transducer (3) consists of a circulation throttle booster (4) and a single master cylinder (5) and that the isolation valve (21) in the to the Single master cylinder (5) connected to the front wheel brake circuit (1) is inserted. 7. Brake system according to claim 6, d a d u r c h g e -k e n n z e i c h n e t that the front wheel brake circuit connected to the circulation throttle booster (4) (2) connected to the actuator (20) via a hydraulically operated valve (29) is locked in the rest position and by applying one from the auxiliary energy circuit derived control pressure (Ap, Ap ') can be switched to passage, and that the hydraulic actuated valve (29) a check valve opening towards the actuator (20) (30) lies parallel. 8. Brake system according to claim 6, d a d u r c h g e -k e n n z e i c h n e t that in the front wheel brake circuit connected to the single master cylinder (5) (1) between the brake pressure transducer (3) and the front brake (12), i.e. in parallel to the isolating valve (21) and the actuator (20), a hydraulically operated valve (33) is inserted, which is switched to pass in the rest position and when applied a control pressure (Ap, tp ') can be switched to blocking. 9. Brake system according to claim 7 or 8, d a d u r c h g e k e n n z E i c h n e t that the between the brake pressure transducer (3) and the front brake (12,13) inserted valve (29,33) controlling pressure (4p, ap ') from the differential pressure can be derived, which is via a throttle section inserted into the auxiliary power supply circuit (31,32) is obtained. 10. Brake system according to claim 9, d a d u r c h g e -k e n n z e 1 c h n e t that the throttle point (31) for generating the control pressure (p), the in the pressure medium line between the brake pressure transducer (3) and the front brake (12,13) inserted valve (29,33) switches, in series between the pressure side of the Pressure medium pump (8) and the brake pressure transducer (3) is inserted. 11. Brake system according to claim 9, d a d u r c h g e -k e n n z e i c h n e t that the throttle point (32) for generating the valve (29, 33) switching Control pressure (Ap ') is inserted in series to a valve (19), which is used to reduce the gain temporarily bridges or short-circuits the auxiliary energy source. 12. Brake system according to claim 6, d a d u r c h g e -k e n n z e i c h n e t that the piston (36) of the actuator (34) by a hydraulically operated, spring-loaded detent (35) can be locked in a basic position in which the with the piston (36) coupled isolation valve (21) is switched to passage, and that the detent (35) can be released by a control pressure (PB). 13. Brake system according to claim 12, d a by gek e n n z e i c h n e t that the control pressure (PB) for releasing the detent (35) can be derived from the differential pressure is that by a in the auxiliary power supply system between the pressure side of the Pump (8) and the brake pressure transducer (3) used throttle point (31) can be generated. 14. Brake system according to claim 6, d a d u r c h g e -k e n n z e i c h n e t that the front wheel brake circuit connected to the circulation throttle amplifier (4) (2) with the actuator (20) via a flow in the pressure part of the pressure medium pump (8) the auxiliary energy source arranged, axially traversed by the pressure medium and piston-cylinder arrangement (38) controlled by the pressure medium flow is connected, whose piston (39) is in the initial position, i.e. as long as the pump (8) is not delivering, interrupts the flow from the wheel brake (13) to the actuator (20) and the through the pressure medium flow is displaceable against the force of a return spring (41) and thereby switching the passage from the wheel brake (13) to the actuator (20) to passage. 15. Brake system according to claim 6, d a d u r c h g e -k e n n z e i c h n e t that the front wheel brake circuit connected to the circulation throttle amplifier (4) (2) with the actuator (20) via a hydraulically releasable check valve (40) is connected, which is open when the pressure to the circulation throttle amplifier (4) connected front wheel brake circuit (2) exceeds a predetermined threshold value.