DE102019207057A1 - Brake system for a motor vehicle and method for operating the brake system - Google Patents

Abstract

Brake system for a motor vehicle with hydraulically actuated first wheel brakes (8c, 8d), which wheels (FL, FR) are assigned to a first vehicle axle (VA), and hydraulically actuated second wheel brakes (8a, 8b), which wheels (RL, RR) one are assigned to the second vehicle axle (HA), a pressurized medium reservoir (4) under atmospheric pressure, an electrically actuated inlet valve (6a-6d) per wheel brake and an electrically actuated outlet valve (7a-7d) per wheel brake, a first electrically controllable pressure supply device (5), which is hydraulically connected to a brake supply line (13) to which the wheel brakes (8a-8d) are connected, a second electrically controllable pressure supply device (2) with a suction connection (28) which is connected to the pressure medium reservoir (4), and one Pressure connection (27), which is hydraulically connected to the brake supply line (13), the first wheel brake n are connected to the pressure medium reservoir (4) via the associated outlet valves (7c, 7d) and a first return line (14b) and the second wheel brakes are connected to the pressure medium reservoir (4 ) are connected, and in exactly one of the two return lines there is an electrically actuated additional valve (91, 92) which can be regulated in an analog manner and via which the outlet valves of the wheel brakes of the corresponding vehicle axle are connected to the pressure medium reservoir (4), as well as methods of operation the brake system.

Description

The invention relates to a brake system for a motor vehicle according to the preamble of claim 1 and a method for operating such a brake system.

From the DE 10 2013 217 954 A1 A brake system for a motor vehicle is known with four hydraulically actuable wheel brakes, an electrically actuable inlet and outlet valve per wheel brake, the wheel brakes being connected to a pressure medium reservoir via the assigned outlet valve, a first and a second electrically controllable pressure supply device, a brake supply line with a electrically operated circuit separating valve, the brake supply line being hydraulically separated into a first and a second line section when the circuit separating valve is closed, the first line section being hydraulically connected to the wheel brakes of one vehicle axle and the one pressure supply device and the second line section being connected to the wheel brakes of the other vehicle axle and the other pressure supply device is hydraulically connected. The two pressure supply devices are designed as linear actuators and each pressure supply device is assigned its own control and regulating unit. Furthermore, a central control and regulating unit is provided which controls the circuit separation valve.

It is an object of the present invention to provide a brake system suitable for highly automated driving and a method for operating such a brake system, which are particularly suitable for motor vehicles with a regenerative braking function.

This object is achieved by a brake system according to claim 1 and a method according to claim 11.

The invention is based on the idea that the first wheel brakes are connected to the pressure medium reservoir via the assigned outlet valves and a first return line and the second wheel brakes are connected to the pressure medium reservoir via the assigned outlet valves and a second return line, and in exactly one of the two return lines an electrically actuated, analogly controllable additional valve is arranged, via which the outlet valves of the wheel brakes of the corresponding vehicle axle are connected to the pressure medium reservoir. This creates a comfortable axis-specific pressure position, e.g. with regenerative braking is possible, only one additional valve is required.

The first vehicle axle is preferably the front axle and the second vehicle axle is the rear axle.

The auxiliary valve is preferably designed to be open when de-energized.

A check valve closing in the direction of the pressure medium reservoir is preferably connected in parallel with the additional valve.

An electrically operable axle isolating valve is preferably arranged in the brake supply line in such a way that when the axle isolating valve is closed, the brake supply line is hydraulically separated into a first and a second line section, the first line section being hydraulically connected to the second wheel brakes and the second pressure supply device and the second line section being connected to the first wheel brakes and the first pressure supply device is hydraulically connected.

The axle isolating valve is preferably designed to be open when de-energized, so that the axle isolating valve does not have to be actuated to actuate all wheel brakes by means of the master brake cylinder, but also the two pressure supply devices.

The first electrically controllable pressure supply device is preferably hydraulically separably connected to the brake supply line, in particular to the second line section, via a first isolating valve. This enables hydraulic separation of the first pressure supply device, e.g. in the event of a leak in the pressure supply device. The first isolating valve is particularly preferably designed to be electrically actuated.

According to a preferred embodiment of the brake system according to the invention, a master brake cylinder which can be actuated by means of a brake pedal and is hydraulically connected to the brake supply line is provided.

The master brake cylinder is preferably hydraulically separably connected to the brake supply line via a second isolating valve, or the suction connection is connected to the master brake cylinder via the second isolating valve.

The master brake cylinder is preferably hydraulically separably connected to the brake supply line, in particular the first line section, via a second isolation valve. The suction port of the second pressure supply device is connected to the master brake cylinder via the second isolating valve. The master brake cylinder enables a driver-operated hydraulic fallback level, for example in the event that both Print delivery facilities fail. The second pressure supply device can also draw in pressure medium from the master brake cylinder, at least when the master brake cylinder is not actuated.

The second isolating valve is particularly preferably designed to be electrically actuated.

The brake system preferably comprises an electrically actuable overflow valve, via which the pressure connection of the second pressure supply device is hydraulically connected to the suction connection of the second pressure supply device. This makes it possible to set or regulate the pressure provided by the second pressure supply device. The overflow valve is therefore connected in parallel with the second pressure supply device.

The overflow valve is preferably designed to be open when de-energized.

The suction port of the second pressure supply device is preferably connected to the pressure medium reservoir via a check valve opening in the direction of the suction port.
This means that the check valve is designed to close in the direction of the pressure medium reservoir.

The brake system preferably comprises a first electrical device with electrical and / or electronic elements which controls the first pressure supply device and a second electrical device with electrical and / or electronic elements which controls the second pressure supply device, the first and the second electrical device being electrical are independent of one another, so that an electrical or electronic fault in one of the electrical devices does not lead to failure of both electrical devices. This provides the redundancy of the electrically controlled print preparation required for highly automated or autonomous driving. The two electrical devices are electrically independent of one another in the sense that failure of the first electrical device does not cause failure of the second electrical device and vice versa, i.e. the two electrical devices are electrically isolated.

The inlet and outlet valves are preferably controlled by the second electrical device, which also controls the second pressure supply device. The inlet and outlet valves can particularly preferably be controlled exclusively by the second electrical device. This has the advantage that the brake system has a high level of availability with regard to the provision of brake functions in which all wheel brakes are actuated, possibly with different wheel brake pressures, in order to e.g. to ensure a short braking distance and maintain the maneuverability of the motor vehicle. Thus, in a fault-free state of the brake system, wheel-specific wheel brake pressures can be set by the first electrical device providing a (central) brake pressure by means of the first pressure supply device and the second electrical device modulating the wheel-specific wheel brake pressures by means of the inlet and outlet valves. However, even if the first pressure supply device or the first electrical device fails, wheel-specific wheel brake pressures can be set by the second electrical device performing braking with wheel-specific wheel brake pressures by means of the second pressure supply device and the inlet and exhaust valves.

The additional valve is preferably also controlled by the second electrical device. The additional valve can particularly preferably be controlled exclusively by the second electrical device. The auxiliary valve and the associated outlet valves can be controlled for a comfortable axis-specific pressure reduction as long as the second electrical device is functional.

The first pressure supply device is preferably controlled exclusively by the first electrical device and the second pressure supply device as well as the inlet and outlet valves and the additional valve are preferably controlled exclusively by the second electrical device. This allows further redundancy in the components, e.g. there is no need for double controllable valves with two independent valve coils or for a pressure supply device with two electrically independent electric motors.

The overflow valve is preferably controlled by the second electrical device. The overflow valve is particularly preferably only controllable by the second electrical device. If the first electrical device fails, the second electrical device can use the second pressure supply device and the overflow valve to set precise pressure profiles on the wheel brakes.

The axis separating valve is preferably controlled by the first electrical device. The axle isolating valve is particularly preferably only controllable by the first electrical device. If the second electrical device fails, the axle separating valve can be used to hydraulically separate the wheel brakes of the two vehicle axles. This enables independent pressure modulation on the wheel brakes of the two vehicle axles.

The first isolating valve is preferably controlled by the first electrical device. The first isolating valve can particularly preferably be controlled exclusively by the first electrical device.

The second isolating valve is preferably controlled by the first electrical device. The second isolating valve can particularly preferably be controlled exclusively by the first electrical device.

The brake system preferably comprises a simulation device, which is operatively connected to the master brake cylinder.

The simulation device is preferably hydraulically connected to the master brake cylinder, in which connection a, in particular normally closed, simulator release valve is arranged.

The simulator release valve is preferably controlled by the first electrical device. Particularly preferably, the simulator release valve can only be controlled by the first electrical device.

Preferably, the master brake cylinder or the simulation device is assigned at least two sensors for detecting a driver brake request variable, wherein one of the sensors is connected to and evaluated by the second electrical device, and the other of the sensors is connected to and by the first electrical device is evaluated. The one of the sensors is particularly preferably connected exclusively to the second electrical device and is evaluated by the latter, while the other of the sensors is exclusively connected to the first electrical device and is evaluated by the latter.

In order to further increase the availability of the brake system compared to a single fault, the first electrical device is preferably supplied by a first electrical energy source and the second electrical device is supplied by a second electrical energy source, which is independent of the first electrical energy source. The first electrical energy source advantageously supplies all those electrical components that are controlled by the first electrical device, while the second electrical energy source supplies all those electrical components that are controlled by the second electrical device.

The brake system preferably comprises a first pressure sensor which is assigned to the second line section and a second pressure sensor which is assigned to the master brake cylinder. The first pressure sensor is preferably, in particular exclusively, connected to the first electrical device and is evaluated by the latter, and the second pressure sensor is, in particular exclusively, connected to the second electrical device and is evaluated by the latter.

A third pressure sensor is preferably provided, which is assigned to the first line section and thus to the pressure outlet of the second pressure supply device. In this way, the pressure at the wheel brakes, which are connected to the first line section, can be regulated more precisely.

The second pressure supply device is preferably formed by a 2-piston pump. This type of pump, which has been tried and tested over many years in motor vehicle brake systems, can be used in the brake system, since pressure relief or pressure reduction can be carried out with sufficient speed and precision by means of the overflow valve in order to be able to provide the above-mentioned most important brake functions in the event of a failure of the first pressure supply device. Piston pumps are inexpensive to manufacture and are based on known technologies, so that their use also poses a very low development risk for the brake system.

The first pressure supply device is preferably formed by a cylinder-piston arrangement with a hydraulic pressure chamber, the piston of which is advanced and retracted by an electromechanical actuator for brake pressure build-up and for brake pressure reduction. In the event of a failure of the second pressure supply device or the second electrical energy source or the second electrical device, the first electrical device preferably uses the first pressure supply device and the axle isolating valve to brake with axle-specific wheel brake pressures.

The invention offers the advantage that the brake system is simple and compact and is suitable for highly automated driving. The brake system enables comfortable (analog-controlled), axle-specific pressure reduction by means of the additional valve, as is desired or required in connection with regenerative braking. In particular, a comfortable and quiet pressure reduction on the lower pressure vehicle axle is also possible.

With regard to the method for operating a brake system, the invention is based on the idea that, in a predetermined state, the Brake system by means of the additional valve, a controlled pressure reduction is carried out on the wheel brakes of the corresponding vehicle axle. It is particularly preferable for the auxiliary valve to carry out a controlled pressure reduction on the wheel brakes of the corresponding vehicle axle during recuperative braking.

Further preferred embodiments of the invention result from the subclaims and the following description with reference to figures.

• 1 ein erstes Ausführungsbeispiel einer erfindungsgemäßen Bremsanlage, und
• 2 ein zweites Ausführungsbeispiel einer erfindungsgemäßen Bremsanlage.

They show schematically

• 1 a first embodiment of a brake system according to the invention, and
• 2 a second embodiment of a brake system according to the invention.

1 shows schematically a first embodiment of a brake system according to the invention for a motor vehicle with four hydraulically actuated wheel brakes 8a . 8b . 8c . 8d , The wheel brake is exemplary 8a the left rear wheel ( RL ), the wheel brake 8b the right rear wheel ( RR ), the wheel brake 8c the left front wheel ( FL ) and the wheel brake 8d the right front wheel ( FR ) assigned. The wheel brakes 8a . 8b are the rear axle HA and the wheel brakes 8c . 8d the front axle VA assigned.

The brake system comprises a first electrically controllable pressure supply device 5 , a second electrically controllable pressure supply device 2 , a pressure medium reservoir under atmospheric pressure 4 and wheel individual brake pressure modulation valves, which act as an intake valve 6a-6d and an exhaust valve 7a - 7d are executed per wheel brake. Furthermore, according to the example, the brake system comprises one by means of a brake pedal 1 actuatable, single-circuit skin brake cylinder 80 and one with the master brake cylinder 80 connected hydraulic simulation device 3 ,

The first electrically controllable pressure supply device 5 is designed as a hydraulic cylinder-piston arrangement (or a single-circuit electrohydraulic actuator (linear actuator)) whose pistons 36 from a schematically indicated electric motor 35 with the interposition of a rotation-translation gear, also shown schematically 39 can be actuated, in particular can be moved back and forth to a pressure in a pressure chamber 37 assemble and disassemble. The piston 36 limits the pressure space 37 the print delivery device 5 , To control the electric motor is the rotor position of the electric motor 35 detecting, only schematically indicated rotor position sensor 44 intended.

To the pressure room 37 the first electrically controllable pressure supply device 5 is a line section 38 connected. The line section 38 is with a brake supply line 13 connected through which all inlet ports of the intake valves 6a-6d with the pressure room 37 the first electrically controllable pressure supply device 5 are connected. The line section is exemplary 38 via an electrically actuated, preferably normally closed, first isolating valve 26 with the brake supply line 13 connected. Through the first isolation valve 26 can the hydraulic connection between the pressure chamber 37 the first electrically controllable pressure supply device 5 and the brake supply line 13 (and thus the inlet connections of the intake valves 6a - 6d) opened and locked.

pressure chamber 37 is independent of the operating state of the piston 36 , via a (suction) line 42 with the pressure medium reservoir 4 connected. On the line 42 is in the direction of the pressure medium reservoir 4 closing check valve 53 arranged. A suction of pressure medium in the pressure chamber 37 is by retracting the piston 36 with the isolation valve closed 26 possible. The cylinder-piston arrangement 5 has no sniffing holes.

The first print delivery device 5 is advantageously a high-performance pressure actuator that implements the normal braking function with maximum comfort and dynamics in the fault-free braking system.

The second electrically controllable pressure supply device 2 is designed, for example, as a two-circuit radial piston pump, the two pressure sides of which are connected together. A single-circuit pump is also conceivable. Pressure supply device 2 has a suction connection 28 which has a hydraulic connection 41 with the pressure medium reservoir 4 communicates, and a pressure port 27 , In the hydraulic connection 41 is in the direction of the suction connection 28 opening check valve 99 arranged. The pressure connection 27 the second print supply device 2 is with the brake supply line 13 connected so that the inlet ports of the intake valves 6a-6d with the pressure connection 27 the second print supply device 2 are connected.

suction 28 is still above the second isolation valve 81 with the master brake cylinder 80 connected.

The second print delivery device 2 is an overflow valve 32 assigned, the control of which can implement a pressure control, in particular a pressure limitation or a pressure reduction. This is the pressure connection 27 the second print supply device 2 via the overflow valve 32 with the suction connection 28 (and thus the pressure medium reservoir 4 ) connected, ie the overflow valve 32 is the print delivery facility 2 connected in parallel. The overflow valve 32 is designed to be open when de-energized, and advantageously designed to be adjustable in an analog manner. By means of the overflow valve 32 can that of the second print supply device 2 pressure provided for the wheel brakes can be limited or reduced.

The second pressure supply device is exemplary 2 a parallel connection from the normally open, analog controllable overflow valve 32 and one for the suction connection 28 non-return valve 63 connected in parallel.

The brake pedal operated master brake cylinder 80 is designed with a single circuit and thus comprises a single hydraulic pressure chamber 88 which by a master brake cylinder piston 89 is limited mechanically with the brake pedal 1 connected is. The master brake cylinder 80 or its pressure room 88 is via a hydraulic connection line 85 with the brake supply line 13 connected. The hydraulic connecting line is exemplary 85 is via a second isolation valve 81 with the brake supply line 13 connected. The second isolation valve 81 is open without current.

The pressure room 88 the master brake cylinder 80 is when the master brake cylinder is not actuated via sniffer holes with the pressure medium reservoir 4 hydraulically connected. In this hydraulic connection there is a parallel connection of an orifice with one in the direction of the pressure medium reservoir 4 closing check valve arranged. For example, the master brake cylinder 80 over a line section 45 which in the line section 41 flows with the pressure medium reservoir 4 hydraulically connected. Cover with check valve is in line section 45 arranged.

piston rod 24 couples the swiveling movement of the brake pedal 1 as a result of pedal actuation with a translational movement of the master brake cylinder piston 89 , the actuation path of a preferably redundant displacement sensor 25 is recorded. As a result, the corresponding piston travel signal is a measure of the brake pedal actuation angle. It represents a driver's braking request. There is also a pressure sensor for recording the driver brake request 20 intended.

simulation device 3 has a simulator piston in a housing 31 on which is a hydraulic chamber 34 from a simulator back chamber 30 separates. simulator piston 31 is supported by a in the simulator rear chamber 30 arranged elastic element 33 (e.g. simulator spring) on the housing. simulation device 3 or their hydraulic chamber 34 is with the pressure room 88 of the skin brake cylinder 80 hydraulically connected. In the hydraulic connection between the master brake cylinder 80 and simulation device 3 is a simulator release valve 83 arranged. The simulator release valve 83 is closed when de-energized. The simulation device 3 can by means of the simulator release valve 83 be switched on and off.

The simulation device 3 gives the driver a comfortable brake pedal feel when the isolation valve 81 is closed and the simulator release valve 83 is open.

The brake system comprises an additional hydraulic grip (by the driver) as a second fallback level in the event of a double fault, for example a failure of the first and second pressure supply devices 2 . 5 ,

In the brake supply line 13 is an electrically actuable, advantageously normally open, axle separating valve 40 arranged through which the brake supply line 13 in a first line section 13a which with the second pressure supply device 2 (whose pressure connection 27 ) is connected, and a second line section 13b , which (for example via the first isolation valve 26 ) with the first pressure supply device 5 is connected, can be separated. Here is the first line section 13a with two of the intake valves, namely the intake valves 6a and 6b , hydraulically connected and the second line section 13b is with the other intake valves, namely the intake valves 6c and 6d , hydraulically connected. By closing the axis separating valve 40 the brake system is thus hydraulically divided into two (partial) brake circuits I and II split or split. It is in the first brake circuit I the second print supply device 2 with only the wheel brakes 8a and 8b the rear axle HA connected, and in the second brake circuit II the first print delivery device 5 with only the wheel brakes 8c and 8d the front axle VA connected.

Master Cylinder 80 is with the first line section 13a connected. For example, the master brake cylinder 80 via the second isolating valve 81 with the first line section 13a connected. In the first line section 13a is in a way a parallel connection of the check valve 63 , Overflow valve 13 and print delivery device 2 arranged.

As already mentioned, the brake system includes each hydraulically actuable wheel brake 8a-8d an inlet valve 6a-6d and an exhaust valve 7a-7d , which are hydraulically connected in pairs via center connections and to the wheel brake 8a-8d are connected. The intake valves 6a-6d is one each to the brake supply line 13 non-specified check valve opening in parallel. The inlet valves are advantageous 6a-6d similarly adjustable.

The outlet ports of the exhaust valves 7a . 7b of the (partial) brake circuit I (or the rear axle brakes 8a . 8b) are via a first (common) return line 14a with the pressure medium reservoir 4 connected. The outlet ports of the exhaust valves 7c . 7d of the (partial) brake circuit II (or the front axle brakes 8c . 8d) are via a second (common) return line 14b with the pressure medium reservoir 4 connected. Return line 14b flows, for example, into (suction) line 42 , Return line 14a flows, for example, into the hydraulic connection 41 ,

Only in the return line 14a the rear axle wheel brakes 8a . 8b is an electrically operated additional valve 91 arranged, via which the outlet valves 7a . 7b the wheel brakes 8a . 8b the rear axle HA with the pressure medium reservoir 4 are connected. additional valve 91 is designed to be adjustable or controlled in the same way (analog valve). additional valve 91 is advantageously open when de-energized.

According to example is in the return line 14a the rear axle wheel brakes 8a . 8b a parallel connection from the additional valve 91 and one in the direction of the pressure medium reservoir 4 closing check valve 93 arranged.

The inlet ports of all intake valves 6a - 6d can by means of the brake supply line 13 be supplied with a pressure from the first pressure supply device 5 or, for example in the event of failure of the first pressure supply device, by the second pressure supply device 2 , or, for example, in the event of failure of both pressure supply devices 2 . 5 , from the master brake cylinder 80 provided.

The brake system includes a first pressure sensor 19 which, for example, the second line section 13b assigned (and with the isolating valve open 26 the pressure of the first pressure supply device 5 measures), and a second pressure sensor 20 , which is the master brake cylinder 80 assigned.

The brake system advantageously includes a third pressure sensor, which is the second pressure supply device 2 assigned. This sensor detects the pressure at the pressure outlet 27 , This can cause pressure in the rear axle wheel brakes 8a . 8b be regulated more precisely.

A pressure relief of the brake system or the wheel brakes in the release position is through the sniffing hole (s) in the master brake cylinder 80 guaranteed.

According to the example, the brake system for leakage monitoring comprises a level measuring device 50 for determining a pressure medium level in the pressure medium reservoir 4 ,

The components are advantageous 2 . 5 . 6a - 6d . 7a - 7d . 91 . 32 . 81 . 40 , and 26 (and the sensors 19 . 20 ) in a first module or structural unit / assembly 200 , in particular in a first hydraulic control and regulation unit, arranged during the master brake cylinder 80 with the simulation device 3 and the valve 83 (and the sensor 25 ) in a separate, second module or structural unit / assembly 300 , in particular in a second hydraulic control and regulating unit.

The dashed line 55 marks the advantageous division of the brake system into the two modules or units 200 . 300 with the property that as few components as possible of the second structural unit 300 (ie the master brake cylinder assembly) are assigned. This is advantageous because this assembly must be placed on the bulkhead while the other (larger) assembly 200 can be placed in the vehicle with minimal restrictions.

Variants of this division can make sense. For example, the mentioned orifice with its parallel check valve in the second assembly 300 be arranged. This means the first assembly 200 be changed less if, in the course of further development of the brake system, the hydraulic penetration and the master brake cylinder assembly are eliminated 300 is replaced by a pure simulator sensor assembly.

A first electrical energy source is used to supply the brake system with electrical energy 57 , for example a first electrical system, and a second electrical energy source that is independent of the first energy source 67 , for example a second electrical system, is provided.

A first electrical device is used to control the brake system 100 with electrical and / or electronic elements (e.g. Microcontrollers, power units, valve drivers, other electronic components, etc.) and a second electrical device 110 with electrical and / or electronic elements (e.g. microcontrollers, power units, valve drivers, other electronic components, etc.). The first electrical device 100 and the second electrical device 110 are electrically independent. The first electrical device 100 controls the first print supply device 5 on (each with an arrow with A featured), the second electrical device 110 controls the second pressure supply device 2 on (each marked with an arrow with B).

In 1 are those electrical or electronic or sensory components that the first electrical device 100 are assigned, indicated by an arrow with A, while those electrical or electronic or sensory components which the second electrical device 110 are assigned, are identified by an arrow with B.

The first print delivery device 5 and the axis separating valve 40 are, advantageously exclusively, from the first electrical device 100 controlled or assigned to them (arrows with A ). Likewise, the isolation valves 26 . 81 and the simulator release valve 83 advantageously only from the first electrical device 100 controlled or assigned to them (arrows with A ).

The second print delivery device 2 whose overflow valve 32 , the intake and exhaust valves 6a-6d . 7a-7d as well as the additional valve 91 are, advantageously exclusively, from the second electrical device 110 controlled or assigned to them (arrows with B ).

According to the example, the first electrical energy source supplies 57 the electrical partition A with energy and the second electrical energy source 67 the electrical partition B.

The first electrical device 100 is also advantageously the sensor 25 assigned to brake request acquisition. The other sensor for braking request detection, for example the sensor 20 , is the other, i.e. the second electrical device 110 assigned.

The exemplary brake system is a HAF-capable brake system with a hydraulic fallback level (HAF: highly automated driving).

The brake system advantageously comprises, in particular, only two pressure sensors 19 and 20 which like in 1 are shown arranged. A third pressure sensor, arranged as described above, is advantageous.

Due to the two different print preparation device, print preparation device 5 as a linear actuator and pressure supply device 2 as a piston pump with parallel overflow valve 32 , the availability of the brake system is increased since a systematic error in one of the pressure supply devices does not also occur in the other pressure supply device.

In 2 a second embodiment of a brake system according to the invention is shown. The brake system of the second embodiment largely corresponds to the brake system of the first embodiment, but is not an additional valve 91 , through which the exhaust valves 7a . 7b the rear axle wheel brakes 8a . 8b with the pressure medium reservoir 4 are connected, provided, but only an electrically actuated, analog regulatable or controllable additional valve 92 (analog valve) through which the exhaust valves 7c . 7d the wheel brakes 8c . 8d the front axle VA with the pressure medium reservoir 4 are connected. additional valve 92 is open without current.

According to example is in the return line 14b the front axle wheel brakes 8c . 8d a parallel connection from the additional valve 92 and one in the direction of the pressure medium reservoir 4 closing check valve 94 arranged.

A braking system like in 1 or 2 shown, which, however, no additional valve 91 or 92 includes, has only a limited ability to (comfortable) axis-specific pressure position, as is required in connection with regenerative braking. Admittedly, the intake valves can be regulated in the same way 6a - 6d Axle-specific (even wheel-specific) pressure build-up possible, but a comfortable and quiet pressure reduction can only be achieved using the pressure supply device 5 and therefore only on the higher pressure axis.

The braking systems of the 1 and 2 solve this problem of a limited ability to set individual axes. To the additional valve 91 or 92 assigned wheel brakes 8a . 8b or 8c . 8d a vehicle axle ( HA . VA ) can with the exhaust valves open 7a . 7b or 7c . 7d and closed axis separating valve 40 by means of the additional valve 91 or 92 comfortable and quiet controlled pressure reduction can be carried out, regardless of the pressure of the wheel brakes of the other vehicle axle.

QUOTES INCLUDE IN THE DESCRIPTION

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Patent literature cited

• DE 102013217954 A1 [0002]

Claims (11)

Brake system for a motor vehicle with • hydraulically actuated first wheel brakes (8c, 8d), which wheels (FL, FR) are assigned to a first vehicle axle (VA), and hydraulically actuated second wheel brakes (8a, 8b), which wheels (RL, RR) are assigned to a second vehicle axle (HA), • a pressure medium reservoir (4) under atmospheric pressure, • an electrically operated inlet valve (6a-6d) per wheel brake (8a-8d) and an electrically operated outlet valve (7a-7d) per wheel brake (8a -8d), • a first electrically controllable pressure supply device (5), which is hydraulically connected to a brake supply line (13) to which the wheel brakes (8a-8d) are connected, • a second electrically controllable pressure supply device (2) with a suction connection ( 28), which is connected to the pressure medium reservoir (4), in particular via a check valve (99) opening in the direction of the suction connection (28) t, and a pressure connection (27) which is hydraulically connected to the brake supply line (13), characterized in that the first wheel brakes (8c, 8d) via the associated outlet valves (7c, 7d) and a first return line (14b) with the Pressure medium reservoir (4) are connected and the second wheel brakes (8a, 8b) are connected to the pressure medium reservoir (4) via the assigned outlet valves (7a, 7b) and a second return line (14a), and that in exactly one of the two return lines (14a , 14b) an electrically actuated additional valve (91, 92) is arranged, via which the outlet valves (7a, 7b; 7c, 7d) of the wheel brakes of the corresponding vehicle axle (HA; VA) are connected to the pressure medium reservoir (4), the additional valve (91, 92) being designed to be controllable analogously. Brake system after Claim 1 , characterized in that the additional valve (91, 92) is open when de-energized. Brake system after Claim 1 or 2 , characterized in that a check valve (93, 94) closing in the direction of the pressure medium reservoir (4) is connected in parallel to the additional valve (91, 92). Brake system according to one of the preceding claims, characterized in that an electrically operable axle separating valve (40) is arranged in the brake supply line (13) such that when the axle separating valve is closed, the brake supply line (13) hydraulically into a first and a second line section (13a, 13b) is separated, the first line section (13a) being hydraulically connected to the second wheel brakes (8a, 8b) and the second pressure supply device (2), and the second line section (13b) being connected to the first wheel brakes (8c, 8d) and the first pressure supply device (5) is hydraulically connected. Brake system after Claim 4 , characterized in that the axle separating valve (40) is designed to be open when de-energized. Brake system according to one of the preceding claims, characterized in that the first electrically controllable pressure supply device (5) is hydraulically separably connected to the brake supply line (13), in particular to the second line section (13b), via a first, in particular electrically operable, separating valve (26) is. Brake system according to one of the preceding claims, characterized in that it comprises a master brake cylinder (80) which is hydraulically separable via a second, in particular electrically operable, separating valve (81) with the brake supply line (13), in particular with the first line section (13a) or that the suction port (28) is connected to the master brake cylinder (80) via the second isolating valve (81). Brake system according to one of the preceding claims, characterized in that an electrically operable overflow valve (32) is provided, via which the pressure connection (27) is hydraulically connected to the suction connection (28). Brake system according to one of the preceding claims, characterized in that it has a first electrical device (100) with electrical and / or electronic elements which controls the first pressure supply device (5) and a second electrical device (110) with electrical and / or electronic Elements which the second pressure supply device (2) controls, the first and the second electrical device (100, 110) being electrically independent of one another. Brake system after Claim 9 , characterized in that the inlet and outlet valves (6a-6d, 7a-7b) and the additional valve (91, 92), in particular exclusively, are controlled by the second electrical device (110). Method for operating a brake system according to one of the Claims 1 to 10 , characterized in that in a predetermined state of the brake system, in particular during recuperative braking, by means of the additional valve (91, 92), a controlled pressure reduction on the wheel brakes the corresponding vehicle axle (HA, VA) is carried out.

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