BRAKE SYSTEM AND METHOD FOR CONTROLLING A BRAKE SYSTEM

A brake system and a method for controlling a brake system. The brake system may include a first module having a first pressure supply unit with an electromotive drive, an optional second pressure supply unit and a first control device for controlling the first pressure supply unit; a second module having a third pressure supply unit, isolation valves and brake-pressure-adjusting valves, and a second control device for controlling the brake-pressure-adjusting valves; and a detection unit for detecting a first case of error. The brake system is designed such that, in the first case of error, in order to provide an ABS function and/or a yaw torque intervention, it implements a (wheel-specific and/or selective) adjustment of the pressures in the wheel brakes by actuating at least one of the brake-pressure-adjusting valves of the second module and/or the isolation valves of the second module and the first pressure supply unit.

The invention relates to a brake system and to a method for controlling a brake system.

The trend toward vehicles which are configured for autonomous driving in terms of the brake system places high demands in terms of the failsafe design, on the one hand, and redundant functions, for example in terms of brake pressure generation, voltage supply and computer functions, on the other hand.

So-called one-box and two-box systems are usually favored. These are composed of an electric brake booster (BKV), a so-called e-booster, and an electronic stability control system (ESP/ESC).

The known solutions have relatively large installation lengths and/or a high weight.

Described in WO2011/098178 as well as DE 10 2014 205 645 A1 (hereunder referred to as variant A, or as follower booster or e-booster) is a solution having a coaxial drive in which an electric motor by way of a gear mechanism and piston acts on the master cylinder piston (HZ piston). The BKV control is performed by way of an electric element and reaction disk as a so-called follower booster, the pedal travel is a function of the brake pressure and the volumetric absorption of the brake system, this requiring long pedal travels in the event of fading or brake circuit failure.

WO2009/065709 shows an e-booster, likewise having a follower booster function (hereunder referred to as variant B, or as follower booster or e-booster). The BKV control here is performed by way of a pedal travel and/or by way of a pedal pressure, thus the pressure used for activating the pedal. A separate pressure supply with an electric motor and plunger acts on the HZ piston by way of the booster piston.

WO2012/019802 shows an assembly similar to WO2011/098178, having a coaxial drive in which an electric motor by way of a gear mechanism and piston acts on the HZ piston (hereunder referred to as variant C). An additional piston/cylinder unit is used here, which acts on a travel simulator piston. In this way, the pedal travel is independent of, for example, fading and brake circuit failure. However, the complexity is high and the installation length is large.

DE 10 2009 033 499 shows a brake booster having an additional ESP unit with hydraulic activation of the booster piston and an external pressure supply (hereunder also referred to as variant D). This assembly having four or five pistons and six solenoid valves (MV) is complex and unfavorable in terms of the installation length. The travel simulator (WS), which does not act hydraulically, lies within the piston/cylinder unit that is disposed upstream of the master cylinder and can neither be damped nor switched by way of a solenoid valve (MV).

All solutions mentioned above have a redundant brake booster function because the braking function in the event of a failure of the BKV motor is guaranteed by the ESP unit with a pump similar to the assistance functions by a vacuum BKV in the autonomous driving mode.

In the event of a failure of the ESP motor, the ABS can continue to function by way of the possibility of pressure modulation by the motor of the brake booster, as described in WO2010/088920, in that the piston of the master brake cylinder is moved in a reciprocating manner for building up and dissipating pressure. If the brake booster is used in combination with an ESP unit with the typical valve circuit of the ESP unit, as outlined in detail for example inFIG.1of DE 10 2014 205 645 A1, the pressure can be built up and dissipated by way of the inlet valves which are open when non-energized (reference signs32a,32b,34b,34aofFIG.1of DE10 2014 205 645 A1) and switchover valves (USV) (reference signs30a,30bofFIG.1of DE 10 2014 205 645 A1), i.e. a common pressure control for all four wheels can be implemented, this not resulting in an optimum stopping distance.

All one-box systems known to date have a so-called travel simulator (in particular for brake-by-wire systems), so as to implement a progressive pedal travel characteristic.

The known systems with an e-booster and ESP have only one redundancy in the pressure supply, i.e. in the event of a failure of the e-booster there is a redundant pressure supply with a redundant output for brake boosting by the ESP. Higher requirements in terms of safety are not taken into account.

The packaging, thus an arrangement of the individual components of the brake system so as to form a ready-to-install unit and an installation volume of this unit are of great importance. In particular in the case of brake systems that are used in motor vehicles which are configured for semi-automatic or even fully automatic driving, many variants, for example with a tandem master (brake) cylinder or a single master (brake) cylinder have to be taken into account. Examples of known packaging variants are an arrangement of a pressure supply unit perpendicular to an axis of the master (brake) cylinder (as described in EP 2 744 691, for example) or an arrangement of the pressure supply unit parallel to the axis of the master (brake) cylinder (as described in DE 10 2016 105 232, for example). The latter is distinguished in particular by a smaller installation width in comparison to the first-mentioned packaging variant.

Proceeding from the prior art, it is an object of the present invention to specify an improved brake system.

The invention is in particular based on the object of achieving a brake system for the use in autonomous driving (hereunder also referred to as AD) and/or for electric vehicles/hybrid vehicles having an increasingly high recuperation output (recuperating energy by braking by way of a generator/or drive motor in the generator operation, respectively). Preferably, the weight is minimized and/or the dimensions of the system are reduced and/or the reliability is increased.

A cost-effective brake system for autonomous driving is preferably to be achieved, said brake system meeting all required redundancies and a very high requirement in terms of safety.

Moreover, a function of ABS which is sufficient in terms of the braking distance and stability, as well as a sufficient recuperation function, are to be achieved by the brake system in the event of a failure of ESP.

It is in particular an object of the present invention to specify an improved brake system as well as a method for controlling a brake system having a redundant pressure supply, a very large range of functions and availability, in particular in the event of the failure of a brake circuit, with simultaneously a very short installation length and low costs. Furthermore to be provided is a method which enables a very high degree of availability even in the event of partial failures/leakages.

In terms of the brake system, the object is achieved according to the invention by a brake system having the features of claim1. In terms of the method, the object is achieved according to the invention by a method having the features of claim18.

The object focused on the brake system is achieved according to the invention in particular by a brake system having:a first module, comprising a first pressure supply unit having an electromotive drive, an optional second pressure supply unit and a first control apparatus for controlling the first pressure supply unit, wherein the first module is specified for impinging at least one first brake circuit by way of a first connection point, and at least one second brake circuit by way of a second connection point, with a pressurizing medium, wherein the brake circuits are assigned wheel brakes,a second module, comprising a third pressure supply unit, in particular a motor/pump unit, isolation valves as well as brake pressure adjustment valves, in particular outlet valves and inlet valves, for adjusting a pressure in the wheel brakes, and a second control apparatus for controlling the brake pressure adjustment valves,a detection unit for detecting a first error event, in particular an at least partial failure of the third pressure supply unit, wherein the brake system in the first error event, for providing an ABS function and/or a yaw torque intervention, is specified for implementing a (wheel-individual and/or selective) adjustment of the pressures in the wheel brakes while actuating at least one of the brake pressure adjustment valves of the second module and/or the isolation valves of the second module and the first pressure supply unit.

The pressure supply unit here can generally be understood to mean a unit, in particular a construction unit, of the brake system that provides a brake pressure. The pressure supply unit thus serves for impinging the at least one brake circuit with the pressurizing medium. The third pressure supply unit is preferably an ESP unit of the type described at the outset. The isolation valves here can be configured so as to be bidirectional, i.e. can be hydraulically permeable in two flow directions. Depending on the design embodiment of the brake system and/or also of the field of application of the brake system, the optional second pressure supply unit can be configured as an electronic pedal or as a central computer.

The at least partial failure of the third pressure supply unit here can be understood to mean that the motor/pump unit fails while the other components of the third pressure supply unit are still able to function.

The isolation valves as well as the brake pressure adjustment valves, in particular the pressure buildup valves and pressure dissipation valves (hereunder also referred to as inlet valves EV and outlet valves AV) are in particular configured as solenoid valves. Solenoid valves have been proven advantageous in particular by virtue of the simple actuation capability of said solenoid valves.

In one embodiment the first pressure supply unit in the first error event is controlled in such a manner that said first pressure supply unit when dissipating pressure for providing the ABS braking operation generates a pressure sink having a lower pressure than the pressures in the wheel brakes.

In a further embodiment, at least some of the isolation valves of the first module are disposed and configured for establishing a hydraulic connection between the brake pressure adjustment valves, in particular the outlet valves and the connection points.

The brake system in the first error event, for dissipating pressure in one of the wheel brakes, here is preferably configured for opening the assigned outlet valve.

In one embodiment, at least some of the isolation valves of the first module are disposed and configured for establishing a hydraulic connection between the brake pressure adjustment valves, in particular the outlet valves and the connection points, wherein the brake system in the first error event, for dissipating pressure in one of the wheel brakes, is preferably configured for opening the assigned outlet valve.

A communications link, in particular a bus link, is expediently configured between the first control apparatus and the second control apparatus, wherein the first control apparatus is preferably configured for receiving pressure measurement values of the second module and/or wheel rotational speed signals by way of the communications link. The communications link can alternatively be an Ethernet or Flexray link. Furthermore alternatively, the communications link can also be configured so as to be wireless or as an analog connection, for example for determining a measurement value.

Furthermore alternatively, the communications link, in particular the bus link, can be configured between the first control apparatus and the second control apparatus, wherein the first control apparatus and the second control apparatus are preferably configured for receiving pressure measurement values of the third pressure supply unit and/or wheel rotational speed signals by way of the communication link. In the event of a failure of the communications link, it is possible in this way to perform ABS controlling by way of the data imported by the two control apparatuses. Receiving here can also be understood to mean importing sensor values and signals of this type from one of the control apparatuses by way of the communications link.

In one embodiment, the first control apparatus and/or the second control apparatus and/or a third control apparatus in the first error event are/is configured for controlling the first pressure supply unit and the brake pressure adjustment valves so as to implement wheel-individual and/or brake circuit-individual pressure feedback control in the wheel brakes or the brake circuits. According to the invention, indirect controlling of the actuators, for example valves, can also take place by way of the respective other control apparatus. The third control apparatus can be understood to mean a central control unit, for example.

In a further embodiment, a first isolation valve of the first module is disposed in a first hydraulic line between the first pressure supply unit and the first connection point. Moreover, according to this embodiment a second isolation valve is disposed in a second hydraulic line between the first pressure supply unit and the second connection point. The brake system here is configured to detect a second error event, in particular a total failure of the third pressure supply unit. The total failure here can be understood to mean that all components of the third pressure supply unit have failed and are no longer able to function. Furthermore, the brake system in the second error event is configured to control the first pressure supply unit and the first and second isolation valve, so as to implement at least one brake circuit-individual pressure feedback control in the at least two brake circuits. The controlling here preferably takes place by way of the first control apparatus.

According to one embodiment, the brake system and in particular the first control apparatus is specified to detect a non-homogenous road condition, in particular a p-split situation, and in the second error event and in the detected non-homogenous road condition, is specified to control the first pressure supply unit. This controlling here serves to adjust a target brake pressure in at least one selected brake circuit of the brake circuits, said target brake pressure being determined as a function of a wheel blocking pressure of that wheel brake of the selected brake circuit that has the coefficient of friction that is higher in comparison to the other wheel brake of the selected brake circuit. The non-homogenous road condition here is detected in such a manner that a pressure differential between the two wheel blocking pressures is detected. A non-homogenous road condition is present when this pressure differential has a percentage value of more than 30% or 40%.

In a third error event, in particular in the event of an additional failure of the wheel sensors mentioned above, or in the communication of the wheel rotational speed signals from the second module to the first module, the brake system, in particular the first control apparatus, in one embodiment in the third error event, by means of the first pressure supply unit, is specified for controlling the pressure buildup and the pressure dissipation, so as to implement a single-channel ABS while using wheel rotational speed sensors, and/or in a fourth error event is specified for implementing an intermittent brake by modulating the pressure between two fixedly adjusted pressure levels in both brake circuits. An improved maneuverability and braking performance of the vehicle as compared to the brake systems known in the prior art is thus also achieved in a further error event and an additional failure of further components of the brake system associated therewith.

At least one pressure sensor for detecting a brake pressure within the at least one brake circuit is expediently provided.

In one embodiment the first hydraulic line between the first pressure supply unit and the first connection point is configured without a valve. Moreover, the second hydraulic line between the first pressure supply unit and the second connection point is configured without a valve. Without a valve here can be understood to mean that no valves are disposed in the first or the second hydraulic line between the first pressure supply unit and the first or the second connection point, respectively.

According to a further embodiment, the first module has a rotary pump, in particular a single-circuit 1-piston pump, or a multi-piston pump, for building up pressure and dissipating pressure. Moreover, the first module according to this embodiment comprises a solenoid valve hydraulically connected to a reservoir, as well as at least one optional pressure transducer. The optional pressure transducer for feedback-controlling the pressure buildup and the pressure dissipation is preferably communicatively connected to the first control apparatus.

According to an alternative embodiment, the first pressure supply unit is configured as a gear pump for building up pressure and dissipating pressure. The gear pump is expediently controlled while using a pressure transducer or as a function of a measurement of a current, in particular a phase current i of the electromotive drive of the gear pump, and of an angle a of a rotor of the electromotive drive. In the case of a present pressure transducer, said measurements can be used for providing a redundancy (hot or cold).

Considering the different variants of design configuration of the first pressure supply unit, the latter thus takes into account different variants of configuration.

In a further embodiment, at least one third isolation valve is provided, said third isolation valve being disposed and configured in such a manner that, in a closed state of the third isolation valve, the first brake circuit is hydraulically decoupled from the first and the second pressure supply unit.

Furthermore, the first hydraulic line and/or the second hydraulic line are/is preferably (in each case) connected to a reservoir by way of a suction valve. The suction valves are used such that the third pressure supply unit can convey volumes directly from the reservoir rapidly with minor hydraulic resistances and that the first and the second pressure supply unit during conveying are decoupled as a result of the operation of the third pressure supply unit and are not compromised by the operation.

According to a further design embodiment, an activation element, in particular a brake pedal, is disposed on the second pressure supply unit. The second pressure supply unit here comprises a master brake cylinder having a single piston that is activatable by means of the activation element and has a pressurized chamber as well as a travel simulator connected to the pressurized chamber. Furthermore, the pressurized chamber by way of a switchable solenoid feed valve FV is connected to at least one brake circuit.

As a result of the embodiments of the brake system according to the invention described above, operation taking into account safety aspects is made possible in particular in the error events listed hereunder (in all or a selection of these error events).

Error event 1: failure of the motor of the third pressure supply unit (ESP unit); 4-channel ABS by feedback control by way of valves and first pressure supply unit;

Error event 2: complete failure of the third pressure supply unit (ESP unit); 2-channel ABS with “select-low”/“select-high” feedback control atypical of the normal operation;

Error event 3: complete failure of the third pressure supply unit (ESP unit), wheel rotational speed sensors are available in a redundant manner and are imported into the first module directly from the wheel brakes; establishment of a 1-channel ABS;

Error event 4: complete failure of the third pressure supply unit (ESP unit) and failure of the wheel rotational speed sensors; establishment of an automatic intermittent brake.

Alternatively or additionally to the ABS control in the error event 1, a yaw torque control can furthermore take place in this error event so that a brake pressure is generated in selectively selected wheels.

In terms of the method, the object is achieved in particular by a method for controlling a brake system, in particular the brake system described above, said method comprising the steps:controlling a first pressure supply unit of a first module by means of a first control apparatus in a normal operation,controlling a multiplicity of brake pressure adjustment valves in a second module in a normal operation,detecting a first error event, in particular a partial failure of the second module,controlling the brake system in the first error event in such a manner that for providing an ABS braking operation and/or a yaw torque intervention a (wheel-individual and/or selective) adjustment of the pressures in the wheel brakes takes place while using at least one, in particular bidirectional, isolation valve of the second module and the first pressure supply unit.

In one embodiment, the method furthermore comprises the steps:detecting a second error event, in particular a total failure of the third pressure supply unit,controlling the first pressure supply unit and at least two isolation valves of the first module in such a manner that, in the second error event, a brake circuit-individual pressure feedback control is implemented in the at least two brake circuits.

According to a further embodiment, the method comprises the steps:detecting a non-homogenous road condition, in particular a p-split situation,controlling the first pressure supply unit in the second error event in such a manner that in non-homogenous road condition that wheel brake of a selected brake circuit that has the coefficient of friction that is higher in comparison to the other wheel brake is utilized for determining a target brake pressure.

In a further embodiment, the method moreover comprises the steps:detecting a third error event, in particular a total failure of the third pressure supply unit and a failure of wheel sensors,controlling the first pressure supply unit in the third error event in such a manner that a 1-channel ABS is implemented, or in a fourth error event an intermittent brake is implemented by modulating the pressure between two predefined pressure levels in at least one of the brake circuits (BK1, BK2).

According to an alternative embodiment, the method furthermore comprises the steps:determining a first wheel blocking pressure on a first wheel brake which is assigned to one of the two brake circuits;determining a second wheel blocking pressure on a wheel brake which is assigned to the same brake circuit, wherein a non-homogenous road condition is detected when the first and the second wheel blocking pressure differ by more than 30 percent.

Advantages similar to those that have been described in conjunction with the brake system are derived for the method.

Components with equivalent functions are in some instances provided with the same reference signs in the figures.

The brake system2according to a first exemplary embodiment as illustrated inFIG.1ahas a first pressure supply unit6in a first embodiment. In this embodiment, the first pressure supply unit6has an electromotive drive8which acts on a piston of a piston/cylinder unit. Furthermore, the brake system2and in particular the first pressure supply unit6has a first control apparatus9which feeds in particular the electromotive drive8with control signals.

The first pressure supply installation6serves here to impinge a first brake circuit BK1and a second brake circuit BK2with a pressurizing medium. To this end, the cylinder of the first pressure supply unit6by way of a hydraulic line is hydraulically connected to the first brake circuit BK1(cf. connection point A1) and to the second brake circuit BK2(cf. connection point A2).

In the exemplary embodiment according toFIG.1a, an isolation valve PD1by way of which the first pressure supply unit6is able to be hydraulically reversibly isolated from the first brake circuit BK1and from the second brake circuit BK2is additionally disposed in this hydraulic line. The isolation valve PD1here is configured as a solenoid valve.

Additionally, the first pressure supply unit6and in particular the cylinder of the first pressure supply unit6has a hydraulic connection line to a reservoir40in which a check valve is disposed. The hydraulic connection to the reservoir40serves for suctioning pressurizing medium from the reservoir40.

Furthermore, the brake system2has a third pressure supply unit90which is only schematically illustrated in fig. la. The third pressure supply unit90is also referred to as an ESP unit, or the ESP unit comprises the third supply unit90, respectively. Moreover, a second control apparatus95which controls the third pressure supply unit90is provided.

A communications link100, in particular a CAN bus link, is configured between the first control apparatus9and the second control apparatus95. The communications link100serves for exchanging data and/or signals between the two control apparatuses9,95.

In particular, no valves are disposed in the hydraulic lines of the first brake circuit BK1as well as of the second brake circuit BK2in the exemplary embodiment according toFIG.1a.

Moreover, a pressure transducer p/U which is disposed between the isolation valve PD1and the first or the second brake circuit BK1, BK2, respectively, is provided in the hydraulic line. This pressure transducer p/U, in particular in an error event (cf. embodiments hereunder) serves for providing pressure information pertaining to the brake circuits BK1, BK2in order for pressure to be adjusted in the brake circuits BK1, BK2.

As an alternative to the pressure transducer p/u, an item of information pertaining to the pressure adjusted by means of the first pressure supply unit6in this embodiment takes place by estimating the pressure by way of a motor rotary encoder a/U and/or the motor current i/u.

FIG.1bshows a circuit diagram of a second exemplary embodiment of the brake system2having the first pressure supply unit6according to the first embodiment.

This exemplary embodiment corresponds substantially to the aforementioned exemplary embodiment of the brake system2according toFIG.1a.A difference here lies in that an isolation valve BP1, TVBK2is in each case disposed in the hydraulic line to the brake circuits BK1, BK2. An adjustment of a brake circuit-individual brake pressure by means of these two isolation valves BP1, TVBK2is in particular possible in an error event.

A circuit diagram of the first exemplary embodiment of the brake system2having the first pressure supply unit6according to a second embodiment is illustrated inFIG.2. This exemplary embodiment of the brake system2likewise corresponds substantially to the design embodiment of the brake system2according toFIG.1a.However, the first pressure supply unit6in the exemplary embodiment according toFIG.2is configured as a rotary pump and in particular as a single-circuit piston pump, in particular a pump having1or a plurality of, in particular3, pistons. The piston pump is embodied in a manner comparable to ESP pump drives in which the piston/pistons by way of an eccentric are driven by a shaft of an electric motor. In this design embodiment, a valve PD2is additionally provided for enabling the pressure buildup or the pressure dissipation, respectively. When building up pressure, the PD2valve can advantageously also be used for compensating pressure pulses of a pump driven by an eccentric. The pressure pulses are very high in particular in the case of a1-piston pump.

The brake system2according to the first exemplary embodiment having a first pressure supply unit6according to a third embodiment, as is illustrated inFIG.3, with the exception of the embodiment of the first pressure supply unit6, likewise corresponds to the brake system2according toFIG.1a.In the exemplary embodiment according toFIG.3, the first pressure supply unit6is configured as a gear pump. Providing an item of information pertaining to the pressure provided by the pressure supply unit6in this exemplary embodiment, as an alternative to the pressure transducer p/u, takes place by estimating a pressure by way of a motor rotary encoder a/U and/or the motor current i/u. By virtue of the mechanical and functional design embodiment of the gear pump, no valve PD2is required in this exemplary embodiment because pressure can also be dissipated by way of the gear pump by a reversal of the rotation direction, for example by embodying the drive motor of the gear pump as a brushless electric motor operated by way of a B6 bridge circuit and operating the electric motor in the4-quadrant operation. Moreover, for reasons related to the operating principle, the pressure pulses are significantly weaker than in the case of an eccentric piston pump.

FIG.4shows a circuit diagram of a third pressure supply unit90(also referred to as an ESP unit) having the motor/pump unit91for use in the brake system2according to the invention. The ESP unit is known and has the main components pump P with motor M, the valves HSV1and HSV2, USV1and USV2, the inlet and outlet valves EV1to EV4and AV1to AV4assigned to the wheel brakes RB1, RB2, RB3, RB4, and one storage chamber (SpK) per brake circuit. This system is described in many publications and patent applications. Said system is already marketed as a 2-box brake system “e-booster+ESP” and is used above all in electric and hybrid vehicles. In this application, only the outlet valves of the ESP unit are actuated by way of the e-booster by way of a CAN interface in interaction with the brake torque of the generator, i.e. recuperation for the avoidance of a buildup of brake pressure in the wheel brakes, and the storage chamber SpK is used for receiving pressurizing medium.

One aspect of the invention lies in that the first control apparatus9by way of a communications link100is communicatively connected to the second control apparatus95(“ECU-ESP”) of the ESP unit and, for achieving safety aspects, at least the inlet valves EV1to EV4are able to be controlled by the first control apparatus9.

A (further) aspect of the invention lies in the wheel-individual pressure dissipation while using the outlet valves AV1to AV4and HSV valves of the ESP unit.

A circuit diagram of the third pressure supply unit90(ESP unit) while dissipating pressure in a first error event is illustrated by way of example in a brake circuit inFIG.5. The first error event here can be understood to mean that a motor M of the third pressure supply unit90has failed. In this case, a pressure dissipation for the purpose of feedback control takes place by way of the first pressure supply unit6. This takes place specifically in that the piston of the first pressure supply unit6is moved back (toward the right in the drawing plane, identified by an arrow) and opening of the outlet valves AV4and AV3as well as of the isolation valve HSV2takes place, said outlet valves AV4and AV3in the normal state being closed when not energized. The valves which in this state are open for the volumetric flow, for highlighting the opened state, are in each case provided with an asterisk (“*”) inFIG.5(left half ofFIG.5). The state of the other solenoid valves is not explicitly explained. In this way, at least the inlet valves EV1-EV4are closed by active energizing when dissipating pressure, for example. The pressure dissipation from the wheel brakes RB3and RB4is in particular shown in an exemplary manner inFIG.5(the flow direction of the pressurizing medium from the wheel brakes to the first pressure supply unit6is identified by arrows). For this purpose, the pressure supply unit90can according to the invention be equipped with isolation valves HSV1, HSV2which, as opposed to the typical use in ESP units, according to the invention are operated bidirectionally. The isolation valves HSV1and HSV2are also used for resupplying fluid from the reservoir40in a normal ESP operation with an active pump. By virtue of the given configuration, pressure from the wheel brakes RB1and RB2, or RB3and RB4, (not illustrated), respectively, can be selectively dissipated by opening and closing the isolation valves HSV1and HSV2when the isolation valves USV1and USV2are closed. A wheel-individual pressure adjustment can take place by correspondingly switching the outlet valves AV1to AV4.

In the first error event, the actuation of the valves, in particular of the isolation valves USV1, USV2, HSV1, HSV2and of the outlet valves AV1to AV4can also take place by the first control apparatus9and not, as in the normal case, by the second control apparatus95. When controlling by the first control apparatus9, the control signals required for this purpose here are transmitted to the third pressure supply unit90by means of the communications link100. However, in the normal operation, in the absence of an error event, the second control apparatus95assumes the actuation of the valves. The normal operation here can be understood to mean a pressure buildup required for example for braking a vehicle in comparison to a pressure buildup for the purpose of feedback control (so as to prevent slipping or blocking of the wheel).

The inlet valves EV1to EV4are closed (by energizing) when dissipating pressure. A hydraulic connection to the first pressure supply unit6is configured by opening the isolation valve HSV2; an outflow of the pressurizing medium here is then facilitated by means of the first pressure supply unit6and not, as customary, by means of the pump P.

The pressure dissipation illustrated and explained by way of example for two wheel brakes RB3, RB4inFIG.5, in an analogous manner can alternatively also take place brake circuit-individually or wheel brake-individually. The wheel brake circuit-individual feedback control is used for the4-channel ABS operation as well as for yaw torque interventions (also referred to as yaw torque feedback control(s)).

A pressure is preferably detected by means of the pressure transducer p/U in the ESP unit during this feedback control, so that information pertaining to the pressure for feedback-controlling the pressure dissipation is present at every point in time.

A pressure buildup in the first error event is illustrated by way of example by the circuit diagram of the third pressure supply unit90according toFIG.6. In this case, the second control apparatus95controls the inlet valves EV1to EV4of the third pressure supply unit90as in the normal operation of the third pressure supply unit90. The outlet valves AV1to AV4are (non-energized) closed when building up pressure. Additionally, the valve USV2or USV1is opened during the pressure buildup, while the valves HSV1, HSV2remain (non-energized) closed. The pressure buildup in the two wheel brakes RB3, RB4is shown by way of example inFIG.6, so reference here is made in each case to the isolation valves HSV2and USV2situated within this brake circuit BK1. Alternatively, the pressure buildup illustrated and explained by way of example for two wheel brakes RB3, RB4inFIG.6, in an analogous manner can also take place brake circuit-individually or wheel brake-individually, as a result of which a wheel-individual pressure buildup and yaw torque intervention can take place.

The isolation valve PD1, if provided, which isolates the first pressure supply unit6from the brake circuits BK1, BK2is operated so as to be open during the pressure buildup. The first pressure supply unit6by way of the hydraulic line conveys pressurizing medium into the wheel brakes RB3, RB4. Also in this exemplary embodiment, the pressure transducer p/U, which according toFIG.6is disposed in the second brake circuit BK2, is preferably utilized for detecting information pertaining to pressure. Alternatively, the controlling of the valves of the third pressure supply unit90in this exemplary embodiment can also be assumed by the first control apparatus9by way of the communications link100.

A temporal profile of vehicle speed VF, wheel circumferential speed VR, reference speed VREF, brake circuit pressure Phfor “high wheel”, PLfor “low wheel” is in each case illustrated inFIGS.7aand7b. The slippage coefficient λ is the wheel speed at which a wheel becomes unstable, and is approximately equal to the reference speed VRFE. In this way, the typical key indicators such as the λ-limit or (reference speed VRFE), subpoint1,1′,2,4for the pressure dissipation Pab(slippage coefficient λ exceeded) and time points3and5for the pressure buildup Pauf(slippage coefficient λ undershot) are illustrated inFIGS.7aand7b.

In homogenous conditions (all vehicle wheels are situated on asphalt, for example) switching takes place to a “select-low” feedback control (FIG.7b), i.e. a corresponding pressure which is so low that no wheel is blocked is adjusted. In this way, approx. 20% of the full braking action is dispensed with.

In non-homogenous conditions, for example p-split, i.e. wheels on a vehicle side on ice, the other vehicle side on a wet or dry road, the “select-high” feedback control (FIG.7a) sets in, i.e. the wheels that are not blocked are feedback-controlled, while the wheels with the low coefficient of friction remain blocked. Here too, approx. 20% of the optimum braking action is dispensed with.

As has already been explained,FIG.7ashows a “select-high” feedback control. The description of the ABS feedback control assumes the general principles that are known from patent applications, brake manuals and brochures. As a result of the tire slippage characteristic, a slippage between the vehicle speed VFand the wheel circumferential speed VR=wheel slippage is thus formed as a brake pressure increases. In the case of a slippage coefficient λ that is a function of many factors, the maximum of the tire circumferential force is exceeded, the latter in the absence of feedback control leading to the wheel blocking. By way of the feedback-controller which evaluates the wheel acceleration (positive and negative) and the slippage λ, the pressure feedback control with the pressure dissipation Paband the pressure buildup Paufbecomes effective with a view to the desired, optimum brake force and cornering force. A reference speed=λ-limit, which corresponds to the optimum slippage λ, is likewise formed by the feedback-controller using complex algorithms.

In this way,FIG.7aspecifically shows an exemplary temporal profile of a “select-high” feedback control in a brake circuit having two wheel brakes. At the time point1, as a result of the pressure buildup Paufby the first pressure supply unit6, the blocking limit at the wheel VR1(at a low coefficient of friction low-p) is reached at the pressure p1, this wheel as a consequence in the case of a further pressure buildup Paufreaching a wheel circumferential speed VR=0 and thus blocking. Consequently, the pressure continues to be built up. A further pressure buildup Paufhas the effect that the wheel VR2at the time point2, shortly upon exceeding the λ-limit at the pressure level p2, likewise becomes unstable and the wheel circumferential speed VR2decreases sharply. Consequently, the pressure is reduced by the pressure supply, for example by restoring the piston. The pressure differential ΔP of the previously determined pressures p1and p2is evaluated. If the pressure differential ΔP=P2−P1is significant, i.e. pressure p2exceeds pressure p1by more than 30%, the “select-high” feedback control (also referred to as selective “high-p” control) is initiated. The pressure is then moderately reduced by Δpab=20% in both brake circuits, i.e. the circuit isolation valves (BP1/BP2, TVBK2; cf.FIG.9) are not utilized for a selective pressure dissipation and are in the opened state.

As a consequence, the wheel VR2does not block at the time point3and again undershoots the λ-slippage limit at the time point3. A pressure buildup in stages follows from the time point3. In a first stage, the pressure is increased by 70% of the previous Δpabvalue, for example, and in a second step increased by a further 30%, so that the pressure p2is reached again and subsequently exceeded. In this phase, the pressure transducer p/U is preferably used for pressure measurement. The slippage limit is again exceeded at the time point4. Thereafter, the pressure is reduced again, as at the time point2, and subsequently increased again in stages so that the wheel undershoots the slippage limit again at the time point5. This feedback control method is continued during the feedback controlling.

FIG.7bspecifically shows an exemplary temporal profile of a “select-low” feedback control in a brake circuit having two wheel brakes. Here, the pressure differential ΔP=P2−P1is relatively minor in the range between 10% and 20%. As a consequence, the wheels with minor pressure differentials become unstable. This is an indication for an operation on a homogenous carriageway. As described previously in the context of the “select-high” feedback control, the pressure is reduced by Δpaband increased again in stages. As opposed to the “select-high” feedback control, the pressure in the case of the “select-low” feedback control is however dissipated more intensely, for example Δpab=40%, so that the low wheel is relieved from the blocked state at the time point6, i.e. as opposed to the “select-high” feedback control, no wheel is operated in the blocked state. The pressure is kept low until first the wheel VR2and then the wheel VR1undershoots the λ-limit at the time point3; then only is the pressure increased again in stages. The slippage limit of the wheel VR1is exceeded again at the time point4, and the pressure is lowered again and subsequently increased in stages.

FIGS.7aand7bshow only the general aspects of the “select-low”/“select-high” feedback control. Many enhancements are conceivable, such as another test in a “select-high” feedback control, when the pressure level is reduced in the “high” wheel. Alternatively, the “select-low” wheel can also exit the blocked state again without feedback control and exceed the λ limit. This potential wheel speed profile is identified by X inFIG.7a. Thereafter, another “select-low”/“select-high” test can take place, optionally with switching over from a “select-high” feedback control to a “select-low” feedback control.

As has already been explained, in one exemplary embodiment, in the second error event switching from a “select-low” feedback control to a “select-high” feedback control takes place by way of the first control apparatus9when the first control apparatus9detects that the vehicle is situated on a non-homogenous hard ground, for example a partially icy road. For this purpose, it is necessary that the brake system2according to the invention by means of the first pressure supply unit6can adjust different pressures in the individual brake circuits BK1, BK2. The design embodiments already shown schematically by means ofFIGS.1b,8and9are particularly suitable for this purpose. In order for this control strategy to be implemented, the control apparatus9monitors the pressures in the individual wheel brakes RB1, RB2, RB3, RB4that lead to a blocking of the wheels. If these pressures between two wheels, in particular within one brake circuit BK1, BK2, deviates by more than 30% from one another, switching by the first control apparatus9takes place from a “select-low” feedback control to a “select-high” feedback control, so as to still achieve a very positive braking result even within said error event.

FIG.8shows a circuit diagram of a brake system2which comprises a first module (referred to as X-boost) and a second module. The first module—the X-boost—has a first pressure supply unit6having an electromotive drive8, as well as a second pressure supply unit14having a master brake cylinder22and an activation element26having a brake pedal. Furthermore provided is a valve installation having various solenoid and check valves.

The second module and in particular the third pressure supply unit90comprises an electrically driven motor/pump unit91having a pump with an electromotive drive. The third pressure supply unit90can be any arbitrary ESP unit. A suitable ESP unit is described in detail in DE 10 2014 205 645 A1. Alternatively, a standard ABS unit without ESP function can be used as the second module.

The two modules (X-boost and ESP unit) are specified for impinging two brake circuits BK1and BK2with pressurizing medium, wherein the modules are preferably hydraulically connected in series. In one exemplary embodiment, the X-boost is fastened to the scuttle of a vehicle, the second module (ESP unit) at two hydraulic interfaces or connection points A1, A2(cf. solid black points inFIG.8relating to BK1, BK2), respectively, being connected thereto by way of hydraulic lines.

The first pressure supply unit6by way of a first hydraulic line HL1is connected to the first brake circuit BK1, or to the corresponding interface, respectively. Furthermore provided is a second hydraulic line HL2for connecting the first pressure supply unit to the second brake circuit, or to the corresponding interface, respectively.

According to the invention, the second pressure supply unit14of the X-boost only has one master brake cylinder22having a piston24and a piston chamber. In the exemplary embodiment, the second pressure supply unit14is embodied with a single circuit and by way of a third hydraulic line HL3and a feed valve69is connected to the brake circuit BK1, or to the corresponding hydraulic interface, respectively. A fluidic connection to the second hydraulic line HL2runs by way of an optional first isolation valve BP1(highlighted by a border with dashed lines). The second pressure supply unit14by closing the feed valve69is able to be isolated from the brake circuits BK1, BK2in such a manner that the activation element26in the normal brake-by-wire operation without errors (for example without a brake circuit failure) acts only on a travel simulator28.

In the exemplary embodiment as perFIG.8, the brake circuits BK1and BK2are able to be isolated by way of the optional first isolation valve BP1(preferably open when not energized), if present. According to the invention, in the event of a failure of the first pressure supply unit6, the master brake cylinder22of the second pressure supply unit14by opening the first isolation valve BP1can in this way be connected either only to the first brake circuit BK1or to the first and the second brake circuit BK1, BK2. For this emergency operation, the feed valve69is configured as a valve that is open when not energized. To the extent that a current is still applied, said feed valve69is open so that the second pressure supply unit14is no longer hydraulically decoupled from the brake circuits BK1, BK2.

The first pressure supply unit6likewise selectively acts on the second brake circuit BK2(first isolation valve BP1closed) or both brake circuits BK1, BK2(first isolation valve BP1opened or open when not energized). The first isolation valve BP1is open in the normal operation so that the first pressure supply unit6supplies both brake circuits BK1, BK2with pressure, and the second pressure supply unit14by the closed feed valve69is decoupled from the first brake circuit BK1. If it is established that volume is lost from the brake circuits BK1, BK2, the brake circuit BK1by means of the first isolation valve BP1can be decoupled from the first pressure supply unit6so that, in the event of a leakage in the first brake circuit BK1, the second brake circuit BK2can continue to be operated without hydraulic fluid losses.

In the exemplary embodiment, the isolation valve BP1is embodied as a solenoid valve, wherein the ball seat of the isolation valve BP1by way of a connector (valve seat connector) is connected to the portion of the hydraulic line that leads to the first pressure supply unit6. In this way, the isolation valve BP1can also be reliably closed by energizing in the event of a failure of the first brake circuit BK1, and is not forced open by higher pressures in the operation of the first pressure supply unit6.

The second pressure supply unit14upon activation of the activation element26feeds the travel simulator28by way of a breather bore in a wall of the master brake cylinder22, such that a progressive haptic resistance in the form of a restoring force as a function of a variable of the activation of the activation element26can be felt.

The variable of the activation here can be understood to mean how “firmly and/or how far” a driver activates the activation element26configured as a brake pedal, and thus pushes the piston24into the master brake cylinder22. The progressive haptic resistance is also referred to as a pedal characteristic.

A travel simulator valve29can be provided for blocking the connection to the travel simulator28.

The second pressure supply unit14has at least one breather bore38which by way of hydraulic lines is connected to a reservoir40. The reservoir40is likewise part of the brake system2.

In the exemplary embodiment, a check valve RVHZ as well as a throttle DR can be disposed in the hydraulic line between the breather bore38and the reservoir40. By means of this check valve RVHZ and the first pressure supply unit6it is possible to carry out a diagnosis pertaining to a state of preservation of sealing elements disposed within the first pressure supply unit6as well as within the travel simulator28. The travel simulator valve29, if present, can be closed when checking the seal of the master brake cylinder22.

As illustrated, the master brake cylinder22has two sealing elements42a,42b,which are configured as annular seals. The breather bore38is disposed between the two sealing elements42a,42b.A throttle DR is disposed in the connection between the breather bore38, which is disposed between the two sealing elements42a,42b,and the reservoir40.

The throttle DR in terms of the flow rate thereof is sized such that the pedal characteristic is not substantially changed (3 mm pedal travel in 10 s) in the event of a failure of the sealing element42a.Moreover, a temperature-related volumetric compensation of the pressurizing medium can take place by way of the throttle DR.

High pressure peaks in the brake circuits BK1and BK2, which can significantly stress the first pressure supply unit6, can be created in an ABS operation of the third pressure supply unit90. In the variant of design embodiment according toFIG.8, a pressure limitation valve ÜV is connected to the piston chamber of the first pressure supply unit6by way of a bore, so that the high pressure peaks are dissipated and damage to the system is avoided.

A suction valve NV is likewise fluidically connected to the piston chamber of the first pressure supply unit6and enables pressurizing medium to be resupplied from the reservoir40. In this way, the first pressure supply unit6can independently introduce additional pressurizing media into the brake circuits BK1, BK2. An additional breather bore provided in the cylinder of the first pressure supply unit6enables a volumetric compensation in the initial position of the piston of the first pressure supply unit6.

The third pressure supply unit90is only schematically illustrated inFIG.8. Said pressure supply unit90ultimately supplies four wheel brakes RB1, RB2, RB3and RB4. In the schematic illustration, the wheel brakes RB1, RB2operate a front axle VA of the vehicle, and the wheel brakes RB3and RB4operate a rear axle HA of the vehicle. An electric drive motor for driving the vehicle is situated on the rear axle HA of the vehicle. The vehicle can be a purely electric vehicle or a hybrid vehicle.

The first brake circuit BK1is connected to the wheel brakes RB1and RB2, and the second brake circuit BK2is connected to the wheel brakes RB3and RB4. A corresponding allocation is advantageous for the hydraulic assembly illustrated inFIG.8.

The third pressure supply unit90furthermore possesses a control apparatus95(“ECU-ESP”).

The second pressure supply unit14likewise possesses a printed circuit board which has a level sensor NST which detects the position of a magnetic float gauge NS within the reservoir40. The PCB furthermore has sensors30a,30bfor detecting the pedal travel as well as a difference in the distance of travel between the piston24and the pedal travel.

A suction valve70b,which connects the pump of the third pressure supply unit90to the reservoir40, is provided in the first brake circuit BK1for providing additional pressurizing medium for the third pressure supply unit90.

When the pump of the third pressure supply unit90requires pressurizing medium for the second brake circuit BK2, the latter can thus be provided from the reservoir40by way of the suction valve70c.

In this way, for suctioning pressurizing medium, the two brake circuits BK1, BK2by the respective hydraulic lines HL1, HL2are in each case connected to the reservoir40by way of one suction valve70bor70c,respectively. In order to achieve optimum suctioning of the pressurizing medium, the suction valve70cpreferably has a diameter in the range from 30 mm to 50 mm and in particular a diameter of 40 mm.

The exemplary embodiment optionally possesses a control of the clearance between the brake pads and the disk brake. The wheel brakes RB1, RB2, RB3, RB4(cf.FIG.8) can be configured as frictionless wheel brakes RB1, RB2, RB3, RB4. In a brake-by-wire system, disk brakes having brake pads which are spaced apart by way of a clearance in the absence of pressure in the brake system enable the frictional resistance to be reduced. This can be achieved by the use of rollback seals, restoring springs of the brake pads, or by actively retracting the brake pads by generating a vacuum by means of the pressure supply6, as is explained in EP2225133by the applicant.

The clearance in the wheel brake RB1, RB2, RB3, RB4, which is variable during operation, can be measured in a wheel-individual or brake circuit-individual manner by evaluating the pressure profile by means of the first pressure supply unit6. According to the invention, corresponding measuring can take place when servicing, or else during the operation of the vehicle. The measurement is preferably performed in a stationary vehicle or after braking.

Using the known clearance values of the wheel brakes RB1, RB2, RB3, RB4, the clearance when activating the wheel brake RB1, RB2, RB3, RB4is first rapidly overcome by means of a piston travel control of the first pressure supply unit6. In this respect, the use of a brushless motor as an electromotive drive8of the first pressure supply unit6with a small time constant is to be preferred, because the action of overcoming the clearance can be implemented without the driver perceiving the latter when activating the brake.

Moreover, the brake system2can be controlled so that the vehicle electric motor is active in the phase of the clearance. In this way, a braking action is generated immediately when activating the brake.

In one exemplary embodiment of the invention, differences in the clearances of the wheel brakes RB1, RB2, RB3, RB4are compensated for in that the inlet valves EV1to EV4of the second module (ESP unit) are actuated, and/or the electric motor of one or a plurality of vehicle axles is utilized for generating a braking action at the beginning of braking. By way of the clearance, stick-slip effects of new brake systems at low speeds can generally be reduced or avoided.

In one exemplary embodiment, the brake system2according to the invention in the event of a failure (error event4) of the ESP unit implements a very simple variant of an intermittent brake. Locking of the wheels is avoided and the steerability is maintained by moving the piston of the first pressure supply unit6in a reciprocating manner between an upper and lower pressure range. As opposed to a 1-channel ABS operation, no measurement values, for example pressure and wheel speeds, are required in this form of deceleration.

The automated intermittent brake leads to sufficient stopping distances (approx. 200% of the stopping distance in the ABS mode in comparison to a full-fledged wheel-individual ABS) and to acceptable stability by maintaining the steerability.

The brake system according to the invention can provide the decisive advantage that the brake pedal acts only on the piston24and by way of the feed valve69is isolated from the brake circuits BK1, BK2. In this way, the function of the automated intermittent brake with the X-boost or X-booster, respectively, cannot be interfered with by the driver as opposed to the prior art (WO2011/098178).

Alternatively to the intermittent brake, a 1-channel ABS operation with “select-low” feedback control (error event3) can be implemented. This leads to a further deterioration of the stopping distance (approx. 400% stopping distance in comparison to the stopping distance with a full-fledged wheel-individual ABS) but to an unrestricted vehicle stability and in terms of this characteristic is superior to the intermittent brake. In this form of the 1-channel ABS operation, measurement values such as, for example, pressure and wheel speeds are required, which can be imported from the ESP unit by way of a communications link/interface, for example a CAN interface.

In order to further increase the availability of the brake system2according to the invention according toFIG.8, the electromotive drive8of the first pressure supply unit6is connected to the control unit9(ECU-DV) of the X-boost by way of two redundant three-phase strands, and the electronic system is embodied so as to be (partially) redundant. For example, two B6bridges can be provided for each strand. Moreover, in at least one exemplary embodiment, the electronic system is connected to two redundant voltage supplies. In this way, the failure probability of the electromotive drive8can be reduced by the factor of 4-10, and the error event (failure of the first pressure supply unit6) can be further significantly reduced.

The control apparatus95of the ESP unit90, as well as the control unit9(ECU-DV) of the X-boost, are connected to one another by way of the communications link100, for example a CAN bus. To this extent, it is possible for control commands to be released to the third pressure supply unit90, said control commands causing an activation of the drive91and/or of the provided valves (cf. alsoFIG.8).

The following safety-relevant redundancies can be implemented using the brake system2as perFIG.8:ensuring a sufficient braking action for meeting the statutory requirements in the event of a brake circuit failure, failure a) of the second pressure supply unit14, b) of the first pressure supply unit6, or c) of the first pressure supply unit6and the third pressure supply unit90(simultaneously), i.e. also meeting statutory requirements in the case of double errors:error event1—failure of the third pressure supply unit90: deceleration by boosting the brake force by way of the first pressure supply unit6in both brake circuits BK1, BK2;error event2—failure of the third pressure supply unit90and of the brake circuit BK1: deceleration by boosting the brake force by way of the first pressure supply unit6, for example on the rear axle;error event3—failure of the third pressure supply unit90and of the second brake circuit BK2: deceleration by the second pressure supply unit14, for example on the front axle (first isolation valve BP1closed)error event4—failure of the first pressure supply unit6: deceleration by boosting the brake force by way of the third pressure supply unit90;error event5—failure of the first pressure supply unit6and of the first brake circuit BK1or of the second brake circuit BK2: deceleration by boosting the brake force by way of the third pressure supply unit90in one of the brake circuits BK1, BK2, optionally facilitated by the vehicle electric motor on one axle;error event6—failure of the first pressure supply unit6and of the third pressure supply unit90: braking by the master brake cylinder on the front axle VA and optionally by the electric drive motor on the rear axle HA;error event7—failure of the on-board network: braking by the second pressure supply unit14optionally on the front axle VA and the rear axle HA;electronic brake force distribution (EBV) in the event of failure of the ESP unit by generating pressure in the first brake circuit BK1by way of the third pressure supply unit90, and generating pressure in the second brake circuit BK2by way of the first pressure supply unit6, with the first isolation valve BP1closed, and controlling the first pressure supply unit6by way of a sensor assembly of the second pressure supply unit14. Required to this end is a S/W brake circuit split, i.e. the wheels of the front axle VA are connected to the first brake circuit BK1, and the wheels of the rear axle HA are connected to the second brake circuit BK2;controlling the clearance between the brake pads and the disk brake;4-channel ABS operation and/or yaw torque feedback-control when actuating the valves of the ESP unit;1-channel ABS operation or implementation of an automated intermittent brake.

FIG.9shows an alternative design embodiment of the X-boost according toFIG.8. As opposed to the exemplary embodiment according toFIG.8, a second isolation valve TVBK2is disposed in the second hydraulic line HL2inFIG.9. This second isolation valve TVBK2enables the second brake circuit BK2to be hydraulically decoupled from the first pressure supply unit6. In this way, the first pressure supply unit6can selectively provide pressurizing medium in the first brake circuit BK1or in the second brake circuit BK2or in both brake circuits. When volumetric loss is detected in the second brake circuit BK2, the latter can be decoupled.

Furthermore, the exemplary embodiment according toFIG.9differs in that a third isolation valve BP2is provided in the first hydraulic line HL1between the first isolation valve BP1and the first connection point A1for the first brake circuit BK1. This third isolation valve BP2is preferably disposed such that the third hydraulic line, in a hydraulic connection between the first isolation valve BP1and the third isolation valve BP2, opens into the first hydraulic line HL1. The third isolation valve BP2enables the first brake circuit BK1to be hydraulically decoupled from the first pressure supply unit6as well as from the second pressure supply unit14. In the case of a failed first pressure supply unit6, it is thus possible for pressurizing medium, proceeding from the second pressure supply unit14, to be introduced into the second brake circuit BK2by way of the feed valve69, the first isolation valve BP1and the second isolation valve TVBK2. No pressurizing medium is dispensed into the first brake circuit BK1when the third isolation valve BP2is closed.

The following safety-relevant redundancies can be implemented using the brake system2as perFIG.9:ensuring a sufficient braking action in the event of a failure of the one or the plurality of pressure supply units,error events1-7: see embodiment 1;error event8—failure of the feed valve69(for example leaky), or failure of the electric actuation: closure of the third hydraulic line HL3by the isolation valves BP1and BP2so that the travel simulator28is fully effective; the first pressure supply unit6adjusts wheel pressures in the brake circuit BK2and/or the ESP unit adjusts wheel pressures in both brake circuits BK1and BK2,further degree of freedom: selectively feeding the pressure of the master brake cylinder into the brake circuit BK1or BK2in the event of a failure of a brake circuit;ensuring a 4-channel ABS feedback control and/or a yaw torque feedback control when actuating the valves of the ESP unit,2-channel ABS operation according to the select-low and select-high method, or 1-channel ABS according to the select-low method with wheel rotational speed sensors;Electronic brake force distribution (EBV) in the event of a failure of the ESP unit by generating pressure in the brake circuit BK1by way of the second pressure supply unit14, and generating pressure in the brake circuit BK2by way of the first pressure supply unit6, with a closed first isolation valve BP1, and controlling the pressure supply by way of the sensor assembly of the second pressure supply unit14. Required to this end is the S/W brake circuit distribution, and the brake force distribution into the brake circuits is controlled by way of the isolation valves BP1, BP2and TVBK2. According to the invention, the piston of the first pressure supply unit6for applying a suitable pressure can be controlled in a reciprocating stroke movement. Optionally, an adjustment of pressure can take place by way of a PWM control of the valves, in particular of the isolation valves;The clearance control is already embodied in the exemplary embodiment as perFIG.8. The exemplary embodiment as perFIG.9offers the additional potential of compensating for the unequal clearance in the wheel brakes RB1, RB2, RB3, RB4of the brake circuits BK1, BK2by a corresponding pilot control prior to the brake force boosting operation by sequentially opening the isolating valves BP1, TVBK2. Alternatively, the PWM operation may also be used so that different flow cross sections to the brake circuits BK1, BK2are established and the unequal clearance can simultaneously be compensated for. A S/W brake circuit split is suitable here. This method is readily possible because the brake circuit isolation valves are a component part of the X-boost module and can be implemented without any temporal delay and susceptibility to faults (utilizing an interface between the X-boost and the ESP unit, for example). In this way, the brake system can be designed in such a manner, for example, that no clearance is provided on the brake pads on the front axle, and a clearance is provided on the rear axle. In this way, a failure of the first pressure supply unit6does not lead either to a temporal delay in braking when pressure is generated by the activation unit and acts according to the invention on the wheel brakes RB1, RB2, RB3, RB4of the front axle VA. Moreover, a greater braking action can be generated by the front axle VA.

A circuit diagram of the third pressure supply unit (ESP unit) while dissipating pressure (cf.FIG.11) or building up pressure (cf.FIG.11) in the first error event during yaw torque feedback control is in each case shown inFIGS.10and11. In principle, the feedback control here is performed in a manner similar to the 4-channel ABS likewise possible in the first error event. In the case of the yaw torque feedback control, however, the pressure dissipation as well as the pressure buildup—as opposed to the 4-channel ABS feedback control—takes place by way of the inlet valves EV1-EV4as well as the USV valves. Opened valves relevant for the flow are in each case provided with an asterisk (*) inFIG.10as well asFIG.11. The state of the other solenoid valves is not explicitly explained. For example, at least the inlet valves EV2, EV3, EV4are thus closed by active energizing during pressure dissipation. To the extent that the valves are valves actuatable by means of a PWM signal, open in the context of this application can also be understood to mean that these valves are actuated by actuation with a PWM signal, such that a predefined opening cross section is established thereby. In this way, a flow rate through the respective valve is able to be controlled by actuating the valves by means of a PWM signal. Specifically, the inlet valves EV1-EV4and the valves USV1, USV2inFIGS.10and11are actuatable by means of a PWM signal. In this way, a flow rate through these valves in the situations described hereunder is able to be feedback-controlled or controlled, respectively.

A wheel-selective yaw torque feedback control during a pressure buildup in the wheel brake RB4is shown in an exemplary manner inFIG.10. To this end, the inlet valve EV1assigned to the respective wheel brake, here the wheel brake RB4, and the isolation valve USV2assigned to the respective brake circuit, here the first brake circuit BK1, are passed through by a flow of pressurizing medium. The valves in this embodiment do not have to be actively actuated because said valves are passively open in the non-energized open state and bidirectionally permit a volumetric flow of the pressurizing medium. For the selective pressure generation in a wheel brake RB4, the other inlet valves EV1-EV3, by way of which pressure is not to be built up (RB1-RB3) are actuated in such a manner that the solenoid valves are moved from the open state to the energized closed state. In this context, actuating in the case of a valve that is open when not energized can be understood to mean that the inlet valves EV1-EV3are closed, i.e. switched so as not to conduct pressurizing medium.

Likewise, the HSV valves for the selective pressure generation in the wheel brake RB4are closed, i.e. switched so as not to conduct pressurizing medium.

In this way, an impingement of pressure from the first pressure supply unit6by way of the isolation valve USV2and the inlet valve EV4takes place exclusively to the wheel brake RB4(schematically indicated by an arrow). In addition to a wheel brake RB1, RB2, RB3, RB4, a yaw torque can be generated in a plurality of wheel brakes RB1, RB2, RB3, RB4. To this end, those inlet valves EV1-EV4in the wheel brakes RB1, RB2, RB3, RB4are closed in each case by way of which a pressure is not to be built up. By way of this enhancement, a yaw torque can be simultaneously generated in, for example,2wheel brakes RB1, RB2, RB3, RB4of one vehicle side. Since brake circuits are typically embodied so as to be black and white, or diagonal, in this instance consequently one wheel brake RB1, RB2, RB3, RB4of one brake circuit is in each case impinged with pressure. A further potential enhancement of the yaw torque feedback control is possible as a result of a sequential or simultaneous multiplex operation of the circuit isolation valves BP1/BP2and TVBK2of the first module (embodiment according toFIG.9). In this way, a pressure in a wheel brake RB1, RB2, RB3, RB4(for example RB4of the right rear wheel) can be brought to a pressure level, wherein the circuit isolation valve TVBK2upon reaching the pressure valve is closed in order to maintain the pressure.

Moreover, another pressure level can be adjusted in a wheel brake RB1, RB2, RB3, RB4of the other brake circuit (for example RB2of the right front wheel), wherein the second brake circuit isolation valve BP1or alternatively BP2is closed in order to maintain the pressure. The brake circuit isolation valves BP1/BP2and TVBK2are required for maintaining pressure because the inlet valves of the wheel brakes RB1, RB2, RB3, RB4have check valves connected in parallel. In this way, maintaining pressure in the second module (ESP unit) is impossible when the pressure has dissipated, or when a lower pressure level is adjusted in the second brake circuit.

The following states thus result for the relevant valves of the third pressure supply unit90for the pressure buildup according toFIG.10:HSV1: closed (not energized)HSV2: closed (not energized)EV4: open (open when not energized, or energized by the PWM method, i.e. partially opened)EV1-EV3: closed (energized)All other valves in the hydraulic, in particular non-energized, initial state

In the case of pressure dissipation, as shown inFIG.11, for example, the return of pressurizing medium takes place in an analogous but reversed manner from the wheel brake RB4by way of the inlet valve EV4and the isolation valve USV2to the first pressure supply unit6. In an analogous manner, the pressure dissipation then also takes place in the event of yaw torque interventions in a plurality of wheel brakes. Here too, the multiplex method is preferably used.

In one embodiment, a plurality of, in particular all four, wheel brakes RB1, RB2, RB3, RB4can additionally be actuated individually and wheel-selectively in an analogous manner, and a wheel-selective yaw torque feedback control can thus be implemented. Alternatively or additionally, the yaw torque feedback control in one embodiment can take place in a brake circuit-selective manner, so that two wheel brakes of one brake circuit are in each case conjointly actuated.

Specifically, the following states are thus derived for the relevant valves of the third pressure supply unit90for the pressure dissipation according toFIG.11:HSV1: closed (non-energized)HSV2: closed (non-energized)EV4: open (open when non-energized or energized by the PWM method, i.e. partially opened)USV1: closed (closed when energized)EV1-EV3: closed (energized)All other valves in the hydraulic, in particular non-energized, initial state

At this point it is to be pointed out that all parts described above are in each case to be considered individually—even without features which have been additionally described in the respective context, even when said features have not been explicitly identified individually as optional features in the respective context, for example by using: in particular, preferably, for example, e.g., optionally, parentheses, etc.—and in combination or any arbitrary sub-combination as independent design embodiments or refinements of the invention, respectively, as defined in particular in the introduction to the specification and the claims. Deviations therefrom are possible. Specifically, it is to be pointed out that the word “in particular” or parentheses do not identify features which are mandatory in the respective context.

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