Control device for a vehicle's braking system and method for operating a vehicle's braking system

Abstract

Control device (10) for a braking system of a vehicle with: a control device (12) by means of which, at least taking into account a target vehicle deceleration (a) that can be specified by a driver by means of an actuation of a brake actuation element (11) of the vehicle and / or by a speed control automatic system of the vehicle, a first target brake pressure to be set in at least a first wheel brake cylinder (14) of a first brake circuit (16) of the brake system and a second target brake pressure to be set in at least a second wheel brake cylinder (18) of a second brake circuit (20) of the brake system can be set, wherein at least one component (24, 26, 28) of the brake system can be controlled by means of the control device (12),so that a first actual brake pressure present in at least the first wheel brake cylinder (14) of the first brake circuit (16) can be varied, taking into account the specified first target brake pressure, and a second actual brake pressure present in at least the second wheel brake cylinder (18) of the second brake circuit (20) can be varied, taking into account the specified second target brake pressure; , characterized by the fact that the first actual brake pressure can be reduced according to the specified first target brake pressure and the second actual brake pressure can be reduced according to the specified second target brake pressure, wherein the control device (12) is designed to output at least one first control signal (30) to a master brake cylinder pressure variability device (24), which can be controlled by means of the at least one first control signal (30) such that the master brake cylinder pressure (pHZ) in a master brake cylinder (32) of the brake system can be adjusted to be less than or equal to a minimum of the first target brake pressure and the second target brake pressure, and to output at least one second control signal (36) to a first switching valve (26) of the first brake circuit (16) and / or to a second switching valve (26) of the second brake circuit (20),wherein the first switching valve (26) is arranged between the master brake cylinder (32) and at least one first wheel inlet valve (28) associated with the at least one first wheel brake cylinder (14), and the second switching valve (26) is arranged between the master brake cylinder (32) and at least one second wheel inlet valve (28) associated with the at least one second wheel brake cylinder (18), and wherein the first switching valve (26) and the second switching valve (26) can be controlled by means of the at least one second control signal (36) such that the first actual brake pressure and / or the second actual brake pressure can be additionally reduced; and , The first actual brake pressure can be increased according to the specified first target brake pressure, and the second actual brake pressure can be increased according to the specified second target brake pressure, wherein the control device (12) is designed to output at least one third control signal (38) to the master brake cylinder pressure variability device (24), which can be controlled by means of the at least one third control signal (38) such that the master brake cylinder pressure (pHZ) can be set to a maximum of the first target brake pressure and the second target brake pressure, and to output at least one fourth control signal (40) to the at least one first wheel inlet valve (28) of the first brake circuit (16) and / or to the at least one second wheel inlet valve (28) of the second brake circuit (20), which can each be controlled by means of the at least one fourth control signal (40) such that the first actual brake pressure and / or the second actual brake pressure can be further increased. are.

Description

[0001] The invention relates to a control device for a vehicle's braking system. The invention also relates to a vehicle's braking system. Furthermore, the invention relates to a method for operating a vehicle's braking system. State of the art

[0002] German patent application DE 10 2010 040 854 A1 describes a hydraulic braking system and a method for its operation. By using the hydraulic braking system or by carrying out the method for its operation, it should be possible to brake a vehicle using at least one electric motor and a hydraulic braking system.

[0003] Furthermore, DE 10 2011 077 329 A1, WO 2011 / 104 056 A1 and DE 10 2010 008 033 A1 each describe control devices and methods for braking a vehicle using its at least one electric motor and a hydraulic braking system interacting with it. Disclosure of the invention

[0004] The invention provides a control device for a braking system of a vehicle with the features of claim 1, a braking system for a vehicle with the features of claim 7 and a method for operating a braking system of a vehicle with the features of claim 8. Advantages of the invention

[0005] The present invention ensures high pressure point accuracy when setting the first actual brake pressure to / equal to the specified first target brake pressure and the second actual brake pressure to / equal to the specified second target brake pressure. Components of an ESP system of the brake system, which are typically already present in a conventional brake system, can be used for this purpose. Thus, existing components can be used to achieve the comfortable and precise pressure point setting made possible by the present invention. The present invention can therefore be implemented without any further development that would increase the manufacturing costs or the installation space required for the brake system.

[0006] Furthermore, the present invention allows for axle-specific modulation of the actual brake pressures. At the same time, the present invention ensures that a desired distribution of braking torques between the front and rear axles can be reliably maintained. Thus, vehicle pitching induced by a disturbance in the desired distribution of braking torques, which the driver often perceives as bothersome, is reliably prevented.

[0007] In an advantageous embodiment, the control device is additionally designed to control, by means of at least one second control signal, a Δp control of the first actual brake pressure to be reduced by the first switching valve and / or a Δp control of the second actual brake pressure to be reduced by the second switching valve. This allows for high accuracy when setting the desired first actual brake pressure and / or the desired second actual brake pressure by means of the resulting pressure reduction. By using so-called Δp control, the dependence of the set first actual brake pressure and / or second actual brake pressure on the volumetric capacity of the hydraulic brake system is also eliminated, at least to a first approximation.

[0008] Alternatively or additionally, the control unit can also be designed to use at least one fourth control signal to control a Δp control of the first actual brake pressure to be increased by means of the at least one first wheel inlet valve and / or a Δp control of the second actual brake pressure to be increased by means of the at least one second wheel inlet valve. Thus, high accuracy can also be guaranteed for the pressure build-up carried out in this way.

[0009] Preferably, the control device is additionally designed to control at least one plunger as a master brake cylinder pressure variability device by means of the at least one first control signal and / or the at least one third control signal. The setting of the desired master brake cylinder pressure can thus be carried out independently of the wheel inlet valves and the changeover valves. In addition, the plunger can be operated by means of a comparatively simple control scheme, since it only needs to ensure a sufficiently large pressure differential, but not an exact pressure. For the present invention, a comparatively inexpensive plunger, in particular with inexpensive control electronics, can therefore be used.

[0010] Preferably, the control device is additionally designed to set the first target brake pressure and / or the second target brake pressure, taking into account at least one generator braking torque that can be exerted on at least one axle assigned to the at least one first wheel brake cylinder and / or the at least one second wheel brake cylinder by means of at least one electric motor. The present invention thus also ensures a constant brake force distribution during recuperation. Due to the high pressure setting accuracy, deceleration fluctuations during recuperation can be minimized. The present invention can therefore also be used to encourage drivers to purchase a vehicle equipped with the at least one electric motor, which allows for more energy-efficient and lower-emission driving.

[0011] In an advantageous further development, the control device is additionally designed to determine, taking into account the setpoint signal, the first target brake pressure, the second target brake pressure, the determined or estimated first actual brake pressure, and / or the determined or estimated second actual brake pressure, a target value for the booster force to be exerted on the brake actuating element by means of a brake booster, and to output a brake booster control signal corresponding to the target value to the brake booster. The target value can be set by the control device in such a way that the driver has a standard brake actuation feel (brake pedal feel) during actuation of the brake actuating element.In particular, the amplifier force specified in this way makes it possible to ensure that the driver feels a counterforce / response from the brake actuation element corresponding to the desired vehicle deceleration during actuation.

[0012] The advantages listed above are also realized in a braking system for a vehicle with such a control device.

[0013] Furthermore, the described advantages can be guaranteed by implementing the corresponding method for operating a vehicle's braking system. The method can be further developed according to the control device embodiments described above. Brief description of the drawings

[0014] Further features and advantages of the present invention are explained below with reference to the figures. They show: Fig. 1 a flowchart to explain a first embodiment of the method; Fig. 2 a coordinate system to illustrate a second embodiment of the method; and Fig. 3 a schematic representation of an embodiment of the control device. Embodiments of the invention

[0015] Fig. Figure 1 shows a flowchart to explain a first embodiment of the method.

[0016] Using the method described below, it is possible to decelerate a vehicle equipped with at least one hydraulic braking system to a target deceleration a specified by the vehicle's driver and / or by the vehicle's adaptive cruise control system. For example, the driver can specify a target value for the desired deceleration a by actuating a braking element of the vehicle, such as a brake pedal. This target value can be, in particular, an adjustment travel of the braking element, such as the pedal travel of a brake pedal, a rod travel, a braking force applied by the driver to the braking element, and / or a corresponding value. The adaptive cruise control system can, for example, be an ACC system.

[0017] The target vehicle deceleration a and the vehicle mass m determine a braking force FVL to be exerted on the left front wheel, a braking force FVR to be exerted on the right front wheel, a braking force FHL to be exerted on the left rear wheel, and a braking force FHR to be exerted on the right rear wheel. If the wheels are braked solely by means of the hydraulic braking system (purely hydraulic braking), the sum of the braking forces FVL, FVR, FHL, and FHR is given by equation (Eq. 1): a=FVL+FVR+FHL+FHRm (purely hydraulic braking)

[0018] Each of the braking forces FVL, FVR, FHL and FHR causes a braking torque MVL, MVR, MHL or MHR on the associated wheel, whereby the braking torque MVL exerted on the left front wheel is determined by the radius of the left front wheel rVL, the braking torque MVR exerted on the right front wheel is determined by the radius of the right front wheel rVR, the braking torque MHL exerted on the left rear wheel is determined by the radius of the left rear wheel rHL, and the braking torque MHR exerted on the right rear wheel is determined by equations (Eq. 2.1) to (Eq. 2.4) with: MVL=FVL*rVL MVR=FVR*rVR MHL=FHL*rHL MHR=FHR*rHR

[0019] The braking torques MVL, MVR, MHL and MHR correlate to a brake pressure pVL in a wheel brake cylinder assigned to the left front wheel, a brake pressure pVR in a wheel brake cylinder assigned to the right front wheel, a brake pressure pHL in a wheel brake cylinder assigned to the left rear wheel or a brake pressure pHR in a wheel brake cylinder assigned to the right rear wheel according to equations (Eq. 3.1) to (Eq. 3.4) with: MVL=pVL*cVL MVR=pVR*cVR MHL=pHL*cHL MHR=pHR*cHR where cVL is a constant of the wheel brake cylinder assigned to the left front wheel, cVR is a constant of the wheel brake cylinder assigned to the right front wheel, cHL is a constant of the wheel brake cylinder assigned to the left rear wheel, and cHR is a constant of the wheel brake cylinder assigned to the right rear wheel.

[0020] As a rule, the wheels arranged on an axle have the same radii rVL, rVR, rHL, and rHR. The constants cVL, cVR, cHL, and cHR of the wheel brake cylinders assigned to a common axle are also normally the same. Equation (Eq. 1) can therefore be rewritten as equation (Eq. 4) with: a=cVRm*rVR*(pVL+pVR)+cHRm*rHR*(pHL+pHR) (purely hydraulic braking) (Instead of cVR and rVR, cVL and rVL and / or instead of cHR and rHR, cHL and rHL can also be used in equation (Eq. 4) and the other equations.)

[0021] The equations given above (Eq. 1 and Eq. 4) apply to the execution of the method described below, in which braking is purely hydraulic. Preferably, however, the method is used to operate a vehicle's braking system with at least one electric motor capable of generating power. In this case, at least one additional generator braking torque can be applied to the vehicle's wheels and / or axles by means of the at least one electric motor. In this way, the brake pressure to be built up in the respective wheel brake cylinders can be reduced by utilizing the at least one electric motor. For each generator braking torque applied to a wheel and / or axle of the vehicle, a "theoretical" brake pressure pgVL, pgVR, pgHL, and pgHR can be derived, which would have to be built up in the respective wheel brake cylinder to produce a friction braking torque corresponding to the generator braking torque.

[0022] If the procedure described below is carried out using a braking system with at least one electric motor that can be used as a generator, the equation given above (Eq. 4) can be extended to equation (Eq. 5) with: a=cVRm*rVR*(pVL+pgVL+pVR+pgVR)+cHRm*rHR*(pHL+pgHL+pHR+pgHR) (hydraulic and regenerative braking), where pgVL is a "theoretical" brake pressure with respect to the wheel brake cylinder of the left front wheel, pgVR is a "theoretical" brake pressure with respect to the wheel brake cylinder of the right front wheel, pgHL is a "theoretical" brake pressure with respect to the wheel brake cylinder of the left rear wheel and pgHR is a "theoretical" brake pressure with respect to the wheel brake cylinder of the right front wheel.

[0023] If the wheel brake cylinders of the same brake circuit have a common brake pressure pVR or pHR, then equation (Eq. 4) simplifies to equation (Eq. 6) with: a=2*cVRm*rVR*pVR+2*cHRm*rHR*pHR (purely hydraulic braking)

[0024] If, in addition, the same generator braking torque is applied to each axle by means of at least one electric motor, equation (Eq. 5) simplifies to equation (Eq. 7) with: a=2*cVRm*rVR*(pVR+pgVR)+2*cHRm*rHR*(pHR+pgHR) (hydraulic and regenerative braking)

[0025] (Instead of pgVR, pgVL and / or instead of pgHR, pgHL can also be used in equation (Eq. 7).)

[0026] Provided that the master cylinder pressure pHZ occurring in the master cylinder of the braking system is present in all wheel brake cylinders, equation (Eq. 6) simplifies to equation (Eq. 8) with: a=2*cVRm*rVR*pHZ+2*cHRm*rHR*pHZ (purely hydraulic braking) (This applies particularly to partial braking.)

[0027] Accordingly, equation (Eq. 7) also simplifies to equation (Eq. 9) with: a=2*cVRm*rVR*(pHZ+pgVR)+2*cHRm*rHR*(pHZ+pgHR) (hydraulic and regenerative braking)

[0028] If the target vehicle deceleration a is to be ensured by controlling the master brake cylinder pressure pHZ, then equations (Eq. 10) and (Eq. 11) must be complied with such that: pHZ=a*m*rVR*rHR2*(cVR*rHR+cHR*rVR) (purely hydraulic braking) pHZ=m*a*rVR*rHR−2*(cVR*pgVR*rHR+cHR*pgHR*rVR)2*(cVR*rHR+cHR*rVR) (hydraulic and regenerative braking)

[0029] However, the present invention eliminates the need to adjust the master brake cylinder pressure pHZ to correspond to equation (Eq. 10) or (Eq. 11). Therefore, no hydraulic component is required for the comparatively precise adjustment / regulation of the master brake cylinder pressure pHZ to carry out the advantageous method. Instead, the method described below implements a much simpler procedure for ensuring the desired target vehicle deceleration a.

[0030] The procedure comprises a process step S1 in which a first target brake pressure to be set in at least one first wheel brake cylinder of a first brake circuit of the brake system and a second target brake pressure to be set in at least one second wheel brake cylinder of a second brake circuit of the brake system are determined. The determination of the first target brake pressure and the second target brake pressure is carried out taking into account at least the target value a (specified by the driver by actuating the brake actuator and / or by the cruise control system) regarding the target vehicle deceleration to be exerted on the vehicle. In this way, for example, the first target brake pressure for the two wheel brake cylinders of the first brake circuit and the second target brake pressure for the two wheel brake cylinders of the second brake circuit can be determined. In particular, equation (Eq.6) (in the case of a braking system without a generator-operated electric motor) or equation (Eq. 7) (in the case of a braking system with at least one generator-operated electric motor) can be used to determine the target brake pressures.

[0031] A constant brake force distribution between the two axles of the vehicle is often preferred. In this case, if the first brake circuit is assigned to a first axle and the second brake circuit to a second axle of the vehicle, equation (Eq. 12) or (Eq. 13) can additionally be taken into account when determining the first target brake pressure and the second target brake pressure, with: C=cVRrVR*pVRcHRrHR*pHR (purely hydraulic braking) C=cVRrVR*(pVR+pgVR)cHRrHR*(pHR+pgHR) (hydraulic and regenerative braking) , where C represents the constant ratio of the braking force distribution.

[0032] However, it should be noted that considering at least one of the equations listed above in process step S1 is optional. The feasibility of process step S1 is not limited by this.

[0033] Following process step S1, the first actual brake pressure present in at least the first wheel brake cylinder of the first brake circuit is varied, taking into account the specified first target brake pressure, and the second actual brake pressure present in at least the wheel brake cylinder of the second brake circuit is varied, taking into account the specified second target brake pressure. For this purpose, at least process steps S2 and S3, or at least process steps S4 and S5, are executed.

[0034] If reducing the first actual brake pressure to equal to / equal to the specified first target brake pressure and the second actual brake pressure to equal to / equal to the specified second target brake pressure is advantageous / desired, process steps S2 and S3 can be carried out. In the first process step, S2, the master cylinder pressure (pHZ) in the master cylinder of the brake system is set to less than or equal to a minimum of the first target brake pressure and the second target brake pressure. For example, the master cylinder pressure (pHZ) can be set / adjusted so that it is less than half the minimum of the first target brake pressure and the second target brake pressure.

[0035] Preferably, the master cylinder pressure pHZ is reduced by means of at least one plunger. Since a comparatively large deviation of the set master cylinder pressure pHZ (compared to a predetermined target pressure) does not lead to any or hardly any disadvantages in the execution of the procedure described here, the control scheme of the at least one plunger used to set the master cylinder pressure pHZ is simplified. Thus, procedure step S2 can be reliably carried out using at least one comparatively inexpensive plunger.

[0036] In process step S3, a first switching valve of the first brake circuit is activated to further reduce the first actual brake pressure, and / or a second switching valve of the second brake circuit is activated to further reduce the second actual brake pressure. This allows for a reliable and rapid pressure reduction corresponding to the difference between the respective target brake pressure and the master cylinder pressure (pHZ). Furthermore, the use of the switching valves, through which brake fluid can be transferred from the respective wheel cylinders into at least one storage volume / plunger, enables return pumping without the need for a return pump. Process step S3 can therefore be performed silently. Moreover, the use of the switching valves ensures that the driver does not experience any vibration or recoil from the brake actuator despite the return pumping.

[0037] Preferably, in process step S3, the first switching valve is controlled to perform a Δp control of the first actual brake pressure to be reduced, and / or the second switching valve is controlled to perform a Δp control of the second actual brake pressure to be reduced. By using Δp control, the dependence of the set actual brake pressures on the volumetric capacity of the brake system is also eliminated, to a first approximation.

[0038] If an increase of the first actual brake pressure to equal to / equal with the specified first target brake pressure and of the second actual brake pressure to equal to / equal with the specified second target brake pressure is desired, process steps S4 and S5 can be performed. In process step S4, the master cylinder pressure pHZ is set to a maximum of both the first and second target brake pressures. For example, the master cylinder pressure pHZ can be set / adjusted to twice the maximum of both the first and second target brake pressures.

[0039] The increase in master cylinder pressure (pHZ) performed in process step S4 can also be achieved using at least one (cost-effective) plunger. The method described here eliminates the conventional limitation of using at least one plunger, which is often only suitable as a "volume regulator" and not as a "pressure regulator" with the desired accuracy. Since the plunger in this method is used solely as a "volume regulator," even a cost-effective plunger is sufficient for this process.

[0040] In process step S5, at least one wheel inlet valve of the first brake circuit is activated to further increase the first actual brake pressure, and / or at least one second wheel inlet valve of the second brake circuit is activated to further increase the second actual brake pressure. Process step S5 also ensures that a pressure increase by a pressure differential corresponding to the difference between the master cylinder pressure (pHZ) and the respective target brake pressure can be reliably and precisely achieved for each wheel cylinder.

[0041] Preferably, in process step S5, at least one first wheel inlet valve is controlled for Δp ​​control of the first actual brake pressure to be increased, and / or at least one second wheel inlet valve is controlled for Δp ​​control of the second actual brake pressure to be increased. It should be noted again that, to a first approximation, the use of Δp control eliminates the dependence of the set actual brake pressures on the hydraulic fluid volume. Since the hydraulic fluid volume fluctuates considerably over the service life of the brake system, the method described here thus ensures the elimination / circumvention of conventional disadvantages / difficulties in operating a hydraulic brake system.

[0042] The method described above allows for optimized operation of the braking system with regard to pressure setting accuracy and noise-optimized control. The method can also be used for the optional utilization of the recuperation potential of the vehicle's at least one generator-operated electric motor.

[0043] Depending on the maximum available generator braking torque of the at least one electric motor, blending by varying the hydraulically applied braking torques MVL, MVR, MHL, and MHR can be reliably and easily implemented using the method described here. Due to the quick and reliable adjustability of the desired actual brake pressures using process steps S2 to S4, the vehicle can react early to changes in the target vehicle deceleration a and / or the maximum achievable generator braking torque. It should be noted again that the method described here can also be implemented if no more precise information regarding the characteristics of the hydraulic system, particularly its volumetric capacity, is available.

[0044] Furthermore, the method described here ensures a distribution of braking torques between the front and rear axles according to the desired constant brake force distribution C. Even during blending, the simple and quick adjustability of the desired actual brake pressures prevents any destabilization of the desired constant brake force distribution C. In particular, this reliably suppresses any pitching of the vehicle that would be perceived as disturbing by the driver.

[0045] In a further training course, the procedure can also include a process step S6. In process step S6, taking into account the target value, the first target brake pressure, the second target brake pressure, the determined or estimated first actual brake pressure, and / or the determined or estimated second actual brake pressure, a target value is defined for the booster force to be exerted on the brake actuating element by means of a brake booster. The brake booster is then controlled accordingly in process step S6. In particular, the booster force exerted by the brake booster can thus be set so that the driver experiences a response from the braking system corresponding to the specified target vehicle deceleration a, regardless of the actual brake pressures present, when the brake actuating element is actuated.The method described here can therefore also ensure a favorable / comfortable brake actuation feel (pedal feel) for the driver.

[0046] Fig. Figure 2 shows a coordinate system to illustrate a second embodiment of the method.

[0047] The abscissa of the coordinate system of Fig. 2 is the time axis t (in seconds s). Using the coordinate of the coordinate system of Fig. 2 are given as pressures p (in bar).

[0048] From time t0, the driver activates the brake actuation element, which functions as a brake pedal. By activating the brake actuation element, the driver transfers brake fluid from the master cylinder of the brake system to the connected wheel cylinders, thereby building up an actual brake pressure pist in the wheel cylinders. (For clarity, we will henceforth refer to only one actual brake pressure pist in the wheel cylinders.)

[0049] The use of at least one electric motor capable of generating power in the braking system is omitted between times t0 and t1. This may be because the generator potential is not yet sufficient between times t0 and t1.

[0050] Only from time t1 onwards is the at least one electric motor used for additional vehicle braking. For example, the at least one electric motor can be used to charge a battery in this way. From time t1 onwards, the at least one electric motor thus generates a non-zero generator braking torque, from which the previously mentioned "theoretical" (generator) brake pressure pgen can be derived. (For clarity, only one "theoretical" brake pressure pgen is assumed.) To ensure that the target vehicle deceleration specified by the driver is not exceeded despite the generator operation of the at least one electric motor, the actual brake pressure pist at the wheel brake cylinders is reduced from time t1 onwards. This is achieved by significantly reducing the master brake cylinder pressure pHZ between times t1 and t2 by executing process step S2.For example, the master brake cylinder pressure pHZ can be reduced to zero up to time t2.

[0051] By performing the above-described process step S3, a desired pressure difference Δp in the master brake cylinders compared to the master brake cylinder pressure pHZ can be set so that, despite the sharp drop in the master brake cylinder pressure pHZ, a higher actual brake pressure pist in the wheel brake cylinders can be reliably maintained.

[0052] As the vehicle speed decreases, the maximum generator braking torque achievable by the at least one electric motor decreases. From time t3 onwards, the generator braking torque achievable by the at least one electric motor therefore decreases again. From time t3 onwards, the "theoretical" (generator) braking pressure pgen also decreases.

[0053] By increasing the actual brake pressure pist, the decrease in the "theoretical" brake pressure pgen can be compensated for / masked. This is achieved by significantly increasing the master cylinder pressure pHZ between times t3 and t4 using process step S4. In particular, the master cylinder pressure pHZ can then be regulated back to its value at time t1.

[0054] By executing process step S5, the steep increase in the master cylinder pressure pHZ can be compensated for, resulting in a desired pressure difference Δp between the master cylinder and the wheel cylinders. Specifically, the actual brake pressure pist can be increased so gradually that it only reaches the same level as the master cylinder pressure pHZ at time t5. From time t6 onwards, the driver reduces the actuation of the brake actuator, and the actual brake pressure pist decreases accordingly. At time t7, the actuation of the brake actuator is complete.

[0055] As shown by the Fig. As can be seen in Figure 2, the actual brake pressure pist can be adjusted to the time-varying "theoretical" (generator) brake pressure pgen using the procedure described here, such that a total brake pressure pges, as the sum of the brake pressures pist and pgen, can be maintained constantly between times t1 and t5. The total brake pressure pges can, in particular, correspond to the specified target vehicle deceleration a.

[0056] Fig. Figure 3 shows a schematic representation of one embodiment of the control device.

[0057] The control device 10 comprises a control unit 12, by means of which a first target brake pressure to be set in at least one first wheel brake cylinder 14 of a first brake circuit 16 of the brake system and a second target brake pressure to be set in at least one second wheel brake cylinder 18 of a second brake circuit 20 of the brake system can be determined. The control unit 12 is designed to execute the setting of the target brake pressures at least taking into account a preset signal 22 with respect to the target vehicle deceleration that can be specified by the driver by actuating the brake actuation element 11 and / or by the (not shown) automatic speed control system.Furthermore, at least one component 24 to 28 of the brake system can be controlled by means of the control device, so that a first actual brake pressure present in at least the first wheel brake cylinder 14 of the first brake circuit 16 can be varied taking into account the specified first target brake pressure and a second actual brake pressure present in at least the second wheel brake cylinder 18 of the second brake circuit 20 can be varied taking into account the specified second target brake pressure.

[0058] For example, the first actual brake pressure can be reduced to / equal to the specified first target brake pressure, and the second actual brake pressure can be reduced to / equal to the specified second target brake pressure. The control device 12 is designed to output at least one first control signal 30 to a master brake cylinder pressure variability device 24, which can be controlled by means of the at least one first control signal 30 such that the master brake cylinder pressure pHZ in a master brake cylinder 32 of the brake system can be adjusted to a minimum of the first target brake pressure and the second target brake pressure. In this case, at least one second control signal 36 can also be output by means of the control device 12 to a first switching valve 26 of the first brake circuit 16 and / or to a second switching valve 26 of the second brake circuit 20.The changeover valves 26 can each be controlled by means of at least one second control signal 36 in such a way that the first actual brake pressure and / or the second actual brake pressure can be further reduced due to a brake fluid transfer through the controlled changeover valves 26.

[0059] Alternatively or additionally, the first actual brake pressure can be increased to or equal to the specified first target brake pressure, and the second actual brake pressure can be increased to or equal to the specified second target brake pressure. In this case, the control device 12 is designed to output at least one third control signal 38 to the master brake cylinder pressure variability device 24, which can be controlled by means of this at least one third control signal 38 such that the master brake cylinder pressure can be set to a maximum of the first target brake pressure and the second target brake pressure. Furthermore, at least one fourth control signal 40 can be output by means of the control device 12 to at least one first wheel inlet valve 28 of the first brake circuit 16 and / or to at least one second wheel inlet valve 28 of the second brake circuit 20.The wheel inlet valves 28 can each be controlled by means of at least one fourth control signal 40 in such a way that the first actual brake pressure and / or the second actual brake pressure can be further increased due to a brake fluid transfer through the controlled wheel inlet valves 28.

[0060] Preferably, the control device 12 is additionally designed to control, by means of at least one second control signal 36, a Δp control of the first actual brake pressure to be reduced by the first switching valve 26 and / or a Δp control of the second actual brake pressure to be reduced by the second switching valve 26. Likewise, the control device 12 can be designed to control, by means of at least one fourth control signal 40, a Δp control of the first actual brake pressure to be increased by the at least one first wheel inlet valve 28 and / or a Δp control of the second actual brake pressure to be increased by the at least one second wheel inlet valve 28. This ensures the advantages already described above.

[0061] Furthermore, the control device 12 can be designed to control at least one plunger 24 as a master brake cylinder pressure variability device 24 by means of at least one first control signal 30 and / or at least one third control signal 38. As explained above, a cost-effective plunger type can be used in conjunction with the control device 12.

[0062] In a further development, the control device 12 is additionally designed to determine the first target brake pressure and / or the second target brake pressure, taking into account at least one generator braking torque that can be exerted on at least one axle assigned to at least one first wheel brake cylinder 14 and / or at least one second wheel brake cylinder 16 by means of at least one electric motor. The control device 10 can thus also be used to blend a time-varying generator braking torque.

[0063] In another embodiment, the control device 12 is additionally designed to determine a target value for the booster force to be exerted on the brake actuation element 11 by means of a brake booster 42, taking into account the setpoint signal 22, the first target brake pressure, the second target brake pressure, the determined or estimated first actual brake pressure, and / or the determined or estimated second actual brake pressure, and to output a brake booster control signal 44 corresponding to the target value to the brake booster 42. The control device 10 can thus, by means of the at least one plunger 24, generate a driving pressure differential for controlling the ESP system, make the desired axle-specific pressure setting with high accuracy via the ESP system, and simultaneously ensure a standard / comfortable brake actuation feel (pedal feel) by controlling the brake booster 42.

[0064] The advantages of the control device 10 are also guaranteed with a braking system equipped with it. The in Fig. The brake system shown in Figure 3 is only partially represented. For example, in addition to the brake fluid reservoir 46, the return pumps 48, and a pressure sensor 50, the brake system may also include wheel outlet valves and accumulator chambers. However, since these components of the brake system are not necessary for the function of the control device 10, their representation is omitted. Fig. 3 waived.

Claims

[1] Control device (10) for a braking system of a vehicle with: a control device (12) by means of which, at least taking into account a target vehicle deceleration (a) that can be specified by a driver by means of an actuation of a brake actuation element (11) of the vehicle and / or by a speed control automatic system of the vehicle, a first target brake pressure to be set in at least a first wheel brake cylinder (14) of a first brake circuit (16) of the brake system and a second target brake pressure to be set in at least a second wheel brake cylinder (18) of a second brake circuit (20) of the brake system can be set, wherein at least one component (24, 26, 28) of the brake system can be controlled by means of the control device (12),so that a first actual brake pressure present in at least the first wheel brake cylinder (14) of the first brake circuit (16) can be varied, taking into account the specified first target brake pressure, and a second actual brake pressure present in at least the second wheel brake cylinder (18) of the second brake circuit (20) can be varied, taking into account the specified second target brake pressure; characterized by , that the first actual brake pressure can be reduced according to the specified first target brake pressure and the second actual brake pressure can be reduced according to the specified second target brake pressure, wherein the control device (12) is designed to output at least one first control signal (30) to a master brake cylinder pressure variability device (24), which can be controlled by means of the at least one first control signal (30) such that the master brake cylinder pressure (pHZ) in a master brake cylinder (32) of the brake system can be adjusted to be less than or equal to a minimum of the first target brake pressure and the second target brake pressure, and to output at least one second control signal (36) to a first switching valve (26) of the first brake circuit (16) and / or to a second switching valve (26) of the second brake circuit (20),wherein the first switching valve (26) is arranged between the master brake cylinder (32) and at least one first wheel inlet valve (28) associated with the at least one first wheel brake cylinder (14), and the second switching valve (26) is arranged between the master brake cylinder (32) and at least one second wheel inlet valve (28) associated with the at least one second wheel brake cylinder (18), and wherein the first switching valve (26) and the second switching valve (26) can be controlled by means of the at least one second control signal (36) such that the first actual brake pressure and / or the second actual brake pressure can be additionally reduced; and, The first actual brake pressure can be increased according to the specified first target brake pressure, and the second actual brake pressure can be increased according to the specified second target brake pressure, wherein the control device (12) is designed to output at least one third control signal (38) to the master brake cylinder pressure variability device (24), which can be controlled by means of the at least one third control signal (38) such that the master brake cylinder pressure (pHZ) can be set to a maximum of the first target brake pressure and the second target brake pressure, and to output at least one fourth control signal (40) to the at least one first wheel inlet valve (28) of the first brake circuit (16) and / or to the at least one second wheel inlet valve (28) of the second brake circuit (20), which can each be controlled by means of the at least one fourth control signal (40) such that the first actual brake pressure and / or the second actual brake pressure can be further increased. are. [2] Control device (10) according to claim 1, wherein the control device (12) is additionally designed to control a Δp control of the first actual brake pressure to be reduced by the first switching valve (26) and / or a Δp control of the second actual brake pressure to be reduced by the second switching valve (26) by means of the at least one second control signal (36). [3] Control device (10) according to claim 1 or 2, wherein the control device (12) is additionally designed to control, by means of the at least one fourth control signal (40), a Δp control of the first actual brake pressure to be increased by the at least one first wheel inlet valve (28) and / or a Δp control of the second actual brake pressure to be increased by the at least one second wheel inlet valve (28). [4] Control device (10) according to one of the preceding claims, wherein the control device (12) is additionally designed to control at least one plunger (24) as a master brake cylinder pressure variability device (24) by means of the at least one first control signal (30) and / or the at least one third control signal (38). [5] Control device (10) according to one of the preceding claims, wherein the control device (12) is additionally designed to determine the first target brake pressure and / or the second target brake pressure, taking into account at least one generator braking torque that can be exerted on at least one axle associated with at least one first wheel brake cylinder (14) and / or at least one second wheel brake cylinder (18) by means of at least one electric motor. [6] Control device (10) according to one of the preceding claims, wherein the control device (12) is additionally designed to determine a target value with respect to an amplifier force to be exerted on the brake actuating element (11) by means of a brake booster (42) taking into account the target signal (22), the first target brake pressure, the second target brake pressure, the determined or estimated first actual brake pressure and / or the determined or estimated second actual brake pressure, and to output a brake booster control signal (44) corresponding to the target value to the brake booster (42). [7] Braking system for a vehicle with a control device (10) according to one of the preceding claims. [8] Method for operating a vehicle braking system comprising the steps: Determining a first target brake pressure to be set in at least one first wheel brake cylinder (14) of a first brake circuit (16) of the brake system and a second target brake pressure to be set in at least one second wheel brake cylinder (18) of a second brake circuit (20) of the brake system, taking into account at least one target value specified by a driver by means of an actuation of a brake actuation element (11) of the vehicle and / or by a cruise control system of the vehicle with regard to a target vehicle deceleration (a) (S1); and Varying a first actual brake pressure present in at least the first wheel brake cylinder (14) of the first brake circuit (16) taking into account the specified first target brake pressure and a second actual brake pressure present in at least the second wheel brake cylinder (18) of the second brake circuit (20) taking into account the specified second target brake pressure; characterized by : Reducing the first actual brake pressure according to the specified first target brake pressure and the second actual brake pressure according to the specified second target brake pressure by: - Setting a master cylinder pressure (pHZ) in a master cylinder (32) of the brake system less than or equal to a minimum of the first target brake pressure and the second target brake pressure (S2); and Actuating a first switching valve (26) of the first brake circuit (16), which is arranged between the master brake cylinder (32) and at least one first wheel inlet valve (28) assigned to at least one first wheel brake cylinder (14), to further reduce the first actual brake pressure and / or actuating a second switching valve (26) of the second brake circuit (20), which is arranged between the master brake cylinder (32) and at least one second wheel inlet valve (28) assigned to at least one second wheel brake cylinder (18), to further reduce the second actual brake pressure (S3); and Increasing the first actual brake pressure according to the specified first target brake pressure and the second actual brake pressure according to the specified second target brake pressure by: - Setting the master cylinder pressure (pHZ) greater than or equal to a maximum of the first target brake pressure and the second target brake pressure (S4); and - Actuating the at least one first wheel inlet valve (28) of the first brake circuit (16) to further increase the first actual brake pressure and / or actuating the at least one second wheel inlet valve (28) of the second brake circuit (20) to further increase the second actual brake pressure (S5). [9] Method according to claim 8, wherein the first switching valve (26) is controlled to perform a Δp control of the first actual brake pressure to be reduced and / or the second switching valve (26) is controlled to perform a Δp control of the second actual brake pressure to be reduced. [10] Method according to claim 8 or 9, wherein the at least one first wheel inlet valve (28) is controlled for a Δp control of the first actual brake pressure to be increased and / or the at least one second wheel inlet valve (28) is controlled for a Δp control of the second actual brake pressure to be increased. [11] Method according to any one of claims 8 to 10, wherein the master brake cylinder pressure (pHZ) is reduced and / or increased by means of at least one plunger (24). [12] Method according to one of claims 8 to 11, wherein, taking into account the target value, the first target brake pressure, the second target brake pressure, the determined or estimated first actual brake pressure and / or the determined or estimated second actual brake pressure, a target value is set with respect to an amplifier force to be exerted on the brake actuating element (11) by means of a brake booster (42) and the brake booster (42) is controlled accordingly (S6).

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