DE10065239A1 - Operation of motor vehicle braking system involves driving changeover valve depending on pressure value decreasing from demand value with time constant between 0 and less than 1 - Google Patents

Abstract

The method involves operating a changeover valve (USV1) in the braking system in connection with an active or partly active pressure build-up depending on a pressure value that decreases with a predefined time constant from a demand value for a pressure limit value of the changeover valve during the pressure build-up. The time constant can adopt values between 0 and less than 1. Independent claims are also included for the following: a controller, a memory element and a computer program.

Description

The present invention relates to a method for Operation of a brake system of a motor vehicle. The Brake system has a brake booster, Wheel brake cylinder assigned to the wheels of the motor vehicle are, and a valve assembly. The valve assembly distributes the brake pressure generated by the brake system the wheel brake cylinders. One included in the braking system Switching valve that is between an active and a passive pressure build-up in the brake system and between the brake booster and the valve assembly is arranged is controlled such that it as a controlled pressure relief valve is operated.

The invention also relates to a control device for a Brake system of a motor vehicle. The brake system points a brake booster, wheel brake cylinder, the wheels are assigned to the motor vehicle, and a Valve arrangement on. The valve arrangement distributes the from the brake system generated brake pressure on the Wheel brake cylinder.

The present invention further relates to a Storage element for a control unit of a brake system Motor vehicle. There is a on the storage element Computer program stored on a computing device,  in particular on a microprocessor, is executable. The Storage element is particularly as a read-only memory, as a random access memory or as a flash memory educated.

Finally, the invention also relates to a Computer program running on a computing device, in particular on a microprocessor, is executable.

State of the art

The prior art is different Brake systems for motor vehicles known. Braking systems for Passenger cars are usually called hydraulic Brake systems trained and have one Brake booster to relieve the driver of the Motor vehicle. With a hydraulic brake system targeted interventions in a braking process, for example Increasing the driving dynamics safety of the motor vehicle, possible. Targeted braking interventions take place, for example, at one Anti-lock braking system (ABS) or with a vehicle dynamics control (FDR).

In FIGS. 2 and 3 known braking systems are shown in the prior art, which differ in the distribution of braking cycles. In Fig. 2 is a so-called. Front axle / Hinterachsaufteilung is shown, in which a brake circuit for the wheel brake cylinders (VL, VR) of the rear wheels affects the front wheels and a brake circuit for the wheel brake cylinders (HL, HR). In Fig. 3 a so-called. Diagonal division is shown, in each of which a brake circuit acts on a wheel brake cylinder (VL, VR) of a front wheel and a wheel brake cylinder (HL, HR) of the diagonally opposite rear wheel.

DE 198 14 216 A1 discloses a method and a device for regulating at least one driving dynamics variable of a motor vehicle. This regulation is based on a brake system of the type shown in FIG. 2. The mode of operation of the brake system shown in FIG. 2 is described in detail in DE 198 14 216 A1, to which express reference is made.

The driver of the motor vehicle actuates a brake pedal 1 to decelerate the motor vehicle. A pre-pressure pVor is built up in a hydraulic circuit of a brake unit 2 via a brake booster. The pre-pressure pVor is applied to an intake valve AV1, ASV2 and a changeover valve USV1, USV2 for each brake circuit. Depending on vehicle parameters, which describe, for example, the dynamic driving stability of the motor vehicle, different wheel brake cylinders VL, VR, HR, HL are acted upon by a brake pressure pKreis. The brake pressure pKreis can be supplied to the individual wheel brake cylinders VL, VR, HR, HL via intake valves EVVL, EVVR, EVHR, EVHL. The brake pressure can be routed away from the wheel brake cylinders VL, VR, HR, HL via exhaust valves AVVL, AVVR, AVHR, AVHL. In order to supply hydraulic fluid to or from the wheel brake cylinders VL, VR, HR, HL if necessary, at least one return pump RFP1, RFP2 is provided in each brake circuit and is driven by an electric motor.

For a normal deceleration of the motor vehicle triggered by the driver, the intake valves AV1, AV2 are closed and the changeover valves USV1, USV2 are open, that is to say in the position shown in FIG. 2. The intake valves EVVL, EVVR, EVHR, EVHL are open and the exhaust valves AVVL, AVVR, AVHR, AVHL are closed. In this way, hydraulic fluid can be guided to the wheel brake cylinders VL, VR, HR, HL and a brake pressure can be built up there.

This type of delay is known as a passive pressure build-up in the brake system.

However, the motor vehicle can also, especially in the frame vehicle dynamics corrections of the motor vehicle from which Control unit of the brake system triggered delayed. For this purpose, the intake valves AV1, AV2 are opened and the Changeover valves UPS1, UPS2 closed. The intake valves EVVL, EVVR, EVHR, EVHL and the exhaust valves AVVL, AVVR, AVHR, AVHL are controlled in such a way that a desired one Brake pressure is applied to the desired wheel brake cylinders. In this way, one or more can be used as required Wheel brake cylinders VL, VR, HR, HL hydraulic fluid fed or carried away and a brake pressure up and be dismantled. With this type of delay occurs a So-called passive pressure build-up in the brake system. At this The type of delay is called an active or partially active pressure build-up in the brake system. At a partially active pressure build-up the driver does that Brake pedal and there is a slight build up of a Brake pressure on the wheel brake cylinder; this brake pressure is not sufficient to stabilize the motor vehicle and is therefore increased.

The changeover valves thus switch the brake system between a passive and an active or partially active Pressure build up around. The known from the prior art Switching valves have the disadvantage, however, that they are constantly on between a minimum pressure and a maximum pressure switch. When the changeover valve is closed, a pressure is applied built up that only when the opening pressure is reached, d. H. the maximum pressure permitted in the brake system, again is broken down. Through this constant switching back and forth of the changeover valves is the braking unit one extreme exposed to high loads because the brake pressure at each  active pressure build-up to the maximum value of the brake pressure increases before it is broken down again.

Brake systems are also from the prior art known in which the switching valves as controllable Pressure relief valves are formed. Such Brake system is known, for example, from DE 196 44 883 A1 which is expressly referred to. With such trained switching valves, the opening pressure of the Switching valves can be changed arbitrarily so that they not constantly between the minimum pressure and the Switch over maximum pressure. With the changeover valve closed rather, a pressure is built up that is already at Reaching the opening pressure, which is well below the in allowable maximum pressure of the brake system, is dismantled again. This makes the brake unit one exposed to much less stress since the Brake pressure not up to every active pressure build-up Maximum value of the brake pressure but only up to that set opening pressure increases before returning is broken down.

In the brake system known from DE 196 44 883 A1 the changeover valve following an active or partially active pressure build-up, however, directly dependent controlled by a minimum pressure value. In the Activation of the changeover valve following one active or partially active pressure build-up is during the active or partially active pressure build-up in the brake system prevailing brake pressure, which is about that on the Changeover valve corresponds to the set opening pressure, not considered. With a relatively high one Opening pressure can be the pressure difference between the Opening pressure and the minimum value must be very large, so that the brake pressure in the brake system afterwards of an active or partially active pressure buildup  drops to the minimum value. That can also be too relative lead to high mechanical loads on the brake system.

Therefore, it is an object of the present invention that mechanical loads on a hydraulic brake system, those following an active or partially active Pressure build-up can occur to reduce.

To achieve this object, the invention suggests of the method of operating a brake system type mentioned above that the switching valve in Connection to an active or partially active pressure build-up in Depending on a pressure value is controlled, the based on a setpoint for a pressure limitation value of the changeover valve during the active or partially active Pressure build-up drops with a predefinable time constant, the time constant taking values between 0 and <1 can.

Advantages of the invention

The changeover valve can, for example, by a control unit of the Brake system controlled and thus the opening pressure can be varied. That according to the inventive method controlled changeover valve opens during one active or partially active pressure build-up not only after Reaching a maximum pressure permitted in the brake system but, depending on certain measured or estimated sizes and various parameters of the Brake system, already after reaching the opening pressure, the usually below that permitted in the braking system Maximum pressure is. Of course, the full one Functionality of the brake system ensured.

The controlled by the inventive method Switch valve thus only switches between one  Minimum pressure and the one set on the changeover valve Opening pressure back and forth. With the changeover valve closed a pressure is built up that already when the Opening pressure, usually before reaching the Maximum pressure, is reduced again.

Following an active or partially active pressure build-up the changeover valve is controlled according to the invention in such a way that the brake pressure does not suddenly drop to a minimum value drops, but slowly with a definable Time constant between 0 and <1 at this minimum value falls off. This can cause mechanical loads on the Brake system that follows an active or a partially active pressure build-up due to a sudden drop of the brake pressure can occur, avoided and the Brake system life can be increased significantly.

According to an advantageous development of the present invention, it is proposed that the pressure value pDBVAng for controlling the changeover valve from the equation

pDBVAng: = pDBVAng - (pDBVAng - pDBVSoll) .ttp

is determined, where pDBVSoll is a setpoint for a Pressure limiting value of the changeover valve during the active or partially active pressure build-up and ttp the Time constant. This equation corresponds to one Time-discretely formulated filtering with a low pass 1. Order.

As another solution to the problem of the present Invention is based on the control unit of the beginning mentioned type suggested that the control device means for carrying out the method according to the invention.

The realization of the inventive method in the form of a Storage element for a control unit of a brake system  a motor vehicle is provided. It is on the Storage element a computer program stored on a computing device, in particular on a microprocessor, executable and for executing the invention Process is suitable. In this case, the Invention by a stored on the memory element Computer program realized so that this with the Computer program provided memory element in the same The invention represents how the method for its Execution the computer program is suitable. As Storage element can in particular be an electrical one Storage medium are used, e.g. a read-only Memroy, a random access memory or a flash memory.

The invention also relates to a computer program for Execution of the method according to the invention is suitable, if it is on a computing device, especially on a Microprocessor, expires. It is particularly preferred if the computer program on a storage element, is stored in particular on a flash memory.

Drawings

Other features, applications and advantages of the Invention result from the following description of embodiments of the invention, which in the Drawing are shown. Thereby form all described or illustrated features for themselves or in any Combination the subject of the invention, regardless of their summary in the claims or their Relationship and regardless of their wording or Representation in the description or in the drawing. It demonstrate:  

Fig. 1 is a flow diagram of a method according to a preferred embodiment;

Fig. 2 shows a first known from the prior art braking system;

Fig. 3 shows a second known from the prior art braking system; and

Fig. 4 shows a brake system in which the inventive method can be used.

Description of the embodiments

In FIGS. 2 and 3 known braking devices 30 are shown in the prior art. Reference is made to the description of the known brake systems 30 in the introduction to the description. The braking devices 30 differ in the distribution of the brake circuits I, II. In Fig. 2 is a so-called. Front axle / Hinterachsaufteilung and in Fig. 3 shows a so-called. Diagonal division. In the brake systems 30 known from the prior art, the changeover valves USV1 and USV2 are designed as pure switching valves, which constantly switch between a minimum pressure and a maximum pressure permitted in the brake system 30 during an active pressure build-up. Due to this constant switching of the changeover valves, the brake unit 32 is exposed to an extremely high load, since the brake pressure rises with each active pressure build-up to the maximum value of the brake pressure before it is reduced again.

A brake system 30 is also known from DE 196 44 883 A1, of which a brake circuit I is shown in FIG. 3. In this brake system 30 , the switchover valves UPS are designed as controllable pressure relief valves. In the case of switchover valves UPS designed in this way, the opening pressure of the switchover valves UPS can be changed as desired, so that they do not constantly switch between the minimum pressure and the maximum pressure. Rather, when the switchover valve UPS is closed, a pressure is built up which is reduced again when the opening pressure is reached, which is generally below the maximum pressure permitted in the brake system 30 . As a result, the brake unit 32 is exposed to a significantly lower load.

In the brake system 30 from FIG. 3, the switchover valve UPS is actuated immediately after an active or partially active pressure build-up, as a function of a minimum pressure value, that is to say from the pressure value to which the brake pressure should drop following an active or partially active pressure build-up . When the switching valve UPS is activated following an active or partially active pressure build-up, a brake pressure prevailing during the active or partially active pressure build-up in the brake system 30 , which approximately corresponds to the opening pressure set on the switch-over valve UPS during the active or partially active pressure build-up, is not taken into account. At a relatively high set opening pressure, the pressure difference between the opening pressure and the minimum value can be very large, so that the brake pressure prevailing in the brake system 30 drops suddenly to the minimum value following an active or partially active pressure build-up. This can also lead to relatively high mechanical loads on the brake system 30 .

In order to avoid this, a method according to the invention for operating a brake system 30 is proposed, in which the switchover valve UPS is controlled in connection with an active or partially active pressure build-up in such a way that the brake pressure prevailing in the brake system 30 slowly follows with the active or partially active pressure build-up a predefinable time constant falls in the range from 0 to <1. To be more precise, a control signal for controlling the switchover valve UPS following an active or partially active pressure build-up is determined as a function of a pressure value which, based on a setpoint for a pressure limit value of the switchover valve, drops with a predefinable time constant during the active or partially active pressure buildup, whereby the time constant can have values between 0 and <1.

In Fig. 1 is a flow diagram of the method according to the invention. The method begins in FIG. 1a in a function block 1 . In function block 2 , a first offset value pSysOff1 is set to 30 bar for an active pressure build-up. In function block 3 , a second offset value pSysOff2 is set to 80 bar for a passive pressure build-up. In function block 4 , an upper limit value pDBV is set to 150 bar for the switching valve UPS designed as a pressure relief valve. In a function block 5 , a tolerance value pDBVTol is set to 20 bar. In a function block 6 , a time constant ttp, with which the brake pressure should drop slowly after an active or partially active pressure build-up, is set to 0.2. In a function block 7 , an estimate pRadHigh is determined for the highest brake pressure at a wheel brake cylinder RBZ of the brake system 30 in the brake circuit I. In a function block 8 , an estimated value pKreis for the actual value of the brake pressure prevailing in the brake unit 32 is determined. In a function block 9 a reaped measured value for the driver form pVor is determined. A measured value for a voltage uVr at a relay of the switchover valve UPS is determined in a function block 10 . In a function block 11 , a value rMagUSV for the ohmic resistance of the relay magnet of the switchover valve UPS is determined. This can be measured or specified. Finally, in a functional block 12, an initial value 0 is set for the pressure pDBVAng, the UPS, the switching valve is controlled in dependency. The process is continued in FIG. 1b. In a function block 13 , a setpoint pSysNW is specified for the setpoint of the brake pressure prevailing in the brake circuit I. Various parameters of the method according to the invention are thus defined and initialized in function blocks 2 to 13 .

A query block 14 checks whether there is an active or partially active pressure build-up in the brake system 30 . An active or partially active pressure build-up exists when pressure build-up is required on the wheel brake cylinder RBZ, at which the highest brake pressure is already applied. If there is an active or partially active pressure build-up, an offset pSysOff for the brake system 30 is set to the value of pSysOff1 = 30 bar in a function block 15 . If there is a passive pressure build-up, the offset pSysOff for the brake system 30 is set to the value of pSysOff2 = 80 bar in a function block 16 . By means of the offset pSysOff, pressure vibrations in the brake system 30 can be taken into account, which have their cause in the delivery properties of the return pumps RFP1, RFP2. This prevents the UPS switching valves from constantly tripping.

In a function block 17, a pressure setpoint pSysSoll from the sum of the predetermined in function block 13 and the offset target value pSysNW pSysOff is determined. In a function block 18 , a maximum limit value pSysMax for the brake pressure in the brake system 30 is determined from the sum of the upper pressure limit value pDBV for the switchover valves UPS specified in function block 4 and the tolerance value pDBVTol specified in function block 5 . A query block 19 checks whether the pressure setpoint pSysSoll is greater than the maximum limit value pSysMax and, if so, the pressure setpoint pSysSoll is set equal to the maximum limit value pSysMax in a function block 20 .

In a function block 21 , a setpoint pDBVSoll for the brake pressure is based on the equation

pDBVSoll: = pSysSoll - pVor + pDBVTol

determined. In a query block 22 , it is checked again whether there is an active or partially active pressure build-up. If so, in a function block 23 the pressure value pDBVAng, depending on which the switchover valve UPS is activated, is set equal to the setpoint pDBVSoll determined in function block 21 . Otherwise, in a function block 24 of the pressure value pDBVAng for controlling the changeover valve UPS with the predetermined time constant is chosen ttp slowly sloping. In the present exemplary embodiment, the equation specified in function block 24 corresponds

pDBVAng: = pDBVAng - (pDBVAng - PDBVSoll) .ttp

a time-discretely formulated filtering with a 1st order low pass. Another choice of the pressure value pDBVAng in the function block 24 is, however, readily possible.

It is crucial that the pressure value, depending on that the UPS switching valve is activated, not abruptly, but gradually with the predefinable time constant ttp is reduced.

The process is continued in Fig. 1c. A control current iDBVSoll for the relay of the switchover valve UPS is determined in a function block 25 . The control current iDBVSoll is a function of the pressure value pDBVAng, the driver admission pressure pVor and the estimated value pKreis for the dependency of the control current iDBVSoll, the voltage uVr applied to the relay of the switch valve UPS and the resistance of the relay of the switch valve UPS according to the equation

PWMUSV: = iDBVSoll / uVr.rMagUSV

determined. The method according to the invention is ended in a function block 27 .

The brake system 30 according to FIG. 4 also includes a control device 31 , which also serves to control the sequence of the method according to the invention. The control unit 31 comprises a microprocessor 32 , on which a computer program can be executed which is suitable for executing the method according to the invention. The computer program is stored on a memory element 33 , which is designed as a flash memory. Before or during the execution of the computer program, the computer program is transferred from the memory element 33 into the microprocessor 32 via a data line 34 . In the control unit 31 , control signals for the changeover valve USV1, the intake valve AV1, the inlet valves EVVL, EVHR and the outlet valves AVVL, AVHR are determined.

Claims (6)

1. Method for operating a brake system ( 30 ) of a motor vehicle, the brake system ( 30 ) being assigned a brake booster, a plurality of wheel brake cylinders (RBZ), the wheels (VL, VR, HL, HR) of the motor vehicle, and a valve arrangement (EV, AV), which distributes the brake pressure generated by the brake system ( 30 ) to the wheel brake cylinders (RBZ), a changeover valve (UPS) contained in the brake system ( 30 ), which switches between an active and a passive pressure build-up in the brake system ( 30 ) is switched and arranged between the brake booster and the valve arrangement (EV, AV), is controlled such that it is operated as a controlled pressure relief valve (DBV), characterized in that the changeover valve (UPS) following an active or partially active pressure build-up in Dependence on a pressure value (pDBVAng) is controlled, which is based on a setpoint (pDBVSoll) for a pressure limiting value of the changeover valve (UPS) falls during the active or partially active pressure build-up with a predefinable time constant (ttp), the time constant (ttp) being able to assume values between 0 and <1. 2. The method according to claim 1, characterized in that the pressure value (pDBVAng) from the equation
pDBVAng: = pDBVAng - (pDBVAng - pDBVSoll) .ttp
is determined. 3. Control unit ( 31 ) for a brake system ( 30 ) of a motor vehicle, the brake system ( 30 ) having a brake booster, wheels (VL, VR, HL, HR) of the motor vehicle associated wheel brake cylinder (RBZ) and a valve arrangement (EV, AV) , which distributes the brake pressure generated by the brake system ( 30 ) to the wheel brake cylinders (RBZ), characterized in that the control device ( 31 ) has means for carrying out a method according to one of claims 1 and 2. 4. Memory element ( 33 ), in particular read-only memory, random access memory or flash memory, for a control device ( 31 ) of a brake system ( 30 ) of a motor vehicle, on which a computer program is stored, which is stored on a computing device, in particular on a microprocessor ( 32 ), executable and suitable for executing a method according to one of claims 1 and 2. 5. Computer program, characterized in that the computer program is suitable for executing a method according to one of claims 1 and 2 if it runs on a computing device, in particular on a microprocessor ( 32 ). 6. Computer program according to claim 5, characterized in that the computer program is stored on a memory element ( 33 ), in particular on a flash memory.