Method and device for regulating a brake system

Abstract

A method for regulating motor vehicle electrohydraulic brake systems having a pressure supply apparatus actuated by a control unit and hydraulically connected to wheel brakes via a pressure regulating valve. The pressure supply apparatus includes a cylinder-piston assembly operated by an electromechanical actuator. A set point pressure value is determined for each wheel brake. The cylinder-piston assembly is actuated to a predetermined pilot pressure in the hydraulic pressure chamber. A pilot pressure actual value and an actuator speed actual value are obtained. A pilot pressure set point value, the pilot pressure set point value and the pilot pressure actual value are fed as input variables to a regulator which outputs an actuator speed set point value. The actuator speed and actual set point values are fed as inputs to the speed regulator. The actuator speed set point value is modified as a function of the number of brakes.

Claims

1. A method for regulating an electrohydraulic brake system for motor vehicles, which can be actuated in a brake-by-wire operating mode, comprising: providing a pressure supply apparatus which can be actuated by an electronic open-loop and closed-loop control unit and which is or can be connected to hydraulically activated wheel brakes and by which the wheel brakes can be activated hydraulically via at least one pressure regulating valve, providing the pressure supply apparatus having a cylinder-piston assembly having a hydraulic pressure chamber, and pressure piston of which can be slid relative to a position of rest by an electromechanical actuator, determining a set point pressure value for each wheel brake, actuating the cylinder-piston assembly in such a way that a predetermined pilot pressure, which is determined from the set point pressure values, is set in the hydraulic pressure chamber by sliding the piston, obtaining a pilot pressure actual value and an actuator speed actual value, determining a pilot pressure set point value and feeding the pilot pressure set point value and the pilot pressure actual value as input variables to a regulator device, provided in a form having a pressure regulator and a speed regulator which is connected downstream of the pressure regulator, wherein the pressure regulator outputs an actuator speed set point value and feeding the actuator speed set point value and the actuator speed actual value as input variables to the speed regulator, and modifying the actuator speed set point value which is fed to the speed regulator as a function of the number of the wheel brakes, the modifying comprises the multiplication of the set point value by a scaling factor (K), and the scaling factor (K) is based on the number of the wheel brakes which are connected to the hydraulic pressure chamber via the at least one pressure regulating valve, and determining a relative volume as a sum of wheel brake relative volumes of the individual wheel brakes, and wherein calculating the respective wheel brake relative volume as quotient of a wheel brake volume of the respective wheel brake and the total volume of the brake system multiplied by the number 100 when the respective wheel brake is currently hydraulically connected and is otherwise zero, and wherein the scaling factor (K) is a function of the relative volume.

2. The method as claimed in claim 1, wherein the scaling factor (K) depends linearly on the relative volume.

3. The method as claimed in claim 2, further comprising the step of determining the scaling factor (K) according to
K.sub.setp=K.sub.min+(1K.sub.min)*V.sub.rel,total/100, wherein K.sub.min is a minimum value between 0 and 1, and V.sub.rel,total denotes the relative volume.

4. The method as claimed in claim 3, wherein K.sub.min is between 0.1 and 0.4.

5. A method for regulating an electrohydraulic brake system for motor vehicles, which can be actuated in a brake-by-wire operating mode, comprising: providing a pressure supply apparatus which can be actuated by an electronic open-loop and closed-loop control unit and which is or can be connected to hydraulically activated wheel brakes and by which the wheel brakes can be activated hydraulically via at least one pressure regulating valve, providing the pressure supply apparatus having a cylinder-piston assembly having a hydraulic pressure chamber, and pressure piston of which can be slid relative to a position of rest by an electromechanical actuator, determining a set point pressure value for each wheel brake, actuating the cylinder-piston assembly in such a way that a predetermined pilot pressure, which is determined from the set point pressure values, is set in the hydraulic pressure chamber by sliding the piston, obtaining a pilot pressure actual value and an actuator speed actual value, determining a pilot pressure set point value and feeding the pilot pressure set point value and the pilot pressure actual value as input variables to a regulator device, provided in a form having a pressure regulator and a speed regulator which is connected downstream of the pressure regulator, wherein the pressure regulator outputs an actuator speed set point value and feeding the actuator speed set point value and the actuator speed actual value as input variables to the speed regulator, modifying the actuator speed set point value which is fed to the speed regulator as a function of the number of the wheel brakes, the modifying comprises the multiplication of the set point value by a scaling factor (K), and the scaling factor (K) is based on the number of the wheel brakes which are connected to the hydraulic pressure chamber via the at least one pressure regulating valve, and wherein the scaling factor (K) is not replaced immediately after a re-calculation but instead a previous scaling factor (K) is changed in the direction of a newly calculated scaling factor, wherein the maximum change in the scaling factor (K) depends on the difference between the previous scaling factor (K) and the newly calculated scaling factor.

6. The method as claimed in claim 1 further comprising wherein considering the state of a respective inlet valve or an actuator connection valve in order to determine the respective wheel brake relative volume.

7. The method as claimed in claim 1 to further comprising determining the scaling factor (K) at regular time intervals.

8. A device for regulating an electrohydraulic brake system comprising: a control unit in communication with a pressure supply apparatus which can be actuated by an electronic open-loop and closed-loop control unit and which is or can be connected to hydraulically activated wheel brakes and by which the wheel brakes can be activated hydraulically via at least one pressure regulating valve, the pressure supply apparatus having a cylinder-piston assembly having a hydraulic pressure chamber, and pressure piston of which can be slid relative to a position of rest by an electromechanical actuator, the control unit being configured to: determine a set point pressure value for each wheel brake, actuate the cylinder-piston assembly in such a way that a predetermined pilot pressure, which is determined from the set point pressure values, is set in the hydraulic pressure chamber by sliding the piston, obtain a pilot pressure actual value and an actuator speed actual value, determine a pilot pressure set point value and feeding the pilot pressure set point value and the pilot pressure actual value as input variables to a regulator device, provided in a form having a pressure regulator and a speed regulator which is connected downstream of the pressure regulator, wherein the pressure regulator outputs an actuator speed set point value and feeding the actuator speed set point value and the actuator speed actual value as input variables to the speed regulator, modify the actuator speed set point value which is fed to the speed regulator as a function of the number of the wheel brakes, the modifying comprises the multiplication of the set point value by a scaling factor (K), and the scaling factor (K) is based on the number of the wheel brakes which are connected to the hydraulic pressure chamber via the at least one pressure regulating valve and portion of a total volume of the brake system, determine a relative volume as a sum of wheel brake relative volumes of the individual wheel brakes, and wherein calculating the respective wheel brake relative volume as quotient of a wheel brake volume of the respective wheel brake and the total volume of the brake system multiplied by the number 100 when the respective wheel brake is currently hydraulically connected and is otherwise zero, and wherein the scaling factor (K) is a function of the relative volume.

9. The device of claim 8, wherein the device is part of an electrohydraulic brake system.

10. The method as claimed in claim 3, wherein K.sub.min is about 0.2.

11. The method as claimed in claim 1 further comprising the scaling factor (K) is determined at a time interval between 1 ms and 5 ms.

12. A device for regulating an electrohydraulic brake system comprising: a control unit in communication with a pressure supply apparatus which can be actuated by an electronic open-loop and closed-loop control unit and which is or can be connected to hydraulically activated wheel brakes and by which the wheel brakes can be activated hydraulically via at least one pressure regulating valve, the pressure supply apparatus having a cylinder-piston assembly having a hydraulic pressure chamber, and pressure piston of which can be slid relative to a position of rest by an electromechanical actuator, the control unit being configured to: determine a set point pressure value for each wheel brake, actuate the cylinder-piston assembly in such a way that a predetermined pilot pressure, which is determined from the set point pressure values, is set in the hydraulic pressure chamber by sliding the piston, obtain a pilot pressure actual value and an actuator speed actual value, determine a pilot pressure set point value and feeding the pilot pressure set point value and the pilot pressure actual value as input variables to a regulator device, provided in a form having a pressure regulator and a speed regulator which is connected downstream of the pressure regulator, wherein the pressure regulator outputs an actuator speed set point value and feeding the actuator speed set point value and the actuator speed actual value as input variables to the speed regulator, modify the actuator speed set point value which is fed to the speed regulator as a function of the number of the wheel brakes, the modifying comprises the multiplication of the set point value by a scaling factor (K), and the scaling factor (K) is based on the number of the wheel brakes which are connected to the hydraulic pressure chamber via the at least one pressure regulating valve, and wherein the scaling factor (K) is not replaced immediately after a re-calculation but instead a previous scaling factor (K) is changed in the direction of a newly calculated scaling factor, wherein the maximum change in the scaling factor (K) depends on the difference between the previous scaling factor (K) and the newly calculated scaling factor.

13. The device of claim 12, wherein the device is part of an electrohydraulic brake system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An exemplary embodiment of the invention will be explained in more detail with reference to a drawing, in which, in the highly schematic illustration:

(2) FIG. 1 shows an electrohydraulic brake system having an open-loop and closed-loop control unit for carrying out the method in a preferred embodiment,

(3) FIG. 2 shows a block circuit diagram of a regulating circuit for carrying out a number of the method steps, and

(4) FIG. 3 shows a block circuit diagram of a further regulating circuit for carrying out a number of the methods step.

(5) Identical parts are provided with the same reference symbols in all the figures.

FURTHER DESCRIPTION OF THE INVENTION

(6) An active o+r electrohydraulic brake system 2 which is illustrated in FIG. 1 includes a pressure supply apparatus 8 which includes an electromechanical actuator 14. The actuator 14 includes an electric motor 20 and a transmission 26, and in order to build up pressure it slides a pressure piston 32 into a hydraulic pressure chamber 38 in the pressure build up direction 44. A cylinder-piston assembly 40 is implemented by means of the pressure piston 32 and the pressure chamber 38. In order to build up pressure, the pressure piston 32 moves, for example, from a position of rest 50 into a pressure position 56, as a result of which a defined volume of pressure medium is forced from the pressure chamber 38 via a line 62, a further line 74 and into a wheel brake circuit 80, where it is forced through an open inlet valve 88 into a brake line 94 and further into a wheel brake 100. Therefore, pressure is built up in the wheel brake 100. Further pressure positions 58, 64, and 66 are shown by way of example. In FIG. 1, only one wheel brake circuit 80 is illustrated. In a motor vehicle, there are usually four wheel brake circuits 80 provided, which can each be connected to the pressure chamber 38 via a separate line 62 and an isolating valve which is connected into the respective line 62. Each wheel brake 100 is then assigned a separate valve pair 88 and 106. An electronic open-loop and closed-loop control unit 102 serves to actuate the components described above. The actuator 14 can be connected hydraulically to the wheel brake circuit 80 via an actuator connection valve 90.

(7) A brake pressure reduction can take place by sliding or moving the pressure piston 32 back in the direction of its position of rest 50, that is to say opposite to the pressure build up direction 44. A rapid brake pressure reduction, such as is required in an ABS regulating process, is also possible by activating the inlet valve 88, with which a non-return valve 92 is connected in parallel, and an outlet valve 106, wherein the outlet valve 106 is connected into a discharge line 112 through which the wheel brake circuit 80 or the brake 100 is connected to a brake fluid container 118 or reservoir. In order to reduce the brake pressure, the inlet valve 88 or pressure regulating valve is closed and the outlet valve 106 is open for a specific time. As a result, brake fluid or pressure medium flows out of the wheel brake 100 via the brake line 94 into the brake fluid container 118. This measure of the pressure reduction is then appropriate if the pressure chamber 38 serves a plurality of wheel brakes in parallel. A non-return valve 124 is connected into a line 120 which branches off from the line 62.

(8) In particular in the case of wheel-specific pressure reduction via the valve pair 88, 106 illustrated in FIG. 1, the volume is discharged from the pressure chamber 38 into the brake fluid container 118, as a result of which the piston 32 moves gradually, in particular during an ABS braking operation, in the direction of the end position 58 (end stop), with the result that after several regulating cycles no further build up of pressure is possible any more. Fluid volume from the brake fluid container 118 can be sucked back into the pressure chamber 38 via the line 120 and the non-return valve 124.

(9) In an alternative refinement of the brake system 2, the pressure chamber 38 can, for safety reasons, be embodied in a multi-circuit, in particular two-circuit fashion, with a plurality of pressure chambers or pressure pistons, wherein the pressure chambers can be assigned diagonally or axle-wise to the wheel circuits or brake circuits.

(10) The need to set a predefined system pressure or system pressure profile by means of a regulating method arises whenever the driver requests a general brake pressure for all the wheels of the motor vehicle by activating the brake pedal or if this pressure request is sent by means of an assistance function (ACC, HSA, HDC etc.), or if a particular wheel-specific brake regulating function, such as, for example, ABS, TCS or ESP, becomes active.

(11) The assistance functions usually require a global brake pressure for all the wheels, similarly to a case of basic braking triggered by the driver using the brake pedal. In such cases, the pressure when the inlet valve 88 is opened is generated at all the brake circuits to the same degree by moving the plunger or pressure piston 32 in advance. The anti-lock braking function ABS limits or reduces generally only the pressure applied by the pressure chamber 38 to individual wheels, in order to keep them at a point of optimum braking slip.

(12) In the case of the traction control TCS, individual wheels which are inclined to spin owing to an excessively drive torque are selectively braked. For this purpose, the brake system must actively generate pressure in the pressure chamber 38, which pressure was not requested by the driver. The pressure from the pressure chamber 38 must then be specifically conducted via the respective valves 88 and 106 into the respective wheel brake 100 of the wheel to be braked, while the brake circuits of the other wheels which remain unregulated are disconnected from the pressure chamber 38 using their inlets valves 88.

(13) The same applies to the electronic stability program ESP. In this context, brake pressures are also applied actively and selectively to individual wheels in order to influence the dynamics of the vehicle about the vertical axis.

(14) In all these cases, the pilot pressure in the chamber or the pressure chamber 38 is to be set in such a way that the wheel with the maximum brake pressure request can be supplied reliably with the necessary brake pressure. At a wheel which requires less brake pressure than in the pilot pressure chamber or the pressure chamber 38, the pressure must be limited by virtue of the fact that the inlet valve 88 which is associated with the wheel is continuously or temporarily closed. If the wheel then requires a lower brake pressure than that already set and if the pilot pressure is higher than the desired wheel pressure, brake fluid must be discharged from the wheel brake 100 into the brake fluid container 118 by means of the associated outlet valve 106.

(15) With respect to the requirements made of a regulating method for setting the required system pressure this means that a continuously changing regulated system is present for the pressure regulation. Depending on how many inlet valves 88 are opened at a particular time, the volume absorption and therefore the rigidity of the total braking system or of the brake system 2 changes. If the pressure in a wheel brake 100 or a plurality of wheel brakes 100 is less than the pressure set in the pressure chamber 38 and the inlet valve 88 which is assigned to the wheel brake 100 then opens in order to build up braking pressure, the additional volume demand which is then present leads to a reduction in the booster pressure, which has to be compensated by a corresponding compensating movement of the pressure piston 32, i.e. the pressure piston 32 is slid a certain amount in the pressure build up direction 44 until the desired pressure in the pressure chamber 38 is reached again. In terms of the system pressure regulator to be considered, the method described above of the wheel-specific build up of pressure and pressure reduction via the valve pair 88, 106 therefore leads to a partially very significant disruptive excitation.

(16) In order to avoid these disruptive excitations, the set point rotation speed of the actuator or its speed can be scaled, with the result that the changes in the rotational speed become smaller and therefore the disruptive excitations become smaller, since the set point rotational speed then does not act as strongly on the regulating circuit.

(17) According to the invention there is then provision that the scaling factor is independent of the regulating function which is activated at that particular time and is obtained only on the basis of the number of wheel brakes 100 which are hydraulically connected to the pressure chamber 38. In order to determine which brakes are hydraulically connected, the state of the respective inlet valves of the wheel brake is checked and/or the state of the respective actuator connection valve.

(18) FIG. 2 illustrates a regulating circuit for carrying out a preferred embodiment of the method in a schematic block circuit diagram. Such a regulating circuit is, for example, a component in a device according to the invention for carrying out the method. The result of a subtraction carried out in a subtraction element 146, or the difference P=P.sub.setpP.sub.act, that is to say the difference between the pressure set point value P.sub.setp and the pressure actual value P.sub.act, is fed into a pressure regulator 140. The output value of the pressure regulator 140 is the set point value for the actuator rotational speed .sub.setp,DR. A speed pilot-control calculation module 152 determines a further actuator rotational speed set point value from the pressure set point value P.sub.setp by differentiation, which actuator rotational speed set point value is superimposed, after weighting with a boosting factor, an additional portion .sub.setp,FFw, on the actuator rotational speed set point value of the pressure regulator 140 to .sub.setp,DR. The two set point rotational speed portions are added together in an adder element 158 and fed to a limiting function 164 for limiting to the minimum or maximum permissible set point rotational speed (.sub.min, .sub.max). The value .sub.setp* which is obtained from this operation is multiplied by the scaling factor K in a multiplication element 170; the result of the operation is then the actuator rotational speed set point value .sub.setp. The actuator speed actual value (.sub.act) and actuator speed set point value (.sub.setp) are fed as inputs to a speed regulator 165, which is connected downstream of the pressure regulator 140.

(19) FIG. 3 illustrates how the scaling factor K is determined. In a calculation element 176, a target value for the scaling factor, specifically K.sub.setp is calculated on the basis of the total relative volume V.sub.Rel,total. In a subtraction element 182, the ultimate value of the scaling factor is subtracted from the last iteration, K.sub.lastloop, from which the difference K between the two values results. This difference is then fed to a change determining module 188 which determines a maximum change K.sub.max of the scaling factor as a function of the difference K. This is done here by means of a step function which assigns one value K.sub.max 60 the various value ranges of the difference K in each case. This ensures that where there are large changes in K.sub.setp, faster tracking of the current scaling factor K to the new target value K.sub.setp takes place initially. The value which is obtained for K.sub.max is in turn limited in a limiting function 194 to a permissible value range, which results in the difference value K.sub.lim, which is then added in an adder element 200 to the scaling factor K from the last iteration, which results in the current scaling factor K. As a result of these measures, the change in the scaling factor K between two successive iterations is limited and therefore as it were attenuated. As a result, excessively severe and sudden changes in the scaling factor K are avoided, with the result that disruptive excitations which arise as a result of sudden changes in the actuator set point rotational speed are avoided.

(20) The definition of K.sub.max is therefore carried out in such a way that for a reduction in the scaling factor, that is to say when K.sub.setp<K, the value for K is adjusted significantly more quickly to the target value K.sub.setp per iteration than is the case when K.sub.setp>K is true, since owing to the now smaller number of wheel brakes which are hydraulically connected to the linear actuator, the regulated system which is to be regulated by the pressure regulator becomes more rigid.

(21) While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.