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The invention discloses methods and control systems for controlling an electronically controllable brake actuating system for automotive vehicles, with a depressurized pressure medium supply reservoir, with at least one pressure source which can be controlled by an electronic control unit. The press

The invention discloses methods and control systems for controlling an electronically controllable brake actuating system for automotive vehicles, with a depressurized pressure medium supply reservoir, with at least one pressure source which can be controlled by an electronic control unit. The pressure source is used to apply pressure to the wheel brakes of the vehicle, with pressure sensors and pressure control valves being associated with the wheel brakes. The pressure control valves are controllable in an analog manner by means of an electric variable in dependence on the differential pressure applied to them.

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1. Method for controlling an electronically controllable brake actuating system for automotive vehicles, said brake actuating system of the type including a depressurized pressure medium supply reservoir, with at least one pressure source controlled by an electronic control unit, said pressure sourc

1. Method for controlling an electronically controllable brake actuating system for automotive vehicles, said brake actuating system of the type including a depressurized pressure medium supply reservoir, with at least one pressure source controlled by an electronic control unit, said pressure source being used to apply pressure to the wheel brakes of the vehicle, with pressure sensors and pressure control valves being associated with said wheel brakes, said pressure control valves being controllable in an analog manner by means of an electric variable in dependence on the differential pressure applied to them and connecting the wheel brakes to the pressure source in a pressure increase phase, being closed or becoming closed in a pressure maintenance phase and connecting the wheel brakes to the pressure medium supply reservoir in a pressure reduction phase, comprising the step of:identifying the presence of a pressure maintenance phase, then, slowly varying the electric variable in the pressure control valve until a predetermined pressure variation takes place in the wheel brake associated with said pressure control valve, whereupon the dependence of the electric variable on the differential pressure is corrected, further including the step of observing cyclically in a time window the pressure variation in the wheel brake associated with the pressure control valve during the variation of the electric variable, and determining the minimum pressure value in each case which, in turn, is taken into account for determining a detection threshold for the pressure change at the inlet of the pressure control valve used for pressure reduction. 2. Method as claimed in claim 1, wherein the pressure control valves (inlet valve 17, 18; outlet valve 27,28) are designed as valves that are closed in their inactive condition, and further including the step of:increasing the variation of the electric actuating variable based on a value that is below the value necessary for opening the pressure control valve. 3. Method as claimed in claim 1 wherein the pressure control valves used for pressure reduction are designed as valves that are normally open in their inactive condition, and wherein the varying step further includes reducing the electric actuator variable based on a value that is above the value necessary for retaining the pressure control valve in the closed condition.4. Method as claimed in claim 1, further including the step of varying the electric variable in defined driving situations.5. Method as claimed in claim 1, further including the step of varying the electric variable during vehicle standstill or in a defined range of the vehicle speed.6. Method as claimed in claim 1, further including the step of varying the electric variable at a low variation speed of a braking pressure nominal value.7. Method as claimed in claim 1, further including the step of varying the electric variable after a minimum duration of the pressure maintenance phase.8. Method as claimed in claim 1, further including the step of discontinuing the electric actuation variable when the difference between nominal pressure and actual pressure exceeds a predetermined tolerance range.9. Method as claimed in claim 8, further including the step of fixing the limits of the tolerance range in dependence on the vehicle speed.10. Method as claimed in claim 1, wherein the pressure control valves are designed as electromagnetically controllable valves, and in that the electric variable is an electric current being supplied to the electromagnetic drive.11. Method as claimed in claim 1, wherein the pressure control valves are configured as piezoelectrically controllable valves, and wherein the electric variable is an electric voltage applied to the piezoelectrically controllable valves.12. Method as claimed in claim 1, further including the step of observing cyclically in a time window the pressure variation in the wheel brake associated with the pressure control valve during the variation of the electric variable determining and the maximum pressure value in each case which, in turn, is taken into account for determining a detection threshold for the pressure change at the outlet of the pressure control valve used for pressure increase.13. Method as claimed in claim 12, wherein a detection threshold E in the window i is defined according to the formulaE=Max(p)|window (i?1)+ε, where ε is a process parameter taking into account valve leakage and malfunctions of the pressure sensor sensing the pressure variation. 14. Method as claimed in claim 13, wherein the opening of the pressure control valve is inferred when the pressure value at the outlet of the pressure control valve exceeds the detection threshold (E) in the time window (i).15. Method as claimed in claim 1, wherein a detection threshold E in the window i is defined according to the formulaE=Max(p)|window (i?1)?ε, where ε is a process parameter taking into account valve leakage and malfunctions of the pressure sensor sensing the pressure variation. 16. Method as claimed in claim 15, wherein opening of the pressure control valve is inferred when the pressure value at the inlet of the pressure control valve drops below the detection threshold (E) in the time window (i).17. Method as claimed in any one of claims 12, wherein at time (tdetect), when the pressure value at the outlet of the pressure control valve used for pressure increase or at the inlet of the pressure control valve used for pressure reduction exceeds or falls below the detection threshold (E), a point of time is calculated according to the formulatreact=tdetect?τwhere τ designates the offset in time between the reaction of the pressure control valve caused by the actuation and the detection of this reaction by way of the change in pressure. 18. Method as claimed in claim 17, wherein the offset in time (τ) is determined in dependence on a signal characterizing the viscosity of the pressure medium.19. Method as claimed in claim 10, wherein the dependence of the actuating current I(Δp) on the differential pressure (Δp) is corrected according to the formulaI(Δp)new=I(Δp)old·(1?λ)+λ·Ireact, where Ireact designates the actuating current value corresponding to the change in pressure in the wheel brake associated with the pressure control valve at time (treact), I(Δp)old designates the value of the dependence of the actuating current I(Δp) on the differential pressure (Δp) in the present operating point (Δp) before the correction (adaption) is carried out, and I(Δp)new designates the value of the dependence of the actuating current I(Δp) on the differential pressure (Δp) after the correction (adaption) is carried out, and the adaption rate λ should be selected from the interval (0, 1). 20. Method as claimed in claim 11, wherein the dependence of the voltage U(Δp) being applied on the differential pressure (Δp) is corrected according to the formulaU(Δp)new=U(Δp)old·(1?λ)+λ·Ureact, where Ureact designates the actuating voltage value corresponding to the change in pressure in the wheel brake associated with the pressure control valve at time (treact), U(Δp)old designates the value of the dependence of the actuating voltage U(Δp) on the differential pressure (Δp) in the present operating point (Δp) before the correction (adaption) is carried out, and U(Δp)new designates the value of the dependence of the actuating voltage U(Δp) on the differential pressure (Δp) after the correction (adaption) is carried out, and the adaption rate λ shall be selected from the interval (0, 1). 21. Method for controlling an electronically controllable brake actuating system for automotive vehicles, with a depressurized pressure medium supply reservoir, with at least one pressure source which can be controlled by an electronic control unit, said pressure source being used to apply pressure to the wheel brakes of the vehicle, with pressure control valves being associated with said wheel brakes, said pressure control valves being controllable in an analog manner by means of an electric variable in dependence on the differential pressure applied to them and connecting the wheel brakes to the pressure source in a pressure increase phase, being closed or becoming closed in a pressure maintenance phase, and connecting the wheel brakes to the pressure medium supply reservoir in a pressure reduction phase, comprising the steps of:determining a frequency of the actuation processes of the pressure control valves and considering said frequency according to a nominal pressure variation to be controlled in the wheel brakes for the correction of the dependence of the electric variable on the differential pressure, determining the number of the actuation processes of the pressure control valve used for pressure reduction during a pressure increase phase of the nominal pressure variation of the duration, and inferring that an excessive actuation of the pressure control valve used for pressure increase from the exceeding of a threshold value comparing the number determined (Nred, Nincr) to a maximum allowed numerical value (Nred*, Nincr*) that is produced according to the formula Nred*=fa·Tincr or Nincr=fa·Tred where fa maximum allowed actuation frequency and Tincr, Tred designates the duration of the phase of rise or fall of the pressure, and in that an excessive actuation of the pressure control valve used for pressure increase or reduction is inferred from the exceeding of the maximum allowed numerical value (Nred*, Nincr*). 22. Method as claimed in claim 21, further including the step of:comparing the number of the actuation processes of the pressure control valve used for pressure increase during a pressure reduction phase of the nominal pressure variation of the duration, and inferring that an excessive actuation of the pressure control valve used for pressure reduction from the exceeding of a threshold value. 23. Method as claimed in claim 21, wherein the pressure control valves are designed as electromagnetically controllable valves, and in that the electric variable is an electric current being supplied to the electromagnetic drive.24. Method as claimed in claim 21, wherein the pressure control valves are configured as piezoelectrically controllable valves, and in that the electric variable is an electric voltage being applied to the piezoelectrically controllable valves.25. Method as claimed in claim 21, wherein the correction of the dependence of the actuating current I(Δp) on the differential pressure (Δp) is carried out according to the formulaI(Δp)new=I(Δp)old?ΔI, where I(Δp)old designates the value of the dependence of the actuating current I(Δp) on the differential pressure (Δp) in the present operating point (Δp) before the correction (reduction) is carried out, and I(Δp)new designates the value of the dependence of the actuating current I(Δp) on the differential pressure (Δp) after the correction (reduction) is carried out. 26. Method as claimed in claim 21, wherein the correction of the dependence of the voltage U(Δp) to be applied on the differential pressure (Δp) is carried out according to the formulaU(Δp)new=U(Δp)old?ΔU, where U(Δp)old designates the value of the dependence of the actuating voltage U(Δp) on the differential pressure (Δp) in the present operating point (Δp) before the correction (reduction) is carried out, and U(Δp)new designates the value of the dependence of the actuating voltage U(Δp) on the differential pressure (Δp) after the correction (reduction) is carried out. 27. An electronically controllable brake actuating system, comprising:a pressure controller having as input quantities, a nominal pressure value that shall be applied to one of the wheel brakes of the vehicle, an actual pressure value that is applied to one of the wheel brakes of the vehicle, a hydraulic differential pressure value disposed at a pressure control valve under review and having an output quantity that is the nominal value of an electric variable used to actuate the pressure control valve, and means for correcting the dependence on the electric variable on the differential pressure value, wherein the pressure controller further includes a linear controller, a pilot control module, and a correction module, and the deviation produced from the nominal pressure value and actual pressure value is sent to the linear controller as an input quantity, while a signal representative of the hydraulic differential pressure prevailing at the pressure control valve under review is sent to the pilot control module, with said pilot control module generating a pilot control value of the electric variable used to actuate the pressure control valve that corresponds to the opening point of the pressure control valve and is added to the output quantity of the linear controller for producing the nominal value of the electric variable used to actuate the pressure control valve, and with the actual pressure value and the differential pressure prevailing at the pressure control valve under review being sent as input quantities to the correction module and the output quantity influencing the performance of the pilot control module. 28. Control system as claimed in claim 27 quantity K1 of the correction module is defined as:wherein the output quantity (K1) of the correction module (45) is defined as a difference: K1=I(Δp)new?I(Δp)old orK1=U(Δp)new?U(Δp)old where I(Δp) or U(Δp)old designates the value of the dependence of the electric actuation variable I(Δp) or U(Δp) on the differential pressure (Δp) in the present operating point (Δp) before the correction (adaption) is carried out, and I(Δp)new or U(Δp)new designates the value of the dependence of the electric actuation variable I(Δp) or U(Δp) on the differential pressure (Δp) after the correction (adaption) is carried out. 29. Control system as claimed in claim 27, wherein that the nominal pressure value (Pnom) is additionally sent as an input quantity to the correction module, and in that its output quantity K2=?ΔI is derived from the comparison of the detected number of the actuation processes (Nred, Nincr) with a maximum allowed numerical value (Nred*, Nincr*), and the dependence of the electric variable is reduced when the maximum allowed numerical value Nred*,Nincr*) is exceeded.30. Method for controlling an electronically controllable brake actuating system for automotive vehicles, said brake actuating system of the type including a depressurized pressure medium supply reservoir, with at least one pressure source controlled by an electronic control unit, said pressure source being used to apply pressure to the wheel brakes of the vehicle, with pressure sensors and pressure control valves being associated with said wheel brakes, said pressure control valves being controllable in an analog manner by means of an electric variable in dependence on the differential pressure applied to them and connecting the wheel brakes to the pressure source in a pressure increase phase, being closed or becoming closed in a pressure maintenance phase and connecting the wheel brakes to the pressure medium supply reservoir in a pressure reduction phase, comprising the step of:identifying the presence of a pressure maintenance phase, then, slowly varying the electric variable in the pressure control valve until a predetermined pressure variation takes place in the wheel brake associated with said pressure control valve, whereupon the dependence of the electric variable on the differential pressure is corrected, wherein the pressure control valves are designed as electromagnetically controllable valves, and in that the electric variable is an electric current being supplied to the electromagnetic drive, wherein the dependence of the voltage U(Δp) being applied on the differential pressure (Δp) is corrected according to the formula ?U(Δp)new=U(Δp)old·(1?λ)+λ·Ureact,where Ureact designates the actuating voltage value corresponding to the change in pressure in the wheel brake associated with the pressure control valve at time (treact), U(Δp)old designates the value of the dependence of the actuating voltage U(Δp) on the differential pressure (Δp) in the present operating point (Δp) before the correction (adaption) is carried out, and U(Δp)new designates the value of the dependence of the actuating voltage U(Δp) on the differential pressure (Δp) after the correction (adaption) is carried out and the adaption rate λ shall be selected from the interval (0, 1). 31. Method for controlling an electronically controllable brake actuating system for automotive vehicles, said brake actuating system of the type including a depressurized pressure medium supply reservoir, with at least one pressure source controlled by an electronic control unit, said pressure source being used to apply pressure to the wheel brakes of the vehicle with pressure sensors and pressure control valves being associated with said wheel brakes, said pressure control valves being controllable in an analog manner by means of an electric variable in dependence on the differential pressure applied to them and connecting the wheel brakes to the pressure source in a pressure increase phase, being closed or becoming closed in a pressure maintenance phase and connecting the wheel brakes to the pressure medium supply reservoir in a pressure reduction phase, comprising the step of:identifying the presence of a pressure maintenance phase, then, slowly varying the electric variable in the pressure control valve until a predetermined pressure variation rakes place in the wheel brake associated with said pressure control valve, whereupon the dependence of the electric variable on the differential pressure is corrected, wherein the pressure control valves are configured as piezoelectrically controllable valves, and wherein the electric variable is an electric voltage applied to the piezoelectric drive, wherein the dependence of the voltage U(Δp) being applied on the differential pressure (Δp) is corrected according to the formula U(Δp)new=U(Δp)old·(1?λ)+λ·Ureact, where Ureact designates the actuating voltage value corresponding to the change in pressure in the wheel brake associated with the pressure control valve at time (treact), U(Δp)old designates the value of the dependence of the actuating voltage U(Δp) on the differential pressure (Δp) in the present operating point (Δp) before the correction (adaption) is carried out and U(Δp)new designates the value of the dependence of the actuating voltage U(Δp) on the differential pressure (Δp) after the correction (adaption) is carried out, and the adaption rate λ shall be selected from the interval (0, 1). 32. Method for controlling an electronically controllable brake actuating system for automotive vehicles, said brake actuating system of the type including a depressurized pressure medium supply reservoir, with at least one pressure source controlled by an electronic control unit, said pressure source being used to apply pressure to the wheel brakes of the vehicle, with pressure sensors and pressure control valves being associated with said wheel brakes, said pressure control valves being controllable in an analog manner by means of an electric variable in dependence on the differential pressure applied to them and connecting the wheel brakes to the pressure source in a pressure increase phase, being closed or becoming closed in a pressure maintenance phase and connecting the wheel brakes to the pressure medium supply reservoir in a pressure reduction phase, comprising the step of:identifying the presence of a pressure maintenance phase, then, slowly varying the electric variable in the pressure control valve until a predetermined pressure variation takes place in the wheel brake associated with said pressure control valve, whereupon the dependence of the electric variable on the differential pressure is corrected, wherein a detection threshold E in the window 1 is defined according to the formula E=Max(p)|window (i?1)+ε, where ε is a process parameter taking into account valve leakage and malfunctions of the pressure sensor sensing the pressure variation, wherein the opening of the pressure control valve is inferred when the pressure value at the outlet of the pressure control valve exceeds the detection threshold (E) in the time window (i). 33. Method for controlling an electronically controllable brake actuating system for automotive vehicles, said brake actuating system of the type including a depressurized pressure medium supply reservoir, with at least one pressure source controlled by an electronic control unit, said pressure source being used to apply pressure to the wheel brakes of the vehicle, with pressure sensors and pressure control valves being associated with said wheel brakes, said pressure control valves being controllable in an analog manner by means of an electric variable in dependence on the differential pressure applied to thorn and connecting the wheel brakes to the pressure source in a pressure increase phase, being closed or becoming closed in a pressure maintenance phase and connecting the wheel brakes to the pressure medium supply reservoir in a pressure reduction phase, comprising the step of:identifying the presence of a pressure maintenance phase, then, slowly varying the electric variable in the pressure control valve with a predetermined pressure variation takes place in the wheel brake associated with said pressure control valve, whereupon the dependence of the electric variable on the differential pressure is corrected, wherein at time (tdetect), when the pressure value at the outlet of the pressure control valve used for pressure increase or at the inlet of the pressure control valve used for pressure reduction exceeds or falls below the detection threshold (E), a point of time is calculated according to the formula treact=tdetect?τwhere τ designates the offset in time between the reaction of the pressure control valve caused by the actuation and the detection of this reaction by way of the change in pressure, wherein the offset in time (τ) is determined in dependence on a signal characterizing the viscosity of the pressure medium.