METHOD FOR CONTROLLING A BRAKING SYSTEM, BRAKING SYSTEM AND MOTOR VEHICLE

Abstract

A method for controlling a braking system of a motor vehicle. The braking system includes hydraulically actuated wheel brakes as well as a linear actuator and a pump as electrohydraulic pressure-generating devices, according to which, during a braking operation of the motor vehicle, a parameter describing an actual behavior of the braking system of the motor vehicle is monitored and compared with a stored threshold value. In the event that the monitored parameter exhibits a defined deviation from the threshold value, the linear actuator and the pump are switched to synchronous operation by simultaneously operating the linear actuator and the pump and applying brake pressure to the hydraulically actuated wheel brakes via the linear actuator and the pump. A current volume consumption of the linear actuator is detected as a parameter describing the actual behavior of the braking system of the motor vehicle.

Claims

1. A method for controlling a braking system of a motor vehicle, wherein the braking system comprises hydraulically actuated wheel brakes and a linear actuator and a pump as electrohydraulic pressure-generating devices, according to which, during a braking operation of the motor vehicle, a parameter describing an actual behavior of the braking system of the motor vehicle is monitored and compared with a stored threshold value, wherein, in the event that the monitored parameter exhibits a defined deviation from the threshold value, the linear actuator and the pump are switched to synchronous operation and the linear actuator and the pump are operated simultaneously and brake pressure is applied to the hydraulically operable wheel brakes via the linear actuator and the pump, wherein a current volume consumption of the linear actuator is detected as the parameter describing the actual behavior of the braking system of the motor vehicle.

2. The method according to claim 1, wherein the current volume consumption is compared with a permanently stored maximum volume consumption value, and, if the current volume consumption is ?than the maximum volume consumption value, the system is switched to synchronous operation.

3. The method according to claim 1, wherein in addition to the current volume consumption of the linear actuator, a current longitudinal acceleration of the motor vehicle resulting therefrom is also detected, and the current volume consumption is compared with a volume consumption threshold value, and, if the current volume consumption is ?than the volume consumption threshold value, the system is switched to synchronous operation, wherein the volume consumption threshold value is obtained from a characteristic curve in which the longitudinal acceleration is plotted as a function of the volume consumption of the linear actuator.

4. The method according to claim 1, wherein in addition to the current volume consumption of the linear actuator, a current brake pressure applied to the hydraulic wheel brakes is also detected, and the detected current brake pressure is compared with a stored limit brake pressure and the current volume consumption is compared with a stored volume consumption limit value, and, if the detected current brake pressure is ?than the stored limit brake pressure and the current volume consumption is ?than the stored volume consumption limit value, the system is switched to synchronous operation.

5. The method according to claim 1, wherein a control signal controlling the pump in synchronous operation is obtained from a characteristic diagram in which a control signal controlling the pump in synchronous operation is read from a characteristic curve in which the set pump motor speed is plotted as a function of the set pressure build-up gradient or the set volume flow of the brake fluid.

6. A braking system for the wheels of a motor vehicle, comprising hydraulically actuated wheel brakes associated with the wheels, a primary system comprising a linear actuator as an electrohydraulic pressure-generating device for supplying the wheel brakes with brake pressure, a secondary system redundant to the primary system and having a pump as an electrohydraulic pressure-generating device, which can be operated in synchronous operation with the primary system, for supplying the wheel brakes with brake pressure, a brake fluid reservoir in fluid communication with the primary system and the secondary system, and a regulating/controlling device for regulating/controlling the braking system, wherein the regulating/controlling device is designed to perform the method according to claim 1.

7. The braking system according to claim 6, wherein the regulating/controlling device is a central regulating/controlling unit which is configured to regulate/control the linear actuator of the primary system and the pump of the secondary system.

8. The braking system according to claim 6, wherein the regulating/controlling device is designed redundantly and comprises a primary regulating/controlling unit and a secondary regulating/controlling unit.

9. A motor vehicle, comprising a braking system, wherein the braking system is designed according to claim 6.

10. The method according to claim 2, wherein in addition to the current volume consumption of the linear actuator, a current longitudinal acceleration of the motor vehicle resulting therefrom is also detected, and the current volume consumption is compared with a volume consumption threshold value, and, if the current volume consumption is ?than the volume consumption threshold value, the system is switched to synchronous operation, wherein the volume consumption threshold value is obtained from a characteristic curve in which the longitudinal acceleration is plotted as a function of the volume consumption of the linear actuator.

11. The method according to claim 2, wherein in addition to the current volume consumption of the linear actuator, a current brake pressure applied to the hydraulic wheel brakes is also detected, and the detected current brake pressure is compared with a stored limit brake pressure and the current volume consumption is compared with a stored volume consumption limit value, and, if the detected current brake pressure is ?than the stored limit brake pressure and the current volume consumption is ?than the stored volume consumption limit value, the system is switched to synchronous operation.

12. The method according to claim 3, wherein in addition to the current volume consumption of the linear actuator, a current brake pressure applied to the hydraulic wheel brakes is also detected, and the detected current brake pressure is compared with a stored limit brake pressure and the current volume consumption is compared with a stored volume consumption limit value, and, if the detected current brake pressure is ?than the stored limit brake pressure and the current volume consumption is ?than the stored volume consumption limit value, the system is switched to synchronous operation.

13. The method according to claim 2, wherein a control signal controlling the pump in synchronous operation is obtained from a characteristic diagram in which a control signal controlling the pump in synchronous operation is read from a characteristic curve in which the set pump motor speed is plotted as a function of the set pressure build-up gradient or the set volume flow of the brake fluid.

14. The method according to claim 3, wherein a control signal controlling the pump in synchronous operation is obtained from a characteristic diagram in which a control signal controlling the pump in synchronous operation is read from a characteristic curve in which the set pump motor speed is plotted as a function of the set pressure build-up gradient or the set volume flow of the brake fluid.

15. The method according to claim 4, wherein a control signal controlling the pump in synchronous operation is obtained from a characteristic diagram in which a control signal controlling the pump in synchronous operation is read from a characteristic curve in which the set pump motor speed is plotted as a function of the set pressure build-up gradient or the set volume flow of the brake fluid.

Description

DETAILED DESCRIPTION

[0008] According to the method for controlling a braking system of a motor vehicle, the braking system comprises hydraulically actuated wheel brakes as well as a linear actuator and a pump, as electrohydraulic pressure-generating devices. In a known manner, a parameter describing or characterizing the actual behavior of the braking system is monitored during a braking process and compared with a stored threshold value, andif the monitored parameter exhibits a defined deviation from the threshold valuethe linear actuator and the pump are switched to synchronous operation by operating the linear actuator and the pump simultaneously and applying braking pressure to the hydraulically actuated wheel brakes via the linear actuator and the pump.

[0009] According to the invention, it is now provided that an actual volume consumption of the linear actuator is used as a parameter describing the actual behavior of the braking system during a braking process.

[0010] Since, according to the invention, the current volume consumption of the linear actuator is used as a parameter for switching to synchronous operation, it is advantageously ensured that the linear actuator can be provided with a smaller size, since a volume delivery appropriate to the load is ensured by means of the pump. Thus, it is now advantageously possible to design the linear actuator with regard to its volume in such a way that the volume of the linear actuator is sufficient to ensure the necessary blocking pressure level (usually approx. 100 bar) for most braking processes, e.g. >90%, since in the other remaining cases in which a higher blocking pressure level is required, the pump intervenes in a supporting manner, i.e. the pump delivers the additional volume to build up the braking pressure. The smaller dimensioning of the linear actuator has the effect of saving weight and requiring less installation space.

[0011] Preferably, the current volume consumption is compared with a fixed stored maximum volume consumption value, and the system switches to synchronous operation if the current volume consumption is ?the maximum volume consumption value. For example, if the linear actuator has a total volume of V.sub.tot=15 cm.sup.3 and a value of 11 cm.sup.3 has been stored as the maximum consumption value, the linear actuator and pump switch to synchronous operation if the detected current volume consumption is ?11 cm.sup.3. Instead of an absolute maximum volume consumption value, it is of course also possible to provide a percentage value related to the total volume V.sub.tot, i.e. for switching to synchronous operation when the current volume consumption ?x % of the total volume V.sub.tot, for example current volume consumption ?75% V.sub.tot.

[0012] A particularly preferred embodiment of the method according to the invention provides that, in addition to the current volume consumption of the linear actuator, a resulting current longitudinal acceleration of the motor vehicle is also detected and the current volume consumption is compared with a volume consumption threshold value, and in thatif the current volume consumption is ?the volume consumption threshold valuesynchronous operation is switched to, wherein the volume consumption threshold value is taken from a characteristic curve in which the longitudinal acceleration is plotted against the volume consumption of the linear actuator. The advantage of this embodiment is that even at low decelerations it can be identified whether the volume of the linear actuator is sufficient for a full deceleration or whether, if necessary, a requirement-based control of the pump is required. Possible supporting points of the characteristic curve could be, for example, longitudinal acceleration ??4 m/s.sup.2; current volume consumption ?50% of the total volume V.sub.tot, as well as longitudinal acceleration ??6 m/s.sup.2; current volume consumption ?70% of the total volume V.sub.tot.

[0013] A further embodiment is characterized in that, in addition to the current volume consumption of the linear actuator, a current braking pressure applied to the hydraulic wheel brakes is also detected, and in that the detected current braking pressure is compared with a stored limit braking pressure and the current volume consumption is compared with a stored volume consumption limit value, and in thatif the detected current braking pressure ?than the stored limit braking pressure and the current volume consumption ?than the stored volume consumption limit value?synchronous operation is switched to.

[0014] If, for example, the linear actuator has a total volume of V.sub.tot=15 cm.sup.3, the stored limit brake pressure is 2 bar (=pressure required to overcome the air gap) and the stored volume consumption limit value V.sub.limit is e.g. V.sub.limit=4 cm.sup.3, the linear actuator and pump are switched to synchronous operation in the method if the detected current volume consumption ?4 cm.sup.3 and the detected current brake pressure is ?2 bar. Instead of an absolute volume consumption limit value, it is of course also possible to provide a percentage value related to the total volume V.sub.tot, such as volume consumption limit V.sub.limit=y % of the total volume V.sub.tot, such as V.sub.limit=25% of the total volume V.sub.tot.

[0015] In order to ensure sufficient volume delivery by the pump in synchronous operation, according to a further preferred embodiment it is provided that the intensity of a control signal controlling the pump is read out from a characteristic curve in which the desired pump motor speed is plotted against the desired pressure build-up gradient or the desired volume flow of the brake fluid.

[0016] Another object of the invention is to develop a braking system for the wheels of a motor vehicle in such a way that the braking system requires less installation space and is lighter in weight.

[0017] In a known manner, the braking system comprises hydraulically actuated wheel brakes associated with the wheels, a primary system having a linear actuator as an electrohydraulic pressure-generating device for supplying the wheel brakes with brake pressure, and a secondary system which is redundant to the primary system, which has a pump as an electrohydraulic pressure-generating device and can be operated in synchronous operation with the primary system, for supplying the wheel brakes with brake pressure. In addition, the braking system comprises in a known manner a brake fluid reservoir containing or storing a hydraulic fluid, which is fluidically connected to the primary system and the secondary system, as well as a closed-loop controlling device for regulating/controlling the braking system.

[0018] The design of the braking system according to the invention has the effect thatas already explaineddue to the control system according to the invention, the electrohydraulic pressure-generating device of the primary system, i.e. the linear actuator, can be dimensioned smaller. In addition to a lower component weight, the smaller size has in particular the advantage that the linear actuator is smaller and thus the braking system comprising the linear actuator requires less installation space.

[0019] Preferably, the regulating/controlling device is designed as a central regulating/controlling unit, which is set up to regulate/control both the linear actuator of the primary system and the pump of the secondary system. This has the advantage of enabling a particularly space-saving and weight-optimized design of the braking system.

[0020] An alternative design is characterized by a redundant design of the regulating/controlling device, i.e. two regulating/controlling units are provided, namely a primary regulating/controlling unit regulating/controlling the linear actuator and a secondary regulating/controlling unit regulating/controlling the pump. This advantageously ensures increased system reliability.

[0021] Another object of the invention is to develop a motor vehicle comprising a braking system in such a way that consumption-optimized driving is possible.

[0022] All explanations of the method for controlling the braking system according to the invention and of the braking system according to the invention can be applied analogously to the motor vehicle according to the invention, so that the advantages mentioned above, in particular a weight saving and thus a consumption-optimized operation of the motor vehicle, are also achieved with the latter.