METHOD FOR HOLDING A MOTOR VEHICLE IN PLACE AND ELECTRICALLY ACTUATED BRAKE

Abstract

A method and apparatus for holding a motor vehicle by means of an electrically actuated brake comprises applying the brake until a target force is reached. For holding purposes, a motor torque is reduced by applying a negative preset value for a target angular velocity for a motor torque of an electric actuator of the brake.

Claims

1. A method for holding a motor vehicle using an electrically actuated brake comprising: applying the brake until a target force is reached; applying a negative preset value for a target angular velocity for a motor torque of an electric actuator of the brake; monitoring an actual angular velocity of the actuator with an actuator speed controller while applying the negative preset value; and applying a quiescent value for the target angular velocity when a magnitude of the actual angular velocity exceeds a threshold value.

2. The method as claimed in claim 1, wherein the actuator speed controller has at least one integral part.

3. The method as claimed in claim 1, wherein the actuator speed controller is a proportional-integral controller.

4. The method as claimed in claim 1, wherein a magnitude of the preset value is at most one revolution per minute.

5. The method as claimed in claim 1, wherein the quiescent value is zero.

6. (canceled)

7. (canceled)

8. The method as claimed in claim 1, wherein the target angular velocity is one of the preset value, originates from a force controller and originates from a position controller depending on an operating state.

9. The method as claimed in claim 8, wherein at least one of the force controller and the position controller are a controller with a proportional action.

10. The method as claimed in claim 1, further comprising limiting the motor torque with a limiter, at the output end of the actuator speed controller such that the motor torque has at least one of a lower value and an upper value.

11. The method as claimed in claim 1, further comprising limiting the target angular velocity with a limiter at the input end of the actuator speed controller such that the target anfular velocity has at least one of a lower value and an upper value.

12. The method as claimed in claim 1, further comprising ending the holding process when one of a target clamping force a target actuator position is changed.

13. The method as claimed in claim 1, further comprising: wherein the method is executed in response to an actual clamping force exceeding an activation threshold value, differing from a target clamping force by a specified threshold value and being constant within a tolerance range at least for a predetermined period of time, and/or which is executed in response to an actual position exceeding a further activation threshold value, differing from a target position by a specified threshold value and being constant within a tolerance range at least for a predetermined period of time.

14. An electrically actuated brake comprising: an electric actuator, and an actuator speed controller with instructions for; applying the brake until a target force is reached; applying a negative preset value for a target angular velocity for a motor torque of the electric actuator of the brake; monitoring an actual angular velocity of the actuator with an actuator speed controller while applying the negative preset value; and applying a quiescent value for the target angular velocity when a magnitude of the actual angular velocity exceeds a threshold value.

15. The brake as claimed in claim 14, wherein the actuator speed controller has at least one integral part.

16. The brake as claimed in claim 14, wherein the actuator speed controller is a proportional-integral controller.

17. The brake as claimed in claim 14, wherein a magnitude of the preset value is at most one revolution per minute.

18. The brake as claimed in claim 14, wherein he quiescent value is zero.

19. The brake as claimed in claim 14, wherein the target angular velocity is one of the preset value, originates from a force controller and originates from a position controller depending on an operating state.

20. The brake as claimed in claim 19, wherein at least one of the force controller and the position controller are a controller with a proportional action.

21. The brake as claimed in claim 14, further comprising instructions for limiting the motor torque with a limiter, at the output end of the actuator speed controller such that the motor torque has at least one of a lower value and an upper value.

22. The brake as claimed in claim 14, further comprising instructions for limiting the target angular velocity with a limiter at the input end of the actuator speed controller such that the target angular velocity has at least one of a lower value and an upper value.

23. The brake as claimed in claim 14, further comprising ending the holding process when one of a target clamping force a target actuator position is changed.

24. The brake as claimed in claim 14, wherein the controller executes the instructions in response to an actual clamping force exceeding an activation threshold value, differing from a target clamping force by a specified threshold value and being constant within a tolerance range at least for a predetermined period of time; and wherein the controller executes the instructions in response to an actual position exceeding a further activation threshold value, differing from a target position by a specified threshold value and being constant within a tolerance range at least for a predetermined period of time.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Further features and advantages will be gathered by a person skilled in the art from the exemplary embodiment described below with reference to the appended drawing, in which:

[0022] FIG. 1 shows a control arrangement for an actuator.

DETAILED DESCRIPTION

[0023] FIG. 1 shows a control arrangement for an actuator of an electrically actuated brake. A force controller KR and a position controller PR are initially present at the input end here. As shown, the force controller KR receives as the input variable a difference between a target clamping force F.sub.Target and an actual clamping force F.sub.Actual, wherein the former is specified and the latter is measured and adjusted. Here, for example, the force with which the linings are pressed against a brake disk or against a brake drum can be considered to be the clamping force. In a similar way, the position controller PR receives as the input a difference between a target actuator position X.sub.Target and an actual actuator position X.sub.Actual.

[0024] The force controller KR generates as the output a target angular velocity .sub.Act,Target,FCtrl, which is multiplied by a first control signal .sub.FCtrl in a multiplier. The output signal of this multiplier is, in turn, passed to an adder. In a similar way, the position controller PR generates as the output signal a target angular velocity .sub.Act,Target,XCtrl which is, in turn, passed to a multiplier and there multiplied by a further control signal .sub.Xctrl. The output signal of the multiplier is passed to the same adder.

[0025] A controller selection RS is present for controlling the controller. As shown, said controller selection can generate the two control values .sub.FCtrl, .sub.XCtrl. Furthermore, said controller selection generates a preset value .sub.Act,Target,Red as required, said preset value likewise being passed to the adder already mentioned. The controller selection RS receives as input variables the target clamping force F.sub.Target, the actual clamping force F.sub.Actual, the actual actuator position X.sub.Actual and an actual angular velocity .sub.Act, the latter being measured by means of a suitable sensor or being determined by differentiation of the actual actuator position X.sub.Actual of the actuator. Said controller selection likewise generates the target actuator position X.sub.Target already mentioned further above. Depending on the operating state, the controller selection RS can use its input variables to select whether an output signal of the force controller KR or the position controller PR is to be used, or whether the preset value .sub.Act,Target,Red is to be used.

[0026] During normal driving operation, the target clamping force F.sub.Target is typically specified by a driver or a vehicle controller and evaluated by the controller selection RS. The force controller KR is typically used to implement a normal braking force request. The first control signal .sub.FCtrl A is accordingly set to one, and the second control signal .sub.Xctrl and the preset value .sub.Act,Target,Red are set to zero. Only the force controller KR is therefore relevant. The output signal of said force controller is passed via the adder already mentioned to a limiter, which ensures that the target angular velocity .sub.Act,Target,FCtrl generated is not smaller than a lower value .sub.Min and not greater than an upper value .sub.Max. An interval is therefore specified, in which corresponding specifications can be judiciously further processed. The output signal of this limiter is then fed as the target angular velocity .sub.Act,Target to a further subtractor, i.e. the actual angular velocity .sub.Act already mentioned further above is subtracted from said target angular velocity. The output signal of this subtractor is then fed to an actuator speed controller AGR, which in the present case is a proportional-integral controller and the output signal of which, after passing through a further limiter, which limits the output signal between a lower value M.sub.Min and an upper value M.sub.Max, is used as the target motor torque M.sub.Act,Target. If this target motor torque M.sub.Act,Target is used correctly, the actuator generates the desired torque, which ultimately leads to the desired target clamping force F.sub.Target being set.

[0027] If, on the other hand, the controller selection RS identifies that the braking process has ended, the first control signal .sub.Fctrl can be set to zero and the second control signal .sub.Xctrl can be set to one. Accordingly, the force controller KR is deactivated and the position controller PR is activated. The target actuator position is set to a value that is to be approached, it being possible, for example, for the target actuator position to be a quiescent position in which there is no longer any contact between a brake shoe and a brake disk or a brake drum. The position controller PR then generates a target angular velocity .sub.Act,Target,XCtrl which is suitable for this and which, as mentioned with reference to the force controller, is likewise forwarded via the adder and the limiter to the subtractor upstream of the actuator speed controller AGR and leads to a target motor torque M.sub.Act,Target, which will ultimately lead to the desired target actuator position X.sub.Target being set. In this case, the actuator position is typically defined such that there is no contact between the lining and the brake disk or brake drum and a certain distance between the brake lining and the brake disk is set.

[0028] If the target clamping force F.sub.Target remains at a value which exceeds an activation threshold value for a relatively long period of time, and the actual clamping force F.sub.Actual is likewise at least largely constant for this period of time and hardly differs from the target clamping force F.sub.Target, for example only differs within a certain interval, the controller selection RS identifies that a hold function is present. In this case, said controller selection sets both control signals .sub.Fctrl, .sub.Xctrl to zero, so that both the force controller KR and the position controller PR are deactivated. For the preset value .sub.Act,Target,Red, a low negative value is output, which is forwarded to the actuator speed controller AGR via the adder, as already described further above. The integral component in the actuator speed controller AGR is successively reduced in the process, with a target motor torque M.sub.Act,Target, which is ultimately aimed at at least slightly releasing the applied brake, being set. While the slightly negative preset value .sub.Act,Target,Red is applied, the actual angular velocity .sub.Act is monitored. If said actual angular velocity, in terms of magnitude, exceeds a threshold value, the preset value .sub.Act,Target,Red is set to a quiescent value of zero again and releasing of the brake is thus stopped. Due to friction, the brake engages again and holds the vehicle stationary, with the measure just described of applying a negative preset value .sub.Act,Target,Red reducing the applied motor torque to a value which is just sufficient to hold the vehicle, as a result of which the material stress is reduced. If there is an increase in the magnitude of the actual angular velocity .sub.Act, which can take place, for example, when the motor vehicle is loaded, the force controller KR can, for example, be reactivated by setting the first control signal .sub.FCtrl to one, and the brake can generate a higher clamping force again. This can prevent the vehicle from rolling away in an undesirable manner.

[0029] If the controller selection RS establishes that the target clamping force F.sub.Target is changed, for example more than one specified threshold value is changed, the holding phase is ended and the force controller KR is reactivated by setting the first control signal .sub.Fctrl to one. The force control can then be executed again in the usual way.

[0030] The mentioned steps of the method can be executed in the order indicated. However, they can also be executed in a different order, insofar as is technically appropriate. In one of its embodiments, for example with a specific combination of steps, the method can be executed in such a way that no further steps are executed. However, in principle, further steps can also be executed, including steps that have not been mentioned.

[0031] It is pointed out that features may be described in combination in the claims and in the description, for example in order to facilitate understanding, even though these can also be used separately from one another. A person skilled in the art will recognize that such features, independently of one another, can also be combined with other features or combinations of features.

[0032] Dependency references in dependent claims may characterize preferred combinations of the respective features but do not exclude other combinations of features.