METHOD FOR MONITORING THE RELEASE BEHAVIOR OF AN ELECTROMECHANICAL WHEEL BRAKE OF A VEHICLE

Abstract

A method for monitoring the release behavior of an electromechanical wheel brake of a vehicle, the wheel brake having at least one electrically controllable force actuator configured to apply a brake-application force to friction partners of the wheel brake. comprises activating the force actuator in accordance with a defined control pattern which is dependent on a present operating state of the wheel brake, a present operating state of further wheel brakes of the vehicle, and/or a present operating state of the vehicle. The activation of the force actuator is interrupted at a defined point in time. The operating parameters of the wheel brake are monitored for a defined period of time after the interruption of the activation. The release behavior of the wheel brake is determined by ascertaining a reaction of the force actuator to the interruption of the activation on the basis of the ascertained operating parameters.

Claims

1. A method for monitoring the release behavior of an electromechanical wheel brake of a vehicle comprising: activating a force actuator to apply a brake application force to friction partners of a wheel brake with a defined control pattern, which is dependent on at least one of a present operating state of the wheel brake, a present operating state of further wheel brakes of the vehicle, and a present operating state of the vehicle; interrupting the activation of the force actuator at a defined point in time; monitoring operating parameters of the wheel brake for a defined period of time after the interruption of the activation; and determining release behavior of the wheel brake by ascertaining a reaction of the force actuator to the interruption on the basis of the ascertained operating parameters.

2. The method as claimed in claim 1, wherein the defined control pattern is a first control pattern which comprises setting and holding the defined brake-application force with the force actuator of the wheel brake.

3. The method as claimed in claim 2, wherein the first control pattern being implemented only when the vehicle is stationary.

4. The method as claimed in claim 2, further comprising implementing a parking brake function which causes the vehicle to be held stationary by at least a proportion of the wheel brakes of the vehicle.

5. The method as claimed in claim 4, further comprising: ascertaining whether the further wheel brakes of the vehicle are collectively imparting a braking force that is sufficient to hold the vehicle stationary before the interruption of the activation; and setting the defined brake-application force to a value higher than a brake-application force for implementing the parking brake function when the braking force imparted by the further wheel brakes is not sufficient to hold the vehicle stationary.

6. The method as claimed in claim 1, further comprising applying a force to one of a pressure piston that is actuatable by electric motor and an application element that is actuatable by electric motor to provide the brake application force.

7. The method as claimed in claim 6, wherein the defined control pattern is a second control pattern which comprises accelerating one of the pressure piston and the application element along the brake-application direction without generation of the brake-application force.

8. The method as claimed in claim 1, wherein the defined control pattern is a third control pattern which comprises reducing a brake-application force that is acting due to a brake actuation.

9. The method as claimed in claim 1, wherein the operating parameters which are monitored comprise at least one of: a profile of the acting brake-application force with respect to time, and the profile of an actuating travel of the wheel brake with respect to time.

10. The method as claimed in claim 9, wherein determining the release behavior is ascertained from one of a difference in the actuating travel and a difference in the brake-application force over a time difference.

11. The method as claimed in claim 10, wherein the release behavior is identified as insufficient when the ascertained difference in the one of the actuating travel and the brake-application force is below a threshold value.

12. The method as claimed in claim 9, wherein determining the release behavior is ascertained from one of a gradient of the actuating travel with respect to time and the brake-application force.

13. The method as claimed in claim 12, wherein the release behavior is identified as insufficient when the ascertained gradient of the actuating travel or the ascertained gradient of the brake-application force is below a threshold value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0026] FIG. 1 shows a flow diagram of an exemplary method;

[0027] FIG. 2 is a schematic illustration of an exemplary force-travel profile of an electromechanical wheel brake;

[0028] FIG. 3 is a further schematic illustration of the exemplary force-travel profile of an electromechanical wheel brake; and

[0029] FIG. 4 is a schematic illustration of the behavior of a force actuator during the implementation of an exemplary control pattern.

DETAILED DESCRIPTION

[0030] In the following text, features that are similar or identical are denoted by the same reference signs.

[0031] FIG. 1 shows a flow diagram of an exemplary embodiment of a method. In a first method step 100, the force actuator of an electromechanical wheel brake is activated in accordance with a defined control pattern. The force actuator may for example be an arrangement with an electromotive drive, downstream of which there is connected a mechanism arrangement with a rotation-translation mechanism, such that a rotation of a drive shaft of the drive is converted into a translational movement. A pressure piston or an application element of a wheel brake may be coupled to the mechanism, such that a rotation of the drive shaft of the drive, or a torque acting on the drive shaft, is converted into a translational movement of the pressure piston or application element or a force acting on the pressure piston or the application element along a brake-application direction.

[0032] The movement of pressure piston or application element, or an exertion of a force on said elements, may cause friction partners of a friction brake to be brought into contact with one another, or to be pressed against one another with a force that is controllable by the controller of the electromotive drive. The friction force that is thus generated causes a braking torque or moment to be exerted on a vehicle wheel that is operatively connected to the wheel brake, which braking torque or moment brakes or prevents a rotation of the vehicle wheel.

[0033] The control pattern in accordance with which the force actuator is activated is dependent on a present operating state of the wheel brake under consideration. For example, the operating state of the wheel brake describes whether the wheel brake is presently exerting a braking force on the associated vehicle wheel, or the wheel brake is situated in an open state, that is to say the friction partners of the wheel brake are not in contact. A further influential factor may also be whether the wheel brake is presently being used to decelerate the vehicle, or whether the wheel brake is being used to implement a parking brake function that is intended to prevent the vehicle from rolling away from a parked brake position. Accordingly, an operating state of the vehicle may also have an influence on what type of control pattern is used in the context of the method. The operating state of the vehicle may for example be ascertained from a wheel rotational speed of a wheel associated with the wheel brake under consideration. Finally, in the selection of the control pattern used, consideration may also be given to the present operating state of the further wheel brakes of the vehicle, that is to say whether the further wheel brakes are presently being used to generate braking forces, and, if applicable, how high these braking forces are.

[0034] Subsequently, in step 102, the activation of the force actuator, that is to say the implementation of the control pattern, is interrupted at a defined point in time. The interruption may be performed such that the activation of the force actuator, which activation was previously controlled within the scope of the control pattern, is stopped, that is to say no further control commands are output to the force actuator. In this way, it is for example possible to simulate an interruption of the power supply of the wheel brake or a failure of the controller owing to an interruption of the signal transmission or a fault of the control unit.

[0035] Subsequently, in step 104, it is ascertained how the wheel brake, and in particular the force actuator with the elements positioned downstream of the force actuator in the action chain (mechanism and friction partners), behaves after the interruption of the activation. For this purpose, the operating parameters of the wheel brake are monitored for a defined period of time after the interruption of the activation. A profile of the position of a pressure piston or application element, or an application force imparted by means of the pressure piston or application element, may be recorded versus the time that has elapsed since the interruption of the activation.

[0036] From the data thus ascertained, it is subsequently ascertained in step 106 whether the release behavior of the wheel brake in the event of an interruption of the activation is sufficient to continue to ensure a sufficient self-release action in the event of a failure of the controller or power supply of the wheel brake. Should it be identified that the release behavior is insufficient, that is to say if, in the event of a fault, an acting braking force is depleted too slowly or the wheel brakes maintain a brake-application force that is too high, provision may furthermore be made for the wheel brake to no longer be used, or to be used only to a limited degree, for implementing a braking demand, and for a corresponding warning to be output to the vehicle driver.

[0037] Different variants of control patterns will be described by way of example below with reference to FIGS. 2, 3 and 4.

[0038] In this regard, FIG. 2 shows an exemplary profile of the brake-application force F.sub.z of an electromechanical wheel brake versus the displacement travel s.sub.K of a pressure piston or of an application element of the electromechanical wheel brake. The profile of the brake-application force upon an application of the wheel brake, that is to say an increase of the brake-application force 200, differs from the profile of the brake-application force in the event of a release of the wheel brake, that is to say a reduction of the brake-application force 202.

[0039] A first variant of a control pattern may be such that the force actuator sets a defined brake-application force A and maintains this over a relatively long period of time. This may be provided for example for the implementation of a parking brake function, wherein, in this case, the corresponding brake-application force is selected such that the wheel brakes that are involved in implementing the parking brake function collectively provide a braking force that prevents the vehicle from rolling away.

[0040] Upon an interruption of the activation of the force actuator, a deformation energy of the wheel brake, for example of the brake caliper, that is commonly stored in the applied wheel brake causes the pressure piston or the application element to be acted on with a force that leads to a release of the brake, that is to say a movement of the pressure piston or application element counter to the brake-application direction. The acting brake-application force is also reduced, wherein the degree to which the brake-application force changes during a movement of the pressure piston or application element over a defined distance provides information regarding whether the wheel brake would self-open to a sufficient degree in the event of a fault. Aside from a consideration of the acting brake-application force F.sub.z versus the displacement travel s.sub.K, it is alternatively or additionally also possible to ascertain and take into consideration the acting brake-application force F.sub.z versus the time t since the interruption of the activation. Furthermore, both differences in brake-application forces ΔF.sub.z over different time differences Δt or differences in the displacement travel Δs.sub.K may be considered, or corresponding gradients calculated, in order to quantify the release behavior of the wheel brake.

[0041] An example of a second control pattern will be described below with reference to FIGS. 3 and 4. FIG. 3 shows once again the exemplary profile, already described with reference to FIG. 2, of the brake-application force F.sub.z of an electromechanical wheel brake versus the displacement travel s.sub.K of a pressure piston or of an application element of the electromechanical wheel brake. However, in this embodiment the range of the displacement travel s.sub.K that is arranged to the left of the vertical coordinate axis. In this range, a displacement of the pressure piston or application element takes place without building up a brake-application force. Consequently, the origin of the coordinate system describes the point along the displacement travel s.sub.K at which the friction partners of the wheel brake come into contact. The range to the left of the coordinate origin describes the air gap range of the wheel brake, that is to say the range in which the friction partners do not come into contact and, therefore, it may initially also be the case that no brake-application force builds up during a displacement of the friction partners.

[0042] As a second control pattern, provision is now made, in this range, for the pressure piston or the application element to be accelerated along the displacement travel s.sub.K proceeding from a point C. Once the pressure piston or the application element reaches the point C′, the activation of the force actuator is interrupted. It is subsequently observed how long the pressure piston or the application element takes to reach the point D along the displacement travel s.sub.K.

[0043] In this regard, FIG. 4 illustrates, by way of example, the position of the pressure piston or application element s.sub.K along the displacement travel versus the time t during an implementation of the second control pattern. An accelerated movement of the pressure piston or application element initially starts, proceeding from a position C, at the time t.sub.0. At the point C′, or at the time t′.sub.c corresponding to this, the activation of the force actuator may be interrupted, such that the pressure piston or the application element run down and the speed decreases again until, at the point D, at a corresponding time t.sub.D, the speed falls below a threshold value. From the duration Δt=t.sub.D−t′.sub.c, it can then be ascertained whether the free running of the force actuator exhibits sufficiently free movement that a reliable release behavior of the electromechanical wheel brake may be assumed.

[0044] A third control pattern may also be described by way of example, proceeding again from the illustration of FIG. 2. The force actuator is initially activated such that a defined brake-application force acts at the point A. This may for example be a brake-application force resulting from a braking demand, which may be triggered for example by an actuation of a brake pedal by a vehicle driver. Subsequently, in a manner controlled on the basis of an ending of the braking demand, the brake-application force F.sub.z is depleted, along the curve 202, by corresponding activation of the force actuator. At a defined point B, however, the activation of the force actuator is interrupted, such that a proportion of the depletion of force is performed by the wheel brake alone. If one for example again considers the gradient of the brake-application force F.sub.z versus the displacement travel s.sub.K or the time t that has elapsed since the interruption of the activation, the self-release capability of the wheel brake may again be determined.

[0045] The above-described control patterns may be combined in any desired manner to form a monitoring profile for the electromechanical wheel brake, such that the release behavior of the wheel brake can be ascertained in different ways in different situations.