Method and Device for Operating a Parking Brake

Abstract

A method for operating a parking brake which has an actuator with an actuating element and an electric motor, the electric motor is operatively connected to the actuating element in order to displace the latter, the electric motor is actuated in order to displace the actuating element by a predefined movement travel, and an actual movement travel of the actuating element is monitored in order to actuate the electric motor. The method includes determining the actual movement travel of the actuating element in a manner which is dependent on a motor current and/or a motor voltage of the electric motor.

Claims

1. A method for operating a parking brake including an actuator having an adjusting element and an electric motor operatively connected to the adjusting element, the method comprising: controlling the electric motor in order to displace the adjusting element along a predetermined movement path; monitoring an actual movement path of the adjusting element so as to control the electric motor; and determining the actual movement path of the adjusting element in dependence upon a motor current of the electric motor and/or a motor voltage of the electric motor.

2. The method as claimed in claim 1, further comprising: determining a rotational speed signal of the electric motor from the motor current and the motor voltage; and determining the actual movement path in further dependence upon the rotational speed signal.

3. The method as claimed in claim 2, further comprising: integrating the rotational speed signal in order to determine the actual movement path.

4. The method as claimed in claim 2, further comprising: integrating the rotational speed signal in dependence upon a motor constant and/or a motor resistance of the electric motor.

5. The method as claimed in claim 4, further comprising: determining the motor constant and the motor resistance when switching on the electric motor.

6. The method as claimed in claim 2, further comprising: determining a motor constant and a motor resistance when switching on the electric motor; integrating the rotational speed signal; and correcting the integrated rotational speed signal using the determined motor constant and the determined motor resistance.

7. A device for operating a parking brake, comprising: an actuator having an adjusting element configured to be displaced along a predetermined movement path, and an electric motor operatively connected to the adjusting element and configured to displace the adjusting element along the predetermined movement path; and a control device operatively connected to the actuator and configured to control the electric motor in order to displace the adjusting element along the predetermined movement path, monitor an actual movement path of the adjusting element so as to control the electric motor, and determine the actual movement path of the adjusting element in dependence upon a motor current of the electric motor and/or a motor voltage of the electric motor.

Description

[0011] The invention is further explained hereinunder with reference to the drawing. In the drawing

[0012] FIG. 1 illustrates an exemplary embodiment of a parking brake in a simplified sectional view and

[0013] FIG. 2 illustrates a simplified equivalent circuit diagram of an electric motor of the parking brake.

[0014] FIG. 1 illustrates a simplified sectional view of a wheel brake device 1 of a brake system of a motor vehicle that is not further illustrated in this figure. Expediently, the motor vehicle comprises at least two wheels that are allocated in each case a corresponding wheel braking device 1. The wheel braking device 1 is embodied as a disc brake and comprises for this purpose a brake caliper 2 that supports the brake pads 3 between which it is possible to clamp or brace a brake disc 4 that is connected in a non-rotatable manner to a wheel of the motor vehicle. For this purpose, an actuator 5 is allocated to the brake caliper 2, said actuator comprising a brake piston 6 that can be hydraulically actuated in order to fixedly clamp the brake disc 4 between the brake pads 3 on demand. As a result of the fixedly clamped arrangement, a friction-type connection that exerts a braking torque on the respective wheel is produced between the brake disc 4 and the brake linings 3.

[0015] The wheel braking device 1 is moreover equipped with an integrated parking brake 7. For this purpose, the wheel braking device 1 comprises an actuator 8 that is formed from an electric motor 9, a gear mechanism 10 and an adjusting element 11. An output shaft of the electric motor 9 is operatively connected to the gear mechanism 10. For this purpose, the output shaft is connected in a non-rotatable manner to a drive spindle 12 that comprises an outer thread that cooperates with an inner thread of the adjusting element 11 that can be displaced along the drive spindle 12. The drive spindle is set into a rotational movement by means of controlling the electric motor 9, and as a consequence, the adjusting element 11 is displaced axially along the drive spindle 12. The adjusting element 11 can be displaced from a release position into a clamping position in which the adjusting element 11 forces the brake piston 6 against the brake disc 4 and as a consequence fixedly clamps or closes the brake disc 4 between the brake pads 3. The adjusting element 11 is arranged coaxially with respect to the brake piston and within the brake piston 6. The parking brake 7 is embodied in particular in a self-locking manner by means of the gear mechanism 10 so that if the electric motor 9 has been actuated, in order to clamp the parking brake, it is possible to release said parking brake only by means of controlling the electric motor 9 in that the drive shaft of the electric motor 9 is driven in the opposite direction and as a consequence the adjusting element 11 is moved out of the clamped position back into the released position.

[0016] In order to release the parking brake 7, the electric motor 9 is expediently controlled in such a manner that the adjusting element 11 is displaced from the clamping position into the release position in such a manner that an air gap is set between the brake pads 3 and the brake disc 4. The term “air gap” is understood to mean a gap between the brake pads 3 and the brake disc 4, said gap ensuring that the brake disc 4 can freely rotate and wear on the brake pads 3 and the brake disc 4 is avoided. In order to ensure that the correct air gap is set, the method described hereinunder is provided, said method being implemented by a control device that is allocated to the braking system or the parking brake 7. The actual movement path of the adjusting element 11 is determined by means of the method and where appropriate is compared to a desired movement path in order to be able to ascertain the adjustment of the adjusting element 11 and thereby the gap between said adjusting element and the brake disc 4 during operation without it being necessary to provide a separate movement path sensor, such as by way of example a Hall sensor or a rotational speed sensor.

[0017] For this purpose it is provided that the actual braking path of the adjusting element 11 is determined in dependence upon an integrated rotational speed signal that is produced from a measured motor current and a measured motor voltage of the electric motor 9 and from correcting values. The motor current and the motor voltage are ascertained and evaluated when switching on the electric motor 9. In particular, the motor resistance R.sub.M and the motor constant K.sub.M are determined in dependence upon the ascertained current values and voltage values. A rotational speed signal is then calculated using the current values and voltage values and these motor parameters, said rotational speed signal being integrated to form a travel signal. Since the motor parameters motor constant and motor resistance are only calculated during the course of the opening procedure, the integration is started with base parameters. These base parameters can be calculated by way of example on the basis of the construction data of the parking brake 7 or are ascertained and stored when producing or first bringing into operation the parking brake 7. The integration is then performed in such a manner that the integration begins and then as soon as prevailing values of the above-mentioned motor parameters motor resistance and motor constant are available, the integration is corrected by means of said prevailing values.

[0018] FIG. 2 illustrates in addition an equivalent circuit diagram of the electric motor 9. A switch-on peak occurs when switching on the electric motor 9 and the motor resistance R.sub.M and the motor constant K.sub.M are determined in dependence upon said switch-on peak. The mass inertia J and the inductivity L.sub.M of the armature of the electric motor 9 are provided as is known. I.sub.L is the idle running current of the electric motor 9 in the load-free state.

[0019] The motor rotational speed n is integrated by way of the task cycles T.sub.cyc to calculate the movement path of the adjusting element 11. The follow equation applies for the voltage balance:

[00001]$U_B=L_M.Math.\frac{\mathrm{di}}{\mathrm{dt}}+R_M.Math.i+u_G$

[0020] The generator voltage U.sub.G is indicated with K.sub.M.Math.ω, wherein ω is the angular frequency. For current values i and for voltage values u that can be measured in the control device, the following consequently applies for ω:

[00002]$\omega =\frac{u-L_M.Math.\frac{\Delta .Math..Math.i}{T_{\mathrm{cyc}}}-R_M.Math.i}{K_M}=\frac{1}{K_M}.Math.\left(u-L_M.Math.\frac{\Delta .Math..Math.i}{T_{\mathrm{cyc}}}\right)-\frac{R_M}{K_M}.Math.i$

[0021] The travel signal is formed by way of a simple integration of the path increments Δ.sub.s, wherein n is the rotational speed and ü is the transmission ratio of the gear mechanism 10:

[00003]${\Delta }_S=n.Math.T_{\mathrm{cyc}}.Math.\stackrel{\mathrm{.Math.}}{u}=\frac{T_{\mathrm{cyc}}.Math.\stackrel{\mathrm{.Math.}}{u}}{2.Math.\pi }.Math.\omega =\frac{T_{\mathrm{cyc}}.Math.\stackrel{\mathrm{.Math.}}{u}}{2.Math.\pi }.Math.\frac{1}{K_M}.Math.\left(u-L_{M.Math.}.Math.\frac{\Delta .Math..Math.i}{T_{\mathrm{cyc}}}\right)-\frac{T_{\mathrm{cyc}}.Math.\stackrel{\mathrm{.Math.}}{u}}{2.Math.\pi }.Math.\frac{R_M}{K_M}.Math.i$$S=.Math.{\Delta }_S=\frac{T_{\mathrm{cyc}}.Math.\stackrel{\mathrm{.Math.}}{u}}{2.Math.\pi }.Math.\frac{1}{K_M}.Math..Math.\left(u-\frac{L_M}{T_{\mathrm{cyc}}}.Math.\Delta .Math..Math.i\right)-\frac{T_{\mathrm{cyc}}.Math.\stackrel{\mathrm{.Math.}}{u}}{2.Math.\pi }.Math.\frac{R_M}{K_M}.Math..Math.i$

[0022] The movement path is consequently calculated by way of two terms that are to be integrated separately, said terms being multiplied with the factors f.sub.1(K.sub.M) and f.sub.2 (K.sub.M, R.sub.M):

[00004]$s=f_1\left(K_M\right).Math..Math.\left(u-\frac{L_M}{T_{\mathrm{cyc}}}.Math.\Delta .Math..Math.i\right)-f_2\left(K_M,R_M\right).Math..Math.i$

[0023] The factors f.sub.1 and f.sub.2 are corrected using the prevailing ascertained motor parameters motor resistance R.sub.M.sub._.sub.new and motor constant K.sub.M.sub._.sub.new, wherein the values of the motor constant and the motor resistance that are used as base values or default values are included in the calculation as K.sub.M.sub._.sub.old or R.sub.M.sub._.sub.old:

[00005]$f_{1.Math.\mathrm{new}}=f_{1.Math.\mathrm{old}}.Math.\frac{K_{M.Math..Math.\_.Math..Math.\mathrm{old}}}{K_{M.Math..Math.\_.Math..Math.\mathrm{new}}}$$f_{2.Math.\mathrm{new}}=f_{2.Math.\mathrm{old}}.Math.\frac{K_{M.Math..Math.\_.Math..Math.\mathrm{old}}.Math.R_{M.Math..Math.\_.Math..Math.\mathrm{new}}}{K_{M.Math..Math.\_.Math..Math.\mathrm{new}}.Math.R_{M.Math..Math.\_.Math..Math.\mathrm{old}}}$

[0024] The movement path when moving the adjusting element 11 from the clamping position into the release position, in other words eventually the opening path of the parking brake 7, can consequently be calculated during the entire controlling procedure, wherein the integration of the path signal already occurs with the beginning of the controlling procedure and is then corrected as soon as the new or prevailing motor parameters motor resistance and motor constant are available.

[0025] It is thereby possible to calculate the actual movement path of the adjusting element 11 in a simple manner when controlling the electric motor 9 so that it is possible to omit additional sensors for ascertaining the movement of the adjusting element 11. The controlling procedure of the electric motor 9 is expediently regulated with the knowledge of the actual movement path so that the actual movement path corresponds in particular to a desired movement path that is provided by means of the control device.