Procedure for adjusting a parking brake in a vehicle

Abstract

In a method for adjusting a parking brake comprising an electromechanical braking device with an electric brake motor to generate an electromechanical clamping force, the standard deviation is determined from a current profile of the brake motor based on measured current values, and if the standard deviation exceeds a limit value, a correction current is determined which is used as the basis for calculating the motor parameters of the brake motor to determine the clamping force.

Description

[0001] The invention relates to a method for adjusting a parking brake in a vehicle according to the preamble of claim 1. State of the art

[0002] German patent application DE 10 2006 052 810 A1 describes a method for estimating the clamping force generated by an electric brake motor in the parking brake of a motor vehicle. The electric brake motor moves a brake piston, which carries a brake pad, axially against a brake disc. The resulting clamping force is determined from a system of differential equations, taking into account the current, the supply voltage of the brake motor, and the motor speed. This system models the electrical and mechanical behavior of the brake motor.

[0003] The brake motor, like several other electrical components, is powered by the vehicle's electrical system. If another component is switched on after the electric brake motor has started, this causes a voltage drop and current drop in the brake motor, which can lead to an incorrect reading of the clamping force being measured.

[0004] To account for the voltage drop or current drop when switching on an additional electrical load when determining the clamping force, DE 10 2012 206 226 A1 describes the calculation of a correction current, which is used as a basis for calculating the motor resistance and motor constants required for determining the clamping force. The correction current is determined from a current value prior to the voltage drop, which is modified by a scaling factor. Disclosure of the invention

[0005] The invention is based on the objective of determining, with high accuracy, the clamping force generated by a parking brake via an electric brake motor using simple measures, even in the case where additional consumers in the vehicle's electrical system are switched on or off during operation of the brake motor.

[0006] This problem is solved according to the invention by the features of claim 1. The dependent claims specify advantageous further developments.

[0007] The method for determining the clamping force is used in electromechanical parking brakes in motor vehicles that have an electric brake motor, the actuation of which generates the desired clamping force. The rotational movement of the rotor of the electric brake motor is transferred into an axial positioning movement of a spindle, via which a brake piston, which carries a brake pad, is pressed axially against a brake disc.

[0008] In principle, it is sufficient to use the electric brake motor as the actuator in the parking brake. However, the parking brake can also be equipped with an auxiliary braking device to provide additional clamping force as needed, supplementing the electromechanical clamping force. This auxiliary braking device is preferably the vehicle's hydraulic brake system, whose hydraulic pressure acts on the brake piston.

[0009] To determine the clamping force currently acting on the electric brake motor, the current motor current is required. From the motor current, the motor load torque can be calculated, and, taking into account the gear reduction and efficiency, the clamping force can be determined. In principle, the current or voltage in the electric brake motor are sufficient as measured variables.

[0010] After the electric brake motor is switched on, the motor current, which is only limited by the armature inductance, initially rises sharply and then drops again due to the start of the armature rotation. Because of its high dynamics, the inrush current surge can be used to estimate the motor's electrical parameters, namely its resistance and constant. Measurements are taken during the subsequent falling portion of the motor current following the inrush current peak to calculate the motor parameters and the clamping force that depends on them.

[0011] If another electrical load, connected to the vehicle's electrical system just like the electric brake motor, is switched on or off during the phase following the inrush current peak, the voltage and current curves change, each switching almost abruptly to a lower or higher value. For example, both the voltage and current curves drop rapidly when an electrical load is switched on. If the motor parameters are determined from the current and voltage values ​​after this jump, the calculated clamping force will be distorted.

[0012] The abrupt change in the current and voltage curves of the brake motor can be compensated or corrected computationally. For this purpose, a correction current is determined, for example, from a current value prior to the abrupt change and a scaling factor multiplied by the current value. This correction current is then used as the basis for calculating the motor parameters required to determine the clamping force.

[0013] In the method according to the invention, the correction current is only used to determine the motor parameters if the standard deviation of a current curve of the brake motor, based on measured current values, exceeds a limit value. Even without switching on or off an additional electrical load, the voltage and current curves of the brake motor are subject to variation. By determining the standard deviation of the current values, it can be established whether current value deviations are due to variation or to the switching on or off of an additional electrical load. Accordingly, different measures can be taken depending on whether the standard deviation exceeds the assigned limit value or not.

[0014] This allows for improved precision in distinguishing the switching on or off of an electrical load from the variation in current values. If the standard deviation exceeds the assigned limit, the correction current is determined, which is then used as the basis for calculating the motor parameters, i.e., the motor resistance and the motor constant.

[0015] However, the method according to the invention can also be applied in cases of significant current fluctuations that are not attributable to the switching on or off of an additional electrical consumer in the vehicle. In this case, too, the standard deviation exceeds a defined limit value, whereupon the correction current is used to determine the motor parameters. The motor parameters determined based on the correction current, which form the basis for the clamping force calculation, exhibit higher accuracy in this case than the motor parameters based on the actually measured current values.

[0016] According to an advantageous embodiment, the standard deviation is not determined directly from the actual, measured current profile, but from a hypothetical maximum current when the brake motor's armature is locked, i.e., when the motor is at standstill. This hypothetical maximum current is determined based on several successive measured current values. The maximum current at standstill is specifically determined as a function of the first and second measured current values, additionally taking into account an idle current.

[0017] The method according to the invention is preferably carried out during the application of the parking brake, during which the clamping force for securing the vehicle is generated. The standard deviation is calculated based on several successive current values, wherein the period considered for calculating the standard deviation is preferably after the inrush current peak of the motor current, which immediately follows the switch-on.

[0018] In principle, the procedure can also be carried out during the release of the parking brake following the inrush current peak, but only effectively until the gear backlash is overcome and the force dissipates. This phase can also be readily identified using the standard deviation.

[0019] It is advantageous to perform the standard deviation calculation repeatedly. For example, it may be useful to determine the standard deviation several times in succession based on measured current values ​​during an idle phase following the inrush current peak, in which the motor current exhibits an approximately constant profile. It is possible to use either a defined number of current values, particularly a constant number, for the standard deviation calculation, or an increasing number of current values ​​over time. As soon as a calculated standard deviation exceeds the limit value, the correction current is determined and used as the basis for calculating the motor parameters.

[0020] The algorithm for determining the motor parameters can be designed to terminate if the standard deviation becomes too large. However, for parameter determination, it is advisable to calculate a minimum number of current value pairs for I before termination. max There must be, for example, five current value pairs.

[0021] The method according to the invention takes place in a control or regulating unit in the vehicle, which is expediently part of the parking brake.

[0022] Further advantages and practical designs can be found in the additional requirements, the figure description, and the drawings. These show: Fig. 1 a section through an electromechanical parking brake for a vehicle in which the clamping force is generated via an electric brake motor, Fig. 2 a diagram showing the time-dependent course of the current, voltage and motor speed during the tightening process of the parking brake.

[0023] In Fig. Figure 1 shows an electromechanical parking brake 1 for securing a vehicle in a stationary position. The parking brake 1 comprises a brake caliper 2 with a clamp 9, which engages a brake disc 10. The parking brake 1 has an electric motor as its actuator, a brake motor 3, which rotates a spindle 4 on which a spindle component 5, designed as a spindle nut, is rotatably mounted. When the spindle 4 rotates, the spindle component 5 is axially adjusted. The spindle component 5 moves within a brake piston 6, which carries a brake pad 7. The brake piston 6 presses the brake pad 7 against the brake disc 10. On the opposite side of the brake disc 10 is another brake pad 8, which is held stationary on the clamp 9.

[0024] Within the brake piston 6, the spindle component 5 can move axially forward towards the brake disc 10 when the spindle 4 rotates, and axially backward when the spindle 4 rotates in the opposite direction until it reaches a stop 11. To generate a clamping force, the spindle component 5 acts on the inner end face of the brake piston 6, thereby pressing the brake piston 6, which is axially displaceable within the parking brake 1, together with the brake pad 7, against the facing end face of the brake disc 10.

[0025] The parking brake can be assisted, if necessary, by a hydraulic vehicle brake, so that the clamping force consists of an electromechanical component and a hydraulic component. With hydraulic assistance, the rear side of the brake piston 6, facing the brake motor, is pressurized with hydraulic fluid.

[0026] In Fig. Figure 2 shows a diagram depicting the current I, voltage U, and speed n of the electric brake motor as a function of time during a clamping process. Furthermore, in Fig. 2 the electromechanical clamping force F Kl The input is the amount of force generated by the electric brake motor, as well as the distance s traveled by the brake motor or an actuator actuated by the brake motor during the clamping process.

[0027] At time t1, the clamping process begins by applying an electrical voltage and energizing the brake motor with the circuit closed. The start-up phase (Phase I) lasts from time t1 to time t2. At time t2, the voltage U and the motor speed n have reached their maximum. The phase between t2 and t3 represents the idle phase (Phase II), in which the current I is at a minimum level. From time t3 to time t4, the force build-up phase (Phase III) follows, during which the brake pads contact the brake disc and the clamping force F increases. Kl The brake disc is pressed against it. At time t4, the electric brake motor is switched off by opening the circuit, so that the rotational speed n of the brake motor subsequently drops to zero.

[0028] The force increase point coincides with the force build-up phase at time t3. The force build-up, or the course of the clamping force F, Kl The force can be determined, for example, from the current I of the brake motor, which generally exhibits the same curve as the electromechanical clamping force. Starting from the low level during the idle phase between t2 and t3, the current rises sharply at the beginning of time t3. This increase in current can be detected and used to determine the point of force increase. In principle, however, the force build-up can also be determined from the voltage or speed curve, or from any combination of current, voltage, and speed signals.

[0029] To determine the clamping force F Kl Without using a speed sensor, the motor constant K is used as a motor parameter. M as well as the motor resistance R MThe required parameters are determined from the voltage and current profiles of the electric brake motor. When the brake motor is switched on, the current rises sharply, slowed only by the armature inductance, and then falls significantly more slowly due to the onset of rotation. During the falling phase, the current profile is essentially determined by the motor's mechanical time constant, which is determined by the armature's moment of inertia J and the motor constant K. M and the motor resistance R M is influenced.

[0030] For an improved determination of the motor constant K M and the motor resistance R MFluctuations in current values ​​are taken into account, which arise from natural variations or from switching an electrical consumer on or off in the vehicle's electrical system. For this purpose, a standard deviation of the brake motor's current curve, based on measured current values, is determined and compared to a limit value. If the standard deviation exceeds the limit value, a correction current is used, which forms the basis for determining the motor parameters.

[0031] The standard deviation is determined based on a theoretical or hypothetical maximum current that would prevail when the motor is at standstill, i.e., with the armature locked. This hypothetical maximum current is calculated from the actual measured current values ​​before or during a winding process at a point in time when the current has at least approximately reached its steady state. For this purpose, the current is measured at two times t in the falling branch after the inrush current peak has been exceeded. 1,m and t 2,m measured and from this the theoretical or hypothetical maximum current I max calculated as the current that would flow with the brake motor off, taking into account the idle current I. L , which is determined in the phase after the inrush current, in which the speed is constant and the no-load current is determined only by the load or by the friction of the motor, the maximum current I is max according to the relationship Imax=(I1−IL)2I2−IL+IL calculated, where I1, I2 are the values ​​at times t 1,m or t 2,m Describe measured current values.

[0032] The times t 1,m and t 2,m These times refer to the start of the current flow. Time t2 is twice as far after the start of the current flow as time t. 1,m .

[0033] From the maximum current I max The standard deviation s can be calculated according to... s=1n−1(∑i=1nImax,i2−1n(∑i=1nImax,i)2) to be calculated, where "n" is the total number of values ​​of the maximum current I to be considered. maxThe determined standard deviation s is compared with an assigned limit value. If the standard deviation s exceeds the limit value, it can be assumed that an electrical consumer connected to the vehicle's electrical system has been switched on or off. However, even without an electrical consumer being switched on or off, the fluctuation range of the current values ​​is too high to determine the engine parameters with sufficient accuracy based on the measured current values. Therefore, if the standard deviation s exceeds the limit value, a correction current I is applied. cor avoided, which is used as the basis for calculating the engine parameters.

[0034] The calculation of the correction current I is described below. cor based on the actual current profile I s described for the case that at time t sprAn additional electrical consumer, which is connected to the vehicle's electrical system just like the electric brake motor, is switched on, whereupon both the voltage and the current drop almost abruptly.

[0035] To use the actual current flow I s on the ideal current flow I cor To deduce which parameter is used as the basis for determining the engine parameters, a scaling factor f is used. cor from the ratio of the voltage step ΔU at time t spr The voltage step U is determined in the voltage profile. The voltage step ΔU is expressed as a ratio to a voltage value U prior to the step. t1 minus a voltage constant U const set: fcor(tspr)=ΔU(tspr)U(t1)−Uconst, where the voltage value U t1 is measured at time t1, which is before the jump time t spr lies.

[0036] With the scaling factor f determined in this waycor will the correction current i cor , which corresponds to the ideal motor current profile without the addition of another load, is determined according to the following relationship: Icor(tspr)=Is(tspr)+fcor(tspr)⋅(It1−IL)

[0037] Herein I refers to cor (t spr ) the corrected current after the jump at time t spr , I s (t spr ) the actual current after the jump at time t spr , f cor (t spr ) the scaling factor after the jump at time t spr , I t1 the current value before the jump at time t1 and I L the idle current, which is stably maintained without load after the inrush current.

[0038] It is advantageous to use several current values ​​I cor at other times t spr+1 , t spr+2 ... t spr+n after the jump, taking into account the scaling factor f corfrom measured current values ​​I at times t2, t3 ... t n+1 before the jump as well as from measured current values ​​I s at times t spr+1 , t spr+2 ... t spr+n calculated after the jump: Icor(tspr+1)=Is(tspr+1)+fcor(tspr)⋅(It2−IL) Icor(tspr+2)=Is(tspr+2)+fcor(tspr)⋅(It3−IL) Icor(tspr+n)=Is(tspr+n)+fcor(tspr)⋅(Im+1−IL)

[0039] In this way, the ideal current profile can be determined over the entire time range by correcting the current value.

[0040] Taking into account the additionally measured motor or operating voltage U B can according to RM=UBImax the motor resistance R M from the ratio of the motor or operating voltage U B and the maximum current I max will be calculated.

[0041] In the event of a voltage drop, the maximum current I maxfrom the corrected current values ​​I cor at time t and twice the time 2t according to Imax=(Icor(t)−IL)2Icor(2t)−IL+IL calculated.

[0042] The voltage constant U const , which are used in the calculation of the scaling factor f cor The input can be expressed as the product of the motor resistance R. M and the idle current I L can be determined. Since the motor resistance R M If the voltage dip compensation value is not yet available at the time of the calculation, a preset value must be used. The maximum current I is then calculated using the compensated current profile. max and motor resistance R M recalculated and the maximum current I max The standard deviation is evaluated. If it is still too large, another iteration must be performed.

[0043] The motor constant K Mcan be determined from parameters of the brake motor, namely from the mechanical time constant τ M of the brake motor, the motor resistance R M and the motor moment of inertia J ges : KM=RM⋅JgesτM, where the mechanical time constant τ M from the relationship τM=tln((Imax−IL) / (I(t)−IL)) can be determined.

[0044] The motor constant K can be determined using the method described above. M The current must be determined before each engagement of the electromechanical parking brake, and with sufficient accuracy even in the case of significant variations in current measurements. This is done taking into account the motor constant K. M The motor load torque in an electric brake motor can be determined if the current is known. The clamping force F can then be calculated from the motor load torque. Kl be determined.

Claims

[1] Method for adjusting a parking brake (1) comprising an electromechanical braking device with an electric brake motor (3) for generating an electromechanical clamping force (F Kl ) includes, where the clamping force (F Kl ) is determined based on current values ​​(I1, I2, I3) of the brake motor, characterized by , that the standard deviation is determined from a current profile of the brake motor, which is based on measured current values, and in the event that the standard deviation exceeds a limit value, a correction current (I) is applied. cor ) is determined, which is used to calculate the engine parameters (R M , K M ) of the brake motor is used as a basis for determining the clamping force. [2] Method according to claim 1, characterized by , that the standard deviation is determined from a hypothetical maximum current when the motor is at standstill, whereby the maximum current is determined from several successive measured current values. [3] Method according to claim 2, characterized by , that the maximum current (I max ) when the engine is off, out of context Imax=(I1−IL)2I2−IL+IL is determined, whereby I L the idle current I1, I2 measured current values ​​at times t 1,m or t 2,m describe. [4] Method according to any one of claims 1 to 3, characterized by , that the correction current (I cor ) taking into account the product of a scaling factor (f cor ) and a current value prior to the increased standard deviation (I t1 ) is determined. [5] Method according to claim 4, characterized by , that the correction current (I cor ) taking into account the product of the scaling factor (f cor ) and the difference between the current value before the increased standard deviation (I) t1 ) and the idle current (I L ) is determined: Icor(tspr)=Is(tspr)+fcor(tspr)⋅(It1−IL), where I cor (t spr ) the corrected current after the increased standard deviation at time t spr I s (t spr ) the actual current after the increased standard deviation at time t spr f cor (t spr ) the scaling factor according to the increased standard deviation at time t spr I t1 the current value before the increased standard deviation I L This refers to the idle current. [6] Method according to claim 4 or 5, characterized by , that different current values ​​at further time points after the increased standard deviation taking into account the scaling factor (f cor ) are calculated from current values ​​before the increased standard deviation. [7] Method according to any one of claims 4 to 6, characterized by , that the scaling factor (f cor) from the ratio of voltage step (ΔU) to a voltage value prior to the increased standard deviation (U) t1 ) is determined. [8] Method according to any one of claims 1 to 7, characterized by , that current values ​​from the tensioning process of the parking brake are used to determine the standard deviation. [9] Method according to any one of claims 1 to 8, characterized by , that current values ​​during the start-up process of the brake motor are used to determine the standard deviation. [10] Method according to claim 9, characterized by that the current values ​​following the inrush current peak are used to determine the standard deviation. [11] Method according to any one of claims 1 to 10, characterized by , that the determination of the standard deviation and / or the correction current (I cor ) is repeated. [12] Control or regulating device for carrying out the method according to any one of claims 1 to 11. [13] Parking brake in a vehicle with a control or regulating unit according to claim 12.

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