Method for determining motor constant, fault condition and / or wear condition as well as contact point, control device, and friction brake

Abstract

To provide a method for determining a motor constant of an electric machine.SOLUTION: Provided is a method for determining a motor constant (Km) of an electric machine (7), in particular the electric machine (7) of an actuator assembly (6). At least one excitation signal (Im) having at least one direct current component (I0) and one alternating current component (Ik) is preset. The machine (7) is drive-controlled using the excitation signal (Im). At least one actual value of a motor current of the machine (7) and one actual value of a rotation rate (ω) of a rotor shaft of the machine (7) are determined in each case. The motor constant (Km) is determined according to the excitation signal (Im) and the actual values.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for determining the motor constant of an electric machine and, depending on the motor constant thus determined, a method for determining the error state and / or the wear state of a friction brake and a method for determining the contact point of two friction partners of a friction brake, respectively.

[0002] The invention further relates to a control device specially adapted to carry out at least one of the methods mentioned, as well as to a friction brake equipped with such a control device. [Background technology]

[0003] Hydraulically operated friction brakes for motor vehicles are known in the prior art. In these hydraulic brakes, pressure sensors in the hydraulic system are typically used to determine the corresponding brake application force, which allows, among other things, the braking moment to be estimated and controlled in a closed loop. However, the uncertainty in the friction pair (fluctuations in the friction value and thus in the braking characteristic value) is a significant limitation on the accuracy of the braking moment estimation.

[0004] Due to the changed boundary conditions, for example in electric vehicles, the use of electromechanically actuated brakes (EMB) can also be attractive. Here, similar to the pressure sensors mentioned, the question of suitable sensor systems at the actuator level arises. The effort or cost required for sensor systems that directly measure driving parameters and actuation forces is significantly higher than for hydraulic brakes, especially since measurements must be made at each wheel actuator and demanding environmental conditions (heat, dust, moisture, vibration, etc.) prevail. Summary of the Invention

[0005] The method for determining a motor constant of an electric machine according to the present invention, having the features of claim 1, comprises presetting at least one excitation signal having at least one DC component and one AC component, controlling the machine with the excitation signal, determining at each instant at least one actual value of the machine's motor current and one actual value of the rotation rate of the machine's rotor shaft, and determining the motor constant in response to the excitation signal and the actual values. One-time determination of system parameters, such as the motor constant or the viscous friction coefficient, is of limited utility due to manufacturing tolerances and degradation effects over the life of components. The invention is therefore based on the idea of ​​providing a method by which at least the motor constant can be easily determined as an important system parameter, especially periodically, as needed. This advantageously ensures that the corresponding component tolerances and wear in the system that affect the motor constant are taken into account. The essence of the invention resides in providing a special excitation signal for controlling the machine, which defines an adjustable motor current as a target current profile. According to the invention, the excitation signal has at least one, especially constant, DC component and one, especially sinusoidal, AC component. The corresponding DC component advantageously ensures that the excitation signal does not have zero crossings, thereby preventing the machine from switching direction of rotation. From the corresponding system response, characterized by the actual values ​​determined in accordance with the present invention of at least the motor current and the rotation rate, the motor constants and, in particular, further parameters, such as the friction coefficient, can then be determined simply by signal processing. The rotation rate here is understood to mean the rotational speed or angular velocity of the machine's rotor shaft. The electric machine is particularly a component of an actuator assembly, for example, an actuator assembly of a friction brake in a motor vehicle. The actuator assembly is particularly designed to displace a corresponding friction partner of the friction brake, for example, via a power train assembly. The friction brake is particularly designed as an electromechanical drum brake, drum brake, or disc brake.The friction partner displaceable by the actuator assembly in this case is, in particular, a brake lining, such as a brake shoe or brake lining arranged on a brake caliper, which is displaced toward a brake drum or brake disc, also having a brake lining, to generate a braking moment. For reliable operation of a machine that is part of a corresponding actuator assembly, such as an actuator assembly for a friction brake, it is therefore essential to periodically re-determine uncertain and / or unknown values ​​of the relevant system parameters. The method according to the present invention provides a particularly advantageously efficient and robust way of repeatedly determining the motor constant as a critical system parameter. Preferably, at least one other system parameter, in particular the Coulomb or viscous friction coefficient of the system, is determined depending on the motor constant thus determined. In this respect, the method according to the present invention provides advantageous multi-parameter identification for the system. Based on the parameters determined by the method according to the present invention, functionalities such as error recognition, damage recognition, and wear recognition can be advantageously realized or the closed-loop control circuit can be re-calibrated. The method is particularly implemented as a periodic self-check routine. The method has the further advantage that no additional sensors are required, but rather the already existing motor position sensor (rotor position sensor) is used, in particular to determine the actual value of the rotational speed, and / or the already existing information / current sensor system is used to determine the actual value of the motor current. In this way, the cost and technical complexity of the actuator assembly are not further increased. It is obvious that the method is not limited to the described application case of a friction brake, but can be used in any actuator assembly having an electric machine.

[0006] According to a preferred embodiment of the invention, the actual time course of the motor current and rotation rate resulting from the excitation signal is determined at each time, and average values ​​are determined as the actual values ​​at each time depending on the actual course. By taking the average values ​​into account, a particularly advantageously simple possibility of determining the actual values ​​is provided.

[0007] It is particularly preferred to determine the actual course over at least two periods of the AC component, whereby the robustness of the method according to the invention is advantageously further increased by determining over a larger number of periods.

[0008] According to a preferred development of the invention, it is provided that the AC component has at least one harmonic frequency, in particular a number of different harmonic frequencies, the use of which advantageously further improves the robustness and accuracy of the determination of the motor constants.

[0009] It is particularly preferred to determine the average value of the motor constants from a number of different excitation signals, which has the advantage that the number of measurement data is increased and thus the robustness of the method according to the invention is further improved.

[0010] According to a preferred development of the invention, it is provided that the motor constants are determined by means of a Fourier transform. The use of a Fourier transform advantageously ensures that the motor constants are determined particularly efficiently.

[0011] Particularly preferably, the machine is a component of an actuator assembly, and the motor constant is determined as a function of at least one Coulomb and / or viscous friction coefficient of the actuator assembly. Taking into account the corresponding friction coefficient provides a particularly advantageously simple relationship with which the motor constant can be determined. For this purpose, a system of equations or a matrix is ​​formed, which includes the corresponding friction coefficient and the motor constant to be determined as unknowns. The motor constant can then be determined particularly efficiently by the aforementioned Fourier transformation.

[0012] According to a preferred development of the invention, the machine is a component of an actuator assembly, and the motor constant is determined as a function of the preload and / or return moment of a spring element of the actuator assembly. Taking the preload and / or return moment into account provides a particularly simple possibility for determining the motor constant. Using a simplified model of the specific application case mentioned above, in particular in a drum brake, a mathematical relationship is established between the return moment of the return spring and the variables mentioned, and the motor constant is determined accordingly. The preload and / or return moment of the return spring are required accordingly as additional known input variables. When the corresponding variables are known, the accuracy of determining the motor constant is advantageously further improved.

[0013] Particularly preferably, the machine is a component of an actuator assembly of a friction brake of a motor vehicle, and it is intended that the machine be controlled by the excitation signal only within the air gap of the friction brake. Controlling only within the air gap has the advantage that the underlying model can be kept particularly simple, since the control is carried out only in the at least approximately no-load range, and in particular the friction pairs and the corresponding forces between the corresponding friction partners of the friction brake do not have to be taken into account.

[0014] The method for determining the error state and / or wear state of a friction brake of a motor vehicle having at least two friction partners, as described in claim 10, is characterized in that the friction brake is provided with an actuator assembly having an electric machine for displacing one of the friction partners toward the other, and the error state and / or wear state is determined as a function of the motor constant of the machine determined by the method described above. In particular, the error state and / or wear state is determined by comparing the motor constant and / or the friction coefficient determined as a function of the motor constant with preset thresholds and / or tolerance bands. The friction brake is preferably configured as an electromechanical drum or disc brake. The corresponding method allows for particularly advantageous application of the determined motor constant. In particular, this advantageously enables simple damage recognition; for example, a determined motor constant (torque / current) below a predetermined limit can be an indicator of machine damage.

[0015] The method according to the present invention for determining the contact point of two friction partners of a friction brake of a motor vehicle, as described in claim 11, is characterized in that the friction brake is assigned an actuator assembly having an electric machine for displacing one of the friction partners toward the other, and the contact point of the friction partners is determined, in particular by a load moment estimator, depending on the motor constants of the machine determined by the method according to the present invention. The contact point, also referred to as the touch point, is understood to be the point at which the friction partners come into contact after the air gap has been overcome. The friction brake is particularly configured as an electromechanical drum or disc brake. The corresponding method provides particularly advantageous application possibilities for the determined motor constants. In this specific application case, the determined system parameters advantageously ensure accurate touch point determination, which in turn determines, in particular, the motor position at which the brake lining comes into contact with the brake disc / brake drum.

[0016] A control device having the features of claim 12 is specially designed to carry out at least one of the methods according to the invention, which results in the advantages already mentioned. In particular, the control device is designed as a computer device assigned to a friction brake of a motor vehicle, preferably arranged in the motor vehicle.

[0017] A friction brake with the features of claim 13, which comprises at least two friction partners, and which is assigned an actuator assembly with an electric machine for displacing one of the friction partners towards the other, is characterized by the control device according to the invention, which also results in the advantages already mentioned. The friction brake, as mentioned above, is in particular configured as an electromechanical drum brake or disc brake.

[0018] Further preferred features and feature combinations can be seen from the above description and the claims.The invention will now be explained in more detail with reference to the drawings. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 illustrates an electromechanical drum brake. [Figure 2] 1 is a graph showing the relationship between the rotation rate and the motor current of a drum brake. [Figure 3] FIG. 10 is a diagram illustrating a method for determining parameters of a drum brake. DETAILED DESCRIPTION OF THE INVENTION

[0020] 1 shows in simplified form and without further illustration an exemplary structure of an electromechanical friction brake 1 for a motor vehicle. The friction brake 1 is configured here as a leading-trailing drum brake and comprises here two first friction partners 2 in the form of brake shoes 3, on which brake linings 4 are arranged, and one second friction partner 5 in the form of a brake drum 5. Each of the first friction partners 2 is assigned to a second friction partner 5.

[0021] An actuator assembly 6 having an electric machine 7 is assigned to the friction brake 1 in this case for displacing the respective first friction partner 2 towards the second friction partner 5. The electric machine 7 is in this case interactively connected to a first end of each first friction partner 2, for example by means of a transmission assembly (not shown), so as to be able to exert a corresponding actuating force F on the first friction partner 2. The friction partner 2 is supported in a receiving part 8 so as to be pivotable about a second end remote from the first end.

[0022] In order for a braking moment to actually be generated, the friction partners 2 must first overcome the air gap 1 until the corresponding brake lining 4 abuts against the brake drum 5. To ensure that the brake linings 4 do not come into rubbing contact with the brake drum 5 in the non-actuated state, spring elements 9 attached at one end to each of the two brake shoes 3 act as return springs with a predetermined preload, which urge the two brake shoes 3 towards each other.

[0023] In the following, an advantageous method for determining various parameters of the described actuator assembly 6, in particular the motor constants of the electric machine 7, will be described with reference to Fig. 3. For this purpose, Fig. 3 shows the method on the basis of a flow chart. In particular, this method ensures that parameters that can change, for example due to component variations or wear over the lifespan, are always determined with high precision. In particular, at least one of the methods described below is implemented by a control device specially configured for this purpose.

[0024] The basis of the method is then a simplified state-space model of the actuator assembly 6. The actuator assembly 6 can thus be described sufficiently accurately as a second-order dynamic system. Nonlinearities are primarily the resulting loads due to the stiffness characteristic of the friction brake 1 and friction effects within the actuator assembly 6. Under the assumption that the method is carried out exclusively within the air gap l, the loads can be neglected.

[0025] The air gap then moves between the two motor positions θ L,min and θ L,max and the motor position θ L,min and θ L,max defines the allowable motor position range as the air gap

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[0026] The friction acting against the motor moment is approximated below, which is common in practice and in the literature. The friction model then consists of three parameters in the form of friction coefficients: one viscous friction factor D and two Coulomb factors C, which apply to the actuation and release of the friction brake 1, respectively. + and C - It is depicted by:

[0027] Since the electrical time constant is generally much smaller than the mechanical time constant, exact modeling of the electric machine 6 can be omitted and instead the motor constant K m The operating current I through m and torque τ m The relationship τ between m ≒I m K m can be utilized.

[0028] The differential equation that approximately describes the system behavior (changes in the rotary motor position θ) is therefore:

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[0029] where J is the total rotating bounce mass of the actuator mechanism (generally known), and

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[0030] The positive scalar ε is to be understood as the Karnopp factor and represents the zero speed band. The corresponding rotor position sensor of the electric machine 6 determines the rotational speed, e.g., by the finite difference method.

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[0031] In step S1, the method starts by presetting at least one excitation signal which comprises at least one DC component and one AC component and driving the machine 7 with the excitation signal, in particular only within the air gap l of the friction brake 1, whereby the AC component preferably has at least one harmonic frequency, in particular a number of different harmonic frequencies.

[0032] The excitation signal is thus composed in particular of one DC component I0 and one or more harmonic AC components I k (t)=a k sin(ω k t+φ k ) and consists of:

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[0033] Using multiple harmonics (K>1) is advantageous for obtaining greater robustness in identifying the motor constants, as will be seen in the following paragraphs.

[0034] In step S2, at least one actual value of the motor current of the machine 7 and one actual value of the rotation rate of the rotor shaft of the machine 7 are then determined at each time. Preferably, for this purpose, the excitation signal (I m ) and calculate the actual time transition resulting from it, and calculate the average value as the actual value at each time according to the actual transition. In particular, the actual transition is calculated by dividing the AC component (I k ) over at least two periods. Particularly preferably, the motor constant is averaged over a number of different excitation signals.

[0035] Depending on the DC component selected, transient processes with rotation rate ω(t) (t>T e ) results in a measurable average rotation rate:

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[0036] At this time, it should be noted that |ω|>ε∀t>T e As a result, there is no stick-slip effect, which is not taken into account in the simplified model. For measurement sequences with different I0, it is very easy to calculate the unknown motor constant K via linear interpolation. m The Coulomb factor and viscous friction can be determined according to

[0037] 2 shows the corresponding rotation rate-motor current graph with a number of measurement points for the motor current I and the rotation rate ω. As already mentioned above, the state space model used contains different friction coefficients as further unknowns. Therefore, the motor constant K m Coulomb friction coefficient C of actuator assembly 6 + ,C - and the viscous friction coefficient D.

[0038] The corresponding determination of the coefficient of friction is preferably carried out via a linear fit on the data points. + (friction coefficient C + (relating to) or G - (friction coefficient C - The slopes of (with respect to) are (1 / K m )Equivalent to D.

[0039] The y-axis intersection is (1 / K m )C s The Coulomb friction is different for positive and negative rotation rates in this example (the dashed line shown corresponds to y = (1 / 2K m )(C + +C - )≠0).

[0040] The relationship that follows from this is

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[0041] With N ≥ 2 independent measurements, this system of equations can be solved:

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[0042] In step S3, the motor constants are then determined as a function of the excitation signal and the actual values. One possibility for this is to solve a system of equations by means of a Fourier transform.

[0043] Based on the assumption of a linear model and the principle of superposition, the system and the excitation signals are then divided in particular into several subsystems:

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[0044] Subsystems ω′1,ω′2,...,ω′ K The transfer function in the Laplace domain of

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[0045] Frequency ω1,ω2,...,ω K via the absolute values ​​of the Fourier coefficients of the rotation rate signal ω(t) at

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[0046] In the first experiment, a frequency of 10-20 Hz and an amplitude of approximately 1 A were used. k was found to be advantageous.

[0047] A second, alternative possibility is to use the motor constant K mis determined depending on the preload and / or return moment of the spring element 9 of the actuator assembly 6.

[0048] As can be seen in Figure 2, the Coulomb friction in an electromechanical drum brake with a return spring can depend on the sign of the rotation rate (different friction when applied than when released). The difference results from the preload of the return spring and the friction in the suspension of the brake shoe.

[0049] The preload of the return spring and the resulting return moment τ F When the friction in the brake shoe suspension is negligible, the motor constant K m can be found after identifying A (see previous paragraph):

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[0050] The method then ends with step S4. Optionally, the just determined motor constant and / or at least one of the above-mentioned friction coefficients may then be used to determine another parameter or used as an input quantity for a method based thereon.

[0051] On the one hand, the method can be a method for determining the error state and / or wear state of a friction brake, where the error state and / or wear state are determined based on the determined motor constant K of the machine 7. m Depending on the motor constant K m and / or motor constant K m The friction coefficients D and C calculated as described above are + ,C - is determined by comparing at least one of the above with a preset threshold and / or tolerance band.

[0052] For example, when the determined system parameters are outside the tolerance band, i.e. when for example the motor constants are below a preset threshold and / or the viscous friction coefficients are above a preset threshold:

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[0053] On the other hand, the method can be a method for determining the contact points of the friction partners 2, 5 of the friction brake 1. Here, the contact points of the friction partners are determined by the motor constant K m is calculated in particular by a load moment estimator.

[0054] Thus, in particular, a load moment estimator is implemented based on the simplified linear actuator model described above, where the model is based on the virtual state variables

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[0055] term

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[0056] 1 Electromechanical friction brake 2. First Friction Partner 3 Brake shoes 4. Brake linings 5 Second friction partner: brake drum 6 Actuator Assembly 7 Electrical Machinery 8 Receiving part 9 Spring Elements F Operating force G + straight line G - straight line I Motor current Air gap S1 Step S2 Step S3 Step S4 Step ω rotation rate

Claims

1. The motor constant (K) of the electric machine (7), in particular the electric machine (7) of the actuator assembly (6) ｍ ) a method for determining At least one DC component (I ０ ) and one AC component (I ｋ ) and at least one excitation signal (I ｍ ) preset, The machine (7) is connected to the excitation signal (I ｍ ) and drive control, determining at each time at least one actual value of the motor current of the machine (7) and one actual value of the rotation rate (ω) of the rotor shaft of the machine (7); The excitation signal (I ｍ ) and the motor constant (K ｍ ) A method for determining the motor constants of an electric machine, particularly an electric machine of an actuator assembly.

2. At each time, the motor current and the rotation rate (ω) of the excitation signal (I ｍ 2. The method according to claim 1, further comprising determining the resulting actual time course from the actual time course, and determining the mean value as the current actual value as a function of the actual time course.

3. The actual transition is expressed as the AC component (I ｋ 3. The method of claim 2, wherein the time period is determined over at least two periods of the time period.

4. The AC component (I ｋ 4. The method according to claim 1, wherein the frequency of the signal is at least one harmonic frequency, in particular a number of different harmonic frequencies.

5. A number of different excitation signals (I ｍ ) by the motor constant (K ｍ 5. The method according to claim 1, wherein the average value of the values ​​of the parameters is determined.

6. The motor constant (K ｍ 6. The method according to claim 1, wherein the sigma is determined by Fourier transformation.

7. The machine (7) is a component of an actuator assembly (6), The motor constant (K ｍ ) to at least one Coulomb coefficient of friction (C ＋ , C － ) and / or viscous friction coefficient (D), 7. The method according to any one of claims 1 to 6, characterized in that

8. The machine (7) is a component of an actuator assembly (6), The motor constant (K ｍ ) depending on the preload and / or return moment of the spring element (9) of the actuator assembly (6); 8. The method according to claim 1, wherein the

9. said machine (7) being a component of an actuator assembly (6) of a friction brake (1) of a motor vehicle; The machine (7) is driven and controlled by the excitation signal only within the air gap of the friction brake (1).

9. The method according to any one of claims 1 to 8, characterized in that

10. A method for determining the error state and / or wear state of a friction brake (1) of a motor vehicle having at least two friction partners (2, 5), in particular an electromechanical drum brake, comprising: The friction brake (1) is assigned an actuator assembly (6) having an electric machine (7) for displacing one of the friction partners (2) towards the other friction partner (5), In the method, The error and / or wear state is determined by the motor constant (K) of the machine (7) determined by the method according to any one of claims 1 to 9. ｍ ), in particular, depending on the motor constant (K ｍ ) and / or the motor constant (K ｍ Friction coefficient (D, C) ＋ , C － ) by comparing it with a preset threshold and / or tolerance band; 10. A method for determining the error state and / or wear state of a friction brake, in particular an electromechanical drum brake, of a motor vehicle having at least two friction partners, characterized in that:

11. A method for determining the contact point of two friction partners (2, 5) of a friction brake (1) of a motor vehicle, in particular an electromechanical drum brake, comprising: The friction brake (1) is assigned an actuator assembly (6) having an electric machine (7) for displacing one of the friction partners (2) towards the other friction partner (5), In the method, The contact points of the friction partners are calculated based on the motor constant (K ｍ ) depending on the load moment estimator, 10. A method for determining the contact point of two friction partners of a friction brake, in particular an electromechanical drum brake, of a motor vehicle, characterized in that:

12. 12. A control device, characterized in that the control device is specially configured to carry out the method according to any one of claims 1 to 9, the method according to claim 10 and / or the method according to claim 11.

13. A friction brake (1) for a motor vehicle, in particular an electromechanical drum brake, at least two friction partners (2, 5), The friction brake (1) is assigned an actuator assembly (6) having an electric machine (7) for displacing one of the friction partners (2) towards the other friction partner (5), In the friction brake (1), A control device according to claim 12, Friction brakes in automobiles, especially electromechanical drum brakes.

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