Method for automating the determination of pressure-volume characteristic curves for brake caliper devices

Abstract

The present invention relates to a method for determining a pressure-volume characteristic curve (2, 6, 9) of a brake caliper device, where the pressure-volume characteristic curve (2, 6, 9) is formed from several pressure-volume data pairs (3), and for each pressure-volume data pair (3) a pressure interpolation value is assigned to a volumetric interpolation value. The objective is to provide a method for automatically determining the pressure-volume characteristic curve (2, 6, 9), said method being able to reduce inaccuracies in the pressure-volume characteristic curve (2, 6, 9) due to wear and manufacturing tolerances of the brake caliper device. The objective is achieved by the fact that the volumetric interpolation value is determined by a compensation calculation on several auxiliary pressure-volume data pairs (4, 5).

Description

[Technical Field]

[0001] The present invention relates to a method for determining a pressure-volume characteristic curve for a brake caliper device, wherein the pressure-volume characteristic curve is formed from several pressure-volume data pairs, and in each pressure-volume data pair, a pressure interpolation is assigned to a volume interpolation. [Background technology]

[0002] Such a brake caliper device can be used, for example, in an automobile. The behavior of the brake caliper device during the braking process of the automobile is described in terms of hydraulic control by a pressure-volume characteristic curve, which shows the volume as a function of pressure. The pressure-volume characteristic curve thus defines the volume that must be displaced in the brake caliper of the brake caliper device in order to generate a desired pressure in the brake piston of the brake caliper of the brake caliper device.

[0003] Here, the pressure-volume characteristic curve is conventionally determined manually based on several pressure-volume data pairs. Thus, for example, 10 pressure-volume data pairs are manually fitted to determine the pressure-volume characteristic curve for a brake caliper device with the aid of an external measurement device. On the one hand, this manual fitting of the pressure-volume characteristic curve involves a great deal of effort, is time-consuming, prone to errors, and may need to be repeated in some cases. On the other hand, manual fitting also cannot accommodate possible individual differences or changes in the pressure-volume characteristic curve over the service life of the brake caliper device.

[0004] Manual determination of the pressure-volume characteristic curve is typically performed as part of a development project for a given type of brake caliper device, where the pressure-volume characteristic curve is clearly defined near the end of the development project based on the applied pressure-volume characteristic curve of the brake caliper device measured or specifications within the development project. However, for some brake caliper devices of the same design, such pressure-volume characteristic curves may differ due to manufacturing tolerances. As a result, the accuracy of the pressure-volume characteristic curve may be less accurate during operation of the brake caliper device than that determined during the development project.

[0005] In addition, after the development project, during operation of the brake caliper device, the brake pads and brake discs of the brake caliper device wear, which also changes the pressure-volume characteristic curve, typically reducing the volume absorption capacity of the brake caliper (i.e., increasing the stiffness of the brake caliper). As the brake caliper device gradually wears, further inaccuracies occur in the pressure-volume characteristic curve.

[0006] Generally, such inaccuracies in the pressure-volume characteristic curve lead to a decrease in the quality of the pressure control and also to a decrease in the robustness of the brake caliper device. It should be noted that the pressure-volume characteristic curve is also used in other parts of the vehicle software, such as volume-based safety monitors or volume-based controls. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention is therefore based on the object of providing an automatic method for determining the pressure-volume characteristic curve, which makes it possible to reduce the inaccuracies in the pressure-volume characteristic curve due to wear and manufacturing tolerances of the brake caliper device. [Means for solving the problem]

[0008] The above objectives are achieved in accordance with the present invention by determining a volume interpolation value by a compensation calculation on several auxiliary pressure-volume data pairs.

[0009] The auxiliary pressure-volume data pairs can be predefined, which eliminates the need for manual selection of the auxiliary pressure-volume data pairs. Standardization reduces the effort required for manual fitting of the pressure-volume characteristic curve. The determination of the pressure-volume characteristic curve can also be automated by performing compensation calculations on the auxiliary pressure-volume data pairs. This simplifies the fitting of the pressure-volume characteristic curve overall. The method according to the present invention is therefore also suitable for two basic applications. On the one hand, the method according to the present invention can be used to calibrate the pressure-volume characteristic curve as part of a development project (end-of-line, workshop, or series application). On the other hand, the method according to the present invention can be used to perform automatic fitting of the pressure-volume characteristic curve when the brake caliper device wears during operation. It should be noted that the influence of the temperature of the brake fluid or brake disc of the brake caliper device can be ignored in the determination of the pressure-volume characteristic curve or can be eliminated by carefully selected ambient conditions. This is because these parameters only cause temporary changes in the pressure-volume characteristic curve compared to wear. Generally, this can counteract the problems of reduced control quality and reduced robustness of the hydraulic monitor.

[0010] Here, auxiliary pressure-volume data pairs in the local vicinity of a pressure interpolant assigned to a volume interpolant advantageously have auxiliary pressure interpolants that are smaller and / or larger than the assigned pressure interpolant.

[0011] As part of the method, several pressure-volume data pairs for determining a pressure-volume characteristic curve are first selected for this purpose. For example, pressure interpolations of the pressure-volume characteristic curve are selected and predefined for this purpose. These pressure interpolations preferably cover the entire range of values ​​of the software signal related to the pressure of the brake caliper device. For example, the pressure interpolations can be selected and defined from 0, 1.25, 2.5, 5, 10, 20, 40, 80, 160, and 327 bar. In a next step, auxiliary pressure interpolations are formed for each of these predefined pressure interpolations. For example, 10 auxiliary pressure interpolations can be selected in a local neighborhood below the specified pressure interpolation. Additionally or alternatively, 10 additional auxiliary pressure interpolations can be selected in a local neighborhood above the specified pressure interpolation. The local neighborhood should be adjusted as close as possible to the specified pressure interpolation. Thus, for example, if a pressure interpolation of 1.25 bar is selected, the local neighborhood below this specified pressure interpolation may be set to, for example, the pressure interval [0.75 bar, 1.25 bar]. The local neighborhood above the specified pressure interpolation may be the interval [1.25 bar, 1.75 bar]. These auxiliary pressure-volume data pairs are acquired and stored.

[0012] Additionally, the compensation calculation preferably determines, preferably by a least squares method, a regression function for the auxiliary pressure-volume data pairs that indicates volume as a function of pressure in a local neighborhood.

[0013] The determination of each volume interpolation value for the assigned pressure interpolation value is performed using the acquired auxiliary pressure-volume data pairs. For this purpose, a regression function for the auxiliary pressure-volume data pairs is determined to remove outliers from the measurement data. This regression function can be determined, for example, using the least squares method. For example, the regression function can be a second-order polynomial. In this way, the regression function groups the determined auxiliary pressure-volume data pairs together in the best possible way.

[0014] It is also advantageous that the volume interpolant is determined as a function value of the regression function at the location of the assigned pressure interpolant.

[0015] The regression function can group the determined auxiliary pressure-volume data pairs together in the best possible way and reliably exclude outliers from the measurement data. Thus, a volume interpolation value for a predefined pressure interpolation value is determined by using the function value of the regression function at the position of each pressure interpolation value as a basis. Thus, the determination of the pressure-volume characteristic curve is less prone to errors overall. The time required to determine the pressure-volume characteristic curve can be reduced.

[0016] In all of this, it is also advantageous that the auxiliary pressure-volume data pairs are measured by a sensor device on the brake caliper device and / or determined by estimation.

[0017] To be as accurate as possible, the determination of the pressure-volume characteristic curve theoretically requires a pressure rise in the brake caliper device of up to 327 bar. However, this is not possible simply because the brake caliper is rigid. Furthermore, such a high pressure rise is not advisable due to the load cycle (alternating bending stress). Therefore, in principle, the sensor device on the brake caliper device can only determine auxiliary pressure-volume data pairs up to a range of 160 bar. Therefore, in calibrating the pressure-volume characteristic curve, it is recommended to use auxiliary pressure-volume data pairs up to 160 bar, because this calibration is more than a static tool for determining the pressure-volume characteristic curve in one go. However, it is impossible to adapt the pressure-volume characteristic curve to the wear of the brake caliper device because these data pairs are obtained from the normal operation of the brake caliper device, which generally results in significantly lower pressures. Nevertheless, despite the absence of data from the sensor device, the pressure-volume characteristic curve in both types of operation should be able to map the entire range of pressure interpolation values ​​as far as possible, i.e., up to a pressure of, for example, 327 bar. To this end, the missing sensor data can be supplemented by the estimation of auxiliary pressure-volume data pairs in pressure ranges that are not accessible by measurement.

[0018] Here, the estimation is preferably performed in the linear region of the pressure-volume characteristic curve by extrapolation of several auxiliary pressure-volume data pairs measured in the linear region.

[0019] The estimation of the auxiliary pressure-volume data pairs is performed separately for low and high pressures. Here, the following characteristics of the brake caliper of the brake caliper device are utilized: In the high-pressure range (above approximately 80 bar), the pressure-volume characteristic curve is almost exclusively determined by the influence of the "rigid" components of the brake caliper (the material of the brake caliper housing). As a result, in these high-pressure ranges, the pressure-volume characteristic curve is approximately a linear relationship. Therefore, if sensor data up to the high-pressure range is available, the linear relationship allows a linear extrapolation of the desired volume interpolation value even at higher pressures (for which no measurement data is available).

[0020] Alternatively, it is advantageously provided that an estimate is made in the non-linear region of the pressure-volume characteristic curve by translating the auxiliary pressure-volume characteristic curve from several auxiliary pressure-volume data pairs measured in the non-linear region.

[0021] This type of estimation is advantageous in the low-pressure range (up to approximately 80 bar) because the influence of the "soft" components of the brake caliper (seals, brake linings, etc.) dominates. As a result, the pressure-volume characteristic curve in this low-pressure range is nonlinear, and the influences of the soft and hard components of the brake caliper are superimposed. Therefore, if only measurement data from the sensor device in the low-pressure range are available, these measurement data cannot be simply extrapolated due to the nonlinear relationship. However, in this range, there may already be measured data from previous measurements by the sensor device (e.g., from a previous calibration), which form an auxiliary pressure-volume characteristic curve in this range. This auxiliary pressure-volume characteristic curve can then be used for estimation and translated by an appropriate volume difference for the required (although unmeasured) data pair. In this way, the pressure-volume characteristic curve at low pressures can be determined and adapted to the wear of the brake caliper device even during operation. However, this adaptation should not be noticeable to the user of the brake caliper device here. Therefore, the pressure-volume characteristic curve should not change significantly in a short time. For this reason, a maximum learning increment may be used in fitting the pressure-volume characteristic curve, so that the pressure-volume characteristic curve only slowly approaches the actual pressure-volume characteristic curve over several fits, but does not approach it abruptly.

[0022] Finally, it is advantageous if the pressure-volume characteristic curve is determined so that it progresses strictly monotonically and / or concavely and / or its derivative has only one maximum value over the entire range of pressure interpolations.

[0023] Before a particular pressure-volume characteristic curve is finally used in a brake caliper device, it must be checked to see if it satisfies certain mathematical criteria: the pressure-volume characteristic curve must progress strictly monotonically, the maximum deviation of the pressure-volume characteristic curve over the useful life of the brake caliper device due to wear must be 30%, the progression of the pressure-volume characteristic curve must be concave, and the derivative of the pressure-volume characteristic curve must have only one maximum value over the entire range of pressure interpolation values ​​(e.g., from 0 bar to 327 bar). These criteria can be derived from empirical data for the most common volume consumable parts (disc brakes, low-resistance brake calipers, drum brakes, and spring consumable parts).

[0024] Finally, the determination of the pressure-volume characteristic curve is advantageously carried out during operation of the brake caliper device and used to compensate for the effects of wear of the brake caliper device.

[0025] This ensures high accuracy of the pressure-volume characteristic curve even as the brake caliper device wears over its service life, ensuring improved quality of hydraulic control and robustness of the hydraulic monitor during operation.

[0026] The above-mentioned characteristics, features, and advantages of the present invention, as well as the manner in which they are achieved, will become clearer and more easily understood in connection with the following description of the embodiments, which is set forth in conjunction with the drawings. [Brief explanation of the drawings]

[0027] [Figure 1] 1 shows pressure-volume characteristic curves at pressure interpolation values ​​with several auxiliary pressure-volume data pairs. [Figure 2] 1 shows an estimate of the pressure-volume characteristic curve. DETAILED DESCRIPTION OF THE INVENTION

[0028] In FIG. 1, there is a pressure-volume diagram 1 illustrating a pressure-volume characteristic curve 2 of a brake caliper device. This pressure-volume characteristic curve 2 shows the volume (vertical axis of the pressure-volume diagram 1) depending on the pressure (horizontal axis of the pressure-volume diagram 1). Thus, the pressure-volume characteristic curve 2 defines the volume that must be displaced within the brake caliper of the brake caliper device to generate a desired pressure on a brake piston of the brake caliper of the brake caliper device.

[0029] To determine the pressure-volume characteristic curve 2, the pressure range is first divided into several pressure interpolations. For example, ten pressure interpolations can be predefined at 0, 1.25, 2.5, 5, 10, 20, 40, 80, 160, and 327 bar, covering the entire range of values ​​of the software signal of the pressure interpolations for a brake caliper device. In FIG. 1, a local neighborhood around the pressure interpolation of 1.25 bar is shown as an example. For this pressure interpolation, a volume interpolation can be determined by the method according to the invention. In the illustrated example, this volume interpolation is 0.2 cm. 3 The pressure interpolation value together with the volume interpolation value forms a pressure-volume data pair 3.

[0030] In the illustrated example, a pressure interpolation of 1.25 bar is predefined. To determine the associated volume interpolation of pressure-volume data pair 3, auxiliary pressure-volume data pairs 4, 5 are used according to the present invention. Here, a first set of auxiliary pressure-volume data pairs 4 is specified for auxiliary pressure interpolations below the 1.25 bar pressure interpolation. These auxiliary pressure interpolations can be found in the interval [0.75 bar, 1.25 bar] in the local vicinity of the 1.25 bar pressure interpolation. Furthermore, a second set of auxiliary pressure-volume data pairs 5 is specified for auxiliary pressure interpolations above the 1.25 bar pressure interpolation. These auxiliary pressure interpolations can be found in the interval [1.25 bar, 1.75 bar] in the local vicinity of the 1.25 bar pressure interpolation. In the example of FIG. 1, the first set of auxiliary pressure-volume data pairs 4 includes 10 auxiliary pressure-volume data pairs. The second set of auxiliary pressure-volume data pairs 5 includes, in the example of FIG. 1, 10 auxiliary pressure-volume data pairs. To eliminate outliers in the measurement data, a second-order polynomial, shown in the example shown, is calculated by the least-squares method and placed through the auxiliary pressure-volume data pairs 4, 5 as a regression function. In this way, the stored auxiliary pressure-volume data pairs 4, 5 are grouped together in the best possible way. The calculated polynomial then calculates a 0.2 cm for a specified pressure interpolation value of 1.25 bar. 3 is used to determine the volume interpolated value of . Thus, the determination of the pressure-volume characteristic curve 2 is less prone to errors overall. The time taken to determine the pressure-volume characteristic curve can be reduced.

[0031] To be as accurate as possible, the determination of the pressure-volume characteristic curve 2 theoretically requires a pressure rise in the brake caliper device of up to 327 bar. However, this is not possible simply because the brake caliper is rigid. Furthermore, such a high pressure rise is not advisable due to the load cycle (alternating bending stress). Therefore, in principle, the sensor device on the brake caliper device can only determine auxiliary pressure-volume data pairs 4, 5 in the range of up to 160 bar. Therefore, in calibrating the pressure-volume characteristic curve 2, it is recommended to use auxiliary pressure-volume data pairs 4, 5 up to 160 bar, since this calibration is more than a static tool for determining the pressure-volume characteristic curve 2 in one go. However, it is impossible to adapt the pressure-volume characteristic curve 2 to the wear of the brake caliper device, since these data pairs are obtained from the normal operation of the brake caliper device, which generally results in significantly lower pressures. Nevertheless, despite the absence of data from the sensor device, the pressure-volume characteristic curve 2 in both types of operation should be able to map the entire range of pressure interpolation values ​​as far as possible, i.e., up to a pressure of, for example, 327 bar. To this end, the missing sensor data can be supplemented by the estimation of auxiliary pressure-volume data pairs 4, 5 in pressure ranges that are inaccessible by measurement. The estimation of auxiliary pressure-volume data pairs 4, 5 is performed separately for low and high pressures.

[0032] FIG. 2 shows in detail the estimation of the auxiliary pressure-volume data pairs 4, 5. Here, the following characteristics of the brake caliper of a brake caliper device are utilized: In the high-pressure range (above approximately 80 bar), the pressure-volume characteristic curve 2 is almost exclusively determined by the influence of the "stiff" components of the brake caliper (the material of the brake caliper housing). As a result, in these high-pressure ranges, the pressure-volume characteristic curve 2 is approximately a linear relationship. Therefore, if sensor data up to the high-pressure range is available, the linear relationship allows a linear extrapolation 6 of the sought volume interpolation value to be performed at even higher pressures (for which no measurement data is available).

[0033] The estimation is performed by translation in the low-pressure range. This is because the influence of the "soft" components of the brake caliper (seals, brake linings, etc.) dominates in the low-pressure range (up to approximately 80 bar). As a result, the pressure-volume characteristic curve 2 in this low-pressure range is nonlinear, and the influences of the soft and hard components of the brake caliper are superimposed. Therefore, if only measurement data from the sensor device in the low-pressure range are available, these measurement data cannot be simply extrapolated due to the nonlinear relationship. However, in this range, there may already be measured data from previous measurements by the sensor device (e.g., from a previous calibration), which form an auxiliary pressure-volume characteristic curve 7 in this range. This auxiliary pressure-volume characteristic curve 7 can then be used for the estimation and translated by an appropriate volume difference 8 for the required data pair. In this way, an adapted pressure-volume characteristic curve 9 at low pressure can be determined, even during operation of the brake caliper device, and can be adapted to the wear of the brake caliper device.

[0034] While the present invention has been more particularly illustrated and described in terms of preferred embodiments, it is not intended to be limited to the disclosed examples. The present invention may also include the following aspects: 1. A method for determining a pressure-volume characteristic curve (2, 6, 9) of a brake caliper device, wherein the pressure-volume characteristic curve (2, 6, 9) is formed from several pressure-volume data pairs (3), and in each pressure-volume data pair (3), a pressure interpolation value is assigned to a volume interpolation value, wherein the volume interpolation value is determined by a compensation calculation on several auxiliary pressure-volume data pairs (4, 5). 2. The method described in claim 1, wherein the auxiliary pressure-volume data pairs (4, 5) in the local vicinity of the pressure interpolation assigned to the volume interpolation have auxiliary pressure interpolations that are smaller and / or larger than the assigned pressure interpolation. 3. The method according to claim 2, wherein the compensation calculation determines, preferably by a least squares method, a regression function for the auxiliary pressure-volume data pairs (4, 5) that indicates the volume as a function of the pressure in the local vicinity. 4. The method of claim 3, wherein the volume interpolation value is determined as a function value of the regression function at the location of the assigned pressure interpolation value. 5. A method according to any one of 1. to 4. above, wherein the auxiliary pressure-volume data pair (4, 5) is measured by a sensor device on the brake caliper device and / or determined by estimation. 6. The method according to claim 5, wherein the estimation is performed in the linear region of the pressure-volume characteristic curve (2, 6, 9) by extrapolation (6) of several auxiliary pressure-volume data pairs (4, 5) measured in the linear region. 7. The method described in 5. above, wherein the estimation is performed in a nonlinear region of the pressure-volume characteristic curve (2, 6, 9) by translating the auxiliary pressure-volume characteristic curve (7) from several auxiliary pressure-volume data pairs (4, 5) measured in the nonlinear region. 8. A method according to any one of 1. to 7. above, wherein the pressure-volume characteristic curve (2, 6, 9) is determined to progress in a strictly monotonically increasing manner and / or to progress concavely and / or its derivative has only one maximum value over the entire range of the pressure interpolation values. 9. A method according to any one of 1. to 8. above, wherein the determination of the pressure-volume characteristic curve (2, 6, 9) is carried out during operation of the brake caliper device and is used to compensate for the effects of wear of the brake caliper device. [Explanation of symbols]

[0035] 1 Pressure-Volume Diagram 2 Pressure-volume characteristic curve 3 Pressure-Volume Data Pairs 4. Auxiliary Pressure-Volume Data Pairs 5. Auxiliary Pressure-Volume Data Pairs 6 Linear extrapolation 7. Auxiliary pressure-volume characteristic curve 8 Volumetric Difference 9 Fitted pressure-volume characteristic curve

Claims

1. 1. A method for automating the determination of a pressure-volume characteristic curve (2, 6, 9) of a brake caliper device, wherein the pressure-volume characteristic curve (2, 6, 9) is formed from several pressure-volume data pairs (3), and for each pressure-volume data pair (3), a pressure interpolation is assigned to a volume interpolation, wherein the volume interpolation is determined by a compensation calculation performed by a computer on several auxiliary pressure-volume data pairs (4, 5).

2. 2. The method of claim 1, wherein the auxiliary pressure-volume data pairs (4, 5) in a local neighborhood of the pressure interpolant assigned to the volume interpolant have auxiliary pressure interpolants that are smaller and / or larger than the assigned pressure interpolant.

3. 3. The method of claim 2, wherein said compensation calculation determines, preferably by a least squares method, a regression function for said auxiliary pressure-volume data pairs (4, 5) indicating said volume as a function of said pressure in said local neighborhood.

4. The method of claim 3 , wherein the volume interpolant is determined as a function value of the regression function at the location of the assigned pressure interpolant.

5. The method according to any one of claims 1 to 4, wherein the auxiliary pressure-volume data pair (4, 5) is measured by a sensor device on the brake caliper device and / or determined by estimation.

6. 6. The method of claim 5, wherein the estimation is performed in a linear region of the pressure-volume characteristic curve by extrapolation (6) of several auxiliary pressure-volume data pairs (4, 5) measured in the linear region.

7. 6. The method of claim 5, wherein the estimation is performed in a nonlinear region of the pressure-volume characteristic curve (2, 6, 9) by translating the auxiliary pressure-volume characteristic curve (7) from several auxiliary pressure-volume data pairs (4, 5) measured in the nonlinear region.

8. 5. The method according to claim 1, wherein the pressure-volume characteristic curve (2, 6, 9) is determined so that it progresses strictly monotonically increasing and / or concavely and / or its derivative has only one maximum value over the entire range of the pressure interpolated values.

9. 5. The method according to claim 1, wherein the determination of the pressure-volume characteristic curve (2, 6, 9) is performed during operation of the brake caliper device and is used to compensate for the effects of wear of the brake caliper device.

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