Method for controlling an electromechanical vehicle brake comprising a diagnostic step for detecting a malfunction of the electromechanical vehicle brake due to icing

Abstract

A method for controlling an electromechanical vehicle brake comprising a first brake element, a second brake element, and an electromechanical actuator, wherein the actuator is configured to bring the first brake element into contact with the second brake element to generate a braking effect and to release the first brake element from the second brake element to terminate the braking effect, the method comprising: performing a diagnostic step in which the actuator is driven to move in a first direction with a force limited compared to a maximum possible force, and in which, based on the distance traveled, it is determined whether the vehicle brake is malfunctioning; if the diagnostic step reveals that the vehicle brake is malfunctioning, performing a malfunction identification step.in which the actuator is driven with maximum force in a second direction opposite to the first direction, and in which the distance traveled is used to determine whether the vehicle brake is malfunctioning due to icing, and if a malfunction due to icing is found in the malfunction identification step, a de-icing step is performed in which the actuator is driven to move in the first direction with a force limited compared to the maximum force.

Description

The present disclosure relates to a method for controlling an electromechanical vehicle brake according to claim 1, an electromechanical vehicle braking system according to claim 9 and a vehicle according to claim 10, comprising such an electromechanical braking system. Electromechanical vehicle brakes have recently gained in importance. Unlike conventional hydraulic vehicle brakes, electromechanical vehicle brakes allow for the generation of individual wheel braking force. Similar to hydraulic vehicle brakes, low ambient temperatures can impair the functionality of electromechanical vehicle brakes, particularly if an electromechanical actuator of the brake system freezes up. This can cause, for example, reduced braking performance, brake overheating, or increased wear of the brake or other components. For example, AT 516 356 A1 describes a method and a device for de-icing brake actuators of a rail vehicle, wherein the brake actuators are designed as pneumatic or hydraulic systems. In this process, the brake actuators are moved from a rest position to a de-icing position, and then an opening force opposing a closing force is applied to remove the icing. Furthermore, a method for controlling an electromechanical vehicle brake is known from DE 10 2023 206 378 A1, wherein the electromechanical vehicle brake can be designed as a parking brake and can comprise a first brake element, a second brake element, and an electromechanical actuator. In a diagnostic step, the current condition, for example, due to ice deposits, is determined, and the vehicle brake is controlled accordingly. In this context, a jerky actuation of the vehicle brake to dislodge dirt or ice can also be provided. The purpose of the present disclosure is to provide a method for controlling an electromechanical vehicle brake and an electromechanical vehicle brake system, with which an icing condition of an electromechanical vehicle brake can be detected and rectified. In a first aspect of the present disclosure, this problem is solved by a method for controlling an electromechanical vehicle brake, which comprises a first brake element, a second brake element, and an electromechanical actuator, wherein the actuator is configured to bring the first brake element into contact with the second brake element to generate a braking effect and to release the first brake element from the second brake element to terminate the braking effect, wherein the method comprises: performing a diagnostic step in which the actuator is driven to a movement in a first direction with a force limited compared to a maximum force, and in which, based on the distance traveled, it is determined whether the vehicle brake has a malfunction; if the diagnostic step reveals that the vehicle brake has a malfunction, performing a malfunction identification step.in which the actuator is driven with maximum force in a second direction opposite to the first direction, and in which the distance traveled is used to determine whether the vehicle brake is malfunctioning due to icing, and if a malfunction due to icing is found in the malfunction identification step, a de-icing step is performed in which the actuator is driven to move in the first direction with a force limited compared to the maximum force. The electromechanical actuator can, for example, comprise an electric motor and a rotary-translational gearbox designed to convert the rotary motion of the electric motor's shaft into a translational motion. This translational motion allows the first brake element to be moved towards or away from the second brake element. The first brake element can, for example, be a brake pad and the second brake element a brake disc. The force used to control an actuator can be regulated by the electrical power supplied to the actuator, such as an electric motor. A maximum force thus corresponds to the maximum electrical power that can be supplied to the actuator. The distance traveled can be a change in the rotational position of an electric motor shaft or a spindle of a rotary-translation gearbox, the distance traveled by a nut of the rotary-translation gearbox that is fixed to a housing, or the displacement of the first brake element. The distance traveled can be determined using a suitable position sensor. The distance traveled can be determined after the actuator has been powered with a predetermined electrical current for a predetermined duration. In other words, a predetermined electrical current is supplied to the actuator for a predetermined time interval, and then the distance traveled by the actuator within that time interval is determined. The present method allows for the determination, based on a simple comparison of the distance traveled with respective threshold values, of whether the vehicle brake is malfunctioning and whether the malfunction is due to ice formation on the actuator or the brake elements. If a malfunction due to icing is detected, a further measure can be taken to remove the icing by moving the actuator in a defined manner, i.e., without additional means. To detect a malfunction, the travel distance during actuator activation in the diagnostic step can first be compared with an initial threshold value, which can be predefined. If the comparison shows that the travel distance is shorter than the initial threshold value, it can be assumed that a malfunction in the vehicle brakes is present. In the subsequent malfunction identification step, it can then be determined what type of malfunction it is, i.e., whether there is icing of the vehicle brake or a malfunction that has another cause, such as a mechanical jam or an electrical problem. In the malfunction identification step, it can be determined that a malfunction is due to icing if the distance traveled in the malfunction identification step is longer than a second threshold that is smaller than the first threshold, and that a malfunction not attributable to icing is present if the distance traveled in the malfunction identification step is smaller than the second threshold. These criteria are based on the fact that, in the case of icing, the actuator can be electrically controlled, and the ice that has formed allows the first brake element to move, at least within a narrow range. Therefore, it is assumed that if the distance traveled is shorter than the first threshold but longer than the second threshold, a malfunction is due to icing. If, however, the distance traveled is shorter than the second threshold, it can be assumed that either the actuator cannot be controlled or that another mechanical problem exists which, even when the actuator is controlled with maximum force, does not allow for a significant movement of the first brake caliper. In this case, it can be assumed that the problem cannot be resolved without a more in-depth investigation, which, for example, can only be carried out in a specialist workshop. In such a case, a corresponding warning message can be issued to the driver to initiate such an investigation. If, however, the malfunction identification step reveals that a malfunction is due to icing, an attempt is made to resolve the malfunction by appropriately reversing the actuator's movement in the first direction to save time and avoid additional costs. After the de-icing step, it can be checked whether the distance traveled during the de-icing step—that is, whether the actuator was activated for a predetermined period—is longer than the initial threshold. If the distance traveled exceeds the first threshold, it can be assumed that de-icing was successful. Conversely, if the distance traveled is less than the first threshold, it is assumed that de-icing was not yet successful. Therefore, the malfunction identification step can then be repeated. The malfunction identification step and the de-icing step can be performed cyclically a predetermined number n1 of times, unless one of the following conditions occurs: on the nth execution of the malfunction identification step, it is found that the distance traveled during the execution of the nth malfunction identification step is shorter than the second threshold, where n is less than or equal to n1, and after the nth execution of the de-icing step, it is found that the distance traveled during the execution of the nth de-icing step is greater than the first threshold, where n is less than n1. This means that the procedure executes a loop in which the malfunction identification step, the de-icing step, and the comparison of the distance traveled with the first threshold are performed sequentially and cyclically. The execution of the loop is interrupted if a malfunction is detected during a specific execution of the malfunction identification step that does not indicate icing, or if the de-icing was successful. However, if, after the nth execution of the de-icing step, it is determined that the distance traveled during the nth de-icing step is still shorter than the initial threshold, a warning message can be issued to the driver, urging them to have the vehicle inspected at a specialist workshop. The procedure can then be terminated. The process may begin with a temperature measurement step in which an outside temperature is recorded, which can be used to assess whether icing is possible. The problem defined at the outset is solved in a second aspect of the present disclosure by an electromechanical vehicle braking system comprising: an electromechanical vehicle brake comprising: a first brake body, a second brake body and an electromechanical actuator, wherein the actuator is configured to bring the first brake body into contact with the second brake body to generate a braking effect and to release the first brake body from the second brake body to terminate the braking effect, and a control device configured to control the electromechanical vehicle brake according to a method described above. Furthermore, a vehicle is provided which has a previously described electromechanical vehicle braking system. The present invention is explained in more detail below with reference to the accompanying drawings. Fig. 1 is a schematic representation of an electromechanical vehicle brake. Fig. 2 shows a flowchart of an exemplary method for controlling the vehicle brake shown in Fig. 1. Fig. 3 shows various characteristic curves that are characteristic of the respective states of the electromechanical vehicle brake shown in Fig. 1. Fig. 1 is a schematic representation of an electromechanical vehicle brake 100. The vehicle brake 100 comprises a first brake element 102, a second brake element 104, and an electromechanical actuator 106, which is configured to bring the first brake element 102 into contact with the second brake element 104 to generate a braking effect and to release the first brake element 102 from the second brake element 104 to terminate the braking effect. The first brake element 102 can, for example, be a brake pad and the second brake element 104 a brake disc. The electromechanical actuator 106 can include: an electric motor 108 and a rotary-translational gear 110, which is designed to convert a rotary motion provided by the electric motor 108 into a translational motion, by means of which the first brake body 102 can be moved towards or away from the second brake body 104. The rotary-translational gear unit 110 can have a first part 112 rotatable by the electric motor 108 and a second part 114 that can be translationally displaced along arrow x. The first part 112 can be rotatably supported on a housing 116 via bearings 112a, 112b. The second part 114 can be rotationally fixed to the housing 116 and slidably mounted relative to the housing 116. The electric motor 108 can be controlled by a control unit 118. The electromechanical vehicle brake 100 and the control unit 118 form an electromechanical braking system 120. In a fault-free state, the second part 114, which is connected to the first brake body 102, is moved along the direction x from the electric motor 108 towards the second brake body 104 to provide a clamping force (braking force), or moved away from it to release the clamping force. The second part 114 is in contact with the housing 116 at the position indicated by reference numeral 114a. At low temperatures below freezing, icing can occur at this point, which can lead to excessive frictional resistance between the second part 114 and the housing 116. This can result in excessive stress on other components of the vehicle brake 100, such as the second part 112 at the position of the bearings 112a, 112b. Fig. 2 shows a flowchart of an exemplary procedure 200, with which a malfunction due to icing can be detected and rectified. After the start of procedure 200 (202), the electric motor 108 is driven to a rotary motion in a first direction with a force limited compared to the maximum possible force for a predetermined time interval (at 204). In step 204, a running index n, which will be explained in more detail later, is also set to zero (n=0). Subsequently, it is checked (at 206) whether the distance traveled by the electric motor 108, which can be determined, for example, by means of a rotor bearing sensor, exceeds a first threshold value s1. If the distance traveled exceeds the first threshold value s1, it is assumed that the vehicle brake 100 is functioning correctly, and the procedure 200 proceeds along the path marked "Y" in Fig. 2 to step 208, in which the rotary motion of the electric motor 108 is continued until a desired position is reached. The procedure 200 is then terminated (at 210). The proper functioning of the vehicle brake 100 is characterized by a linear increase in the distance traveled by the electric motor 108 during a predetermined time interval in which electrical power is supplied to the electric motor 108, as shown in the t (time)-s (distance) diagram labeled “(A)” in Fig. 3. This allows the distance traveled sa to exceed the threshold value s1 after the electric motor 108 has been activated with a predetermined electrical power in the time interval between times t0 and t1. If, however, step 206 determines that the distance traveled is less than the first threshold value s1, it is assumed that the vehicle brake 100 is malfunctioning. Steps 204 and 206 thus determine whether a malfunction exists or not. These two steps, 204 and 206, can therefore be considered together as a diagnostic step. If a malfunction is detected during the diagnostic step, the procedure 200 proceeds along the path marked "N" to step 212, in which the electric motor 108 is driven with maximum force in a second direction opposite to the first. In this step 212, the running index n is also increased by 1 (n=n+1). In step 214, it is then determined whether the distance traveled exceeds a second threshold s2, which is lower than the first threshold s1. If the distance traveled is greater than the second threshold s2, it is determined that icing is present. Conversely, if it is determined that the distance traveled is less than the second threshold s2, it is determined that an error has occurred that is not attributable to icing. The time courses of the distances traveled sb and sc in the event of a malfunction are illustrated in the diagrams labeled "(B)" and "(C)" respectively in Fig. 3. In diagram (B), the distance traveled sb at time t1, i.e., after the electric motor has been activated in the time interval between t0 and t1, lies between the first threshold value s1 and the second threshold value s2. Since a certain, albeit limited, distance has been traveled here, it is assumed that icing of the actuator 106 is present, for example at position 114a, because in such a case the actuator 106 can travel the limited distance due to its elastic behavior. In diagram (C) in Fig. 3, the distance traveled sc is less than the second threshold s2, which indicates a fault that is not due to icing, such as a serious mechanical fault or an electrical fault that impairs the control of the electric motor 108. Since the malfunction is identified in steps 212 and 214, these two steps 212 and 214 are together referred to as the malfunction identification step. If in step 214 it is determined that the distance traveled is less than the second threshold s2, the procedure 200 proceeds along the path marked "N" to step 216, in which a warning message is issued informing that the vehicle brake 100 has a fault which should be investigated further in a specialist workshop. If, however, in step 214 it is determined that the distance traveled is greater than the second threshold value s2, the procedure 200 proceeds along the path marked "Y" to step 218, in which the electric motor is driven to move in the first direction with a force limited compared to the maximum possible force. This step is subsequently referred to as the de-icing step. Here, an attempt is made to resolve the malfunction by appropriately adjusting the electric motor 108 in the first direction. After the de-icing step 218, it can be checked in the subsequent step 220 whether the distance traveled during the de-icing step 218 is longer than the first threshold value s1. If the distance traveled is longer than the first threshold value s1, it can be assumed that the de-icing was successful. Procedure 200 then proceeds to step 226 along the path marked "Y", in which the electric motor 108 continues to rotate in the first direction until a desired end position is reached. The procedure can then be terminated (at 210). If, however, step 220 reveals that the distance traveled is shorter than the first threshold value s1, it is assumed that de-icing has not yet been successful. Therefore, the malfunction identification steps 212 and 214 can then be repeated. The malfunction identification step 212, 214 and the de-icing step 218 can be performed cyclically a predetermined number n1 of times, unless one of the following conditions occurs: Condition 1: On an nth execution of the malfunction identification step 212, 214, it is found that the distance traveled during the execution of the nth malfunction identification step 212, 214 is shorter than the second threshold s2, where n is less than or equal to n1. If the distance traveled is shorter than the second threshold s2, a serious electrical or mechanical fault is assumed, as described above, and the procedure advances to step 216 and is then terminated. Condition 2: After the nth execution of de-icing step 218, it is found that the distance traveled during the execution of the nth de-icing step is greater than the first threshold s1 (n less than n1).It is assumed that the de-icing was successful. The procedure then proceeds to step 226, as described above, and is subsequently terminated. Before the malfunction identification step 212, 214 is repeated after an unsuccessful de-icing step 218, the value of the running index n is first compared with the specified value n1 in step 222 to ensure that the cyclic repetition of the malfunction identification step 212, 214 and the de-icing step 218 is performed only a specified number n1 of times. If step 222 determines that n equals n1 (n=n1), the procedure 200 proceeds to step 224, in which a warning message is issued indicating that a critical error has occurred. The procedure can then be terminated. However, if in step 222 it is determined that n is less than n1 (n <n1), schreitet das Verfahren 200 über den mit „N“ gekennzeichneten Pfad zu dem Schritt 212 voran, in welchem der Laufindex n um 1 erhöht wird, wodurch die Anzahl der verbleibenden Wiederholungen des Fehlfunktionsidentifikationsschrittes 212, 214 und des Enteisungsschrittes 218 um 1 verringert wird. The procedure can also include a temperature measurement step in which an outside temperature is determined. This allows verification of whether icing of the actuator 106 is possible. Furthermore, a vehicle is provided which has an electromechanical vehicle braking system 120 as described above.

Claims

Method (200) for controlling an electromechanical vehicle brake (100) comprising a first brake body (102), a second brake body (104), and an electromechanical actuator (106), wherein the actuator (106) is configured to bring the first brake body (102) into contact with the second brake body (104) to generate a braking effect and to release the first brake body (102) from the second brake body (104) to terminate the braking effect, wherein the method (200) comprises: performing a diagnostic step (204, 206) in which the actuator (106) is driven to move in a first direction with a force limited compared to a maximum possible force, and in which it is determined, based on the distance traveled, whether the vehicle brake (100) has a malfunction; if, in the diagnostic step (204, 206), it is determined that the vehicle brake (100) has a malfunction,Performing a malfunction identification step (212, 214) in which the actuator (106) is driven in a second direction opposite to the first direction with maximum force and in which the distance traveled is used to determine whether the vehicle brake (100) is malfunctioning due to icing, and if a malfunction due to icing is detected in the malfunction identification step (212, 214), performing a de-icing step (218) in which the actuator (106) is driven to move in the first direction with a force limited compared to the maximum force. Method (200) according to claim 1, wherein in the diagnostic step (204, 206) it is determined that a malfunction is present if the distance traveled in the diagnostic step (204, 206) is shorter than a first threshold value (s1). Method (200) according to claim 1 or 2, wherein in the malfunction identification step (212, 214) it is determined that: a malfunction due to icing is present if the distance traveled in the malfunction identification step (212, 214) is longer than a second threshold (s2) that is smaller than the first threshold (s1), and a malfunction not attributable to icing is present if the distance traveled in the malfunction identification step (212, 214) is shorter than the second threshold (s2). Method (200) according to claim 3, wherein, when it is determined that a malfunction is present which is not due to icing, a warning is issued (216) and the method is terminated. Method (200) according to one of claims 1 to 4, further comprising: checking after the de-icing step (218) whether the distance traveled during the de-icing step (218) is longer than the first threshold value (s1) or not. Method (200) according to claim 5, wherein, if after the de-icing step (218) it is determined that the distance traveled during the de-icing step (218) is shorter than the first threshold (s1), the malfunction identification step (212, 214) is performed again. Method (200) according to claim 6, wherein the malfunction identification step (212, 214) and the de-icing step (218) are performed cyclically a predetermined number n1 of times, unless one of the following conditions occurs: upon an nth performance of the malfunction identification step (212, 214), it is found that the distance traveled during the performance of the nth malfunction identification step (212, 214) is shorter than the second threshold (s2), where n is less than or equal to n1, and after the nth performance of the de-icing step (218), it is found that the distance traveled during the performance of the nth de-icing step (218) is greater than the first threshold (s1), where n is less than n1. Method (200) according to claim 7, wherein, if after the n1th execution of the de-icing step (218) it is determined that the distance traveled during the execution of the n1th de-icing step (218) is shorter than the first threshold (s1), a warning is issued (224) and the method is terminated. Electromechanical vehicle braking system (120) comprising: an electromechanical vehicle brake (100) comprising: a first brake body (102), a second brake body (104) and an electromechanical actuator (106), wherein the actuator (106) is configured to bring the first brake body (102) into contact with the second brake body (104) to generate a braking effect and to release the first brake body (102) from the second brake body (104) to terminate the braking effect, and a control device (118) configured to control the electromechanical vehicle brake (100) according to a method (200) according to any one of claims 1 to 8. Vehicle comprising an electromechanical vehicle braking system (120) according to claim 9.

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