METHOD FOR OPERATING A BRAKE SYSTEM FOR A MOTOR VEHICLE, CORRESPONDING BRAKE SYSTEM FOR A MOTOR VEHICLE AND COMPUTER PROGRAM PRODUCT

Description

[0001] The invention relates to a method for operating a braking system for a motor vehicle, which has a service brake device with at least one wheel brake and in which a brake pressure applied to the wheel brake to generate a braking force acting on a brake disc of the wheel brake is adjusted, at least temporarily, depending on a setting of a control element. The invention further relates to a braking system for a motor vehicle and a computer program product.

[0002] For example, the prior art documents DE 10 2014 119 024 A1 and EP 3 186 122 B1 describe a method for monitoring the braking performance of a vehicle, wherein the method includes: providing a brake monitoring system, which has at least one microprocessor on the vehicle, for at least some braking events, wherein the brake monitoring system determines a braking requirement and a vehicle deceleration; differentiating between qualifying and non-qualifying braking events, including determining that a braking event is a non-qualifying event, at least in part as a reaction to determining that a delivery pressure is exerted for a period that is less than or equal to a threshold value;Defining a dataset of qualifying braking events, wherein each braking event in the dataset includes a specific braking demand and a specific vehicle deceleration; applying a statistical trend analysis procedure to the dataset to determine a linear trend in the vehicle deceleration and braking demand; providing a reference for the vehicle deceleration and braking demand; and comparing at least one trend value with at least one reference value.

[0003] The object of the invention is to propose a method for operating a braking system for a motor vehicle which has advantages over known methods, in particular ensuring compliance with an emission limit value.

[0004] According to the invention, this is achieved by a method for operating a braking system for a motor vehicle with the features of claim 1.

[0005] Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims. It should be noted that the exemplary embodiments described in the description are not limiting; rather, any variations of the features disclosed in the description, the claims, and the figures are possible. The method serves to operate the braking system. This is preferably a component of the motor vehicle, but can, of course, also be separate from it. The braking system serves to brake the motor vehicle, i.e., to decelerate or reduce the speed of the motor vehicle, in particular to a standstill, and / or to lock the motor vehicle in a standstill.For the first scenario, the braking system includes a service brake device which applies braking force, at least temporarily, to at least one wheel of the motor vehicle, preferably to several or all wheels. This braking force can also be referred to as the service brake force. If there are multiple wheels, the at least one wheel is considered a component of these multiple wheels. Where this description refers to "the wheel" or "the at least one wheel," the descriptions are equivalent. They are also preferably applicable to each of the multiple wheels.

[0006] The at least one wheel is assigned to the wheel axle of the motor vehicle, onto which the braking force is applied by means of the service brake system, or on which the braking force is effected. The wheel axle is, for example, a rear axle or a front axle of the motor vehicle. Preferably, the service brake system is designed and configured to apply the braking force, at least temporarily, to several wheels of the wheel axle and / or wheels of several wheel axles. Particularly preferably, the service brake system is used to apply the braking force, or to brake the corresponding wheels, at least temporarily, to several or all wheel axles of the motor vehicle or their wheels.

[0007] The service brake system has at least one wheel brake assigned to the at least one wheel or wheel axle. Preferably, the service brake system has several wheel brakes, each assigned to a wheel or wheel axle of the motor vehicle. Particularly preferably, the wheel brakes are located on several wheels and / or wheel axles; in particular, each wheel and / or wheel axle of the motor vehicle has its own separate wheel brake. The braking force is applied to the wheel axle or the respective wheel of the motor vehicle by means of the wheel brake. The braking force is understood here to be the force exerted on the brake disc of the wheel brake in its circumferential direction with respect to an axis of rotation of the brake disc, in particular by means of a brake caliper.To exert braking force on the brake disc, the brake caliper presses one or more brake pads against the brake disc, depending on the braking pressure applied to the wheel brake. The braking force is therefore preferably proportional, or at least approximately proportional, to the braking pressure.

[0008] The braking force produced by the service brake system can usually be adjusted as desired. This is done depending on the setting of the control element, which the driver of the vehicle uses to specify the braking force. The control element is arranged within reach of the driver from inside the passenger compartment of the vehicle; in particular, it is located at least partially within or projecting into the passenger compartment. The control element is most preferably designed as a brake pedal, i.e., it is intended and designed for operation by the driver's foot.

[0009] The braking system evaluates the setting of the control element, for example, its position, and determines the braking force specified by the driver from this setting. This can also be referred to as the target braking force. The service brake system is controlled, at least temporarily, in such a way that it exerts a braking force on the vehicle's axle or at least one wheel that corresponds to the target braking force. In particular, the service brake system is given a target braking force corresponding to the target braking force, and it adjusts the actual braking force acting on the axle or at least one wheel so that it corresponds to the target braking force and thus to the target braking force.

[0010] The service brake system is, for example, at least temporarily connected to the control element purely electronically, so that the control of the wheel brake(s) is carried out at least temporarily purely electronically, depending on the setting of the control element. However, it can also be provided that a mechanical and / or hydraulic fallback system exists between the control element and the wheel brake, so that in the event of a failure of the electronic connection, the braking force can still be applied or adjusted via the control element. Particularly preferred is the control element permanently connected purely electronically to the service brake system, or conversely, the service brake system permanently connected purely electronically to the control element.

[0011] The generation of braking force, depending on the control element's setting, is handled by a control unit of the braking system. To do this, the control unit evaluates the control element's setting, determines the braking force or the target braking force, and activates the service brake system to generate the actual braking force, which corresponds to the target braking force or the preset braking force. For this purpose, the control element's setting is transmitted to the control unit, primarily via a data transmission connection.

[0012] When the wheel brakes are used to generate braking force, abrasion occurs, particularly of the brake disc and / or brake pads attached to the caliper. This abrasion is released as dust into the vehicle's environment, representing emissions from the braking system. It therefore affects the vehicle's overall emissions, which are comprised, for example, of emissions from the vehicle's drive system and emissions from the braking system. Various measures are being considered to reduce braking system emissions. For instance, it is possible to extract the brake disc and / or brake pad abrasion, particularly from a wheel well, and separate it from the extracted air using a filter. However, this is complex and requires additional components that take up installation space.

[0013] For this reason, according to the invention, the brake disc is to be provided with a coating designed to reduce emissions. The coating ensures that less abrasion is generated when the wheel brake is used to brake or decelerate the vehicle compared to a brake disc without the coating, for example, one made of gray cast iron. However, the coating wears down during operation of the braking system, for example, due to the continued, albeit reduced, abrasion and / or damage to the coating. A brake disc with a worn coating, however, results in a greater amount of abrasion compared to a brake disc with an unworn coating.

[0014] This can lead to the vehicle exhibiting total emissions during operation that are higher than the intended emissions, thus exceeding the emission limit. Therefore, it is planned to monitor the condition of the coating. For this purpose, the condition of the coating is determined from the brake pressure applied to the wheel brake and the resulting deceleration of the vehicle. While the braking force is acting on the brake disc of the wheel brake, the brake pressure used and the deceleration of the vehicle occurring under this pressure are recorded. The condition of the coating is then determined from this data; the condition of the coating is thus a function of the brake pressure and the deceleration.

[0015] The condition of the coating is assessed to determine whether it is defective or intact. For example, a pressure-deceleration curve is stored for this purpose, plotting the brake pressure required for a specific deceleration against the deceleration. Due to the coating, the pressure-deceleration curve will typically be flatter than for a brake disc without the coating. The condition of the coating can then be determined, for example, using the pressure-deceleration curve, based on the brake pressure applied to the wheel brake and the resulting deceleration. If the brake pressure corresponds to the brake pressure calculated from the pressure-deceleration curve for the given deceleration of the vehicle, then the coating is considered to be intact.

[0016] However, if it deviates from this, particularly by more than a defined tolerance, the coating defect is detected. If this occurs, a fault signal is preferably generated and / or the coating defect is indicated to the driver of the vehicle, for example, visually, audibly, and / or haptically. In any case, the described procedure ensures that the braking system and / or the vehicle is operated as intended, in particular in compliance with emission limits for the braking system and / or total emissions.

[0017] A further development of the invention provides that a brake disc coated with the coating by laser coating is used as the brake disc. The brake disc consists of a brake disc material, for example, conventionally gray cast iron. The coating is applied to the brake disc, whereby, according to the invention, this is done by laser coating. The coating consists of a coating material that is preferably different from the brake disc material. The coating material preferably has a higher hardness than the brake disc material. For example, a hard material is used as the coating material, so that the coating can also be referred to as a hard material coating. For example, tungsten carbide is used as the coating material. The laser coating is carried out, for example, by laser powder deposition welding.The coating is preferably produced with a coating thickness of at most 200 µm, at most 150 µm, or at most 100 µm. Using such a brake disc significantly reduces emissions from the braking system.

[0018] A further development of the invention provides that a coating defect is detected if the deceleration deviates from a target deceleration value stored for the brake pressure. This has essentially already been mentioned. The target deceleration value is stored as a function of the brake pressure, namely in the form of the pressure / deceleration characteristic curve. This curve relates different brake pressures to the decelerations that occur at each pressure. If the actual deceleration, which can also be referred to as the actual deceleration, deviates from the target deceleration value, it can be assumed that the coating has a defect. The deviation of the deceleration from the target deceleration value can be either towards smaller or larger decelerations.In other words, the coating is only deemed to be in good working order if the retardation corresponds to the target retardation value, particularly taking into account a defined tolerance. Otherwise, a coating defect is detected. This ensures a reliable assessment of the coating's condition.

[0019] According to the invention, the vehicle weight is determined, and based on this vehicle weight, a deceleration force acting on the vehicle is calculated from the vehicle's deceleration. The deceleration is not directly used to determine the condition of the coating; instead, it is first converted into the deceleration force. The deceleration force is understood to be the force that acts on the vehicle during the braking force acting on the brake disc, causing it to decelerate. The vehicle weight is used to calculate the deceleration force; in particular, the deceleration force is obtained by multiplying the vehicle weight by the deceleration.The vehicle weight is typically determined during braking system operation anyway, for example by using known vehicle parameters provided via the CAN bus. Determining the deceleration force allows for a highly accurate assessment of the coating's condition.

[0020] According to the invention, a coefficient of friction of the wheel brake is determined based on the brake pressure and the deceleration force. Both the brake pressure and the deceleration force are known. In particular, a contact force is determined from the brake pressure, with which the brake pads are pressed against the brake disc. From this contact force, or brake pressure, on the one hand, and the deceleration force on the other, the coefficient of friction present at the wheel brake between the brake disc and the brake pads can be determined. Based on the coefficient of friction, the condition of the coating can then be determined with high accuracy.

[0021] The invention provides that a deviation of the coefficient of friction from a target value indicates a defect in the coating. The coefficient of friction is determined as described. The target value for the brake disc or the coating is stored, particularly in the brake system's control unit. Preferably, when the brake disc is installed, the target value for a completely intact coating is stored. If, subsequently, the actual coefficient of friction deviates from the target value during operation of the brake system, it is concluded that the coating is defective. In other words, the system only recognizes that the coating is correct if the coefficient of friction corresponds to the stored target value, particularly taking into account a defined tolerance.If, however, the coefficient of friction deviates from the target value, especially by more than the specified tolerance, the coating defect is detected. This reliably identifies and thus prevents excessively high emissions from the braking system.

[0022] A further development of the invention provides that the deceleration setpoint and / or the coefficient setpoint are determined and stored during the break-in period of the brake system. The break-in period begins after the brake disc is installed in the brake system or wheel brake. For example, during the installation of the brake disc, the previously stored setpoint is deleted. The break-in period is then initiated. This continues until the deceleration for different brake pressures and / or the coefficient of friction have been reliably determined. Once this is the case, they are stored as the deceleration setpoint and / or coefficient setpoint, respectively, and subsequently used to determine the condition of the coating. This ensures that the brake system is reliably adjusted to the specific brake disc installed.

[0023] A further development of the invention provides that a coating defect is only detected after repeated deviations of the deceleration from the target deceleration value and / or the coefficient of friction from the target coefficient value. The deviation in deceleration or coefficient of friction is not necessarily caused by the coating defect, but can occur, for example, due to environmental conditions of the vehicle. In particular, foreign substances such as water, salt, or the like may be present between the brake disc and the brake pads. For this reason, the coating defect is not detected immediately upon the occurrence of the deviation. Rather, it is necessary for the deviation to occur repeatedly, especially at certain minimum time intervals.Preferably, a coating defect is only detected if the deviation occurs repeatedly and a specified time interval exists between each deviation. This reliably prevents false detection of the coating defect.

[0024] The invention further relates to a braking system for a motor vehicle, in particular for carrying out the method as described herein, wherein the braking system comprises a service brake device with at least one wheel brake and is designed and configured to adjust, at least temporarily, the brake pressure applied to the wheel brake to generate a braking force acting on a brake disc of the wheel brake, depending on the setting of a control element. The braking system is further designed and configured to determine the condition of a coating on a brake disc of the wheel brake based on the brake pressure applied to the wheel brake and the resulting deceleration of the motor vehicle.

[0025] The advantages of such a brake system design and such a procedure have already been mentioned. Both the brake system for the motor vehicle and the method for operating it may be further developed as described in this document, and reference is made to these details.

[0026] Furthermore, the invention relates to a computer program product comprising commands that cause the braking system for the motor vehicle to execute the described method as described herein. For the advantages and possible advantageous embodiments, reference is made to the description in its entirety.

[0027] The invention is explained in more detail below with reference to the embodiment shown in the drawing, without limiting the invention. The only illustration shown is the Figure 1 is a schematic representation of an area of ​​a braking system for a motor vehicle.

[0028] The Figure 1Figure 1 shows a schematic representation of a section of a braking system 1 for a motor vehicle. The braking system 1 has a service brake device 2, which in turn has a wheel brake 3 shown here. The wheel brake 3 is assigned to a wheel or wheel axle of the motor vehicle. It has a brake disc 4 and a brake caliper 5, on which brake pads (not shown here) are arranged on opposite sides of the brake disc 4. To generate a braking force, brake pressure is applied to the wheel brake 3. This forces the brake pads from the brake caliper 5 against the brake disc 4, so that the braking force is generated due to the frictional engagement between the brake disc 4 and the brake pads. The brake disc 4 is provided with a coating, in particular made of a hard material, to reduce abrasion that occurs during the generation of the braking force.

[0029] To reliably comply with the emission limits specified for the braking system, it is necessary to monitor the condition of the coating 6. For this purpose, the brake pressure applied to the wheel brake 3 and the resulting deceleration of the vehicle are used. In other words, the condition of the coating 6 is a function of the brake pressure and the deceleration of the vehicle achieved by means of the wheel brake 3. For example, a pressure / deceleration characteristic curve stored in a control unit of the braking system 1 is used for this purpose. However, it may also be possible to determine the current coefficient of friction of the wheel brake 3, or between the brake disc 4 and the brake pads, and compare it with a target value. In any case, the condition of the coating 6 is reliably detected, and in particular, any defects in the coating 6 are identified.In this case, a fault signal is preferably generated and / or the fault is displayed to the driver of the vehicle. This ensures that the emission limits can be reliably met by the braking system 1. REFERENCE MARK LIST:

[0030] 1. Brake system 2. Service brake device 3. Wheel brake 4. Brake disc 5. Brake caliper 6. Coating

Claims

1. Method for operating a braking system (1) for a motor vehicle having a service braking apparatus (2) with at least one wheel brake (3) and a brake pressure acting on the wheel brake (3) for generating a braking force acting on a brake disc (4) of the wheel brake (3) at least temporarily, as a function of a setting an operating element, wherein a state of a coating (6) of a brake disc (4) of the wheel brake (3) is determined on the basis of the brake pressure applied to the wheel brake (3) and a deceleration resulting from this of the motor vehicle, wherein a vehicle weight of the motor vehicle is determined and, on the basis of the vehicle weight, a deceleration force acting on the motor vehicle is calculated from the deceleration of the motor vehicle, characterized in that a friction coefficient of the wheel brake (3) is determined on the basis of the brake pressure and the deceleration force, and if the friction coefficient deviates from a coefficient setpoint, a defect in the coating (6) is detected.

2. Method according to claim 1, characterized in thata brake disc (4) provided with the coating (6) by laser coating is used as the brake disc (4).

3. Method according to any one of the preceding claims, characterized in that if the deceleration deviates from a deceleration setpoint stored for the brake pressure, a defect in the coating (6) is detected.

4. Method according to claim 1 or 2, characterized in that the deceleration setpoint and / or the coefficient setpoint are determined and stored during a running-in operation of the brake system (1).

5. Method according to claim 1 or 2, characterized in that the defect in the coating (6) is only detected when the deceleration deviates from the deceleration setpoint and / or the friction coefficient deviates from the coefficient setpoint multiple times.

6. Braking system (1) for a motor vehicle, in particular for performing the method according to one or more of the preceding claims, wherein the braking system (1) has a service braking apparatus (2) with at least one wheel brake (3) and is provided and configured to adjust a braking pressure applied to the wheel brake (3) for generating a braking force acting on a brake disc (4) of the wheel brake (3) at least temporarily, as a function of a setting of an operating element, wherein the brake system (1) is further provided and configured to determine a state of a coating (6) of a brake disc (4) of the wheel brake (3) on the basis of the brake pressure applied to the wheel brake (3) and a deceleration resulting from this of the motor vehicle, wherein a vehicle weight of the motor vehicle is determined and, on the basis of the vehicle weight, a deceleration force acting on the motor vehicle is calculated from the deceleration of the motor vehicle, characterized in that a friction coefficient of the wheel brake (3) is determined on the basis of the brake pressure and the deceleration force, and if the friction coefficient deviates from a coefficient setpoint, the defect in the coating (6) is detected.

7. Computer program product comprising commands, which, when executed by a computer, cause the braking system (1) according to claim 6 to carry out the method according to one or more of claims 1 to 5.