Method for operating brake system of motor vehicle, corresponding brake system of motor vehicle, and computer program product

Abstract

The invention relates to a method for operating a brake system (1) of a motor vehicle, comprising a service brake device (2) having at least one wheel brake (3), which brake system adjusts a brake pressure applied to the wheel brake (3) at least in short time as a function of the setting of an operating element, the brake pressure is used to generate a brake force acting on a brake disc (4) of the wheel brake (3). According to the invention, the state of the coating (6) of the brake disc (4) of the wheel brake (3) is determined on the basis of the brake pressure present on the wheel brake (3) and the deceleration of the motor vehicle caused by said brake pressure. The invention also relates to a brake system (1) for a motor vehicle and to a computer program product.

Description

Technical Field

[0001] The invention relates to a method for operating a braking system of a motor vehicle, the braking system comprising a service brake device having at least one wheel brake, the braking system regulating, at least temporarily, a braking pressure applied to the wheel brake as a function of a setting of an operating element, the braking pressure being used to generate a braking force acting on a brake disk of the wheel brake. The invention also relates to a braking system for a motor vehicle and a computer program product. Background Art

[0002] Prior art, for example, is known from document EP 3 186 122 B1. It describes a method for monitoring the braking performance of a vehicle, the method comprising the following steps: providing a braking monitoring system for at least some braking events, the braking monitoring system having at least one microprocessor on the vehicle, wherein the braking monitoring system determines a braking demand and determines a vehicle deceleration; distinguishing between qualified braking events and unqualified braking events, including determining that a braking event is an unqualified event at least in part in response to determining that the duration of application of the exhaust pressure is less than or equal to a threshold; defining a data set of qualified braking events, each braking event in the data set including a determined braking demand and a determined vehicle deceleration; applying a statistical trend analysis method to the data set to generate a vehicle deceleration and braking demand trend; providing a reference for vehicle deceleration and braking demand; comparing at least one trend value with at least one reference value. Summary of the invention

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

[0004] This is achieved according to the invention by a method for operating a brake system of a motor vehicle having the features of claim 1. It is provided that the state of the coating of the brake disks of the wheel brakes is determined as a function of the brake pressure present at the wheel brakes and the deceleration of the motor vehicle caused by the brake pressure.

[0005] Advantageous embodiments with suitable developments of the invention are described in the dependent claims. It should be noted that the exemplary embodiments explained in the description are not limiting; rather, any variants of the features disclosed in the description, claims and drawings can be implemented.

[0006] The method is used to operate a braking system. It is preferably a component of a motor vehicle, but of course it can also exist independently of the motor vehicle. The braking system is used to brake the motor vehicle, to slow down or reduce the speed of the motor vehicle, in particular until the motor vehicle stops, and / or to keep the motor vehicle at a standstill. In the former case, the braking system has a service brake device, which applies a braking force to at least one wheel of the motor vehicle, preferably to a plurality of or all wheels of the motor vehicle, at least temporarily. This braking force can also be called a service braking force. If there are multiple wheels, the at least one wheel is considered to be a component of these multiple wheels. If the scope of this description refers to a wheel or at least one wheel, these explanations are equivalent. These explanations can also preferably be transferred to each of the multiple wheels.

[0007] The at least one wheel is assigned to an axle of the motor vehicle, to which a braking force is applied or generated by the service brake device. The axle is, for example, a rear axle or a front axle of the motor vehicle. The service brake device is preferably arranged and designed to apply a braking force at least temporarily to a plurality of wheels of an axle and / or to the wheels of a plurality of axles. The service brake device is particularly preferably used to apply a braking force at least temporarily to a plurality or all axles or their wheels of the motor vehicle, or to brake the corresponding wheels.

[0008] The service brake device has at least one wheel brake, which is assigned to at least one wheel or at least one axle. The service brake device preferably has a plurality of wheel brakes, each wheel brake being assigned to a wheel or an axle of the motor vehicle. It is particularly preferred that wheel brakes are arranged on a plurality of wheels and / or axles, in particular, each wheel and / or each axle of the motor vehicle is assigned a separate wheel brake. Through the wheel brakes, a braking force is applied to the axle or the corresponding wheel of the motor vehicle. Here, the braking force is to be understood as a force applied to the brake disc by a brake caliper in the circumferential direction of the brake disc relative to the axis of rotation of the brake disc of the wheel brake. In order to generate a braking force on the brake disc, the brake caliper pushes one or more brake pads onto the brake disc, that is, according to the brake pressure applied to the wheel brake. In this regard, the braking force is preferably proportional to the brake pressure or at least approximately proportional.

[0009] The braking force generated by the service brake device can usually be adjusted as desired. This is done by the arrangement of an operating element, via which the driver of the motor vehicle applies the braking force. The operating element is arranged so that it can be reached by the driver from the passenger compartment of the motor vehicle, in particular, it is at least partially located in the passenger compartment or projects into the passenger compartment. The operating element is particularly preferably designed as a brake pedal, i.e. it is arranged and designed for operation by the driver's foot or by the driver's foot.

[0010] The brake system evaluates the setting of the operating element, such as its position, and determines the braking force given by the driver from this setting. This can also be called a set braking force. The service brake device is controlled at least temporarily so that it applies a braking force corresponding to / equivalent to / consistent with the set braking force to the axle or at least one wheel of the motor vehicle. In particular, a theoretical braking force corresponding to the set braking force is given to the service brake device, and the service brake device adjusts the actual braking force acting on the axle or at least one wheel so that the actual braking force is consistent with the theoretical braking force and thus consistent with the set braking force.

[0011] The service brake device is, for example, at least temporarily connected to the operating element in a purely electronic manner, so that, depending on the setting of the operating element, one or more wheel brakes are actuated at least temporarily in a purely electronic manner. However, it can also be provided that a mechanical and / or hydraulic backup stage is provided between the operating element and the wheel brakes, so that in the event of a failure of the electronic connection, the braking force can still be generated or adjusted using the operating element. Particularly preferably, the operating element is permanently connected to the service brake device in a purely electronic manner, or vice versa, the service brake device is permanently connected to the operating element in a purely electronic manner.

[0012] The braking force is generated by a controller in the brake system as a function of the setting of the operating element. To this end, the controller evaluates the setting of the operating element, determines the braking force or the set braking force, and controls the service brake device to generate an actual braking force that corresponds to the set braking force or the set braking force. To this end, the setting of the operating element is transmitted to the controller, in particular via a data transmission link.

[0013] When the wheel brakes are used to generate braking forces, wear occurs, in particular of the brake discs and / or brake pads fastened to the brake calipers. This wear enters the external environment of the motor vehicle in the form of dust, which constitutes emissions from the brake system. It therefore affects the overall emissions of the motor vehicle, which consist, for example, of emissions from the power unit of the motor vehicle and emissions from the brake system. In order to reduce the emissions from the brake system, various measures are considered. For example, wear from the brake discs and / or brake pads can be sucked off, in particular from the wheel arches of the motor vehicle, and separated from the sucked-in air using filters. However, this is complex and requires additional components, which require installation space.

[0014] For this purpose, according to the invention, the brake disc should be provided with a coating which is designed to reduce emissions. The coating thus ensures that when the wheel brakes are used to brake or decelerate the motor vehicle, less wear occurs than in a brake disc designed without a coating (e.g. made of grey cast iron). However, during operation of the brake system, the coating can wear away, for example due to wear which still occurs to a small extent and / or due to damage to the coating. A brake disc with a worn coating, in turn, causes a greater amount of wear than a brake disc with a non-worn coating.

[0015] This can lead to the total emissions of the motor vehicle during its operation being higher than the actually prescribed emissions, i.e. exceeding the emission limit value. It is therefore proposed to monitor the state of the coating. To this end, the state of the coating is determined from the brake pressure applied to the wheel brakes and the deceleration of the motor vehicle caused by the brake pressure. When there is a braking force acting on the brake disks of the wheel brakes, the brake pressure used for this purpose and the deceleration of the motor vehicle occurring when the brake pressure is present are detected. The state of the coating is then determined from this; the state of the coating is therefore a function of the brake pressure and the deceleration.

[0016] Based on this state, it can be assessed whether the coating is defective or still good. For this purpose, for example, a pressure / deceleration characteristic curve is stored, in which the brake pressure required for a certain deceleration is plotted against the deceleration. Due to the coating, the pressure / deceleration characteristic curve is usually flatter than when the brake disc is not coated. Based on the brake pressure applied to the wheel brakes and the resulting deceleration, the pressure / deceleration characteristic curve can be used, for example, to identify the state of the coating. If the brake pressure corresponds to the brake pressure derived from the pressure / deceleration characteristic curve for the current deceleration of the motor vehicle, it is determined that the coating is good.

[0017] However, if the brake pressure deviates from this, in particular if the deviation exceeds a given tolerance, a defect in the coating is detected. If this is the case, a fault signal is preferably generated and / or the defect in the coating is communicated to the driver of the motor vehicle, for example visually, acoustically and / or haptically. In either case, the technical measures described ensure that the brake system or the motor vehicle is operated within the prescribed framework, in particular that limit values ​​for brake system emissions and / or total emissions are observed.

[0018] A further development of the invention provides that the brake disc is a brake disc provided with a coating by laser coating. The brake disc is made of a brake disc material, for example, empirically made of grey cast iron. According to the invention, the coating is applied to the brake disc by laser coating. The coating comprises a coating material which 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 powder laser cladding. Preferably, the coating achieves a coating thickness of at most 200 μm, at most 150 μm or at most 100 μm. By using such a brake disc, the emissions of the brake system are significantly reduced.

[0019] A refinement of the invention proposes that a defect in the coating is detected when the deceleration deviates from a theoretical deceleration value stored in relation to the brake pressure. This has already been pointed out in principle. The theoretical deceleration value is stored in relation to the brake pressure, i.e. in the form of a pressure / deceleration characteristic curve. The pressure / deceleration characteristic curve relates different brake pressures to the decelerations that occur at different brake pressures. If the actually existing deceleration (which may also be referred to as actual deceleration) deviates from the theoretical deceleration value, it can be assumed that the coating is defective. The deviation of the deceleration from the theoretical deceleration value can be either in the direction of a smaller deceleration or in the direction of a larger deceleration. In other words, the coating is considered good only when the deceleration complies with the theoretical deceleration value, in particular when it complies with the theoretical deceleration value taking into account a given tolerance. Otherwise, the coating is judged to be defective. This enables a reliable assessment of the state of the coating.

[0020] A development of the invention provides that the vehicle weight of the motor vehicle is determined and that the deceleration force acting on the motor vehicle is calculated as a function of the vehicle weight from the deceleration of the motor vehicle. The deceleration is therefore not used directly to determine the state of the coating, but is first converted into a deceleration force. A deceleration force is to be understood as a force which acts on the motor vehicle to brake or decelerate the motor vehicle while the braking force acts on the brake disc. To calculate the deceleration force, the vehicle weight of the motor vehicle is taken into account, in particular the deceleration force is obtained from the product of the vehicle weight and the deceleration. The vehicle weight is usually determined in the first place during the operation of the brake system, for example by using known state variables of the motor vehicle, which are provided, for example, via a CAN bus. Determining the deceleration force allows the state of the coating to be determined with high precision.

[0021] A further development of the invention provides that the friction coefficient of the wheel brake is determined as a function of the brake pressure and the deceleration force. The brake pressure and the deceleration force are both known. In particular, the contact pressure for pressing the brake pad onto the brake disc is determined by the brake pressure. The friction coefficient existing between the brake disc and the brake pad on the wheel brake can be determined on the basis of the contact pressure or the brake pressure on the one hand and the deceleration force on the other hand. The state of the coating can in turn be determined with high precision on the basis of this friction coefficient.

[0022] A further development of the invention provides that a defect in the coating is detected when the friction coefficient deviates from a theoretical value for the coefficient. The friction coefficient can be determined in the manner described. The theoretical value for the coefficient can be stored for the brake disc or the coating, in particular in a control unit of the brake system. Preferably, the theoretical value for the coefficient is stored for an intact, contactless coating when the brake disc is installed. If the actually existing friction coefficient subsequently deviates from the theoretical value for the coefficient during operation of the brake system, a defect in the coating is inferred.

[0023] In other words, the coating is considered good only if the friction coefficient corresponds to a stored theoretical coefficient value, in particular taking into account a given tolerance. However, if the friction coefficient deviates from the theoretical coefficient value, in particular by more than a given tolerance, a defect in the coating is detected. Inadmissibly high emissions from the brake system can thus be reliably detected and thus avoided.

[0024] A development of the invention provides that a deceleration setpoint value and / or a coefficient setpoint value are determined and stored during a run-in operation of the brake system. The run-in operation takes place after or begins after the brake disc is installed in the brake system or wheel brake. For example, when the brake disc is installed, the previously stored setpoint value is deleted. The run-in operation then begins. This continues until the deceleration for different brake pressures and / or the friction coefficient is reliably determined. If the deceleration and / or the friction coefficient are reliably determined for different brake pressures, this deceleration and / or this friction coefficient is stored as a deceleration setpoint value or coefficient setpoint value and is subsequently used to determine the coating state. As a result, the brake system can be reliably adjusted in response to the installed brake disc.

[0025] An improved solution of the present invention proposes that a coating defect is only identified when the deceleration deviates from the theoretical value of the deceleration multiple times and / or the friction coefficient deviates from the theoretical value of the coefficient multiple times. The deviation of the deceleration or the friction coefficient is not necessarily caused by a coating defect, but may occur, for example, due to the environmental conditions of the motor vehicle. In particular, it may happen that foreign matter such as water, salt, etc. is present between the brake disc and the brake pad. Therefore, once a deviation occurs, the coating defect is not immediately determined. Instead, it is necessary for the deviation to occur multiple times, in particular, the deviation occurs at a certain minimum time interval. Therefore, it is preferably only when the deviation occurs multiple times and there is at least a certain time interval between the individual deviations that the coating is determined to be defective. In this way, misjudgment of coating defects is reliably avoided.

[0026] The invention also relates to a braking system for a motor vehicle, in particular for carrying out a method according to an embodiment of the present description, wherein the braking system has a service brake device with at least one wheel brake, the braking system being arranged and designed to adjust, at least temporarily, a brake pressure applied to the wheel brake as a function of a setting of an operating element, the brake pressure being used to generate a braking force acting on a brake disk of the wheel brake. The braking system is also arranged and designed to determine the state of a coating of a brake disk of the wheel brake as a function of the brake pressure applied to the wheel brake and the deceleration of the motor vehicle caused by the brake pressure.

[0027] The advantages of this embodiment of the brake system or this technical solution have already been pointed out.Both the brake system for a motor vehicle and the method for operating the brake system can be developed according to the embodiments in the present description, to which reference is therefore made.

[0028] Furthermore, the invention relates to a computer program product comprising instructions which, when executed by a brake system of a motor vehicle according to an embodiment of the present description, implement the described method. With regard to advantages and possible advantageous developments, reference is made to the entire description.

[0029] The features and feature combinations described in the specification, in particular the features and feature combinations described in the following description of the figures and / or shown in the figures, can be used not only in the respective given combination, but also in other combinations or alone, without departing from the scope of the present invention. Therefore, embodiments that are not explicitly shown or described in the specification and / or the figures, but are revealed from the described embodiments or can be derived therefrom, are also considered to be included in the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will be described in more detail below with reference to the embodiments shown in the accompanying drawings, but without limiting the present invention. Here, the only accompanying drawing shows:

[0031] Figure 1 It is a partial schematic diagram of the braking system of a motor vehicle. DETAILED DESCRIPTION

[0032] Figure 1 A schematic partial view of a brake system 1 for a motor vehicle is shown. The brake 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 of the motor vehicle or to an axle of the motor vehicle. It has a brake disc 4 and a brake caliper 5, on both sides of which brake pads (not shown here) are arranged on the brake caliper 5. In order to generate a braking force, a brake pressure is applied to the wheel brake 3. As a result, the brake pads are pushed onto the brake disc 4 by the brake caliper, so that a braking force is generated due to the friction between the brake disc 4 and the brake pads. The brake disc 4 is provided with a coating, in particular a coating containing a hard material, in order to reduce the wear that occurs during the generation of the braking force.

[0033] In order to reliably comply with the emission limits specified for the brake system, it is necessary to monitor the state of the coating 6. For this purpose, the brake pressure applied to the wheel brake 3 and the deceleration of the motor vehicle caused by the brake pressure are taken into account. In other words, the state of the coating 6 is derived based on the brake pressure and the deceleration of the motor vehicle achieved by the wheel brake 3. For this purpose, for example, a pressure / deceleration characteristic curve stored in a controller of the brake system 1 can be taken into account. However, it can also be provided that the friction coefficient currently existing between the wheel brake 3 or the brake disc 4 and the brake pad is determined and compared with a theoretical value. In any case, the state of the coating 6 can be reliably determined, in particular, whether the coating 6 is defective. In this case, it is preferred to generate a fault signal and / or display the fault to the driver of the motor vehicle. Therefore, the emission limits can be reliably complied with by the brake system 1.

[0034] List of reference numerals:

[0035] 1Brake system

[0036] 2 Service brake system

[0037] 3 wheel brakes

[0038] 4 brake discs

[0039] 5 Brake calipers

[0040] 6. Cladding

Claims

1. A method for operating a braking system (1) of a motor vehicle, the braking system comprising a service brake device (2) having at least one wheel brake (3), the braking system regulating, at least temporarily, a braking pressure applied to the wheel brake (3) as a function of a setting of an operating element, the braking pressure being used to generate a braking force acting on a brake disk (4) of the wheel brake (3), characterized in that: The state of a coating (6) of a brake disk (4) of a wheel brake (3) is determined as a function of the brake pressure applied to the wheel brake (3) and the deceleration of the motor vehicle caused by the brake pressure.

2. The method according to claim 1, characterized in that: The brake disc (4) is a brake disc (4) provided with a coating (6) by laser coating.

3. The method according to any one of the preceding claims, characterized in that In the event of a deceleration deviation from a target deceleration value stored with respect to the brake pressure, a defect in the coating (6) is detected.

4. The method according to any one of the preceding claims, characterized in that The vehicle weight of the motor vehicle is determined and the deceleration force acting on the motor vehicle is calculated from the deceleration of the motor vehicle as a function of the vehicle weight.

5. The method according to any one of the preceding claims, characterized in that The friction coefficient of the wheel brake (3) is determined based on the braking pressure and the deceleration force.

6. The method according to any one of the preceding claims, characterized in that In the event that the friction coefficient deviates from the theoretical value of the coefficient, a defect in the coating (6) is detected.

7. The method according to any one of the preceding claims, characterized in that During the running-in operation of the brake system (1), a deceleration target value and / or a coefficient target value are determined and stored.

8. The method according to any one of the preceding claims, characterized in that A defect in the coating (6) is detected only if the deceleration deviates several times from the deceleration target value and / or the friction coefficient deviates several times from the coefficient target value.

9. A braking system (1) for a motor vehicle, in particular for carrying out the method according to one or more of the preceding claims, wherein: The brake system comprises a service brake device (2) having at least one wheel brake (3), the brake system being arranged and designed to adjust, at least temporarily, a brake pressure applied to the wheel brake (3) according to the setting of an operating element, the brake pressure being used to generate a braking force acting on a brake disc (4) of the wheel brake (3), and being characterized in that the brake system (1) is also arranged and designed to determine a state of a coating (6) of a brake disc (4) of the wheel brake (3) according to the brake pressure applied to the wheel brake (3) and the deceleration of the motor vehicle caused by the brake pressure.

10. A computer program product comprising instructions which, when executed by a braking system (1) according to claim 9, implement the method according to one or more of claims 1 to 8.

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