Brake system, method for operating same, and motor vehicle

Abstract

The invention relates to a method for operating a brake system (12) of a motor vehicle (10), said brake system comprising a control unit (14) and at least one friction brake (16) having a first brake element (18) and at least one second brake element (20) which are brought into contact by a pressure acting thereon, said pressure being providable by means of an actuator (22), as a result of which a braking torque that acts on at least one wheel (24) (in particular, one friction brake per wheel) of the motor vehicle (10) is generated due to friction. For the first brake element (18) and / or the at least one second brake element (20), a material is used that makes the relationship between pressure and braking torque non-linear and makes the braking torque temperature-dependent. The invention also relates to a brake system (12) and to a motor vehicle (10).

Description

[0001] 24-1886 PIF

[0002] 1

[0003] Method for operating a braking system, braking system and motor vehicle

[0004] The invention relates to a method for operating a braking system of a motor vehicle according to claim 1. Furthermore, the invention relates to a braking system and a corresponding motor vehicle according to claims 8 and 10.

[0005] The requirements for vehicle emissions, particularly particulate matter emissions, are constantly increasing and are, for example, stipulated by standards set by legislators. The planned Euro 7 standard may necessitate a revision of braking systems or the use of particle-reducing brake pads. The use of new materials can also alter the braking characteristics of the brakes.

[0006] DE 102021 214093 A1 discloses a method for determining a force gradient and a brake arrangement. EP 2528790 B1 discloses a method for operating a brake system for a motor vehicle, and EP 2365473 B1 further discloses a method for determining a measure of an acting braking force or frictional force on a disc brake.

[0007] The object of the present invention is to provide a method, a braking system and a motor vehicle by which a changed braking behavior occurring in particular due to new materials which are used for braking elements of a friction brake can be compensated in the broadest possible range of applications.

[0008] This problem is solved according to the invention by the subject matter of the independent claims. Advantageous embodiments and further developments of the invention are the subject matter of the dependent claims, the description, and the drawings.

[0009] A first aspect of the invention relates to a method for operating a braking system of a motor vehicle, which has a control unit and at least one friction brake, with a first brake element and at least one second brake element, 24-1886 PIF

[0010] 2

[0011] The brake elements are brought into contact by a pressure applied to them via an actuator, thereby generating a braking torque due to friction, which acts on at least one wheel of the motor vehicle. In this method, a material is used for the first brake element and / or the at least one second brake element, resulting in a non-linear relationship between pressure and braking torque. Furthermore, the braking torque is temperature-dependent and, in particular, also non-linear.

[0012] The motor vehicle can be, in particular, a passenger car or a truck. The control unit can, in particular, comprise an electronic computing device and be designed as a component of a driver assistance system, by which, for example, a braking signal can be applied. The at least one brake, or friction brake, is, in particular, designed as a disc brake. The brake elements can be a brake pad and / or a brake disc. For example, one of the brake elements can be rigidly connected to the wheel, whereby the braking torque acts on the wheel and thus enables deceleration of the motor vehicle. Advantageously, a friction brake is provided for each wheel of the motor vehicle, wherein, in particular, the respective first brake element of each is rotationally fixed to the wheel.

[0013] In conventional disc brakes according to the prior art, the relationship between the pressure generated when the two brake elements contact each other is linear to the resulting braking torque. However, due to the materials used for the brake elements, this is not the case with the brake system according to the invention.

[0014] The invention is based on the finding that, during the development of particle-reduced brake pads and brake discs, which are being tested to meet the potential requirements of a Euro 7 standard, altered physical properties have been observed compared to the prior art. Measurements under various brake pressures revealed that braking performance decreases at higher pressures and that a non-linear relationship can occur. In conjunction with the prior art in brake control, this leads to significant discrepancies in braking performance, which could potentially compromise vehicle safety. 24-1886 PIF

[0015] 3

[0016] Tests on the pressure dependence of braking performance with the new materials also revealed that brake temperature has a significant influence on the non-linear braking ratio.

[0017] The method according to the invention thus comprises the following steps:

[0018] The first step involves the brake system's control unit detecting a braking signal, which is provided, for example, by an actuator such as a brake pedal and / or a driver assistance system. This signal specifies the braking torque. The braking torque specified by this signal corresponds to a target braking torque and therefore a desired deceleration, which is intended to act on at least one wheel and thus on the vehicle to brake.

[0019] In a second step, the current temperature of the first brake element and / or at least one second brake element is determined. In other words, the temperature of the friction brake components is measured, for example, using a sensor, in particular a temperature sensor.

[0020] In a third step, the control unit determines the pressure required for the specified braking torque based on the non-linear relationship between pressure and braking torque, taking into account the determined current temperature. The control unit thus calculates the pressure required for the contact between the first and at least one second brake element to achieve the desired deceleration.

[0021] In a fourth step, the actuator is activated based on the brake signal, which, depending on the specified braking torque, provides the specific pressure for the contact between the first brake element and at least one second brake element, so that the specified braking torque is generated by friction.

[0022] It has been shown that a CP value, which describes the relationship between brake pressure and applied braking torque, is not linear for novel materials that can be used for brake elements. According to the current state of the art, integrated braking (IB) is used for controlling vehicle brakes, which is essentially a software component based on 24-1886 PIF.

[0023] 4

[0024] An integrated brake can be formed by a control unit and combined with hardware, such as an actuator or pressure build-up actuator. This integrated brake assumes that the physics of the brake developed so far allows for the use of a constant CP value. However, it has been found that the CP value does not behave linearly depending on the materials, so that with an integrated brake using a fixed CP value, a discrepancy occurs between the target and actual braking torque, with deviations of up to 50 percent being possible.

[0025] Using a state-of-the-art IB (Integrated Brake System) would, for example, not only result in incorrect braking torques being applied to each wheel, thereby hindering many functions that are crucial for vehicle stability and thus for safety, but also for the driving experience. This includes, for example, incorrect application of braking torques by vehicle stabilization, ABS, brake control, and / or driver assistance systems.

[0026] In other words, the inventive method proposes a control system or control design that takes into account the findings on new, non-linear properties of materials with regard to their braking properties or the CP value, and in addition to the pressure, includes the temperature of the brake elements in order to generate the pressure required by the actuator to bring the brake elements into contact with the desired braking torque, or to convert the corresponding pressure into the desired braking torque, so that possible Euro 7 brakes can be taken into account.

[0027] This offers the advantage of improved braking performance. A further advantage is that it allows for better pedal feel during braking and ensures precise control of the braking force by the driver.

[0028] In an advantageous embodiment of the invention, the required pressure is determined using a lookup table stored in a memory area of ​​the control unit. Additionally or alternatively, the required pressure is determined by a function, in particular, for example, a function by which the CP value can be determined as a function of the pressure, by a processor, in particular, for example, a CPU, of the control unit and / or using a characteristic curve. In other words, a conversion table is used by which corresponding pressure values ​​are determined. 24-1886 PIF

[0029] 5

[0030] Braking force or braking torque pairs are statically defined and, particularly for efficient operation of the control unit, are retrieved based on the brake signal. The memory location can be, for example, RAM, but also non-volatile memory such as flash memory. This offers the advantage that the process can be carried out particularly efficiently, as calculations during the determination process can be avoided. Furthermore, it is advantageous that the table can be multidimensional, allowing, for example, corresponding pressure values ​​to be stored for different temperature ranges.

[0031] Additionally or alternatively, in other words, the required pressure is calculated based on the brake signal using a function stored, for example, in the memory area, particularly in real time. Furthermore, a characteristic curve can be stored, which can be used to determine the pressure. This offers the advantage of a particularly efficient pressure determination.

[0032] In a further advantageous embodiment of the invention, the current temperature is determined by means of a sensor and / or by calculation. In other words, a sensor, in particular a temperature sensor, is provided which is configured to determine the temperature of the first brake element and / or of at least one second brake element and, in particular, to transmit or make available to the control unit. Additionally or alternatively, the control unit and / or another electronic computing device can, for example, use a model, more precisely a brake temperature model, to calculate or estimate the current temperature based on data such as wheel rotational speed, vehicle speed, driving time, and the like.Furthermore, for example, an average value of the current temperatures of the first and at least one second brake element, as measured by a sensor, can be calculated. This offers the advantage that the temperature, particularly via the sensor, can be determined with exceptional precision, thus enabling a particularly accurate determination of the pressure required for the specified braking torque.

[0033] In a further advantageous embodiment of the invention, if at least two friction brakes are provided, the temperature and pressure for the respective friction brake are determined for the first brake element and / or the at least one second brake element of at least two of the at least two friction brakes. 24-1886 PIF

[0034] 6

[0035] This means that, for example, when cornering, different temperatures can occur at the respective brake elements of each friction brake due to differing loads on the front and rear wheels. Therefore, a different pressure must be applied to each brake to achieve the desired braking performance. This offers the advantage of allowing for particularly precise adjustment of the braking torque.

[0036] In a further advantageous embodiment of the invention, a disc brake is used as the friction brake. Additionally or alternatively, the first brake element and / or the second brake element are designed as a brake shoe and / or brake disc. In particular, the first brake element can be the brake disc, and thus the at least one second brake element can be the brake shoe. In other words, the brake system comprises at least one disc brake, which in particular has a brake disc rotating on the hub of one of the wheels of the motor vehicle to be braked. This disc can be pressurized from both sides by brake pads, or brake pads or friction linings can be pressed against the disc. The brake pads can be mounted in a so-called brake caliper, which surrounds the brake disc.The brake is activated primarily hydraulically by the actuator, which builds up pressure by pressing the brake shoe, or at least one brake pad, against the brake disc. This offers the advantage that the method is particularly suitable for the standard type of brake used in motor vehicles, which has been enhanced with new materials for the brake components.

[0037] In a further advantageous embodiment of the invention, a coating on the brake shoe and / or a coating on the brake disc is used to address the non-linear relationship between pressure and braking torque. In other words, the ratio of the pressure coefficient (CP) value to braking torque is constant in conventional disc brakes and is influenced by novel coatings, which are currently under development to comply with future standards for operating a motor vehicle, in such a way that the braking behavior becomes non-linear, thereby enabling the method to demonstrate its advantages over conventional methods for operating integrated brakes.

[0038] In a further advantageous embodiment of the invention, the brake signal is provided by a vehicle stabilization control system, for example ESP, for a brake control system, for example ABS, and / or a driver assistance system. (With other 24-1886 PIF)

[0039] 7

[0040] In other words, the braking signal is not provided by the driver of the vehicle, but can be provided by a vehicle system that is specifically designed to ensure stable and therefore safe driving. This offers the advantage that the method can be used particularly effectively to stabilize the vehicle.

[0041] In an advantageous embodiment of the invention, the braking torque generated by the actuator scales linearly with the actuation of the brake pedal, which provides the braking signal. In other words, for a driver, the brake pedal's response to the braking torque is linear, as is particularly typical of conventional vehicles. Without this method, the described phenomenon of non-linear behavior in a braking system, especially one with a disc brake, would result in the pedal feeling sharp at low pressure and dull at high pressure, which is advantageously avoided by this embodiment.

[0042] A second aspect of the invention relates to a braking system for a motor vehicle, comprising a control unit and at least one friction brake, with a first braking element and at least one second braking element, which must be brought into contact by a pressure acting on them, provided by an actuator, whereby a braking torque acting on at least one wheel of the motor vehicle can be generated due to friction, and the first braking element and / or the at least one second braking element are formed from a material in which the relationship between pressure and braking torque is non-linear and the braking torque is furthermore temperature-dependent, wherein the braking system can be operated by means of a method according to the first aspect of the invention.

[0043] Advantageous embodiments and further developments of the invention, as well as advantages of the first aspect of the invention, are to be regarded as advantageous embodiments and further developments, as well as advantages of the second aspect of the invention, and vice versa.

[0044] In an advantageous embodiment of the invention, a temperature measuring unit is provided, which may in particular have at least one temperature sensor that can detect the temperature of the first brake element and / or the at least one second brake element, either by contact and / or without contact. In other words, a temperature measuring unit is provided, particularly also in the case of multiple friction brakes, which can determine the temperature of the associated brake elements for each of the friction brakes, which are in particular each provided for a wheel of the motor vehicle. 24-1886 PIF

[0045] 8

[0046] This offers the advantage that the control unit can be provided with particularly precise current temperature information, i.e., information about the current temperatures at the friction brakes.

[0047] A third aspect relates to a motor vehicle with a braking system according to the second aspect of the invention and / or designed to carry out a method according to the first aspect of the invention.

[0048] Advantageous embodiments and further developments, as well as advantages of the first aspect of the invention and the second aspect of the invention, are to be regarded as advantageous embodiments and further developments, as well as advantages of the third aspect of the invention, and vice versa.

[0049] Further features of the invention will become apparent from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown in the figures alone, are not only usable in the combinations specified, but also in other combinations or on their own.

[0050] The invention will now be explained in more detail with reference to a preferred embodiment and the drawings. The drawings show:

[0051] Fig. 1 shows a schematic side view of a motor vehicle including a braking system;

[0052] Fig. 2 shows a diagram of a braking torque ratio between braking torque and braking pressure for conventional disc brakes and disc brakes with non-linear braking behavior;

[0053] Fig. 3 shows a diagram between CP value and brake pressure for the two disc brakes according to Fig. 2; and

[0054] Fig. 4 shows a diagram of the relationship between braking torque and CP value as a function of temperature for a braking system according to Fig. 1 with a disc brake exhibiting nonlinear braking behavior according to Figs. 2 and 3. 24-1886 PIF

[0055] 9

[0056] Fig. 1 shows a schematic side view of a motor vehicle 10 with a braking system 12. The braking system 12 comprises a control unit 14 and at least one friction brake 16, with a first brake element 18 and at least one second brake element 20, which are brought into contact, or can be brought into contact, by a pressure acting on them by means of an actuator 22, whereby a braking torque is generated due to friction, which acts on at least one wheel 24, wherein in particular one friction brake 16 is provided for each wheel 24 on the motor vehicle 10. A material is used for the first brake element 18 and / or the at least one second brake element 20, which results in a non-linear relationship between pressure and braking torque. Furthermore, the braking torque is temperature-dependent and also, in particular, non-linear.

[0057] Based on the motor vehicle 10 and its associated braking system 12, a method for operating the braking system 12 and / or the motor vehicle 10 will be presented. The method serves to brake the motor vehicle 10 by means of the braking system 12 through pressure provided by the actuator 22 between the at least two braking elements 18 and 20, i.e., the first braking element 18 and the at least one second braking element 20, thereby decelerating at least one of the wheels 24.

[0058] In this case, at least one friction brake 16 or the respective friction brake 16 of the respective wheel 24 is designed as a disc brake, such that the first brake element 18 is designed, for example, as a brake disc and / or the at least second brake element 20 is designed, for example, as a brake shoe, so that the brake disc is touched on both sides by the brake shoes by means of the pressure built up by the actuator 22 in order to build up the corresponding friction.

[0059] Furthermore, a temperature measuring unit 26 is provided for the brake system 12, which includes at least one sensor and is designed to detect the temperature of the respective brake elements 16 and / or 18 of the respective friction brake 16 in contact and / or without contact, so that it is possible to determine a current temperature by means of at least one sensor and / or by means of a calculation.

[0060] The procedure includes the following steps: 24-1886 PIF

[0061] 10

[0062] In a first step, a brake signal is detected, which specifies the braking torque or is provided by a user and a driver assistance system. The specified braking torque is intended to act on at least one wheel 24 or to decelerate the vehicle 10, with the brake signal being detected by the control unit 14 of the brake system 12.

[0063] In a second step, the current temperature of the first brake element 18 and / or the at least second brake element 20 is determined.

[0064] In a third step, the control unit 14 determines the pressure to be applied for the specified braking torque or for the target braking torque based on the non-linear relationship, depending on the determined current temperature.

[0065] Then, in a fourth step, the actuator 22 is activated based on the brake signal, which, depending on the specified braking torque, provides the specific pressure for the contact between the first brake element 18 and the at least one second brake element 20, so that the intended braking torque is generated.

[0066] Fig. 2 shows a diagram of the brake pressure (p) as a function of a braking torque (M) for a friction brake 16, which is designed as a conventional disc brake (according to the prior art, SdT), and for a friction brake 16 of the brake system 12, which is designed in particular as a disc brake and which uses a material for at least one of the brake elements 18 and / or 20, which shows a non-linear relationship between the braking torque and the brake pressure.

[0067] For example, a material could be a coating for one of the brake elements 18, which is designed in particular as a brake pad or brake shoe and / or brake disc of a disc brake. The material is intended to be used in particular to emit very little brake abrasion and thus particulate matter, in order to minimize environmental impact.

[0068] Experiments have shown that new materials, which are used as friction lining for the friction brake 16 and are optimized for this purpose, exhibit a particularly high 24-1886 PIF

[0069] 11

[0070] To generate low brake wear, the aforementioned non-linear behavior is exhibited.

[0071] If braking were to be carried out using a conventional integrated braking system, the braking effect would decrease considerably when the brake is firmly applied, as can be seen in Fig. 2.

[0072] Fig. 3 shows the relationship between CP value and brake pressure, showing the relationship for a conventional brake system (according to the prior art, SdT) with linear behavior, in which the CP value is constant, and for the non-linear braking behavior according to the brake system 12 presented here or its friction brake 16.

[0073] Thus, with new materials, which are used in particular to potentially meet the requirements of the Euro 7 standard, a pressure-dependent loss of the CP value occurs. In the case of disc brakes, where the surface area between the disc and pad does not change, one can speak of a loss of friction coefficient.

[0074] With a conventional braking system, the disadvantage without the method presented here would be that the desired braking torque would not be correctly implemented, and the decrease in CP value would be noticeable in the pedal feel, particularly because there would be no clear pressure point and therefore poor modulation due to the changing braking torques. Furthermore, the pedal feel would be too sharp at low pressure and too dull at high pressure.

[0075] Furthermore, Fig. 4 shows the braking torque as a function of the CP value for different temperatures. Thus, the pressure specified by the actuator 22 for the respective friction brake 16 is determined, whereby the temperature is determined separately for each of the friction brakes 16, since they can have different temperatures, and the characteristic curves shown in Fig. 4 can be determined accordingly.

[0076] Therefore, the method is specifically designed so that the braking torque generated by actuator 22 scales linearly with the actuation of a brake pedal, which provides the brake signal. Furthermore, the brake signal is used, for example, by a vehicle control system for stabilization, such as ESP, ABS and / or 24-1886 PIF.

[0077] 12

[0078] Brake control and / or driver assistance system provided, which is used in particular to achieve the most advantageous stability of the vehicle.

[0079] For example, the CP value parameter can be updated, particularly as a pressure-dependent parameter, via a characteristic curve. Furthermore, a function can be used, whereby, depending on the computing power of a control unit 14 (e.g., one with an electronic computing device), a function is used for the calculation, and this can result in latency, which should be kept as low as possible. For particularly low latency, instead of an active function, a lookup table can be stored in a memory area of ​​the control unit 14, which sets the desired braking torque to the correct pressure. This allows for a direct conversion of the desired braking torque without latency.

[0080] In order to optimize the braking performance for both vehicle stabilization and metering, it is advantageous to consider the non-linear behavior as a function of the temperature of at least one of the brake elements 18 and / or 20 according to the method.

[0081] The motor vehicle 10 presented here, as well as the braking system 12 and the appropriate method, provide nonlinearity compensation and temperature compensation to improve the braking performance of the motor vehicle 10. -1886 PIF

[0082] 13

[0083] Reference symbol list

[0084] Motor vehicle brake system control unit friction brake

[0085] first brake element second brake element actuator

[0086] wheel

[0087] Temperature measuring unit

Claims

24-1886 PIF 14 Patent claims 1. Method for operating a braking system (12) of a motor vehicle (10), which has a control unit (14) and at least one friction brake (16), with a first brake element (18) and at least one second brake element (20), which are brought into contact by a pressure acting on them by means of an actuator (22), whereby a braking torque is formed due to friction, which acts on at least one wheel (24) of the motor vehicle (10), and for the first brake element (18) and / or the at least one second brake element (20) a material is used in which a relationship between pressure and braking torque is not linear and the braking torque is temperature-dependent, comprising the steps: - Detection of a brake signal by which the braking torque (target braking torque) acting on the wheel (22) is specified by the control unit (14) of the brake system (12); - Determining the current temperature of the first brake element and / or at least one second brake element; - Determining the pressure to be applied for the specified braking torque based on the non-linear relationship as a function of the determined current temperature by the control unit (14); and - Activation of the actuator (22) based on the brake signal, which provides the specified pressure for the contact between the first and at least one second brake element (18) depending on the specified braking torque, so that the specified braking torque is generated by friction.

2. Method according to claim 1 , characterized by the fact that Determining the pressure to be applied is done using a lookup table stored in a memory area of ​​the control unit (14), and / or by means of a function executed by a processor of the control unit (14), and / or using a characteristic curve. 24-1886 PIF 15 3. Method according to claim 1 or 2, characterized by the fact that Determining the current temperature is done using a sensor and / or a calculation.

4. Method according to any one of the preceding claims, characterized by the fact that where the temperature is determined for the first brake element (18) and / or the at least one second brake element (20) of at least two friction brakes (16), and the pressure is determined for each friction brake (16).

5. Method according to any one of the preceding claims, characterized by the fact that when at least one friction brake (16) is a disc brake and / or the first brake element (18) and / or the second brake element (18) is designed as a brake shoe and / or brake disc.

6. Method according to any one of the preceding claims, characterized by the fact that The brake signal is provided by a vehicle control system for vehicle stabilization, for brake control and / or for a driver assistance system.

7. Method according to any of the preceding claims, characterized by the fact that The braking torque generated by the actuator (22) scales linearly with the actuation of a brake pedal, which provides the braking signal.

8. Braking system (12) for a motor vehicle (10), comprising a control unit (14) and at least one friction brake (16), with a first brake element (18) and at least one second brake element (20), which can be brought into contact by a pressure acting on them, provided by an actuator (22), whereby a braking torque acting on at least one wheel (24) of the motor vehicle (10) can be generated due to friction, and the first brake element (18) and / or at least one second brake element (20) is formed from a material, 24-1886 PIF 16 in which the relationship between pressure and braking torque is not linear and the braking torque is temperature-dependent, and the braking system (12) can be operated using a method according to one of claims 1 to 7.

9. Brake system (12) according to claim 8, characterized by the fact that a temperature measuring unit (26) is provided which is designed to detect the temperature of the first brake element (18) and / or of at least one second brake element (20) in contact and / or without contact.

10. Motor vehicle (10) with a braking system (12) according to claim 8 or 9 and / or equipped to perform a method according to one of claims 1 to 7.

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