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) 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 dependent on a vehicle condition. The invention also relates to a brake system (12) and to a motor vehicle (10).

Description

[0001] 24-2054 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 9 and 10.

[0005] The requirements for vehicle emissions, particularly particulate matter emissions, are constantly increasing and are, for example, stipulated by legal standards. 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, 24-2054 PIF

[0010] 2

[0011] The brake elements are brought into contact by a pressure applied to them by means of 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, which results in a non-linear relationship between pressure and braking torque. Furthermore, the braking torque depends on a driving condition, such as, in particular, the speed of the motor vehicle, and this dependency may also involve non-linearity.

[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. 24-2054 PIF

[0015] 3

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

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

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

[0019] In a second step, the vehicle's condition is determined. This determination can be made, for example, using a recorded measurement from which the condition can be inferred. Furthermore, it can be calculated using corresponding measured variables; for instance, the vehicle speed can be deduced from the wheel rotation speed.

[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 vehicle state. 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 by the brake signal, which, depending on the specified braking torque, provides the required pressure for contact between the first brake element and at least one second brake element, so that the specified braking torque is generated by friction. 24-2054 PIF

[0022] 4

[0023] It has been shown that the 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 components. According to the current state of the art, integrated braking (IB) is used to control vehicle brakes. IB is essentially a software component implemented on a control unit and combined with hardware, such as an actuator for pressure build-up. Integrated braking systems assume that the physics of the brakes developed so far allow for a constant CP value. However, it has been found that the CP value does not behave linearly depending on the material. Therefore, with an integrated braking system that has a fixed CP value, a discrepancy occurs between the target and actual braking torque, with deviations of up to 50 percent being possible.

[0024] 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.

[0025] 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 at 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.

[0026] In particular, 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. 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 can have 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, which in particular is of 24-2054 PIF.

[0027] 5

[0028] Brakes are devices that can apply pressure to both sides of a disc using brake pads, or by pressing brake pads or friction linings against the disc. The brake pads can be mounted in a caliper that surrounds the brake disc. The brake is activated primarily hydraulically by an actuator that builds up pressure by pressing the brake pad, or at least one brake pad, against the brake disc.

[0029] In particular, 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 CP value to braking torque is constant in conventional disc brakes, but is influenced by novel coatings, currently under development to meet future standards for operating a motor vehicle, in such a way that the braking behavior becomes non-linear, thus giving the method advantages over conventional methods for operating integrated brakes.

[0030] The method according to the invention offers the advantage of enabling advantageous braking of the motor vehicle. A further advantage is that a favorable pedal feel can be achieved during braking, and, moreover, the driver can ensure precise control of the braking deceleration.

[0031] In an advantageous embodiment of the invention, the vehicle state is a speed and / or a braking state, such as deceleration, of the motor vehicle. Tests regarding new brake pads for Euro 7 standard brakes have shown that, in addition to pressure dependence, vehicle speed also has a particularly significant influence on the non-linear braking behavior. In other words, vehicle speed, but also, for example, vehicle acceleration, such as that caused by deceleration using the brakes, is taken into account in order to determine the correction or setting for the correct braking torque and the necessary pressure. This offers the advantage that the braking system can be adjusted particularly advantageously at any speed that the motor vehicle can achieve due to its drive system. 24-2054 PIF

[0032] 6

[0033] In a further advantageous embodiment of the invention, the vehicle condition is derived from a measured value of a parameter such as speed, wheel speed, deceleration, and / or brake pressure. In other words, in addition to a known data set of braking characteristics, signals containing vehicle speed, drive speed, deceleration, and / or brake pressure are used to determine the condition, particularly its physical state. This offers the advantage that, for example, braking performance can be influenced particularly effectively in the event of additional degradation.

[0034] In a further advantageous embodiment of the invention, the vehicle condition is determined without the use of a Kalman filter. In other words, a condition estimation algorithm is used that provides a particularly advantageous estimate of the vehicle condition from noisy, insufficient, and / or erroneous measured values ​​based on a system model that, for example, represents a function of the vehicle's braking system or brake assembly. Thus, measured values, especially intermediate values, can be determined based on a prediction, and consequently, an advantageous vehicle condition estimate and the resulting required pressure can be calculated. Therefore, the method offers the advantage of being particularly precise.

[0035] In a further advantageous embodiment of the invention, the pressure to be applied is determined by means of a self-learning model. In other words, a method, and in particular an algorithm, is used by which future pressures can be advantageously derived from previously determined pressures, especially from the feedback of several measured variables. In other words, a model is provided that can be updated based on self-learning methods, such as those provided by the algorithm and / or an artificial neural network. This offers the advantage that the process can be carried out particularly efficiently.

[0036] 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.

[0037] 7

[0038] 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.

[0039] 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.

[0040] 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. In other words, the brake signal is not provided by the driver of the vehicle, but can be provided by a vehicle system that serves in particular to ensure stable and therefore safe driving of the vehicle. This offers the advantage that the method can be used particularly advantageously for stabilizing 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 are actuated by a 24-2054 PIF

[0043] 8

[0044] must be brought into contact with an acting pressure 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 brake element and / or the at least one second brake 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 brake system can be operated by means of a method according to the first aspect of the invention.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] The invention will now be explained in more detail with reference to a preferred embodiment and the drawings. The drawings show:

[0050] Fig. 1 shows a schematic side view of a motor vehicle with a braking system, based on which a method for operating the braking system and thus the motor vehicle is outlined; 24-2054 PIF

[0051] 9

[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 for the relationship between CP value and brake pressure for the two disc brakes according to Fig. 2.

[0054] 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, whereby the relationship between pressure and braking torque is non-linear. Furthermore, the braking torque depends on a vehicle condition, in particular the speed of the motor vehicle 10, whereby the dependence is also, in particular, non-linear.

[0055] 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.

[0056] In this configuration, at least one friction brake 16, or the respective friction brake 16 of each wheel 24, is designed as a disc brake, such that the first brake element 18 is, for example, designed as a brake disc and / or the at least second brake element 20 is, for example, designed as a brake shoe, so that the brake disc is contacted on both sides by the brake shoes by means of the pressure built up by the actuator 22, in order to generate the corresponding friction. 24-2054 PIF

[0057] 10

[0058] Furthermore, a temperature measuring unit could be provided for the brake system 12, which includes at least one sensor and is designed to detect the temperature of the respective brake elements 18 and / or 20 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.

[0059] The procedure for operating the brake system 12 comprises the following steps:

[0060] 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.

[0061] In a second step, the driving condition is determined, for example based on the speed of a brake pressure and a torque (torque request), which are recorded and supplied to the control unit 14 via a bus system 26.

[0062] In the third step, the pressure required for the specified braking torque or the desired target braking torque is determined based on the non-linear relationship and the driving condition, which is characterized in particular by the data transmitted by the bus or bus system 26. For this purpose, a characteristic map 28, which includes the relationship between CP value, brake pressure and speed, can be used, for example.

[0063] 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.

[0064] 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 disc brake 24-2054 PIF, in particular

[0065] 11

[0066] a designed friction brake 16 of the brake system 12, which uses a material for at least one of the brake elements 18 and / or 20, through which a non-linear relationship of the braking torque to the braking pressure is shown.

[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 used as friction linings for the friction brake 16, which are optimized to produce particularly low brake abrasion, exhibit the aforementioned non-linear behavior.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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. 24-2054 PIF

[0073] 12

[0074] Therefore, the method is specifically designed such 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 provided, for example, by a vehicle control system for stabilization purposes, such as ESP, ABS, and / or brake control and / or a driver assistance system, which is used in particular to optimize vehicle stability.

[0075] 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.

[0076] 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.

[0077] The motor vehicle 10 presented here, as well as the braking system 12 and the appropriate method, provide non-linearity compensation and temperature compensation to improve the braking performance of the motor vehicle 10.

[0078] Furthermore, in the case of additional integration, braking performance can be optimized if, in addition to the brake characteristic data set, known signals such as vehicle speed, wheel speed, deceleration, and brake pressure are used to physically determine the new state or vehicle state. To compensate for measurement noise or inaccuracies in the signal measurements used to determine the vehicle state, Kalman filtering can be employed, for example, which allows for an acceptable estimation of the brake state based on statistics of the measurement noise. 24-2054 PIF

[0079] 13

[0080] This ensures that the brake control system or brake system 12 is always able to deliver and utilize the desired braking characteristics in real time. This guarantees particularly advantageous performance of the brakes or brake system 12, thus ensuring a particularly high level of safety and driving comfort for the vehicle 10.

[0081] Furthermore, the control unit 14, or a brake control system such as the integrated brake, can be designed so that self-learning takes place from the outset based on the measured data, for example through feedback loops, so that the brake always determines the optimal, particularly advantageous pressure for the desired braking torque. This can also result in particularly low costs for an integrated brake (IB). -2054 PIF

[0082] 14

[0083] Reference symbol list

[0084] Motor vehicle brake system control unit friction brake

[0085] first brake element second brake element actuator

[0086] wheel

[0087] bus system

[0088] Characteristic map

Claims

24-2054 PIF 15 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 depends on a vehicle condition, comprising the steps: - Detection of a brake signal by which the braking torque acting on the wheel (22) is specified by the control unit (14) of the brake system (12); - Determining the vehicle's condition; - Determining the pressure to be applied for the specified braking torque based on the non-linear relationship depending on the vehicle state 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 The vehicle condition is a speed and / or braking condition of the motor vehicle (10).

3. Method according to claim 1 or 2, characterized by the fact that The vehicle condition is assessed based on a measured value of a quantity, such as the 24-2054 PIF 16 Speed, wheel speed, deceleration and / or brake pressure is derived.

4. Method according to any one of the preceding claims, characterized by the fact that The vehicle's condition is determined using a Kalman filter.

5. Method according to any one of the preceding claims, characterized by the fact that The determination of the pressure to be applied is carried out using a self-learning model.

6. Method according to any one of the preceding claims, 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.

7. Method according to any 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.

8. Method according to any one 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.

9. 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) 24-2054 PIF 17 and / or at least a second brake element (20) is formed from a material in which the relationship between pressure and braking torque is not linear and the braking torque depends on a vehicle condition, and the brake system (12) can be operated using a method according to one of claims 1 to 8.

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

Images