Method for operating a motor vehicle, brake system and motor vehicle

Abstract

The invention relates to a method for operating a motor vehicle (10) comprising a brake system (12) that has a control unit (14) and a friction brake (16), comprising a first brake element (18) and a second brake element (18) that are brought into contact by a pressure acting thereon, which can be provided by means of an actuator (20), as a result of which a braking torque that acts on at least one wheel (22) of the motor vehicle (10) is formed on account of friction, and a material is used for the first brake element (18) and / or second brake element (18), through which a relationship between pressure and braking torque is non-linear. The invention further relates to a brake system (12) and a motor vehicle (10).

Description

[0001] Methods for operating a motor vehicle, braking system and motor vehicle

[0002] The invention relates to a method for operating a motor vehicle with a braking system according to claim 1. Furthermore, the invention relates to a braking system and a corresponding motor vehicle according to claims 9 and 10.

[0003] Increasing demands on vehicle emissions, particularly particulate matter emissions, such as those stipulated by the upcoming Euro 7 standard, necessitate a redesign of braking systems and / or the use of particle-reducing brake pads. The use of new materials can alter the braking characteristics of the brakes.

[0004] DE 102021 214 093 A1 discloses a method for determining a force gradient and a brake arrangement. EP 2 528 790 B1 discloses a method for operating a brake system for a motor vehicle, and EP 2 365 473 B1 further discloses a method for determining a measure of an acting braking force or frictional force on a disc brake.

[0005] The object of the present invention is to provide a method, a braking system and a motor vehicle by which a change in braking behavior that may occur, in particular due to new materials, can be compensated.

[0006] 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.

[0007] A first aspect of the invention relates to a method for operating a motor vehicle with a braking system comprising a control unit and a friction brake, with a first brake element and a second brake element which are brought into contact by a pressure acting on them, mediated by an actuator, whereby a braking torque is formed due to friction, which acts on at least one wheel of the motor vehicle, and a material is used for the first brake element and / or the second brake element, whereby a relationship between pressure and braking torque is not linear, at least in a partial area in which the braking system is operated.

[0008] 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, which can, for example, issue a braking signal. The brake is, in particular, designed as a disc brake. The brake elements can be a brake pad and / or a brake disc. One of the brake elements can, for example, be rigidly connected to the wheel, whereby the braking torque acts on the wheel and thus enables the deceleration of the motor vehicle. In conventional disc brakes, the relationship between the pressure generated by the contact of the two brake elements with each other is linear to the resulting braking torque.

[0009] 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.

[0010] Therefore, the inventive method comprises the following steps:

[0011] In the first step, the brake system's control unit detects a brake signal, which is provided, for example, by a brake signal or actuator and / or a driver assistance system that specifies the braking torque. The control unit thus receives a predetermined brake signal. The braking torque corresponds to the desired deceleration that is to act on the wheel and therefore the vehicle. In the second step, the control unit determines the pressure required to achieve the predetermined braking torque, based on the non-linear relationship between pressure and braking torque. The control unit thus determines the pressure required for the contact between the two brake elements to achieve the desired deceleration.

[0012] In a third step, an actuator is activated based on the brake signal, which provides the pressure for contact between the two brake elements depending on the specified braking torque, so that the specified braking torque is generated by friction.

[0013] 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.

[0014] 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.

[0015] In other words, the inventive method proposes a controller design that takes into account the findings regarding new, non-linear material properties for potential Euro 7 brakes in order to convert the correct braking torques into the respective pressure, or vice versa. This offers the advantage of enabling efficient braking of the vehicle. A further advantage is that a favorable pedal feel can be achieved during braking, and, moreover, the driver can ensure precise modulation of the braking deceleration.

[0016] 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. In other words, a conversion table is used by which corresponding pressure-braking force or braking torque pairs are statically defined and, particularly for efficient operation of the control unit, retrieved based on the brake signal. The memory area can be, for example, RAM, but also non-volatile memory such as flash memory. This offers the advantage that the method can be carried out particularly efficiently, since, in particular, no calculations are required during the determination process. Furthermore, it is advantageous that the table can be multidimensional, so that, for example, corresponding pressure values ​​can be stored for different temperature ranges.

[0017] In a further advantageous embodiment of the invention, 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 by means of a characteristic curve. In other words, the necessary pressure is calculated based on the brake signal using a function, in particular, for example, also stored in the memory area, especially in real time. Additionally or alternatively, a characteristic curve is also stored, based on which the determination can be carried out. This offers the advantage that the pressure can be determined particularly efficiently.

[0018] 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 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 designed as the first or second brake element and can be pressurized from both sides by brake pads, or brake pads or friction linings can be pressed against the disc, with the brake pads thus forming the first or second brake element. The brake pads can be mounted in a so-called brake caliper, which surrounds the brake disc.In this system, 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.

[0019] 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.

[0020] 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.

[0021] 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 the braking system, especially one comprising 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. In a further advantageous embodiment of the invention, the determination is carried out as a function of a temperature, in particular the temperature of at least one of the brake elements.It has been shown that during highly dynamic driving, where at least one of the brake elements reaches a temperature of, for example, around 500 degrees Celsius, the CP value drops considerably. Therefore, determining the braking torque as a function of temperature is advantageous. This allows the braking system to decelerate the vehicle particularly effectively.

[0022] A second aspect of the invention relates to a braking system for a motor vehicle, comprising a control unit and a friction brake, with a first braking element and a second braking element that can be brought into contact by a pressure acting on them, provided by an actuator, whereby a braking torque can be generated due to friction, which acts on at least one wheel of the motor vehicle. In the braking system according to the invention, the first braking element and / or the second braking element are formed from a material in which the relationship between pressure and braking torque is not linear, and furthermore, the braking system can be operated by a method according to the first aspect of the invention.

[0023] Advantageous embodiments and further developments, 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.

[0024] 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.

[0025] 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.

[0026] 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 those subsequently mentioned in the description of the figures and / or shown in the figures alone, are usable not only in the combinations specified, but also in other combinations or individually. The invention will now be explained in more detail with reference to a preferred embodiment and the drawings.

[0027] It shows:

[0028] Fig. 1 a schematic side view of a motor vehicle comprising a

[0029] Brake system;

[0030] Fig. 2 shows a diagram of a braking torque ratio between

[0031] Braking torque and brake pressure for conventional disc brakes and disc brakes with non-linear braking behavior; and

[0032] Fig. 3 shows a diagram between CP value and brake pressure for the two

[0033] Brake pressures as shown in Fig. 2.

[0034] 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 a friction brake 16, with a first braking element 18 and a second braking element 18, which can be brought into contact by an actuator 20, so that a pressure acts on them when they are brought into contact, whereby a braking torque can be generated due to friction, which acts on at least one wheel 22 of the motor vehicle 10, and the first braking element 18 and / or the second braking element 18 are made of a material in which the relationship between pressure and braking torque is not linear.

[0035] Furthermore, a method for operating a motor vehicle 10 will be presented using the motor vehicle 10 and the associated braking system 12. The method serves to brake the motor vehicle 10 by means of the braking system 12 through pressure provided by the actuator 20 between the two brake elements 18 or through contact between the two brake elements 18.

[0036] The procedure comprises the following steps: In a first step, a brake signal is detected by the control unit 14 of the brake system 12, which specifies the braking torque that acts or is intended to act on at least one wheel 22.

[0037] In a second step, the control unit 14 determines the pressure that can be applied for the specified braking torque based on the non-linear relationship.

[0038] Furthermore, in a third step, an actuator 20 is activated based on the brake signal, which provides the pressure for the contact of the two brake elements 18 depending on the specified braking torque, so that the specified braking torque is generated by friction.

[0039] 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 uses a material for at least one of the brake elements 18, which shows a non-linear relationship between the braking torque and the brake pressure.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] Fig. 3 shows the relationship between CP value and brake pressure, showing the relationship for a conventional brake system (according to the state of the 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.

[0044] 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.

[0045] 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.

[0046] Therefore, the method is specifically designed so that the braking torque generated by actuator 20 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.

[0047] 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.

[0048] To optimize braking performance for both vehicle stabilization and metering, it is advantageous to consider the non-linear behavior according to the method, and it is further advantageous if the pressure is determined as a function of the temperature of at least one of the brake elements 18.

[0049] The motor vehicle 10 presented here, as well as the braking system 12 and the appropriate method, results in a non-linearity compensation to improve the braking performance of the motor vehicle 10.

[0050] Reference symbol list for motor vehicle brake system control unit friction brake brake element actuator

[0051] wheel

Claims

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

2. Method according to claim 1, characterized in that the determination of the pressure to be applied is carried out using a lookup table which is stored in a memory area of ​​the control unit (14).

3. Method according to claim 1 or 2, characterized in that the determination of the pressure to be applied is carried out by means of a function, by a processor of the control unit (14), and / or on the basis of a characteristic curve.

4. Method according to one of the preceding claims, characterized in that a disc brake is used as the friction brake (16) and / or the first brake element (18) and / or the second brake element (18) is designed as a brake shoe and / or brake disc.

5. Method according to claim 4, characterized in that a coating of the brake shoe and / or the brake disc is used for the non-linear relationship between pressure and braking torque.

6. Method according to one of the preceding claims, characterized in 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 one of the preceding claims, characterized in that the braking torque generated by the actuator (20) scales linearly with actuation of a brake pedal, by which the brake signal is provided.

8. Method according to one of the preceding claims, characterized in that the determination is carried out as a function of a temperature, in particular of at least one of the brake elements (18).

9. Braking system (12) for a motor vehicle (10), comprising a control unit (14) and a friction brake (16), with a first brake element (18) and a second brake element (18) which can be brought into contact by a pressure acting on them, provided by an actuator (20), whereby a braking torque can be generated due to friction, which acts on at least one wheel (22) of the motor vehicle (10), and the first brake element (18) and / or second brake element (18) is made of a material in which the relationship between pressure and braking torque is not linear, and the The braking 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 any one of claims 1 to 8.

Images