ELECTROMECHANICAL BRAKE SYSTEM FOR A MOTOR VEHICLE, METHOD

Description

[0001] The invention relates to an electromechanical braking system for a motor vehicle, comprising four wheel brake devices, four primary electric motors, four secondary electric motors, two control units, and a backup control unit.

[0002] Furthermore, the invention relates to a method for operating such a braking system. State of the art

[0003] To perform automated braking maneuvers, for example in the context of autonomous driving, a vehicle's braking system must have actuators that can be controlled independently of a driver's use of the brake pedal. Such a braking system is, for example, an electromechanical braking system and has a wheel brake device for each wheel of the vehicle. Each of these wheel brake devices is actuated by its associated electric motor to decelerate the vehicle. The braking system has one or more control units to control the electric motors.

[0004] It is legally mandated that, for safety reasons, braking systems must be designed in such a way that even in the event of a malfunction, i.e., if one of the components of the braking system fails, the vehicle can still be braked with a specified minimum deceleration. In hydraulic braking systems, a mechanical linkage between the brake pedal and the wheel brakes is typically provided for emergency operation.

[0005] However, if the braking system is designed as a purely electromechanical system, in particular as a so-called "brake-by-wire" braking system, in which no mechanical emergency actuation is possible, braking in the event of a fault is usually ensured by the fact that components of the braking system are installed redundantly and / or perform redundancy functions for each other.

[0006] Such braking systems with redundant components are known from the prior art. For example, European patent application EP 3 318 458 B1 discloses an electric braking device for a motor vehicle with three control units, wherein each of the control units controls two braking mechanisms for braking two wheels, and wherein, in the event of a failure of one or two of the control units, at least one of the other control units controls the respective braking mechanisms of the failed control unit, so that the motor vehicle can continue to be braked. In particular, two of the control units are designed as diagonal wheel control units, and the third as a front wheel control unit. Alternatively, it is provided that the control units are designed such that they can each control all four braking mechanisms.However, redundancy for the braking mechanisms themselves is not provided, so if one of the braking mechanisms fails, the braking performance of the vehicle is reduced.

[0007] Furthermore, US patent 2009 / 223752 A1 discloses an electromechanical braking system for a motor vehicle, comprising four wheel brake devices, four primary electric motors, four secondary electric motors, and two control units, wherein the control units are designed to acquire and / or evaluate sensor data from the wheel brake devices and / or sensors associated with the motor vehicle, and wherein each of the wheel brake devices is assigned to one of the primary electric motors and one of the secondary electric motors for actuating the respective wheel brake devices. Disclosure of the invention

[0008] The braking system according to the invention, with the features of claim 1, is characterized in that the control units and / or the backup control unit are configured for acquiring and / or evaluating sensor data from the wheel brake devices and / or sensors associated with the motor vehicle, that each of the wheel brake devices is assigned to one of the primary electric motors and one of the secondary electric motors for actuating the respective wheel brake devices, and that each of the control units is assigned to two of the primary electric motors of two of the wheel brake devices, and the backup control unit is assigned to the four secondary electric motors of the wheel brake devices for controlling the electric motors. This achieves advantageous redundancy for both the actuation of the brake devices and the control of the electric motors assigned to the wheel brake devices.Each wheel brake device is assigned to one of the control units, the backup control unit, one of the primary electric motors, and one of the secondary electric motors, ensuring that the braking system's performance remains fully available even if one or more of the control units and / or electric motors fail. The electric motors are not only functionally assigned to their respective wheel brake devices—meaning they are mechanically coupled to the brake device—but also spatially, meaning they are located directly at the respective wheel brake device. Each secondary electric motor provides redundancy for one of the primary electric motors. Therefore, the secondary electric motors are only used if the corresponding primary electric motor fails.It is particularly conceivable that the secondary electric motors are specified in such a way that they only achieve a legally required minimum deceleration during braking, and therefore have a lower maximum electrical power and size than the primary electric motors. This advantageously saves installation space despite the existing redundancy. The control units and / or the backup control unit are functionally assigned to the wheel brake devices, i.e., electrically connected to the wheel brake devices via signals, and are located at any point in the vehicle, or at least spatially assigned to one of the wheel brake devices, i.e., specifically located on the wheel brake device itself.By assigning control units to two wheel brake devices each, and the backup control unit to all four wheel brake devices, only three control units instead of eight are required to achieve the advantageous redundancy, thus reducing the complexity and cost of the braking system. By designing the control units to evaluate and / or acquire sensor data, the need for additional, specially designed control units is advantageously eliminated, or redundancy is created for such control units by installing at least one sensor redundantly and / or assigning it to two control units, in particular one of the control units and the backup control unit.

[0009] According to a preferred embodiment of the invention, the sensors are configured as rotor position sensors, speed sensors, airbag sensors, and / or distance sensors. This configuration advantageously ensures that sensor data relevant for controlling the electric motors is directly acquired and / or evaluated by the control units. For example, if the electric motors are designed as electrically annotated electric motors, the precise angular position of their rotors must be determined for control purposes. If the control unit acquires this information directly via corresponding rotor position sensors, a particularly advantageous and efficient control of the electric motors is ensured. Using speed sensors assigned to the wheels of the vehicle, the wheel speed is determined and can be taken into account during braking, for example, to advantageously prevent one of the wheels from locking up.Based on sensor data from airbag sensors and / or distance sensors, hazardous situations and / or accident situations can be detected, allowing the control units to initiate braking, particularly emergency braking, if necessary. Preferably, at least one of the sensors is designed or arranged as a wheel-mounted sensor, especially as a microphone for noise monitoring. This also advantageously ensures direct acquisition and / or evaluation of relevant sensor data.

[0010] According to a preferred embodiment of the invention, the primary and / or secondary electric motors are designed as electrically commutated or brushless electric motors, respectively. Designing the electric motors as electrically commutated motors advantageously ensures efficient actuation of the wheel brake devices. Preferably, only the primary electric motors are designed as electrically commutated motors, and the secondary electric motors as DC motors, which are advantageously space-saving. Alternatively, the primary and / or secondary electric motors are designed as three-phase asynchronous motors. This results in advantageously cost-effective design of the electric motors, particularly because such motors do not require rotor position sensors to detect the angular position of their rotors.It is also conceivable that one of the primary electric motors and one of the secondary electric motors are each designed as a single electric motor with a primary motor winding and a secondary motor winding, in particular stator windings, wherein the primary motor winding and the secondary motor winding can be controlled independently of each other, and wherein when the primary motor winding is controlled, the electric motor is used as the primary electric motor, and when the secondary motor winding is controlled, the electric motor is used as the secondary electric motor. The assignment of the motor windings to the control units is analogous to the assignment of the electric motors to the control units described above. This also results in an advantageously cost-effective design for the electric motors, particularly because one of the primary electric motors and one of the secondary electric motors are thus arranged in a common housing with only one rotor.

[0011] According to a preferred embodiment of the invention, the control units are arranged directly on each of the wheel brake devices to which they are assigned as primary electric motors. This arrangement of the control units advantageously minimizes the length of the potentially fault-prone electrical lines between the respective primary electric motor and the control unit, thereby increasing the reliability of the control signal. Alternatively, the control units and / or the backup control unit are arranged in a protected area of ​​the vehicle where they are exposed to lower temperature requirements and environmental influences than near the wheel brake devices, where they can be designed to be less robust and thus advantageously more cost-effective.

[0012] According to a preferred embodiment of the invention, the wheel brake devices assigned to each control unit are arranged on the same wheel axle of the motor vehicle. Such an arrangement advantageously ensures that, even if one of the control units and the backup control unit fail, at least both wheel brake devices on one of the two axles can be actuated by the remaining control unit. The braking system is designed with parallel axle-wise redundancy.

[0013] According to a preferred embodiment of the invention, it is alternatively provided that the wheel brake devices assigned to each control unit are assigned to different wheel axles of the motor vehicle and are arranged at opposite ends of the wheel axles. Such an assignment advantageously ensures that each control unit controls one of the electric motors on each of the two axles, and thus, even if one of the control units and the backup control unit fail, one of the wheel brake devices on each of the two axles can still be actuated. The braking system is designed with diagonal axle-wise redundancy.

[0014] The method according to the invention, with the features of claim 7, is characterized in that the electric motors, the control units, and the backup control unit of the braking system are monitored for functionality, and that a substitute reaction is triggered if one of the electric motors, one of the control units, or the backup control unit fails. By monitoring for functionality and triggering the substitute reaction, it is advantageously ensured that a failure of one of the electric motors, one of the control units, and / or the backup control unit is detected immediately, and that the braking effect of the braking system is maintained.

[0015] According to a preferred embodiment of the invention, if one of the primary electric motors fails, the secondary electric motor assigned to the same wheel brake device is activated as a substitute. By activating the secondary electric motor, the continued operation of the wheel brake device is advantageously ensured.

[0016] According to a preferred embodiment of the invention, if one of the control units fails, the backup control unit is activated as a substitute response. By activating the backup control unit, the continued operation of all four wheel brake devices is advantageously ensured.

[0017] According to a preferred embodiment of the invention, a warning message is issued as a substitute response, particularly on a display device assigned to the driver of the motor vehicle. Issuing the warning message advantageously ensures that the driver is immediately informed of the failure and can take appropriate measures, in particular to abort the journey and / or visit a workshop. Preferably, the warning message is issued simultaneously with one of the substitute responses described above, in which a failure of one of the control units and / or another of the electric motors is compensated for by suitable control of the backup control unit and / or one of the electric motors. If only the failure of one of the secondary electric motors or the backup control unit is detected, in particular no change to the control is necessary; issuing the warning message is sufficient.Preferably, the warning message is issued depending on the relevance or severity of the failure, for example, using different color codes. For instance, a failure of one of the secondary electric motors or the backup control unit would be indicated by a yellow warning light, while a failure of one of the primary electric motors and / or one of the control units would be indicated by a red warning light. Similarly, it would be advantageous to issue different instructions to the driver, such as a request to immediately stop driving in the event of a failure of one of the primary electric motors and / or one of the control units.

[0018] Further preferred features and combinations of features will become apparent from the foregoing and from the claims. The invention will now be explained in more detail with reference to the drawing. The only illustration shown is... Figure a schematic representation of an electromechanical braking system.

[0019] The following describes, with reference to the figure, an advantageous electromechanical braking system 1 for a motor vehicle (not shown in detail). The braking system 1 has exactly four wheel brake devices 2. Each of the wheel brake devices 2 is assigned to one of the wheels of the motor vehicle (also not shown). In the present embodiment, the braking system 1 is purely electromechanical and therefore has no hydraulic components or hydraulic fluid circuit for actuating the wheel brake devices 2.

[0020] Braking is achieved by directly actuating the wheel brake devices 2, which are designed as friction brake devices. For this purpose, the brake system 1 comprises exactly four primary electric motors 3 and exactly four secondary electric motors 4. In the present embodiment, the electric motors 3 and 4 are designed as electrically commutated electric motors. Each of the wheel brake devices 2 is assigned to one of the primary electric motors 3 and one of the secondary electric motors 4 for actuating the respective wheel brake device 2.

[0021] Furthermore, the braking system 1 has exactly two control units 5 and exactly one backup control unit 8. Each of the control units 5 is assigned to two of the primary electric motors 3 of two of the wheel brake devices 2, and the backup control unit 8 is assigned to the four secondary electric motors 4 of the wheel brake devices 2 for controlling the electric motors 3, 4. The control units 5 are each arranged directly on one of the wheel brake devices 2 to which they are assigned their primary electric motor 3.

[0022] Each of the secondary electric motors 4 assumes a redundancy function for the primary electric motor 3 assigned to the same wheel brake device 2. If the corresponding primary electric motor 3 fails, the secondary electric motor 4 assigned to the same wheel brake device 2 is then activated.

[0023] The backup control unit 8 also provides redundancy for the control units 5. If one of the control units 5 fails, the backup control unit 8 is then activated.

[0024] The control units 5 and / or the backup control unit 8 are further configured to acquire and / or evaluate sensor data from the wheel brake devices 2 and / or sensors 6 associated with the motor vehicle. These sensors include, in particular, rotor position sensors of one of the electric motors 3, 4, speed sensors of one of the wheels of the motor vehicle, airbag sensors of the motor vehicle, and / or distance sensors of the motor vehicle.

[0025] Furthermore, as indicated by the double arrows, the control units 5 and the backup control unit 8 are interconnected via a bus system, such as Ethernet, FlexRay, or CAN, and also communicate with other control units 7 of the vehicle. At least one of the other control units 7 is, for example, configured to further process the sensor data acquired or evaluated by the control units 5 or the backup control unit 8.

[0026] Furthermore, at least one of the other control units 7 is designed to monitor the functionality of the electric motors 3,4 as well as the control units 5 and the backup control unit 8, and to trigger suitable replacement reactions in the event of failure of one of the electric motors 3,4, one of the control units 5 and / or the backup control unit 8, in particular to change the control as described above and / or to issue an error message.

Claims

1. Electromechanical braking system (1) for a motor vehicle, having four wheel braking devices (2), having four primary electric motors (3), having four secondary electric motors (4), having two control units (5), and having a backup control unit (8), - wherein the control units (5) and / or the backup control unit (8) are designed to capture and / or evaluate sensor data from the wheel braking devices (2) and / or sensors (6) associated with the motor vehicle, - wherein each of the wheel braking devices (2) is respectively assigned one of the primary electric motors (3) and one of the secondary electric motors (4) in each case for the purpose of actuating the respective wheel braking devices (2), and - wherein each of the control units (5) is respectively assigned to two of the primary electric motors (3) of two of the wheel braking devices (2) and the backup control unit (8) is assigned to the four secondary electric motors (4) of the wheel braking devices (2) for the purpose of actuating the electric motors (3,4).

2. Braking system according to Claim 1, characterized in that the sensors (6) are in the form of rotor position sensors, speed sensors, airbag sensors and / or distance sensors.

3. Braking system according to one of the preceding claims, characterized in that the primary electric motors (3) and / or the secondary electric motors (4) are in the form of electrically commutated electric motors.

4. Braking system according to one of the preceding claims, characterized in that the control units (5) are each directly arranged on one of the wheel braking devices (2), to the primary electric motor (3) of which they are assigned.

5. Braking system according to one of the preceding claims, characterized in that the wheel braking devices (2) respectively assigned to the control units (5) are each arranged on the same wheel axle of the motor vehicle.

6. Braking system according to one of Claims 1 to 3, characterized in that the wheel braking devices (2) respectively assigned to the control units (5) are each assigned to different wheel axles of the motor vehicle and are arranged at opposite ends of the wheel axles.

7. Method for operating an electromechanical braking system (1) according to one of Claims 1 to 6, characterized in that the electric motors (3,4), the control units (5) and the backup control unit (8) of the braking system (1) are monitored for functionality, and in that a substitute response is triggered if one of the electric motors (3,4), one of the control units (5) or the backup control unit (8) fails.

8. Method according to Claim 7, characterized in that, if one of the primary electric motors (3) fails, the secondary electric motor (4) assigned to the same wheel braking device (2) is actuated as the substitute response.

9. Method according to either of Claims 7 and 8, characterized in that the backup control unit (8) is actuated as the substitute response if one of the control units (5) fails.

10. Method according to one of Claims 7 to 9, characterized in that a warning message is output as the substitute response, in particular on a display device assigned to a driver of the motor vehicle.