ELECTROMECHANICAL BRAKE SYSTEM FOR A MOTOR VEHICLE, METHOD FOR OPERATING THE BRAKE SYSTEM

Description

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

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

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

[0004] For safety reasons, braking systems are legally required to be designed in such a way that even in the event of a fault, i.e., the failure of one of the braking system components, the vehicle can still be braked with a specified minimum deceleration. Hydraulic braking systems typically feature a mechanical coupling between the brake pedal and the wheel brakes for emergency application.

[0005] However, if the braking system is designed as a purely electromechanical, 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 redundantly installing components of the braking system and / or taking over redundancy functions for each other.

[0006] Such braking systems with redundant components are known from the prior art. For example, the published 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 to design the control units such that they can each control all four braking mechanisms.However, redundancy for the braking mechanisms themselves is not provided, so that if one of the braking mechanisms fails, the braking performance of the vehicle is reduced.

[0007] A similar braking system is also known from US 2011 / 320099 A1. 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 are designed to acquire and / or evaluate sensor data from the wheel brake devices and / or sensors assigned to the motor vehicle, that each of the wheel brake devices is assigned 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 two of the primary electric motors of two of the wheel brake devices and two of the secondary electric motors of two other wheel brake devices for controlling the electric motors. This achieves advantageous redundancy both for the actuation of the brake devices and for the control of the electric motors assigned to the wheel brake devices.Both control units, one of the primary electric motors and one of the secondary electric motors, are assigned to each of the wheel brake devices, so that the braking performance of the braking system is still fully available even if one of the control units and / or one or more of the electric motors fails. The electric motors are not only functionally assigned to the respective wheel brake device, i.e., they are operatively connected or mechanically coupled to the braking device, but are also spatially assigned, i.e., they are arranged on the respective wheel brake device. Each of the secondary electric motors represents redundancy to one of the primary electric motors. The secondary electric motors are therefore only used if the respective primary electric motor fails.It is particularly conceivable for the secondary electric motors to be specified in such a way that they only achieve a legally required minimum deceleration during braking, and thus have a lower maximum electrical output and size than the primary electric motors. This advantageously saves installation space despite the existing redundancy. The control units are in particular only functionally assigned to the wheel brake devices, i.e. are electrically connected to the wheel brake devices via signaling, and are arranged anywhere in the vehicle, or are each also spatially assigned to at least one of the wheel brake devices, i.e. are arranged in particular on the wheel brake device. By assigning control units to four wheel brake devices each, only two instead of eight control units are required to achieve the advantageous redundancy, thus reducing the complexity and cost of the braking system.By designing the control units for evaluating and / or recording sensor data, it is advantageous to dispense with additional, specially designed control units or to create redundancy to such control units by installing at least one of the sensors redundantly and / or assigning it to both control units.

[0009] According to a preferred development of the invention, the sensors are designed as rotor position sensors, speed sensors, airbag sensors and / or distance sensors. Such a design of the sensors advantageously ensures that sensor data relevant for controlling the electric motors is directly recorded and / or evaluated by the control units. If the electric motors are designed, for example, as electrically annotated electric motors, the precise angular position of their rotors must be recorded for control. If the control unit records this directly via corresponding rotor position sensors, particularly advantageous, efficient control of the electric motors is guaranteed. With the help of speed sensors assigned to the wheels of the motor 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.Based on the sensor data from airbag sensors and / or distance sensors, dangerous situations and / or accident situations can be identified, 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 sensor close to the wheel, particularly as a microphone for noise monitoring. This also advantageously ensures direct recording and / or evaluation of relevant sensor data.

[0010] According to a preferred development of the invention, the primary electric motors and / or the secondary electric motors are designed as electrically commutated or brushless electric motors. Designing the electric motors as electrically commutated electric motors advantageously ensures that the wheel brake devices are actuated efficiently. Preferably, only the primary electric motors are designed as electrically commutated electric motors, and the secondary electric motors as DC motors, which advantageously save space. Alternatively, the primary electric motors and / or the secondary electric motors are designed as three-phase asynchronous motors. This advantageously makes the electric motors cost-effective, particularly because such motors do not require rotor position sensors to detect the angular position of their rotors.It is also conceivable for one of the primary electric motors and one of the secondary electric motors to be designed as a common 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 one another, 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 motor windings are assigned to the control units in a similar way to the assignment of the electric motors to the control units described above. As a result, the electric motors are also advantageously designed to be cost-effective, in particular because one of the primary electric motors and one of the secondary electric motors are arranged in a common housing with only one rotor.

[0011] According to a preferred development of the invention, the control units are each arranged closer to at least one of the two wheel brake devices, whose primary electric motor they are assigned to, than to one of the two wheel brake devices, whose secondary electric motor they are assigned to. Such an arrangement of the control units advantageously ensures that the length of the potentially error-prone electrical lines between at least one of the primary electric motors and the respective control unit is minimized, thus increasing the reliability of the control. Alternatively, the control units are arranged in a protected area of ​​the motor vehicle, where they are exposed to lower temperature requirements and environmental influences than in the vicinity of the wheel brake devices, where they are less robust and thus advantageously more cost-effective.

[0012] According to a preferred development of the invention, the two wheel brake devices, whose primary electric motors are respectively assigned to the control units, are arranged on the same wheel axle of the motor vehicle. Such an arrangement advantageously ensures that the control units each assume a redundant function for one another on the same wheel axle, and thus, if one control unit fails, all wheel brake devices on both axles can still be actuated, namely by two of the primary electric motors on one axle and by two of the secondary electric motors on the other axle. The braking system is designed with parallel axle-by-axle redundancy.

[0013] According to a preferred development of the invention, it is alternatively provided that the two wheel brake devices, whose primary electric motors are respectively assigned to the control units, are each 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 of the control units controls one of the primary and one of the secondary electric motors on each of the two axles, and thus, if one control unit fails, all wheel brake devices on both axles can still be actuated, namely on each axle by one of the primary and one of the secondary electric motors. The braking system is designed with diagonal axle redundancy.

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

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

[0016] According to a preferred development of the invention, if one of the control units fails, the other control unit is activated as a fallback reaction. By activating the other control unit, the actuation of all four wheel brake devices is advantageously ensured.

[0017] According to a preferred development of the invention, it is provided that a warning message is output as a substitute reaction, in particular on a display device assigned to a driver of the motor vehicle. Outputting the warning message advantageously ensures that the driver is immediately informed of the failure and can take suitable measures, in particular aborting the journey and / or visiting a workshop. The warning message is preferably output simultaneously with one of the substitute reactions described above, in which a failure of another of the control units and / or another of the electric motors is compensated for by appropriately controlling one of the control units and / or one of the electric motors. If only the failure of one of the secondary electric motors is detected, in particular no change in the control is necessary; outputting 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 coding. For example, a failure of one of the secondary electric motors would be indicated simply 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. Likewise, different instructions could advantageously be issued to the driver, for example, a request to immediately interrupt the journey if one of the primary electric motors and / or one of the control units fails.

[0018] Further preferred features and combinations of features emerge from the above description and from the claims. The invention is explained in more detail below with reference to the drawing. The sole FigureA schematic representation of an electromechanical braking system.

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

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

[0021] In addition, the braking system 1 has exactly two control units 5. 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 two of the secondary electric motors 4 of two other wheel brake devices 2 for controlling the electric motors 3, 4. The two wheel brake devices 2, whose primary electric motors 3 the control units 5 are each assigned to, are each assigned to the same wheel axle of the motor vehicle. The control units 5 are each arranged closer to the two wheel brake devices 2, whose primary electric motors 3 they are assigned to, than to the two wheel brake devices 2, whose secondary electric motors 4 they are assigned to.

[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 controlled.

[0023] Likewise, each of the control units 5 assumes a redundancy function for the other control unit 5. If one of the control units 5 fails, the other control unit 5 is then controlled.

[0024] The control units 5 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. The sensors are, 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 double arrows, the control units 5 are connected to each other and to other control units 7 of the motor vehicle via a bus system, for example, Ethernet, Flexray, or CAN. At least one of the other control units 7 is configured, for example, to further process the sensor data acquired or evaluated by the control units 5.

[0026] In addition, for example, at least one of the further control units 7 is designed to monitor the electric motors 3, 4 and the control units 5 for functionality and, in the event of failure of one of the electric motors 3, 4 and / or one of the control units 5, to trigger suitable substitute reactions, in particular to change the control as described above and / or to output an error message.

Claims

1. Electromechanical braking system (1) for a motor vehicle, having four wheel braking devices (2) and having two control units (5), - wherein the control units (5) are designed to capture and / or evaluate sensor data from the wheel braking devices (2) and / or sensors (6) assigned to the motor vehicle, characterized in that the braking system comprises four primary and four secondary electric motors, - 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 two of the secondary electric motors (4) of two others 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 arranged closer to at least one of the two wheel braking devices (2), to the primary electric motor (3) of which they are assigned, than to one of the two wheel braking devices (2), to the secondary electric motor (4) of which they are assigned.

5. Braking system according to one of the preceding claims, characterized in that the two wheel braking devices (2), to the primary electric motors (3) of which the control units (5) are each assigned, are 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 two wheel braking devices (2), to the primary electric motors (3) of which the control units (5) are each assigned, 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) and the control units (5) 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) or one of the control units (5) 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, if one of the control units (5) fails, the other control unit (5) is actuated as the substitute response.

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.