BRAKING SYSTEM FOR AN AUTONOMOUS VEHICLE

Description

[0001] The invention relates to a braking system in an at least partially autonomous vehicle according to the preamble of claim 1.

[0002] In a vehicle that is at least partially autonomous, the braking system must be designed for autonomous brake pressure build-up as well as for autonomous driver assistance control (for example, ABS or ESP functions). Depending on the system configuration, the braking system must be able to perform both braking and steering tasks in the event of a malfunction, automatically bringing the vehicle to a safe stop and holding it there. For this purpose, the braking system is equipped with a primary brake control system and a redundant secondary brake control system.

[0003] In a typical braking system, the primary brake control system comprises a primary control unit and one electromechanical primary actuator for each vehicle wheel to actuate the vehicle wheel brake. Based on a target deceleration input generated in a pilot system (for example, a driver assistance system) and / or a target deceleration input generated by the vehicle via a brake pedal, the primary control unit generates a primary control signal to actuate the respective electromechanical primary actuator.

[0004] In current technology, the secondary brake control system has reduced functionality compared to the primary brake control system. Therefore, in the event of a brake system failure, the use of highly automated driving functions is only possible under driving conditions that are, for example, less demanding in terms of lateral dynamics. Thus, its use on highway sections is possible, but limitations arise from the curve radius of highways, which must be as large as possible, or from good road surface conditions. The functions are also limited with regard to maximum speed. The maximum speed for automated driving at Level 3 or 4 is 130 km / h during normal operation. When using the secondary brake control system, however, the maximum speed is currently limited to 80 km / h. Furthermore, in current vehicles, the parking lock function is integrated into the vehicle's transmission structure in a component-efficient manner.

[0005] A braking system with an additional module is known from DE 10 2017 211 955 A1. A drive train with a hydrodynamic retarder is known from DE 10 2011 120 614 A1. A brake pressure control device for a road vehicle is known from DE 195 43 583 C1. An example of a redundant electromechanical braking system is disclosed from US 2009 223752 A1.

[0006] The object of the invention is to provide a braking system in an at least partially autonomous vehicle whose secondary brake control system has increased functionality compared to the prior art.

[0007] The problem is solved by the features of claim 1. Preferred embodiments of the invention are disclosed in the dependent claims.

[0008] The invention relates to a braking system in an at least partially autonomous, two-track vehicle with a front axle and a rear axle. The braking system has a wheel brake for each wheel, to which both a primary brake control system and a redundant secondary brake control system are assigned. The primary brake control system consists of a primary control unit and an electromechanical primary actuator for each wheel to actuate the wheel brake. In normal driving operation, the primary control unit generates a primary control signal based on a target deceleration input, which is generated by a pilot system or by the driver via a brake pedal. The respective electromechanical primary actuator is then controlled by means of this primary control signal.

[0009] To enhance functionality, according to the characterizing part of claim 1, the secondary brake control system comprises a secondary control unit independent of the primary control unit and an electromechanical secondary actuator independent of the primary actuator for each vehicle wheel. Based on the target deceleration setpoint, which is generated in the pilot system and / or by the driver via the brake pedal, the secondary control unit generates a secondary control signal that actuates the respective electromechanical secondary actuator.

[0010] The braking system according to the invention thus operates entirely without brake fluid, using a dry system topology. Braking force is applied via electromechanical actuators at the wheel brakes, operating without hydraulics. The input signal of a driver's braking request can be detected by means of a foot pedal simulator unit. The redundant sensors integrated into the foot pedal simulator unit convert the mechanical movement of the brake pedal into an electrical signal. This signal is sent to the primary and secondary control units via simple wiring. Both control units can be supplied with electrical power via a redundant vehicle electrical system and dual wiring. Each control unit can also receive the wheel speeds from each wheel via redundant speed sensors and a dual signal line.Furthermore, the two control units can be connected to a redundant bus system via a duplicate bus line. Additionally, a redundant bus line (hereinafter generally referred to as a connection signal line) can be provided for information transmission between the two control units.

[0011] The electromechanical primary and secondary actuators on the wheels are controlled by the control units. Each control unit manages a total of four actuators. Each of these actuators is integrated into a different brake caliper. The actuators are simple actuators controlled by a working current switched by the control unit. No components for processing information or working currents are integrated into the actuators.

[0012] The invention achieves a more efficient fallback system compared to the prior art through the design of a dry braking system. The networking of the primary and secondary brake control system components enables lateral stabilization of the vehicle even in the event of a fault. The improved dynamics allow for greater overall deceleration in the event of a fault. Furthermore, the elimination of a parking lock installed in the vehicle's gearbox is made possible.

[0013] According to the invention, the dry system concept utilizes a dual integration of components to safeguard the secondary brake control system. The functions of the system components are redundant. If one component fails, a second component is available to take over its functions. Likewise, all system components can be in operation during normal operation. In one embodiment, none of the components can be redundant and they can only function in the event of a failure.

[0014] As soon as the driver presses the foot pedal simulator, an electrical signal is generated and transmitted to the two control units, which process this signal. The driver is therefore completely mechanically decoupled from the braking system. The two control units actuate the electromechanical actuators on the wheel brakes, which generate the braking force. Due to the networked design, a single control unit can generate individual braking force at all four wheels. Pulling to one side due to an uneven build-up of braking force, which can occur due to differing processing times of the control units, is thus eliminated. Here, four wheel brakes are always controlled by one control unit, ensuring identical latency times for building up braking force. Brake force regulation is achieved by moving the electric motor back and forth.

[0015] The dry braking system according to the invention is based on a duplicate version of each system component. If one component fails, a second component is available that can continue to perform the same functions independently. The most critical failure of a system component is the failure of a control unit. In such a failure, the functions of 50% of the electromechanical actuators are discontinued, as they are no longer controlled by the failed control unit. However, this does not necessarily mean that the vehicle's deceleration decreases by 50%. The limiting factor for maximum vehicle deceleration is the coefficient of friction between the tires and the road surface. The primary braking system is designed so that wheel lock-up is always achieved during braking. The clamping force of the brake calipers is so high that, theoretically, a higher braking force could be achieved than can actually be transmitted to the road surface.

[0016] The clamping force of a single electromechanical actuator must be designed so that the electromechanical actuator can independently enable the wheels to be locked.

[0017] The secondary brake control system according to the invention can also adjust the individual wheel braking force. The longitudinal and lateral stabilization functions of the vehicle remain intact even in the event of a fault in the primary brake control system. Compared to the primary brake control system, the secondary brake control system has no limitations overall and enables all the functions that the primary brake control system can also perform.

[0018] The holding function is achieved by means of a working current acting on at least one electromechanical actuator per wheel. This builds up and maintains a braking force. Furthermore, the system topology allows for the safeguarding of the holding function in the event of a fault, as a second electromechanical actuator per wheel can be controlled.

[0019] Several variations are possible regarding the parking function. By incorporating a locking function in the electromechanical actuators, blocking of the actuator is ensured, and parking force can be maintained. To meet the requirement that, in the event of a fault in the primary brake control system, the parking force is transferred to at least two wheels, at least four of the eight electromechanical actuators must have a locking function. Each control unit must be able to control at least two actuators for the locking function. The specific wheels on which this locking function is integrated is irrelevant. However, the optimal design for integrating the locking function is to integrate a locking function into each wheel brake of the vehicle. In this case, the locking functions of opposing wheel brakes are each controlled by a separate control unit.This surpasses the state of the art for vehicles with a single driven axle, allowing the vehicle to park with four wheels instead of two during normal operation. The state of the art for vehicles with all-wheel drive and a parking lock is not achieved, as the parking lock in these vehicles also acts on all four wheels. Additionally, this state of the art achieves power transmission through positive and frictional engagement.

[0020] In the event of a critical fault, i.e., a failure of a control unit, it is still possible to transmit the parking force via two wheels. The parking force is then applied to one wheel each on the front and rear axles. Additionally, the parking force is always applied to a right and a left wheel. This reduces the influence of road conditions.

[0021] The following are key aspects of the invention described in detail: Preferably, the primary control unit and the secondary control unit can be identical in construction and function. Similarly, the primary and secondary actuators can also be identical in construction and function.

[0022] Preferably, the brake pedal can be part of a foot pedal simulator unit with at least one pedal sensor. The foot pedal simulator unit can convert the mechanical pedal movement into an electrical foot pedal signal, which represents the driver-generated target deceleration input.

[0023] To further increase system safety, it is preferable to provide a primary electrical system and a redundant secondary electrical system. These can independently supply the primary and secondary control units with electrical power.

[0024] In a technical implementation, each vehicle wheel can be assigned a primary and a secondary speed sensor. The primary speed sensor is connected to the primary control unit. Similarly, the secondary speed sensor is connected to the secondary control unit.

[0025] It is preferred that the pilot system is in signal communication with the primary control unit via a primary signal line. Alternatively, the pilot system can also be in signal communication with the secondary control unit via a secondary signal line.

[0026] In a first implementation variant, only the primary brake control system can be used during normal driving operation, while the secondary brake control system is deactivated. Preferably, the primary control unit can be connected to the secondary control unit via a signal line. Status information can be exchanged between the two control units via this signal line. If the primary control unit diagnoses a fault in the primary brake control system, a fault signal is generated, which can then be used to activate the secondary control unit via the signal line. In this case, the secondary brake control system takes over the implementation of the target deceleration setting from the primary brake control system.

[0027] In an alternative operating mode, both the primary and secondary brake control systems can be in use during normal driving. In this case, the two brake control systems operate in parallel even during normal driving.

[0028] In a further development of the invention, at least one of the electromechanical primary actuators and at least one of the electromechanical secondary actuators can each have a locking function by means of which, in a parking situation, the actuator blocks the associated vehicle wheel by applying the brakes. Preferably, all actuators are equipped with such a locking function.

[0029] An embodiment of the invention is described below with reference to the accompanying figure.

[0030] The figure shows a schematic block diagram of the braking system of a two-track autonomous vehicle with a front axle and a rear axle. Accordingly, each of the two front wheels (VL, VR) and each of the two rear wheels (HR, HL) is assigned a wheel brake 1. The wheel brake 1 has a brake caliper 2, which can be pressurized via an electromechanical primary actuator 3 and an electromechanical secondary actuator 5. This brings the brake caliper 2, with its brake pads (not shown), into contact with the brake disc 7 of the wheel brake 1. The electromechanical primary actuator 3 is part of a primary brake control system (BRS1), while the electromechanical secondary actuator 5 is part of a secondary brake control system (BRS2). All actuators 3 and 5 operate without hydraulics.

[0031] The primary brake control system BRS1, as shown in the figure, consists of a primary control unit 9 and a total of four electromechanical primary actuators 3, each assigned to one of the vehicle wheel brakes 1. In addition, the primary control unit 9 is connected to a primary speed sensor 11 for each of the vehicle wheels (left, right, right, left).

[0032] The redundant secondary brake control system BRS2 has identical components to the primary brake control system BRS1. Accordingly, the secondary brake control system BRS2 consists of a secondary control unit 13 and an electromechanical secondary actuator 5 for each vehicle wheel. The secondary control unit 13 is also connected to secondary wheel speed sensors 15, which are provided for each vehicle wheel.

[0033] In normal driving operation, primary control signals y 1 are generated in the primary control unit 9 based on a target deceleration setpoint VP generated in a pilot system 17 (for example, a driver assistance system with ABS and EPS functions) and / or a target deceleration setpoint VB generated by the driver via a brake pedal 19. The primary control signals y 1 are used to control the respective electromechanical primary actuators 3 to perform various braking or steering tasks.

[0034] The primary control unit 9 and the secondary control unit 13 are each supplied with electrical energy independently of each other by a primary electrical system 31 and a redundant secondary electrical system 33.

[0035] In the figure, the brake pedal 19 is a foot pedal simulator unit with a pressure sensor 21 and a displacement sensor 23. The foot pedal simulator unit converts the pedal movement detected by the two sensors 21, 23 into an electrical foot pedal signal that corresponds to the driver-generated target deceleration setpoint VB.

[0036] In the figure, the pilot system 17 is connected to the primary control unit 9 via a primary signal line 25, while the pilot system 17 is connected to the secondary control unit 13 via an independent secondary signal line 27. Furthermore, the two control units 9 and 13 are connected to each other via a connecting signal line 29. Status information can be exchanged between the two control units 9 and 13 via the connecting signal line 29.

[0037] In normal driving operation, only the primary brake control system BRS1 is in use in the depicted configuration, while the redundant secondary brake control system BRS2 is deactivated. If a diagnostic module in the primary control unit 9 detects a fault in the primary brake control system BRS1, a fault signal SF is generated, which is read from the primary control unit 9 to the secondary control unit 13 via the connecting signal line 29. The secondary brake control system BRS2 then takes over the implementation of the target deceleration specifications VP and VB.

[0038] Alternatively, both the primary brake control system BRS1 and the secondary brake control system BRS2 can be in use during normal driving operation, so that both brake control systems operate in parallel.

[0039] In addition, the electromechanical primary and secondary actuators 9, 13 each have a locking function by means of which, in a parking situation, the respective actuator 3, 5 blocks the assigned vehicle wheel by applying the brakes. REFERENCE MARK LIST:

[0040] 1 Vehicle wheel brake 2 Brake caliper 3, 5 Primary and secondary actuators 7 Brake disc 9 Primary control unit 11 Primary speed sensor 13 Secondary control unit 15 Secondary speed sensors 17 Pilot system 19 Brake pedal 21 Pressure sensor 23 Position sensor 25 Primary signal line 27 Secondary signal line 29 Connection signal line 31 Primary electrical system 33 Secondary electrical system SF Fault signal VP , VB Target deceleration specifications y 1 , y 2 Control signals BRS1 Primary brake control system BRS2 Secondary brake control system

Claims

1. Braking system in an at least partially autonomous vehicle, with a vehicle wheel brake (1) for each vehicle wheel (VR, VL, HR, HL), to which both a primary brake control system (BRS1) and a redundant secondary brake control system (BRS2) are assigned, wherein the primary brake control system (BRS1) has a primary control unit (9) and, for each vehicle wheel (VR, VL, HR, HL), an electromechanical primary actuator (3) for actuating the vehicle wheel brake (1), and wherein, on the basis of a setpoint deceleration specification (VP) generated in a pilot system (17) and / or a setpoint deceleration specification (VB) generated by the driver by means of a brake pedal (19), the primary control unit (9) generates primary control signals (y1) for controlling the respective electromechanical primary actuator (3), characterized in that the secondary brake control system (BRS2) has a secondary control unit (13) that is independent of the primary control unit (9) and, for each vehicle wheel (VR, VL, HR, HL) an electromechanical secondary actuator (5) that is independent of the primary actuator (3), and in that the secondary control unit (13) generates secondary control signals (y2) for controlling the respective electromechanical secondary actuator (5) on the basis of the setpoint deceleration specification (VP, VB) generated in the pilot system (17).

2. Braking system according to claim 1, characterized in that the brake pedal (19) is part of a foot pedal simulator unit with at least one pedal sensor (21, 23), and in that the foot pedal simulator unit converts the mechanical pedal movement into an electrical foot pedal signal, which is the setpoint deceleration specification (VB) generated on the driver's side.

3. Braking system according to claim 1 or 2, characterized in that a primary vehicle electrical system (31) and a redundant secondary vehicle electrical system (33) are provided, which independently of one another supply the primary control unit (9) and the secondary control unit (13) with electrical energy respectively.

4. Braking system according to any one of the preceding claims, characterized in that each vehicle wheel (HR, HL, VR, VL) is assigned a primary speed sensor (11) and a secondary speed sensor (15), which are each in signal communication with the primary control unit (9) and the secondary control unit (13).

5. Braking system according to any one of the preceding claims, characterized in that the pilot system (17) is in signal communication with the primary control unit (9) via a primary signal line (25), and in that the pilot system (17) is in signal communication with the secondary control unit (13) via a secondary signal line (27) independent thereof.

6. Braking system according to any one of the preceding claims, characterized in that a connecting signal line (29) is laid between the primary control unit (9) and the secondary control unit (13), via which status information can be exchanged between the control units (9, 13), and in that, in particular, in the event of a fault in the primary brake control system (BRS1), the primary control unit (9) generates an error signal (SF) with which the secondary control unit (13) can be activated via the connecting signal line (29), so that the secondary brake control system (BRS2) takes over implementation of the setpoint deceleration specification (VB, VP) instead of the primary brake control system (BRS1).

7. Braking system according to one of claims 1 to 5, characterized in that, in normal driving operation, both the primary brake control system (BRS1) and the secondary brake control system (BRS2) are in use, so that both brake control systems (BRS1, BRS2) operate in parallel.

8. Braking system according to any one of the preceding claims, characterized in that at least one of the electromechanical actuators (3, 5) has a locking function by means of which, in a parking situation, the actuator (3, 5) locks the associated vehicle wheel (VL, VR, HR, HL) by actuating the brake.

9. Braking system according to any one of the preceding claims, characterized in that the primary control unit (9) and the secondary control unit (13) are identical in design, and / or in that the primary actuator (3) and the secondary actuator (5) are identical in design.