METHOD FOR OPERATING A BRAKE SYSTEM AND BRAKE SYSTEM

Description

[0001] The invention relates to a method for operating a braking system with a first braking circuit and a second braking circuit, and to a braking system for carrying out such a method.

[0002] Braking systems are primarily used to decelerate motor vehicles. Due to their critical importance for road safety, they are typically designed to withstand certain failure scenarios, ensuring that braking is still possible even in the event of a malfunction. These requirements can be even more stringent for highly autonomous vehicles.

[0003] DE 102019215360 A1 shows a generic brake system with a first brake circuit and a second brake circuit.

[0004] Furthermore, DE 102017216118 A1 teaches how to switch to different operating modes in the event of a fault such as a leak. Two embodiments of how to handle a leak are disclosed.

[0005] A first reaction is referred to as the second operating procedure. In this case, the first braking system is passive (without power) and a braking request from the virtual driver (autopilot) is implemented exclusively by the second braking system (so-called exclusive operating concept).

[0006] In a third operating procedure, a cooperative operating concept of the first and second braking systems is implemented. Here, pressure is built up in all four wheel brakes by means of the second pressure supply device.

[0007] It is therefore an object of the invention to provide a method for operating a braking system which is implemented as an alternative or better method compared to known methods. It is further an object of the invention to provide an associated braking system. This is achieved according to the invention by a method and a braking system according to the respective main claims. Advantageous embodiments can be found, for example, in the respective dependent claims. The content of the claims is incorporated into the description by express reference.

[0008] The invention relates to a method for operating a braking system according to claim 1, comprising a first braking circuit and a second braking circuit. The braking system includes a pump and a linear actuator. The method comprises the following steps: Disconnecting the first brake circuit from the second brake circuit, then applying pressure to the first brake circuit using the pump, and applying pressure to the second brake circuit using the linear actuator.

[0009] This procedure allows the first brake circuit to be isolated from the second brake circuit, and subsequently, both brake circuits can be actuated independently. This can be particularly advantageous if a leak is detected, as the brake circuits are isolated and thus a leak present in only one brake circuit does not affect the other. The procedure is specifically understood to mean that the actuation of the first brake circuit by the pump and the actuation of the second brake circuit by the linear actuator are carried out simultaneously or within a common timeframe, specifically after the first brake circuit has been isolated from the second brake circuit.

[0010] A brake circuit can be understood, in particular, as an arrangement of lines and / or valves in a brake system, whereby a brake circuit is typically assigned to an axle (in the case of a black-white split) or to a pair of diagonally opposite wheels (in the case of a diagonal split). A linear actuator is, in particular, a hydrostatically operating pressure generator that operates discontinuously, i.e., it periodically charges up and then releases pressure. It can, in particular, be implemented by means of a piston that is movable within a cylinder by an electric motor. A pump is understood, in particular, as a hydrodynamically operating device for generating pressure that can provide a continuous volume flow.

[0011] Pressurizing a brake circuit means, in particular, that pressure is generated within the brake circuit, which can then be used for braking. The precise control of the pressurization of a wheel can be achieved, in particular, by means of respective inlet and / or outlet valves.

[0012] According to the invention, the method is implemented in response to a detected leak. In particular, the method has proven advantageous in such a case, as the effects of the leak can be limited to a brake circuit.

[0013] A leak can be detected, for example, when the fluid level in a brake fluid reservoir falls below a predetermined threshold. This typically indicates that fluid is leaking somewhere within the brake system, as the brake system should otherwise be a hydraulically closed system. Another measure or monitoring function, for example, on a primary brake system or on the brake system itself, can also detect a leak, particularly in such a way that it triggers the closure of a circuit breaker valve.

[0014] The first brake circuit can be assigned to a front axle. The second brake circuit can be assigned to a rear axle. This has proven advantageous for typical applications, although the reverse assignment is also possible. A diagonal assignment is also possible.

[0015] The linear actuator can be located in a first module of the braking system. The pump can be located in a second module of the braking system. The modules can be separate from each other. This allows for separate arrangement of the modules, thus making better use of space, for example, in an engine compartment. Furthermore, it allows the use of standardized components, which may also be suitable for other purposes and can be assembled modularly.

[0016] According to one embodiment, the first module also includes a master brake cylinder, which is manually actuated and fluidically connected to the first and / or second brake circuits. This allows for a brake system that can also be manually actuated and, for example, has a hydraulic backup system. However, the method can also be applied in a non-hydraulically coupled brake system, in which, for example, there is no longer a manually actuated master brake cylinder. In this case, for instance, an electronic brake pedal can be used.

[0017] The first and second brake circuits can be connected, for example, by means of a circuit isolating valve. The brake circuits can be separated from each other, in particular by closing the circuit isolating valve.

[0018] The first and second brake circuits can, for example, work together to generate a predetermined braking effect. This braking effect can be initiated by a driver assistance system or by a driver braking request. For instance, this can be achieved by sensing the brake pedal. This allows the vehicle to decelerate according to the braking request.

[0019] The braking effect can be initiated, for example, by a driver request, a driver assistance system, and / or an autonomous driving system. An autonomous driving system, in particular, can be a system that steers the vehicle independently without driver intervention. In this case, the increased safety made possible by this method is especially advantageous, as autonomous vehicles are subject to higher safety requirements.

[0020] The pump and the linear actuator can draw brake fluid independently of each other. Specifically, they can draw brake fluid from a brake fluid reservoir. This independent drawing reduces the impact of a leak. For example, they can have separate suction lines, each leading separately to the brake fluid reservoir.

[0021] Slip control can be implemented, particularly at individual wheel brakes, via dedicated wheel valves. This allows for targeted intervention to set a desired pressure at the wheel brakes.

[0022] The outlet valves of the first brake circuit, which connect to the second brake circuit, can be closed, particularly during the procedure. This prevents brake fluid from flowing back from the first to the second brake circuit, thus allowing for better localization of the leak.

[0023] According to one embodiment, after separating the brake circuits, the pump can pump fluid for a first brake in a first circuit and fluid for a second brake in a second circuit. The two circuits can be completely separate from each other. Each circuit can have its own reservoir for storing fluid. This ensures an independent supply to the pump and allows a leak to be localized to either of the two brakes supplied by the pump.

[0024] The pump can be, in particular, a piston pump. This typically enables continuous pumping. It can, in particular, be driven by an electric motor.

[0025] The invention further relates to a braking system for a motor vehicle. The braking system comprises a first braking circuit and a second braking circuit. It includes a pump which is fluidically connected to the first braking circuit. It includes a linear actuator which is fluidically connected to the second braking circuit. Furthermore, the braking system includes a circuit isolator valve which fluidly connects the first and second braking circuits. The braking system also includes a control device which is configured to execute a method as described herein. All embodiments and variants described herein may be used with regard to the method.

[0026] The braking system allows for the advantages already described above. Regarding the individual features, please refer to the above description of the process, which can be applied accordingly to the braking system.

[0027] In other words, in the event of a fault, particularly a leak, the circuit separation between the front and rear axles can be maintained, and a pressure build-up request can be partially fulfilled by both remaining pressure regulators. For example, a pressure regulator from an additional module can generate a partial pressure build-up at the front axle, supplying pressure to both front wheels. The rear axle can be supplied by a pressure regulator from another module, particularly a larger module, which could itself be a brake system. This ensures that a leak in one wheel brake circuit does not lead to a complete system failure.It has been shown that this achieves a deceleration that is still more than double the required deceleration of an auxiliary braking system of 2.44 m / s², as a three-circuit brake split is created, actuated by two actuators. The division of the brake circuits into three is achieved by an additional module with a dual-circuit piston pump, each circuit of which has its own internal brake fluid reservoir. This means that even if one front wheel is affected by a leak, the pressure-actuating capability remains at the remaining front wheel.

[0028] The pressure control mode described here can be called an additive mode, since both actuators contribute additively to the vehicle's deceleration. In the event of a "leakage" fault, driver request detection is usually still available. This allows both an external braking request, for example from a virtual driver or an autopilot, and a braking request from a human driver via the brake pedal to be executed in this mode.

[0029] The front axle-specific braking request of a virtual driver can be implemented, for example, by an additional module using a two-piston pump with closed isolation valves and open intake valves, connecting the pump's suction side to internal fluid chambers. Pressure reduction can then be achieved by means of a release valve, allowing the pressure to be released back into the internal fluid chamber. In the event of a leak in the rear axle brake circuit, the front axle brakes can thus be applied independently.

[0030] The implementation of a virtual driver's rear-axle braking request can be achieved by switching a circuit isolator valve and controlling a linear actuator, analogous to the behavior in this fault scenario in a vehicle without an autopilot system. In the event of a leak in the front axle brake circuit, the rear axle brakes can thus be independently applied with brake pressure.

[0031] An additional module can, for example, be designed to enable slip control to ensure vehicle stability based on measured wheel signals and the resulting vehicle speed. During the activated ASI braking mode, a dedicated actuator unit is responsible for slip control. Slip control on the front axle can be handled by a backup control unit of an additional module, while slip control on the rear axle can be managed by the main control unit of the braking system. For this purpose, the wheel speed signals from the respective wheels can be provided to the control units in this operating mode. This can be achieved in the overall system through redundant wheel sensor signals or through intelligent distribution of the wheel sensor signals via electrical switching in the control units.It may be useful to exchange a calculated vehicle reference speed between the two control signals via bus signals.

[0032] The operating concept described herein can be used, in particular, to address the issue of four wheel brakes as a fallback in a braking system for autonomous driving. A required pressure build-up at the front wheel brakes (generated by a partial driver request initiated via the brake pedal or a braking request from the Virtual Driver in autonomous driving mode) occurs upon detection of a leakage fault (detected, for example, via a brake fluid warning switch) by activating a backup braking system, which can be housed in an additional module. Pressure can be built up in the front wheel brake calipers by activating the pump motor, opening pump suction valves, and closing isolating valves to the primary braking system. Pressure reduction can occur via pressure relief valves, for example, in a main module, or by opening isolating valves.Slip control can be achieved by appropriately switching the aforementioned wheel valves, particularly depending on the measured wheel slip. In the primary brake system, a circuit isolator valve can be closed if a leak is detected. Pressure build-up at the rear brake calipers can be achieved by actuating a pressure regulator, such as a linear actuator. Slip control for both rear wheels can be achieved by controlling the respective pressure-holding and pressure-releasing valves.

[0033] The operating concept of a redundant braking system described herein enables the necessary brake circuit separation even in the event of a detected leak. In this fault scenario, the braking system is typically always capable of achieving more than twice the legally required deceleration of an auxiliary braking system (2.44 m / s²) in the event of a single failure, as the system then splits into a three-circuit braking system. No additional system components are required, meaning a cost-effective system expansion is implemented.

[0034] The invention will now be described using the figure. This shows: Fig. 1 : a braking system.

[0035] Fig. 1 schematically shows a braking system 10.

[0036] The brake system 10 comprises a linear actuator 40 and a pump 50. The linear actuator 40 is a discontinuous delivery system. The pump 50 is a continuous piston pump. Both the linear actuator 40 and the pump 50 are each driven by their own motor M.

[0037] The braking system 10 has a first brake circuit I and a second brake circuit II. As shown, the first brake circuit I is connected to the pump 50. The second brake circuit II, on the other hand, is connected to the linear actuator 40.

[0038] The braking system 10 has a total of four wheel brakes: a first wheel brake B1, a second wheel brake B2, a third wheel brake B3, and a fourth wheel brake B4. The first and second wheel brakes B1 and B2 are connected to the first brake circuit I. The third and fourth wheel brakes B3 and B4 are connected to the second brake circuit II. Therefore, an individual pressure can be set for the first and second brakes B1 and B2 independently of the third and fourth brakes B3 and B4; or, in other words, the pressure can be adjusted on both brake circuits independently. I, II with the respective connected wheel brakes B, an individual pressure is generated and adjusted purely electrically.

[0039] As shown, the braking system 10 is divided into a first module 12 and a second module 14. Modules 12 and 14 can also be referred to as blocks. The first module 12 can be called the main module. The second module 14 can be called the auxiliary module.

[0040] An electronic control device 16 is provided for controlling the brake system 10, which is configured to execute a method according to the invention. The control device 16 also performs other control tasks. The second module 14 additionally has an independent control device 18.

[0041] The first module 12 is a standard braking system that could also be used independently. The second module 14 is an additional module for highly automated driving, which includes the additional pump 50. This pump ensures that the braking system 10 can continue to operate, at least partially, even if components of the first module 12 fail.

[0042] As shown, the braking system 10 includes a master brake cylinder 20 with a brake pedal 25 connected to it. This allows a driver to communicate a braking request and, in the event of a hydraulic backup system, to build up brake pressure. The braking system 10 includes a simulator 30, which is connected to the master brake cylinder 20 via a simulator valve SV. The master brake cylinder 20 and simulator 30 are connected to the other hydraulic components via a isolating valve TV. In normal braking operation, the simulator valve SV is open and the isolating valve TV is closed, so that the master brake cylinder 20 is only connected to the simulator 30, and a driver thus feels a force generated by the simulator 30. There is no direct hydraulic effect; rather, a driver braking request is detected by an integrated displacement sensor U / s and / or a pressure sensor U / p.The driver's braking request is then implemented automatically via the linear actuator 40 and the pump 50.

[0043] The two brake circuits I and II are connected via a circuit isolating valve KTV. This allows pressure equalization when the circuit isolating valve KTV is open and separation of the two brake circuits when the circuit isolating valve KTV is closed. The second brake circuit II is connected to the linear actuator 40 via a switching valve ZV.

[0044] The brake system 10 also includes a fluid reservoir, which is designed as a conventional brake fluid reservoir 60. This serves in particular as a return line and for supplying the fluid-consuming components. This will not be discussed in further detail, as it is a known design.

[0045] The first and second wheel brakes B1, B2 are connected to the first and second wheel connections R1, R2 of the second module 14. These are connected to inlet valves E1, E2 and outlet valves A1, A2 of the first module 12. Therefore, they can be actuated both from the first module 12 and pressurized by pump 50 of the second module 14. The second module 14 contains a total of six valves V1, V2, V3, V4, V5, V6, which will not be discussed in detail here unless required to explain their functionality.

[0046] The third and fourth wheel brakes B3, B4, on the other hand, are directly connected to the third and fourth wheel connections R3, R4 of the first module 12, namely to the respective inlet valves E3, E4 and exhaust valves A3, A4 as shown.

[0047] The brake fluid reservoir 60 has a level sensor U / s which monitors the fluid level in the brake fluid reservoir 60. If the fluid level falls below a predetermined threshold, a leak is assumed to be present.

[0048] In the event of a leak, the circuit isolating valve KTV can be closed first. This localizes the leak and allows the two brake circuits I and II to be pressurized independently.

[0049] The first brake circuit I is pressurized by pump 50. For this purpose, valves V1 and V2 of the second module 14 are closed. To build up pressure in the connected wheel brakes, pump 50 is activated and valves V5 and V6 of the second module 14 are opened until a target pressure is reached. This pumps fluid for the first brake B1 from pump 50 through a first reservoir 62, and fluid for the second brake B2 is also pumped from pump 50 through a second reservoir 64. Reservoirs 62 and 64 act as local reservoirs, ensuring a constant supply of fluid to pump 50. In the event of a fluid connection failure between the first module 12 and the second module 14, pressure buildup can continue independently.If the pressure needs to be reduced again, this can be done via the valves V3 and V4 of the second module 14; the valves V1 and V2 are typically reopened when braking is complete.

[0050] The second brake circuit II is pressurized by means of the linear actuator 40. Thus, both brake circuits are... I, The two brake circuits are independently pressurized electrically. The pressure can also be adjusted accordingly. In particular, the two brake circuits can be... I, II together achieve a desired braking effect, which can be specified in particular by a driver braking request or an autonomous driving system.

[0051] The first and second brakes, B1 and B2, can be assigned to a front axle. The third and fourth brakes, B3 and B4, can be assigned to a rear axle. However, other configurations are also possible. Reference symbol list:

[0052] 10 Brake system 12 First module 14 Second module 16 Control device 18 Control device 20 Master brake cylinder 25 Brake pedal 30 Simulator 40 Linear actuator 50 Pump 60 Brake fluid reservoir 62 First reservoir 64 Second reservoir V Valves SV Simulator valve TV Separator valve ZV Switching valve KTV Circuit separator valve A Exhaust valves E Inlet valves R Wheel connections B Brakes I First brake circuit II Second brake circuit

Claims

1. A method of operating a braking system (10) having a first brake circuit (I) and a second brake circuit (II), wherein the braking system (10) has a pump (50) and a linear actuator (40), wherein the method performs the following steps in response to a detected leak: - isolating the first brake circuit (I) from the second brake circuit (II), then - acting upon the first brake circuit (I) by means of the pump (50), and - acting upon the second brake circuit (II) by means of the linear actuator (40), wherein the first brake circuit is acted upon by means of the pump and the second brake circuit is acted upon by means of the linear actuator simultaneously or in a common time period.

2. The method as claimed in claim 1, - wherein the leakage is detected when a liquid level in a brake fluid reservoir (60) falls below a predefined threshold value.

3. The method as claimed in any one of the preceding claims, - wherein the first brake circuit (I) is assigned to a front axle and the second brake circuit (II) is assigned to a rear axle.

4. The method as claimed in any one of the preceding claims, - wherein the linear actuator (40) is arranged in a first module (12) of the braking system (10) and the pump (50) is arranged in a second module (14) of the braking system (10), wherein the modules (12, 14) are separate from one another.

5. The method as claimed in any one of the preceding claims, - wherein a master brake cylinder (20), which is manually actuatable and is fluidically connected to the first brake circuit (I) and / or the second brake circuit (II), is also arranged in the first module (12).

6. The method as claimed in any one of the preceding claims, - wherein the first brake circuit (I) and the second brake circuit (II) are connected by means of a circuit isolating valve (KTV), and - wherein the brake circuits (I, II) are isolated by closing the circuit isolating valve (KTV).

7. The method as claimed in any one of the preceding claims, - wherein the first brake circuit (I) and the second brake circuit (II) together generate a predefined braking effect.

8. The method as claimed in claim 7, - wherein the braking effect is predefined by a driver braking intention and / or a driver assistance system and / or a system for autonomous driving.

9. The method as claimed in any one of the preceding claims, - wherein the pump (50) and the linear actuator (40) aspirate brake fluid independently of one another.

10. The method as claimed in claim 9, - wherein the pump (50) and the linear actuator (40) aspirate brake fluid from a brake fluid reservoir (60).

11. The method as claimed in any one of the preceding claims, - wherein slip control is performed at respective wheel brakes (B) via assigned wheel valves (E, A).

12. The method as claimed in any one of the preceding claims, - wherein outlet valves (V1, V2) of the first brake circuit (I), which establish a connection to the second brake circuit (II), are closed.

13. The method as claimed in any one of the preceding claims, - wherein, after the isolation of the brake circuits, the pump (50) pumps fluid for a first brake B1 in a first circuit and pumps fluid for a second brake B2 in a second circuit.

14. A braking system (10) for a motor vehicle, having - a first brake circuit (I), - a second brake circuit (II), - a pump (50) which is fluidically connected to the first brake circuit (I), - a linear actuator (40) which is fluidically connected to the second brake circuit (II), - a circuit isolating valve (KTV) which fluidically connects the first brake circuit (I) and the second brake circuit (II), and - a control device (16), which is configured to carry out a method as claimed in any one of the preceding claims.