Braking system for motor vehicles and method for operating a braking system

Description

[0001] The invention relates to a braking system for motor vehicles, comprising a master brake cylinder actuatable by means of a brake pedal, which comprises only one pressure chamber, an electrically controllable pressure supply device, a pressure fluid reservoir, in particular one under atmospheric pressure, from which the master brake cylinder and the pressure supply device are supplied with pressure fluid, and at least four hydraulically actuatable wheel brakes, wherein the at least two wheel brakes can be actuated selectively by means of the master brake cylinder or by means of the pressure supply device, wherein the pressure chamber of the master brake cylinder is separably connected via a separating valve to a first brake circuit supply line, to which at least one of the wheel brakes is connected. The invention also relates to methods for operating the braking system.

[0002] WO 00 / 59762 A1 discloses a braking system in which two of the four wheel brakes can be actuated by a master brake cylinder or a pressure supply device, while the other two wheel brakes can only be actuated by the pressure supply device.

[0003] DE 10 2014 225 958 A1 discloses a brake system with two pressure fluid reservoirs, each of which comprises a fill level detection device used to detect leaks.

[0004] The subsequently published EP 3 568 328 A1 shows an alternative, compact, and cost-effective braking system for a brake-by-wire operating mode and for a fallback operating mode in a motor vehicle. For this purpose, the braking system is designed as a single-circuit system when de-energized. However, it can be switched to a dual-circuit system if required, with each circuit being pressurized by one of the two pressure sources.

[0005] The subsequently published EP 3 568 327 A1 shows a braking system for a motor vehicle that is simple in design and cost-effective, yet offers the highest possible availability required for highly automated driving. If one of the electrically controllable pressure supply devices fails, the most important braking functions can be performed autonomously or via an autopilot function. For this purpose, wheel-specific and at least brake-circuit-specific pressures are provided, as well as the setting of precise brake pressure curves, including pressure build-up, pressure reduction, and pressure maintenance.

[0006] From the generic DE 10 2012 219 390 A1, a braking system for motor vehicles with a master brake cylinder comprising only one pressure chamber is known. This braking system can be operated in a "brake-by-wire" mode, in which the four wheel brakes of the motor vehicle are actuated with pressure fluid from an electrically controllable pressure supply device. The braking system can also be operated in a fallback mode, in which the four wheel brakes are actuated with pressure fluid from a master cylinder.

[0007] In such a braking system, leaks may occur that are so small that they cannot be detected and located by measuring the volume in the pressure supply device during braking system operation. Furthermore, leaks may occur outside of braking system operation (e.g., while the ignition is off) that cannot be detected or located using conventional means.

[0008] It is therefore an object of the present invention to provide a braking system and a method for its operation which is designed in such a way that a sufficient braking effect is ensured even in the event of such leaks.

[0009] This object is achieved by a braking system according to claim 1 and a method according to claim 7.

[0010] According to the invention, the at least four wheel brakes are divided into at least a first wheel brake group and a second wheel brake group, wherein the first wheel brake group is connected to the first brake circuit supply line. The pressure supply device is connected to a second brake circuit supply line, to which the second wheel brake group is connected. The first brake circuit supply line is detachably connected to the second brake circuit supply line via a connecting valve. The first wheel brake group comprises a first and a second wheel brake of the at least four wheel brakes, and the second wheel brake group comprises a third and a fourth wheel brake of the at least four wheel brakes.

[0011] This has the advantage that the braking system can be divided into two brake circuits. The first brake circuit, which includes the first brake circuit supply line and the first wheel brake group and is connected to the master brake cylinder, can be completely hydraulically separated from the second brake circuit, which includes the second brake circuit supply line and the second wheel brake group and is connected to the pressure supply device, by the connecting valve. A leak in one of the two brake circuits does not affect the other brake circuit when the connecting valve is closed.

[0012] This ensures that the braking effect is maintained. This procedure is particularly advantageous if a leak occurs outside of an ignition cycle and therefore cannot be easily located.

[0013] According to the invention, the connecting valve is designed to be closed when de-energized. This has the advantage that the braking system is divided into two brake circuits in the de-energized state, for example, when the ignition is off.

[0014] Advantageously, the isolation valve is designed to be open when de-energized. This ensures that the driver can build up braking force through the first wheel brake group at least through pedal force at any time, even if the brake system control fails.

[0015] According to a preferred embodiment of the invention, the pressure supply device is directly connected to the second brake circuit supply line. The term "directly connected" here means that no electrically, hydraulically, or mechanically actuated valve is arranged between the pressure supply device and the second brake circuit supply line.

[0016] Particularly preferably, the pressure supply device is connected to at least one inlet valve of the second wheel brake group without the interposition of an electrically, hydraulically or mechanically actuated valve, wherein the inlet valve is preferably designed to be open when de-energized.

[0017] According to an alternative preferred embodiment of the invention, the pressure supply device is connected to the second brake circuit supply line via a connection valve. The connection valve is preferably designed to be open when de-energized.

[0018] This design with an additional sequence valve allows for an advantageous operating mode in the event that the pressure supply device has failed, but the valves can still be operated. The isolation valve and the connecting valve are then opened, and the sequence valve is closed. In this valve position, the driver can apply braking force to all wheel brakes using pedal force. The closed sequence valve prevents pressure fluid from escaping into the pressure supply device.

[0019] Advantageously, the first and second wheel brakes are arranged on opposite sides of the vehicle. Accordingly, the third and fourth wheel brakes are also arranged on opposite sides of the vehicle. This means that the first wheel brake group comprises wheel brakes on both sides of the vehicle, and the second wheel brake group also comprises wheel brakes on both sides of the vehicle. This has the advantage that, even during braking with only one of the brake circuits (i.e., with only one wheel brake group, in particular only the first and second or only the third and fourth wheel brakes), the vehicle's swaying is prevented or at least reduced.

[0020] Preferably, the connecting valve is designed such that it is not overflowed at least up to a pressure difference corresponding to a full-stop wheel brake pressure. This has the advantage that in the event that pressure can no longer be built up in one of the two brake circuits due to a leak when the brake circuit is separated, any built-up brake pressure in the other brake circuit does not escape via the connecting valve but is completely directed into the corresponding wheel brakes.

[0021] According to a preferred embodiment of the invention, the pressure supply device is designed as a linear actuator in which a piston is displaced axially in a hydraulic pressure supply device pressure chamber to build up pressure, wherein the pressure supply device pressure chamber is provided with at least one radial bore which is arranged such that the pressure supply device pressure chamber is in communication with the pressure medium reservoir via the radial bore in the unactuated position of the piston, wherein the connection is blocked by actuation of the piston.

[0022] According to a further preferred embodiment of the invention, the pressure supply device is designed as a linear actuator in which, to build up pressure, a piston is displaced axially within a hydraulic pressure supply device pressure chamber. The pressure supply device pressure chamber is connected to the pressure medium reservoir via a suction valve. The suction valve is opened mechanically when the piston is in the unactuated position. The unactuated position is the position in which no pressure buildup occurs.

[0023] The invention also relates to a method for operating the brake system, wherein the pressure fluid reservoir is equipped with a device for determining a pressure fluid level. The brake system is operated in a fallback mode when the determined level falls below a predetermined limit.

[0024] Preferably, the braking system can be operated in normal mode, in which the wheel brakes, i.e., advantageously both the first wheel brake group and the second wheel brake group, are actuated by means of the pressure supply device, particularly preferably by switching the connecting valve to the open state and the isolating valve to the closed state. The braking system is preferably operated in normal mode when the determined level is above the predetermined limit. This operating mode corresponds to a so-called "by-wire" operating mode, in which the wheel brakes are decoupled from the brake pedal and the braking pressure is built up solely by the pressure supply device.

[0025] Preferably, the connecting valve is kept permanently closed in the fallback mode. This separates the braking system into two braking circuits during the fallback mode.

[0026] Particularly preferably, in the fallback operating mode, the first wheel brake group is actuated by means of the master brake cylinder and the second wheel brake group is actuated by means of the pressure supply device.

[0027] Particularly preferably, in the fallback mode, the first and second wheel brakes are actuated by means of the master brake cylinder and the third and fourth wheel brakes are actuated by means of the pressure supply device.

[0028] If a failure of at least one valve in the braking system is detected, the braking system is preferably operated in fallback mode. This means that even in situations where no pressure loss has been detected, but braking effectiveness cannot be ensured in single-circuit operation of the braking system due to a defective valve, the system switches to fallback mode with brake circuit separation.

[0029] According to a preferred embodiment of the invention, the wheel brakes are each separably connected to the pressure fluid reservoir via an outlet valve, particularly preferably via a common return line. In the fallback mode, the outlet valves are kept closed. This prevents a transfer of pressure fluid between the brake circuits.

[0030] Further preferred embodiments of the invention emerge from the subclaims and the following description with reference to figures.

[0031] It shows schematically: Fig. 1 shows an embodiment of a braking system according to the invention.

[0032] In Figure 1An embodiment of a brake system according to the invention for a motor vehicle is shown. The brake system comprises a master brake cylinder 21, which has a single pressure chamber 210. The master brake cylinder 21 is actuated directly by the driver of the motor vehicle via a brake pedal 20. The pressure chamber 210 is connected to a pressure fluid reservoir 18 and is supplied with pressure fluid from there. The pressure chamber 210 of the master brake cylinder 21 is detachably connected to a first brake circuit supply line 110 via a separating valve 150. The separating valve 150 is designed, for example, to be open when de-energized. A first hydraulically actuated wheel brake 60 and a second hydraulically actuated wheel brake 62 are connected to the first brake circuit supply line 110. The first wheel brake and the second wheel brake form a first wheel brake group.Conveniently, the first and second wheel brakes 60, 62 are each detachably connected to the first brake circuit supply line 110 via an inlet valve 180, 182. The inlet valves 180, 182 are designed, for example, to be open when de-energized.

[0033] The braking system also includes a pressure supply device 22. The pressure supply device 22 includes, for example, a motor M, by means of which a piston 41 can be displaced in a hydraulic pressure supply device pressure chamber 42 (DBE pressure chamber), thereby building up pressure. The pressure supply device 22 is connected to the pressure fluid reservoir 18 and is supplied with pressure fluid from it.

[0034] The pressure supply device 22 is connected to a second brake circuit supply line 112. A third hydraulically actuated wheel brake 64 and a fourth hydraulically actuated wheel brake 66 are connected to the second brake circuit supply line 112. The third wheel brake and the fourth wheel brake form a second wheel brake group. The third and fourth wheel brakes 64, 66 are expediently connected to the second brake circuit supply line 112 via an inlet valve 184, 186 each. The inlet valves 184, 186 are designed, for example, to be open when de-energized.

[0035] The first and second wheel brakes 60, 62 are arranged, for example, on different sides of the vehicle, advantageously on the front axle or a diagonal. Accordingly, the third and fourth wheel brakes 64, 66 are also arranged on different sides of the vehicle.

[0036] For example, the first wheel brake 60 is the front left wheel brake (FL), the second wheel brake 62 is the rear right wheel brake (RR), the third wheel brake 64 is the front right wheel brake (FR), and the fourth wheel brake 60 is the rear left wheel brake (RL). Other arrangements are also possible.

[0037] According to one embodiment of the invention, the pressure supply device 22 is connected directly to the second brake circuit supply line 112, that is to say that the brake circuit supply line 112 hydraulically connects the DBE pressure chamber 42 to the inlet valves 194, 196 of the third and fourth wheel brakes 64, 66 without the interposition of another electrically, hydraulically or mechanically actuated valve.

[0038] In an alternative embodiment of the invention, the pressure supply device 22 is detachably connected to the second brake circuit supply line 112 via a connection valve 300. The connection valve is preferably designed to be open when de-energized. The optional connection valve 300 is Fig. 1 shown in a dashed box.

[0039] The first brake circuit supply line 110 is detachably connected to the second brake circuit supply line 112 via a connecting valve 184, i.e., the connecting valve 184 is arranged between the first brake circuit supply line 110 and the second brake circuit supply line 112. The connecting valve 184 is designed, for example, to be closed when de-energized.

[0040] Preferably, the wheel brakes 60, 62, 64, 66 are connected via outlet valves 190, 192, 194, 196 to a common return line and via this to the pressure medium reservoir 18.

[0041] For example, the pressure fluid reservoir 18 is equipped with a device 30 for determining a pressure fluid level p. The device 30 can, for example, detect when the level p falls below a predetermined limit value s 1 . A drop in the level below the limit value s 1 indicates that a leak has occurred within the brake system, causing a loss of pressure fluid.

[0042] In one embodiment of the invention, the pressure fluid reservoir 18 comprises two chambers (not shown), which are separated, for example, by bulkheads. The master brake cylinder 21 is connected to a first of the chambers, and the pressure supply device 22 is connected to a second of the chambers. This ensures a separate supply of pressure fluid for each of the two brake circuits in the fallback mode.

[0043] For example, the isolation valve 150 is open when de-energized, the connecting valve 184 is closed when de-energized, the inlet valves 180, 182, 184, 186 are open when de-energized, and the outlet valves 190, 192, 194, 196 are closed when de-energized. In the de-energized state of the brake system, the system is thus separated into two brake circuits as described above. In the event of a leak with the ignition off, the pressure loss is limited to one brake circuit.

[0044] For example, the connecting valve 184 is designed in such a way that it is not overflowed at least up to a pressure difference that corresponds to a full braking wheel brake pressure.

[0045] For example, the pressure supply device 22 is designed as a linear actuator in which the piston 41 is displaced axially into the hydraulic DBE pressure chamber 42 to build up pressure.

[0046] According to one embodiment of the invention, the DBE pressure chamber 42 is provided with at least one radial bore arranged such that, in the unactuated position of the piston 41, the DBE pressure chamber 42 communicates with the pressure medium reservoir 18 via the radial bore, wherein the connection is blocked by actuation of the piston 41. The unactuated position of the piston designates the position of the piston in which no pressure is built up by the pressure supply device 22.

[0047] According to a further embodiment of the invention, the DBE pressure chamber 42 is connected to the pressure medium reservoir 18 via a suction valve, wherein the suction valve is opened mechanically when the piston 41 is in the unactuated position.

[0048] The braking system can, for example, be operated in a normal mode, which corresponds to a so-called "by-wire" mode. In normal mode, the master brake cylinder 21 is separated from the first brake circuit supply line 110 by closing the isolating valve 150. The connecting valve 184 is opened, so that the first brake circuit supply line 110 and the second brake circuit supply line 112 are hydraulically connected. If the driver actuates the brake pedal 20, the actuation is detected, and the displaced pressure medium is recorded by a simulation device 24, which provides a desired pedal feel using methods known per se. Based on the detected actuation, a pressure to be provided by the pressure supply device 22 is determined.This pressure is set by appropriately controlling the pressure supply device 22 and is fed into the first, second, third and fourth wheel brakes 60, 62, 64, 66 via the brake circuit supply lines 112 and 110.

[0049] In normal operation, pressure build-up by the pressure supply device 22 can also be carried out independently of actuation of the brake pedal 20.

[0050] Brake pressure can be released by opening the exhaust valves 190, 192, 194, and 196 in the wheel brakes. The inlet valves 180, 182, 184, and 186 and the outlet valves 190, 192, 194, and 196 can be individually switched to set different pressures in the wheel brakes. The brake system can perform familiar brake control functions (e.g., EBD, ABS, ASR, ESC, ACC, etc.).

[0051] For example, the braking system is operated in a fallback mode when the level p falls below the specified limit value s 1 . In the fallback mode, the connecting valve 184 is preferably closed. This effectively separates the braking system into two separate braking circuits.

[0052] The first brake circuit comprises the first and second wheel brakes 60, 62 and the first brake circuit supply line 110. The first brake circuit is connected to the master brake cylinder 21 via the isolating valve 150. The isolating valve 150 is expediently opened or remains in its open state so that pressure can be supplied to the first and second wheel brakes 60, 62 via the master brake cylinder 21. The first and second wheel brakes 60, 62 are actuated by means of the master brake cylinder 21.

[0053] The second brake circuit comprises the third and fourth wheel brakes 64, 66 and the second brake circuit supply line 112. The second brake circuit is connected to the pressure supply device 22, and pressure in this brake circuit is provided in the fallback mode via the pressure supply device 22. The third and fourth wheel brakes 64, 66 are actuated by the pressure supply device 22.

[0054] In the fallback mode, for example, the outlet valves 190, 192, 194, 196 of the wheel brakes are kept closed, preventing any movement of pressure fluid between the chambers of the pressure fluid reservoir 18 and thus between the brake circuits. Control functions that cause the outlet valves to open are deactivated, for example.

[0055] Even if a failure of one of the valves is detected, the braking system will, for example, be operated in fallback mode.

[0056] A further exemplary embodiment of the invention is described below.

[0057] In the de-energized state of the brake system, a permanent separation of two brake circuits in the brake system is established and one brake circuit is supplied with pressure from the master brake cylinder 21, the other brake circuit from the pressure supply device 22. In the present circuit diagram of the Figure 1One of the brake circuits (here the FL and RR wheels) is connected to the master brake cylinder 21 via the normally open isolating valve 150 and to the pressure supply device 22 via the normally closed connecting valve 184 (pressure sequence valve). The other brake circuit (here FR and RL) is directly connected to the pressure supply device 22. After the device for determining a level 30 (e.g., reservoir warning device) is triggered, all valves (for example, at least isolating valve 150 and connecting valve 184, preferably also other valves of the brake system) are de-energized. The two brake circuits are supplied by their respective pressure sources (master brake cylinder 21 and pressure supply device 22). This fallback mode can also be used if all valves fail, but the sensors (in particular pressure sensors 202, 203 and pedal travel sensor 201) and the pressure supply device 22 are still available.This is another advantage of the invention. In the de-energized fallback mode, only two wheel brakes are supplied with pressure.

[0058] Note that the connecting valve 184 is modified to remain closed against sufficiently large pressure differences. To equalize pressure in the brake circuit of the pressure supply device 22, the pressure supply device 22 should be provided with a bleed hole. Alternatively, the linear actuator 22 could open a suction valve in the release-side stop via a mechanical connection.

Claims

1. Brake system for motor vehicles which comprises a master brake cylinder (21) which can be actuated by means of a brake pedal (20) and comprises only one pressure chamber (210); an electrically controllable pressure supply device (22); a pressure medium reservoir (18) which is, in particular, under atmospheric pressure and from which the master brake cylinder (21) and the pressure supply device (22) are supplied with pressure medium; and at least four hydraulically actuable wheel brakes (60, 62, 64, 66), wherein the wheel brakes (60, 62, 64, 66) can optionally be actuated by means of the master brake cylinder (21) or by means of the pressure supply device (22); wherein the pressure chamber (210) of the master brake cylinder is separably connected via an isolating valve (150) to a first brake circuit supply line (110), to which at least one of the wheel brakes (60, 62) is connected, characterized in that the wheel brakes (60, 62, 64, 66) are divided into at least a first wheel brake group and a second wheel brake group, wherein the first wheel brake group comprises a first and a second wheel brake (60, 62), and the second wheel brake group comprises a third and fourth wheel brake (64, 66), wherein the first wheel brake group is connected to the first brake circuit supply line (110), and in that the pressure supply device (22) is connected to a second brake circuit supply line (112), to which the second wheel brake group (64, 66) is connected, wherein the first brake circuit supply line (110) is separably connected via a connecting valve (184) to the second brake circuit supply line (112), wherein the connecting valve (184) is of normally closed design.

2. Brake system according to Claim 1, characterized in that the first and the second wheel brake (60, 62) are arranged on opposite sides of the vehicle.

3. Brake system according to Claim 1 or 2, characterized in that the isolating valve (150) is of normally open design.

4. Brake system according to one of Claims 1 to 3, characterized in that the pressure supply device (22) is directly connected to the second brake circuit supply line (112).

5. Brake system according to one of Claims 1 to 3, characterized in that the pressure supply device (22) is connected to the second brake circuit supply line (112) via a sequence valve (300) which is, in particular, normally open.

6. Brake system according to one of the preceding claims, characterized in that the connecting valve (184) is configured such that it is not opened at least up to a pressure difference which corresponds to a wheel brake pressure for full braking.

7. Method for operating a brake system according to one of the preceding claims, characterized in that the pressure medium reservoir (18) is equipped with a device (30) for determining a level (p) of the pressure medium, and in that the brake system is operated in a fallback operating mode if the determined level (p) falls below a predefined threshold value (s1).

8. Method according to Claim 7, characterized in that the brake system can be operated in a normal operating mode, in which the first wheel brake group and the second wheel brake group (60, 62, 64, 66) are actuated by means of the pressure supply device (22), in particular by the connecting valve (184) being switched into the open state and the isolating valve (150) being switched into the closed state, and in that the brake system is operated in the normal operating mode when the determined level (p) lies above the predefined threshold value (s1).

9. Method according to Claim 7 or 8, characterized in that, in the fallback operating mode, the connecting valve (184) is held permanently closed.

10. Method according to one of Claims 7 to 9, characterized in that, in the fallback operating mode, the first wheel brake group (60, 62) is actuated by means of the master brake cylinder (21), and the second wheel brake group (64, 66) is actuated by means of the pressure supply device (22).

11. Method according to one of Claims 7 to 10, characterized in that, when failure of at least one valve of the brake system is detected, the brake system is operated in the fallback operating mode.

12. Method according to one of Claims 7 to 11, characterized in that the wheel brakes (60, 62, 64, 66) are separably connected to the pressure medium reservoir (18) via a respective outlet valve (190, 192, 194, 196), in particular via a common return line, and the outlet valves are held closed in the fallback operating mode.