CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase Application of PCT International Application No. PCT/EP2018/074609, filed Sep. 12, 2018, which claims priority to German Patent Application No. 10 2017 216 617.7, filed Sep. 20, 2017, the contents of such applications being incorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to a brake system and to a method for operating such a brake system.

BACKGROUND OF THE INVENTION

A generic brake system with two electrically controllable pressure sources for a motor vehicle with four hydraulically actuatable wheel brakes is known from DE 10 2013 217 954 A1, incorporated by reference herein. Here, the wheel brakes, for actuation in various operating modes, are connected to the two electrically controllable pressure sources and also to a brake pedal-actuatable master brake cylinder. In addition to inlet and outlet valves, the brake system comprises a circuit separation valve and a total of four isolating valves for separating the master brake cylinder and the, furthermore, the brake system comprises a central control and regulating unit, a first control and regulating unit assigned to the first pressure source and a second control and regulating unit assigned to the second pressure source. The first and second control and regulating units each serve to control the corresponding pressure source. The circuit separation valve is actuated by means of the central control and regulating unit. The actuation of the two pressure source isolating valves is also carried out by means of the central control and regulating unit.

In future brake systems, which should also be suitable for highly automated driving, a mechanical and/or hydraulic fallback level, in which the driver can actuate the wheel brakes using muscle power, is intended to be dispensed with.

DE 10 2013 223 859 A1, incorporated by reference herein, discloses a brake system for hydraulically actuatable wheel brakes with a simulation device which can be actuated by means of a brake pedal, no mechanical and/or hydraulic operative connection between the brake pedal and the wheel brakes being provided. There is a single electrically controllable pressure source with a stepped piston and two sealing elements in order to achieve increased availability of the brake system.

SUMMARY OF THE INVENTION

An aspect of the present invention is a brake system suitable for highly automated driving for a motor vehicle with at least four hydraulically actuatable wheel brakes, which can do without a mechanical and/or hydraulic fallback level and yet still has a high level of availability and thus offers sufficient safety for highly automated driving or an autopilot function.

An aspect of the invention is based on the idea that in a brake system which has a first electrically controllable pressure source which is separably connected to a first brake circuit supply line via a first isolating valve, a second electrically controllable pressure source which is separably connected to a second brake circuit supply line via a second isolating valve, at least four electrically actuatable inlet valves, the first brake circuit supply line being connected to two of the inlet valves and the second brake circuit supply line being connected to the two other inlet valves, an electrically actuatable outlet valve per wheel brake for discharging pressure medium from the wheel brake, an electrically actuatable circuit separation device, by means of which the first brake circuit supply line and the second brake circuit supply line are hydraulically separated when the circuit separation device is in an unactuated state, and by means of which the first brake circuit supply line and the second brake circuit supply line are hydraulically connected to one another when the circuit separation device is in an actuated state, a first electronic device by means of which the first pressure source is actuated, and a second electronic device by means of which the second pressure source is actuated, the second electronic device being electrically independent of the first electronic device, there is provision that the first isolating valve assigned to the first pressure source is actuated by the second electronic device, and the second isolating valve assigned to the second pressure source is actuated by the first electronic device.

The two electronic devices are electrically independent of one another in the sense that a failure of the first electronic device does not cause a failure of the second electronic device and vice versa, that is to say the two electronic devices are electrically isolated. The first electronic device is therefore advantageously supplied by a first electrical energy supply, and the second electronic device is supplied by a second electrical energy supply, the first electrical energy supply being independent of the second electrical energy supply. The two electronic devices can be arranged in a common housing or on a common printed circuit board, for example in a common electronic control and regulating unit (ECU). Alternatively, the two electronic devices can be arranged in two separate housings or on two separate printed circuit boards, for example in two electronic control and regulating units (ECU).

The first electronic device is designed to actuate or control the first pressure source. The first pressure source is preferably also supplied with electrical energy by the first electronic device. Correspondingly, the second pressure source is actuated or controlled by means of the second electronic device. The second pressure source is preferably also supplied with electrical energy by the second electronic device.

The first isolating valve is preferably actuated only by the second electronic device, and the second isolating valve is actuated only by the first electronic device. That is to say that the first electronic device is not designed to actuate the first isolating valve, and the second electronic device is not designed to actuate the second isolating valve. Nor is there provided a further electronic device, for example a central electronic device, which actuates the first and the second isolating valve.

The first pressure source is preferably connected to the first brake circuit supply line via exactly one actuatable valve, namely the first isolating valve, that is to say no further actuatable valve is arranged between the first isolating valve and the two inlet valves connected to the first brake circuit supply line. The flow resistance from the pressure source to the corresponding wheel brakes is thus kept as low as possible.

Correspondingly, the second pressure source is preferably connected to the second brake circuit supply line via exactly one actuatable valve, namely the second isolating valve, that is to say no further actuatable valve is arranged between the second isolating valve and the two inlet valves connected to the second brake circuit supply line.

The first and the second isolating valve are preferably designed to be normally open. It is therefore not necessary to switch/open the isolating valves when the brake system is operating correctly, which prevents switching noises. A, for example defective, pressure source can be separated by closing the associated isolating valve by means of the electronic device assigned to the other pressure source.

The circuit separation device of the brake system is, so to speak, designed to be normally closed.

The circuit separation device can preferably be actuated both by means of the first electronic device and by means of the second electronic device, or the circuit separation device is actuated both by means of the first electronic device and by means of the second electronic device in order to hydraulically connect the first brake circuit supply line and the second brake circuit supply line to one another.

The circuit separation device preferably comprises a first electrically actuatable circuit separation valve, which is designed to be normally closed, and a second electrically actuatable circuit separation valve, which is designed to be normally closed, the two circuit separation valves being connected in parallel with one another. The first circuit separation valve is particularly preferably actuated by the first electronic device, and the second circuit separation valve is actuated by the second electronic device. The first circuit separation valve is advantageously actuated only by the first electronic device, and the second circuit separation valve is actuated only by the second electronic device, as a result of which the use of double-activatable valves is unnecessary.

The brake system preferably comprises a simulation device for generating a brake pedal feel, which is coupled to a brake pedal, no mechanical and/or hydraulic operative connection between the brake pedal and the wheel brakes being provided. The simulation device is therefore not hydraulically connected to the wheel brakes. The brake system also does not comprise a brake pedal-actuatable master brake cylinder that is connected to one of the wheel brakes.

The first pressure source is preferably formed by a (first) cylinder-piston arrangement with a (first) hydraulic pressure chamber, the (first) piston of which is actuated by a (first) electromechanical actuator, the (first) pressure chamber in an unactuated state of the (first) piston being connected via at least one first snifter hole to a first connecting line which is connected to the pressure medium reservoir. The first pressure source particularly preferably comprises exactly one (first) hydraulic pressure chamber, that is to say the first pressure source is constructed in a single circuit.

The second pressure source is preferably also formed by a (second) cylinder-piston arrangement with a (second) hydraulic pressure chamber, the (second) piston of which is actuated by an electromechanical second actuator (32,52), the (second) pressure chamber in an unactuated state of the (second) piston being connected via at least one second snifter hole to a second connecting line which is connected to the pressure medium reservoir. The second pressure source particularly preferably comprises exactly one (second) hydraulic pressure chamber, that is to say the second pressure source is constructed in a single circuit.

According to a preferred development of an aspect of the invention, the inlet and outlet valves are all actuated by the same electronic device. All inlet and outlet valves are particularly preferably actuated only by the same electronic device.

A wheel speed sensor is preferably provided for each wheel assigned to a wheel brake, the signals from the wheel speed sensors being supplied to and evaluated by the same electronic device which actuates the inlet and outlet valves. In addition to building up pressure, wheel-specific slip control is thus also possible by means of this electronic device.

A driving dynamics sensor system is preferably provided, the signals from which are supplied to and evaluated by the electronic device other than the electronic device which actuates the inlet and outlet valves. In the event of a failure of the electronic device which actuates the inlet and outlet valves, in addition to central pressure control, axle-by-axle pressure control by means of the other electronic device is thus also possible (axle multiplex method). This enables the steerability (for example in the case of braked avoidance maneuvers by an autopilot) and the stability to be maintained.

The brake system preferably comprises a measuring device for detecting a pressure medium level of the pressure medium reservoir. The pressure medium reservoir is advantageously divided into two chambers by a partition, a first chamber being assigned to the first pressure source and a second chamber being assigned to the second pressure source. The measuring device is particularly preferably arranged in the first chamber.

An aspect of the invention offers the advantage that in the event that one of the electronic devices fails, the other electronic device can be used to build up brake pressure at all four wheel brakes, it also being possible to set different brake pressures at least axle by axle.

In the fault-free case of the brake system, the pressure is preferably provided at the wheel brakes by means of the first pressure source. The first pressure source is therefore preferably dimensioned to be stronger or larger than the second pressure source. The signals from the driving dynamics sensor system are particularly preferably supplied to and evaluated by the first electronic device (which is assigned to the first pressure source). The inlet and outlet valves are actuated by the second electronic device.

An aspect of the invention also relates to a method for operating a brake system according to an aspect of the invention.

In the event of a failure of the first pressure source, the first isolating valve is preferably closed by means of the second electronic device, and the second pressure source is actuated to build up a brake pressure.

Furthermore, in the event of a failure of the first pressure source, the circuit separation device is preferably actuated by means of the second electronic device, so that the first brake circuit supply line and the second brake circuit supply line are hydraulically connected to one another. In this way, pressure can be built up at the four wheel brakes by means of the second pressure source.

In the event of a failure of the first pressure source, the inlet and outlet valves are preferably actuated by means of the second electronic device in order to set wheel-specific brake pressures. This enables antilock or traction control functions of the brake system even if the first pressure source fails.

In the event of a failure of the second pressure source, the second isolating valve is preferably closed by means of the first electronic device, and the first pressure source is actuated to build up a brake pressure.

Furthermore, in the event of a failure of the second pressure source, the circuit separation device is preferably actuated by means of the first electronic device, so that the first brake circuit supply line and the second brake circuit supply line are hydraulically connected to one another. In this way, pressure can be built up and regulated at the four wheel brakes by means of the first pressure source.

In the event of a failure of the second pressure source, the first pressure source and the circuit separation device are preferably actuated by means of the first electronic device in order to set axle-specific brake pressures on the wheel brakes in accordance with an axle multiplex method.

