SERVICE BRAKE APPLICATION UTILIZING A MULTI-CIRCUIT HYDRAULIC- POWER VEHICLE BRAKE SYSTEM

Abstract

Wheel brakes of one vehicle axle of a dual-circuit hydraulic-power vehicle brake system for an electric or hybrid vehicle are connected to one brake circuit. Brake pressure is applied by a power brake-pressure generator to the two brake circuits with a time offset. It is thereby possible to compensate for a deceleration effect of an electric motor of the vehicle, which is operated as a generator during a braking.

Claims

1. A method of service braking utilizing a multi-circuit hydraulic-power vehicle brake system, the vehicle brake system including at least two brake circuits, a power brake-pressure generator to which each of the brake circuits is connected by way of a power valve each, and at least one hydraulic wheel brake in each brake circuit of the brake circuits which is connected to the brake circuit by way of one inlet valve each, wheel-brake pressures in the wheel brakes being reducible by opening outlet valves, one of which is connected to each of the wheel brake, the method comprising: generating a brake-circuit pressure in a first one of the brake circuits by the power brake-pressure generator including by opening the power valve of first one of the brake circuits and closing the power valves of the other brake circuits.

2. The method of service braking as recited in claim 1, wherein the brake-circuit pressure is reduced in a second one of the brake circuits by the power brake-pressure generator including by opening the power valve of the second one of the brake circuits and closing the power valves of the other brake circuits.

3. The method of service braking as recited in claim 1, wherein the brake-circuit pressures in the brake circuits are generated by the power brake-pressure generator with a time offset.

4. The method of service braking as recited in claim 1, wherein: (i) the inlet valves are continuously operated valves, and/or (ii) the outlet valves and/or the power valves are switching valves.

5. The method of service braking as recited in claim 1, wherein the vehicle brake system has a brake master cylinder, operable by muscular energy, for a secondary braking, to which the brake circuits are connected by one isolating valve each, the isolating valves being closed during the service braking.

6. The method of service braking as recited in claim 1, wherein wheel brakes of one vehicle axle are connected to one of the brake circuits and/or wheel brakes of different vehicle axles are connected to different brake circuits.

7. The method of service braking as recited in claim 1, wherein a vehicle equipped with the vehicle brake system has a rotating electric machine which is able to be driven by a vehicle wheel and which is operated as a generator to decelerate the vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0017] The single FIGURE shows a hydraulic circuit diagram of a multi-circuit hydraulic-power vehicle brake system for carrying out the service brake application according to an example embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0018] The FIGURE shows a multi-circuit, namely, a dual-circuit hydraulic-power vehicle brake system 1 having two brake circuits I, II with two hydraulic wheel brakes 2 each. Vehicle brake system 1 has a dual-circuit brake master cylinder 4 operable with muscular energy utilizing a foot-brake pedal 3, and a power brake-pressure generator 5. The two brake circuits I, II are connected hydraulically in parallel to brake master cylinder 4 and to power brake-pressure generator 5, each brake circuit I, II being connected by one isolating valve 6 each to brake master cylinder 4, and by one power valve 7 each to power brake-pressure generator 5.

[0019] In one of the two brake circuits I, a piston/cylinder unit 9 having a spring-loaded piston 10 is connected as pedal-travel simulator 11 by way of a simulator valve 8 to one chamber of dual-circuit brake master cylinder 4.

[0020] Brake master cylinder 4 has an unpressurized brake-fluid reservoir 12 having three chambers, the two brake circuits I, II of brake master cylinder 4 being connected to two of the three chambers of brake-fluid reservoir 12. One of the two chambers of brake master cylinder 4 is connected to brake-fluid reservoir 12 via a test valve 13, and the other chamber is connected directly to brake-fluid reservoir 12.

[0021] Power brake-pressure generator 5 has a piston/cylinder unit 14 whose piston 15 is displaceable in a cylinder 18 of piston/cylinder unit 14 by non-muscular energy utilizing an electric motor 16 via a screw drive 17 in order to generate a brake pressure. The two brake circuits I, II of vehicle brake system 1 are connected to cylinder 18 of power brake-pressure generator 5 via the two power valves 7.

[0022] Cylinder 18 of piston/cylinder unit 14 of power brake-pressure generator 5 is connected via a non-return valve 19, traversable in the direction of cylinder 18, to one of the three chambers of brake-fluid reservoir 12, and specifically the chamber to which brake master cylinder 4 is not connected. In addition, cylinder 18 of piston/cylinder unit 14 of power brake-pressure generator 5 is connected directly to brake-fluid reservoir 12 by a brake line 20 without interposition of a valve. At the beginning of its displacement, piston 15 of power brake-pressure generator 5 passes over an outlet of this brake line 20 into cylinder 18 of piston/cylinder unit 14, so that during actuation of power brake-pressure generator 5, piston/cylinder unit 14 of power brake-pressure generator 5 is disconnected hydraulically from brake-fluid reservoir 12.

[0023] Each wheel brake 2 is connected via an inlet valve 21 to one of the two brake circuits I, II, and via an outlet valve 22 to unpressurized brake-fluid reservoir 12.

[0024] In the specific embodiment of the invention shown and described, isolating valves 6, power valves 7, simulator valve 8, test valve 13, inlet valves 21 and outlet valves 22 are 2/2-way solenoid valves, isolating valves 6, test valve 13 and inlet valves 21 being open in their currentless normal positions, and power valves 7, simulator valve 8 and outlet valves 22 being closed in their currentless normal positions. For better controllability of wheel-brake pressures in wheel brakes 2, in the specific embodiment of the invention illustrated and described, inlet valves 21 are continuously operated valves, and the other valves 6, 7, 8, 13, 22 are simpler switching valves. The invention does not rule out other types of valves. Continuously operated valves feature a continuous transition between a closed and an open position and vice versa, whereas switching valves have only the two switching positions, open and closed. Continuously operated valves may also be regarded as throttle valves having a controllable through-flow cross-section or controllable flow resistance.

[0025] Wheel brakes 2 of one vehicle axle are connected in each case to the same brake circuit I, II.

[0026] Vehicle brake system 1 is provided for an electric vehicle or a hybrid vehicle, thus, for a vehicle which has one or more electric motors 23 for its drive. A hybrid vehicle has a further drive, e.g., a combustion engine. The vehicle may have electric motors 23 for single, several or all vehicle wheels. In the drawing, an electric motor 23 is shown for vehicle wheels of each vehicle axle.

[0027] A service brake application according to the invention is carried out as a power braking utilizing power brake-pressure generator 5. To that end, a brake pressure is generated by power brake-pressure generator 5, and by opening a power valve 7, the brake pressure of power brake-pressure generator 5 is applied to one brake circuit, e.g., brake circuit I. The brake pressure prevailing in brake circuit I is also referred to as brake-circuit pressure. Inlet valves 21 remain open and outlet valves 22 remain closed, so that the brake-circuit pressure is applied to wheel brakes 2 connected to the one brake circuit I and are thus actuated. The brake pressure prevailing in wheel brakes 2 is also referred to as wheel-brake pressure. The brake-circuit pressure and the wheel-brake pressures may be increased or decreased by a forward or backward displacement of piston 15 in cylinder 18 of piston/cylinder unit 14 of power brake-pressure generator 5, the brake-circuit pressure and the wheel-brake pressures remaining constant when piston 15 is motionless.

[0028] In the other brake circuit II, the brake-circuit pressure is generated, increased, reduced or held constant by power brake-pressure generator 5 in the same manner with a time offset. The brake-circuit pressures in brake circuits I, II are thus generated, increased, reduced or held constant by power brake-pressure generator 5 with a time offset. It is also possible to initially generate the brake-circuit pressures in the two brake circuits I, II simultaneously, and only then to increase, reduce or keep the brake-circuit pressures constant in brake circuits I, II with a time offset.

[0029] To decelerate the vehicle, electric motors 23 are operated as generators to generate electrical energy. Therefore, they may also be regarded generally as rotating electric machines 24. Braking forces of wheel brakes 2 are decreased commensurate with a deceleration effect of electric motors 23 in generator operation, that is, lower brake-circuit pressures are generated than would be necessary without the deceleration effect of electric motors 23 in generator operation. Since the vehicle wheels of one vehicle axle are drive-connected to one electric motor 23 and their wheel brakes 2 are connected to the same brake circuit I, II, it is possible to compensate well for the deceleration effect of electric motors 23 in generator operation.

[0030] During the service brake application, brake master cylinder 4 is disconnected hydraulically from brake circuits I, II by closing isolating valves 6. Brake master cylinder 4 is used as setpoint generator for the brake-circuit pressures to be generated by power brake-pressure generator 5, which may be different in the two brake circuits I, II. Simulator valve 8 is opened during the service brake application, so that brake master cylinder 4 is able to displace brake fluid into pedal-travel simulator 11, and a piston travel and a pedal travel are possible at brake master cylinder 4.

[0031] In the event power brake-pressure generator 5 malfunctions or fails, a secondary braking is possible by actuating brake master cylinder 4 using muscular energy, in doing so, isolating valves 6 remaining open and power valves 7 remaining closed.

[0032] Inlet valves 21 and outlet valves 22 form wheel-brake pressure-control valve assemblies by which a wheel-specific control of the wheel-brake pressure is possible individually in each wheel brake 2 of vehicle brake system 1. A slip control is thereby possible. Such slip controls include antilock braking systems, traction control systems and vehicle dynamics controls or electronic stability programs, the latter also commonly being referred to as anti-slip control systems. The abbreviations ABS, TCS and VDC or ESP are customary for these slip controls. Such slip controls are familiar and are not explained in greater detail here. An axle-wise slip control by power brake-pressure generator 5 is also possible.

[0033] By closing inlet valve 21 and opening outlet valve 22 of a wheel brake 2, the wheel-brake pressure in this wheel brake 2 may be dropped below the brake-circuit pressure of the brake circuit I, II to which this wheel brake 2 is connected.

[0034] During the service brake application according to the present invention, inlet valves 21 of the brake circuit I, II which is disconnected hydraulically from power brake-pressure generator 5 by closure of its power valve 7, may be closed in order to avoid an increase in the wheel-brake pressures in wheel brakes 2 of this brake circuit I, II in the event closed power valve 7 does not close absolutely imperviously.