WO2007071558A1

WO2007071558A1 - Method for the operation of a hydraulic brake system for motor vehicles

Info

Publication number: WO2007071558A1
Application number: PCT/EP2006/069361
Authority: WO
Inventors: Roland Gröschl; Michael Hitzel; Martin Baechle
Original assignee: Continental Teves Ag & Co. Ohg
Priority date: 2005-12-21
Filing date: 2006-12-06
Publication date: 2007-06-28
Also published as: DE102006042930A1

Abstract

The invention relates to a method for operating a hydraulic brake system for motor vehicles which is composed of a service brake system and a parking brake mechanism. The brake pistons of the wheel brakes (3) of the rear axle are impinged upon by a hydraulic pressure supplied by the hydraulic pump (4, 20) so as to begin or end a braking process during a standstill. In order to extend the service life of the hydraulic pump (4, 20), the hydraulic pump (4, 20) is operated in a suction-throttled manner if the driver of the vehicle simultaneously actuates the pedal-actuated pressure transducer (10) via the operator's element to operate the hydraulic pump (4, 20) when starting or ending a braking process during a standstill.

Description

Method for operating a hydraulic brake system for motor vehicles

The present invention relates to a method for operating a hydraulic brake system for motor vehicles, comprising a service brake system and a parking brake device, the service brake system having a pedalbetä- tigable, hydraulic pressure transducer with a master cylinder downstream, are connected to the two brake circuits with at least one externally controllable hydraulic pump , wherein in each case a brake circuit is a separating valve, an electric switching valve and a provided with inlet and outlet valves hydraulically actuated front wheel and associated with inlet and outlet valves hydraulically actuated rear axle wheel brake is assigned, and wherein the parking brake device comprises means for locking the Having brake piston of the rear axle wheel brakes, wherein for the initiation or termination of a parking brake operation, the brake piston of Hinte- rachs wheel brakes with one of the hydraulic pump available be applied tion hydraulic pressure.

To initiate a parking brake operation pressure is built up with the hydraulic pump in the rear axle wheel brakes until the required preload force is achieved. Then the brake pistons of the rear axle wheel brakes are mechanically locked and the hydraulic pressure released again. It must therefore be an autonomous pressure build-up, wherein the hydraulic pump removes the required amount of liquid from the master cylinder and the reservoir. If the driver simultaneously presses to operating the pedal-operated pressure transducer, the driver feels on the brake pedal 11, the Pumpensaugpulsationen the commonly used 2-piston pump, which is distracting. In addition, the pressure applied by the vehicle driver via the pressure transducer loads on the suction side of the pump, which in the most serious case can lead to jamming of the pump mechanism. In any case, the pump is subject to greatly increased wear during load changes with suction-side pre-pressure, resulting in a reduced service life.

From DE 10 2004 025 202 B4 a method is already known which at least partially overcomes the disadvantages just described. In the previously known method, it is provided that to bring about a parking brake condition, the pedal-operated pressure transducer is decoupled from the brake circuits and the pump. Subsequently, the pump promotes pressure medium from the front-wheel brakes to the Hinterachsradbremsen, where the parking brake device is located. The pressure medium volume of the front axle wheel brakes is discharged into a low-pressure accumulator, from which the pump sucks the pressure medium. If the pressure medium volume of the Vorderachsradbremsen for activation of the parking brake device to the rear wheel brakes is not sufficient pressure medium must be nachgefördert, which is to be regarded as less advantageous.

It is therefore an object of the present invention to develop an alternative method which overcomes the problems mentioned above.

This object is achieved in that the hydraulic pump is operated throttled suction when at the same time to operate the hydraulic pump during the Initiation or termination of a parking brake operation of pedal-actuable pressure transducer is actuated by the vehicle driver. By this measure, the vehicle driver spokes on the brake pedal 11 no pressure pulsations caused by the pump.

It is provided that the electrical switching valves are controlled such that a smaller volume of pressure medium flows from the master cylinder to the pump as is predicable by the pump. As a result of this measure, the brake pressure applied by the vehicle driver is kept away from the pump suction side, and the particularly high service life of critical load changes with a braking pressure on the pump suction side are reduced or completely avoided.

A particularly advantageous development of the method according to the invention provides that the following method steps are carried out:

Closing the isolation valves and closing the inlet valves associated with the front-axle wheel brakes;

- Control of the hydraulic pump;

- Pulsation-like opening and closing of the electrical changeover valves.

In a further advantageous development of the method according to the invention, it is provided that the pulse-pause ratio for the pulsation-like opening and closing of the electrical changeover valves is selected so that the volume of hydraulic pressure medium flowing through the electrical changeover valves is less than that volume of hydraulic pressure medium required by the pump, which is determined from the product of the pump speed with the pump displacement. The pump speed is determined by means of a voltage model. A further advantageous embodiment provides that the pulsation-like opening and closing of the electrical switching valves for the brake circuits is in push-pull. By this measure, a more harmonious pedal feel is feasible.

The invention will be explained in more detail below with reference to an exemplary embodiment in conjunction with the accompanying drawing, the single figure shows a schematically illustrated circuit diagram of a hydraulic brake system to which the inventive method durchfuhrbar.

The schematic diagram of a brake system for motor vehicles shown schematically in FIG. 1 has two brake circuits I, II. Each of the two brake circuits I, II is associated with a front axle wheel brake 2 and a rear wheel brake 3. One speaks in such an arrangement also of a diagonal division. The front-wheel brakes 2, in contrast to the rear wheel brakes 3 no means for locking the brake piston. The rear axle wheel brakes 3 with locking means will be described in more detail. The wheel brakes 2, 3 are acted upon via inlet valves 7, 13 by a pedal-operated pressure transducer 10, which is shown in Fig. 1 as a vacuum brake booster with downstream master cylinder 1, with pressure. The pressure reduction in the wheel brakes 2, 3 via exhaust valves 8, 14, whereby the brake fluid in low-pressure accumulator 15, 16 is required. In addition, the brake system has an electronic control unit 9, as well as for the wheel brakes 2, 3 on both vehicle axles two hydraulic pumps 4, 20, which together for the implementation of anti-lock regulations (ABS) and regulations in the electronic stability program (ESP) are necessary. In addition, the generate hydraulic pumps 4, 20 a necessary for the activation and deactivation of the parking brake device hydraulic pressure, as will be explained in more detail below.

Starting from the pedal-operated pressure transducer 10 with a downstream master cylinder 1 downstream of each of the two brake circuits I, II, a separating valve 6 and an electric switching valve 5 are assigned. The isolation valve 6 is a normally open SO valve and is needed for all controls during an active pressure build-up by the hydraulic pumps 4, 20. The isolation valves 6 are closed in these active pressure buildup phases by the hydraulic pumps 4, 20, so that the pressure build-up is not controlled in the master cylinder 1. The electrical switching valve 5 - also called EUV for short - is a normally closed SG valve, which establishes or interrupts a connection between the master brake cylinder 1 and the suction side of the pump 4, 20. In the activated state, the electrical switching valve is open and the pump 4, 20 can suck brake fluid from the master cylinder 1 and provide, for example, for a traction control available.

A rear axle wheel brake 3 with integrated parking brake function is described, for example, in DE 10 2004 062 810 A1 and will not be explained again in detail here. The content of DE 10 2004 062 810 A1 is intended to be incorporated by reference into this disclosure.

For locking the parking brake device of such a rear wheel brake 3, a hydraulic pressure is built up by the aforementioned hydraulic pumps 4, 20. Subsequently, an electromagnet is energized, whereby the rear axle wheel brake is locked in its applied state. Then the electromagnet will not work more energized and the armature plate 21 and the power transmission element 39 are no longer maintained. The rear axle wheel brakes thus need no energy and no hydraulic pressure to maintain the lock in the applied state.

To release the lock, in turn, a hydraulic pressure in the rear wheel brakes 3 is controlled.

If the driver simultaneously actuates the pedal-operated pressure transmitter 10 for pump operation, then the vehicle driver on the brake pedal 11 senses the pump suction pulsations of the hydraulic pumps 4, 20, which is perceived as disturbing. In addition, the pressure applied by the driver via the pressure transducer 10 loads on the suction side of the pump 4, 20, which can lead to jamming of the pump mechanism in the most serious case. In any case, the pump 4, 20 subject to load changes with suction upstream form a greatly increased wear, resulting in a reduced life.

One way to decouple the brake pressure from the pump driver via the pedal-operated pressure transducer 10 from the pump suction side is to allow suitable circuitry for the electrical changeover valves 5 to flow through only as much fluid volume as can be carried away by the pump 4, 20. The pump runs slightly suction throttled. For this reason, it is provided in the present method that the hydraulic pump 4, 20 is operated with suction throttling, if at the same time the operation of the hydraulic pump 4, 20 during the initiation or termination of a parking brake operation of the pedalbetätigba- repressor 10 is actuated by the driver. In this case, the electrical switching valves 5 are activated in such a way. ert that a smaller volume of pressure medium flows from the master cylinder 1 to the pump 4, 20 as by the pump 4, 20 is fordable.

When the vehicle driver depresses the brake pedal 11 and at the same time requests an initiation or termination of a parking brake operation via the operating element 12, the separating valves 6 are closed. The intake valves 13 of the front-wheel brakes 2 are also closed. Subsequently, the pumps 4, 20 are driven with a predetermined timing pattern. The result is a speed of the pumps 4,20 and thus a certain, depending on the geometric characteristics of the pump 4, 20 volume flow. Such a clock pattern, with which the pumps 4, 20 are driven, for example, 8ms on and 12ms off. Since the electrical switching valves 5 are closed, a cavitation bubble is formed in the suction space between the check valve 19 on the suction side of the pump 4, 20 and the electrical switching valve 5. The electrical switching valves 5 are now activated with a short pulse, that is, it opens Only a very short and it flows a comparatively small volume of pressure medium from the master cylinder 5 to the suction side of the pump 4, 20. This comparatively small volume of pressure medium is dependent on the pulse length with which the electrical switching valve 5 is opened and the pressure difference between the master cylinder 1 and the Suction side of the pump 4, 20. The pulse length for short-term opening of the electrical switching valve is dimensioned so that the flowed-through volume of pressure medium, although the Kavitationsblase reduced, but not completely closed. After the electrical switching valve 5 is closed again, the pump 4, 20 increases the Kavitationsblase by demanding the flowed-through pressure medium volume again. Subsequently, the next opening pulse the electrical switching valve 5 is supplied. This means that at no time the predetermined by FFV on the pressure transducer 10 pressure on the suction side of the pump 4, 20 is applied.

The pulse width just mentioned for short-term opening of the electrical switching valve 5 or the pulse-pause ratio at the electrical switching valve 5 is thus chosen such that the volume of hydraulic pressure medium flowing through the electrical switching valves 5 is less than the volume of hydraulic pressure medium demandable by the pump 4, 20. The volume of hydraulic pressure medium required by the pump 4, 20 is determined from the mathematical product of the pump speed and the pump displacement. The pump stroke is known from the pump geometry, while the pump speed is determined for example by means of a voltage model.

In the just-mentioned short-term opening of the electric switching valves 5, pressure medium flows from the master cylinder to the pump 4, 20. Since it is assumed in the present method that the vehicle operator actuates the brake pedal 11, the brake pedal sags slightly each time the electrical switching valves 5 are opened , In order to achieve a more harmonious pedal feel, therefore, the electrical switching valves 5 for the two brake circuits I, II are driven in push-pull.

Alternatively, analogue controllable valves can be used as switching valves 5, with which a gleichmaßiger volume flow can be realized. A pulsed control is not necessary in this alternative embodiment.

Due to the described controls of the electrical Um- Shift valves 5 so the brake pressure taken by the driver is kept away from the pump suction side. The particularly strong life critical load changes with driver Einbremsdruck on the pump suction side are reduced or completely avoided.

LIST OF REFERENCE NUMBERS

1 master cylinder

2 front axle wheel brakes

3 rear axle wheel brakes

4 hydraulic pump

5 electrical switching valve

6 isolation valve

7 intake valve rear axle

8 exhaust valve rear axle

9 control unit

10 pedal-operated pressure transducer

11 brake pedal

12 control element

13 intake valves front axle

14 exhaust valves front axle

15 low pressure accumulator

16 low pressure accumulators

17 wheel speed sensors front axle

18 wheel speed sensors rear axle

19 check valve

20 hydraulic pump

Claims

claims

1. A method for operating a hydraulic brake system for motor vehicles, comprising a service brake system and a parking brake device, wherein the service brake system has a pedal-operated hydraulic pressure transducer (10) with a downstream master cylinder (1), at the two brake circuits (I, II) with at least one externally controllable, hydraulic pump (4, 20) are connected, wherein in each case a brake circuit (I, II) an isolating valve (6), an electrical switching valve (5) and a with inlet and outlet valves (13, 14) provided hydraulically actuated front axle Wheel brake (2) and with an inlet and outlet valves (7, 8) provided with hydraulically actuated rear axle wheel brake (3) is assigned, and wherein the parking brake device comprises means for locking the brake piston of the rear wheel brakes (3), wherein the initiation or End of a parking brake operation, the brake pistons of the rear axle wheel brakes (3) with one of the Hydraulic pump (4, 20) are provided pressurized hydraulic pressure, characterized in that the hydraulic pump (4, 20) is operated throttled suction when at the same time to operate the hydraulic pump (4, 20) during the initiation or termination of a parking brake operation the pedal-operated pressure transducer (10) is actuated by the driver.

2. The method according to claim 1, characterized in that the electrical switching valves (5) are controlled such that a smaller volume of pressure fluid from the master cylinder (1) to the pump (4, 20) flows as by the pump (4, 20) is conveyed.

3. The method according to claim 1 or 2, characterized in that the following method steps are carried out:

- Closing the isolation valves (6) and closing the front axle wheel brakes (2) associated with intake valves

(13);

- Control of the hydraulic pump (4, 20);

- Pulsationsartiges opening and closing of the electrical switching valves (5).

4. The method according to claim 2, characterized in that the pulse-pause ratio for the pulsation-like opening and closing of the electrical switching valves (5) is selected so that the volume of hydraulic pressure fluid flowing through the electrical switching valves (5), lower is the volume of hydraulic pressure medium that can be demanded by the pump (4, 20), which is determined from the product of the pump speed with the pump displacement.

5. The method according to claim 2 or 3, characterized in that the pulsation-like opening and closing of the electrical switching valves (5) for the brake circuits (I, II) takes place in push-pull.

6. The method according to any one of the preceding claims, characterized in that the pump speed is determined by means of a voltage model.