The present invention relates to a method for the operation of a hydraulic brake system with an integrated parking-brake function for motor vehicles having two vehicle axles, said system substantially comprising a pedal-operated pressure generator, at least one hydraulic pump, an operating element which is connected to an electronic control and regulation unit, and wheel brakes provided with inlet and outlet valves, with the wheel brakes associated with the second vehicle axle including a means for executing a parking-brake operation.
U.S. Pat. No. 4,215,767 discloses a hydraulic vehicle brake with a parking-brake device of this type. To execute a parking-brake operation, it is provided in the prior art system that the pressure is built up in the operating pressure chamber by means of a hydraulic pump, whereby a brake piston is displaced that is lockable by way of a threaded-nut/spindle combination furnished with friction surfaces. Disturbing noise which develops during pressure build-up due to the hydraulic pump must be considered a disadvantage though.
In view of the above, an object of the invention is to disclose a method for reducing noise that develops due to the hydraulic pump when pressure is built up for executing a parking-brake operation.
According to the method, this object is achieved by driving the hydraulic pump in such a fashion that the pressure which is necessary to initiate and/or terminate a parking-brake operation is built up with a minimum possible pressure-increase gradient. This provision achieves a low-noise pressure build-up.
In a particularly favorable improvement, the driving mode of the hydraulic pump is determined by the operator.
In this arrangement, a short actuation of the operating element by the operator is used to drive the hydraulic pump in such a fashion that the pressure required to execute a parking-brake operation is built up more slowly in the wheel brakes associated with the second axle than is the case with an actuation of the operating element over a long period of time.
It is provided in an especially favorable embodiment that the pressure that is introduced into the wheel brakes during a service brake phase is used to initiate a parking-brake operation.
In another favorable improvement of the method of the invention, at least the following steps are performed in the transition from a service-brake operation to a parking-brake operation:
Actuation of the operating element by the operator;
Closing the inlet valves of the wheel brakes associated with the first axle;
Pressure build-up performed by the hydraulic pump in the wheel brakes associated with the second axle;
Closing the inlet valves and opening the outlet valves of the wheel brakes associated with the second axle and activation of the means for performing a parking-brake operation.
The invention will be explained in detail in the following by way of an embodiment making reference to the accompanying drawings.
In the drawings:
The circuit diagram of a brake system for motor vehicles represented in
The hydraulic wheel brake 2 for motor vehicles illustrated in
The wheel brake 2 illustrated in the drawings includes a working storage 10 on the side of the brake housing 1 remote from the brake piston 6. Working storage 10 is mainly composed of an accumulator piston 94 bounding the service pressure chamber 7 and a spring element 90 and ensures that the application force acting on the brake pads 24, 25 during the parking-brake operation is almost independent of thermally induced length variations in the area of the brake housing 1. To achieve a parking-brake function, a means for locking the brake piston 6 is required, said means comprising a locking device configured as a threaded-nut/spindle arrangement and a first friction surface 98 on the accumulator piston 94. The threaded-nut/spindle arrangement, whose threaded nut 15 is designed integrally with the brake piston 6 includes a spindle 16 which is coupled to the threaded nut 15 by means of thread without self-locking engagement. Spindle 16 has a second friction surface 97 cooperating with the above-mentioned first friction surface 98 on the accumulator piston 94 when the brake piston 6 is locked.
There is further provision of an arresting unit which is arranged outside the working storage 10 and formed of two electromagnetic control members designed as electromagnets 91, the armatures 92 thereof being rigidly connected to an arresting element 23 designed as a slide. During service brake operations the accumulator piston 94 is blocked by the slide 93 because translational motion of a force-transmitting member 96 in the direction of the brake piston 6 is prevented, said member being rigidly connected to the accumulator piston 94. For this purpose, the force-transmitting member 96 is configured in such a fashion that it has two projections being received in recesses provided in the slide 93. The force-transmitting member 96 is prevented from moving in the direction of the brake piston 6 because the projections are supported on the slide 93. When the slide 93 is moved by the electromagnet 91 in such a fashion that the projections of the force-transmitting member 96 are in alignment with the recesses on the slide 93, the force-transmitting member 96 or the accumulator piston 94, respectively, can move in the direction of the brake piston 6.
To carry out a parking-brake operation, the hydraulic pump 4 mentioned with respect to
The method of the invention described hereinbelow by way of
Further, the method of the invention provides that the driving mode of the hydraulic pump 4 is determined by the operator. With a short activation of the operating element 12 by the operator, the hydraulic pump 4 is driven in such a way that the pressure required for introducing and terminating a parking-brake operation is built up slowly, that means with a low pressure increase gradient. The pressure increase can be stopped by a continued activation of the operating element 12. As has been mentioned already, the noise produced by the hydraulic pump 4 cannot be noticed by the operator due to the slow pressure increase. In case the operator desires a rapid pressure increase to introduce or terminate a parking-brake operation, he/she is required to activate the operating element 12 longer, that means preferably longer than 3 seconds. Thereafter, the necessary pressure is built up with a maximum possible pressure increase gradient predetermined by the structural features of the hydraulic pump 4. In an alternative of the method of the invention, the pressure increase gradient is linearly linked to the activation time of the operating element 12. This provision allows the operator to handle the speed of the pressure build-up independently.
Furthermore, it is provided in the described method that the pressure introduced into the wheel brakes 2, 3 of the rear and the front axles during a service brake operation is used to initiate a parking-brake operation. The basic situation is that the operator uses the service brake to bring the vehicle to standstill. To do so, the operator applies the brake pedal 11, whereupon pressure is built up in the wheel brakes 2, 3. After the operator has brought the motor vehicle to standstill, he usually continues depressing the brake pedal 11. The inlet valves 17 of the wheel brakes associated with the front axle are closed and the pressure introduced during the service brake operation is shut in the wheel brakes 3 of the front axle after the operator has actuated the operating element 12. Thereafter follows a slow pressure build-up by way of the hydraulic pump 4 into the wheel brakes 2 of the rear axle until the accumulator piston 94 described already by way of
Number | Date | Country | Kind |
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103 15 956.8 | Apr 2003 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP04/50473 | 4/7/2004 | WO | 10/11/2005 |