Fluid-pressure and analogous brake systems – Speed-controlled – With failure responsive means
Reexamination Certificate
1999-01-29
2002-06-04
Dickson, Paul N. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
With failure responsive means
C303S122080, C303S122090
Reexamination Certificate
active
06398318
ABSTRACT:
BACKGROUND INFORMATION
International Patent Publication No. WO 97/21570 describes a conventional braking system. This conventional braking system has a master brake cylinder, to which wheel brake cylinders are connected via wheel-brake pressure-modulation valve arrangements having a brake-pressure build-up valve and a brake-pressure reducing valve. Brake fluid released from the wheel brake cylinders through the brake-pressure reducing valves can be delivered by a return pump back in the direction of the master brake cylinder, or in the direction of the wheel brake cylinders again for renewed pressure build-up. A precharging pump is used to feed brake fluid from a reservoir to the return pump when the master brake cylinder is not actuated. Given appropriate switching of valves in the known vehicle braking system, brake pressure can be built up in the vehicle braking system both by the return pump and by the precharging pump. Furthermore, for slip control, this vehicle braking system has wheel-rotation sensors, as well as an electronic controller which evaluates signals from the wheel rotation sensors and controls the pumps and valves of the vehicle braking system. This conventional vehicle braking system has a brake-slip control, traction-control, and an operating-dynamics control device.
Methods and devices for monitoring a braking system contained in a vehicle are known. For example, German Patent Application No. 38 28 931 describes a method for monitoring the functioning of a braking system. To do so, the travel, the speed and the acceleration of the master-cylinder piston are detected by a sensor. The brake-actuation data thus detected are routed to the electronic controller. The wheel data, i.e. the wheel circumferential velocity, is detected by a wheel sensor and routed to the controller. The electronic controller checks whether the wheel data correlate to the brake-actuation data which correspond to a proper braking. If this is not the case, a pump is operated by closing a switch, the pump delivering pressurized media into the wheel brake cylinder which could not be supplied with pressurized media before because of the malfunction. However, because of its design, in this method it is only possible to monitor the braking system when it is actuated by the driver. It is not possible to monitor the braking system independently of the driver, i.e. at arbitrary points of time.
German Patent Application No. 41 18 597 describes a device for detecting and eliminating a storage-fluid leakage. The hydraulic system in which this device is incorporated includes a storage reservoir, an actuator that is actuated by fluid fed from the storage, and a control valve having an open position and closed position, respectively, for a fluid connection or a fluid shut-off between the storage and the actuator. In addition, the device includes a leakage sensor which generates an output signal indicative of a leakage flow of the fluid from the storage through the control valve in the closed position. This output signal is fed to a device, which is capable of moving the valve element of the control valve back and forth in response to the presence of the output signal. Due to the back and forth movement of the valve element, it is brought into the correct seating on the valve seat, thus ensuring a complete closure of the control valve. The fluid leakages can come about because of foreign bodies present between the valve seat and the valve element. The disadvantage of the device described above is that, besides evaluating the pump performance, in addition a pressure-operated switch is necessary for detecting the leakage.
German Patent Application No. 39 22 947 describes a hydraulic braking system which contains brake-pressure modulators that make it possible to prevent the vehicle wheels from locking as a result of brake pressures which are too high. The brake-pressure modulators include brake-line lock valves and cylinders having pistons, in response to whose displacement, pressurized media escapes from the wheel brakes to reduce the brake pressure. The piston displacements are controlled via valve configurations which are connected to a servo pressure source. Failure of the servo pressure source, if there is even a small leak of a valve arrangement, can lead to at least partial loss of braking force during a braking operation. To detect and indicate possibly existing leakiness, a control unit, acting on the valve arrangements, is adjusted, such that it controls the valve arrangements into different positions, and at the same time, observes via a pressure sensor whether logically assigned pressures are changing unacceptably. This conventional braking system also has the disadvantage that pressure sensors are necessary to implement the monitoring. It may be that it is possible to monitor the braking system independently of the driver, however the braking medium necessary for this is made available starting from a storage reservoir. Because of this, a constant pressure of the braking medium is not absolutely ensured, which can possibly lead to an impairment of the implemented monitoring.
Thus, one of the objects of the present invention is to improve conventional methods and devices, respectively, for checking or monitoring a braking system, so that, first, by using sensors (e.g., wheel r.p.m. sensors), which are present in a braking system equipped with a slip-control device, no additional sensors (e.g., pressure sensors) are necessary. Second, it is possible to monitor the braking system independently of an actuation of the braking system by the driver. At the same time, in performing the above, uniform conditions should exist (e.g., uniform pressure ratios).
SUMMARY OF THE INVENTION
A braking system according to the present invention contains at least one brake circuit. This brake circuit includes first valve configurations on the output side, each composed of a first valve, in particular an intake valve, and a second valve, in particular a discharge valve. Wheel brake cylinders allocated to the brake circuit are connected to the first valve configurations. The braking system furthermore contains a reservoir for accommodating braking medium and, on the incoming side, includes a first valve, in particular a switch-over valve, and a second valve, in particular a suction valve, the reservoir being connected to these two valves. In addition, the braking system has at least one pump which is capable of delivering braking medium to at least two wheel brake cylinders. The braking system according to the present invention has a first pump, in particular a precharging pump, which on the intake side, is directly connected to the reservoir, and which is capable of delivering braking medium in the direction of the wheel brake cylinders, and a second pump per brake circuit, in particular a return pump, which is connected to the first valve configurations in the brake circuit, and which is capable of delivering braking medium into or out of the wheel brake cylinders.
According to a method of the present invention, the at least one pump is actuated, and the first valve configurations are driven by pre-determined driving signals during predetermined vehicle states. During the actuation of the pump and the first valve configurations, a wheel-performance variable is ascertained for at least one wheel of the vehicle, the wheel-performance variable describing the wheel performance, in particular the wheel-rotation performance, of the corresponding wheel. The braking system is checked for a first and/or second fault as a function of this wheel-performance variable.
The wheel slippage and/or wheel r.p.m. and/or wheel velocity is utilized as the wheel-performance variable. One of the advantages of using the above-specified variables is that they can be ascertained using the wheel r.p.m. sensors which are at hand anyway in a braking system equipped with a slip-control (e.g., traction-control) system. Therefore, no additional sensors such as pressure sensors are necessary. Moreover, modification of the braking system, as f
Dickson Paul N.
Robert Bosch GmGH
Williams Thomas J.
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