1. Field of the Invention
The present invention is directed to a master cylinder, particularly for an anti-locking hydraulic brake system comprising means for determining the position of the master piston within the longitudinal bore of the master cylinder housing.
2. Description of the Related Art
A brake system including a master cylinder of the general type described above is disclosed in German Specification DE-OS 37 51 603. The master cylinder, through a brake conduit, is in communication with a wheel brake. The brake conduit can be blocked by means of an inlet valve. The wheel brake, through a by-pass provided by an outlet valve, is in communication with a reservoir. A pump delivers fluid from the reservoir into the working chamber of the master cylinder. During deceleration, the rotating pattern of the wheel is permanently monitored to immediately detect if a wheel tends to lock. Upon detection of a locking condition, the pump drive is actuated to cause the pump to deliver fluid into the master cylinder. By opening and closing the inlet and outlet valves, the pressure in the wheel brake can be so modulated that the brake torque attains a value corresponding to the friction between tire and road. The pressure fluid delivered by the pump into the working chamber of the master cylinder forces the master piston back into its initial position. To prevent the piston from being completely returned, it has previously been suggested that the position of the master piston be determined and the pump delivery be regulated in response to the determined position of the master piston. According to greater detail in the aforementioned German Specification, it is insured that the master piston, during a brake slip control, assumes a position in advance of its initial position.
The means for determining the position of the master piston, according to the German Specification, may comprise, for example, a plunger actuating a switch and being excited by a ramp on the master piston. According to another embodiment in which the master cylinder is actuated by a vacuum brake force booster, a switch is positioned in the housing wall of the brake force booster, and the switch is actuated by the booster wall.
Both of the above proposed solutions disadvantageously require special structures for the master cylinder or for the vacuum brake force booster. Moreover, there is a high possibility of malfunction because the proposed corrective means do not work in a contact-free manner with the consequence that substantial adjustment efforts are needed to insure precise positioning of the master piston during a brake slip control.