Method of and system for controlling brakes

Abstract

The ABS is provided with a modulator, and when the ABS is activated, control of the caliper pressure by the driver, is modified by the operation of the modulator having the aforementioned inlet valve (normally closed to a pressurized fluid source) and aforementioned outlet valve (normally open to a fluid exit), both controlled by the above-described control logic circuit. The modulator increases or decreases the caliper pressure, in response to changes in the pressurized fluid, regulated by such valves. Depending on the operation of the control logic circuit described above, three events may occur. When the inlet and outlet valves are not operated (i.e. their normal state), the modulator releases pressurized fluid through the output valve, and increases caliper pressure, to increase braking up to a predetermined maximum. If only the outlet valve is operated (i.e. both the inlet and outlet valves are closed), the modulator remains in a constant state and likewise, the caliper pressure is kept constant. If both the inlet and outlet valves are operated (i.e. opened and closed respectively), then in response to the increased pressurized fluid, the modulator effects a decrease in caliper pressure to reduce braking. The above is summarized in FIG. 2. Thus it is seen that the brake control is effected by setting a threshold value for each of the slip ratio .lambda. and the acceleration/deceleration .alpha., and determining whether the actual state of each wheel (i.e. .lambda.and .alpha.), is at their respective threshold value or above (less). It is thus necessary to set processing times as short as possible to improve the operating speed of an actuator which executes the process referred to above. However, there are limitations on the operating speed of the actuator, and an improvement is actually difficult to achieve. In another prior art system, the modulator comprises an input hydraulic chamber which communicates with a master cylinder, for