| 摘要 |
A vehicle skid control system including a wheel speed transducer, skid control circuitry responsive to the transducer for generating a control current output and a skid control valve responsive to the control current for providing single-gain control in a skid control mode under normal operating conditions. The skid control valve includes a first stage for generating a control pressure from a source of substantially constant fluid pressure which is normally controlled exclusively by the current output of the valve driver, which control pressure is representative of the threshhold pressure which an input metered pressure should not exceed if a skid condition is to be avoided. The control valve further includes a second stage pressure balancing system responsive to allow a metered supply pressure to be applied to a brake port as long as the metered pressure does not exceed the first stage control pressure. Under normal operating conditions, when the metered pressure exceeds the control pressure the second stage becomes operative to modulate the brake port pressure in accordance with the control pressure completely independently of variations in the metered pressure, as long as the metered pressure remains above the control pressure from the first stage, thereby providing the single gain characteristic in the skid control mode. In a hydraulic failure condition, when the source of substantially constant fluid pressure in the first stage fails, means in the valve connect said first stage to said metered pressure. The valve thereby prevents the pressure in the brake port from dropping to zero as a result of such failure by substituting the metered pressure for the substantially constant pressure.
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