| 摘要 |
PROBLEM TO BE SOLVED: To make holding pressures variable in a simple constitution during operation of an HSA(hill start assist) valve and to prevent the pressures from being affected by the air pressure of an air tank. SOLUTION: First and second solenoid switching valves 51, 57 are set in a shutoff position 11 with a vehicle at standstill and a brake pedal 1 operated. Since air at the indicating pressure inlets 47c, 48c of first and second relay valves 47, 48 is stopped from flowing toward a brake valve 2, the first and second relay valves 47, 48 are held operated, with the result that brake actuators 11, 22, 23 are also held operated, keeping wheels braked. The brake holding pressures of the brake actuators 11, 12, 23 come to match the set valve-opening pressures of second and fourth check valves 53, 59. When the brake holding pressures are small, the pedal 2 is operated to increase the output pressures of the first and second relay valve 47, 49, thus increasing the brake holding pressures. |
