| 摘要 |
The booster is installed downstream of a vehicle's power steering gear. The booster has a power piston and a valve seat piston assembly reciprocably mounted in a bore of the booster housing. The valve seat piston assembly includes two nested control pistons separated by a rubber cushion member which permits limited relative control piston movements. Hydraulic inlet pressure is introduced into the housing bore between these pistons and flows through a normally open poppet valve, which acts as a booster control valve. Movement of the booster input push rod restricts hydraulic fluid flow through the control valve and causes pressure to be built up in the power chamber between the power piston and the valve seat piston assembly. The pressure acts on the power piston to move the booster output member. The pressure also holds one of the control pistons of the valve seat piston assembly in position against the bore end wall so that it does not move during normal power boost operation. The other control piston, on which the control valve seat is formed, moves to compress the cushion member as apply force is increased. The reaction travel obtained gives brake pedal travel characteristics nearly matching those of current vacuum power boosters. In the power mode brake pedal travel can be very low, permitting a high brake pedal ratio for the no-power operating mode.
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