Patent ID: 6397724
Filing Date: 2002-06-04
Classification: B60T

Abstract:
A negative pressure type servo unit comprising:a housing in which is formed at least one pressure space: a movable wall installed in the housing for progressing and regressing relative to the housing and dividing the pressure space into a front chamber communicated with a negative pressure source and a rear chamber selectively communicated with the front chamber and atmosphere; a power piston coupled to the movable wall; an input member arranged at an inner portion of the power piston and movable in a forward and rearward direction by operating a brake; a plunger arranged to the input member coaxially inside the power piston and movable in the forward and rearward direction, and movable in the forward and rearward direction by moving the input member; a seal member arranged between the plunger and the input member; a valve mechanism for communicating the rear chamber with the atmosphere and cutting off the rear chamber from the atmosphere, and communicating the negative pressure source with the rear chamber and cutting off the negative pressure chamber from the rear chamber by moving the plunger, the valve mechanism including an atmospheric valve for communicating the rear chamber with the atmosphere and cutting off the rear chamber from the atmosphere in accordance with the movement of the plunger and a negative pressure valve for communicating the negative pressure source with the rear chamber and cutting off the negative pressure source from the rear chamber in accordance with movement of the plunger, the atmospheric valve including an atmospheric valve seat arranged at the plunger and an atmospheric sealing portion adapted to contact and be spaced from the atmospheric valve seat, the negative pressure valve including a negative pressure valve seat arranged at the power piston and a negative pressure sealing portion adapted to contact and be spaced from the negative pressure valve seat, communication between the rear chamber and the atmosphere being cut off by bringing the atmospheric valve seat into contact with the atmospheric sealing portion and the rear chamber being communicated with the atmosphere by moving the atmospheric valve seat away from the atmospheric sealing portion, and communication between the rear chamber and the front chamber being cut off by bringing the negative pressure valve seat into contact with the negative pressure sealing portion and the rear chamber being communicated with the front chamber by detaching the negative pressure valve seat from the negative pressure sealing portion; an output member for outputting a progressive force of the power piston to outside the unit by being made to progress as a result of progress of the power piston in accordance with movement of the movable wall; an actuator adapted to move the plunger; the seal member comprising a first engaging portion engaged with the input member so that the engaging portion is movable integrally with the input member while the plunger and the input member have relative movement and a second engaging portion engaged with the plunger so that the second engaging portion is movable integrally with the plunger while the plunger and the input member have relative movement; and the atmospheric valve and the negative pressure valve being arranged to separate from each other in the forward and rearward direction and the atmospheric valve being arranged on a rear side of the negative pressure valve, and the second engaging portion being arranged between the atmospheric valve and the negative pressure valve in the forward and rearward direction.