| 摘要 |
A hydraulic actuator for a vehicle brake system is provided with an auxiliary mechanical actuator e.g. a handbrake cam which is fitted to a first component (e.g. a first piston) of the hydraulic actuator and acts through an automatic slack adjuster on a second component (e.g. a second piston) of the hydraulic actuator. The adjuster comprises a rotatable push rod and a non-rotatable nut with a screw-thread connection therebetween. The rotatable push rod has a portion which is sealed to the first piston and upon which the mechanical actuator acts. A relatively light spring biasses at least the above mentioned portion of the rotatable push rod away from the mechanical actuator and automatic adjustment comprising rotation of the rotatable push rod is effected when there is at least a tendency for the above mentioned push rod portion to be displaced and the applied hydraulic pressure is at a relatively low value at which the force applied by the hydraulic pressure to the the above mentioned push rod portion is less than the force of the spring. When the applied hydraulic pressure is above this predetermined relatively low value there is no tendency for the rotatable push rod to move away from the mechanical actuator and no adjustment can take place. The adjuster is thereby rendered load insensitive, i.e. it will not overadjust in the event of brake deflection on heavy brake application. |
