| 摘要 |
A vehicular hydraulic brake apparatus comprises a tandem master cylinder having front and rear sections respectively connected by independent front and rear wheel braking hydraulic circuits to front and rear wheel brake cylinders. The rear wheel braking hydraulic circuit is provided therein with a deceleration-responsive braking pressure control device having pressure inlet and outlet normally communicated with each other. The pressure control device has an inertia valve comprising a ball and a valve seat and a first differential piston both disposed between the pressure inlet and outlet. When the deceleration of an associated vehicle reaches a predetermined value, the ball is moved to close the valve for thereby interrupting the communication between the pressure inlet and outlet. In normal operative condition of the apparatus, the differential piston is operative to modulate the inlet pressure after the valve closure and transmit the modulated pressure to the rear wheel brake cylinders. The pressure control device has a second piston having opposite ends exposed to hydraulic pressures in the front and rear wheel braking hydraulic circuits, respectively, so that when a failure should occur in the front wheel braking hydraulic circuit, the second piston is moved in a direction by the pressure in the rear wheel braking hydraulic circuit. The second piston has a cam which forces a plunger into locking engagement with the first piston against movement at least in upstream direction, whereby the hydraulic pressure produced in the rear section of the tandem master cylinder is not consumed for upstream movement of the first differential piston but can be used solely to actuate pistons in the rear wheel brake cylinders.
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