Hydraulic brake system

Abstract

A vehicle having a hydraulic power brake system and a hydraulic power steering system, each having its own pump may utilize the power steering system pump as an emergency back up pump for the power brake system should the pump for the power brake system fail. The fluid under pressure in the accumulator for the power brake system will act upon failure of the power brake pump to initiate the switch over to the power steering pump.

What is claimed is: 
     
       1. A hydraulic control system for a powered vehicle comprising hydraulic source means, first and second hydraulic servo motors, closed hydraulic circuit means containing said hydraulic .[.pressure.]. source means and said first servo motor, accumulator means fluidically connected in said closed hydraulic circuit means, control valve means fluidically connected with said first servo motor and said accumulator means for establishing fluid communication therebetween in response to manual operation of said control valve means, first pump means in said closed circuit means for pumping hydraulic fluid under pressure to said accumulator means, and open hydraulic circuit means for fluidically connecting said second servo motor with said hydraulic .[.pressure.]. source means, second pump means in said open hydraulic circuit means for pumping hydraulic fluid under pressure to said second servo motor, unloading valve means in said open hydraulic circuit means, means connecting said closed hydraulic circuit means to said unloading valve means whereby said unloading valve means may act under the influence of the hydraulic pressure prevailing in said closed hydraulic circuit means, and additional means connecting said unloading valve means to said accumulator .[.valve.].  means so that said unloading valve means is adapted to deliver hydraulic fluid under pressure from said second pump means to said accumulator means when the pressure of the hydraulic fluid from said first pump means falls below a predetermined pressure. 
     
     
       2. A hydraulic control system as set forth in claim 1 further comprising an intensifier means connected between said unloading valve means and said accumulator means for intensifying the pressure of the hydraulic fluid conveyed from said second pump means to said accumulator means. 
     
     
       3. A hydraulic control system as set forth in claim 1 wherein said first servo motor is comprised of a pair of hydraulically energizable brake means, said control valve means being operable to control the connection of said .[.accumulators.]. .Iadd.accumulator means .Iaddend.with said brake means in response to actuation of a brake pedal and first safety valve means is provided in said closed hydraulic circuit for interruption of hydraulic pressure in the related hydraulic system including .[.either of said accumulators.]. .Iadd.said accumulator means .Iaddend.should it become disabled. .Iadd. 4. A hydraulic control system as set forth in claim 3 wherein said first safety valve means comprises a cylinder body having a longitudinal and axial bore, a piston slidably mounted in the latter and defining two separate chambers within said bore, a pair of springs adapted for positioning said piston at its balanced position, fluid passage means formed in said piston, inlet port means formed at said cylinder body and kept in respective communication with said separate chambers, said inlet port means leading through respective pipings to said first pump means and said unloading valve means, respectively, and additional control valve means provided in said chambers and adapted for control of fluid communication between said inlet port means and outlet port means formed at said cylinder body and leading to said accumulator means. .Iaddend..Iadd. 5. A hydraulic control system as set forth in claim 4 wherein said fluid passage means comprise a cross-shaped passage formed in and through said piston and said additional control valve means are comprised of ball valve means adapted for control of fluid communication between said cross-shaped passage and said separate chambers, respectively, a slidable valve holder means holding said ball valve means, and spring means for urging said holder means toward said piston. .Iaddend. .Iadd. 6. A hydraulic control system as set forth in claim 4 wherein second safety valve means is provided between said accumulator means, on the one hand, and said control valve means, on the other, for interrupting the fluid communication of a disabled one of said hydraulic circuits related respectively with said accumulator means. .Iaddend..Iadd. 7. A hydraulic control system as set forth in claim 6 wherein said second safety valve means comprises a main body having chambers communicating fluidically with said control valve means, two inlet ports formed at said main body and fluidically communicating with said accumulator means, a pair of valve means provided in said chambers adapted for fluid flow interruption between the latter and said inlet ports and spring means urging said both valve means in the interrupting direction of said inlet ports. .Iaddend. .Iadd. 8. A hydraulic control system as set forth in claim 3 wherein additional safety valve means is provided between said accumulator means and said unloading valve means and actuatable by accumulated fluid pressure in said accumulator means, the operation of said unloading valve means being controlled by actuation of said additional safety valve means. .Iaddend..Iadd. 9. A hydraulic control system as set forth in claim 8 wherein said additional safety valve means comprises a main body having a longitudinal and axial bore, a piston slidably mounted in the latter and having a central and axial bore, spring means for urging said piston only in its one axial direction, valve means adapted for cooperation with valve seat means formed on said piston, two chambers formed within said bore and partially defined by said piston and the last mentioned valve means and kept in fluid communication with said accumulator means, respectively, fluid passage means for establishing fluid communication between said last mentioned bore and outlet port means formed at said last mentioned body and kept in fluid communication with said unloading valve means, said foregoing valve means being adapted normally for interrupting one of said two chambers and said outlet port means and further adapted for interrupting fluid communication, should one of related hydraulic circuits with said both chambers become disabled, between the chamber which is related with said disabled circuit, and said outlet port means. .Iaddend. .Iadd. 10. A hydraulic control system as set forth in claim 3 wherein additional safety valve means is provided between said control valve means and said brake means, for fluid interruption of a disabled hydraulic circuit related with said brake means. .Iaddend..Iadd. 11. A hydraulic control system as set forth in claim 10 wherein said additional safety valve means comprises a main body having an internal longitudinal bore, a piston slidably mounted in the latter for partially defining two separate chambers in said bore, spring means adapted for urging said piston towards its balanced position, inlet port means formed at said main body for connecting said chambers and said control valve means, respectively, outlet port means formed at said main body adapted for connecting said both chambers and said brake means in mutual fluid communication, respectively, and a pair of valve means arranged respectively within said both chambers and adapted for control of fluid communication between said both control valve means and said brake means, respectively. .Iaddend..Iadd. 12. A hydraulic control system as set forth in claim 3 wherein said unloading valve means comprises a main body having an inner and longitudinal bore, a spool valve member slidably mounted within said bore, a chamber defined by one end of said spool valve member and said main body and in fluid communication with said closed hydraulic circuit, and spring means acting upon the opposite end of said spool valve member for resiliently urging the latter against the action of fluid pressure prevailing in said last mentioned chamber, said spool valve member being adapted for conveying hydraulic pressure from said second pump means towards said accumulator means, should the fluid pressure prevailing in said last mentioned chamber fall below a predetermined level. .Iaddend..Iadd. 13. A hydraulic control system as set forth in claim 2 wherein said intensifier means comprises a main body having an inner and longitudinal bore, a piston slidably mounted in the latter for partially defining three separate chambers therein, the first chamber of said three chambers being kept in fluid communication with said second pump means when said unloading valve means is actuated while the second chamber of said three chambers is kept in fluid communication with said second servo motor and the third chamber of said chambers is kept in fluid communication with said accumulator means, the fluid communication between said second chamber and said second servo motor is caused to interrupt and fluid communication between said second chamber and said second pump means is established, while fluid communication between said first chamber and said second pump means is interrupted and that between said first chamber and said second servo motor is established and maintained, when the fluid pressure prevailing in said first chamber attains at least a predetermined level, and further valve means are provided for recovering said first valve means in its initial position when said piston shifts in the reducing direction of the fluid pressure prevailing in said third chamber. .Iaddend.