Motor vehicle open-center series hydraulic circuit with accumulator

Claim 2

A motor vehicle fluid power circuit comprising a pump having an outlet side, a steering valve, a fluid pressure actuated brake booster, and an accumulator, first means hydraulically connecting said pump outlet side to said brake booster and hydraulically connecting said pump outlet side to said steering valve, valve spool means connected in said first means and having one end exposed to the pressure of said pump outlet side and another end exposed to the working pressure in said brake booster, said valve spool means in response to the working pressure in said brake booster on said other end throttling fluid flow from said pump outlet side and maintaining the pressure of said pump outlet side at at least a predetermined pressure differential above the working pressure of said brake booster under normal operating conditions, means hydraulically connecting said pump outlet side to said accumulator for charging thereof under normal operating conditions, means responsive to movement of said valve spool means in response to a fluid pressure failure in said pump pressure on said one end for supplying pressurized fluid from said accumulator to said valve spool means, and in response to said fluid pressure failure in said pump pressure on said one end said valve spool means hydraulically connects said accumulator fluid pressure to said brake booster and hydraulically isolates said accumulator and brake booster from said pump outlet side and sTeering valve.

Claim 3

A motor vehicle fluid power circuit as defined in claim 1 including an electrically actuated solenoid valve hydraulically connected to said accumulator and preventing fluid flow in a direction from said accumulator to said brake booster under normal operating conditions, and said means responsive to movement of said valve spool means including electrical actuating means to actuate said solenoid valve to permit fluid flow in a direction from said accumulator to said brake booster in response to a fluid pressure failure in said pump.

Claim 4

A motor vehicle fluid power circuit as defined in claim 1 including an electrically actuated solenoid valve hydraulically connected to said accumulator and preventing fluid flow in a direction from said accumulator to said brake booster under normal conditions, said brake booster includes an input rod movable between a deactuated position and an actuated position, and electrical switch means actuated by said input rod for preventing actuation of said solenoid valve when said input rod is in said deactuated position whereby fluid flow in a direction from said accumulator to said brake booster is always prevented when said input rod is in said deactuated position.

Claim 5

A motor vehicle fluid power circuit as defined in claim 1 wherein said valve spool means includes a control spool slidably disposed in a bore, said control spool includes a first land movable between an open position and a closed position for throttling fluid flow from said pump outlet side to said steering valve, and said control spool includes a second land hydraulically connecting said accumulator to said brake booster in response to a fluid pressure failure in said pump pressure on said one end.

Claim 6

A motor vehicle fluid power circuit as defined in claim 4 wherein said second land hydraulically isolates said brake booster from said accumulator under normal operating conditions.

Claim 7

A motor vehicle fluid power circuit as defined in claim 5 with said means hydraulically connecting said accumulator to said brake booster including a charging passage hydraulically connecting said pump outlet side to said accumulator when the fluid pressure level of said pump outlet side is greater than the fluid pressure level of said accumulator.

Claim 8

A motor vehicle fluid power circuit comprising a pump having an outlet side, a steering valve, a fluid pressure actuated brake booster having a power chamber and a power chamber inlet passage, and an accumulator, first means hydraulically connecting said pump outlet side to said brake booster and hydraulically connecting said pump outlet side to said steering valve, said first means including a bore, said bore having a pump port hydraulically connected to said pump outlet side and a steering valve port hydraulically connected to said steering valve and a power chamber port hydraulically connected to said brake booster power chamber inlet passage and an accumulator port hydraulically connected to said accumulator, said pump port being disposed at the middle of said bore, said steering valve port being disposed at one end of said bore, said accumulator port being disposed at the other end of said bore, and said power chamber port being disposed between said pump port and said accumulator port, a control spool slidably disposed in said bore, means connecting said brake booster power chamber to one of said ends of said bore, a first land on said control spool movable as a result of movement of said control spool responsive to the working pressure in said brake booster power chamber, between an open position and a closed position for throttling fluid flow from said pump port to said steering valve port and maintaining the pressure of said pump port at at least a predetermined pressure level above the working pressure in said brake booster power chamber, a second land on said control spool disposed between said accumulator port and said power chamber port under normal operating conditions, said first means further includIng means hydraulically connecting said pump outlet side to said accumulator for charging thereof under normal operating conditions and means responsive to movement of said control spool in response to a fluid pressure failure in said pump port for supplying pressurized fluid from said accumulator to said control spool, and biasing means moving said second land in a direction toward said one end of said bore to a position between said power chamber port and said pump port in response to a fluid pressure failure in said pump port, whereby said second land hydraulically connects said accumulator port to said power chamber port and hydraulically isolates said accumulator and power chamber ports from said pump and steering valve ports in response to a fluid pressure failure in said pump port.

Claim 9

A motor vehicle fluid power circuit comprising a pump having an outlet side, a steering valve, a fluid pressure actuated brake booster having a power chamber and a power chamber inlet passage, and an accumulator, first means hydraulically connecting said pump outlet side to said brake booster and hydraulically connecting said pump outlet side to said steering valve, said first means including a bore, said bore having a pump port hydraulically connected to said pump outlet side and a steering valve port hydraulically connected to said steering valve and a power chamber port hydraulically connected to said brake booster power chamber inlet passage and an accumulator port hydraulically connected to said accumulator, said pump port being disposed at the middle of said bore, said steering valve port being disposed at one end of said bore, said accumulator port being disposed at the other end of said bore, and said power chamber port being disposed between said pump port and said accumulator port, a control spool slidably disposed in said bore, means connecting said brake booster power chamber to one of said ends of said bore, a first land on said control spool movable as a result of movement of said control spool responsive to the working pressure in said brake booster power chamber, between an open position and a closed position for throttling fluid flow from said pump port to said steering valve port and maintaining the pressure of said pump port at at least a predetermined pressure level above the working pressure in said brake booster power chamber, a second land on said control spool disposed between said accumulator port and said power chamber port under normal operating conditions, said first means further includIng means hydraulically connecting said pump outlet side to said accumulator for charging thereof under normal operating conditions and means responsive to movement of said control spool in response to a fluid pressure failure in said pump port for supplying pressurized fluid from said accumulator to said control spool, and biasing means moving said second land in a direction toward said one end of said bore to a position between said power chamber port and said pump port in response to a fluid pressure failure in said pump port, whereby said second land hydraulically connects said accumulator port to said power chamber port and hydraulically isolates said accumulator and power chamber ports from said pump and steering valve ports in response to a fluid pressure failure in said pump port.

Claim 10

A motor vehicle fluid power circuit as defined in claim 7 wherein said control spool includes one end face disposed in said one end of said bore and another end face disposed in said other end of said bore, said one end face is exposed to the fluid pressure in said pump port to urge said first land in a direction toward said open position, and said other end face is exposed to the fluid pressure in said brake booster power chamber to urge said first land in a direction toward said closed position.

Claim 11

A motor vehicle fluid power circuit as defined in claim 8 with said biasing means including a spring acting against said other end face of said control spool urging said first land in a direction toward said closed position, whereby said predetermined pressure differential is equal to the effective pressure of said spring acting against said other end face.

Claim 12

A motor vehicle fluid power circuit as defined in claim 7 wherein said pump is a constant displacement pump and said steering valve is an open center valve.

Claim 13

A motor vehicle fluid power circuit as defined in claim 7 with said means hydraulically connecting said pump outlet side to said accumulator including a charging passage for permitting fluid flow around said second land from said pump port to said accumulator port for charging said accumulator when the fluid pressure level in said pump port exceeds the fluid pressure level in said accumulator.

Claim 14

A motor vehicle fluid power circuit as defined in claim 11 including a one way check valve in said charging passage preventing flow of fluid in a direction from said accumulator port to said pump port.

Claim 15

A motor vehicle fluid power circuit as defined in claim 12 wherein said charging passage extends through said control spool and around said second land.

Claim 16

A motor vehicle fluid power circuit as defined in claim 7 including an electrically actuated solenoid valve hydraulically connected to said accumulator and said means responsive to movement of said control spool including an electrical actuating means for actuating said solenoid valve and engageable by said control spool, said solenoid valve preventing fluid flow in a direction from said accumulator to said brake booster under normal operating conditions, and said control spool electrically actuates said solenoid valve to permit fluid flow in a direction from said accumulator to said brake booster in response to a fluid pressure failure in said pump.

Claim 17

A motor vehicle fluid power circuit as defined in claim 7 including an electrically actuated solenoid valve hydraulically connected to said accumulator and preventing fluid flow in a direction from said accumulator to said brake booster under normal conditions; said brake booster includes an input rod movable between a deactuated position and an actuated position, and electrical switch means actuated by said input rod for preventing actuation of said solenoid valve when said input rod is in said deactuated position, whereby fluid flow in a direction from said accumulator to said brake booster is always prevented when said input rod is in said deactuated position.

Claim 18

A motor vehicle fluid power circuit as defined in claim 15 including an electrIcally actuated failure indicator means, said means responsive to movement of said control spool including an electrical actuating means for actuating said indicator means and engageable by said control spool, and said control spool continuously actuates said failure indicator means in response to a fluid pressure failure in said pump port, whereby said failure indicator means is continously actuated and said solenoid valve is intermittently actuated in response to a fluid pressure failure in said pump port.