Hydraulic systems

Claim 2

In a hydraulic system for a motor vehicle, a reservoir containing hydraulic fluid, means connecting said reservoir to a pump having an output providing hydraulic fluid under pressure, means defining a hydraulic brake circuit connected to the pump output and containing at least one brake motor and a valve for selectively applying fluid pressure from the pump to said motor, means defining a hydraulic auxiliary device circuit connected to the pump output and control means operatively connected to be automatically responsive to either a predetermined drop in hydraulic fluid pressure at the pump output or to a predetermined fall in the hydraulic fluid level in said reservoir, or both, for disabling said auxiliary device circuit while maintaining available pump output pressure at said brake circuit.

Claim 3

In the hydraulic system defined in claim 1, said auxiliary device circuit comprising a branch passage connected to a passage connecting the pump output to said brake circuit, and said control means comprising a normallY open valve in said branch passage operably connected to pressure responsive means disposed between the pump and the brake motor and to liquid level responsive means at the reservoir.

Claim 4

A hydraulic system as claimed in claim 2, wherein said normally open valve in the branch passage is a solenoid-operated valve that includes a main valve element controlling fluid flow between an inlet port connected to the pump output and a delivery port connected to the auxiliary device circuit, said valve element being subjected at one side to inlet port pressure normally urging said valve element in a direction to permit fluid communication between said inlet and delivery ports, spring means acting on the other side of said valve element loading the valve element to bias it in the opposite direction, and a pilot valve operable upon energization of the solenoid of said solenoid -operated valve to admit inlet port pressure to the other side of said valve element whereby fluid pressures at both sides of the valve element are balanced and the valve element moves under its spring loading to close off the delivery port.

Claim 5

In the hydraulic system defined in claim 1, said control means comprising a pressure sensitive switch connected to be responsive to pump outlet pressure and a level responsive switch at the reservoir, and there being a normally open solenoid valve in said auxiliary device circuit having an electrical energizing circuit wherein said switches are connected in parallel.

Claim 6

In the hydraulic system defined in claim 4, said level responsive switch being a float actuated switch.