Load sensing steering system with dual power source

A system for providing pressurized fluid, on demand, to a primary load circuit and to an auxiliary load circuit means, the primary load circuit including means providing a load pressure signal representative of the demand for fluid by the primary load circuit, said system comprising:

• a. a first source of pressurized fluid;
• b. first flow control valve means including an inlet port in fluid communication with said first fluid source, a first primary outlet port, a first auxiliary outlet port, and first means biasing said valve means toward a position permitting substantially all of the flow from said inlet port to pass to said first primary outlet port;
• c. first primary fluid conduit means communicating between said first primary outlet port and the primary load circuit;
• d. auxiliary fluid conduit means communicating between said first auxiliary outlet port and the auxiliary load circuit means;
• e. a second source of pressurized fluid;
• f. second flow control valve means including an inlet port in fluid communication with said second fluid source, a second primary outlet port, a second auxiliary outlet port in fluid communication with the auxiliary load circuit means, and second means biasing said valve means toward a position permitting substantially all of the flow from said inlet port to pass to said second primary outlet port;
• g. second primary fluid conduit means communicating between said second primary fluid outlet and said first primary fluid conduit means;
• h. means communicating a pressure signal from said first primary fluid conduit means to exert a biasing force on each of said first and second flow control valve means in opposition to that of said first and second biasing means, respectively;
• i. first means communicating the load pressure signal from the primary load circuit to exert a biasing force on said first flow control valve means in the same direction as said first biasing means;
• j. second means communicating the load pressure signal to exert a biasing force on said second flow control valve means in the same direction as said second biasing means;
• and
• k. third valve means disposed in said second signal communicating means and including an inlet port, a signal port, a tank port, and third means biasing said valve means toward a position permitting communication of said load pressure signal, and means communicating a pressure signal from said auxiliary fluid conduit means to exert a biasing force on said third valve means in opposition to that exerted by said third biasing means and toward a position blocking communication of said load pressure signal and relieving said load pressure signal at said second flow control valve means.

A valve assembly adapted to control the communication of a load pressure signal from a first load circuit to a valve means in response to the flow of pressurized fluid from a fluid source to a second load circuit through conduit means, said valve assembly comprising:

• a. a housing defining a fluid inlet port adapted to receive said load pressure signal from the first load circuit, a signal port to be connected in fluid communication with the valve means, a tank port, a pressure port adapted to communicate with the conduit means and a valve bore;
• b. valve means disposed in said valve bore, said valve means defining first fluid passage means disposed to communicate fluid from said pressure port to said tank port and second fluid passage means in continuous fluid communication with said first fluid passage means;
• c. means biasing said valve means toward a position permitting fluid communication between said fluid inlet port and said signal port and blocking communication between said signal port and said second fluid passage means;
• and
• d. said valve means being subjected to a biasing force, in opposition to that exerted by said biasing means, by fluid at said pressure port, and, when the fluid pressure at said pressure port overcomes said biasing means, said valve means being moved to a position blocking fluid communication between said fluid inlet port and said signal port and permitting fluid communication between said signal port and said second fluid passage means.