Abstract: An apparatus (10) for use in turning steerable vehicle wheels (14, 16) includes a first pump (30) driven by an engine (42) of the vehicle to supply fluid to the fluid inlet (38) of a power steering motor assembly (12). A second pump (46) is driven by the engine (42) to supply fluid under pressure to the power steering motor assembly (12). The second pump (46) has an input (48) connected in fluid communication with an output (36) of the first pump (30) when a pressure at the fluid inlet (38) is below a predetermined value.

Abstract: An apparatus (10) for use in turning steerable vehicle wheels (14, 16) includes a first pump (30) driven by an engine (42) of the vehicle to supply fluid to the fluid inlet (38) of a power steering motor assembly (12). A second pump (46) is driven by the engine (42) to supply fluid under pressure to the power steering motor assembly (12). The second pump (46) has an input (48) connected in fluid communication with an output (36) of the first pump (30) when a pressure at the fluid inlet (38) is below a predetermined value.

Abstract: A constant displacement pump and an associated flow control mechanism are disclosed. The flow control mechanism includes a variable orifice, i.e., a pintle and valve seat in the outlet from the pump. The pressure drop across the variable orifice controls the position of a bypass valve. The position of the pintle member relative to the valve seat is controlled by fluid pressure acting on one end of the pintle member. The fluid pressure acting on the one end of the pintle member may be infinitely varied so that the position of the pintle member with respect to the valve seat may be infinitely varied. Fluid pressure acting on the one end of the pintle member is controlled by an electrical solenoid which infinitely positions a pilot member relative to a fluid pressure passage joining the opposite ends of the pintle member.