Pump suitable for a hydraulic steering power system having an auxiliary power source

Claim 1

An auxiliary hydraulic fluid pump assembly having a fluid inlet passage that is constructed to be operative when the fluid pressure in said inlet passage falls below a preset minimum, said pump comprising a housing having a cylindrical portion with an interior surface defining a first bore, a pump piston reciprocable between first and second positions within said first bore, eccentric driving means constructed to engage one end of said pump piston and cause the reciprocation thereof, said pump piston having a peripheral flange adjacent its said one end, a first coil spring surrounding said cylindrical portion and engaging said flange, said first coil spring being constructed to urge said pump piston into engagement with said eccentric driving means, the other end of said piston and said first bore defining an expansible chamber, a fluid discharge passage and said fluid inlet passage communicating with said chamber, a first check valve disposed in said fluid discharge passage and a second check valve disposed in said fluid inlet passage, a second bore in said housing arranged along an axis generally perpendicular to the axis of said pump piston, said second bore having a large bore portion and a small bore portion, said small bore portion opening into said first bore, a blocking piston having a large piston portion slidably mounted in said large bore portion, said pump piston having an annular recess on its side, said blocking piston having a pilot portion disposed in said small bore portion, said blocking piston being reciprocable in said second bore between an extended position and a retracted position, said pilot portion being constructed to protrude inwardly from the end of said small bore portion and engage said annular recess of said pump piston when said block piston is in its said extended position and thereby prevent the reciprocation of said pump piston, a second coil spring arranged concentrically with respect to said pilot portion and engaging said large piston portion, said second coil spring being constructed to urge said blocking piston to its said retracted position and said pilot portion out of engagement with said pump piston, a fluid chamber disposed within said housing and defined in part by said large piston portion of said blocking piston and said large bore portion of said second bore, passage means disposed in said housing constructed to provide fluid pressure communication between a point in said inlet passage upstream of said second check valve and said fluid chamber whereby fluid pressure in said inlet passage urges said pilot portion against the force of said second coil spring acting upon said blocking piston and into engagement with said pump piston.