Motor vehicle fuel pump assembly with pressure relief orifice

In a motor vehicle fuel pump assembly having

• a tubular shell,
• an electric motor in said tubular shell including an armature shaft supported on said shell for rotation about a centerline of said shell at speeds varying between a minimum corresponding to a minimum fuel demand and a maximum corresponding to a maximum fuel demand, and
• a roller vane pump stage including
• an inlet side plate in said shell in a plane perpendicular to said centerline having an arc-shaped inlet port therein whereat an inlet fluid pressure of said roller vane stage prevails,
• a discharge side plate in said shell in a plane perpendicular to said centerline having an arc-shaped discharge port therein whereat a discharge fluid pressure of said roller vane pump stage prevails,
• a rotor between said inlet and said discharge side plates connected to said armature shaft for rotation as a unit therewith and having a plurality of outward opening circumferentially spaced roller pockets therein,
• a plurality of rollers each disposed in a respective one of said roller pockets, and
• a cam ring between said inlet and said discharge side plates having a cam edge facing said rotor with an inlet ramp in a first angular interval subtended by said inlet port and a discharge ramp in a second angular interval subtended by said discharge port and an intermediate ramp in a third angular interval subtended between a downstream end of said discharge port and an upstream end of said inlet port,
• rotation of said rotor being operative to move each of said pockets successively through said third angular interval in a direction from said second angular interval toward said first angular interval so that a fluid pressure prevailing in each of said successive pockets wholly within said third angular interval is generally equal to said discharge pressure of said roller vane pump stage,
• the improvement comprising:
• means defining a bleed orifice in said inlet side plate substantially smaller than each of said roller pockets and located radially to intercept said successive ones of said roller pockets during rotation of said rotor about said centerline and located circumferentially in a segment of an angular interval subtended by said intermediate ramp characterized by flow communication of said bleed orifice with said successive ones of said roller pockets and simultaneous isolation of said successive ones of said roller pockets from each of said inlet and said discharge ports, and
• means effecting flow communication between said bleed orifice and a receiver means remote from said inlet port having a prevailing pressure therein substantially equal to said inlet pressure of said roller vane pump stags and operative to accept a variable flow rate from said bleed orifice.