Discharge valve for injection pumps of internal combustion engines

Claim 1

A piston-type injection pump for supplying fuel through a discharge conduit to an injector of an internal combustion engine, the pump comprising, in combination a cylinder having a fuel supply port in a wall thereof, a piston supported for rotation and reciprocation in the cylinder to effect the pressure and suction strokes of the pump, the piston having a profiled peripheral edge cooperable with the fuel supply port in the cylinder during the piston movement for effecting a flow of fuel through the fuel supply port, the space between the piston and the associated end of the cylinder defining a first chamber; means associated with the cylinder and disposed downstream of the first chamber for defining a second chamber separated from but in fluid communication with the first chamber, said second chamber having upper, lower and side walls, a discharge channel, the downstream end of the second chamber communicating with the upstream end of the discharge channel; a relief piston being movably mounted in said second chamber between an upstream position in which the relief piston contacts the upper wall of said second chamber and a downstream position in which the relief piston is spaced a predetermined minimum distance from the lower wall of said second chamber, said side wall defining an annular space in said second chamber disposed between said relief piston and side wall, said side wall and relief piston defining a maximum flow-through area for the fuel therebetween when said relief piston is in said upstream position, said maximum flow-through area being substantially equal to the cross-sectional flow-through area of said discharge channel.