Metering fuel by compressibility

Claim 1

In an engine fuel supply system comprising a fuel pump (14) and drain (48): an improved fuel injector mechanism comprising housing means forming a control chamber (22) and a fuel injection chamber (18) having a discharge orifice (12); a slidable needle valve (20) having a first end area exposed to the control chamber and a second end area exposed to the injection chamber, the end areas of the needle valve being approximately the same so that forces attributable to fuel pressure have negligible biasing effect on the valve when the control chamber and injection chamber are fully pressurized; spring means (24) biasing the needle valve in a direction wherein its second end areas closes the discharge orifice when both of the aforementioned chambers are pressurized; means defining a rigid non-elastic fuel storage chamber (32) continuously connected to the injection chamber; a first flow passage (44) within the housing means continuously connected to the aforementioned control chamber (22); an engine-programmed valve (26a) movable within the housing means to alternately connect the first flow passage (44) to the fuel pump or the drain; a second passage (50) connecting the aforementioned storage chamber to the first flow passage; and a check valve (34) in said second passage permitting flow from the first passage to the storage chamber but preventing backflow from the storage chamber to the first passage; the engine-programmed valve (26a) having a first position wherein pressurized fuel from the pump is delivered through the first passage (44) to the control chamber (22) and second passage (50), for thereby filling the fuel storage chamber (32) and injection chamber (18) with pressurized fuel; the spring means (24) being effective to bias the needle valve (20) to a position closing the discharge orifice (12) when said engine-programmed valve is in its first position; said engine-programmed valve having a second position wherein pressurized fuel is exhausted from the control chamber (22) through the first passage (44) to the drain (48), whereby the control chamber pressure is reduced to enable the injection chamber pressure to move the needle valve to a position opening the discharge orifice; the spring means developing a substantial force for thereby closing the needle valve while the injection chamber pressure is appreciably above atmospheric, whereby the time at which the needle valve closes is determined by pressure rather than the engine-programmed valve.