IMV valve for Delphi
Perhaps the most common approach to metering the fuel at the inlet to the high pressure pump is to use a Fuel Metering Valve (FMV), also referred to as an Inlet Metering Valve (IMV), which provides a variable cross-sectional area dependent on the flow requirements. Figure 4 [Catania 2011] illustrates the principle of inlet metering using a FMV. Fuel flow rate Q0 is supplied by the in-line electric pump to the FMV. A portion of the flow, Qc, passes through a calibrated orifice (3) into the cooling and lubrication circuit. This flow, also equal to Q0–(Q1+Q2), is constant for fixed conditions at the electric supply-pump discharge. The solenoid-controlled valve (2) is designed so that, in the absence of any current signal from the ECU, the high pressure pump sucks the maximum flow rate at the respective pump rotational speed. Another orifice (4) dampens pressure oscillations which are induced in the high pressure pump feed by the reciprocating pump. When the solenoid is energized, the cross sectional area of valve (2) reduces to lower the flow rate Q2 and consequently increase the pressure at the inlet of the overflow valve (1). The overflow valve (1) remains closed until the spring force acting one side balances the pressure force acting on the other side. As soon as the pressure force increases to offset this balance, the valve opens to discharge excess flow (Q1) and regulate the inlet pressure according to injection system fuel demand.
Similar valves would be used in such pump designs as the Bosch CP 3.2 and Delphi DFP1 .The control opening can have a variety of shapes including circular, triangular, rectangular , a key-hole shape. This key-hole shape provides two control regions. Region 1, distinguished by the slit-like opening and a low fuel flow rate change with valve stroke, is used to control the fuel flow rate to the pump during engine idling and low part load operation. Region 2, distinguished by the rapidly rising flow rate with increasing valve stroke, corresponds to mid-load up to full load operation of the engine.