Differential Pressure Regulator: Description and Operation

Component Locations:

The electro-hydraulic actuator is bolted to the side of the fuel distributor. It consists of a plate valve fastened between two electromagnets.

Fig. 12 Electro-Hydraulic Actuator (Sectional View):

By varying the electric current to the electro-hydraulic actuator and changing the strength of the magnets, the plate valve can be moved. The varying position of the plate valve controls the quantity of fuel allowed into the lower chamber of the fuel distributor, causing the differential pressure to vary. The operating range is from -50 to +150mA. Differential pressure will be from 0 bar to about 1.6 bar (24 PSI) less than system pressure.
The electro-hydraulic actuator is constructed so that without any operating current, such as in an electrical failure, the plate valve would deflect enough under system pressure to maintain a differential pressure of about 0.4 bar. This combined with the 0.2 bar difference caused by the pressure regulating springs in the fuel distributor will result in a difference of 0.2 bar between the upper and lower chambers in the fuel distributor. Since this pressure difference is the same as on the earlier CIS system, the car will still be driveable in the event of an electrical failure. However, it will run roughly because of the resultant lean air/fuel mixture.

Fig. 48 Electro-Hydraulic Actuator Rich Condition:

When the current supplied to the electro-hydraulic actuator is increased, the plate valve deflects to the left and restricts the flow of fuel to the lower chamber causing the pressure regulating valves to deflect downward. The result is increased fuel flow to the injectors and a richer air/fuel ratio.

Fig. 49 Electro-Hydraulic Actuator Lean Condition:

When the current supplied to the electro-hydraulic actuator is reduced, the plate valve moves to the right and allows more fuel into the lower chamber. The pressure in the lower chamber increases and deflects the pressure regulating valves upward. The quantity of fuel to the injectors is consequently reduced resulting in a leaner air/fuel mixture.