Principle of operation

Principle of operation

Fuel taken up from tank (11) and filtered by filter (12), flows to feed pump (7) which increases fuel pressure.

Under the effect of the feed pump pressure regulator valve (2), the pressure increases in more or less linear fashion as engine rpm rises.

Valve (2) also by-passes the feed pump (7) during priming.

Fuel flows from the feed pump to metering device (6), which calculates the amount of fuel to be sent to pumping element (4) and thus the effective output of the injectors.

The position of metering device (6) is controlled by speed regulator (13) on the basis of accelerator pedal position.

The pumping element consists of two opposing plungers which slide radially in the rotor and are operated by the profile of a ring with cams via rollers and sliding pads.

The plungers lack return springs because they are pressed outward by centrifugal force and the pressure of the fuel entering during the supply stage.

The rollers which drive the plungers come into contact with the cam profile at different points according to the length of travel during the fuel supply stage.

This travel is dependent upon the amount of fuel entering the pumping chamber, regulated by the metering device, and upon plunger expansion time determined by pump rotating speed.

During the injection stage, the plunger control rollers come into contact with the cams and the plungers are pushed inward to raise the pressure and bring about injection.

At the end of the injection stage, the plungers are pushed outward to lower the pressure. Fuel delivery stops and valve (5) seals off the outlet pipe.

Valve (5) not only closes the delivery pipe but also instantaneously lowers the pressure in the pipe leading to injector (10). This quickly shuts off injection to prevent the injector dripping.

The maximum quantity of fuel which may be fed into the pumping element (4) during each cycle is determined by a maximum flow regulator.

Pressure inside pumping element (4) is maintained at a constant level by pressurisation valve (9).

Turbocharging control valve (1) increases the fuel flow. Increased turbocharging pressure compresses a membrane located inside the valve to move a piston which transfers feed pressure to the sliding pad actuator located inside pumping element (4). The sliding pads move to alter plunger travel and thus also the quantity of fuel injected.

Solenoid (8), controlled by a electronic control unit, alters the pump delivery advance to bring about an increase when engine load exceeds a given threshold.

The engine stop solenoid (3) is protected by a tamper-proof cover.

During engine operation, the solenoid remains active so that fuel may flow from feed pump (7) to the intake duct.

When the key is turned to switch off the engine, the solenoid is deactivated to shut off the fuel flow. The metering device feed chamber is no longer supplied with fuel and the engine stops.