The injection pressure is generated dependent on the engine speed in this cam driven system, i.e. when the speed increases, the pressure increases proportionally.
In conjunction with an electronic controller and a high-pressure magnetic valve, the so-called EDC (Electronic Diesel Control) gives this time-controlled diesel injection technology a large degree of flexibility in varying the injection parameters. In this way, several injections can be controlled in an injection cycle, and thus a pilot injection can be carried out before the main injection. This makes a softer combustion possible, which results in a considerable reduction of engine noise, particularly when cold starting.

The supplying of the fuel from the tank to the pump occurs via a fly pump, which is integrated in the housing of the distributor injection pump. The generation of high pressure is performed by a radial piston pump with a cam ring and from two to four radial pistons (depending on the make). The amount injected is controlled via the duration of closing of the high-pressure magnetic valve; the delivery start is determined by the closing time of the magnetic valve. The adjusting of the injection time in relation to the engine’s crank angle is done by the integrated injection timing mechanism. This is adjusted via a clocked magnetic valve.

Needle stroke (mm)/ Time (ms)

Needle stroke curve with pilot injection at idle speed
(dual-spring valve body)

Tests

The tests of the VP44 are focused on the statistical injection quantity behaviour as dependent on various parameters (control duration of the magnetic valve, speed, pressures, temperatures). In addition, sensitivity and precision statements about various equipment (valve body combinations) and quantity measuring systems can be made here. The equipment available at the institute (Moehwald injection pump test stand, continuous quantity measuring system, injection quantity indicator) as well as the necessary measuring technology for the measuring of injection pressures, temperatures and needle strokes permits detailed test results. As a highly-specific measuring system, the injection quantity indicator is even capable of carrying out separate measurements of the pilot injection and main injection quantities.