Quantity control in deceleration mode, function

W07.15-1236-75

Shown on cylinder 4 unit pump on engine 541.9

1 Unit pump

2 High pressure pipe

3 Pressure pipe connection

4 Nozzle holder combination

5 Plunger-and-barrel assembly

6 Supply passage

7 Solenoid valve

8 High pressure chamber

9 Return flow channel

B Fuel feed

C Fuel high-pressure

D Fuel return flow

The solenoid valves in the unit pumps are not actuated if the vehicle is decelerating that is the specified engine torque demanded by the drive control (FR) is less than the current actual engine torque.

The unit pumps cannot build up the fuel pressure required to achieve injection since the fuel from the high-pressure chamber (8) is pushed by the upwards movement of the plunger-and-barrel assembly (5) through the opened (de-energized) solenoid valve (7) first into the diversion chamber and then into the return flow channel (9).

Thus the fuel pressure which is being applied at the injection nozzles in the nozzle holder combinations is not sufficient to lift the nozzle needle off its seat against the spring force. This means that the opening pressure of the injection nozzles is not reached and no injection occurs.

This improves the exhaust characteristic of the engine, increases the braking effect of the engine and significantly reduces fuel consumption.