Volkswagen Marine TDI 100-5 User Manual page 40

Engine electronic systems
Functional description
Injection timing device
The mechanical injection timing device in the
distributor-type injection pump operates with the
aid of the speed-dependent fuel pressure in the
pump interior.
It is necessary to inject fuel earlier as the engine
speed increases. The start of injection is varied by
the turning movement of the rolling ring. This is
controlled by the change in the fuel pressure in
the pump interior. The fuel pressure increases as
the engine speed increases. The control unit
controls the start of injection valve by means of a
clock pulse (pulse duty factor). The pressure in the
pump interior changes corresponding to the
pulse duty factor. One start of injection operation
is assigned to each clock pulse. This facilitates
infinitely variable control of the start of injection
from maximum advance to retard setting.
Engine control unit
From the incoming sensor signals, the engine
control unit calculates the set start of injection
and sends the signals for the necessary pulse
duty factor to the start of injection valve.
Start of injection valve
The valve converts the pulse duty factor into a
change in the pump interior pressure (control
pressure).
Note
To provide a clear illustration, the objects in the
enlargements have been turned through 90°!
To intake side of
vane pump
Superior 40 Technology
Rolling ring
Pressure roller
Advance
Retard
Spring
Pin
Piston of injection timing device
Fuel pressure in
pump interior