Injector Needle Damping - Volkswagen 1.9-Liter TDI Owner's Manual

Injector needle damping

During the pre-injection phase, the stroke
of the injector needle is dampened by a
hydraulic cushion. As a result, it is possible
to meter the injection quantity exactly.
Function
In the first third of the total stroke, the
injector needle is opened undamped.
The pre-injection quantity is injected into
the combustion chamber.
As soon as the damping piston plunges into
the bore in the injector housing, the fuel
above the injector needle can only be
displaced into the injector spring chamber
through a leakage gap.
This creates a hydraulic cushion which
limits the injector needle stroke during the
pre-injection phase.
Pump Injection System
Injector
Spring
Chamber
Injector
Spring
Injector
Housing
Undamped
Stroke
SSP209/035
Injector
Spring
Chamber
Injector
Spring
Injector
Housing
Leakage Gap
Hydraulic
Cushion
Damping
Piston
SSP209/036
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