Variable Valve Timing - Volkswagen Passat ‘97 User Manual

2.8-ltr. V6 Engine ACK

Variable valve timing

It provides high torque when driving in low gears
at low speeds, thus improving fuel economy and
reducing exhaust emissions.
At low speeds, the piston moves so slowly that
the gas mixture in the intake manifold follows
the movement of the piston.
The inlet valve must be closed early so that the
fuel-air mixture is not forced back into the
intake manifold.
At high speeds, the flow rate inside the intake
manifold is so high that the mixture can continue
to flow into the cylinder although the piston is
moving back up.
The inlet valve is closed when the fuel-air mixture
can no longer enter the cylinder.
In engines with variable valve timing, the closing
times of the inlet valve are adapted to the speed
range.
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High output is needed at high speeds. To
achieve both, the cylinder must be well-filled
in all speed ranges.
Injection valve
closes early
Injection valve
closes late
SSP 192/130
SSP 192/131