With closed control valves a negative
wave, caused by the descending piston
and the inertia of the gas in the longer
duct, accelerates the air column in the
duct. At resonance rpm the inertia
causes the air to ram into the cylinder
just before the inlet valve closes. This
results in a considerable gain in vol-
umetric efficiency and hence in-
creased torque.
Figure 16 shows the calculated in-
stantaneous pressure variation at the
inlet valve antler full load and res-
onant rpm with open and closed con-
trol valve. The increase in pressure be-
tween BDC and inlet valve closing is
clearly visible.
The V-VIS system thus provides a
major increase in engine torque in the
most used medium range of engine
speed during normal driving. The sys-
tem requires an absolutely tight clo-
sure of the valves to work effectively.
This is achieved by using stainless
steel valves with soft heat resistant
rubber sealing lips. These form a tight
seal against the cast wall of tine ducts,
thus avoiding expensive internal ma-
chining of the ducts.
Control information is fed from the
throttle potentiometer and the ignition
system to a solenoid valve which con-
trols the vacuum driven servo unit to
operate the split valve spindles via a
torque balanced beam. This also to aid
tight valve closure (figure 17).
