Air inlet system
Inlet air is taken ahead of the radiator
and passes through the air filter and air
mass meter of hot-fim type. The air
temperature is thermostatically regu-
lated to a minimum of +10° C by mix-
ing with warm air taken from the ex-
haust manifold. The inlet air then
passes through the throttle housing.
Air inlet manifold
Figure 14
The geometry of the inlet manifold
was designed with the aid of simulated
unsteady compressible air flow. Dy-
namometer testing confirmed the com-
puter models and the result is V-VIS
(Volvo Variable Induction System). V-
VIS consists of a conventional plenum
chamber with twin inlet ducts to each
cylinder, parallel but of different
length. The compact "roll" shape
achieves good space and use of materi-
al at minimum weight.
The shorter ducts are closed by a set
of electro-pneumatically controlled
valves when the throttle is more than
80 per cent open and with engine speed
lying between 1500 and 4100 rpm. At
smaller throttle opening, or at other
revs, the valves remain open and form
part of the wall of the short ducts in or-
der to minimize flow losses. Figure 15
shows the calculated volumetric ef-
ficiencies with open and closed control
valves.
