Audi A3 Sportback, Сервисная инструкция, Страница: 26 / 60

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Toothed belt drive
As with all Audi 4-cylinder inline engines, the timing
gear is designed as a toothed belt drive and directly
drives the exhaust camshaft.
The toothed belt tensioning system carried over
from the naturally aspirated engine has been
modified to meet the much higher demands placed
on the toothed belt drive including:
● turbo-related higher valve spring pressures
●
turbo-related valve timing associated with the 42°
crank angle adjustment range of the continuous
variable valve timing on the intake camshaft
●
high-pressure pump drive by a triple cam on the
intake camshaft.
The result is the elliptical toothed belt sprocket on
the crankshaft.
The CTC toothed belt sprocket* used here for the
first time greatly reduces the torsional vibration of
the camshaft and the tensile forces acting on the
toothed belt.
* CTC toothed belt sprocket = c rankshaft t orsional
c ancellation
Function
The toothed belt sprocket is positioned on the
crankshaft at TDC of cylinder 1, as shown in
Fig. 332_023. When the working cycle begins, high
tensile forces act on the toothed belt. They are
reduced by the elliptical shape of the toothed belt
sprocket because the flat side of the sprocket gear
allows a slight slackening of the toothed belt. The
resulting torsional vibration counteracts the
torsional vibration of the 2nd engine order at the
antinode of the timing gear without producing too
much excitation in the other RPM ranges.
Engine
332_023