Audi A3 Sportback 332 Specifications download pdf (Page 26)

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 = crankshaft torsional

cancellation

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

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Audi A3 Sportback 332 Specifications Page 26