M 20 GEARBOX
FIAT PUNTO TRAINING OUTLINE
Fiat Auto S.p.A.
After Sales Training
5 M20 gearbox
5.1 Features
The M20/6 gearbox belongs to a new family of three-axle transmission units aimed at
improving driveability and characterized by enhanced compact design compared with
traditional, two-axle gearbox units.
This type of gearbox can sustain and transmit very high torque values (230 Nm): for this
reason, it has been fitted to the most performing diesel engine versions (1.3 Multijet 16V, 90
HP).
Below are the main features of this gearbox:
very good gear shift control;
optimum synchronization;
very high transmissible torque;
small dimensions.
The gearbox configuration is of the transverse type, with 3 shafts and a differential.
HCR (High Contact Ratio) toothing is provided for all the gears.
Precision finishing after the thermal treatment is provided for all the gears and the final
reduction, in order to ensure total toothing accuracy and, therefore, noiseless operation.
Both the wheelcase and the clutch housing have been optimized for lightweight and
soundproofing features by means of a F.E.M. (Finite Element Method) structural analysis
method.
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The synchromesh for all the forwards gears and the reverse gear is of the free-loop brass type
(Borg-Warner type) and is placed on the countershafts (upper shaft for the 3
rd
, 4
th
gears and
the reverse gear; lower shaft for the 1
st
, 2
nd
, 5
th
and 6
th
gears).