Page 127 - Automotive Engineering

CH AP TER 5 .1 Transmissions and driveline

the plate to rotate freely when the clutch pedal is
depressed.
Fig. 5.1-15 shows the whole clutch system. By
depressing the diaphragm spring, the pressure on the
driven plate is released. This actuation of the spring is
achieved by hydraulics, cable or, on older vehicles, may
have been mechanical linkage. When the load on the
cover plate is released, the driven plate is allowed to
rotate freely inside the assembly and the drive to the
transmission is disconnected.

5.1.3.6 Automated manual transmission

With the introduction of a number of vehicles recently,
automation of synchromesh, ‘manual’ transmissions is
Fig. 5.1-14 Diagram of clutch when released. becoming more popular. The reason for the develop-
ment of these transmissions is twofold; firstly, they can
show an economy benefit over both manual and ATs.
race of the bearing rotates with the diaphragm spring and This is because they are more efficient than automatics
clutch cover. The force applied and travel of the bearing and can be programmed to change gear more effectively
are determined by the lever ratio built into the clutch than most drivers would. Secondly, automated manual
pedal, hydraulics (or cable) and release lever. There is transmissions are gaining in popularity in the perfor-
often significant development in this area as the loads and mance car market, probably because of the links to
movement of the pedal have to be as low as possible for Formula 1 racing and as a result of clever marketing!
the driver while ensuring the clutch will operate cor- Examples include: BMW M3, MMC Smart, VW Lupo
rectly throughout the life of the clutch plate. As the and Alfa 156.
clutch plate wears, the position of the various compo- These developments started some time ago with the
nents and the load applied by the spring vary. Obviously, introduction of automated clutches on several vehicles
the load has to always be sufficient to clamp the driven including the Renault Twingo, Saab 900 Sensonic and
plate and not allow any slip, and yet fully clear to allow Ferrari. These cars retained the normal gear lever but

Fig. 5.1-15 Diagram of clutch and actuation mechanism.

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