DESCRIPTION AND OPERATION
Differential and viscous coupling
The Morse chain 8 drives a conventional type
differential 9. The front and rear output shafts 10 and
11 are splined to the differential output pinions. The
front output shaft 10 forms the outer member of the
viscous coupling, while the inner member plates are
splined to the rear output shaft 11.
Its only function is to limit the maximum difference in
speed between the two shafts, with the effect of
automatically locking the differential.
The maximum difference in speed permitted by the
viscous coupling must however be sufficient to allow
the vehicle to be driven on a dry road surface, in a
circle on full lock, without inducing ’wind up’ or
causing damage to the transmission.
The viscous coupling has alternate plates splined to
the inner and outer members.
One set of plates is splined to 10, the outer
member/front shaft and the other plates are splined
the rear output shaft 11. The coupling is filled with a
special silicone jelly which allows sufficient slip to
occur in normal driving conditions but, which increase
the drag between the plates as the speed difference
and temperature rises, thus eliminating the need for a
manual differential lock.