THE SALISBURY "POWR-LOK"
DIFFERENTIAL UNIT
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WHY LIMITED SLIP DIFFERENTIALS ARE NEEDED
The purpose of a conventional differential is to provide equal torque
division between the two road wheels whilst compensating for the difference
in speed between the wheels when cornering. Since equal torque division
is obtained at all times, the total torque transmitted is limited by the
wheel with least adhesion. Whilst the limitation in performance of the
conventional differential has been noticeable in the past when driving on
ice or snow, these same factors are now assuming greater importance, due
to the trend towards a lighter weight on the axle, combined with greater
torque output from the engine. The Limited Slip Differential propor-
tions the torque so that, at all times, the wheel with greater adhesion will
transmit the greater portion of the torque available, whilst maintaining
the necessary differential action on cornering.
POWR-LOK
The Powr-Lok design combines excellent performance with low
initial cost and durability, and it is important to note that no other
assembly combines these advantages to the same degree. In operation, the
Powr-Lok combines the basic elements of the conventional differential
with the restraint of friction clutches which provide the necessary torque
bias. These basic features have been incorporated in a number of alter-
native designs but the Powr-Lok is unique in combining three alternative
methods of loading which are supplementary and provide the necessary
desirable qualities.
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CONSTRUCTION
The cross pins which carry the pinion mates are so constructed that
there is clearance at the intersection to permit relative movement between
the two parts, each shaft having milled cam flats located in vee slots in the
differential case halves. The pinion mates have shoulders engaging
abutment faces on the clutch rings mounted adjacent to the differential
side gears. The clutch rings and side gears have common splines locating
on the axle shaft and the clutch rings are additionally provided with splined
hubs carrying the alternative internally splined clutch plates. The
remainder of the clutch plates are provided with 4 external lugs locating
in slots in the differential case halves. All clutch plates are specially
treated to obtain the desired friction characteristics and are flat with the
exception of one plate for each assembly which is dished to provide a
Belleville spring.
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General