Q2-30. The purpose of the slip joint is to allow the
The purpose of the differential is to adjust for the
propeller shaft to shorten or lengthen so that
difference in distance the driven wheels travel when
it can be used in several different types of SE?
the vehicle turns. For example, if a 90-degree turn was
made on a 20-foot radius, the inner wheel would travel
about 31 feet and the outer wheel would travel nearly
39 feet. The differential permits each axle to turn at a
Q2-31. What is the purpose of the universal joint?
different rate and still be driven as a single unit.
1. It permits the change of direction of drive
2. It can be used in several different types of
The drive pinion, connected to the propeller shaft,
3. It allows the differential to apply power to
rotates the drive ring gear and the differential case that
one set of wheels at a time
is attached to it (fig. 2-84). When both wheels are
4. It can shorten or lengthen depending on
rotating at the same speed, as they do on a smooth
movement of the rear axle
straight surface, the differential pinions do not rotate
on their trunnions but serve to lock the drive ring gear
and differential case with the differential side gears and
axles, making them turn as one unit. In this case there is
LEARNING OBJECTIVES: Identify the
no relative motion between the drive ring gear and the
purpose of differentials. Identify procedures
axles, and the teeth of the differential pinions do not
for inspecting, checking, and adjusting
move over the teeth of the differential side gears.
d i ff e r e n t i a l s . I d e n t i f y t r o u b l e s h o o t i n g
When the vehicle turns, one wheel must turn faster
p r o c e d u r e s f o r d i ff e r e n t i a l s . I d e n t i f y
than the other. The differential side gear driving the
maintenance procedures for differentials.
outside wheel through the axle turns faster than the
side gear of the inside wheel. For the drive ring gear to
The differential is connected to the propeller shaft
remain meshed with the two differential side gears,
by the final drive. The final drive consists of a pinion
each turning at different speeds, the differential
gear driven by the propeller shaft. The pinion turns a
pinions must turn on their trunnions. The amount by
ring gear that is part of the differential. The function of
which the differential pinions cause the inside side
the ring gear and pinion is to change the direction of the
gear to slow in the rate of turn is the amount by which
power transmitted through the propeller shaft by 90° in
they will cause the outside side gear to increase the rate
order to drive the axles. The ring gear and pinion also
of turn. The average speed of the two side gears is
provide fixed reduction between the speed of the
always equal to the speed of the drive ring gear. For
propeller shaft and the axles. The gear ratio is
determined by dividing the number of teeth on the ring
gear by the number of teeth on the pinion. Most
aviation support equipments have bevel gears (fig.
2-83) in the final drive. Straight bevel gears are very
noisy; therefore, spiral bevel gears are used on most
equipment. The ring gear and pinion are housed in the
differential housing and lubricated by gear oil.
DRIVE RING GEAR
SPIRAL BEVEL GEAR
SPUR BEVEL GEAR
Figure 2-83.--Ring gear and pinion.
Figure 2-84.--Rear axles and differential.