The following sections
describe power flow for the gear ranges of the transaxle.
When the transaxle is
placed in neutral, the engaged clutch drives the input shaft and gear
cluster assembly in a clockwise direction. The first/second and
third/fourth synchronizers on the pinion shaft are not engaged, so the
pinion shaft gears are not locked to the pinion shaft. The pinion shaft
and the pinion gear do not turn, so there is no output to the transaxle
differential ring gear.
In first gear, the
first/second synchronizer engages the first speed gear to the pinion
shaft, locking it to the pinion shaft. The cluster's first gear,
rotating clockwise, drives the first speed gear and the pinion shaft in
a counterclockwise direction. The counterclockwise turning pinion on the
end of the pinion shaft drives the differential ring gear, differential
gearing, drive shafts, and wheels in a clockwise direction.
As the shift from first to
second gear is made, the first/second synchronizer disengages the first
speed gear on the pinion shaft and engages the second speed gear. With
the second speed gear locked to the pinion shaft. Power flow and
direction is similar to first gear with the exception that flow is now
through the second speed gear and synchronizer to the pinion shaft and
With the clutch disengaged,
the first/second synchronizer sleeve disengages from the second speed
gear on the pinion shaft and returns to its midway or neutral position
between the first and second speed gears. As the driver moves the shift
lever from its second gear position through neutral to the third gear
position, the gear lever inside the transaxle housing moves from the
first/second synchronizer position to the third/fourth synchronizer
position. It engages the third/fourth synchronizer and locks it to the
third speed gear on the pinion shaft. Power flow is then through the
third speed gear to the synchronizer and pinion shaft to the pinion gear
and differential ring gear.
The action of the shift
lever moves the third/fourth synchronizer sleeve away from the pinion
shaft third speed gear and toward the fourth speed gear, locking it to
the pinion shaft.
When the shift lever is
placed in reverse, the reverse idler gear shifts into mesh with the
input cluster reverse gear and the reverse speed gear. The reverse speed
gear is the sleeve of the first/second synchronizer. To act as the
reverse speed gear, the synchronizer sleeve is designed with spur teeth
machined around its outside edge.
The reverse idler gear
changes the direction of rotation of the pinion shaft reverse speed gear
so that the vehicle backs up.
Like transmissions, some
transaxles have five forward speeds. Normally, fourth and fifth gears
for smaller cars have overdrive ratios. These high gear ratios
compensate for very low final drive gear ratios. Low final drive ratios
provide great torque multiplication, which is needed to safely
accelerate with a small engine.
FINAL DRIVE GEARS AND
All vehicles use a
differential to provide an additional gear reduction (torque increase)
above and beyond what the transmission or transaxle gearing can produce.
this is known as the final drive gear.
In a transmission equipped
vehicle, the differential gearing is located in the rear axle housing.
In a transaxle, however, the final reduction is produced by the final
drive gears housed in the transaxle case.
The final drive gears
consist of the pinion shaft pinion gear and the large differential ring
gear. The fact that the driving pinion gear is much smaller than the
driven ring gear leaves no doubt that there is substantial gear
reduction and torque multiplication in the final drive gears. A typical
final drive ratio in a transaxle is 3.78:1. This is calculated by
dividing the number of teeth on the driving ring gear (68) by the number
of teeth on the driven pinion gear (18):68/18 = 3.78.
To obtain the overall gear
ratio or the final gear reduction at the drive axles and drive wheels,
the final gear ratio is multiplied by the gear ratio generated by the
input cluster and pinion shaft gears for each gear range.
For example, first gear
cluster and pinion shaft gears produce a gear ratio of 3.16:1. When
multiplied by the final drive ratio of 3.78:1, the overall ratio is 3.16
x 3.78 = 11.94:1. This means driving torque at the drive axles and
wheels is 11.94 times greater than engine torque at the input shaft.