Transaxle Power Flows


Transaxle Power Flows

The following sections describe power flow for the gear ranges of the transaxle.

Neutral

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.

First

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.

Second

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 pinion.

Third

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.

Fourth

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.

Reverse

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 OVERALL RATIOS

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.

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