Transmission/Transaxle Design

Transmission/Transaxle Design

The internal components of a transmission or transaxle consist of a parallel set of metal shafts on which meshing gearsets of different ratios are mounted. By moving the shift lever, gear ratios can be selected to generate different amounts of output torque and speed.

The gears are mounted or fixed to the shafts in a number of ways. They can be internally splined or keyed to a shaft. Gears can also be manufactured as an integral part of the shaft. Gears that must be able to freewheel around the shaft during certain speed ranges are mounted to the shaft using bushings or bearings.

The shafts and gears are contained in a transmission or transaxle case or housing. The components of this housing include the main case body, side or top cover plates, extension housings, and bearing retainers. The metal components are bolted together with gaskets providing a leak-proof seal at all joints. The case is filled with transmission fluid to provide constant lubrication and cooling for the spinning gears and shafts.

Transmission Features

Although they operate in a similar fashion, the layout, components, and terminology used in transmissions and transaxle are not exactly the same.

A transmission has three specific shafts: the input shaft, the countergear shaft, and the mainshaft or output shaft. The clutch gear is an integral part of the transmission's input shaft and always rotates with the input shaft.

The counter gear is actually several gears machined out of a single piece of steel. The counter gear may also be called the countergear or cluster gear. The counter gear mounts on roller bearings on the countershaft. The countershaft is pinned in place and does not turn. Washers control the amount of end play of the unit in the transmission case.

The main gears on the main shaft or output shaft transfer rotation from the counter gears to the output shaft. The main gears are also called speed gears. They are mounted on the output shaft using roller bearings. Speed gears freewheel around the output shaft until they are locked to it by the engagement of their shift synchronizer unit.

Power flows from the transmission input shaft to the clutch gear. The clutch gear meshes with the large counter gear of the counter gear cluster. This cluster gear is now rotating. Since the cluster gear is meshed with the speed gears on the mainshaft, the speed gears are also turning.

There can be no power output until one of the speed gears is locked to the mainshaft. This is done by activating a shift fork, which moves its synchronizer to engage the selected speed gear to the mainshaft. Power travels along the counter gear until it reaches this selected speed gear. It then passes through this gear back to the mainshaft and out of the transmission to the driveline.

Transaxle Features

Transaxles use many of the design and operating principles found in transmissions. But because the transaxle also contains the differential gearing and drive axle connections, there are major differences in some areas of operation. This transaxle uses fully synchronized, constant mesh helical gears on all forward speeds and spur gears for reverse.

A transaxle has two separate shafts - an input shaft and an output shaft. The input shaft is the driving shaft. It is normally located above and parallel to the output shaft. The output shaft is the driven shaft. The transaxles main (speed) gears freewheel around the output shaft unless they are locked to the shaft by their synchronizer assembly. The main speed gears are in constant mesh with the input shaft drive gears. The drive gears turn whenever the input shaft turns.

The names used to describe transaxle shaft vary between manufacturers. The service manuals of some vehicles refer to the input shaft as the mainshaft and the output as the driven pinion or drive shaft. Others call the input shaft and its gears the input gear cluster and refer to the output shaft as the mainshaft. For clarity, this text uses the terms input gear cluster for the input shaft and its drive gears, and pinion shaft for the output shaft.

A pinion gear is machined onto the end of the transaxle's pinion shaft. This pinion gear is in constant mesh with the differential ring gear located in the lower portion of the transaxle housing. Because the pinion gear is part of the pinion shaft, it must rotate whenever the pinion shaft turns. With the pinion rotating, engine torque flows through the ring gear and differential gearing tot he drive shafts and driving wheels.

More Manual Transmissions And Transaxles

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