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Module 2- Apply and Hold Devices (Page 1 of 6)


The ENGINE burns fuel and converts chemical energy into mechanical energy. The engine is a powerplant - it "creates" power / torque.

The CRANKSHAFT converts the reciprocating motion (up and down motion) of the pistons into rotary motion. The flywheel bolts to the back of the crankshaft.

You have already been introduced to the torque converter. The TORQUE CONVERTER is a fluid coupling that transfers the torque from the engine to the automatic transmission.

The pump / impeller of the torque converter is bolted to the flywheel. The turbine of the torque converter is attatched to the transmission input shaft. See diagram below.

As you have learned from module 1, the automatic transmission provides many different gear ratios and gears depending on the driving conditions. (ie: normal driving, trying to pass a car in front of you, towing a boat, racing etc...)

The automatic transmission uses planetary gear sets to provide these gears. See diagram below. As you have learned in module 1, in order to provide different gear ratios (1st, 2nd, 3rd OD) or directions (forward and reverse), one planetary gear component must be HELD, one must be the INPUT (driven by the engine) and one must be the OUTPUT (driving the rear wheels).

Confused? Then go back to Module 1.

Again, as we have investigated in the previous module, sometimes sun gear is connected to the input. In some gears, the sun gear is held stationary. Pictured below are two sun gears.

Sometimes the planet carrier is driven by the engine (to obtain overdrive gear). Sometimes the planet carrier is held stationary (to obtain reverse gear). Other times, the planet carrier is driving the rear wheels (to obtain reduction gears). Pictured below are two planet carriers.

How does the automatic transmission perform these tasks? It uses hold / apply devices. There are three devices are are used to hold or drive each member of the planetary gear set.

Module 2 - (Page 1 of 6)