Components of the Drive Train.

Introduction to the High Mobility Multi- Purpose Wheeled Vehicle HMMVV
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drives, differentials, live axles, devices for resisting drive torques and

thrust, and the bearings used therein.

a. Components of the Drive Train.

The drive train on the HMMWV

consists of seven components that work together to transmit power to the

wheels.

In the paragraphs that follow, each of these components will be

discussed.

b. Engine. The first component in the HMMWV drive train is the engine.

However, since the engine was discussed previously in lesson one, task two

beginning on page 7, it will not be discussed here.

c. Transmission.

The HMMWV family of vehicles are equipped with a

series 400 hydromatic automatic transmission (THM 400), manufactured by

General Motors, with some parts from the 475 hydromatic transmission. The

transmission holds six quarts of Dexron II transmission fluid and maintains

The transmission contains a three element torque convertor, compound

planetary gear set, three multiple disc clutches, one sprag and one roller,

and two friction bands. The torque convertor couples the engine smoothly to

the planetary gear through oil, and provides additional hydraulic torque

multiplication when required. The compound planetary gear set gives three

forward ratios and one reverse.

Changing of the gear ratios is fully

automatic in relation to vehicle speed and engine torque input. The torque

from the engine is transmitted to the transmission through the flex plate.

Vehicle speed and engine torque signals are constantly fed to the

transmission to provide the appropriate gear ratio for maximum efficiency

and performance at all throttle openings.

d. Transfer Case.

The transfer case directs engine-to-transmission

power to the front and rear differentials simultaneously.

This condition

means the vehicle is always in four-wheel drive. The transfer case allows

for selection of three driving ranges and a neutral position. The transfer

case used on the HMMWV is a New Process 218 (MOD), two speed, locking,

chain-driven transfer.

The transfer case holds 3.5 quarts of Dexron II

transmission fluid.