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A very brief introduction: Transmissions and Transaxles

December 2, 2011

I hereby admit that I am a nerd.

Ever wondered how your transmission works? Your car is propelled by power and torque, and a lot of this is accomplished by gears.

Without the mechanical advantage of the gearing within a transmission or transaxle, the engine would remain at low speeds and produce extremely limited torque.  (More on torque later).

The gearing of a transmission or transaxle is necessary to move a vehicle in a different direction.  The crankshaft rotates in the same direction all the time.  This means that if the power from the crankshaft were to go right to the drive wheels, we could only drive the car in one direction.  One direction for the crankshaft, one direction for the car.  How do we enable it to drive in reverse? We need the gearing provided by the transmission or transaxle.  We also need gearing for neutral, which stops the power from going to the wheels.

Wait, I thought I had a transmission? What the heck is a transaxle?

There are some major differences between a transmission and a transaxle.  Firstly, a car with a transaxle is commonly front-wheel-drive, while transmissions are generally found in vehicles that are rear-wheel-drive.

Transaxles are also unique in that the differential and transmission gearing are in the same case housing.  (Also, more on differentials later).

Four-wheel-drive vehicles are generally equipped with a transmission and transfer case, which is found on the side or back of the transmission, and transfers power from the transmission to two separate drive shafts.  From there, power goes from one drive shaft to a differential on the front drive axle.  The second drive shaft connects to a rear drive axle differential.  I’ll break that down in future posts on transmissions, transaxles, and differentials.

For the most part, transmissions and transaxles are in constant mesh, meaning that whether or not a gear is locked in place—locked to the output shaft—the gear is still in mesh with its counter gear.  To clarify, the output shaft is exactly what it sounds like; power is generated and becomes the output that is sent through the drive train to the wheels.

Another commonality between transmissions and transaxles is that they have various speed gears, one reverse speed—which is usually provided by an idler gear that is placed between a drive gear and a driven gear—and a neutral gear.  Overdrive—fifth and sixth gears—actually reduces engine speeds while at the same time increasing the actual speed of the vehicle and improving fuel economy.

Pretty wild, eh?

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