News flash! January 2010

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Q: What is a transmission?

A: A transmission is an assembly of various components. Its function is to transfer the power from the engine to the drive shaft, and thus to the wheels in order for a vehicle to move forward or backward. A transmission uses the low torque power (or twisting power) of the engine and generates maximum torque required to move a vehicle by the use of gears. The torque produced is varied by meshing different size gears. The first transmission design was a manual transmission which preceded the automatic transmission by several decades. One of the first automatic transmissions was built by General Motors in 1938. Today, there are many designs and types of transmissions available including synchromesh, variable and CTV (continuously variable transmission).

Q: How does the transmission generate power?

A: A transmission uses the low torque power (or twisting power) of the engine and generates maximum torque required to move a vehicle by the use of gears. Torque is generated by meshing different size gears the same way a lever is used to generate various forces. When using only a small amount of force at one end of a lever, a greater force can be denerated at the onther end of the lever. The lesser force will require moving a longer distance while the larger force will only move a short distance. The teeth on the diameter of gears act similar to a series of levers. Torque (twisting power) transmitter from a small gear turns a larger gear at a slower speed. This actually multiplies the torque (twisting power) but at the same time it reduces the speed the larger gear is turning.

A small weight can move a heavy weight by using a lever and distance.

Gears are toothed wheels that are like many levers.

Q: What is the manual transmission?

A: There are two types of manual transmissions. A sliding-gear type and a constant mesh design. When the sliding gear design is in neutral only the main drive and cluster gears are turning. When a driver uses the gear pedal and moves the sifter lever, gears in the transmission are moved to mesh. Different diameter size gears can be meshed which in turn varies the torque.

More modern transmissions are a constant mesh type manual transmission. This design uses a similar gear arrangement as the sliding gear type; however, all the mainshaft gears are in constant mesh with the cluster gears. This is possible because the gears on the mainshaft are not splined to the shaft and are free to rotate. Alongside each gear on the mainshaft is clutch with a hub that is splined to the shaft and an outer ring that can slide over against each gear. Moving the sift linkage moves the clutch against the adjacent mainshaft gear, causing the teeth to interlock and then lock the gear to the mainshaft. In addition, there are synchronizers, forks, rings, and sleeves that are designed to prevent gears from grinding or clashing during engagement.

A manual transmission allows the driver to select gears he needs to cope with different road conditions and speeds. To shift gears, a dirver must depress the clutch pedal to disconnect the engine from the transmission. At that point, the driver can move the shift lever to move collars in the transmission that will engage various gears. The driver selects gears to mesh. The number of teeth on the meshing gears will determine the gear ratio. Gear ratio will determine the amount of torque available for the driving gear. Engaging gear teeth from a driven gear with 30 teeth to a driving gear of ten teeth will give a ratio of 3:1. The driven gear will rotate one third the speed of the driving gear, but it will pass on three times the torque. Higher torque is usually needed in order to begin moving a parked vehicle or for going uphill.

Q: What is a differential?

A: In a rear wheel drive vehicle, a differential is usually in the rear end of the vehicle. It is the link for the engine power from the front of the vehicle to the rear wheels. The differential is designed to turn the flow of power 90 degrees at the same time it steps down the engine revolutions. It is an assembly of components designed to split power, allowing each output to spin at different speeds.

Front wheel drive, four wheel drive and all wheel drive use various designs to direct engine power to their wheels. However, each uses similar principals. Some vehicles need a differential between each set of drive wheels for the front and the back wheels. The differential assembly contains a variety of gears, housings, gaskets and shafts. A ring gear and bevel type gears mesh together to pass power to the wheels.

Bevel gears are conical and can mesh together to change direction of power flow by 90 degrees.

Q: What is the shift lever?

A: The shift lever for a manual transmission is mounted on the floor or steering column of the vehicle. this lever moves shift forks inside the transmission to engage gears. Shift forks fit into grooves machined into the circumference of the shift collars. Each collar is two-faced and locks one gear to the output shaft when moved forward, and locks another gear when it is moved back. Each shift fork is attached toa rod in a directly shifted transmission or to a lever and rod in a transmission with a side linkage. When the driver moves the shift lever, it pivots on a ball-in-socket and moves a control rod in the opposite direction. A collar grips a gear and when the clutch pedal is released, power is transmitted through the transmission to the wheels.

Q: What is gear ratio?

A: The number of teeth on meshing gears determine the gear ratio. Gear ratio will determine amount of torque available for the driving gear. Engaging gear teeth from a driven gear with 30 teeth to a driving gear of ten teeth will give a ratio of 3:1. The driven gear will rotate one third the speed of the driving gear, but it will pass on three times the torque. Higher torque is usually needed in order to begin moving a parked vehicle or for going uphill.

Q: What is a transfer case?

A: A transfer case is an auxiliary transmission usually placed in the vehicle driveline between the main transmission and the rear axle. The main tranmission can be either a manual or an automatic. Thetransfer case divides the power entering the front of the case into two or more separate outputs, and is commonly used to drive the front axle from one output and the rear axle from another. A transfer case is the component needed for every 4 wheel drive vehicle. The transfer case may also add performance for unusual traction requirements, such as snow plowing or winches. Someimes a transfer case is also referred to as a gearbox.