A. Clutch. Transmission.

The parts of the automobile that transmitpower from the engine to the driving wheels make up the power train. These are the clutch, transmission, drive shaft, and differential. In most cars power is delivered to the rear wheels. Increasing numbers of car engines, however, transmit power to the front wheels. This improves traction. It also eliminates the drive shaft and the hump in the car's floor to accommodate it. This, in turn, increases interior legroom. An alternative with similar advantages is the rear-engine, rear-wheel drive car. Four-wheel drive cars have even better traction and are generally used to travel rough country or to drive through snow. Some have a part-time feature in which a flickof a lever transmits power to a set of wheels to provide four-wheel drive.

Clutch. It is not practical to connect the wheels of an automobile directly to the engine. A device is needed to uncouple the wheels from the running engine so that the driver can warm the engine and keep it running while the vehicle is not moving. The engine must also be separated from the gearboxwhen the driver is shifting gears. Most automobiles provide for this uncoupling either with a friction (disk) clutch or with a fluid coupling.

Transmission. The transmission is a device installed at some point between the engine and the driving wheels of a vehicle to change speed and power. Power from the engine is provided in the form of torque, or twisting force. The amount of this force varies a great deal, depending on the individual characteristics of the engine and the speed at which the engine is running. At high speeds the torque is greater. The amount of torque needed to move a car is not always directly related to speed. When a car is travelling at moderate speed on a level road, the engine does not need to supply much torque to keep it going. When the car is starting from a dead stop or moving up a hill, however, the engine must deliver enough torque to get or keep the car moving. Turning speed (revolutions per minute) from the engine may be reduced or increased by gears and thus converted to provide greater torque or greater speed.

The gearshift lever of a car moves shifting forks, which engage or disengage various combinations of gears. These combinations provide more or less torque and speed, and they determine the direction in which the vehicle will move. Most modern cars are equipped with an automatic transmission, which alters the combinations of gears or of torque converters without the movement of a lever by hand.

Standard gear transmission. The conversion of engine speed and the resulting torque may be accomplished by engaging various combinations of large and small gears. The so-called standard transmission for many years has been a gearboxwith a combination of gears. The standard gearbox usually provides three forward speeds and one reverse speed. Four and five forward speeds are not uncommon, especially on sports cars, and some trucks have even more.

Another means of changing speed and torque is through the use of planetary transmission. Just as the planets in space move around the sun, so planetary gears move around a sun gear.

Automatic transmission. Although all automatic transmissions essentially eliminate the driver's need to shift gears and use a clutch, the design and construction of automatic transmissions may vary with each manufacturer. One form of automatic transmission is a hydraulic torque converter, which achieves the same shifting effect as a gear transmission.

Date: 2015-12-18; view: 744