Automobile Transmissions and Power Steering
Automobiles, trucks, buses, and tractors all depend on transmissions to deliver power from the engine to the wheels, The gasoline and diesel engines that power these vehicles cannot be connected directly to the wheels, because the engines must keep turning at a certain seed to keep from stalling. Also, different amount of torque (turning force) must be delivered to the wheels at different times. A large amount of force is needed to get a car moving from a standstill. Less force is needed to keep the car moving once it is rolling. Going up a hill of driving at high speed requires still other amount of force. It is the job of the transmission to deliver the particular amount of force that is needed. The transmission also allows a motor vehicle to back up -----gasoline and diesel engines can run in only one direction, but the transmission can reverse the direction of the force. And when a car stops, the transmission lets the engine keep running without moving the wheels.
The heart of any transmission——even an automatic one—is a set of gears. Gears do not change the power of an engine, but they can increase the torque by decreasing the speed. They can also increase the speed by decreasing the torque.
The automobile transmission uses a series of gears which enables the engine to continue to operate at maximum efficiency when the vehicle’s speed is altered. Setting an automobile in motion requires a large amount of power to overcome the inertia of the vehicle’s weight. This process requires high engine speed, needed for high power, and a gradual increase in a vehicle’s speed to avoid a jerky start. To do this, a low gear ratio is allows the crankshaft to revolve several times in order to turn the real axle once. The low gear ratio is used for starting, climbing steep slops, and other situations in which maximum power is required .As power needs are reduced, a second, higher gear ratio is used which rotates the rear axle with fewer revolutions of the crankshaft. As the car’s speed increases, successively higher gear ratios are used until the drive from the engine to the rear wheels passes through the transmission without reduction. Two principle types of transmission are used, manual and automatic.
The manual transmission system permits the driver to select the desired gear ratio by manipulating a shift lever. Besides the forward speed gears, additional gearing is incorporated to permit the vehicle to operate in reverse. Manually operated passenger car transmission used in the United States and Canada usually have there speeds forward and one in reverse. Trucks, tractors, buses, and other heavy-duty vehicles have as many as 10 forward speeds and 2 in reverse. These units are basically five-speed transmissions with a two-speed auxiliary gearbox. Transmission that are to be shifted with the vehicle in motion incorporate synchromesh units to prevent gears from clashing as they are meshed. The synchromesh unit synchronizes the speed of the gears so that they revolve at the same speed as they slide into engagement.
The automatic transmission system changes gear ratios automatically in response to changes in engine speed or throttle setting. The use of automatic transmissions increased tremendously after World War Ⅱ, and they are installed in more than half of the automobile produced in the United States. Automobiles equipped with an automatic transmission have a control lever which allows the driver to select neutral, low, drive, and reverse. The engine is started in neutral, and the lever is moved to “drive”for normal operation when moving forward. In “drive”position the vehicles can accelerate from rest to maximum speed by simply depressing the accelerator. The “low” position prevent the transmission from shifting out of the lower gear ratios.
