Automotive Systems

Formerly Automotive Systems I

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Development of Power


The power of an internal combustion engine comes from burning a mixture of fuel and air in a small, enclosed space. When this mixture bums, it expands greatly, and the push or pressure created is used to move the piston, thereby rotating the crankshaft. This motion is eventually sent to the wheels that move the vehicle.

Since similar action occurs in each cylinder of an engine, let’s use one cylinder to describe the steps in the development of power. The one-cylinder engine consists of four basic parts, as shown in Figure 2-3.

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First, we must have a cylinder that is closed at one end; this cylinder is similar to a tall metal can that is stationary within the engine block.

Inside this cylinder is the piston—a movable plug. It fits snugly into the cylinder but can still slide up and down easily. This piston movement is caused by fuel burning in the cylinder and results in production of reciprocating motion.

You have already learned that the up-and-down movement of the piston is called reciprocating motion. This motion must be changed into rotary motion, so the wheels or tracks of a vehicle can rotate. This change is accomplished by a throw on the crankshaft and the connecting rod which connects the piston and crankshaft throw.

The throw is an offset section of the crankshaft that scribes a circle, as the shaft rotates. The top end of the connecting rod is connected to the piston and must therefore go up and down. The lower end of the connecting rod is attached to the crankshaft. The lower end of the connecting rod also, moves up and down but because it is attached to the crankshaft, it must also move in a circle.

When the piston of the engine slides downward because of the pressure of the expanding gases in the cylinder, the upper end of the connecting rod moves downward with the piston in a straight line. The lower end of the connecting rod moves down and in a circular motion at the same time. This moves the throw and, in turn, the throw rotates the crankshaft; this rotation is the desired result. So remember, the crankshaft and connecting rod combination is a mechanism for the purpose of changing straight line, or reciprocating motion to circular, or rotary motion.

Published by SweetHaven Publishing Services
Based upon a text provided by the U.S. Navy

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