First, we must have a cylinder that is closed at one
All internal combustion engines, whether gasoline
end; this cylinder is similar to a tall metal can and is
or diesel, are basically the same. We can best
stationary within the engine block. Inside this cylinder
demonstrate this by saying they all rely on three
is the piston, a movable metal plug, which fits snugly
things--fuel, air, and ignition. Fuel contains potential
into the cylinder, but can still slide up and down easily.
energy for operating the engine. Air contains the
This movement of the piston is caused by the burning of
oxygen necessary for combustion, and ignition starts
fuel in the cylinder, which results in the production of
combustion. All are fundamental, and the engine will
reciprocating motion.
not operate without all of them. Any discussion of
engines must be based on these three factors and the
You have already learned that the up-and-down
steps and mechanisms involved in delivering them to
movement of the piston is called "reciprocating
the combustion chamber at the proper time.
motion." This motion must be changed to rotary
motion. This change is accomplished by a throw on the
DEVELOPMENT OF POWER
crankshaft and a connecting rod, which connects the
piston and the crankshaft throw.
The power of the internal combustion engine
comes from burning a mixture of fuel and air in a small,
The throw is an offset section of the crankshaft,
enclosed space. When this mixture burns, it expands
which scribes a circle as the shaft rotates. The top end
greatly, and the push or pressure created is used to move
of the connecting rod is connected to the piston;
the piston, thereby rotating the crankshaft. This
therefore, it must go up and down. The lower end of the
movement is eventually sent back to the wheels to drive
connecting rod is attached to the crankshaft. The lower
the vehicle.
end of the connecting rod also moves up and down but,
because it is attached to the crankshaft, it must also
Since similar action occurs in all cylinders of an
move in a circle.
engine, let's use one cylinder to describe the steps in the
development of power. The 1-cylinder engine consists
When the piston of the engine slides downward
of four basic parts, as shown in figure 3-2.
because of the pressure of the expanding gases in the
cylinder, the upper end of the connecting rod moves
ASf03002
Figure 3-2.--Cylinder, piston, connecting rod, and crankshaft for a 1-cylinder engine.
3-2
