Chapter 1 The Automobile 11
right and left sides are denoted as if you were sitting
in the car looking forward.
Fuel Effi ciency
Fuel effi ciency, or fuel economy, is a rating of how
far a vehicle can travel on only one gallon of fuel
(gasoline, diesel oil, or stored electrical energy). The
EPA tests and rates cars to give them an average city
and highway fuel economy rating. A typical fuel
economy rating for a small economy car might be
40 miles per gallon (mpg) city and 43 mpg highway.
Estimated city EPA fuel economy testing is done
with a preset number of stops so the car has to accel-
erate to cruising speeds. Estimated highway EPA
fuel economy ratings are for steady state interstate
cruising speeds.
Engine
The engine provides the energy to propel (move)
the vehicle and operate other vehicle systems.
Most engines consume gasoline or diesel fuel. The
fuel burns inside the engine to produce heat. This
heat causes hot gas expansion, creating high pres-
sure inside the engine to move its parts to produce
power. See Figure 1-10.
Basic Engine Parts
The basic parts of an engine are shown in
Figures 1-10 and 1-11. Refer to these illustrations
as each part is introduced.
• Block—The metal casting that holds all the
other engine parts in place is the block.
• Cylinder—The cylinder is a round hole that is
bored (machined) in the block. It guides piston
movement.
• Piston—The piston is a cylindrical component
that transfers the energy of combustion (burn-
ing of air-fuel mixture) to the connecting rod.
• Rings—The small gap around the sides of the
piston are sealed by rings. They keep combus-
tion pressure and oil from leaking between the
piston and the cylinder wall (cylinder surface).
• Connecting rod—The connecting rod links the
piston to the crankshaft.
• Crankshaft—The crankshaft changes the recip-
rocating (up-and-down) motion of the piston
and rod into useful rotary (spinning) motion.
• Cylinder head—The top of the cylinder is cov-
ered and sealed by the cylinder head. It also
holds the valves, rocker arms, and often, the
camshaft.
• Combustion chamber—The combustion cham-
ber is a small cavity (hollow area) between the
top of the piston and the bottom of the cylinder
head. The burning, or combustion, of the air-
fuel mixture occurs in the combustion chamber.
• Valves—The valves open and close to control
the fl ow of air or an air-fuel mixture into the
combustion chamber and exhaust gases out of
the combustion chamber.
• Camshaft—The opening of the valves is con-
trolled by the camshaft.
• Valve springs—The valve springs keep the
valves closed when they do not need to be open.
• Rocker arms—The rocker arms transfer cam-
shaft action to the valves.
• Lifters—The lifters, or cam followers, ride on
the camshaft and transfer motion to the other
parts of the valve train.
• Flywheel—The fl ywheel helps keep the crank-
shaft turning smoothly. It also provides a large
gear that is engaged by the starting motor dur-
ing engine starting.
Automotive Engines
Automobile engines normally use a four-stroke
cycle. Four separate piston strokes (up or down
movements) are needed to produce one cycle (com-
plete series of events). The piston must slide down,
up, down, and up again to convert heat energy (burn-
ing fuel) into kinetic energy (spinning crankshaft).
Tech Tip
For more information on the four-stroke cycle,
see Chapter 11.
Automotive engines are multi-cylinder engines,
which means they have more than one piston and
cylinder. Today’s vehicles can have 2-, 3-, 4-, 6-, 8-, 10-,
or 12-cylinder engines. Additional cylinders gener-
ally increase engine size and power output, but they
lower fuel economy. The industry trend is to smaller
engines with 2, 3, and 4 cylinders. More power is
needed for speeding up, or accelerating, as well as
towing and traveling uphill. Look at Figure 1-12.
The additional cylinders smooth engine operation
because there is less time (degrees of crankshaft rota-
tion) between power (energy producing) strokes.