Page 20 - Understanding Automotive Electronics

2735 | CH 1 Page 7 Tuesday, March 10, 1998 10:52 AM

AUTOMOTIVE FUNDAMENTALS 1

Engine Block

Conventional internal The cylinders are cast in the engine block and machined to a smooth
combustion engines finish. The pistons fit tightly into the cylinder and have rings that provide a
convert the movement tight sliding seal against the cylinder wall. The pistons are connected to the
of pistons to the rota- crankshaft by connecting rods, as shown in Figure 1.3. The crankshaft converts
tional energy used to the up and down motion of the pistons to the rotary motion needed to drive
drive the wheels. the wheels.

Figure 1.3
Piston Connection to
Crankshaft (Source:
Crouse)

FPO

Cylinder Head

The cylinder head contains an intake and exhaust valve for each cylinder.
When both valves are closed, the head seals the top of the cylinder while the
piston rings seal the bottom of the cylinder.
The valves are operated by off-center (eccentric) cams on the camshaft,
which is driven by the crankshaft as shown in Figure 1.4. The camshaft rotates
at exactly half the crankshaft speed because a complete cycle of any cylinder
involves two complete crankshaft rotations and only one sequence of opening
and closing of the associated intake and exhaust valves. The valves are normally
held closed by powerful springs. When the time comes for a valve to open, the
lobe on the cam forces the pushrod upward against one end of the rocker arm.
The other end of the rocker arm moves downward and forces the valve open.
(Note: Some engines have the camshaft above the head, eliminating the
pushrods. This is called an overhead cam engine.)
UNDERSTANDING AUTOMOTIVE ELECTRONICS 7