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HYDRAULIC BRAKES
The hydraulic brake system used in the
automobile
is a multiple piston system. A multiple piston
system allows forces to be transmitted to two
or more pistons in the manner indicated in figure
2-21. Note that the pressure set up by the force
applied to the input piston (1) is transmitted undiminished
to both output pistons (2 and 3), and
that the resultant force on each piston is proportional
to its area. The multiplication of forces
from the input piston to each output piston is
the same as that explained earlier.
The hydraulic brake system from the master
cylinders
to the wheel cylinders on most automobiles operates in a way similar to the system illustrated in figure 2-22.
Figure 2-21.—Multiple piston system.
When the brake pedal is depressed, the
pressure on the brake pedal moves the piston
within the master cylinder, forcing the
brake fluid
from the master cylinder through the tubing and
flexible hose to the wheel cylinders. The
wheel
cylinders contain two opposed output pistons,
each of which is attached to a brake shoe
fitted
inside the brake drum. Each output piston pushes
the attached brake shoe against the wall
of the
brake drum, thus retarding the rotation of the
wheel. When pressure on the pedal is
released, the
springs on the brake shoes return the wheel
cylinder pistons to their released
positions. This
action forces the displaced brake fluid back
through the flexible hose and tubing to
the master
cylinder.
The force applied to the brake pedal produces
a proportional force on each of the
output
pistons, which in turn apply the brake shoes
frictionally to the turning wheels to
retard
rotation.
As previously mentioned, the hydraulic brake
system on most automobiles operates in a
similar
way, as shown in figure 2-22. It is beyond the
scope of this manual to discuss the
various brake systems.
Figure 2-22.—An automobile brake system.
