Anti-Lock Brake System
On U.S. EX with ABS option
The ABS works by measuring how
fast the wheels are turning during
braking and comparing their
speed. If any wheel is rotating
much slower than the others (on
the verge of locking up and
skidding), the system reduces
hydraulic pressure to that wheel's
brake caliper. When that wheel's
speed matches the other wheels,
the system applies normal
hydraulic pressure. This can take
place several times per second at
each wheel. You feel the ABS
working as rapid pulsations in the
brake pedal.
Each wheel has a wheel speed
sensor assembly. As the wheel
rotates, the sensor sends
electrical pulses to the ABS
control unit. The pulse frequency
varies with the wheel speed.
The electrical output of the ABS
control unit is connected to the
modulator/solenoid unit. During
braking, the ABS control unit
monitors the pulse frequencies
from the four wheels. When the
control unit detects a wheel
locking up, it energizes the
appropriate solenoid in the
modulator/solenoid unit. There
are three solenoids: one for each
front wheel, and one for the rear
wheels. The energized solenoid
reduces hydraulic pressure to one
side of a modulator valve. This, in
turn, reduces hydraulic pressure
in the brake line going to the
affected wheel. When that wheel
speeds up because of the reduced
braking effort, the control unit
de-energizes the solenoid. This
builds hydraulic pressure on the
modulator valve. The pressure
increases in the hydraulic line to
the wheel.
For the system to react quickly,
the modulator/solenoid unit must
have brake fluid under high
pressure. This is supplied by a
diaphragm-type accumulator that
is pressurized by an electric
pump. A pressure-sensing switch
on the accumulator controls this
pump.
The control unit also contains
error detection circuitry. It
monitors the operation of the
wheel sensors, solenoids, pump,
and electronics. If the control unit
detects any faults, it shuts off
power to the pump motor and
solenoids. The light on the
instrument panel comes on. The
brakes then work like a
conventional system without
anti-lock capabilities.
Technical Information
Main Menu
Table of Contents
▲
▼