Hino 600, Workshop Manual, Page: 389 / 451

ABS (ABS : HYDRAULIC (E VERSION)) BR03–5
BASIC PRINCIPLE
Based on its relationship with the slip ratio, which is determined from the
wheels' rotational speed and the vehicle's speed, ABS controls the brake
force so that it will be most effective.
When the driver applies the brakes, the rotation of the wheels is controlled
and the vehicle speed drops. However, the momentum of the vehicle
attempts to push it forward further even though the rotation of the wheels is
being braked. At this point, slipping will occur if there is a gap between the
wheels' rotational speed and the vehicle's speed. The slip ratio is a value
that indicates the rate of slippage.
The graph shown at left shows the relationship between the friction coeffi-
cient of the tires and of the road surface and the slip ratio.
In an ABS-equipped vehicle, the brake force is controlled to ensure that it is
within the range where the friction coefficient is high (shaded portion of the
graph) without locking the wheels. This ensures efficient braking perfor-
mance.
OPERATION
The ABS ECU calculates the wheel speed and wheel acceleration speed
for each of the 4 wheels, from 4 wheel sensor signals, and determines the
wheel slip conditions. And depending on these conditions, control signals
are output to the ABS actuator solenoid valves in 3 modes (pressure
increase, pressure maintenance, and pressure reduction). Control signals
are output independently to the front and rear wheels and to the left and
right wheels.
Slip ratio 0 % : No slipping between the wheels and the
road surface
100 % : Wheels locked
Slip ratio =
Vehicle's speed - Wheel's rotational speed
Vehicle's speed
100 %
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Wheel cylinder fluid pressure
SPEED
TIME
LOW
Vehicle body speed
HIGH
Wheel speed
Wheel speed
Control signal
Pressure
reduction
HIGH
Pressure
maintenance
Pressure
increase
+
Ð
0
0
tionaccelera
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