Wheel Slip And Hydraulic Control - Yamaha 2012 TMAX XP500A Service Manual

Wheel slip and hydraulic control

The ABS ECU calculates the wheel speed of each wheel according to the rotation signal received
from the front and rear wheel sensors. In addition, the ABS ECU calculates the vehicle chassis
speed and the rate of speed reduction based on the wheel speed values.
The difference between the chassis speed and the wheel speed calculated in the slip ratio formula is
equal to the wheel slip. When the wheel speed is suddenly reduced, the wheel has a tendency to
lock. When the wheel slip and the wheel speed reduction rate exceed the preset values, the ABS
ECU determines that the wheel has a tendency to lock.
If the slip is large and the wheel has a tendency to lock (point A in the following figure), the ABS
ECU reduces the brake fluid pressure in the brake caliper. Once the ABS ECU determines that the
tendency of the wheel to lock has diminished after the brake fluid pressure is reduced, it increases
the hydraulic pressure (point B in the following figure). The hydraulic pressure is initially increased
quickly, and then it is increased gradually.
a. Chassis speed
b. Wheel speed
c. Brake force
d. Depressurizing phase
e. Pressurizing phase
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