Yamaha Vmax VMX17C 2009 Service Manual page 15

a. Friction force between the tire and road
surface
b. Brake force
c. Side force
d. Slip ratio (%)
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 de-
termines 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
b
a
c
B
f
a
g
1-6
d
e
d
e. Less slippery road surface
f. Controlling zone
g. Slippery road surface
FEATURES