Subaru LEGACY 2002 Quick Reference Index page 396

ABS
F: ABS CONTROL CYCLE CURVES
Depressing the brake pedal increases the brake fluid pressure in each wheel cylinder, which in
turn decreases the wheel speed (or increases the wheel deceleration rate). When the brake fluid
pressure is increased to a level of point "A" of the brake fluid pressure curve in the diagram below
(at which the wheel deceleration rate exceeds threshold "–b
"hold" control. At the same time, the ABSCM calculates a "dummy" vehicle speed which is a ref-
erence speed it uses in the next stage of control.
When the wheel speed then drops below the slip ratio setting, i.e., a speed lower than the "dummy"
vehicle speed by the predetermined value (at point "B" of the pressure curve), the ABSCM makes
a control to prevent the wheel from locking, or a pressure "decrease" control.
As the wheel cylinder pressure decreases, the wheel speed starts increasing (or the wheel accel-
eration rate starts rising). When the wheel acceleration rate exceeds threshold "+b
of the pressure curve), the ABSCM makes a pressure "hold" control. When the wheel acceleration
rate exceeds threshold "+b
wheel lock-up will not occur and then makes a pressure "increase" control.
When the wheel acceleration rate drops below threshold "+b
curve), the ABSCM starts pressure "hold" and "increase" control cycles at a given interval.
When the wheel deceleration rate then exceeds threshold "–b
curve), the ABSCM immediately makes a pressure "decrease" control.
Brake fluid
Pressure
Increase
Hold
Decrease
ANTI-LOCK BRAKE SYSTEM (ABS)
" (at point "D" of the pressure curve), the ABSCM recognizes that
20
Slip ratio setting
Inlet valve
OFF
ON
ON
"), the ABSCM makes a pressure
0
20
Outlet valve
OFF
OFF
ON
ABS-18
" (at point "C"
10
", (at point "E" of the pressure
" (at point "F" of the pressure
0
B4H2239B