APRILIA ETV mille Workshop Manual page 340

ETV mille
ABS OPERATION
General information:
- The front and rear circuits are identical.
- The ABS isolator valve (16-17) is normally open and is closed when the system activates to prevent wheel lockout.
- The dump valve (14-15) is normally closed and is opened when the system activates to prevent wheel lockout.
- When the system is in the stand-by mode, the ABS controller monitors wheel speed to detect possible wheel skidding.
- When in the stand-by mode, the system does not affect braking and brake application is controlled by the rider as in con-
ventional (non ABS equipped) braking systems.
Phases of ABS operation (the following description is referred to the front braking circuit, but applies to the rear braking cir-
cuit as well):
1) Initial brake application: the rider applies the brake as in conventional braking.
2) ABS detects a dangerous condition (wheel starting to skid): The system closes the isolator valve (16) and opens the
dump valve (14) at the same time. At this stage, the rider has no control over brake pressure and the ABS releases
some of the pressure in the callipers (4). Excess fluid is diverted into the front reservoir (12) until the ABS pump (11)
switches on automatically to pump the fluid back to the reservoir (5).
3) ABS maintains low pressure: pressure in the callipers (4) is kept low until the wheel regains normal speed/traction.
The fluid removed from the calliper (4) is restored to the circuit at the portion between the brake master cylinder (5)
and the ABS isolator valve (16).
4) ABS restores pressure: the isolator valve (16) is opened briefly as many times as needed to increase pressure in the
callipers (4) until achieving maximum deceleration. At this time, ABS restores brake control to the rider.
5) The whole process is repeated until wheel traction is restored or the vehicle is stopped.
Release 00/2004 - 04
ABS
9
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