Anti-Lock Brake System <Abs); System Description - Triumph Thunderbird Service Manual

Anti-lock Brake System <ABS)
System Description
The ABS versions of the Thunderbird are fitted with an
electronic anti-lock brake system which is designed to
prevent the wheels from locking or skidding by reducing
braking effort to the front or rear brake caliper as
required.
The system consists of a hydraulic modulator and ECM
assembly mounted to a bracket beneath the swinging
arm, a front wheel speed sensor mounted to the front
fork, and a rear wheel speed sensor mounted to the rear
brake caliper carrier.
Both front and rear wheels have a pulser ring mounted on
to the wheel hub.
The front and rear master cylinders are connected via
lines to the modulator and from the modulator the lines
connect to the brake calipers. The calipers and master
cylinders are identical to the non-ABS equipped
motorcycle.
The front and rear brake circuits operate as separate
systems. The front and rear brakes are not connected in
any way inside the modulator.
The modulator ECM continuously calculates the front and
rear wheel speeds, and from these inputs the ECM
calculates the estimated motorcycle speed, wheel
deceleration/acceleration, the wheel speed difference and
the wheel slip (skid) rate. This is calculated by comparing
the calculated wheel speeds with the calculated vehicle
speed, so that if one wheel speed deviates significantly
from the other two readings, this wheel is calculated to be
slipping (skidding).
Under braking, if the modulator detects that either wheel
is about to slip, due to the brake force exceeding the
available traction between the tyre and road surface (the
wheel will begin to slip or 'skid'), the ECM very rapidly
releases and re-applies the brake pressure to prevent the
wheel from slipping.
This is felt through the brake pedal or lever as a rapid
'pulsing'.
If the rider reduces braking effort, or traction increases (so
that traction exceeds braking force, the wheel will rotate
once more) the wheel will no longer lock up. The ABS
system will detect this and stop controlling brake pressure,
and return to its monitoring state.
The system has a self diagnostic function built-in which
monitors the fail safe relay, solenoid valves, motor relay,
wheel speed sensors, power supply and ground, as well as
internal ECM functions.
In
the event of a malfunction
being detected, the ECM will illuminate the ABS warning
light, and store a diagnostic trouble code in the system
memory. This stored data can then be recovered using
the Triumph diagnostic tool which is mandatory for all
Triumph dealers. In this way, precise diagnosis of a fault
can be made and the fault quickly rectified.
Under normal operation, the ABS warning light will stay
illuminated after ignition on until the vehicle speed
exceeds 6 mph (10 km/h). The ABS performs a self check
and if no faults are found the light is extinguished.
If
a
trouble code is stored the ABS warning light will stay
illuminated and the ABS will not function, however the
brakes will operate normally. If the ABS warning light does
not extinguish, or illuminates whilst the motorcycle is
being ridden, refer to the ABS system diagnostics (see
page 12.42).
12.38 SelVice Manual - Thunderbird