Operating Principle; Key To Abs Hydraulic System - Ducati MONSTER 821 Workshop Manual

Operating principle

The Ducati ABS brake system manages the front and rear brake systems separately. The operating
mechanism consists of a pulse generator (phonic wheel), with a ring of slots, fitted onto each wheel. There
are HALL sensors on LH fork leg bottom end and on rear brake calliper holder plate. With vehicle running,
they read the slots on the phonic wheel thereby detecting instant wheel speed. These sensors output data
to ABS ECU, which contains a software with a special control algorithm developed by Ducati. The software
compares the vehicle average speed with the instant wheel speed reading and assesses any slipping
condition. If control values are exceeded when the rider commands a certain pressure on brake calliper, the
control unit shall hydraulically control the braking system, which is nearly locked up. The system can
modulate pressure at the calliper through a set of solenoid valves which first prevent any further increase
of hydraulic pressure (1 valve closing), and then make the pressure decrease (2 valve opening). The 2
valve is opened in a series of pulses (with less than 10 milliseconds between successive pulses), to reduce
pressure in steps. When the wheel begins to turn again in response to the diminished braking force applied
and its rotation speed reaches the reference value, the 2 release valve will be closed. Simultaneously, the
inlet valve 1 is reopened, restoring normal operation of the brake system. The ABS control unit can monitor
and modulate brake force in the three following different conditions: dry road surface (high grip), wet or
slippery road surface (poor grip) and uneven road surface. ABS functionality is disabled at vehicle speeds
lower than 5 km/h.
The hydraulic component of the ABS system consists of a primary circuit (from the cylinder to the control
unit and from the control unit to the calliper) and a secondary circuit (completely within the control unit).
Please find below a chart explaining ABS hydraulic operation.
Key to ABS hydraulic system colours:
Green: oil delivery
Light blue: oil return

Key to ABS hydraulic system

A Rear brake master cylinder
B Front brake master cylinder
1A Rear brake calliper inlet valve
1B Front brake calliper inlet valve
2A Rear brake calliper exhaust valve
2B Front brake calliper exhaust valve
3 Master cylinder
4 Little tanks
5A Rear calliper
5B Left front calliper
6B Right front calliper
7 Pressure transducer
Brake system diagram.
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