ABS - DESCRIPTION

DESCRIPTION

The ABS electronic anti-lock braking system regulates the braking pressure transmitted to the wheels, preventing them from losing grip whatever the tyre and road conditions.

The system is designed to be incorporated with the braking system (using the same hydraulic fluid) without preventing the operation of the actual braking system if the ABS fails.

Four sensors, located on each of the four wheels, indicatae the speed of each wheel to the electronic control unit, recording any situations involving locking, slipping or loss of grip.

In these situations, the control unit controls the solenoid valves which modulate the pressure in the hydraulic circuit, preventing the wheels from locking and restoring grip conditions for the vehicle which ensures optimum handling of the vehicle and excellent stopping distances.

The sensors are the "active" type, supplied by the control unit; they consist of a magnetic resistive receiver with a magnetic codifier incorporated in the hub bearing so that the signal is less affected by electromagnetic interference and variations in temperature.

The ABS control unit also controls the distribution of the braking load between the front and rear axles meaning that the mechanical load proportioning valve used previously can be dispensed with (EBD function: Electronic Brake Distribution ).

The control unit is equipped with an autodiagnostic function: when an error in the ABS function is detected, the warning light comes on and, at the same time, the system is deactivated; in these conditions the vehicle brakes using the traditional system only.

When the control unit detects an error which also affects the EBD function, it turns on the "ABS failure" warning light and the "low brake fluid and handbrake" warning light.

In these conditions the rear braking distribution control is deactivated: the driver must therefore proceed very carefully to the first authorised service centre.

For more details

See descriptions 3340 ANTI-LOCK BRAKING SYSTEM (ABS)

The ABS control unit calculates the speed of the vehicle starting from the figures that are supplied by the drive wheel sensors (with the ABS control unit calculating the average value) and from the actual circumference of the wheels themselves, supplied by the Body Computer: this speedometer signal is then sent, via the CAN, to the nodes that require this information. The ABS control unit also produces a discreet signal which replicates the vehicle speed information calculated and transmitted via the CAN.

The control unit power supply lines are protected by two special fuses located in the engine compartment junction unit; the ignition-operated supply is protected by a specific fuse in the junction unit under the dashboard.