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, indicate 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. This ensures optimum handling of the vehicle and excellent stopping distances.

The sensors are active ones, 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 a self-diagnostic function: when an error in the ABS function is detected, the warning light comes on and the system is deactivated at the same time. 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 applied 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.

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 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 ESP (Electronic Stability Program) system is linked to the ABS and controls the stability of the vehicle, intervening, if necessary, on the drive torque and braking the wheels in a differentiated manner: If grip is lost, it helps to restore the vehicle to the correct trajectory. The most comprehensive versions of the ABS control unit also implements ESP (Electronic Stability Program) and ASR (Anti Slip Regulation) functions in addition to the HH "Hill Holder" function and the HBA (Hydraulic Brake Assist) function.

The ESP system also acts on the engine and brakes to generate a stabilising torque when the ABS sensors detect conditions that cause the vehicle to slip. The ESP system has a specific sensor in addition to the ABS sensors: this sensor detects vehicle rotation about the vertical axis and lateral acceleration (centrifugal force) (yaw sensor); it also uses steering sensor signals from the electric power steering control unit supplied via the CAN.

With the HH function, a longitudinal acceleration sensor is also used that is built into the yaw sensor. The ESP system also uses information from the pressure sensor that measures pressure in the hydraulic circuit: this sensor is built into the hydraulic control unit.

The H.B.A. system aids the driver in emergency braking situations when the brake pedal is activated quickly and in poor load maintenance conditions; the system intervenes when the pressure gradient exceeds a certain level (fast application of brake pedal - emergency braking), multiplying the braking pressure at the wheels applied by the driver, thereby producing the maximum deceleration that can be achieved.

The Hill Holder system is designed to assist the driver when setting off on an incline. In effect, the HH is capable of automatically providing sufficient braking torque to keep the vehicle stationary until the clutch is fully released and the engine torque is sufficient to start the vehicle comfortably.

The HH is automatically activated when the brake pedal is pressed in conjunction with the following conditions: the vehicle speed equal to zero, the gradient more than 2% and the clutch pedal pressed; the moment the brake pedal is released, with all the other conditions being equal, the Hill Holder keeps the braking system pressurized for 2 seconds to allow the driver to move their foot from the brake pedal to the accelerator pedal without the vehicle slipping backwards and without using the parking brake.

Once the accelerator is pressed, the Hill Holder continues to keep the vehicle still for a further 10 seconds or until the engine torque is sufficient to start the vehicle.The HH is not activated with reverse gear engaged.

This version sees the introduction of additional innovative features:

- DST (drive steering control): on surfaces with poor grip corrections are made automatically and oversteer is controlled thanks to the conversation with the steering control unit.

- CBC: this function improves the distribution of the braking pressure at the four wheels (to fully exploit the grip available on the ground) when braking round bends when the ABS intervenes. This improves stopping distances round bends and, above all, vehicle stability.

- E-Q2 system: the Electronic Q2 system takes advantage of the braking system producing behaviour very similar to a limited slip differential. The front braking system, in cornering acceleration conditions, acts appropriately on the inner wheel, increasing the drive of the outer wheel (with more load) and sharing the torque between the front drive wheels dynamically and continuously according to the driving conditions and the road surface.

For more details

    See descriptions 3340 ANTI-LOCK BRAKING SYSTEM (ABS)

    See descriptions 3350 TRACTION CONTROL

The control unit supply lines are protected by dedicated fuses in the engine compartment junction unit.