The electronic anti-lock and anti-slip system for the wheels (ABS with ASR) regulates the braking pressure transmitted to the wheels preventing them from losing grip in all road surface and tyre conditions.It is linked to the VDC system (VEHICLE DYNAMICS CONTROL) which controls the stability of the vehicle, intervening, if necessary, on the drive torque and braking the wheels in a differentiated manner: in cases of a loss of grip, it contributes to returning the vehicle to the correct path.The system is designed to integrate and not replace the traditional mechanical braking syste, thereby guaranteeing effective safety in the case of problems: the intervention takes place on the same brake fluid as in the regular mechanical circuit.Four sensors, located on each of the four wheels, signal the speed of each wheel to the electronic control unit, thereby detecting any locking, slipping or loss of grip situations.If these situations occur, the electronic control unit operates the solenoid valves, which modulate the pressure in the hydraulic circuit, preventing locking and restoring the vehicle to the permissible grip limits, which affords the least possible braking distance without losing control of the steering.The sensors are the active type, in other words they consist of a receiver and a magnetic codifier integrated in the hub bearing: in these conditions the signal does not suffer from interference of an electro-magnetic nature or related to the temperature.In addition, the control unit manages the distribution of the braking load on the rear axle, replacing the mechanical brake distributor used previously (EBD function: Electronic Brake Distribution ):The braking control unit which manages the system is equipped with an autodiagnostic function: the moment an error or failure is detected in the function, the system is immediately deactivated (in this case the vehicle is braked using the conventiona sytem) and, at the same time, the warning light in the instrument panel comes on and the failure message is shown on the display. If the control unit also detects an error in the EBD function, it operates the ABS failure warning light and also the insufficient brake fluid and handbrake applied warning light.The braking control unit calculates the speed of the vehicle starting from the figures that are supplied by the wheel sensors (with the control unit calculating the average value) and from the actual circumference of the wheels themselves, supplied by the Body Computer. this signal (speedometer signal) is then transmitted, via the CAN, to all the nodes that require this information for their functions.The VDC system intervenes on the engine and the brakes producing a stabilizing torque the moment the ABS sensors detect conditions that will lead to the vehicle slipping.The braking control unit also produces a discreet signal which replicates the vehicle speed information calculated and transmitted via the CAN.In addition to the components on the ABS, these are the specific components for the VDC sytem:
control unit for detecting the position of the steering wheel (steering angle control unit);
control unit for detecting the rotation of the vehicle around the vertical axis and centrifugal lateral acceleration (slewing control unit);
The braking control unit detects and processes the information coming from the four sensors on the wheels and is therefore capable of recognizing the position of the vehicle, at any given moment, and of comparing it with the ideal path that the driver wishes to follow. If there are discrepancies, the control unit selects and immediately implements suitable operations to restore the ideal path for the vehicle: the braking of one or more wheels, with forces of different intensity, depending on the situation is implemented and, if necessary the power transmitted by the engine is reduced.The VDC function is activated automatically the moment the engine is started up and there is no specific control for the driver to switch it off manually: the system remains on until the key-off.The supply lines for the braking control unit are protected by two special maxifuses located inside the engine comparment junction unit; the supply controlled by the ignition (INT) comes from a specific fuse inside the dashboard control unit.The VDC warning light located in the instrument panel flashes if the system is operating on the vehicle braking system to advise the driver tha the VDC system has intervened.When, on the other hand, the braking control unit detects an error in the VDC function, the warning light comes on, this time constantly. (The same warning light is also used for the ASR / TCS function because the VDC and ASR / TCS systems are always linked, See E7021 ASR / TCS