125002521 - E7022 VDC - DESCRIPTION

Description

The antilock braking and anti-slip regulation systems (BOSCH 5.7 ABS with ASR) modulate brake pressure sent to the wheels to prevent loss of grip under all tyre and road surface conditions by cutting in automatically whenever one or both drive wheels begin to slip.The system is designed to complement the normal mechanical braking system and not to replace it. In this way it ensures effective safety in the case of anomalies: the ABS uses the same fluid as the conventional mechanical braking system.Four sensors fitted to the four wheels inform the electronic control unit of wheel speed at every moment. In this way, they detect wheel lock, wheel slip and loss of grip.Under these conditions, the control unit sends specific instructions to solenoids that modulate hydraulic circuit pressure to eliminate lock and restore the car to within grip limits. This ensures the shortest possible stopping distance, without losing control of the steering.The sensors are active, i.e. they consist of a Hall-effect receiver that faces a magnetic coding device built into the hub bearing. Under these conditions, the signal is less influenced by electromagnetic interference and temperature.The control unit also controls brakeforce distribution over the rear axle and thus replaces the mechanical load proportioning valve used previously (EBD function: Electronic Brake Distribution).The control unit is equipped with a self-diagnostic function: when an error occurs in the ABS system, a warning light is turned on and the system is simultaneously deactivated. Under these conditions, the car brakes using only the conventional system.When the control unit detects an error in the EBD function, it simultaneously turns on the ''insufficient brake fluid level'' and ''handbrake on'' warning light as well as the ABS warning light.

Under these conditions, the rear brake distribution control is also deactivated and the car must be driven with great care.

The ASR system increases vehicle stability and active safety by controlling drive wheel slip. If slip is caused by excessive power transmission, it cuts in to reduce engine power through communication with the engine management control unit; if slip is detected at a single wheel, the system cuts in to brake the slipping wheel by acting on the modulation solenoid.The ABS-ASR system is combined with a VDC (VEHICLE DYNAMIC CONTROL) system, which controls vehicle stability by modulating drive torque and braking the wheels differentially, if there is a loss of grip, thus helping to return the car to its correct trajectory.The VDC system acts on the engine and brakes to generate a stabilising torque when the ABS sensors detect conditions that could lead to the vehicle slipping.

The VDC system includes the following specific components over and above those of the ABS:

• a sensor which detects the steering wheel position (steering sensor);
• a sensor which detects the vehicle''s rotation around the vertical axis and side acceleration (centrifugal force) (yaw sensor);
• a sensor that detects pressure on the hydraulic ABS unit (pressure sensor).

By processing information from the sensors, the control unit is able to find out car position moment by moment and compare the position with the driver''s ideal trajectory. If the values do not tally, within a fraction of a second the control unit chooses and implements more effective actions to restore the vehicle to its trajectory immediately: it applies a braking force of different intensity to one or more wheels and reduces power transmitted by the engine if necessary.The VDC comes on automatically when the vehicle is started up and cannot be switched off.ASR comes on automatically whenever the engine is started. The system can be deactivated by operating a button on the central console. When the system is off, a led on the button comes on at the same time as a warning light on the control panel.The warning light flashes when the system cuts in to notifiy the driver that the ASR or VDC system has cut in due to road surface grip conditions.The warning light comes on in fixed mode when the control unit detects an error in the ASR function or VDC function.