E7022 Vdc

Description

The electronic anti-lock brake system (BOSCH 5.7 ABS with ASR) governs braking pressure sent to the wheels and prevents loss of grip under all tyre and road surface conditions.

This 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 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 brake force 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. 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.

For more details Characteristic of working principle 3340 Anti-lock brake system (abs) .

The ABS control unit computes true vehicle speed using values supplied by sensors on both drive wheels (the ABS control unit computes an average reading) and the true wheel circumference supplied by the body computer. This speed signal is then sent to nodes that require the information via the CAN network. The ABS control unit also generates a discrete signal that copies the vehicle speed information computed and transmitted via the CAN network.

The control unit supply lines are protected by a special maxifuse located in the engine bay control unit. ignition-operated power supply from a special fuse in the underfacia control unit.

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.

A warning light on the control panel flashes when the system cuts in to notify the driver that the VDC system has come on.

When the control unit detects an error in the VDC function, the warning light is made to stay on in fixed mode.

Note

The same warning light is also used for the ASR function; The VDC systems is connected to the ASR system Wiring diagram E7021 ASR / TCS .

Description of operation

The ABS electronic control unit M50 is supplied (at pin 2 and 6) directly by the battery via a line protected by maxifuse F4, housed in the engine compartment junction unit B1.

The ignition-operated supply (INT/A) reaches pin 23 from the line protected by the fuse F42 of under facia control unit B2.

The control unit is earthed via pins 1 and 5.

The four sensors K70, K71, K75, K76 send wheel speed signals to pins 28-12, 15-16, 13-14 and 30-31 of M50 respectively.

Brake pedal switch I30 sends an enablement signal to pin 14 of control unit M50: the ABS cannot intervene unless the brake pedal is pressed. The switch I30 is supplied when the ignition is switched on (INT) from fuse F37 of junction unit B2.

The 'ASR OFF' control button on panel H35 sends a deactivation signal to pin 27 of M50, while pin 18 viene relays a signal that turns on a led on panel H35 when the system is off.

Pin 37 of M50 emits a discrete speed signal for transmission to Body Computer M1; the same signal is also copied to the CAN network.

Steering sensor K58 is supplied by ABS control unit M50 at pin 39 and receives a reference earth from pin 21: the signal that detects sudden changes in steering direction is sent via the CAN line to engine control unit M1 and ABS control unit M50.

Yaw sensor K74 is supplied from ABS control unit M50 at pin 39, while it receives a reference earth from pin 21: control and command signals are exchanged with ABS control unit M50, at pins 8, 9, 10 and 41.

Pressure sensor K72 is supplied from ABS control unit M50 at pin 42, while it receives a reference earth from pin 25: the pressure detection signal is sent to pin 26 of ABS control unit M50.

Pins 24 and 40 of ABS control unit M50 connect to Body Computer M1 and instrument panel E50 to control the ABS warning light and - if the problem lies in the EBD function - the low brake fluid level and handbrake warning lights. The VDC and ASR functions manage the relevant warning light as described previously.

Self-diagnostic data can be read by connecting to connector G of Body Computer M1- pin 1: it receives signals from pin 11 of the control unit M50 via the special diagnostic line.

Wiring diagram

Components

Component location