SAFETY

Braking system and active safety systems

The Alfa Crosswagon Q4 braking system is hydraulic, power-assisted and consists of two independent crossover circuits. This particularly effective system offers prompt, smooth braking and short stopping distances.

In particular, the GTA-derived front discs are ventilated with a diameter of 330 millimetres and come with Brembo fixed aluminium callipers with four pistons (38 and 42 mm) with a shiny black finish.

The rear discs are only slightly smaller at 276 millimetres. In addition to a high-performing brake system, the Crosswagon Q4 also comes with a BOSCH 5.7 ABS, one of the most advanced systems available on the market today. It features four active sensors and a hydraulic control unit with 12 solenoids.

The ABS contains an electronic brakeforce distributor (EBD). This device apportions braking action over all four wheels to prevent locking and ensure full control of the car under all conditions.

The system also adapts its operation to wheel grip conditions and brake pad efficiency to reduce pad overheating. Lastly, the Crosswagon Q4 assures absolute mastery of the car under all conditions, however tough, due to its VDC and ASR system.

VDC (Vehicle Dynamic Control)

The VDC is Alfa Romeo's version of the ESP (Electronic Stability Program), a system that cuts in under extreme conditions when car stability is at risk and also helps the driver to control the car. As befits a true Alfa, the VDC is a sporting device that offers outstanding roadholding. It allows the driver the full satisfaction of controlling the car as long as conditions are normal but cuts in just before things become critical. The VDC is permanently engaged.

The MSR (Motor Schleppmoment Regelung) cuts in when the gear is shifted down abruptly in low grip conditions. This device restores torque to the engine to prevent the wheel skidding as a result of lock.

To achieve this result, the VDC continually monitors tyre grip in both longitudinal and lateral directions. If the car skids, it cuts in to restore directionality and ride stability. It uses sensors to detect rotation of the car body about its vertical axis (yaw speed), car lateral acceleration and the steering wheel angle set by the driver (which indicates the chosen direction).

It then goes on to compare these data with parameters generated by a computer and establishes - via a complex mathematical model - whether the car is cornering within its grip limits or if the front or rear is about to skid (understeer or oversteer). To restore the correct trajectory, it then generates a yawing movement in the opposite direction to the movement that gave rise to the instability by braking the appropriate wheel (interior or exterior) individually and reducing engine power (via the throttle). This is the key attribute of the device designed by Alfa Romeo engineers.

It acts in a modulated fashion on the brakes to ensure the action is as smooth as possible (and the drive is not therefore disturbed). The engine power reduction is contained to ensure outstanding performance and great driving satisfaction at all times.

As it carries out its complex task, the VDC stays in constant communication with the brake sensors and engine control unit but also with:

• a Body computer that constantly exchanges information with the ABS, engine management unit and automatic transmission unit;

• an electronic throttle (that communicates with the ABS in turn);

• a control panel (active warning lights);

• the steering wheel and steering column (via the steering sensor);

• a gyroscopic sensor installed on the passenger compartment floor to record car yaw and lateral acceleration.

ASR (Anti Slip Regulation)

The ASR (Anti Slip Regulation) system, an integral part of the VDC, optimises traction at any speed with the aid of the brakes and engine control.

The device computes degree of slip on the basis of wheel rpm calculated by the ABS sensors and activates two different control systems to restore grip: when an excessive power demand causes both drive wheels to slip (e.g. in the case of aquaplaning or when accelerating over an unsurfaced, snowy or icy road), it reduces engine torque by reducing the throttle opening angle and thus air flow; if only one wheel slips (e.g. the inside wheel following acceleration or dynamic load changes), this is automatically braked without the driver touching the brake pedal. The resulting effect is similar to that of a self-locking differential.

This allows the Alfa Crosswagon Q4 to acquit itself with ease over ice - only one wheel needs to grip to allow the car to exert traction - and under off-road conditions when the car is twisted and suspended on two diagonally opposed wheels with one of the other wheels hanging in space.

The ASR is activated automatically whenever the engine is started but must be turned off by means of a cut-out switch on the central console. The ASR need be turned off only when snow chains are used because the wheel must be able to slip by tiny amounts to pile up the snow so that force can be transmitted to the ground and the ASR tend to prevent this occurring.