Workshop : Driver Assistance


Words Martin Pretorius

You pride yourself on the hardcore abilities of your off-roader. Its specification sheet checks all the boxes: a ladder frame chassis with plenty of ground clearance, a torquey engine and manual gearbox, a four-wheel drive system with a low-range transfer case, and a rear differential lock.
And yet, every now and again, you’ve noticed a softroader with mud tyres and a body-lift to overcome the same obstacle as your dedicated, specialised machine. How is this even possible, with no diff lock or low-range transfer case in sight?

The answer lies in their electronic control systems, for modern softroaders rely heavily on computer wizardry to keep them going. They can cope with crossaxle situations even with their usual lack of suspension flex, and they sometimes dangle a wheel in the air, yet manage to
continue crawling along only with the aid of clever traction management. But they still need four-wheel drive to do this…

Not all four-wheel-drive systems are equally accomplished off-road. The majority of small-to-medium sized SUVs offer on demand all-wheel drive, most often supplied by Haldex Traction in Sweden (now part of Borg-Warner), which means that they are front-wheel driven until the control unit
detects wheel slip and engages drive to the rear wheels.

This drive engagement is usually by means of an electronically controlled clutch, and can send up to 50% of the engine’s torque to the rear axle. It is, unfortunately, a reactive system, which means that it waits for some wheel spin before engaging, unless the vehicle is equipped with an override switch for the clutch engagement.

The advantage of these on-demand systems revolves around reduced driveline losses, which improves fuel economy, but they are significantly less robust than mechanical transfer cases. Extended use in harsh off-road conditions can overheat their hydraulic systems and clutch packs, leading
to malfunctions and eventual damage to the hardware – not ideal when you’re trying to cross the Namib desert in February, but still acceptable in snowed-under countries where it might be a challenge to reach your ski resort of choice.

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