TraXon Winter Testing Testing transmissions in the permafrost

In Swedish Lapland, a ZF Vehicle Test team is making final adjustments to the TraXon automatic transmission system at temperatures of minus 20 degrees Celsius. Not all members of the test engineering team find that especially cold.

A heavy curtain of snowflakes is whirling down from the sky. The wind is howling, the thermometer is showing minus 21.5 degrees Celsius. Welcome to Arjeplog. Here, less than 60 miles south of the Arctic Circle, biting cold is a fact of life. But for ZF test driver Marcus Haug, it still isn’t cold enough. “Conditions aren’t perfect,” he says, “although they’re pretty good.”

The ZF test team traveled to Lapland so they could put the company’s TraXon automatic transmission system through a final series of practical tests. But in January 2015, temperatures here only dropped to slightly below minus 20 degrees Celsius, rather than the more usual minus 30 or lower. So the test vehicles must spend the night in the cold chamber. “Overnight, the transmission fluid cools down to minus 32 degrees, becoming thick as honey. The effect is great for testing, but unfortunately doesn’t happen at current outdoor temperatures,” explains application engineer Achim Chiandetti.

Cold starts and rocking free

Moving off instead of spinning on the spot: the winter testing schedule also covers the rock-free function.

Engineer Chiandetti and driver Jürgen Pechar are testing the 12-speed version of the transmission in a EURO 6 truck. Sitting in the cab, the engineer starts by using his laptop computer to check all the electrohydraulic valves, making sure their seals are still tight and their operational efficiency is unaffected; as yet, neither engine nor heating have been switched on. Then he gives Pechar the signal to start. The truck rumbles into life and he drives off, bringing the diesel engine and transmission quickly up to operating temperature. From the passenger seat, Chiandetti issues precise instructions on the shifting sequence.

Just a snowball’s throw away, the second vehicle still hasn’t moved from the spot – in fact, the drive wheels are spinning on the icy surface, unable to find a grip. It’s a common problem for truckers parking in cold regions: the cold snow starts to melt under the warm tires of a newly parked truck, then quickly freezes solid again due to the very low temperatures. If you were sitting in a vehicle with manual transmission, you could use some clever clutch action to rock the vehicle to and fro by engaging and then disengaging the engine. But TraXon is fully automatic – so instead, it has a “rock-free” function. This engages the clutch one gear higher than the gear that was actually selected, and also sets it up so it is super-easy to control via the electronic gas pedal. While test driver Andreas Arnegger rocks the truck free, application engineer Daniel Gelder busily records all the relevant data on his laptop. Certain parameters may need to be adjusted subsequently. “We’re optimizing the assistance system now so that later, any and every truck driver will find it really easy and intuitive to use,” explains the engineer.

Video: Testing TraXon in Sweden

In Arjeplog a ZF Vehicle Test team is making final adjustments to the TraXon automatic transmission system.

Repeating road tests as often as needed

“The key to effective testing is that we should be able to repeat all these dynamic, real-world road tests as many times as we need to, under identical extreme conditions,” explains test driver Marcus Haug. A typical example: testing how the TraXon transmission behaves on icy surfaces. “Wheels lock up very quickly on ice, so the transmission control unit must be able to recognize what’s happening and respond accordingly,” explains function developer Bemetz. The challenge for the control unit is first, to disengage much faster than usual to prevent the engine from stalling. Second, it must realize that although the wheels are standing still, the truck itself is sliding, so that it doesn’t attempt to engage a low starting gear in this situation. If it did shift into low gear as soon as the driver released the brake pedal – despite the fact the vehicle is still sliding at high speed – the consequences could be very serious. “Horror scenarios range from major clutch damage through to an uncontrollably skidding semi,” emphasizes test driver Arnegger. “Our cold-climate-aware transmission electronics always know precisely what’s required for safe driving!”

The testing area

Every winter, test centers in the far North exert an almost magnetic attraction on vehicle manufacturers and suppliers alike. Between November and March, a total of some 30,000 auto testers from around 20 countries assemble in the countryside surrounding Arjeplog. The town itself has just 3100 inhabitants. The rise of northern Sweden’s municipalities to become the world’s largest automotive winter test center first began in 1967, when a carmaker made the journey to Arvidsjaur to run engine tests. Those early years had little in common with today’s high standards of test-driving. Back then, the developers brought their own brooms and shovels so they could shift snow off the icy surfaces. To check whether the ice was safe to drive on, they would send unmanned cars out over the lakes with their auto transmissions set to “Drive”. But as more and more specialists became aware of the region’s stable winter climate and total seclusion – ideal conditions for winter testing – a professional testing infrastructure swiftly took shape in this remote corner of Lapland.

Pictures: Joscha Kinstner

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