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VEHICLE TRANSMISSIONS

HeavyTorque Issue Five: Vehicle Transmissions

LAYING DOWN THE POWER

TRUCK TRANSMISSIONS HAVE SEEN PROBABLY MORE CHANGE IN THE LAST TWENTY YEARS THAN EVEN ENGINES, AND THAT’S ALLOWING FOR THE TURMOIL CREATED BY SUCCESSIVE EURO EMISSIONS STANDARDS. WE LOOK AT THE BIG DRIVELINE CHANGES, AND ASK A MAJOR MANUFACTURER OF FULLY AUTOMATIC TRANSMISSIONS, ALLISON, HOW THEY ARE WEATHERING THE STORM. IAN NORWELL REPORTS.

The unrivalled march of transmission innovations over the last twenty years has left the old traditional ratio changers in the shade. They’ve certainly marginalized the eight, twelve and sixteen-speed manual boxes. The range-change four-over-four (with or without splitter) was the industry staple not that long ago. To find one now, you’d best drop in on a vintage truck show. When electronics took over from plain electrical, the writing was already on the wall – for those with eyes to read it. Getting conventional gearboxes, engines, and clutches to talk to each other without bothering the driver, brought us the AMT (automated manual transmission). A big advantage here was the use of existing (and proven) major components. In fact, the smoothness and accuracy of shifting allowed many to dump the weight and complexity of synchromesh, previously essential when shifts were managed by clutch-and-boot. But they weren’t at the party long before other devices, adding more functionality, turned up. Cruise control, and his smarter brothers, adaptive and predictive, have changed truck driving forever. A recent excursion with Mandy Wannerton, DAF’s driver-training manager, showed the now ‘normal’ level of automation. Mandy commented: “You drive a truck more with your hands and fingers these days, than with your feet.” She’s right. Playing tunes on the steering-wheel-switches which control these devices, and adjusting the over and under-speed as required, is a far cry from stirring a stick in a crunchy box of cogs. So much for the manual box, its coffin seemingly coach-bolted down. The automated box has moved in to stay, but what about the automatic? That smooth, fluid-coupling torque-converter? Well, no surprise, that’s not been idle either.

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