Better Roads

November 2013

Better Roads Digital Magazine

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Page 27 of 80

HighwayContractor By Jack Roberts, Truck Editor Allison's automatic transmission features fluid drive and a torque converter. Adherents argue these provide 100-percent power and double rim pull, making them ideal for vocational applications. Automatic or Manual? More choices — and it's not just what you 'feel' like R evolutions can be subtle things. Unless there's an army or angry mob storming down Main Street, it's not always easy to tell when you're in one. That's what makes trucks today so interesting. The advent of automatic and automated transmissions in heavy-duty commercial vehicles is changing things. In many ways, the explosion in popularity of these units during the past decade is an offshoot of the rapid evolution being seen in onboard vehicle computers. Automatic transmissions are nothing new. They've been around in automotive applications in one form or the other since the 1940s. But adapting them for use in heavy-duty trucks proved to be difficult for a variety of reasons – not the least of which was the inability of mechanical engines and transmissions to "talk" to one another and ensure optimal vehicle performance in the bewildering array of applications, road conditions and cargo/payload configurations. Early attempts to develop and introduce them met with less-than-acceptable results. There were durability issues. But most complaints tended to focus on performance issues. Before the arrival of today's powerful and compact electroniccontrol modules, early transmissions had a hard time figuring out what drivers wanted. Complaints concerning frequent, uneven shifts while accelerating were common, as were prob26 November 2013 Better Roads lems with "searching," when transmissions would struggle in hilly terrain to find – and stick with – an optimal gear. Other problems along those lines emerged at low speeds. Dry Clutches and Torque Convertors Although the term "automatic" is being used to refer to all non-manual gearboxes, it's important to note there are actually two types of automatic transmissions available for heavyduty trucks: automated manual and automatic transmissions. Both types are two-pedal designs, and most drivers would be hard-pressed to tell much of a difference between them. The basic difference is automated manuals are manual gearboxes with all the clutch actuation and gearshifts handled by electronically controlled systems. True automatic transmissions feature planetary gearing with disc packs for clutches and with torque converters. "In this context, an automatic for a Class 8 truck is usually fully automatic, like a typical car transmission, with planetary gearing with several multi-disc packs for clutches," says Ed Saxman, product marketing manager with Volvo Trucks North America. "These transmissions have a torque converter to enable powershifts of the planetary epicyclic gearing units that provide the various gear ratios. An automated manual transmission uses the gearbox of a manual transmission and

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