AWKnowledge

Notes from the Editor

Automated mechanical transmissions have taken off in a big way in European trucks, their acceptance with vehicle buyers having accelerated markedly in the last five years. Scania, Volvo and DaimlerChrysler have all developed in-house systems, while MAN, DAF and Iveco rely on ZF's AS-tronic design. Only Scania, on a matter of safety-related principle, has retained the clutch pedal for starting away and coming to rest. But the rest have advanced to true two-pedal control - equivalent from the driver's point of view to a full torque converter automatic.

Similar developments are now concentrating the minds of driveline engineers in the passenger car industry. So, if an AMT can do the same job at much less cost and, in many applications, with less of a fuel penalty, can we expect demand for traditional torque converter transmissions to have disappeared in a few years time?

It would seem not - unless the shifting smoothness achieved with a fluid coupling can be matched by a yet-to-be seen AMT. Almost literally a crunch issue in such a development is that of being able (or not) to move from one ratio to the next without breaking the drive. The Zeroshift technology described this week in John Mortimer's feature article addresses that issue head-on. It is an all-mechanical transmission that provides unbroken torque through each shift.

That is admirable from a fuel efficiency (and transmission wear and tear) aspect. On a rising gradient downshifts can be delayed, because no allowance need be made for lost momentum, as in a synchromesh shift. By the same token faster upshifts can be implemented sooner on a gradually easing gradient. It would seem that there is still some R&D work to do by the Zeroshift team to match the shift smoothness which the best torque converter set-ups can deliver, and which is demanded in executive cars and, crucially, in city buses.

Editorial board member, Commercial Vehicles

Alan Bunting CEng, MIMechE, ASAE, is a writer, and former professional engineer, specialising in commercial vehicle and powertrain topics

REPRODUCED WITH PERMISSION FROM AW KNOWLEDGE.

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