Intelligent auto-shifting can help save fuel
By: Alan Bunting, Tuesday, August 25, 2009, AutomotiveWorld.com
When vehicle manufacturers invite component suppliers to tender for a contract, they inevitably focus initially on each company's past performance, including its record of reliability at meeting just-in-time deliveries, as well of course on maintaining previously agreed product quality standards. But in the powertrain area there is now an additional consideration. Does the engine or driveline component being offered by the supplier bring performance advantages, perhaps most especially by way of fuel efficiency (and CO2 emissions reduction) improvements?
ZF Friedrichshafen AG, the world's largest producer of commercial vehicle transmissions, is endeavouring to show that, mainly for buses, its latest driveline developments can deliver fuel savings of up to 5% through a combination of friction-loss reduction and its 'terrain adaptive' TopoDyn gearshift programme. The company introduced its EcoLife six-speed automatic transmission in 2007. Aimed principally at the city bus market, but with potential in other applications, for example on/off-highway tipper/dumptrucks and refuse collection vehicles, EcoLife is a further development of ZF's well-established EcoMat torque-converter automatic box.
A key innovation is that a torsional damper is incorporated into what is effectively a redesigned torque converter. It is said to reduce hydraulic losses during initial acceleration. Meanwhile, a transmission fluid with reduced viscosity, newly developed for ZF, has further cut the thrashing losses which, from a fuel consumption perspective, remain the Achilles' heel of fluid coupling based transmissions, when compared with a manual gearbox, automated or otherwise.
Further fuel savings can be expected when ZF's TopoDyn shift control system is specified. It is essentially a software program which constantly adapts the points at which up- and down-shifts occur. Continuous input signals derived from the topography of the route and the load on the driveline - which necessarily varies with changing vehicle weight and driver demand through the accelerator pedal - determine optimum road and engine gearshift speeds for the best fuel economy.
One should add that Allison Transmission, ZF's main competitor globally in the truck and bus automatic transmission market, has its own ratio-change control program, known as LBSS (load-based shifting schedules). Indeed, both companies now offer what they call hybrid versions of their automatic transmissions, in which the torque converter is effectively replaced by an electric machine - a motor/generator able to replicate the traditional role of the torque converter, but 'steplessly'. The ratio best suited to the conditions, from a driveline efficiency point of view, and determined by topography and transmission load signals, is infinitely variable.
It seems inevitable that the software programs behind the TopoDyn and LBSS intelligent shifting programs will before long be adapted to the control electronics of AMTs (automated mechanical transmissions) such as ZF's well-entrenched AS-tronic for truck applications where, arguably, fuel costs are even more critical than in buses. As with earlier AMT developments there could, in Europe anyway, be a race between ZF and each of the three heavy truck makers who continue to produce their own gearboxes in-house, namely Daimler, Scania and Volvo, to introduce such a fuel-saving transmission control regime.
The opinions expressed here are those of the author and do not necessarily reflect the positions of Automotive World Ltd.
Published on Tuesday, August 25, 2009
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