ZF modifies 8-speed tranny, now stop/start approved
In the name of increased efficiency, and quite possibly playing the game of automotive one-upmanship, luxury automakers such as Mercedes Benz, BMW and Lexus have been adding more and more gear ratios to their automatic transmissions. By allowing a computer to choose the most appropriate ratio for any given scenario, the vehicle's engine is required to only make as much power as absolutely necessary, potentially saving fuel in the process. ZF, one of the largest transmission makers in the world, claims that their new 8-speed unit boasts an efficiency increase of eleven percent over its older 6-speed unit. The transmission giant has just developed a new modification, though, which could increase the overall vehicle efficiency even further. By adding a hydraulic impulse storage unit, the new ZF unit can support stop/start functionality, which they claim can result in an additional five percent reduction in fuel consumption.
[Source: Just-Auto - sub. req'd.]
Reader Comments (Page 1 of 1)
Will 8:33AM (5/02/2008)
And to think some car companies STILL sell cars with 4-speed transmissions!
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Richard 8:48AM (5/02/2008)
Impressive. Doing this in the transmission - presumably within the same form factor - might make it a lot easier for some car companies to add start/stop to their product lines. The alternative is reworking quite a lot to move towards a starter/alternator combination, with the additional batteries that implies, which seems to be harder to implement.
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Karkus 11:17AM (5/02/2008)
Good to see transmissions becoming more flexible to work with various fuel savings technologies. Seems like MB is really trying to save fuel in all kinds of ways. (hybrid, start stop, diesel, etc)
And here's a small nitpick about the statement about how 8 gears allow to engine to only make the minimum amount of power necessary for a given situation.
It seems to me that the power required to accelerate a certain amount over a certain time is independent of how many gears you have (assuming the transmission losses are equal). But things like rpm and torque and fuel consumption will be different based on what gear your are in (and how many you have).
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