Maximizing Efficiency with a Continuously Variable Transmission

AI Thread Summary
The discussion centers on the efficiency of continuously variable transmissions (CVTs) compared to manual transmissions, with manual transmissions achieving efficiencies of about 96% to 98%. CVT manufacturers often do not disclose efficiency figures, making it difficult to ascertain their performance. While CVTs are claimed to offer 5-10% lower fuel consumption, real-world data suggests they may not outperform traditional gearboxes. The efficiency of CVTs can vary significantly based on design and operating conditions, with some systems optimizing engine RPM for better overall efficiency. The conversation highlights the need for more transparency in CVT efficiency metrics to better understand their performance relative to manual transmissions.
kandelabr
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I wonder what's the best efficiency that's possible to achieve with a continously variable transmission. I've googled a lot and can't find anything useful (with useful i mean an approximate value in [%]).
thanks.
 
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The following website has a good discussion of the various types of continuusly variable transmissions (CVTs)
http://en.wikipedia.org/wiki/Continuously_variable_transmission
None of the CVTs have efficiencies as high as manual transmissions: about 96% in all but the 1:1 gear which is about 98%. Manufactirers of CVTs will not disclose the efficiencies of their designs; it is proprietary.

Note that manual transmissions in standard automobiles do not require water cooling. If a particular CVT requires water cooling, that is proof that it is less efficient than a manual transmission.
 
yes, I've seen this page. I've read quite a lot of stuff regarding cvt's, but never found anything like efficiency.

are you sure it's 96 to 98%?
i was told in school a pair of gearwheels has 99% efficiency; either i was told wrong or efficiency of standard transmission should also be around 98%. there's still some friction in those things.

cars with cvt's should have 5-10% lower fuel consumption, but they either have the same or even higher than cars with standard gearboxes. i don't think that this 2% difference would make such an impact on fuel consumption.

anyway, i don't know where, on well-made pair of gears, 2% could be lost... :)
 
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I found a measurement (see attachment) that shows that a 5 speed manual in passenger cars has an efficiency of about 96% in gears 1,2,3,and 5, and an efficiency of about 98% in 4th (1:1) gear. Recall that the input and output shafts are co-aligned, so that in gears 1,2,3, and 5 there are two gear-to-gear contacts. As in other transmissions, the efficiencies depend on both RPM and torque.
 

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This article gives a loss of 8% (page 11). There is more than one type of CVT and some systems gain overall better efficiency by allowing the ICE to run at a more efficient RPM and get overall lower emissions.
http://www.torotrak.com/Resources/Torotrak/IQPC_2008.pdf
 
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thanks a lot for this data, means a lot to me, really.
 
nucleus said:
This article gives a loss of 8% (page 11). There is more than one type of CVT and some systems gain overall better efficiency by allowing the ICE to run at a more efficient RPM and get overall lower emissions.
http://www.torotrak.com/Resources/Torotrak/IQPC_2008.pdf
For engine brake power output less than the power at the power corresponding to the maximum efficiency ("sweet spot" usually about 35% of redline and 80% of maximum torque), the maximum efficiency for a given power output is usually about 50% to 80% of maximum torque and a lower RPM than the "sweet spot". Cruising at city speeds usually requires about 10 kW or less. and should not require running above about 30% of redline. IF a CVT HAS WATER COOLING, then it is less efficient than a manual transmission (typ 96% to 98%).
Review this paper for the physics and eficiency of automobile engines
http://sitemaker.umich.edu/mhross/files/fueleff_physicsautossanders.pdf
 
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http://www.zeroshift.com/pdf/Seamless%20AMT%20Offers%20Efficient%20Alternative%20To%20CVT.pdf
http://www.zeroshift.com/pdf/Seamless%20AMT%20Offers%20Efficient%20Alternative%20To%20CVT.pdf"

Manual - 97%
Automatic - 86%
CVT belt - 88%
CVT torroidal - 93%
 
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yes! that's what i was looking for, thanks!
 
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Where is a comparison to the efficiency of the planetary CVT used in the Prius. The Prius CVT is unique in that it allows both an electric motor and a gasoline engine to simultaneously drive the vehicle in forward direction (but only electric motor in reverse).
Bob S
 
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