(1982), have resulted in lowered expectations of benefits. A more recent test conducted by the
Netherlands Testing Organization on a Plymouth Voyager van with a 3.3 LV6 and a four-speed
automatic replaced by a Van Doorne CVT showed fuel economy benefits of 13 percent on the
city cycle and 5 percent on the highway cycle for a 9.5 percent improvement (over a four-speed
automatic).^163 These figures, however, may be unrepresentative of more average applications as
supplier companies usually provide the best possible benefit estimates. The current consensus
among auto manufacturers is that the CVT will be 4 to 8 percent more efficient than current four-
speed automatics with lockup. A 6 percent improvement, including the benefit of the electronic
control required to maximize CVT benefits, would be consistent with the measured results from
the Subaru Justy CVT sold in the United States.
The benefits for the CVT, however, are associated with current engine technology. Reduction
of fuel consumption is associated with two effects: reduced friction losses owing to lower engine
rpm, and reduced pumping losses owing to operation at higher load. In the future, engines
equipped with variable valve timing and direct injection stratified charge engines will have much
lower pumping losses than current engines, thus reducing part of the CVT fuel economy
reduction potential. Typically, this would reduce the benefits of CVTs to about half the value
estimated for current engines, or to approximately 3 percent.Electronic transmission control (ETC)
ETC systems to control shift schedules and torque converter lockup can replace the hydraulic
controls used in most transmissions. Such systems were first introduced in Toyota’s A43DE
transmission in 1982. The benefit of the ETC system lies in the potential to maximize fuel
economy by tailoring shifts and torque converter lockup to the driving schedule. Domestic auto
manufacturers, however, claim that the measured benefits are small, because most modem
nonelectronic transmissions have been optimized for the FTP test cycle. In 1994, more than half
of all vehicles had ETC. Although several electronically controlled transmissions are available,
“paired sample” comparisons are impossible as no example is available of the same car/engine
combination with nonelectronic and electronic transmissions. Regression studies across different
models of similar weight and performance show a 0.9 percent advantage^164 for the electronic
transmission. However, it appears there is potential for greater improvement with some loss of
smoothness or “feel.”
Estimates by Ross and DeCicco^165 have claimed very large benefits for ETC by following an
aggressive shift profile, and they estimate fuel economy benefits as great as 9 percent. These
benefits have been estimated from simulation models, although detailed documentation of the
input assumptions and shift schedule followed is unavailable. Clearly, shifting very early into a
high gear (such as by shifting from second gear to fourth gear directly) and operating the engine
at very low rpm and high torque can produce significant gains in fuel economy--but at a great cost(^163) E. Hendricks, “Qualitative and Quantitative Influences of a CVT on Fuel Economy and Vehicle Performance," SAE paper 930668, March
1993. (^164) H.T. McAdams, “Projection of Automotive Fuel
Economy to the Year 2000: Critique of the Berger-Smith-Andrews Methodology,” rep@
prepared for Martin Marietta Energy Systems, July 1991. 165
M. Ross and J. DeCicco, “An UpdateAssessment of Near-Term Potential for Improved Automotive Fuel Economy,” ACEEE publication,
May 1993.