Naturally aspirated gasoline engines and cylinder deactivation
The technology assessments conducted by the Environmental Protection Agency (EPA) and the National Highway Traffic Safety Administration (NHTSA) to inform the 2017–2025 passenger vehicle fuel economy and greenhouse gas emissions regulations were conducted five years ago. EPA and NHTSA projected that DCTs would overtake conventional automatics by 2021 and continue to increase market share through 2025. However, due to numerous consumer acceptance issues (which may be due primarily to calibration, rather than the actual hardware), their sales have not reached levels indicative of such a transition. While some of the technical challenges faced by DCTs are being solved, the solutions will likely make them slightly more expensive and slightly less efficient than projected by the agencies. Although DCTs remain an attractive option in terms of comparative cost-effectiveness and efficiency, they are unlikely to match the penetration estimates in the rulemaking.
Since then, years of incremental improvements have shown that CVTs can, and are, a good alternative transmission. Rapid improvements in continuously variable transmissions and conventional automatics have compensated for slower than projected growth in the use of dual-clutch automated manual transmissions. Market share has grown rapidly since 2012 and consumer acceptance issues no longer seem to be plaguing CVTs. Although the agencies did not explicitly predict the costs or benefits of CVTs in the rulemaking, CVTs today appear to be on track to match the benefit estimates available in EPA’s lumped parameter model and they cost less than conventional automatics.
This paper is one of a series that the ICCT, in collaboration with automotive suppliers, is undertaking to profile and evaluate technological developments in engines, transmissions, vehicle body design and lightweighting, and other measures. Each paper in the series will assess:
- How current costs, benefits, market penetration compare to projections that were made for the rulemaking
- Recent technology developments that were not considered in the rulemaking and how they impact cost and benefits
- Customer acceptance issues, such as real-world fuel economy, performance, drivability, reliability, and safety