Attachment D Examples of Technology Improvements
PAST IMPROVEMENTS
Over the past several years, DaimlerChrysler has introduced a new family of engines, replacing engines with push rods and overhead valves. One of them, the 2.7 liter engine, produces 200 horsepower, 40 more than its older equivalent, yet uses 10 percent less fuel. Had it been kept at the same power, fuel economy presumably could have been improved significantly more. Several technologies were used to achieve these improvements, including overhead cams (OHC), 4 valves/cylinder (the committee’s estimated average contribution of these together is 3 percent), reduced engine size (6 percent when combined with a supercharger for even greater downsizing), and reduced friction losses (3 percent). According to the committee’s values, these technologies would have contributed some 12 percent to fuel consumption reduction on average. Had DaimlerChrysler included variable valve timing and lift, fuel economy improvements of well over 20 percent might have been achieved for the same output. DaimlerChrysler used other factors, including electronic exhaust gas recirculation (EGR) which is tuned for high fuel economy as well as low emissions and lower idle speed, which were not included in the committee’s list. This example is included to illustrate how much improvement is possible with redesign and technology upgrades.
FUTURE POTENTIAL
The variable compression ratio (VCR) engine, pioneered by Saab (which is now part of GM), is reported to achieve a 30 percent fuel consumption reduction (equivalent to a fuel economy gain of 43 percent) compared to a naturally aspirated conventional engine (GM, 2001). The Saab VCR uses a supercharger to achieve the same power as a larger engine. Most engines, in particular supercharged and turbocharged engines, must have a lower-than-optimal compression ratio to avoid knocking at high load. The compression ratio in the Saab engine can vary between 8 and 14. Variable compression allows the engine to work at high efficiency and produce a very high output (150 bhp/liter—more than twice the level of most current engines).
In the committee’s analysis, all Path 3 engine technologies, production-intent and emerging including VCR, collectively result in an average fuel consumption reduction of 24 percent for midsize cars. Thus the committee’s projection is conservative relative to Saab’s 30 percent reduction, especially since the Saab VCR is presumably benchmarked against European engines that already have more of these sophisticated technologies than U.S. manufacturers use.
In the long term, even more innovative concepts may become available. For example, the hydraulic hybrid vehicle is drawing attention because it can store a much higher fraction of the energy from regenerative braking than can a HEV. One research group estimates that a car equivalent to a Ford Taurus could achieve 61 mpg in the urban driving cycle (Beachley and Fronczak, 1997).
Toyota is taking another approach, using a capacitor to store energy from regenerative braking. Toyota estimates that the four passenger prototype it is building will achieve 88 mpg (Toyota, 2001).
REFERENCES
Norman H. Beachley and Frank J. Fronczak, Advances in Accumulator Car Design, SAE 972645, Presented at the Future Transportation Technology Conference, San Diego, California, August 6–8, 1997.
General Motors Website. <www.gm.com/cgi-bin/pr_display.pl?1228>.
Toyota Website. <http://global.toyota.com/tokyomotorshow/es3/data.htm>.
