Advanced Automotive Technology: Visions of a Super-Efficient Family Car

It appears the OTA results are very similar to the SIMPLEV results on the highway cycle but
differ significantly on the city cycle. The reason maybe partly because there is no hot or cold-start
fuel penalty in the SIMPLEV model, partly because OTA assumes that the engine operates
around but not exactly at the optimal bsfc, and partly because of OTA’s assumed lower
regenerative braking efficiency.

Another researcher^62 estimates a 100 percent fuel economy improvement from a series hybrid
configuration, in a comprehensive analysis that fortunately uses a mid-size car for its starting
point, facilitating comparisons with OTA’s analysis. Many of the assumptions in the analysis do
not appear to be consistent with OTA’s stated objective of obtaining vehicle performance that
rivals that of conventional vehicles. Among the major differences are:

l l l l l l

The small engine operates at a single point and provides 35 kW of power. Its efficiency is rated at 36.5

percent, which is higher than any engine of that size available today.

The entire energy storage is by an ultracapacitor that stores only 0.5 kwh.

ultracapacitor scenario considered by OTA, but the paper does not address

acceleration or gradability, or multiple hot restarts.

This is similar to the

the issue of sustained

Generator efficiency is assumed at 96 percent, and the engine operates 11 percent of the time on the

FTP.

The efficiencies of electric storage, motor, and transmission are combined and are assumed to be 80

percent. In OTA’s analysis, the battery, motor and transmission combined efficiency is around 0.68.

All inertia loss is assumed to be braking loss, and braking energy

analysis, the value of recovered inertia loss is less than 60 percent.

Cold start and hot restart fuel consumption penalties are ignored.

recovery is 90 percent. In OTA’s

This researcher also combines the hybrid configuration with a lower weight, lower air drag, and
lower rolling resistance design and calculates a fuel efficiency of 83.1 mpg. The car weight, drag,
and rolling resistance are roughly comparable to the 2005(0) scenarios used here, for which OTA
calculates a 61 mpg fuel economy.

A third paper^63 concludes that a subcompact car can attain several hundred mpg based on an
unusually optimistic set of input assumptions;

(^61) A. Burke, "Electric-Hybrid SuperCar Designs Using Ultracapacitors,"preprint of paper to be presented at 30th IECEC Conference, August
1995. (^62) M. Ross and W. Wu, "Fuel Economy of a Hybrid Car Based On a Buffered Fuel: Engine Operating at its Optimal Point,” SAE paper 95000,”
February 1995. (^63) Lovins, et al., see footnote 47.