Study of Accumulator Passenger Cars Based on the Ifield Hydrostatic Pump/Motor Unit

摘要

The use of hydraulic accumulators for energy storage in passenger automobiles has the theoretical potential of providing a significant improvement in fuel economy under urban driving conditions. Until now, however, the concept has suffered from the unavailability of hydrostatic variable-displacement pump/motor units with satisfactory efficiency characteristics. A new design, called the Ifield accumulator, has significantly higher efficiencies than any other known units, and has the potential to make high-mileage accumulator vehicles a practical reality. A preliminary study was done to determine: the potential fuel economy improvement of an Ifield accumulator vehicle, and whether or not additional research and development work in this area is justified. The study was based on efficiency data in equation form provided by Ifield. The calculated results are quite promising, indicating mileage on the order of 60 mpg for a 3000-lb vehicle over the Federal Urban Driving Cycle (FUDC), and mileage on the order of 85 mpg for the New York City Cycle. These figures appear to be feasible not only on a system with two pump/motor units, but on one with a single pump/motor unit as well. The latter appears attractive because of price considerations. Fuel economy figures compare favorably with those of a comparable flywheel energy-storage vehicle. The above figures are based on the use of accumulators with plastic foam as a heat sink to provide nearly isothermal operation with correspondingly low thermodynamic losses. With a conventional accumulator, the fuel mileage calculated for the FUDC drops approximately 9%. The required accumulator weight has been calculated to be about 100 lb, using state-of-the-art composite construction. Foam, if used, would add approximately 30% to the weight. (ERA citation 07:011174)