Electric Vehicle Propulsion And Battery Technology 1975-1995

Abstract

There have been active electric and hybrid vehicle and associated battery programs in the United Stated and other industrialized counties since about 1975. Significant progress in electric propulsion systems and batteries has been made in the last fifteen years resulting in the design and building of electric and hybrid approaching that of conventional ICE vehicles for many mission applications. A quantitative review of the progress made in the various technology areas associated with electric vehicles has been pjerformed. The areas considered were motors (AC and DC), power electronics and microprocessor-based controllers, traction batteries, and transaxles. It was found that the size and weight of the motor and controller were greatly reduced and their efficiency improved to the point that the electric driveline components are no longer any deterrent to designing electric vehicles with speed and acceleration performance comparable to that of conventional ICE vehicles. A single-shaft motor/transaxle assembly has been developed by Ford and General Electric, which is small and lighter than the engine/transmission in the ICE vehicle. Progress on traction batteries for electric vehicles has been less dramatic than for the motor and controller. Nickel-Iron (NiFe), Nickel-Cadmium (NiCd), Sodium-Sulfur (NaS), and Zinc-Bromine (ZnBr) batteries are being tested in vehicles, but Lead-acid remains the only commercially available, affordable option for electric vehicles to be produced in any quantity. Sealed and tubular design lead-acid batteries are available with an energy density of 25-35 Wh/kg and a power density of 90-125 W/kg. The advanced batteries have energy densities of about 50 Wh/kg for NiFe and NiCd, 75 Wh/kg for NaS, and 65 Wh/kg for ZnBr. The power density of all the batteries exceeds the 79 W/kg value needed to meet the FUDS driving cycle. In general, progress on batteries has been slower than was projected in the electric vehicle technology assessments made in 1980 and earlier. A number of electric vehicles have been built and tested using the advanced electric vehicle technology developed since 1980. These vehicles have exhibited good performance accelerating to 48 km/h in 10 seconds or less and attaining speeds in excess of 100 km/h. Better performance is easily achieved by increasing peak motor power. The range of the advanced vehicles depends strongly on the energy density of the batteries used. Using lead-acid batteries, the range would be 90-120 km depending on vehicle type and driving schedule. Using NaS batteries, ranges of 300-400 km can be achieved on the FUDS cycle and at highway speeds of 88 km/h. The mass marketing of electric vehicles now depends on the initial cost and cycle life of the advanced batteries being tested in vehicles. Hybrid vehicles utilizing an electric driveline and heat engine in parallel have been built and tested in both the United States and Europe. The vehicles functioned well on both electric and engine power and offer the possibility of using primarily electricity for city driving and chemical fuels for long intercity trips. The hybrids could result in up to a 75% saving of chemical fuels compared to a conventional ICE vehicle of the same utility.