At the fourth SAE Hybrid Vehicle Technologies Symposium, held Feb. 7-8 in San Diego, carmakers and researchers discussed both the progress being made in hybrid electric vehicles (HEVs) and the challenges that lie ahead. As usual, the most frequently discussed topic was battery technology and the outlook for breakthroughs. Although the batteries were a concern for many conference participants, new hybrids will hit the streets this year with the NiMH battery technology already in use in more than 14 models in North America. Even though the conference's focus was on electric hybrids, attendees were shown an air hybrid alternative that provides yet another possible powertrain option for future vehicles.
The first products from the Global Hybrid Cooperation of General Motors, DaimlerChrysler and the BMW Group will appear later this year. In the fall, GM will introduce the front wheel drive (FWD) Chevrolet Tahoe and GMC Yukon based on electric variable transmission technology (EVT). Vehicles from all three companies will use a two-mode transmission with four fixed mechanical gears. Peter Savagian, engineering director for Hybrid Power Systems at General Motors says the two-mode hybrid improves the balance of electric motors and transmission content with smaller motor and smoother operation. The use of one mode for low speeds and light loads and the second mode for highway speeds allows the system to achieve a 25 percent improvement in overall fuel economy.
Hybrids Without Batteries
Independent engine development company, Scuderi Group has quite a different approach to hybrids. The company's Split-Cycle Engine, also called an air hybrid, divides the four strokes of the traditional Otto cycle (intake compression, power and exhaust) over a paired combination of one compression cylinder and one power cylinder. A compression cylinder compresses the gas, which is then transferred to the power cylinder through a gas passage. A set of uniquely timed valves in the gas passage maintain a precharged pressure through all four strokes of the cycle. After the piston in the power cylinder reaches top dead center, the gas is quickly transferred to the power cylinder and ignited to produce the power stroke. Initial testing of the hybrid indicates that it could be up to 33 percent more efficient than a conventional engine. Furthermore, converting an existing engine to an air hybrid could cost between $200 and $300 instead of the $2000 to $3000 cost penalty of HEVs.
Better Batteries Beckon
Both Toyota and Honda, the leading hybrid vehicle makers, use Ni-MH batteries. Honda's Ttsuya Haseb, assistant chief engineer for the Automobile R&D Center of Honda R&D Co. Ltd., pointed out that among the numerous engineering changes made between the 2002 and the 2006 Civic hybrids for improving performance and efficiency, several were made to the batteries. By increasing the thickness of current collecting plates, changing to a highly conductive electrolyte and increasing the reaction surface area with a thinner and longer electrode, Honda reduced the internal battery pack resistance by 36 percent.
However, the great hybrid and plug-in hope appears to be Li-Ion cell technology. A123Systems, already contracted to develop Li-Ion batteries by the United States Advanced Battery Consortium (USABC), will supply advanced Li-Ion batteries through its Tier 1 partner, Cobasys LLC that are optimized for plug in hybrid vehicles to GM. The first use of Li-Ion batteries will occur in a utility vehicle and not passenger vehicles. Eaton's Utility HEV will have more than 200 units in service in early 2007. The design uses Li-Ion storage and has achieved 40 to 60 percent reduction in fuel consumption in target applications.