Hybrid drive systems, the PNGV near-term power trains of choice, use energy-storage devices to reduce fluctuations in demand on the primary power plant, thereby permitting the use of a smaller power plant operating closer to optimum conditions for increased energy-conversion efficiency and reduced emissions. These storage devices also allow recovery of a portion of the vehicle’s kinetic energy during braking operations.
In this chapter, the committee continues its evaluation of the candidate energy-conversion and energy-storage technologies that survived the 1997 technology selection process, as well as of candidate electrical and electronic systems and advanced structural materials for the vehicle body.
The committee reviewed R&D programs for: four-stroke internal-combustion reciprocating engines, fuel cells, electrochemical storage systems (rechargeable batteries), power electronics and electrical systems, and structural materials and safety to assess their progress toward commercial applicability. In the committee’s opinion, PNGV has continued to make significant progress on the development of candidate systems and the identification of critical technologies that must be addressed to make each system commercially viable.
Indeed, global competitiveness is one of the objectives of the PNGV program. In fact, previous committee reports have specifically addressed the directions and trends of international development programs. The committee is aware that the PNGV partnership continues to maintain awareness of international programs and, in many cases, the USCAR partners are participating in those developments through international operations and coalitions. Therefore, a separate section on international developments has not been included in this report.
The internal combustion engine continues to be the primary candidate power plant for meeting near-term PNGV program goals. To meet the fuel economy target of Goal 3, the internal combustion engine will have to be integrated into an HEV configuration. The CIDI or diesel engine is the most fuel efficient internal combustion engine being developed. Consequently, in the near term, maximizing the efficiency of a diesel engine and integrating it into an HEV will provide maximum vehicle efficiency. However, as will be discussed below, the challenges of meeting the new California Air Resources Board (CARB) and EPA Tier 2 emission standards have called into question the viability of the CIDI engine as the primary energy converter in PNGV’s time frame. As a result of the new standards, the technical team working on the 4SDI (four-stroke direct-injection) engine began focusing more on emissions control research for the CIDI engine. In addition, they are continuing research programs on other combustion systems for internal combustion engines, namely the homogeneous-charge compression-ignition engine, the gasoline direct-injection engine, and the homogeneous-charge spark-ignition engine.