process for demonstration vehicles will depend heavily on the results of systems analyses.

All but one of the committee's recommendations in the third report were addressed by the PNGV systems analysis technical team. The exception was that an assessment be made of the value of the expenditures during 1996 for the TASC/SWRI contractor team. During the committee's present review, the team outlined its accomplishments and its plans for 1998. The committee concluded that considerable progress has been made in the past year and that effective systems analysis is now in place to provide design support to the technical teams. The vehicle and subsystem models being created should effectively support the technology selection process. Table 3-1 outlines the systems analysis team's responses to the recommendations and observations in the committee's third report. In general, the responses, combined with presentations to the committee, indicated that the team had responded effectively to the committee's concerns. The major exception was that cost and reliability models have not been reviewed with the committee. The committee believes that both models are necessary to the effective selection of technologies for concept vehicles that will meet the program's objectives.

PROGRAM STATUS AND FUTURE PLANS

Modeling

During the committee's review, the systems analysis technical team made a presentation describing the computer models being developed, showing typical simulation assumptions for specific vehicle configurations, detailing data on fuel economy for parallel and series hybrid vehicles, and describing the sensitivity of fuel economy to changes in vehicle mass. Detailed charts and supporting analysis were presented summarizing the timing and status of subsystem models for all the subsystems being considered. As expected, the model results varied widely, from the internal combustion engine, for which model predictions correlate well with actual data, to the Stirling engine, for which a good model may not yet exist. The PNGV management stated that the precision of the systems analysis tools, in general, exceeds the accuracy of data available for each subsystem. The committee understood this to mean that the analytical models are very powerful and complete and that the simulation models are accurate, provided that they are based on adequate subsystem and component performance data. The PNGV must now build and test subsystems and vehicles that will provide performance data to compare to the performance predicted in the models.

A summary of technical tasks and timing was also presented, and the committee was given detailed plans and schedules for each model requirement indicating the status of each subsystem relative to selected key parameters, including performance, efficiency, emissions, thermal and load transients, heat rejection, scaling, volume and aspect ratio, ride and handling, cost, and reliability. These



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