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Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles
ing engine test procedure while also incorporating existing component data. At this point, it appears that pure simulation would be the less expensive option.
When simulation models are used, inputs are required to represent components. Some of these inputs may come from standardized tests, such as a test for tire rolling resistance or a wind tunnel test for aerodynamic drag. These inputs may also come from simulation models, if the models are validated and sufficiently accurate. For example, a CFD model may be used to determine the Cd of a vehicle in place of wind tunnel testing. Data used in a model for regulatory approaches will need to come from a standard test or analysis process that is recognized by the entire industry. Many new test and analysis procedure standards will be needed. It may be necessary to approve both codes and experimental facilities to insure quality control and uniformity in the determination of wind drag.
Figure 8-4 shows an outline of how a power train test can be combined with a vehicle simulation model to determine the fuel consumption of a vehicle. This is the CIL approach. This figure shows a hybrid electric power train with a diesel engine including exhaust aftertreatment. The power train is tested in a test cell, where the dynamometer load is determined by a vehicle model. The vehicle model, in turn, uses input data for parameters such as rolling resistance, mass, and aerodynamic drag. The vehicle model is exercised over a specified route, and the resulting power demands are applied on the power train by the dynamometer. The resulting fuel consumption is experimentally measured.
The choice of test cycle is a critical part of any vehicle fuel consumption test or simulation. Test cycles selected for regulatory use will need to reflect real-world duty cycles to the extent possible. Parameters of importance include maximum speed, average speed, speed fluctuation, number of stops, and amount of idling. It will not be possible to faithfully reproduce the duty cycle to be experienced by every vehicle, so similar applications will be represented by one or a few duty cycles for regulatory purposes.
Overall Regulatory Structure
Applying a regulatory system that pushes technology in the drive train, tires, and vehicle shape (aerodynamics) ensures that incentives are applied at the foundation of the major vehicle systems that influence fuel consumption.
Given the high fuel consumption sensitivity of some medium- and heavy-duty vehicle purchasers, it appears that one priority should be to ensure that accurate information on the fuel consumption characteristics of a completed vehicle is available to the purchaser. Having such information would help drive the selection of vehicles with the lowest fuel consumption for the task performed. The notion of regulating the final-stage manufacturer and including a requirement on the component manufacturers to provide relevant performance data to the purchaser will be an important part of the regulation.
FIGURE 8-4 CIL test of a hybrid vehicle power train to determine vehicle fuel consumption on a specific test route.