Browse Publications Technical Papers 2019-01-0311

Improved Approach for Analytically Derived CO2 Prediction of Medium Duty Chassis Certified Vehicles 2019-01-0311

Medium duty vehicles come in many design variations, which makes testing them all for CO2 impractical. As a result there are multiple ways of reporting CO2 emissions. Actual tests may be performed, data substitution may be used, or CO2 values may be estimated using an analytical correction. The correction accounts for variations in road load force coefficients (f0, f1, f2), weight, and axle ratio. The Code of Federal Regulations defines this Analytically Derived CO2 equation (ADC) using a limited set of historical data. The current ADC equation prediction error of ~120 g/mile is about 4 to 5 times higher than test-to-test variability, which has restricted its use. An improved method is desired to (1) reduce testing expense and complexity, and (2) provide a better CO2 estimate. Previous work on light duty vehicles has demonstrated a physical linear relation between vehicle fuel consumption, powertrain properties and total vehicle work [SAE 2018-01-0322]. This functional form is used to improve the accuracy of the ADC equation, and avoids collinearity and non-orthogonality of the predictor variables. The form also guides the design of experiments to avoid biased regression coefficients. Simulation and measurement results show that the proposed approach reduces the prediction error to 40 g/mile


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