Construction of a Trip Dynamic Factor to Characterize the Real Driving Emissions of Vehicles
In order to make the vehicle emission of regulatory type certification more genuinely reflect the emission level of vehicles under actual use conditions,the actual driving emission(RDE)test procedure has been established and widely used.However,the RDE test is easily affected by uncertain factors such as the driver's operating behavior,traffic conditions,road slope,etc.The boundary of the travel dynamics test is particularly sensitive to the influence of the RDE test results.In order to effectively characterize the travel dynamics characteristics associated with the actual driving emission characteristics of the vehicle,the instantaneous parameters describing the vehicle's driving state are extracted,including vehicle speed,acceleration,engine speed,torque,power change rate,and vehicle-specific power.The factor analysis method is used to extract the common factors from the variable group,and the linear combination of the common factors constructs the travel dynamics factor.In order to verify the validity of the travel dynamics factor,the test vehicle is designed to carry out the RDE test under conservative driving,neutral driving,and aggressive driving styles.The instantaneous data of the RDE test under conservative,neutral,and aggressive driving styles are divided into data windows by the moving average window method.The emission data of these data windows are regarded as road emission data samples for the calculation of dynamic factors,correlation analysis,and consistency tests.The research shows that the travel dynamics factor can reflect the difference of driving style in RDE test by the variance percentage of the constituent factors.Under various driving styles,the travel dynamics factors are well correlated with pollutant emissions,and the functional relationship between the two does not change with the difference in driving style.It has been proved that the dynamic factor is an accurate measure of the dynamic characteristics of the trip associated with vehicle driving emissions.
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