The effect of exhaust aftertreatment and engine temperature on IOLS for CVT powertrains

An investigation has been conducted into the scope for Ideal Operating Lines (IOLs) to improve fuel consumption and CO, HC, NOx and PM emissions of a vehicle equipped with a CVT. This simulation was performed using the ADVISOR code within the MATLAB/Simulink environment. The ADVISOR code was modified to investigate the effect of a range of IOLs on a vehicle equipped with either a Spark Ignition (SI) or Diesel engine coupled to a CVT. The work addresses two issues often neglected during the calibration process due to the complex interactions involved. The work seeks to demonstrate that a simple simulation based tool is able to inform the calibration process at an early stage of vehicle development. First, the effect of the exhaust aftertreatment device on engine-out emissions for differing IOLs was analysed. In the case of the SI engine it was found that internal catalyst temperature increased more rapidly with the IOLs for HC and NOx. Consequently, maximum conversion efficiencies were reached more quickly than with the IOLs for fuel consumption and CO. As a result, IOLs derived with reference to engine-out emissions were unable to deliver the lowest tailpipe emissions results in some cases. Simulation of the entire system as demonstrated here is able to address this deficiency. The second area discussed is the analysis of fuel usage and emissions production as a function of engine temperature. An IOL-based optimisation approach is proposed to improve fuel consumption and NOx and PM emissions during the engine's warm up period. The approach was compared to a common technique of using IOLs calculated for hot operation and it was found that improvements of around 5% can be obtained for emissions. However, the scope for optimisation of fuel consumption was negligible due to the relatively stable fuel consumption characteristic during warm up.