Emission and Drivability Tradeo s in a Variable Cam Timing SI Engine with Electronic Throttle

Tradeo s between low feedgas emissions and smooth brake torque are discussed in the context of an engine equipped with variable camshaft timing VCT The use of VCT lowers the generation of feedgas emissions but adversely a ects the torque response However with the addition of an electronic throttle and knowledge of online torque the tradeo s between emissions and drivability in the VCT engine can be lessened conventional non VCT engine torque response can be achieved while simultane ously preserving most of the emissions bene ts gained by using VCT Introduction Previous papers have described the use of variable cam timing VCT in a conventional SI engine to reduce HC and NOx feedgas emissions while simultaneously im proving fuel economy It was noted in that there are signi cant interactions between the performance outputs torque TQ cam phasing CAM and air fuel ratio A F These interactions impose tradeo s among drivability feedgas emissions and catalytic converter ef ciency In particular the quicker the cam actuator can move the faster feedgas emissions can be lowered On the other hand moving the cam too quickly will result in large deviations from stoichiometric air fuel ratio as well as hesitation in torque response both of which are unde sirable The authors in regulate air fuel ratio using a multivariable controller the problem of regulating torque response in a VCT engine was not directly addressed It has been observed that tradeo s among drivabil ity fuel economy and emissions are less severe with the availability of an electronic throttle In this paper we study how this additional actuator together with an on line torque sensor allow us to preserve the feedgas emis sions improvements shown in while maintaining the torque performance of a conventional engine We will de sign a multivariable feedback controller to assess the performance improvements a orded by the new actu ator and sensor Our control design expands the usage of retarded cam phasing over a larger operating regime Control Systems Laboratory Department of Electrical Engi neering and Computer Science University of Michigan Ann Arbor MI work supported in part by the National Science Foundation under contract NSF ECS and FORDMO CO Ford Motor Company Scienti c Research Laboratory PO Box Mail Drop SRL Dearborn MI of the engine to further lower emissions and improve fuel economy The term VCT w ET will be used throughout the rest of this paper to represent a VCT engine using an electronic throttle and online torque sensor VCT w MT denotes a VCT engine using a mechanical throttle linkage and conventional engine refers to an equivalent engine with xed cam timing and mechanical throttle linkage