Unified Framework for Detection and Mitigation of Cyclic Torque Imbalance in Gasoline Engines
Torque imbalance is a wide-ranging problem, common in all internal combustion engines irrespective of their type. It is desirable to achieve consistent torque contribution from engine cylinders to prevent excessive torsional vibrations in the crankshaft. Torque generation is not smooth in internal combustion engines as successive work phases of the combustion cycle produce periodically time-varying torque. Thus, the role of torque imbalance control is signicant in reducing such variations. In the last three decades, considerable research efforts have been made to improve engine control systems for compliance with policies and regulations to minimize exhaust emissions and enhance fuel economy. Progression in the eld of electronics and embedded systems has made it possible to implement complex control techniques in a small-scale engine control unit.
Cyclic torque imbalance is one of the types of engine torque imbalance, which exists due to variations in the torque, generated by combustion cycles in an engine cylinder. It causes non-smooth engine power and excessive stresses in engine components. Minimizing imbalance in the cyclic torque is important to achieve better fuel economy, reduced exhaust emissions and limit degradation as well as aging effects of engine components. Although, cyclic torque imbalance was sporadically studied; however, it was not considered a concern until measurement of consecutive engine cycles was made possible. Cyclic torque balancing approach is comprised of detecting imbalance in the torque and mitigating its causes to decrease the difference between work output of successive combustion cycles in an engine cylinder.
In this dissertation, a model based novel unied framework is proposed for detection and mitigation of cyclic toque imbalance in gasoline engines. First Principle Based Engine Model is employed to formulate the proposed framework, which is comprised of sliding mode based observer and fault tolerant controller. Uniform second order sliding mode observer is used for estimation of the unknown input i.e. net piston force (fn) from engine speed dynamics to detect imbalance in the cyclic torque. No extra sensors and hardware are required for evaluation of the proposed estimation technique. Fault in fuel injection subsystem is induced to generate imbalance
in the cyclic torque. Model of single cylinder gasoline engine is developed in GT-Power to validate the proposed estimation technique. First Principle Based Engine Model is transformed to get direct relation between engine speed and injector pulse width. Estimated net piston force ( ^ fn) is used to design the control law for observer based fault tolerant control techniques to mitigate imbalance in the cyclic torque by reconguration of the control input and attenuation of the fault in fuel injection subsystem. Results of numerical simulation have demonstrated that desired objective is achieved by the proposed model based unied framework.
Another contribution of the research work presented in this dissertation is to propose a fault tolerant speed tracking control technique for gasoline engines. Variations appear in engine speed due to torque imbalance. Output speed of the engine is kept at prescribed set-points, despite occurrence of the fault in fuel injection subsystem. The proposed technique is also robust to disturbances in the form of fluctuating load torque. Transformation in First Principle Based Engine Model is employed for torque management by tracking varying speed prole of the engine. Reference data is acquired from engine test rig to validate the proposed fault tolerant speed tracking control technique.