Engine Idle Speed Control Performance Assessment Based On The LQG Benchmark

The engine idle speed control represents the most basic vehicle control problemhas a great research meaning. Meanwhile, control performance assessment as arelatively young branch of research in last two decades, has attracted considerableconcern of the academic and engineering. The center content of the paper is to studythe engine idle speed control system, and integrate of the load disturbanceperformance analysis and LQG benchmark performance assessment to4designedPID controllers.First, the background of this paper has been studied, the importance of controlperformance assessment and idle speed control has been described, and thetheoretical research and application development path of control performanceassessment are exhibited in detail, from the Harris index to some of the moreadvanced performance benchmarks. Idle speed control strategy and controlalgorithm is introduced as well.Then, the LQG benchmark performance assessment algorithm is studied. Thebenchmark provides the lower bound in the form of the output and input variances,and also gives the performance limit curve, and the minimum achievable inputvariances corresponding to the output variances and the minimum achievable outputvariances corresponding to the input variances of different weights. Then threealgorithms are studied in detail: based on the state space model, based on polynomialand based on the closed-loop subspace. Next, the use and difference of these threealgorithms is illustrated by a simulation example. The advantages, disadvantages andthe conditions of use of these three algorithms are summarized. But these methodscan only be effective to the situation that without measurable disturbance. In thesituation of containing measurable disturbance, the closed-loop subspace method isextended to be able to handle.Furthermore, based on the mean value model theory and the basic theory of thermodynamic, the mathematical model of the engine idle speed system isestablished, which including the throttle model, intake manifold model, air massflow into the cylinder model, the torque generated model and the inertial model.Engine parameters and data are obtained from the simulation software enDYNA tofit the model parameters. Using Matlab/Simulink to establish nonlinear engine idlespeed system model. Basic calibration of the model on the same input has been doneto prove the validity and accuracy of the model.Finally, basing the established nonlinear engine mean model, a linear discretemodel was developed at the reference work point. With throttle opening angle as thecontrol input, load torque as the disturbance input, engine speed as the control output,intake manifold pressure and speed as the state variables, a state space equation isestablished. PID control principle is applied to control design of idle speed system.Finally, performance assessment of load disturbance rejection and based on the LQGbenchmark was carried out for4designed PID controller. The assessment of loaddisturbance rejection performance can evaluate the response when an abrupt loadtorque work on engine idle speed control system. The LQG benchmark performanceassessment can evaluate the response of noise in the input and output and load torquedisturbance. The closed-loop input and output operate data was used to calculate theperformance of the control loop. The combination of these two performanceassessments can help the engineer or the driver to take remedial measures in thedesign step and before the failure.