AN ADAPTIVE MICROPROCESSOR-BASED IDLE MODE CONTROL SYSTEM FOR MULTICYLINDER INTERNAL COMBUSTION ENGINES
Abstract
The optimum idle operating point of an internal combustion engine, in terms of fuel economy, emission levels, and idle quality (roughness), is a function of engine operating and environmental conditions. In current idle speed control systems the idle operating point is defined by an idle speed set-point, typically a preprogrammed function of the measured engine coolant temperature. These control systems do not have the capability of adjusting the idle operating point for changing environmental or engine operating conditions. In these systems the idle speed set-point is set sufficiently high to assure a smooth idle over the wide range of environmental and engine operating conditions encountered. This thesis reports on the results of a project undertaken to develop an idle mode control system with the ability to adjust the idle operating point in response to changes in engine operating and environmental conditions. The system developed continually identifies and maintains idle operation at the optimum operating point, defined in terms of engine crankshaft speed (fuel consumption) and roughness level, under any operating conditions. Thus, the idle mode control system redefines the idle speed set-point based on the current operating conditions. The basis for the idle mode control system reported herein, is the roughness index, a quantitative measure of the engine roughness level. A technique for determining the roughness index based on the cyclic fluctuations of the engine crankshaft speed was developed. The validity of this technique was verified both on a digital computer engine simulation model and experimentally on a test engine. Excellent correlation between the measured roughness index and predicted results were obtained. The hardware and software necessary to implement the idle mode control system were developed. Results of experimental studies on a test engine verified that the controller is capable of responding to changes in the engine roughness level introduced as a result of varying air-to-fuel ratios. The results also demonstrate the ability of the idle mode control system to adaptively adjust the idle operation for changing engine operating temperatures.
Degree
Ph.D.
Subject Area
Mechanical engineering
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