Intelligent Idle Speed Control for Modern Intelligent Automobiles
Abstract
The paper presents an application of a recently developed Fuzzy logic controller for time-delay systems to the idle speed control (ISC) problem in spark ignition (SI) internal combustion (IC) engines. Automobiles spark ignition engines spend a large percentage of their time operating in the idle speed region. The engine idle speed control system design is a difficult problem because are inherently nonlinear, incorporating variable time delays characteristics exists everywhere between the input and output of an engine. The output time delay which varies inversely with the engine speed makes the control process even harder. Furthermore, disturbances caused by different operating conditions may arise during engine idle speed running. All these reasons have increased difficulties to control the idle speed accurately.
Engines are inherently nonlinear, incorporating variable time delays and discontinuities which make modeling difficult, and for this reason their control is well suited to optimization using Fuzzy logic algorithms. This paper aims to apply Fuzzy logical controller to maintain a constant idle speed, in this experiment, a SAAB B202 engine was used to identify idle speed appearance. The developed model has a control-design oriented philosophy and is capable to significantly minimize the varying of idle speed within an engine speed.
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Introduction
The problem of idle speed control is to maintain the engine speed at a prescribed set-point in the presence of various disturbances such as those due to air conditioning, transmission engagement or power steering accessory load torques [1]. The engine torque is normally adjusted by manipulating the intake air amount or the advance ignition timing according to the disturbance experienced by the engine [2,3]. According to Environmental Protection Administration, R.O.C. experimental statistics, a car stop and go every day, idle time of more than 30 minutes a year will waste 640 liters of gasoline, resulting in 3.4 kg of organic compounds, the release of 54.3 kg of carbon monoxide and 1.4 tons of carbon dioxide [4].
When the automotive release the accelerator, the engines speed slows. At a preset speed the engine idle circuit takes over and the engine runs at the lowest speed possible without stalling. An idle speed around 500 to 900 revolution per minute (RPM). The engine’s idle speed also changes, based on outside conditions. A computer is adjusting the idle speed, based on complex calculations.
In the past, adjusting an engine’s idle speed was easy. Manufactures have removed these adjustments on modern automotives. The engine control module (ECM) now determines the speed at which an engine idles, based on several input sensors manual adjustment of idle speed is not possible on modern automotive and diagnosis of problems is a bit complex.
When the engine has a carburetor, they always provide a means to adjust the idle speed. A simple turn of a screw corrected the problem if the engine’s idle speed was too slow or too fast. With electronic fuel injection they eliminate the manual adjustment and the computer makes all corrections to the engine’s idle speed.
Conclusion
Idle speed control is one of the highest confrontations for automobile industry and researchers as they were addressing many issues in relation to engine stalling at rest position and fuel saving economy. An engine model plays a major role in defining the correct parameters for control system. So, we defined the engine model based on certain aspects and analyzed it properly to fit in the system.
Idle speed control problem is effectively eliminated by the use of intelligent fuzzy logic to control the electronic throttle. In comparison to previously published experiments, less deviation range, and more steady testing period were observed. The experimental result shows that a stable fuzzy logic control can be realized to control the nonlinear hysteretic electronic throttle motor. Results were carried over to the real time implementation of fuzzy logic control to control an actual electronic throttle in Saab 9000. Testing vehicle idle performance additionally increased in stability, and engine vacuum deviation was also escalated.