31-12-2010, 02:02 PM
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Introduction
Engine and other automobile systems are increasingly controlled electronically. This has led to improved fuel economy, reduced pollution, improved driving safety and reduced manufacturing costs. However the automobile is a hostile environment: especially in the engine compartment, where high temperature, humidity, vibration, electrical interference and a fine cocktail of potentially corrosive pollutants are present. These hostile factors may cause electrical contacts to deteriorate, surface resistances to fall and sensitive electronic systems to fail in a variety of modes. Some of these failure modes will be benign, whereas others may be dangerous and cause accidents and endanger to human life.
A cruise control system, or vehicle speed control system can keep a vehicle's speed constant on long runs and therefore may help prevent driver fatigue [2-5]. If the driver hands over speed control to a cruise control system, then the capability of the system to control speed to the set value is just as critical to safety as is the capability of the driver to control speed manually. So the cruise control system design is imperative and important to an automobile.
Summary
To keep an automobile’s speed constant, a speed control design method using fuzzy logic is
presented. PI fuzzy controller and PD fuzzy controller design schemes are given to regulate a vehicle’s speed to a driver-specified value. The simulation results show the validity and of the proposed technique.
The control design procedure can be summarized as follows:
① Modeling and performance objectives
Basically, the role of modeling a fuzzy control design is quite similar to its role in
conventional control system design. In fuzzy control there is a more significant emphasis on the use of heuristics. Conventional feedback controller design entails constructing a controller to meet the closed-loop specifications (such as disturbance rejection properties, insensitivity to plant parameter variations, stability, overshoot, steady-state error et al), which is also applied to fuzzy control design.
② Fuzzy controller design
Fuzzy control design essentially amounts to (1) choosing the fuzzy controller inputs and
outputs (2) choosing the preprocessing that is needed for the controller inputs and possibly postprocessing that is needed for the outputs, and (3) designing the four components of the fuzzy controller: (a) The fuzzification interface simply modifies the inputs so that they can be interpreted and compared to the rules in the rule-base. (b) The “rule-base” holds the knowledge, in the form of a set of rules, of how best to control the system. © The inference engine evaluates which control rules are relevant at the current time and then decides what the input to the plant should be. And (d) the defuzzification interface converts the conclusions reached by the inference engine into the inputs to the plant.
③ Computer simulation
To prove the effectivity of the controller design and check up whether the design requirements are realized or not.