17-05-2012, 12:03 PM
Antilock-Braking System Using Fuzzy Logic
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Abstract
This paper deals with study and tests on an experimental car with antilock-braking system (ABS) and vehicle speed estimation using fuzzy logic. Vehicle dynamics and braking systems are complex and behave strongly non-linear which causes difficulties in developing a classical controller for ABS. Fuzzy logic, however facilitates such system designs and improves tuning abilities. The underlying control philosophy takes into consideration wheel acceleration as well as wheel slip in order to recognize blocking tendencies. The knowledge of the actual vehicle velocity is necessary to calculate wheel slips. This is done by means of a fuzzy estimator, which weighs the inputs of a longitudinal acceleration sensor and four wheel speed sensors. If lockup tendency is detected, magnetic valves are switched to reduce brake pressure. Performance evaluation is based both on computer simulations and an experimental car. To guarantee realtime ability (one control cycle takes seven milliseconds) and to relieve the electronic control unit (ECU), all fuzzy calculations are made by the fuzzy coprocessor SAE 81C99A. Measurements in the experimental car prove the functionality of this automotive fuzzy hardware system.
Introduction
Fuzzy Control, a relatively new, intelligent, knowledge based control technique performs exceptionally well in nonlinear, complex and even in not mathematically describable systems. Thus the use of fuzzy logic for an antilock-braking system (ABS) seems to be promising.
Antilock-Braking Systems
The aim of an ABS is to minimize brake distance while steerability is retained even under hard braking. To understand the underlying physical effect which leads to wheel-blocking during braking, consider Figure 1a:
Vehicle Speed
A crucial point in the development of wheel slip control systems is the determination of the vehicle speed. There are several methods possible: until now the velocity is measured with inductive sensors for the wheel rotational speed. Especially in the case of brake slips the measured speed does not correspond with reality. To obtain very accurate results, optical or microwave sensors take advantage of a correlation method. However, these sensors are very expensive and will not be used for ABS.
Sensors and Actuators
The experimental car was fitted with sensors and actuators shown in Figure 2. Each wheel is connected to a metallic gearwheel, which induces a current within an attached sensor. The frequency of the rectangular shaped current is proportional to the angular frequency w i, j and can be evaluated by a microcontroller. Inaddition to common ABS fitted cars, a capacitive acceleration sensor for measuring the longitudinal acceleration ax is implemented.
[attachment=22225]
Abstract
This paper deals with study and tests on an experimental car with antilock-braking system (ABS) and vehicle speed estimation using fuzzy logic. Vehicle dynamics and braking systems are complex and behave strongly non-linear which causes difficulties in developing a classical controller for ABS. Fuzzy logic, however facilitates such system designs and improves tuning abilities. The underlying control philosophy takes into consideration wheel acceleration as well as wheel slip in order to recognize blocking tendencies. The knowledge of the actual vehicle velocity is necessary to calculate wheel slips. This is done by means of a fuzzy estimator, which weighs the inputs of a longitudinal acceleration sensor and four wheel speed sensors. If lockup tendency is detected, magnetic valves are switched to reduce brake pressure. Performance evaluation is based both on computer simulations and an experimental car. To guarantee realtime ability (one control cycle takes seven milliseconds) and to relieve the electronic control unit (ECU), all fuzzy calculations are made by the fuzzy coprocessor SAE 81C99A. Measurements in the experimental car prove the functionality of this automotive fuzzy hardware system.
Introduction
Fuzzy Control, a relatively new, intelligent, knowledge based control technique performs exceptionally well in nonlinear, complex and even in not mathematically describable systems. Thus the use of fuzzy logic for an antilock-braking system (ABS) seems to be promising.
Antilock-Braking Systems
The aim of an ABS is to minimize brake distance while steerability is retained even under hard braking. To understand the underlying physical effect which leads to wheel-blocking during braking, consider Figure 1a:
Vehicle Speed
A crucial point in the development of wheel slip control systems is the determination of the vehicle speed. There are several methods possible: until now the velocity is measured with inductive sensors for the wheel rotational speed. Especially in the case of brake slips the measured speed does not correspond with reality. To obtain very accurate results, optical or microwave sensors take advantage of a correlation method. However, these sensors are very expensive and will not be used for ABS.
Sensors and Actuators
The experimental car was fitted with sensors and actuators shown in Figure 2. Each wheel is connected to a metallic gearwheel, which induces a current within an attached sensor. The frequency of the rectangular shaped current is proportional to the angular frequency w i, j and can be evaluated by a microcontroller. Inaddition to common ABS fitted cars, a capacitive acceleration sensor for measuring the longitudinal acceleration ax is implemented.