Design and Implementation of Microcontroller Based Motor Vehicle Speed Governor using a Magnetostrictive Amorphous Wire Speed Sensor

Abstract

Kenya is ranked among countries with highest rate of road accidents globally by world health organization. The government has put in place several systems to curb accidents and among them is a vehicle speed governor. This is a device which limits top speed of a vehicle. This research focused on an electronic vehicle speed governor which consists of three key elements namely: vehicle speed sensor, controller unit and actuator. There are various systems to prevent excessive speeding in roads and highways. These include use of Intelligent Speed Adaptation (ISA) system and speed governors. Most developing countries like Kenya adopt use of speed governors since ISA requires immense infrastructural investment. Design and performance of a vehicle speed governor depends highly on the speed sensing mechanism. Some conventional vehicle speed sensor such as variable reluctance sensor whose output signal is of a low magnitude and voltage pulse magnitude depends on shaft speed and requires complex circuitry for signal processing. Another problem experienced with current speed governors is vehicle jerking when top speed limit is attained. This is due to sudden fuel cut to the engine at top speed limit. To address this problem, this research focused on design of a vehicle speed governor prototype using Magnetostrictive Amorphous Wire (MAW) as speed sensor which has various advantages over variable reluctance sensor such as stable voltage pulses, voltage pulse output with appreciable high magnitude and also digital signal that is easy to interface with digital devices. It also involved design of control algorithm based on Pulse Width Modulation (PWM) technique to enable gradual fuel control when top vehicle speed is attained. xiv This thesis presents design and implementation of the vehicle speed sensor using MAW sensor in a vehicle, circuits for signal processing and speed governor control unit. A microcontroller based algorithm for the speed governor based on PWM duty cycle was also developed and experiments conducted through simulation and actual experiments. For the speed sensor, results obtained show that it is a good choice for vehicle speed sensing and its unique features provide an excellent platform for interfacing with the control unit developed. With the control unit developed using atmega 32 microcontroller, speed processing and display was achieved. From the results obtained, it was concluded that the MAW sensor and use of PWM algorithm could be a suitable choice for application in automotive industry for vehicle electronic speed governor development.