DESIGN AND CONSTRUCTION OF A LOW FUEL INDICATOR SYSTEM
Fuel low level indicator is an instrument used to indicate the level of fuel contained in a tank. Commonly used in most motor vehicles. As used in vehicles, the device consists of two parts: The sensing unit and the indicator
The sensing unit usually uses a float connected to a potentiometer, typically printed ink design in a modern automobile. As the tank empties, the float drops and slides a moving contact along the resistor, increasing its resistance
A low fuel indicator system for a motor vehicle comprises a light-emitting indicator which is energized or de-energized by an output signal derived from a voltage comparator which receives a reference voltage from a reference voltage source and a variable voltage signal from a time delay circuit, which variable voltage signal is derived from a voltage signal generated by a fuel level sensor in a fuel tank of the vehicle. The light-emitting indicator is energized when the fuel level in the fuel tank falls below a predetermined low level, and time delay circuit operates to isolate the voltage comparator and light-emitting indicator from temporary variations in fuel level produced by "fuel-slosh" in the fuel tank caused by variations in the motion or orientation of the motor vehicle.
CHAPTER ONE
1.0 INTRODUCTION
This invention relates to a low fuel indicator system for a motor vehicle for monitoring the operation of a fuel level sensor in a fuel tank in said motor vehicle, and, in particular, to a low fuel indicator system in which a visible indicator means is used to indicate that a predetermined low level of fuel has been reached in a fuel tank of a motor vehicle.
Motor vehicles customarily use a fuel level sensor in the fuel tank which monitors the change in level of the fuel contained within the tank and transmits an indication of the fuel level as an electrical signal, quite commonly a voltage signal, to an electrically operable fuel gauge situated on an instrument panel of the motor vehicle. It is customary to have such fuel gauges calibrated in terms of the quantity of fuel remaining in the fuel tank, and to mark distinctively one end of the scale reading to indicate that the fuel level has fallen to such a low level that re-fueling of the tank is required. Unfortunately, this warning portion of the scale of the fuel indicator tends to be small, and easily overlooked by a driver of the motor vehicle. Consequently, there is a need for said driver of the vehicle to be made aware of the low level of fuel in the tank by means of an easily visible indicator means, preferably one that is a light-emitting means. The operation of such a light-emitting means would then quickly and effectively call the attention of the driver to the fact that fuel level in the tank was becoming unacceptably low. It is desirable in such a system that the light-emitting indicator means should indicate accurately when a predetermined level of fuel has been reached in the tank, but it is necessary to avoid, in this respect, any tendency for such a light-emitting indicator means to become energized as a result of the fuel in the fuel tank varying rapidly in level due to motion of the motor vehicle and/or orientation of the motor vehicle relative to the road surface.
A low fuel indicator system according to the present invention, for monitoring the operation of a fuel level sensor in a fuel tank in a motor vehicle, comprises a light-emitting indicator means connected to a voltage comparator means having two inputs thereto, one of said inputs being derived from a reference voltage source and the other of said inputs being derived from a voltage signal produced from a time delay circuit when said time delay circuit is provided with a voltage signal from said fuel sensor, said voltage comparator means being operable, when the system is installed in said motor vehicle, to compare said two inputs so as to energize said light-emitting indicator means when said fuel sensor voltage signal corresponds to a predetermined low level of fuel in said tank and to de-energize said light-emitting indicator means when said fuel sensor voltage signal corresponds to levels of fuel above said predetermined level, said time delay circuit on said other of the inputs to the comparator being operable so as to substantially isolate the comparator from the effects of rapid fluctuations in fuel level in said tank caused by motion or orientation of the motor vehicle.
Preferably the low fuel indicator system includes a time delay override circuit which is operable, when the system is installed in motor vehicle, to by-pass the time delay circuit for a short predetermined time period when the ignition system of said motor vehicle is initially switched on, and is then rendered non-operable at the end of said short predetermined time period.
In this, the light-emitting indicator means is a light-emitting diode, the reference voltage source comprises a resistor network connectable between a regulated voltage source and a ground potential, and the time delay circuit comprises a capacitor connectable between said regulated voltage source and said other input to the comparator means, and a resistor connectable between said fuel level sensor and said other input to the comparator means. Such a low fuel indicator system according to this embodiment finds application in motor vehicles which utilize a regulated voltage source to operate other indicating instruments (such as a bi-metal fuel gauge) on an instrument panel in the motor vehicle. Advantageously, a low fuel indicator system according to this embodiment of the invention is housed in the instrument panel adjacent a fuel gauge connectable to said fuel level sensor.
A second embodiment of the present invention is a low fuel indicator system in which the light-emitting indicator means is an incandescent lamp connected to the output of the voltage comparator means through a transistor switching circuit, the reference voltage source comprising a resistor network connected between a voltage-regulating circuit and a ground potential, and the time delay circuit comprises a capacitor connected between said voltage-regulating circuit and said other input to the comparator means, and a resistor connectable between said fuel level sensor and said other input to the comparator means.
1.2 OBJECTIVE OF THE PROJECT
Low fuel indicator system for monitoring the operation of a fuel level sensor in a fuel tank in a motor vehicle having an ignition system, said indicator system having an input line supplied by the ignition system.
1.3 SIGNIFICACE OF THE PROJECT
A low fuel indicator system is useful in motor vehicles not employing a regulated voltage source for instruments, such as those motor vehicles fitted with an air-core fuel gauge, since the system is designed to operate from direct battery potential. Advantageously a low fuel indicator system forms part of an in-line connector designed to snap into position in an instrument panel wiring harness of a motor vehicle.
1.4 SCOPE OF THE PROJECT
A low fuel indicator system for monitoring the operation of a fuel level sensor in a fuel tank in a motor vehicle having an ignition system, said indicator system having an input line supplied by the ignition system and comprising; voltage comparator means having an output and first and second inputs, a time delay circuit, light-emitting indicator means connected to the output, the first input being connected to a reference voltage source and the second input being connected through the time delay circuit to said fuel level sensor to receive a voltage signal from said fuel sensor, said time delay circuit substantially isolating the comparator from the effects of rapid fluctuations in fuel level in said tank, said voltage comparator means being operable to compare the voltages on said two inputs to energize said light-emitting indicator means when said fuel sensor voltage signal corresponds to a predetermined low level of fuel in said tank, the time delay circuit comprising a capacitor connected between the input line and the second input and a resistor connected between the fuel level sensor and the second comparator input so that when the ignition system is initially switched on a voltage dependent on the capacitor charging rate is applied to the second input to energize the indicator means for a variable time period dependent upon the relative fuel level so that high fuel levels correspond to short indication periods and increasingly lower fuel levels approaching the predetermined low level result in increasingly longer indicator periods, whereby a fuel level indication is provided by the variable time period.
1.5 LIMITATION OF THE PROJECT
The sensor could be affected by corrosion which can lead to malfunction of the device. It is designed to be powered by the automobile battery, that is, by 12v battery.
1.6 PROJECT WORK ORGANISATION
The various stages involved in the development of this project have been properly put into five chapters to enhance comprehensive and concise reading. In this project thesis, the project is organized sequentially as follows:
Chapter one of this work is on the introduction to low fuel indicator. In this chapter, the background, significance, objective limitation and problem of a low fuel indicator were discussed.
Chapter two is on literature review of low fuel indicator. In this chapter, all the literature pertaining to this work was reviewed.
Chapter three is on design methodology. In this chapter all the method involved during the design and construction were discussed.
Chapter four is on testing analysis. All testing that result accurate functionality was analyzed.
Chapter five is on conclusion, recommendation and references.
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