FUEL GAUGE FOR AN AUTOMOTIVE VEHICLE

Field of Invention

The present invention relates to a fuel gauge for an automotive vehicle and more particularly to a capacitance based fuel gauge for an automotive vehicle.

Background of Invention

Conventional automobile fuel gauges involve the use of a float type fuel level measuring arrangement. Although, the structure of such fuel gauges is simple, they have numerous limitations and disadvantages such as poor accuracy, low reliability and short life due to damage of float due to mechanical vibrations, thereby leading to high warranty costs. To circumvent all these drawbacks, capacitance based fuel level measurement systems came into use. Capacitance based fuel level measurement systems known in the art, involve the use of tubular or coaxial construction for the capacitor in order to increase the capacitance value. Such systems involve the use of complex circuitry and are difficult to manufacture, consequently, leading to increase in assembly time and higher costs. Further, these systems lack the ability to sense minute changes in capacitance of the order of few tens of picofarads. Also, the known coaxial type capacitance based fuel level measurement systems can fit only in vertical direction and cannot be used in all automotive vehicles.

Therefore, it an object of the present invention to provide a capacitance based fuel gauge for an automotive vehicle capable of sensing minute changes in capacitance of the order of few tens of picofarads. It is also an object of the invention to provide a capacitance based fuel gauge for an automotive vehicle with improved accuracy, improved reliability and durability, having a high degree of freedom of design and which at the same time is cost efficient and is easy to manufacture with simple circuitry.

Summary of the Invention

The present invention is directed to a fuel gauge for an automotive vehicle and particularly deals with a capacitance based fuel gauge. The present invention of the capacitance based fuel gauge comprises a crystal controlled oscillator, a zener clipping circuit, a higher order resistor capacitor (RC) low pass filter, a differentiator, a peak detector and a driver circuit. A square wave form of constant frequency generated by the crystal controlled oscillator is passed to the zener clipping circuit, which aids in maintaining the amplitude of the square wave constant. The output signal from the zener clipping circuit, which is of constant amplitude and constant frequency is fed to the higher order RC low pass filter to get a sine wave with minimal harmonic distortion. This sine wave forms the excitation signal for the differentiator, which comprises a capacitance based fuel level sensor. The capacitance based fuel level sensor is characterized by two Printed Circuit Board (PCB) plates arranged parallely inside a fuel tank of the automotive vehicle. The differentiator comprising the capacitance based fuel level sensor differentiates the sine wave outputted from the higher order RC low pass filter. This differentiated sine wave forms the output signal of the capacitance based fuel level sensor and its amplitude directly corresponds to the level of fuel inside the fuel tank. The peak detector detects the amplitude of this output signal and the driver circuit finally converts the output of the peak detector into appropriate rider readable fuel level information. The present capacitance based fuel gauge thus aids in sensing even minute changes in capacitance of the order of few tens of picofarads.

The nature and further characteristic features of the present invention will be made clearer from the following descriptions made with reference to the accompanying drawings.

Brief Description of Drawings

Figure 1 illustrates a typical two wheeled automotive vehicle.

Figure 2 illustrates a capacitance based fuel gauge according to the present invention.

Detailed Description of the Preferred Embodiments

An embodiment of a capacitance based fuel gauge in accordance to the present invention will be described hereunder with reference to the accompanying drawings. Various features of the capacitance based fuel gauge in accordance to the present invention will become discernible from the following description set out hereunder. It is further to be noted that terms "upper", "lower", "right", "left", "rearward", "forward", "downward" and like terms are used herein based on the illustrated state or in a standing state of an automotive vehicle with a driver riding thereon. Furthermore, a longitudinal axis refers to a front to rear axis relative to the vehicle, while a lateral axis refers to a side to side, or left to right axis relative to the vehicle. It is also to be noted that although the present embodiment is exemplified for a two wheeled automotive vehicle, however, the present embodiment may not be restricted only to a two wheeled automotive vehicle and is applicable to any automotive vehicle which uses liquid fuel. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

Figure, 1 illustrates a typical two wheeled automotive vehicle. The vehicle includes a body frame 19, a fuel tank 56, an engine 41 a front wheel 25, and a rear wheel 27, and. Body frame 19 includes a head pipe 12, a main tube 17, a down tube 22, and seat rails 18. The head pipe 12 is provided at the front end of body frame 19 to support a steering shaft 11 disposed within head pipe 12. The upper and lower ends of the steering shaft 11 are fixed to an upper bracket 13 and a lower bracket 14 respectively. Upper bracket 13 and lower bracket 14 retain front fork 16 that supports the front wheel 25. The front . wheel 25 is connected at the lower end of the front fork 16, and the upper portion of the front wheel 25 is covered by a front fender 54 mounted to a lower portion of the front fork 16. A handlebar 15 is fixed to the upper bracket 13 and can rotate to both sides. A head light 36 is arranged on an upper portion of the front fork 16.

In the front portion of the body frame 19 a fuel tank 56 is arranged immediately behind the handle bar 15 and is disposed over the engine unit 41. The fuel tank 56 is provided therein with a fuel gauge (not shown), which detects a fuel level in the fuel tank 56 and indicates the quantity of remaining fuel to a user.

A down tube 22 extends downwardly and rearwardly from the head pipe 12 and is located in front of the engine 41. A bracket 55 is provided at a lower end of the down tube 22 for supporting the engine 41. A Main tube 17 located above the engine 41 stretches rearwards from the head pipe 12 and connects a rear portion of the engine 41. A vertical pipe 28 is connected to the rear end of main tube 17 and it serves as a connecting portion for seat rails 18. The seat rails 18 extend rearwardly from the main tube 17 to support a seat 57 disposed above the seat rails 18. A side stand 58 is arranged on a lower portion of the engine unit 41. Left and right rear arm bracket portions (not shown) support a swing arm 26, and a rear wheel 27 is connected to rear end of the swing arm 26. A rear wheel suspension 34 is arranged between the swing arm 26 and the seat rails 18. A tail light unit 64 is disposed on a rear cover 61. A pillion footrest 31 is connected to the vertical pipe 28. A grab rail 62 is also provided on the rear of the seat rails 18.

Rear wheel 27 is supported at a rear end of the swing arm 26 and rotates by the driving force of the engine unit 41 transmitted through a transmission system.

Figure 2 illustrates the fuel gauge for an automotive vehicle as per the present invention. The fuel gauge as per the present invention, which is a capacitance based fuel gauge, comprises a crystal controlled oscillator 102, a zener clipping circuit 103, a higher order Resistor-Capacitor (RC) low pass filter 104, a differentiator 105, a peak detector 106 and a driver circuit 107, wherein the differentiator 105 comprises a capacitance based fuel level sensor.

The crystal controlled oscillator 102 generates a constant frequency square wave, which is fed as input to the zener clipping circuit 103. The zener clipping circuit 103 maintains the amplitude of the square wave generated by the crystal controlled oscillator 102 constant. This output of constant amplitude from the zener clipping circuit 103 is fed to the higher order RC low pass filter 104 to get a sine wave with minimal harmonic distortion. This sine wave of minimal harmonic distortion is obtained by maintaining the amplitude and frequency of the sine wave constant and this sine wave thus obtained, acts as an excitation signal for the differentiator 105.

The capacitance based fuel level sensor, comprised in the differentiator 105, is characterized by two Printed Circuit Board (PCB) plates 101 arranged parallely inside the fuel tank 56 of the two wheeled automotive vehicle. The PCB plates 101 are kept partially immersed in the fuel inside the fuel tank 56 and the fuel is admitted in the gap between the PCB plates 101. Capacitance developed between the PCB plates 101 and detected by the sensor is received by the differentiator 105 and the same is differentiated by the differentiator, for which the sine wave received from the RC low pass filter 104 acts as the excitation signal.

The differentiated sine wave forms the output signal of the capacitance based fuel level sensor and its amplitude is detected by the peak detector 106.

Since the dielectric constant of air differs from that of the fuel, the capacitance at the capacitance based fuel level sensor varies according to the area immersed in fuel between the PCB plates 101. As a result, the amplitude of the sine wave outputted from the capacitance based fuel level sensor will be
directly proportional to the fuel level inside the fuel tank 56. A capacitance in the range of 10 picofarads to 500 picofarads can be easily formed at the PCB plates 101 depending on the shape and size of the PCB plates 101. A capacitance in the above mentioned range is obtained by preferably
maintaining the distance between the PCB plates in the range of 0.5mm to 1.0mm. Thus, even minute changes in capacitance of the order of few tens of picofarads corresponding to the change in fuel level inside the fuel tank 56 can be measured by the present fuel gauge. ......

A driver circuit 107 converts an output of the peak detector 106 into appropriate user readable fuel level information.

The construction of the PCB plates can be modified according to the dimensions of the fuel tank. Thereby, the fuel gauge according to the present invention can be used in any automotive vehicle. High accuracy of fuel level measurement is ensured because of the highly stable excitation signal used. Further, manufacturability and cost efficiency is enhanced since the fuel gauge as per the present invention uses only discreet components in its circuitry and hence is very simple in construction.
While the present invention has been shown and described with reference to the foregoing preferred embodiment, it will be apparent to those skilled in the art that changes in form, connection, and detail may be made therein without departing from the spirit and scope of the invention as defined in the appended claims:

We Claim:

1. A fuel gauge for an automotive vehicle, the fuel gauge comprising:

a crystal controlled oscillator which generates a constant frequency square wave;

a zener clipping circuit which maintains constant an amplitude of the square wave generated by the crystal controlled oscillator;

a higher order resistor capacitor (RC) low pass filter which generates a constant frequency constant amplitude sine wave from the square wave outputted by the zener clipping circuit;

a differentiator which differentiates the constant frequency constant amplitude sine wave outputted from the higher order resistor capacitor RC low pass filter, wherein the differentiator comprises a capacitance
based fuel level sensor;

a peak detector which detects amplitude of a differentiated sine wave outputted from the differentiator; and

a driver circuit which generates fuel level information for a rider from an output of the peak detector.

2. A fuel gauge for an automotive vehicle, as claimed in claim 1, wherein the constant frequency constant amplitude sine wave generated by the higher order resistor capacitor (RC) low pass filter acts as an excitation, signal for the differentiator.

3. A fuel gauge for an automotive vehicle, as claimed in claim 1, wherein the capacitance based fuel level sensor is characterized by two Printed Circuit Board (PCB) plates arranged parallely inside a fuel tank of the automotive vehicle.

4. A fuel gauge for an automotive vehicle as claimed in claim 1, wherein distance between the Printed Circuit Board (PCB) plates is in the range 0.5mm to 1mm.

5. A fuel gauge for an automotive vehicle, as claimed in claim 1, wherein the differentiated sine wave outputted from the differentiator forms an output signal of the capacitor based fuel level sensor.

6. A fuel gauge for an automotive vehicle, as claimed in claim 1, wherein amplitude of the differentiated sine wave outputted from the differentiator corresponds to a fuel level inside the fuel tank of the automotive vehicle.

7. A fuel gauge for an automotive vehicle as claimed in claim 1, wherein capacitance in the range of 10 picofarads to 500 picofarads is detected by the capacitance based fuel level sensor.

8. A method for determining a fuel level inside a fuel tank of an automotive vehicle, the method comprising the steps of:

generating a constant frequency square wave by means of a crystal . controlled oscillator;

maintaining constant an amplitude of the square wave generated by the crystal controlled oscillator by means of a zener clipping circuit;

generating a constant frequency constant amplitude sine wave from the square wave outputted by the zener clipping circuit by means of a higher order resistor capacitor (RC) low pass filter;

differentiating the constant frequency constant amplitude sine wave outputted from the higher order resistor (RC) low pass filter by means of a differentiator, wherein the differentiator comprises a capacitor
based fuel level sensor;

detecting an amplitude of differentiated sine wave outputted from the differentiator by means of a peak detector; and

generating fuel level information for a rider from an output of the peak detector by means of a driver circuit.