TECHNICAL FIELD

The present invention is related to fuel gauge calibration using PWM (Pulse Width Modulation).

BACKGROUND

The Fuel gauges used in the instrument cluster are indicated by C3 system. These gauges are controlled by the resistance values from the tank unit of the vehicle, the gauges are of very low accuracy at a tolerance of 7 ° angle. When these C3 gauges are produced in large quantity consistency between the gauges is poor. In order to maintain the consistency each and every C3 system can be calibrated using microcontroller, which controls the instrument cluster.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Figure 1 shows block diagram of the fuel gauge calibrating system.

Figure 2 shows LCD Display of instrument cluster displaying fuel level.

Figure 3 shows detailed block diagram representation of fuel gauge calibrating system.

DETAIL DESCRIPTION

The primary embodiment of the invention is a method for calibrating fuel gauge comprising acts of varying fuel gauge resistance to a predetermined level; setting upper digit value of the fuel gauge to a predefined check point value by applying pulse width modulation (PWM) pulses; and setting bottom digit of the fuel gauge to a predefined tolerance count value by applying PWM pulses for calibrating said fuel gauge.
In yet another embodiment of the method the check point value ranges from about 1 unit to about 7 units.

In still another embodiment of the method the tolerance count value ranges from about 0.1 to about 0.6.

In still another embodiment of the method the PWM pulses are produced from microcontrollers.

In still another embodiment of the method the PWM pulses have varying duty cycle.
Another embodiment of the present invention is a system to calibrate fuel gauge comprises fuel gauge to measure fuel level in fuel tank; instrument cluster with LCD Display, wherein LCD displays readings of the fuel gauge; and microcontroller to generate PWM (pulse width modulation) pulses at predetermined intervals to calibrate the fuel gauge.

In yet another embodiment of the present invention the instrument cluster comprises key switches to vary reading of the fuel gauge.

In still another embodiment of the present invention the fuel gauge comprises fuel sensing circuit to sense fuel level of a fuel tank in vehicles.

In still another embodiment of the present invention the fuel gauge indicates the value sensed by the fuel sensing circuit.

The present invention provides calibration method and system for fuel gauges. C3 fuel gauges when produced in large quantity consistency between the gauges are poor. In order to maintain the consistency each and every C3 system can be calibrated using microcontroller, which controls the instrument cluster.

The Fuel gauges used in the instrument cluster are indicated by C3 system. These gauges are controlled by the resistance values from the tank unit of the vehicle, the gauges are of very low accuracy at a tolerance of 7 ° angle. In order to compensate the accuracy, PWM (Pulse Width Modulation) pulses generated by the microcontroller are used for the respective resistance input from the tank unit.

The PWM pulses of varying duty cycle are produced using microcontroller (02) and applied as input to the fuel gauge (01). By using the PWM pulses accuracy of the Fuel indication is achieved.

The fuel value of the float unit is sensed by the fuel sensing circuit (03) the corresponding indication for the fuel sensed is indicated by fuel gauge (01). The block diagram of the same is shown in figure 1. The microcontroller provides the PWM pulse signal to the fuel gauge to indicate the angular position which is shown in the figure 3. Depending on the angle indicted by the fuel gauge for the checkpoint values, if the fuel gauge indication does not fall within tolerance angle, the PWM pulses for which the angle indicated is adjusted in such a manner to meet the tolerance value. The detail schematic diagram of the fuel gauge along with the microcontroller is shown in the figure 3.

For every resistance input from the tank unit the micro controller produces pulses of different duty cycle in a 200Hz frequency. The respective duty cycle for specified level as follow:

For the above duty corresponding level is indicated in the fuel gauge. The corresponding angle indicated by the pointer can be adjusted by using calibration because the angle indication varies from gauge to gauge for the same duty cycle input.

The following provides the fuel gauge calibration procedure:

The first step is to set the fuel gauge Resistance at FULL level i.e. by pressing the set switch (04) for more than 10Sec at Trip B. Thus the cluster enters into fuel calibration mode.

Next step is to continuously press the MODE switch to select Upper digit. The upper digit is as shown in the figure 2 in the LCD display. Then set the respective CHECK POINT (1 TO 7) by single pressing SET switch (04) and then it enters into bottom digit.
Third step is selecting the Bottom digit by continuous pressing the MODE switch as and setting the respective TOLERANCE COUNT (0.1 TO 0.6) by single pressing SET switch. The bottom digit is as shown in the figure 2 in the LCD display. Then the cluster exit out of calibration mode.

Calibration is possible only when odometer value is less than 30KM, and only at descending sequence.

By choosing the digits as per the table calibration can be done for the respective check points. The following table 1 shows the check points and the corresponding values during the calibration.

Table 1:

After calibrating the check point immediate response can be observed by again entering into calibration mode

The technique used in the present invention reduces the rework process and rejection ratio due to out of tolerance in indicated angle. PWM calibration using press switches is without any high cost impact. Already existing calibrations is done by using I2C techniques which involve a high cost implementation in production line.

Finally, while the present invention has been described with reference to a few specific embodiments, the description is illustrative of the invention and is not to be construed as limiting the invention. Various modifications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.

We Claim:

1. A method for calibrating a fuel gauge comprising acts of:

a. varying fuel gauge resistance to a predetermined level;

b. setting upper digit of the fuel gauge to a predefined check point value by applying pulse width modulation (PWM) pulses; and

c. setting bottom digit of the fuel gauge to a predefined tolerance count value by applying PWM pulses for calibrating said fuel gauge.

2. The method as claimed in claim 1, wherein the check point value ranges from about 1 unit to about 7 units.

3. The method as claimed in claim 1, wherein the tolerance count value ranges from about 0.1 to about 0.6.

4. The method as claimed in claim 1, wherein the PWM pulses are produced by a microcontroller.

5. The method as claimed in claim 1, wherein the PWM pulses have varying duty cycle of 34%, 56% and 78%.

6. A system to calibrate fuel gauge (01) comprises:

a. fuel gauge (01) to measure fuel level in fuel tank;

b. instrument cluster with LCD Display, wherein LCD displays readings of the
fuel gauge; and

c. microcontroller (02) to generate PWM (pulse width modulation) pulses at
predetermined intervals to calibrate the fuel gauge.

7. The system as claimed in claim 6, wherein the instrument cluster comprises key switches (04) to set the fuel gauge reading.

8. The system as claimed in claim 6, wherein the fuel gauge (02) comprises fuel sensing circuit (03) to sense fuel level of a fuel tank in vehicles.

9. The system as claimed in claim 8, wherein the fuel gauge indicates the value sensed by the fuel sensing circuit (03).