CLIAMS:I Claim:
1. A method for determining fuel filter contamination in a gaseous fuel powered internal combustion engine, said method comprising the steps of:
determining at least one parameter downstream a fuel filter when gaseous fuel flows through the fuel filter;
determining the parameter(s) determined in step (a) when gaseous fuel flow through the fuel filter is interrupted;
computing the difference between the values determined in step (b) and step (a);
comparing the difference computed in step (c) with a predefined reference value; and
deriving information regarding contamination of the fuel filter based on comparison in step (d).
2. The method for determining fuel filter contamination in a gaseous fuel powered internal combustion engine as claimed in claim 1, wherein the determined parameter is pressure, said pressure measured by means of a pressure sensor disposed downstream the fuel filter.
3. The method for determining fuel filter contamination in a gaseous fuel powered internal combustion engine as claimed in claim 1, wherein the fuel filter is disposed upstream a pressure regulator.
4. The method for determining fuel filter contamination in a gaseous fuel powered internal combustion engine as claimed in claim 1, wherein the fuel filter is disposed downstream a pressure regulator.
5. An electronic control unit for determining contamination of a fuel filter in a gaseous fuel powered internal combustion engine, said electronic control unit operable to:
interrupt gaseous fuel flow through said fuel filter;
compute difference in values of atleast one parameter downstream said fuel filter before and after interruption of gaseous fuel flow in step(a); and
ascertain fuel filter contamination based on comparison of difference computed in step(b) with a predefined reference value preset in said electronic control unit.
6. The electronic control unit for determining contamination of a fuel filter in a gaseous fuel powered internal combustion engine as claimed in claim 5, wherein the parameter determined is pressure and wherein said values of pressure is determined by a pressure sensor disposed downstream said fuel filter.
7. The electronic control unit for determining contamination of a fuel filter in a gaseous fuel powered internal combustion engine as claimed in claim 5, wherein said fuel filter is disposed downstream a pressure regulator.
8. The electronic control unit for determining contamination of a fuel filter in a gaseous fuel powered internal combustion engine as claimed in claim 5, wherein said fuel filter is disposed upstream a pressure regulator. ,TagSPECI:The following specification particularly describes the invention and the manner in which it is to be performed.

Field of Invention
[001] The present invention relates to a method and apparatus for determining fuel filter contamination in a gaseous fuel powered internal combustion engine.

Description of Prior Art
[002] Presence of impurities in gaseous fuel (for eg. oil, particulates) used to power internal combustion engines is commonplace. Such impurities may result in defects in the fuel supply system or fuel injection system of vehicles powered by such internal combustion engines. To avoid this, fuel supply systems of vehicles are generally fitted with fuel filters. Fuel filters trap fuel impurities and prevents exposure of the fuel supply system and fuel injection system to impurities/foreign particles in gaseous fuel. Clogging of fuel filters beyond a particular limit makes it mandatory for it to be replaced after a certain period of time or vehicle usage. Failure to replace fuel filter results in restriction in flow of gaseous fuel, leading to loss of engine power or even to engine stalling.

[003] Vehicle manufacturers generally prescribe replacement intervals for fuel filters (for eg. one year or 20,000kms). This interval varies in case of different vehicles and is chosen with enough safety margins to prevent any issue due to overloaded filter. It is hence probable that fuel filters may get replaced unnecessarily or in other words the fuel filter may get replaced based on the prescription of the vehicle manufacturer even before its best functioning days are over, which in turn leads to higher maintenance costs and wastage. Prior art Patent WO2011158709A1discloses a method that seeks to solve this problem. Said prior art estimates filter contamination by measuring pressure difference across the fuel filter during gaseous fuel operation by employing multiple pressure sensors. The method and apparatus which forms the basis of the present invention discloses an alternative and much improved method for determining fuel filter contamination in a gaseous fuel powered internal combustion engine.

Brief description of drawings
[004] Fig. 1 is a schematic drawing illustrating a first embodiment of the present invention.
[005] Fig. 2 is a schematic drawing illustrating a second embodiment of the present invention.
[006] Fig. 3 is a graphical representation illustrating change in parameter values during working of the present invention.
[007] Fig. 4 is a graphical representation illustrating rate of gaseous flow through the fuel filter during working of the present invention.

Detailed Description of Invention
[008] The present invention is hereinafter described with reference to the accompanying figures. The same reference numerals are used throughout the figures to reference like features and components.

[009] Fuel feed systems in typical gaseous fuel vehicles or bi-fuel vehicles consists of a fuel tank from which fuel is fed to the fuel injectors through fuel feed lines. The gaseous fuel pressure is reduced before it is fed to the fuel injectors using a pressure regulator. As aforementioned, the present invention seeks to disclose an improved method and apparatus for determining fuel filter contamination in a gaseous fuel powered internal combustion engine. Fig. 1 is a schematic drawing illustrating a first embodiment of the present invention. Referring to Fig. 1, gaseous fuel stored in a fuel cylinder 105 is fed to a fuel injection system 104 after passing through a fuel filter 100. As shown in Fig.1, in the first embodiment, the fuel filter 100 is disposed upstream a pressure regulator 103. Fig. 2 is a schematic drawing illustrating a second embodiment of the present invention. In said second embodiment, the fuel filter 100 is disposed downstream the pressure regulator 103.

[0010] The method disclosed in the present invention consists the steps of firstly determining value(s) of one or more parameters downstream the fuel filter 100 when gaseous fuel flows through the fuel filter 100, interrupting gaseous fuel flow through the fuel filter 100 and determining the values(s) of the same parameter or parameters determined in the previous step, computing the difference in values between the parameter(s) determined in the first two steps, that is, computing the difference in value(s) of parameters(s) calculated when gaseous fuel flows through the fuel filter and the when gaseous fuel flow is interrupted and lastly estimating fuel filter contamination by comparing the difference calculated in the previous step with a predefined reference value. The value(s) of the parameter(s) is/are determined by way of sensor(s) 101 arranged downstream the fuel filter 100. The parameter determined could be, for example pressure, and the pressure values are determined by way of a pressure sensor disposed downstream the fuel filter.

[0011] The above disclosed method can be further explained by referring to Fig. 3 and Fig. 4. Said figures graphically illustrate the manner in which the above described method is performed. Pressure is the reference parameter used for plotting graphical representation in Fig. 3 and rate of change of pressure in case of contaminated filters is what is illustrated. It may be noted that pressure is just an example of one of the many parameters that can be determined. Use of ‘pressure’ as the parameter is merely for explanatory purposes and there is no intention whatsoever to limit the scope of this invention to said parameter (pressure).

[0012] The graphical representation in Fig. 3 has been divided into 5 operating zones. Fig. 4 illustrates rate of gaseous fuel flow through the fuel filter 100 for each corresponding operating zone in Fig. 3. The solid line in Fig. 3 illustrates the pressure level downstream the fuel filter 100 when gaseous fuel flow is interrupted or the pressure downstream the fuel filter 100 when the fuel filter contamination level is zero percent. The broken line indicates the pressure level when gaseous fuel flows through a contaminated fuel filter.

[0013] As evident from Fig.3, pressure downstream the fuel filter 100 decreases with increase in fuel filter contamination. Higher the fuel filter contamination, lesser will be the pressure downstream the fuel filter 100. Zone 1 in Fig. 3 illustrates pressure level when gaseous fuel flows through the fuel filter. Zone 1 in Fig. 4 indicates rate of fuel flow through the fuel filter corresponding to Zone 1 in Fig. 3. The corresponding pressure value is determined by a pressure sensor disposed downstream the fuel filter. Zone 2 and Zone 3 in Fig.3 illustrates rise in pressure level when gaseous fuel flow through the fuel filter is interrupted. Interruption in gaseous fuel flow can also be seen indicated in Zone 2 and Zone 3 of Fig.4. Fuel flow is interrupted by a programmable Electronic Control Unit (ECU). This can be done, for example, by closing the fuel injector system 104 in bi-fuel vehicles or by closing a solenoid valve 102. The corresponding pressure value when fuel flow is interrupted is then determined. The pressure values determined in the above two steps is then inputted to the programmable ECU. The ECU is configured to compute the difference between the two pressure values. The ECU is further configured to compare the said difference with a predefined reference value and to thereby estimate fuel filter contamination. The predefined reference value is preset in the ECU. If the difference computed is greater than the predefined reference value, the ECU concludes that the fuel filter is highly contaminated and requires replacement. In such instances, the user is intimated through an indication means in the vehicle user interface. Once the pressure value (when fuel supply is interrupted) is determined, gaseous fuel supply is resumed as indicated in Zone 4 and Zone 5 of Fig. 4. Once gaseous fuel supply is resumed, pressure downstream the fuel filter reduces (in case of contaminated filters) as can be seen in Zone 4 and Zone 5 of Fig. 3.

[0014] Apart from fuel filter contamination; there may be other influencing factors which may lead to variation in parameter(s) downstream the fuel filter 100. Such factors include fuel filter construction, mass flow, fuel feed line dimensions and temperature of the gaseous fuel. Estimation of fuel filter contamination using the method disclosed in the present invention, can be performed in predefined regular intervals based on for example time, driving distance, drive cycle etc.. The present invention can also be used as a service tool in vehicle service centers for failure diagnosis. The accurate determination of fuel filter contamination due to the present invention reduces service costs and ensures that the fuel filter is fully utilized. Further, drawbacks in prior art such as use of multiple parameter sensors are avoided and filter contamination can be estimated during all engine operating conditions.

[0015] The above description is illustrative and there is no intention whatsoever to limit the scope of the invention. All modifications and variations of the present invention which would be obvious to a person skilled in the art are intended to be included within the scope of the following claims. The above mentioned modifications and variations include, but is not limited to, parameters determined, position of mounting/installation of gaseous fuel filter, type and material of fuel filter. The scope of this description is only limited by the scope of the claims.