Patent ID: 7189572

Claim:
A method for determining whether water content of an inside of a fuel cell is short of excessive, said method comprising the steps of: measuring water content of the inside of said fuel cell as an index of present water content (PWC) based on conductivity of electrolyte of said fuel cell; estimating, as an index of future water content (FWC), water content of the inside of said fuel cell at a time point when time elapsed after said measuring step is performed reaches a predetermined length; comparing said PWC index and said FWC index; and determining whether the water content of the inside of said fuel cell is short or excessive based on a result of said comparing step; wherein said measuring step comprises the steps of: measuring an output voltage and an output current of said fuel cell; estimating a voltage drop corresponding to resistance of the electrolyte of said fuel cell based on said measured output voltage of said fuel cell; calculating said resistance of said electrolyte by dividing said voltage drop by said measured output current of said fuel cell; calculating a reciprocal of said resistance of said electrolyte; calculating, as measured conductivity, the conductivity of said electrolyte using said reciprocal of said resistance; obtaining inlet-side conductivity of said electrolyte; obtaining saturation conductivity of said electrolyte; and calculating, as said PWC index, a point Xp′ at which conductivity equals said saturation conductivity based on said measured conductivity, said inlet-side conductivity and said saturation conductivity; and at said step of calculating said point Xp′, said point Xp′ is calculated using the following formula: Xp ′=2(σ max −σ mesured )/(σ max −σ in ) where σ max is said saturation conductivity, σ mesured is said measured conductivity, and σ in is said inlet-side conductivity.