Patent ID: 8268494

Claim:
A method of controlling a fuel cell system to detect airtightness, wherein the fuel cell system includes: a fuel cell having a fuel gas passage and an oxidizing gas passage which are so formed as to be in contact with an anode and a cathode respectively, the anode and the cathode being formed on opposed sides of a polymer electrolyte membrane respectively; a fuel gas feeder configured to feed a fuel gas to said fuel gas passage; an oxidizing gas feeder configured to feed an oxidizing gas to said oxidizing gas passage; a fuel gas exhaust passage configured to flow an excessive fuel gas discharged from said fuel gas passage; an oxidizing gas exhaust passage configured to flow an excessive oxidizing gas discharged from said oxidizing gas passage; a test gas feeder configured to feed a test gas to either said fuel gas passage or said oxidizing gas passage; a flow rate detector configured to detect a flow rate of the test gas; a first passage blocking device configured to block off either said fuel gas exhaust passage or said oxidizing gas exhaust passage to which the test gas is fed; a second passage blocking device and a third passage blocking device which are configured to respectively block off gas passages connected to an outlet side and an inlet side of said fuel gas passage which is not fed with the test gas, or respectively block off gas passages connected to an outlet side and an inlet side of said oxidizing gas passage which is not fed with the test gas; and a controller; wherein the method comprises the steps of: (a) controlling, by the controller, said first to third passage blocking devices to block off their associated passages, and the test gas feeder to feed the test gas to the fuel cell, and obtaining a first airtightness value of said flow rate detector, (b) controlling, by the controller, said first passage blocking device to block off its associated passage, while controlling said second and third passage blocking devices so as not to block off either of their associated passages, and obtaining a second airtightness value of said flow rate detector; and (c) obtaining a difference between the first airtightness value and the second airtightness value to determine airtightness of the fuel cell.