Fuel cell system

Abstract

The present invention provides a fuel cell system that can quickly decrease a current/voltage characteristic. A fuel cell system includes an introduction piping which connects a discharging piping and a supply piping in communication with each other, and which introduces part of oxidant-off gas in the supply piping, and a circulation on-off valve provided in the introduction piping. The fuel cell system decreases the supply amount of air by an air compressor when a fuel cell is activated at a low temperature to decrease the air-stoichiometry of the fuel cell, and opens the circulation on-off valve to introduce the oxidant-off gas in the supply piping through the introduction piping, thereby causing the oxidant-off gas to circulate.

What is claimed is: 
     
         1 . A fuel cell system comprising:
 a fuel cell which comprises an anode and a cathode and which generates power when a fuel gas and an oxidant gas are supplied to the anode and the cathode, respectively;   an oxidant gas supplying unit that supplies the oxidant gas to the cathode;   an oxidant gas supplying flow channel through which the oxidant gas to be supplied to the cathode flows;   an oxidant-off gas discharging flow channel through which an oxidant-off gas discharged from the cathode flows;   an oxidant-off gas introducing flow channel which is in communication with the oxidant-off gas discharging flow channel and the oxidant gas supplying flow channel, and which introduces part of the oxidant-off gas to the oxidant gas supplying flow channel;   a circulation on-off valve provided in the oxidant-off gas introducing flow channel;   a stoichiometry decreasing process unit which decreases a supply amount of the oxidant gas by the oxidant gas supplying unit when a predetermined condition is satisfied and decreases a stoichiometry of the oxidant gas of the fuel cell to decrease a current/voltage characteristic of the fuel cell; and   an oxidant-off gas circulating process unit which opens the circulation on-off valve after a process by the stoichiometry decreasing process unit to introduce the oxidant-off gas into the oxidant gas supplying flow channel through the oxidant-off gas introducing flow channel, and causes the oxidant-off gas to circulate.   
     
     
         2 . The fuel cell system according to  claim 1 , further comprising a low-temperature activation determining unit which determines whether or not the fuel cell is in a low-temperature activation condition when the fuel cell is activated,
 wherein when determining that the fuel cell is in a low-temperature activation condition, the low-temperature activation determining unit determines that the predetermined condition is satisfied.   
     
     
         3 . The fuel cell system according to  claim 1 , further comprising a discharging on-off valve provided in the oxidant-off gas discharging flow channel at a downstream side of a communication point with the oxidant-off gas introducing flow channel,
 wherein the oxidant-off gas circulating process unit opens the circulation on-off valve and closes the discharging on-off valve.   
     
     
         4 . The fuel cell system according to  claim 2 , further comprising a discharging on-off valve provided in the oxidant-off gas discharging flow channel at a downstream side of a communication point with the oxidant-off gas introducing flow channel,
 wherein the oxidant-off gas circulating process unit opens the circulation on-off valve and closes the discharging on-off valve.   
     
     
         5 . The fuel cell system according to  claim 2 , further comprising a discharging on-off valve provided in the oxidant-off gas discharging flow channel at a downstream side of a communication point with the oxidant-off gas introducing flow channel,
 wherein the oxidant-off gas circulating process unit opens the circulation on-off valve and closes the discharging on-off valve.   
     
     
         6 . The fuel cell system according to  claim 1 , further comprising a current/voltage characteristic attainment determining unit which determines whether or not the current/voltage characteristic reaches a predetermined current/voltage characteristic,
 wherein when the current/voltage characteristic attainment determining unit determines that the current/voltage characteristic reaches the predetermined current/voltage characteristic, the stoichiometry decreasing process unit terminates the process of decreasing the stoichiometry.   
     
     
         7 . The fuel cell system according to  claim 2 , further comprising a current/voltage characteristic attainment determining unit which determines whether or not the current/voltage characteristic reaches a predetermined current/voltage characteristic,
 wherein when the current/voltage characteristic attainment determining unit determines that the current/voltage characteristic reaches the predetermined current/voltage characteristic, the stoichiometry decreasing process unit terminates the process of decreasing the stoichiometry.   
     
     
         8 . The fuel cell system according to  claim 3 , further comprising a current/voltage characteristic attainment determining unit which determines whether or not the current/voltage characteristic reaches a predetermined current/voltage characteristic,
 wherein when the current/voltage characteristic attainment determining unit determines that the current/voltage characteristic reaches the predetermined current/voltage characteristic, the stoichiometry decreasing process unit terminates the process of decreasing the stoichiometry.   
     
     
         9 . The fuel cell system according to  claim 4 , further comprising a current/voltage characteristic attainment determining unit which determines whether or not the current/voltage characteristic reaches a predetermined current/voltage characteristic,
 wherein when the current/voltage characteristic attainment determining unit determines that the current/voltage characteristic reaches the predetermined current/voltage characteristic, the stoichiometry decreasing process unit terminates the process of decreasing the stoichiometry.   
     
     
         10 . The fuel cell system according to  claim 1 , further comprising a clocking unit that counts a time elapsed after a decrease of the stoichiometry is started,
 wherein when the elapsed time counted by the clocking unit reaches a predetermined time, the stoichiometry decreasing process unit terminates the process of decreasing the stoichiometry.   
     
     
         11 . The fuel cell system according to  claim 2 , further comprising a clocking unit that counts a time elapsed after a decrease of the stoichiometry is started,
 wherein when the elapsed time counted by the clocking unit reaches a predetermined time, the stoichiometry decreasing process unit terminates the process of decreasing the stoichiometry.   
     
     
         12 . The fuel cell system according to  claim 3 , further comprising a clocking unit that counts a time elapsed after a decrease of the stoichiometry is started,
 wherein when the elapsed time counted by the clocking unit reaches a predetermined time, the stoichiometry decreasing process unit terminates the process of decreasing the stoichiometry.   
     
     
         13 . The fuel cell system according to  claim 4 , further comprising a clocking unit that counts a time elapsed after a decrease of the stoichiometry is started,
 wherein when the elapsed time counted by the clocking unit reaches a predetermined time, the stoichiometry decreasing process unit terminates the process of decreasing the stoichiometry.