# US 2008/0187791 A1 · Fuel cell system and scavenging method therefor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2008/0187791 A1 - Document ID: US20080187791A1 - Status: Published application - Kind: A1 - Application number: 12/011,853 - Filed: 2008-01-30 - Published: 2008-08-07 - Earliest claimed: 2007-02-01 - Assignees: Honda Motor Co., Ltd. - Inventors: Yuji Matsumoto; Koichiro Miyata - Web page: https://patentgrep.com/patent/US20080187791A1 ## CPC - H01M 8/04432: {Pressure differences, e.g. between anode and cathode} - H01M 8/04179: {by purging or increasing flow or pressure of reactants} - H01M 8/04231: {Purging of the reactants} - H01M 8/04253: {Means for solving freezing problems} - H01M 8/04358: {of the coolant} - H01M 8/04746: Pressure; Flow - H01M 8/04783: {Pressure differences, e.g. between anode and cathode} - H01M 8/04955: Shut-off or shut-down of fuel cells - Y02E 60/50: Fuel cells - H01M: PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY - Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION ## Abstract A fuel cell system includes a scavenging gas supply device for supplying a scavenging gas to a fuel cell stack; a scavenging switching valve for performing switching between first scavenging for performing scavenging by supplying the scavenging gas to one of a cathode gas passage and an anode gas passage, and second scavenging for performing scavenging by supplying the scavenging gas to the other gas passage; a pressure control device for controlling the pressure of the scavenging gas; and a control part for controlling operations of the scavenging gas supply device, the scavenging switching valve, and the pressure control device. When the scavenging is switched from the first scavenging to the second scavenging via the scavenging switching valve, the pressure of the scavenging gas at the upstream side with respect to the scavenging switching valve becomes lower than the pressure of the scavenging gas during the first scavenging. ## Claims ### Claim 1 A fuel cell system comprising: a fuel cell stack in which a cathode gas and an anode gas are respectively supplied to a cathode gas passage and an anode gas passage so as to generate electric power; a scavenging gas supply device for supplying a scavenging gas to the fuel cell stack; a scavenging switching valve for performing switching between first scavenging for performing scavenging by supplying the scavenging gas to one of the cathode gas passage and the anode gas passage, and second scavenging for performing scavenging by supplying the scavenging gas to the other one of the cathode gas passage and the anode gas passage; a scavenging gas pressure control device for controlling the pressure of the scavenging gas; and a control part for controlling operations of the scavenging gas supply device, the scavenging switching valve, and the scavenging gas pressure control device, wherein the control part controls the pressure of the scavenging gas by using the scavenging gas pressure control device in such a manner that when the scavenging is switched from the first scavenging to the second scavenging via the scavenging switching valve, the pressure of the scavenging gas at the upstream side with respect to the scavenging switching valve becomes lower than the pressure of the scavenging gas during the first scavenging. ### Claim 2 (depends on 1) The fuel cell system in accordance with claim 1, wherein: the first scavenging is cathode scavenging performed by supplying the scavenging gas to the cathode gas passage, and the second scavenging is pressure scavenging performed by supplying the scavenging gas to the anode gas passage. ### Claim 3 (depends on 2) The fuel cell system in accordance with claim 2, wherein: the scavenging switching valve is a discharge valve for controlling discharge of the scavenging gas from the anode gas passage. ### Claim 4 (depends on 2) The fuel cell system in accordance with claim 2, wherein: the scavenging gas pressure control device is a back pressure valve by which the scavenging gas discharged from the cathode gas passage can be controlled. ### Claim 5 (depends on 1) The fuel cell system in accordance with claim 1, wherein: pressure difference between the upstream and downstream sides with respect to the scavenging switching valve is measured, and when the scavenging is switched from the first scavenging to the second scavenging, the pressure of the scavenging gas is reduced until the measured pressure difference becomes lower than a predetermined value. ### Claim 6 (depends on 1) The fuel cell system in accordance with claim 1, wherein: when the scavenging is switched from the first scavenging to the second scavenging, the pressure of the scavenging gas is reduced until a predetermined time has elapsed. ### Claim 7 (depends on 1) The fuel cell system in accordance with claim 1, wherein: the scavenging gas pressure control device is a compressor whose rotation speed is variable. ### Claim 8 A fuel cell system comprising: a fuel cell stack in which a cathode gas and an anode gas are respectively supplied to a cathode gas passage and an anode gas passage so as to generate electric power; a scavenging gas supply device for supplying a scavenging gas to the fuel cell stack; an anode scavenging gas passage through which the scavenging gas for scavenging the anode gas passage flows; an anode scavenging control valve, which is provided at the anode scavenging gas passage, and opened when scavenging of the anode gas passage is started; a scavenging gas pressure control device for controlling the pressure of the scavenging gas; and a control part for controlling operations of the scavenging gas supply device, the anode scavenging control valve, and the scavenging gas pressure control device, wherein the control part controls the pressure of the scavenging gas by using the scavenging gas pressure control device in such a manner that when the anode scavenging control valve is opened, the pressure of the scavenging gas at the upstream side with respect to the anode scavenging control valve becomes lower than the pressure of the scavenging gas during the scavenging of the anode gas passage. ### Claim 9 (depends on 8) The fuel cell system in accordance with claim 8, wherein: the anode scavenging control valve is a discharge valve for controlling discharge of the scavenging gas from the anode gas passage; and the control part opens the discharge valve after storing the scavenging gas at the upstream side with respect to the anode scavenging control valve, by using the scavenging gas supply device. ### Claim 10 (depends on 8) The fuel cell system in accordance with claim 8, wherein: pressure difference between the upstream and downstream sides with respect to the anode scavenging control valve is measured, and when the anode scavenging control valve is opened, the pressure of the scavenging gas is reduced until the measured pressure difference becomes lower than a predetermined value. ### Claim 11 (depends on 8) The fuel cell system in accordance with claim 8, wherein: when the anode scavenging control valve is opened, the pressure of the scavenging gas is reduced until a predetermined time has elapsed. ### Claim 12 A scavenging method of a fuel cell system, wherein: the fuel cell system includes: a fuel cell stack in which a cathode gas and an anode gas are respectively supplied to a cathode gas passage and an anode gas passage so as to generate electric power; a scavenging gas supply device for supplying a scavenging gas to the fuel cell stack; and a scavenging switching valve for performing switching between first scavenging for performing scavenging by supplying the scavenging gas to one of the cathode gas passage and the anode gas passage, and second scavenging for performing scavenging by supplying the scavenging gas to the other one of the cathode gas passage and the anode gas passage; and the method comprises the steps of: performing the first scavenging; controlling the pressure of the scavenging gas by making the pressure of the scavenging gas at the upstream side with respect to the scavenging switching valve be lower than the pressure of the scavenging gas during the first scavenging; and switching the scavenging switching valve. ### Claim 13 (depends on 12) The scavenging method in accordance with claim 12, further comprising the step of: measuring pressure difference between the upstream and downstream sides with respect to the scavenging switching valve, wherein: the step of controlling the pressure of the scavenging gas includes reducing the pressure of the scavenging gas until the measured pressure difference becomes lower than a predetermined value. ### Claim 14 (depends on 12) The scavenging method in accordance with claim 12, wherein: the step of controlling the pressure of the scavenging gas includes reducing the pressure of the scavenging gas until a predetermined time has elapsed.