Humidity sensor and method of using the humidity sensor

• US 20040237646A1
• Filed: 06/01/2004
• Published: 12/02/2004
• Est. Priority Date: 05/30/2003
• Status: Active Grant

• Current Assignee: NGK Spark PLUG Company Limited
• Original Assignee: NGK Spark PLUG Company Limited
• Inventors: Kato, Kenji, Fujita, Hiroki, Inoue, Ryuji, Fujita, Koichi, Ishida, Noboru, Sugaya, Satoshi
• Granted Patent: US 7,210,333 B2
• Time in Patent Office: Days
• US Class Current: 73/335.05
• CPC Class Codes: G01N 27/121 for determining moisture content, e.g. humidity, of the fluid moisture content of the tested material G01N27/048

Abstract

A humidity-sensitive porous layer (13) of a humidity-sensitive element section (3) of a humidity sensor (1) is formed of a crystalline phase oxide grains such as Al₂O₃—SnO₂—TiO₂ and of a glass phase such as silicate glass covering the crystalline phase. The glass phase contains an alkali metal oxide and/or alkaline earth metal oxide such as Li₂O. The humidity sensitive porous layer (13) assumes a skeletal structure that is formed of crystalline phase oxide grains covered or coated with the glass phase. A heater (17) of the humidity sensor is controlled to heat the humidity-sensitive element section (3) at a temperature ranging from 500° C. to 800° C. so as to clean off the humidity-sensitive element section while an internal combustion engine is running and exhausting fouling substances. Measurement of Humidity in an exhaust gas exhausted from an exhaust gas purifying apparatus of an internal combustion engine is carried out by using the humidity sensor (1), so long as the exhaust gas temperature does not exceed 100° C. regardless of whether or not the engine is running.

Claims

1. A humidity sensor for use in an exhaust gas purifying apparatus of an internal combustion engine, comprising a humidity-sensitive element section having a humidity-sensitive porous layer and detection electrodes formed on the humidity-sensitive layer,

wherein the humidity-sensitive element comprises a crystalline phase formed of at least one oxide, and a glass phase, and

said humidity sensor comprising heater means for heating the humidity-sensitive element section at a cleaning temperature of from 500°

C. to 800°

C. during a time at which humidity measurement is not carried out by the humidity sensor.

2. The humidity sensor as claimed in claim 1, wherein the humidity-sensitive porous layer has a skeletal structure formed of the crystalline phase and the glass phase, and a surface of the skeletal structure is covered with the glass phase.

3. The humidity sensor as claimed in claim 1, wherein the detection electrodes contain platinum.

4. The humidity sensor as claimed in claim 1, wherein the glass phase comprises at least one selected from the group consisting of silicate glass, phosphate glass and borate glass.

5. The humidity sensor as claimed in claim 1, wherein the glass phase has a softening point of 800°

C. to 1,200°

C.

6. The humidity sensor as claimed in claim 1, wherein the humidity-sensitive porous layer contains the glass phase in an amount of 10 mol % to 56 mol %.

7. The humidity sensor as claimed in claim 1, comprising means for detecting, from humidity variation of exhaust gas, a condition or state of an exhaust-gas-purifying apparatus of an internal combustion engine.

8. The humidity sensor as claimed in claim 1, further comprising means for heating the humidity-sensitive element section to a temperature higher than the cleaning temperature of 500°

C. to 800°

C. after the internal combustion engine is stopped.

9. The humidity sensor as claimed in claim 1, further comprising means for heating the humidity-sensitive element section to a temperature higher than 800°

C. but not exceeding 1200°

C. after the internal combustion engine is stopped.

10. The humidity sensor as claimed in claim 1, further comprising means for heating the humidity-sensitive element section to the cleaning temperature of 500°

C. to 800°

C. at all times while the internal combustion engine is running.

11. The humidity sensor as claimed in claim 1, comprising heater means for heating the humidity-sensitive element section at a cleaning temperature of from 500°

C. to 800°

C. for a predetermined time while the internal combustion engine is running and exhausting an exhaust gas having a temperature exceeding 100°

C. and for heating the humidity-sensitive element section for a predetermined time to a temperature higher than 800°

C. but not exceeding 1200°

C. after the internal combustion engine is stopped, said humidity sensor measuring humidity of the exhaust gas after the internal combustion engine is started and while the exhaust gas temperature is not higher than 100°

C., and/or said humidity sensor measuring humidity of the exhaust gas after the internal combustion engine is stopped and the exhaust gas has cooled to a temperature of not higher than 100°

C.

12. The humidity sensor as claimed in claim 1, further comprising temperature detection means for detecting a temperature of the humidity-sensitive element section;

and means for controlling the heater means such that the temperature detection means assumes a predetermined resistance.

13. The humidity sensor as claimed in claim 12, wherein said temperature detection means comprises a temperature sensor including a temperature sensitive resistor.

14. The humidity sensor as claimed in claim 12, wherein said temperature detection means comprises said heater means, said heater means having a resistance which varies with temperature.

15. The humidity sensor as claimed in claim 1, wherein said glass phase contains a glass component including an alkali metal oxide and/or an alkaline earth metal oxide in an amount of 0.5 mol % (namely 0.5% by mole) to 30 mol % of the glass phase.

16. The humidity sensor as claimed in claim 2, wherein said glass phase contains a glass component including an alkali metal oxide and/or an alkaline earth metal oxide.

17. The humidity sensor as claimed in claim 1, wherein the humidity-sensitive element consists essentially of a crystalline phase formed of at least one oxide, and a glass phase.

18. A method for measuring humidity of an exhaust gas exhausted from an internal combustion engine using a humidity sensor comprising a humidity-sensitive element section having a humidity-sensitive porous layer and detection electrodes formed on the humidity-sensitive porous layer, and a heater for heating the humidity-sensitive element section, said method comprises:

heating the humidity-sensitive element section with said heater to a cleaning temperature that removes fouling substances adhered on a surface of the humidity-sensitive porous layer, and

measuring the humidity of exhaust gas having a temperature not higher than 100°

C. based on impedance or resistance measured across the detection electrodes.

19. The method for measuring humidity as claimed in claim 18, wherein said cleaning temperature ranges from 500°

C. to 800°

C. when the internal combustion engine is running.

20. The method for measuring humidity as claimed in claim 18, wherein said cleaning temperature ranges from 500°

C. to 1200°

C. when the internal combustion engine is stopped.

21. The method for measuring humidity as claimed in claim 18, which comprises elevating said temperature beyond 800°

C. up to 1200°

C. with said heater after the internal combustion engine is stopped.

22. The method for measuring humidity as claimed in claim 18, which comprises (i) heating the humidity-sensitive element section with said heater to a cleaning temperature ranging from 500°

C. to 800°

C. so as to clean a surface of the humidity-sensitive porous layer while the internal combustion engine is running and exhausting an exhaust gas having a temperature exceeding 100°

C., (ii) after the internal combustion engine is stopped, heating the humidity-sensitive element section to a temperature higher than 800°

C. but not exceeding 1200°

C., and (iii) measuring humidity of the exhaust gas after the internal combustion engine is started and while the exhaust gas temperature is not higher than 100°

C.

23. The method for measuring humidity as claimed in claim 18, wherein humidity measurement is carried out after the internal combustion engine is started and/or after the internal combustion engine is stopped.

24. The method for measuring humidity as clamed in claim 18, which comprises heating the humidity-sensitive element section to a temperature higher than said cleaning temperature after the internal combustion engine is stopped.

25. The method for measuring humidity as claimed in claim 18, wherein the humidity-sensitive porous layer comprises a crystalline phase formed of an oxide, and a glass phase that contains an alkali metal oxide and/or an alkaline earth metal oxide, said humidity-sensitive porous layer containing the glass phase in an amount of 10 mol % to 56 mol % and said glass phase containing the alkali metal oxide and/or an alkaline earth metal oxide in an amount of 0.5 mol % (namely 0.5% by mole) to 30 mol % of the total glass phase.

26. The method for measuring humidity as claimed in claim 18, which comprises (i) heating the humidity-sensitive element section with said heater to a cleaning temperature ranging from 500°

C. to 800°

C. so as to clean a surface of the humidity-sensitive porous layer while the internal combustion engine is running and exhausting an exhaust gas having a temperature exceeding 100°

C., (ii) after the internal combustion engine is stopped, heating the humidity-sensitive element section to a temperature higher than 500°

C. but not exceeding 1200°

C., and (iii) measuring humidity of the exhaust gas while the exhaust gas temperature is not higher than 100°

C.

27. The method for measuring humidity as claimed in as claimed in claim 18, comprising heating the humidity-sensitive element section to the cleaning temperature of 500°

C. to 800°

C. at all times while the internal combustion engine is running.

29. The method for measuring humidity as claimed in claim 23, comprising measuring humidity of the exhaust gas when the exhaust gas shows a temperature of not higher than 100°

C.

28. The method for measuring humidity as claimed in 27, further comprising heating the humidity-sensitive element section to a temperature of 500°

C. to 1200°

C. when or after the engine is stopped.