Glow plug and method of manufacturing the same, and ion current detector

• US 6,483,079 B2
• Filed: 12/09/1997
• Issued: 11/19/2002
• Est. Priority Date: 04/10/1996
• Status: Expired due to Term

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Murai, Hiroyuki, Sato, Yasuyuki, Shibata, Masamichi, Kurano, Atsushi
• Primary Examiner(s): Jeffery, John A.
• Application Number:
  US08/973,799
• Publication Number:
  US 20020036192A1
• Time in Patent Office: 1,806 Days
• Field of Search: 219/270, 219/544, 123/145.A, 123/145.R, 361/264-266
• US Class Current: 219/270
• CPC Class Codes: F02P 17/12 Testing characteristics of the spark, ignition voltage or current testing of sparking plugs H01T13/60
• CPC Class Codes: F02P 19/028 the glow plug being combined with or used as a sensor
• CPC Class Codes: F02P 2017/125 Measuring ionisation of combustion gas, e.g. by using ignition circuits
• CPC Class Codes: F23N 2227/42 Ceramic glow ignition
• CPC Class Codes: F23N 5/12 using ionisation-sensitive elements, i.e. flame rods
• CPC Class Codes: F23Q 2007/002 with sensing means
• CPC Class Codes: F23Q 2007/004 Manufacturing or assembling methods
• CPC Class Codes: F23Q 7/001 Glowing plugs for internal-combustion engines

Abstract

The present invention is to provide a glow plug (1) with an ion current detecting function, which is mounted in a combustion chamber of a Diesel engine. The glow plug includes an insulator (8); a heating element (6) embedded in the insulator and energized through a pair of lead wires (11a, 11b) to generate heat; and an ion current detecting electrode (14) embedded in the insulator with a portion exposed into a flame in the combustion chamber so that an ionization state in the flame can be detected. The heating element of the glow plug promotes ignition and combustion of fuel in the combustion chamber (7) due to its heating action caused when running the heating element hot. The ion current detecting electrode detects an ionization state in the combustion flame. When detecting ion current, the ion current detecting electrode and the adjacent inner wall of the combustion chamber form two electrodes for capturing positive and negative ions existing between both when burning the fuel. In such structure, the ion current can be detected precisely in spite of very simple structure. It is therefore possible to effectively use the information for combustion control. Further, since the ion current detecting function is added to the glow plug, an inexpensive ion current detecting sensor can be provided.

Claims

1. A glow plug with a portion exposed into a combustion chamber for burning fuel comprising:

an insulator;

a heating element embedded in the insulator and energized through a pair of lead wires to generate heat; and

an ion current detecting electrode embedded in said insulator, with a portion of the ion current detecting electrode exposed to a flame in a combustion chamber so that an ionization state in the flame can be detected.

2. A glow plug as set forth in claim 1, wherein said heating element and said ion current detecting electrode is electrically connected to each other.

3. A glow plug as set forth in claim 2, wherein said heating element and said ion current detecting electrode are integrally formed.

4. A glow plug as set forth in claim 2, wherein lead wires reside between said heating element and said ion current detecting electrode.

5. A glow plug as set forth in claim 2, wherein connecting portions to a power source is provided at both ends of said heating element,

said ion current detecting electrode is electrically connected to the midway of said conductive heating-element, and

when R1 denotes electric resistance of a first heating section of said heating element from the first end of said heating element, corresponding to a positive side in passing a DC current through said heating element, to a center of a first connecting portion, at which said ion current detecting electrode is first connected to said heating element; R2 denotes electric resistance of a second heating section of said heating element from the center of the first connecting portion, where a connection between said heating element and said ion current detecting electrode is first established, to the second end of said heating element corresponding to a negative side in passing a DC current through the heating element; and

r denotes electric resistance between the first connecting portion and the opening end of said ion current detecting electrode, it satisfies the relationship of R2>

r.

6. A glow plug as set forth in claim 5, wherein the relationship between the electric resistance R2 and the electric resistance r exhibits R2≧

r.

7. A glow plug as set forth in claim 5 or 6, wherein said ion current detecting electrode is constructed of the main composition of a conductive ceramic material made of more than one kind of metallic silicide, carbide, nitride or boride, or a mixture of a conductive ceramic material and a nonconductive ceramic material.

8. A glow plug as set forth in claim 5, wherein said ion current detecting electrode is constructed of the main composition of a material made of one kind of refractory metal having a melting point of 1200°

C. or higher, or a mixture of the refractory metal material and a nonconductive ceramic material.

9. A glow plug as set forth in claim 5, wherein the exposed portion of said ion current detecting electrode exposed from said insulator is provided with a portion made of more than one kind of noble metal such as Pt, Ir, Rh, Ru and Pd.

10. A glow plug as set forth in claim 2, wherein said insulator and said ion current detecting electrode forms said main body retained in the housing, and the tip of said ion current detecting electrode is exposed from said insulator into the flame with positioning it more than 2 mm away from the tip of said housing.

11. A glow plug as set forth in claim 10, wherein when R (Ω

) denotes the total electric resistance of said conductive heating-element and B (Ω

) denotes the electric resistance from the positive end of said conductive heating-element to the tip of said ion current detecting electrode, the relationship between the resistances R and B satisfies

12. A glow plug as set forth in claim 1, wherein said heating element and said ion current detecting electrode are insulated from each other.

13. An ion current detector using the glow plug of claim 5 for detecting ion current resulting from fuel combustion, comprising:

switching means for turning on or off the power supply to said heating element;

leakage current detection means for detecting a leakage current from said ion current detecting electrode in a predetermined stage before fuel combustion; and

operation means for operating said switching means to temporarily energize said heating element when the leakage current detected by said leakage current detection means is larger than a predetermined threshold.

14. An ion current detector as set forth in claim 13, wherein said leakage current detection means is operated to detect the leakage current when pressure in the combustion chamber rises.

15. A glow plug as set forth in claim 1, wherein at least the portion of said ion current detecting electrode exposed to the flame is made of a conductive ceramic material.

16. A glow plug as set forth in claim 1, wherein said heating element and said ion current detecting electrode are produced dividedly from each other by using mixtures having different components or different particle sizes.

17. A glow plug as set forth in claim 1, wherein at least the exposed portion of said ion current detecting electrode that contacts the flame has a conductive mixed-sinter that is constructed by surrounding a nonconductive ceramic particle with conductive ceramic particles, with an sintering auxiliary of more than one kind of oxide of rare-earth element contained therein,

the structure of the mixed sinter composed of a first crystal phase and a grain boundary phase between the first crystal phases with portion of the grain boundary phase or the entire grain boundary phase crystallized into a second crystal phase.

18. A glow plug as set forth in claim 17, wherein the content of said sintering auxiliary to the total weight of said conductive ceramic material and said nonconductive ceramic material is between 3 wt % and 25 wt %.

19. A glow plug as set forth in claim 17 or 18, wherein said second crystal phase exists in said grain boundary phase of said ion current detecting electrode with a degree of crystallization of more than 5%.

20. A glow plug as set forth in claim 17, wherein said nonconductive ceramic material is silicon nitride and said conductive ceramic material is more than one kind of materials such as metallic carbide, silicide, nitride and boride.

21. A glow plug as set forth in claim 1, wherein the exposed portion of said ion current detecting electrode exposed from said insulator into the flame has a surface roughness Rz ranging from 0.1 to 30 μ

m (mean value of 10 points).

22. A glow plug as set forth in claim 21, wherein the area of the exposed portion provided at the tip of said ion current detecting electrode is set in a range from 1×

10<sup>−

6</sup> to 0.5 cm².

23. A glow plug as set forth in claim 21 or 22, wherein said ion current detecting electrode is electrically connected to said conductive heating-element.

24. A glow plug as set forth in claim 1, wherein at least top portion of said ion current detecting electrode is covered with a nonconductive porous layer having a communication hole through which said ion current detecting electrode can be opened into the flame.

25. A glow plug as set forth in claim 24, wherein the thickness of said nonconductive porous layer is between 0.2 mm and 1.5 mm.

26. A glow plug as set forth in claim 24 or 25, wherein said nonconductive porous layer and said insulator are made of the same material.

27. A glow plug as set forth in claim 24, wherein said ion current detecting electrode can be used for said conductive heating-element.

28. A glow plug as set forth in claim 1, wherein when K denotes the coefficient of linear expansion of said ion current detecting electrode, H denotes the coefficient of linear expansion of said conductive heating-element and S denotes the coefficient of linear expansion of said insulator, the relationship among K, H and S satisfies

29. A glow plug as set forth in claim 28, wherein the coefficients of linear expansion K, H and S further satisfies the following relationship:

30. A glow plug as set forth in claim 28 or 29, wherein said ion current detecting electrode is constructed of the main composition of a conductive ceramic material made of more than one kind of metallic silicide, carbide, nitride or boride, or a mixture of a conductive ceramic material and a nonconductive ceramic material.

31. A glow plug as set forth in claim 28, wherein said ion current detecting electrode is constructed of the main composition of a material made of one kind of refractory metal having a melting point of 1200°

C. or higher, or a mixture of the refractory metal material and a nonconductive ceramic material.

32. A glow plug as set forth in claim 1, wherein a conductive layer is further provided on the surface of said insulator so as to cover the exposed portion of said ion current detecting electrode exposed from said insulator into the flame, with establishing an electrical connection to said ion current detecting electrode.

33. A glow plug as set forth in claim 32, wherein said conductive layer has a through hole for partially exposing said insulator so that an edged portion will be formed on the side of the through hole exposed into the flame.

34. A glow plug as set forth in claim 33, wherein the edged portion has a rectangular shape in cross section.

35. A glow plug as set forth in claim 32, wherein said conductive layer has net structure so that the surface of said insulator will be exposed from meshes of the net.

36. A glow plug as set forth in claim 32, wherein said conductive layer is made of metal or conductive ceramic material.

37. A glow plug as set forth in claim 32, wherein said conductive layer is between 1 μ

m and 20 μ

m in thickness.

38. A glow plug as set forth in claim 1, wherein said insulator includes a first insulating substrate, a covering insulating substrate provided on the front face of the first insulating substrate, and a second insulating substrate stacked on the back face of the first insulating substrate,

said heating element is formed by printing between the front face of the first insulating substrate and the covering insulating substrate, said pair of lead wires are formed by printing between the front face of the first insulating substrate and the covering insulating substrate so as to be connected to both ends of said heating element, and

said ion current detecting electrode is provided between the first and second insulating substrates.

39. A glow plug as set forth in claim 38, wherein each outer surface of the first insulating substrate and the covering insulating substrate has a curved surface portion.

40. A glow plug as set forth in claim 38, wherein said ion current detecting electrode is formed by printing on the front face of the second insulating substrate.

41. A glow plug as set forth in claim 38, wherein said ion current detecting electrode is made of a conductive wire and provided between the front face of the second insulating substrate and the back face of the first insulating substrate.

42. A glow plug as set forth in claim 38, wherein the tip of said ion current detecting electrode is exposed at the top portion of the second insulating substrate so as to be exposed into the flame.

43. A glow plug as set forth in claim 38, wherein said ion current detecting electrode is made of more than one kind of ceramic materials MoSi₂, WC and TiN.

44. A glow plug as set forth in claim 38, wherein said ion current detecting electrode is made of refractory metal containing more than one kind of metals W, Mo and Ti.

45. A glow plug as set forth in claim 38, wherein the exposed portion of said ion current detecting electrode exposed from the second insulating substrate is provided with more than one kind of noble metal such as Pt, Ir, Rh, Ru and Pd.

46. A glow plug as set forth in any one of claims 38 through 45, wherein the top portion of said glow plug itself is made into a semi-spherical shape.

47. A glow plug as set forth in claim 1, wherein said insulator has a first insulating and a second insulating substrate, and said conductive heating-element, said lead wires connected to both ends of said conductive heating-element and said ion current detecting electrode are sandwiched between the first insulating and the second insulating substrate.

48. A glow plug as set forth in claim 1, wherein said insulator is a rod-like insulator, said heating element is formed by printing inside the rod-like insulator, said pair of lead wires are electrically connected to both ends of said heating element and drawn out to the outside of the rod-like insulator, and

said ion current detecting electrode is provided inside said rod-like insulator with electrical insulation from said heating element established.

49. A glow plug as set forth in claim 48, wherein said the tip of said ion current detecting electrode is exposed at the top portion of said rod-like insulator so as to be exposed into the flame.

50. A glow plug as set forth in claim 49, wherein the exposed portion of said ion current detecting electrode exposed from said rod-like insulator is provided with more than one kind of noble metals Pt, Ir, Rh, Ru and Pd.

51. A glow plug as set forth in claim 48, wherein said ion current detecting electrode is made of more than one kind of ceramic materials MoSi₂, WC and TiN.

52. A glow plug as set forth in claim 51, wherein the exposed portion of said ion current detecting electrode exposed from said rod-like insulator is provided with more than one kind of noble metals Pt, Ir, Rh, Ru and Pd.

53. A glow plug as set forth in claim 48, wherein said ion current detecting electrode is made of refractory metal containing more than one kind of metals W, Mo and Ti.

54. A glow plug as set forth in claim 53, wherein the exposed portion of said ion current detecting electrode exposed from said rod-like insulator is provided with more than one kind of noble metals Pt, Ir, Rh, Ru and Pd.

55. A glow plug as set forth in claim 48, wherein the top portion of said rod-like insulator is made into a semi-spherical shape.

56. A glow plug as set forth in claim 1, wherein said insulator is a rod-like insulator constituted of an electrically insulating core shaft with a hollow portion therein and an insulating substrate covering the outer core shaft, said heating element is formed by printing between the core shaft and the insulating substrate inside said rod-like insulator, said pair of lead wires are electrically connected to both ends of said heating element and drawn out to the outside of said rod-like insulator, and

said ion current detecting electrode is inserted in and fixed to the hollow portion of the core shaft with electrical insulation from said heating element established.

57. A glow plug as set forth in claim 56, wherein said heating element is formed by printing on the inside surface of the insulating substrate.

58. A glow plug as set forth in claim 1, wherein said insulator is a rod-like insulator;

said heating element is provided inside the rod-like insulator;

said pair of lead wires are electrically connected to both ends of said heating element and drawn out to the outside of said rod-like insulator; and

said ion current detecting electrode is put in a groove with electrical insulation from the heating element established, the groove provided axially on the outer surface of said rod-like insulator.

59. A glow plug as set forth in claim 58, wherein the groove with said ion current detecting electrode therein is filled with a nonconductive coating material so that said ion current detecting electrode can be covered therewith.

60. A glow plug as set forth in claim 58 or 59, wherein said heating element and said lead wires are formed by printing.

86. A method of manufacturing said glow plug of claim 56, comprising the steps of:

preparing a product of the core shaft having the hollow portion and composed of electrically nonconductive ceramic material, and inserting said ion current detecting electrode into the hollow portion,

forming said heating element and said lead wires on the surface of the product of the insulating substrate composed of electrically nonconductive ceramic material by using a printing technique,

placing the product of the core shaft on the printed surface of the insulating substrate and winding the insulating substrate around the outer core shaft, and

heating and baking the core shaft and the insulating substrate.

61. An ion current detector comprising:

a glow plug provided with a heating element projecting into a combustion chamber, the heating element supplied with power from a power source to generate heat;

ion current detection means using said glow plug for detecting ion current produced when burning fuel;

switching means for switching over between a heating-element running state of said glow plug and an ion current detecting state of said ion current detection means;

operation means for operating said switching means to temporarily switch over to the ion current detecting state at least immediately after fuel ignition stage under the heating-element running state of said glow plug.

62. An ion current detector as set forth in claim 61, wherein said operation means operates said switching means to switch over to the ion current detecting state for a predetermined period of time after each stage of fuel injection into the combustion chamber.

63. An ion current detector as set forth in claim 61, wherein said operation means operates at a predetermined frequency to switch over between the heating-element running state and the ion current detecting state.

64. An ion current detector as set forth in claim 61, wherein said glow plug comprising a pair of lead wires for producing current through said heat element, an insulator embedding said heating element therein, and an ion current detecting electrode integrally formed with said heating element, and said ion current detector uses said glow plug for detecting ion current produced when burning fuel.

65. An ion current detector as set forth in claim 61, further comprising:

leakage current detection means for detecting a leakage current flowing from the exposed electrode portion in a predetermined stage before fuel ignition under the ion current detecting state of said glow plug; and

second operation means for operating said switching means to temporarily switch over from the ion current detecting state to the heating-element running state when the leakage current detected by said leakage current detection means is larger than a given threshold.

66. An ion current detector as set forth in claim 65, wherein said leakage current detection means detects a leakage current when pressure in the combustion chamber rises.

67. An ion current detector as set forth in claim 65, wherein said leakage current detection means detects a leakage current in response to the timing of fuel injection into the combustion chamber.

68. An ion current detector as set forth in claim 65, wherein said second operation means holds said switching means in the heating-element running state for a period of time according to the leakage current value detected by said leakage current detection means.

69. An ion current detector as set forth in claim 65, further comprising a high-pass filter responsible to the ion current detected, wherein an output signal of said high-pass filter is supplied to a processor as an ion current detection signal.

70. An ion current detector as set forth in claim 69, wherein a threshold for use in judging the level of the leakage current is set to a value near the acceptable maximum value.

71. An ion current detector as set forth in claim 69 or 70, further comprising comparison means responsible to the output signal of said high-pass filter, which uses a threshold for use in detecting combustion conditions as the threshold value to be compared with the output signal of said high-pass filter.

72. An ion current detector that uses a glow plug having a heating element energized through a pair of conductive wires to generate heat, comprising:

switching means for switching over between a first state and a second state, the first state for applying a supply voltage from a power source to the conductive wire pair, and the second state for shutting an electric path between said conductive wire pair and said power source and applying the supply voltage between said heating element and a wall portion of a combustion chamber; and

ion current detection means for detecting ion current resulting from fuel combustion by using the voltage supplied from said power source in the second state.

73. An ion current detector as set forth in claim 72, wherein said power source is connected through said switching means to the electric path between said heating element and the wall portion of said combustion chamber.

74. An ion current detector as set forth in claim 72, wherein said power source is directly connected to the electric path between said heating element and the wall portion of said combustion chamber.

75. An ion current detector as set forth in claim 72, wherein the power source for applying voltage to said conductive wire pair in the first state and the power source for applying voltage between said heating element and the wall portion of said combustion chamber in the second state are provided separately.

76. An ion current detector as set forth in claim 72, wherein the power source for applying voltage to said conductive wire pair in the first state and the power source for applying voltage between said heating element and the wall portion of said combustion chamber in the second state are constructed by a common power source.

77. An ion current detector as set forth in claim 72, said ion current detector used in a Diesel engine, wherein

one end of said power source is connected to one conductive wire coupled to said heating element while the other is connected to a cylinder head of the Diesel engine for holding said glow plug.

78. An ion current detector as set forth in claim 72, wherein a constant voltage circuit is provided between said power source and one wire of said conductive wire pair for regulating the supply voltage of said power source to a constant value.

79. An ion current detector as set forth in claim 72, wherein a plurality of glow plugs are connected in parallel and power-supply paths to individual glow plugs are switched at the same time by said switching means.

80. An ion current detector as set forth in claim 72, wherein a voltage detector for ion current detection is provided between one conductive wire of said glow plug and the ground contact.

81. An ion current detector as set forth in claim 72, wherein a capacitor is provided between one conductive wire of said glow plug and said voltage detector.

82. An ion current detector as set forth in claim 72, wherein an ion current detecting resistor is provided on the grounded side of said power source separately provided, and ion current is detected from a potential difference between both terminals of the ion current detecting resistor.

83. A glow plug used in said ion current detector as set forth in claim 72, wherein

a heating element portion having a heating element is so provided that it projects into a combustion chamber for burning fuel, and

an ion current detecting electrode to the inner wall of said combustion chamber is formed in said heating element.

84. A glow plug used in said ion current detector as set forth in claim 72, comprising a heating element portion provided with a heat resisting insulator and a heating element embedded in the heat resisting insulator, wherein

a portion of said heating element is exposed from said heat resisting insulator and the exposed portion is used as an ion current detecting electrode to the inner wall of said combustion chamber.

85. A glow plug as set forth in claim 83 or 84, wherein said heating element is made of a ceramic material.