Ion sensor glow plug assembly

[0002] This application is related to U.S. Ser. Nos. 09/378167; 09/377355; and Ser. No. 09/375766, which are copending and assigned to the assignee of the present application.

[0003] The present invention claims the priority date of copending U.S. Provisional Patent Application Serial No. 60/189,147, filed Mar. 14, 2000.

[0004] The present invention relates generally to glow plugs for engines and, more particularly, to an ion sensor glow plug assembly for an engine of a vehicle.

[0005] It is known to provide an ion sensor for an engine of a vehicle. The ion sensor is used as a closed loop feedback to detect fuel injection timing and intensity of combustion in each cylinder of the engine so as to control and improve engine performance.

[0006] It is also known to provide a glow plug for a compression ignition engine such as a diesel engine. The glow plug typically has a metal glow tip that extends into a chamber of the engine. The purpose of the glow plug is to aid in cold starting of the diesel engine.

[0007] Although the above ion sensors and glow plugs have worked, it is desirable to combine the two to provide an ion sensor glow plug assembly. It is also desirable to provide an ion sensor glow plug assembly that is self-cleaning for soot in a compression ignition engine such as a diesel engine of a vehicle.

[0008] It is, therefore, one object of the present invention to provide an ion sensor glow plug assembly for an engine of a vehicle.

[0009] It is another object of the present invention to provide an ion sensor glow plug assembly that is self-cleaning for soot in a compression ignition engine of a vehicle.

[0010] To achieve the foregoing objects, the present invention is an ion sensor glow plug assembly including a metal shell for attachment to a cylinder head of a compression ignition engine and having a passageway extending axially therethrough. The ion sensor glow plug assembly also includes a center terminal disposed at least partially in the passageway of the shell and connected to a source of power to create a heating circuit. The ion sensor glow plug assembly includes a glow sheath disposed at least partially in the passageway of the shell and about the center terminal to create an ion sensing circuit. The ion sensor glow plug assembly further includes a coating disposed about a portion of the glow sheath between the glow sheath and the shell to isolate the shell from the glow sheath and extending axially into a glow area of the glow sheath to clean off soot on the glow sheath by glowing.

[0011] One advantage of the present invention is that an ion sensor glow plug assembly is provided for an engine of a vehicle. Another advantage of the present invention is that the ion sensor glow plug assembly is self-cleaning for soot in a compression ignition engine such as a diesel engine. Yet another advantage of the present invention is that the ion sensor glow plug assembly incorporates a metal glow sheath with a ceramic barrier coating deposited on it to isolate it from a steel shell for ion sensing purposes. A further advantage of the present invention is that the ion sensor glow plug assembly allows closed loop control of a compression ignition engine such as a diesel engine.

[0012] Other objects, features, and advantages of the present invention will be readily appreciated, as the same becomes better understood, after reading the subsequent description taken in conjunction with the accompanying drawings.

[0013] FIG. 1 is a fragmentary elevational view of an ion sensor glow plug assembly, according to the present invention, illustrated in operational relationship with an engine of a vehicle.

[0014] FIG. 2 is a view similar to FIG. 1 of the ion sensor glow plug assembly illustrated in operational relationship with another engine.

[0015] FIG. 3 is a fragmentary elevational view of the ion sensor glow plug assembly of FIGS. 1 and 2.

[0016] Referring to the drawings and in particular FIGS. 1 and 2, one embodiment of an ion sensor glow plug assembly 10, according to the present invention, is shown for a compression ignition engine, generally indicated at 12, such as a diesel engine in a vehicle (not shown). As illustrated in FIG. 1, the compression ignition engine 12 may be an open chamber type diesel engine including a cylinder block 14 defining a cylinder 16 closed by a cylinder head 18. The compression ignition engine 12 also includes a piston 20 reciprocal in the cylinder 16 and defines a recessed bowl, which together with the cylinder head 18 forms a combustion chamber 22. The compression ignition engine 12 includes an injection nozzle or injector 24 mounted in the cylinder head 18, which sprays fuel into the combustion chamber 22 for compression ignition therein. The compression ignition engine 12 further includes the ion sensor glow plug assembly 10 mounted in the cylinder head 18 and extending into the combustion chamber 22 for a function to be described. It should be appreciated that, except for the ion sensor glow plug assembly 10, the compression ignition engine 12 is conventional and known in the art.

[0017] As illustrated in FIG. 2, the compression ignition engine 12 may be pre-chamber type diesel engine including a cylinder block 30 defining a cylinder 32 closed by a cylinder head 34. The compression ignition engine 12 also includes a piston 36 reciprocal in the cylinder 32. The piston 36 and cylinder head 34 form a combustion chamber 38, which connects with a pre-combustion chamber or pre-chamber 40 within the cylinder head 34. The compression ignition engine 12 includes an injection nozzle or injector 42 mounted in the cylinder head 34 for injecting fuel into the pre-chamber 40. The compression ignition engine 12 includes the ion sensor glow plug assembly 10 mounted in the cylinder head 34 and extending into the pre-chamber 40 for a function to be described. It should be appreciated that, except for the ion sensor glow plug assembly 10, the compression ignition engine 12 is conventional and known in the art.

[0018] Referring to FIG. 3, the ion sensor glow plug assembly 10 includes a housing or shell 46 extending axially for engaging the cylinder head 18,34. The shell 46 is generally cylindrical in shape and has a passageway 48 extending axially therethrough. The shell 46 has a plurality of exterior threads 50 for threaded engagement with the cylinder head 18,34. The exterior threads 50 are of a ten-millimeter (10 mm) by one millimeter (1 mm) type. The shell 46 has a reduced diameter end 52 adjacent one end of the exterior threads 50 and a hexagonal shaped end 54 adjacent the other end of the exterior threads 50 for a function to be described. The hexagonal shaped end 54 is of a ten millimeter (10 mm) type. The shell 46 is made of a metal material such as steel.

[0019] The ion sensor glow plug assembly 10 may include a seal 56 disposed partially in the passageway 48 at the hexagonal shaped end 54 of the shell 46 and an electrical connector (not shown) disposed adjacent the seal 56 for a function to be described. The seal 56 is made of either a plastic or elastomeric material. It should be appreciated that the electrical connector is conventional and known in the art.

[0020] The ion sensor glow plug assembly 10 includes a glow sheath 58 partially disposed in the passageway 48 of the shell 46. The glow sheath 58 is generally cylindrical and tubular in shape. The glow sheath 58 has a closed end 60 spaced axially from the reduced diameter end 52 of the shell 46. The glow sheath 58 extends axially from the closed end 60 into the passageway 48 of the shell 46 to an open end 62. The glow sheath 58 has a predetermined outer diameter of approximately 3.5 mm to approximately 5.0 mm. The glow sheath 58 is made of a metal material such as a nickel base alloy Inconel 601 or 600. The glow sheath 58 is secured by suitable means such as a press-fit into the shell 46.

[0021] The ion sensor glow plug assembly 10 also includes a first coating 64 on a portion of the glow sheath 58 that is partially disposed in the shell 46 and extending into the passageway 48. The first coating 64 is disposed annularly about the glow sheath 58 and extends radially and axially. The first coating 64 has one end spaced from the open end 62 of the glow sheath 58 and extends axially past the reduced diameter end 52 of the shell 46 into the glow area of the glow sheath 58. The first coating 64 has a radial thickness of 0.001 inches to 0.010 inches. The first coating 64 is made of an insulating material such as alumina (Al₂O₃) or other suitable ceramic material. The first coating 64 is extended into the high temperature glow area of a glow sheath 58 to burn off, by glowing, any soot (carbon) and moisture formation on the glow sheath 58 that may create reduced resistance between the shell 46 and glow sheath 58. The first coating 64 is impregnated into the outside diameter of the glow sheath 58 using a thermal particle depositing process such as High Velocity Oxy-Fuel (HVOF), D-Gun, or Plasma Jet Spraying, which process is conventional and known in the art. It should be appreciated that the first coating 64 isolates the glow sheath 58 from the shell 46, thus creating an ion sensing circuit, and retains a resistance sufficient for ion sensing during glowing and/or engine operation.

[0022] The ion sensor glow plug assembly 10 includes a second or conformal coating 66 disposed over a portion of the first coating 64. The second coating 66 is a relatively thin layer to mechanically retain the glow sheath 58 in the shell 46. The second coating 66 is made of a high temperature material such as polyamides, loctite, silicones or the like having high resistivity at high temperature such as four hundred degrees centigrade (400° C.). The second coating 66 is applied over the impregnated first coating 64 in the press-fit area thereof. It should be appreciated that the second coating 66 can be cured before or after final assembly. It should also be appreciated that the second coating 66 prevents moisture formation between the glow sheath 58 and shell 46 and seals off combustion gases from passing between the first coating 64 and the passageway 48 of the shell 46.

[0023] The ion sensor glow plug assembly 10 includes a center or centerwire terminal 68 partially disposed within the glow sheath 58. The center terminal 68 is generally a metal wire and extends axially. The center terminal 68 has one end spaced axially from the closed end 60 of the glow sheath 58 and extends axially through the passageway 48 to another end that matingly engages the electrical connector. The center terminal 68 is made of a metal material such as nickel (Ni), nickel-chromium (Ni—Cr) or nickel-chromium-iron (Ni—Cr—Fe). It should be appreciated that the center terminal 68 is a first heater terminal for heater portion 82 of an electrical coil 78 to be described.

[0024] The ion sensor glow plug assembly 10 includes a seal 70 inserted into and disposed in the open end 62 of the glow sheath 58. The seal 70 has an aperture 72 extending axially therethrough and the center terminal 68 extends axially through aperture 72 in the seal 70. The seal 70 is made of either a plastic or elastomeric material. It should be appreciated that the seal 70 seals the open end 62 of the glow sheath 58.

[0025] The ion sensor glow plug assembly 10 includes a second terminal 74 having insulation 76 over a portion thereof and extending through the seal 56. The second terminal 74 is attached to an outside diameter of an upper end 62 of the glow sheath 58 by suitable means such as welding. The second terminal 74 matingly engages the electrical connector. It should be appreciated that the second terminal 74 is used for both a second heater terminal for the heater portion 82 of the electrical coil 78 to be described and an ion sensor terminal for the glow sheath 58.

[0026] The ion sensor glow plug assembly 10 includes an electrical coil 78 disposed about a portion of the center terminal 68. The electrical coil 78 has a first or current regulating portion 80 having one end disposed about the center terminal 68 by spot welding and extending axially. The current regulating portion 80 is made of a metal material such as nickel-iron (Ni—Fe) or cobalt-iron (Co—Fe). The electrical coil 78 has a second or heating portion 82. The heating portion 82 has one end connected to the current regulating portion 80 by suitable means such as spot welding and another end connected to the closed end 60 of the glow sheath 58 by suitable means such as resistance welding. The heating portion 82 is made of a metal material such as nickel-chromium (Ni—Cr) or iron-chromium-aluminum (Fe—Cr—Al). It should be appreciated that the second terminal 74 and center terminal 68 act as terminals for the electrical coil 78 to create a heating circuit and are connected to the electrical connector, which, in turn, is connected to an electronic controller (not shown). It should be appreciated that the controller is conventional and known in the art.

[0027] The ion sensor glow plug assembly 10 further includes a filling material 84 disposed in the glow sheath 58. The filling material 84 is made of a ceramic powder material such as magnesia or alumina. The filling material 84 is disposed inside the glow sheath 58 and around the electrical coil 78 and center terminal 68. The filling material 84 provides mechanical support of the center terminal 68 and electrical coil 78 in an x-y direction. The filling material 84 also acts as a heat conductor from the electrical coil 78 to the glow sheath 58 during glowing. It should be appreciated that the filling material provides both electrical insulation and thermal conduction between the center terminal 68, electrical coil 78, and glow sheath 58.

[0028] To assemble the ion sensor glow plug assembly 10, the heating portion 82 of the electrical coil 78 is joined such as by welding to the current regulating portion 80 of the electrical coil 78. The current regulating portion 80 of the electrical coil 78 is joined such as by welding to the center terminal 68, which is the first heater terminal. The center terminal 68 and the heating portion 82 of the electrical coil 78 are then joined such as by welding to the closed end 60 of the glow sheath 58. Ceramic powder, made of magnesia or alumina, is then inserted to the inside of the glow sheath 58 and compacted around the terminal/electrical coil 78 by vibration. The seal 70 is then inserted into the upper or open end 62 of the glow sheath 58. The glow sheath 58 is then swaged to a smaller size to further compact the filling material 84 for electrical insulation and for thermal conductivity between the center terminal 68, electrical coil 78, and glow sheath 58. The outer diameter of the glow sheath 58 is then impregnated with the first coating 64 using conventional Plasma Jet, High Velocity Oxy-Fuel (HVOF) or D-Gun® molten particle deposition processes. The second terminal 74 is attached to the upper end 62 of the glow sheath 58 by suitable means such as welding. Next, a thin second coating 66 is applied over the first coating 64. The glow sheath 58 is then mechanically retained such as by being press-fitted into the shell 46 through its lower end. The seal 56 is then inserted into the upper or open end of the passageway 48 of the shell 46. The ion sensor glow plug assembly 10 may be heated before or after final assembly to cure the second coating 66. The ion sensor glow plug assembly 10 is then completely assembled.

[0029] In operation of the ion sensor glow plug assembly 10, the center terminal 68 carries the supply voltage from the electrical connector for the heating circuit. Current flows from the electrical connector to the center terminal 68, which passes through the current regulating portion 80 and heating portion 82 of the electrical coil 78, glow sheath 58, and second terminal 74 back to the electrical connector to form a glow plug electrical/heating circuit. The second terminal 74 and glow sheath 58 carry the supply voltage from the electrical connector for the ion sensor circuit. An electrical switch (not shown) is used upstream to connect or switch the second terminal from heating or glowing to ion sensing when glowing is not needed. When there is combustion in the cylinder 16,32, the burnt gases are ionized and conduct or carry current from the electrical connector through the second terminal 74 to the glow sheath 58 and through the ionized gases to an engine ground, which is the piston 20,36 or the shell 46. The exposed portion of the first coating 64 is extended into the high temperature area or glowing area of the glow sheath 58 which will burn off by glowing any soot (carbon) and moisture formation on the glow sheath 58 that may create reduced resistance or a short between the glow sheath 58 and the shell 46 to provide the soot self-cleaning feature of the ion sensor glow plug assembly 10. It should be appreciated that first coating 64 and second coating 66 create an electrical barrier between the glow sheath 58 and the shell 46 so that both glowing and ion sensing can be created since these two functions do not operate simultaneously. It should also be appreciated that the second coating 66 is used as a lubricant and a sealant to aid in reducing the press-fit force during assembly and to seal off any possible combustion gas leakage between the glow sheath 58, first coating 64, and the passageway 48 of the shell 46. It should further be appreciated that the second coating 66, if polyimide is used, can prevent moisture adhering to it and hence reduce the possibility of electrical shorting between the glow sheath 58 and the shell 46.

[0030] The present invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation.

[0031] Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the present invention may be practiced other than as specifically described.