Abstract:
An ion sensor glow plug assembly includes a metal shell for attachment to a cylinder head of a compression ignition engine. The ion sensor glow plug assembly also includes a center terminal at least partially disposed in the metal shell and connected to a source of power to create a heating circuit. The ion sensor glow plug assembly includes a metal glow sheath disposed at least partially in the metal shell and about the center terminal. The ion sensor glow plug assembly further includes an insulative seal disposed at least partially around the metal glow sheath to isolate the metal shell from the metal glow sheath to create an ion sensing circuit.

Description:
TECHNICAL FIELD 
     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. 
     BACKGROUND OF THE INVENTION 
     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. 
     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 ceramic 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. 
     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. 
     SUMMARY OF THE INVENTION 
     It is, therefore, one object of the present invention to provide an ion sensor glow plug assembly for an engine of a vehicle. 
     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. 
     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. The ion sensor glow plug assembly also includes a center terminal at least partially disposed in the metal shell and connected to a source of power to create a heating circuit. The ion sensor glow plug assembly includes a metal glow sheath disposed at least partially in the metal shell and about the center terminal. The ion sensor glow plug assembly further includes an insulative seal disposed at least partially around the metal glow sheath to isolate the metal shell from the metal glow sheath to create an ion sensing circuit. 
     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 carbon self-cleaning ion sensor into a glow plug. Still another advantage of the present invention is that the ion sensor glow plug assembly incorporates a metal glow sheath. 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. 
     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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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. 
     FIG. 2 is a view similar to FIG. 1 of the ion sensor glow plug assembly illustrated in operational relationship with another engine. 
     FIG. 3 is a fragmentary elevational view of the ion sensor glow plug assembly of FIGS. 1 and 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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. 
     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. 
     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) type. The shell  46  has a reduced diameter end  52  adjacent one end of the exterior threads  50  forming a shell seat  53  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. 
     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  58  such as a tr-axial mating connector 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  58  mates with terminals of the ion sensor glow plug assembly  10 . 
     The ion sensor glow plug assembly  10  also includes an insulator  60  partially disposed in the shell  46  and extending into the passageway  48 . The insulator  60  is generally cylindrical in shape and extends axially. The insulator  60  has a passageway  62  extending axially therethrough. The insulator  60  has an insulator seat  64  extending radially outwardly and axially. The insulator  60  is made of a ceramic material such as alumina. The insulator  60  is extended into a glow area of a glow sheath  78  to be described to glow the glow sheath  78  and clean off any soot (carbon) that may induce a short circuit between the shell  46  and glow sheath  78 . It should be appreciated that the shell seat  53  is crimped to retain the insulator  60  to the shell  46 . 
     The ion sensor glow plug assembly  10  includes a gasket or seal  66  disposed between the insulator  60  and the shell  46  to provide vibration damping and mechanical support. The gasket  66  is made of a relatively soft material such as copper or steel. The gasket  66  is disposed in the passageway  48  between the shell seat  53  and the insulator seat  64 . 
     The ion sensor glow plug assembly  10  includes a coating  68  disposed about one end of the insulator  60 . The coating  68  is generally cylindrical in shape and extends axially over the insulator seat  64  of the insulator  60 . The coating  68  has an aperture  70  extending axially therethrough. The coating  68  is made of an insulating material such as polyamide, preferably PI 2545. The ion sensor glow plug assembly  10  includes a matting  71  disposed in the passageway  48  adjacent the coating  68 . The matting  71  is generally annular and made of an insulating material such as intumescent fiber. It should be appreciated that the coating  68  and matting  71  prevent soot and/or humidity from shorting a surface of a seal  72  to be described. 
     The ion sensor glow plug assembly  10  includes a seal  72  disposed adjacent one end of the matting  71 . The seal  72  is generally cylindrical in shape and has an aperture  74  extending axially therethrough. The seal  72  is made of an insulating material such as glass and is pre-formed. The ion sensor glow plug assembly  10  includes a seal ring  76  disposed about the seal  72  and overlapping one end of the matting  71 . The seal ring  76  is generally annular and made of an insulating material such as Inconel  600 . It should be appreciated that the seal  76  isolates the shell  46  from a glow sheath  78  to be described to create an ion sensing circuit. 
     The ion sensor glow plug assembly  10  includes a glow sheath  78  partially disposed in the passageway  48  of the shell  46 . The glow sheath  78  is generally cylindrical and tubular in shape. The glow sheath  78  has a closed end  80  spaced axially from the end of the insulator  60 . The glow sheath  78  extends axially from the closed end  80  through the apertures  62  and  74  of the insulator  60  and seal  72 , respectively, to an open end  82 . The open end  82  matingly engages the electrical connector  58 . The glow sheath  78  is made of a metal material such as Inconel 601 or 600. The glow sheath  78  is secured by the seal  72  and seal ring  76  and subsequently press-fitted and secured into the shell  46 . 
     The ion sensor glow plug assembly  10  includes a center or centerwire terminal  84  disposed within the glow sheath  78 . The center terminal  84  is generally cylindrical in shape and extends axially. The center terminal  84  has one end spaced axially from the closed end  80  of the glow sheath  78  and extends axially to another end that matingly engages the electrical connector  58 . The center terminal  84  is made of a metal material such as nickel (Ni) or nickel-chromium (Ni—Cr). 
     The ion sensor glow plug assembly  10  includes an inner tube  86  disposed about a portion of the center terminal  84 . The inner tube  86  has one end spaced a predetermined distance such as fifty (50) to eighty (80) millimeters (mm) from the closed end  80  of the glow sheath  78 . The inner tube  86  extends axially to a second end spaced a predetermined distance from the other end of the center terminal  84  and matingly engages the electrical connector  58 . The inner tube  86  is made of a metal material such as nickel (Ni) or the like. It should be appreciated that the inner tube  86  is spaced radially from the center terminal  84 . It should also be appreciated that the axial distance from the end of the inner tube  86  to the end of the glow sheath  78  is a high temperature glow area or glow tip of the glow sheath  78 . 
     The ion sensor glow plug assembly  10  includes an electrical coil  88  disposed about a portion of the center terminal  84 . The electrical coil  88  has a first or current regulating portion  90  having one end disposed about the inner tube  86  and extending axially. The current regulating portion  90  is connected to the inner tube  86  by suitable means such as welding. The current regulating portion  90  is made of a metal material such as nickel-iron (Ni—Fe) or cobalt-iron (Co—Fe). The electrical coil  88  has a second or heating portion  92  disposed about the end of the center terminal  84 . The heating portion  92  has one end connected to the current regulating portion  90  by suitable means such as spot welding and another end connected to the end of the center terminal  84  by suitable means such as spot welding. The heating portion  92  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 inner tube  86  and center terminal  84  act as terminals for the electrical coil  88  to create a heating circuit and are connected to the electronic connector  58 , 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. 
     The ion sensor glow plug assembly  10  further includes a filling material compound  94  disposed in the glow sheath  78  and inner tube  86 . The filling material  94  is made of a ceramic material such as magnesia or alumina. The filling material  94  is a plurality of ceramic tubes disposed in the open end of the glow sheath  78  and inner tube  86  which are crushed to fill the glow sheath  78  and inner tube  86 . The filling material  94  is disposed between the electrical coil  88  and center terminal  84  and between the inner tube  86  and center terminal  84  and between the inner tube  86  and glow sheath  78 . The filling material  94  provides mechanical support of the center terminal  84 , electrical coil  88  and inner tube  86  in an x-y direction. The filling material  94  also acts as a heat conductor from the electrical coil  88  to the glow sheath  78  during glowing. 
     To assemble the ion sensor glow plug assembly  10 , the heating portion  92  of the electrical coil  88  is joined such as by welding to the current regulating portion  90  of the electrical coil  88 . The heating portion  92  is then joined such as by welding to the center terminal  84 , which is the first heater terminal. The current regulating portion  90  of the electrical coil  88  is joined such as by welding to the inner tube  86 , which is the second heater terminal. Crushable ceramic tubes, made of magnesia or alumina, are then inserted to the inside and outside of the terminals/electrical coil  88 , which is, in turn, inserted into the glow sheath  78 . The glow sheath  78  is then swaged to a smaller size to crush and compact the filling material  94 . The glow sheath  78  is then glass sealed using the seal ring  76  and seal  72  in a conveyor belt furnace (not shown) with a heating and cooling temperature profile up to a maximum temperature of one thousand degrees centigrade (1000° C.). The glass sealed glow sheath assembly  78 , 72 , 76  is then press-fitted into the shell  46  through its lower end. The matting  70 , having a decomposition temperature of seven hundred degrees centigrade (700° C.), is then inserted into the passageway  48  between the lower end of the seal  72  and the inner diameter of the shell  46 . The coating  68  may also be added. The insulator  60  and gasket  66  are then inserted into the passageway  48  and the shell  46  is crimped over the gasket  66  to form the shell seat  53 . The shell seat  53  is then machined. The ion sensor glow plug assembly  10  is then heated at one hundred twenty degrees centigrade (120° C.) for approximately thirty (30) minutes to cure the coating  68 . The electrical connector  58  and seal  56  are then inserted into the upper or open end of the passageway  48  of the shell  46 , making connections to the heater terminals of the center terminal  84  and inner tube  86  and ion sensor terminal or glow sheath  78 . The ion sensor glow plug assembly  10  is then completely assembled. 
     In operation of the ion sensor glow plug assembly  10 , current flows from the electrical connector  58  to the center terminal  84 , which passes through the heating portion  92  and current regulating portion  90  of the electrical coil  88  and inner tube  86  back to the electrical connector  58  to form a glow plug circuit. The glow sheath  78  carries the supply voltage from the electrical connector  58  for the ion sensor circuit. When there is combustion in the cylinder  16 , 32 , the burnt gases are ionized and conduct or carry current from the electrical connector  58  to the glow sheath  78  and through the ionized gas to an engine ground, which is the piston  22 , 36  or the shell  46 . The exposed portion of the insulator  60  is disposed in the high temperature area of the glow sheath  78  which will burn off by glowing any soot and moisture formation on the insulator  60  that may create a short between the glow sheath  78  and the shell seat  53  to provide the soot self-cleaning feature of the ion sensor glow plug assembly  10 . It should be appreciated that the matting  70  and/or coating  68  prevent soot such as carbon from seeping through the clearance between the insulator  60  and the glow sheath  78 , resulting in bridging or shorting of the seal  72 . 
     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. 
     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.