Patent Publication Number: US-7214908-B2

Title: Glow plug integrated pressure sensor with filter trap

Description:
This application claims the benefit of Provisional Application No. 60/581,310, filed Jun. 17, 2004. 
   BACKGROUND OF THE INVENTION  
   The field of the invention pertains to pressure sensors for measuring in real time pressure inside internal combustion chambers in engines and, in particular, fiber optic pressure sensors in spark plugs and glow plugs. 
   By providing an aperture in a glow plug for a fiber optic pressure sensor, a separate aperture into the combustion chamber is not necessary. However, the glow plug environment can be extreme with instantaneous temperatures in thousands of degrees Fahrenheit, rapid cyclic pressure changes and befouling combustion products. To control some of the effects of the extreme environment and provide more accurate pressure measurements over long-term operation, the following improvements to glow plug integrated pressure sensors have been developed. 
   SUMMARY OF THE INVENTION  
   The aperture or axial pressure passage of the integrated glow plug and pressure sensor is provided with a porous filter inserted therein. The purpose of the filter is four-fold: (1) the filter acts as a trap for combustion deposits, (2) the filter burns combustion deposits when the glow plug heater is on, (3) the filter acts as a heat shield for reducing thermal shock error of the pressure sensor, and (4) the filter damps acoustic high frequency ringing associated with the pressure passage. 
   The filter is preferably made of a corrosion-resistant wire mesh, such as already used in diesel particulate filters. The wire mesh filter can be easily modified in dimensions and porosity to accomplish all of the four functions above. With the radial pressure access hole located in the glow plug section that heats to over 600° C., the combustion deposits burn out whenever the glow plug is turned on. As an alternative, the filter may be made of a suitably porous ceramic material. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a partial cross-section of a first version of the integral glow plug; 
       FIG. 1   a  is an external view of the first version of the integral glow plug; 
       FIG. 1   b  is an external view of the socket end of the first version of the integral glow plug; 
       FIG. 2  is a partial cross-section of a second version of the integral glow plug; 
       FIG. 2   a  is an external view of the second version of the integral glow plug; 
       FIG. 2   b  is an external view of the socket end of the second version of the integral glow plug; 
       FIG. 3  is a partial cross-section of a third version of the integral glow plug; 
       FIG. 3   a  is an external view of the third version of the integral glow plug; and 
       FIG. 3   b  is an external view of the socket end of the third version of the integral glow plug. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS  
   Illustrated in  FIGS. 1 ,  1   a  and  1   b  is a glow plug having a ceramic heater shell  10  with a resistance heater  12  therein. Supporting the ceramic heater shell  10  is a metal heater sleeve  14  in turn supported by the glow plug shell  16 . A plurality of radial pressure access holes  18  are formed in the metal heater sleeve  14  and communicate with a central axial passage or hole  20  through the metal heater sleeve. Separate axially directed holes are provided for the heater wires  22  and  24  leading to the resistance heater  12 . 
   Located within the central axial hole  20  is a fiber optic pressure sensor  26  laser welded into the hole at  27  and having a sensor diaphragm  28 . Also located in the central axial hole  20  is a porous filter  30  of cylindrical shape. The porous filter  30  covers the radial pressure access holes  18  from the inside such that the sensor diaphragm  28  is only exposed to gases that have passed through the filter  30 . 
   The porous filter  30  is preferably made of a high-temperature-resistant metal, such as high nickel stainless steel or refractory metal alloy, such as Inconel® or Hastelloy®. The metal mesh now commonly used for diesel exhaust particulate filters is suitable for the porous filter  30 . 
   The heater wires  22  and  24  and fiber optic cable  32  lead to a socket  34  at the glow plug end opposite the ceramic heater shell. 
   Illustrated in  FIGS. 2 ,  2   a  and  2   b  is a glow plug of an alternative embodiment having a ceramic heater shell  40  with a resistance heater  42  therein. The ceramic heater shell  40  is formed with a plurality of radial pressure access holes  48  in communication with a central axial hole  50  also formed in the ceramic heater shell. Located in the central axial hole  50  is a porous filter  60  of cylindrical shape. 
   Supporting the ceramic heater shell  40  is a metal heater sleeve  44  having the central axial hole  50  extended there through. Also extending through the metal heater sleeve  44  is a pair of axially directed holes containing the heater wires  52  and  54  leading to the resistance heater  42 . 
   Located within the central axial hole  50  of the metal heater sleeve  44  is a fiber optic pressure sensor  56  laser welded into the hole at  57  and having a sensor diaphragm  58 . The entire assembly is supported by the glow plug shell  46 . 
   As above, the heater wires  52  and  54  and fiber optic cable  62  lead to a socket  64  at the glow plug end opposite the ceramic heater shell  40 . 
   Illustrated in  FIGS. 3 ,  3   a  and  3   b  is a glow plug of another alternative embodiment having a metal sheath  70  enclosing a ceramic interior  72  and a coil  69  mounted on an electrode  68 . The metal sheath  70  is mounted on a heater sleeve  74  in turn separated from the electrode  68  by a ceramic insert  66 . The heater sleeve  74 , electrode  68  and ceramic insert  66  are formed with a plurality of radial pressure access holes  78  in communication with a central axial hole  80  also formed in the electrode. Located in the central axial hole  80  is a porous filter  90  of cylindrical shape. 
   Welded to the electrode  68  at  82  is an electrode tube  84 , and located in the electrode tube and central axial hole  80  is a fiber optic pressure sensor  86  having a sensor diaphragm  88 . The entire assembly is supported by the glow plug shell  76 . The electrode tube  84  and fiber optic cable  92  lead to a socket  94  at the glow plug end opposite the metal sheath  70 .