Glow plug integrated pressure sensor with filter trap

In an integrated glow plug and pressure sensor having a passage leading to the pressure sensor, a porous filter is inserted in the passage. The porous filter provides a four-fold improvement in pressure measurement by (1) acting as a trap for combustion deposits, (2) burning combustion deposits when the glow plug heater is on, (3) acting as a heat shield for reducing thermal shock error of the pressure sensor, and (4) damping acoustic high frequency ringing associated with the pressure passage.

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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Illustrated inFIGS. 1,1aand1bis a glow plug having a ceramic heater shell10with a resistance heater12therein. Supporting the ceramic heater shell10is a metal heater sleeve14in turn supported by the glow plug shell16. A plurality of radial pressure access holes18are formed in the metal heater sleeve14and communicate with a central axial passage or hole20through the metal heater sleeve. Separate axially directed holes are provided for the heater wires22and24leading to the resistance heater12.

Located within the central axial hole20is a fiber optic pressure sensor26laser welded into the hole at27and having a sensor diaphragm28. Also located in the central axial hole20is a porous filter30of cylindrical shape. The porous filter30covers the radial pressure access holes18from the inside such that the sensor diaphragm28is only exposed to gases that have passed through the filter30.

The porous filter30is 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 filter30.

The heater wires22and24and fiber optic cable32lead to a socket34at the glow plug end opposite the ceramic heater shell.

Illustrated inFIGS. 2,2aand2bis a glow plug of an alternative embodiment having a ceramic heater shell40with a resistance heater42therein. The ceramic heater shell40is formed with a plurality of radial pressure access holes48in communication with a central axial hole50also formed in the ceramic heater shell. Located in the central axial hole50is a porous filter60of cylindrical shape.

Supporting the ceramic heater shell40is a metal heater sleeve44having the central axial hole50extended there through. Also extending through the metal heater sleeve44is a pair of axially directed holes containing the heater wires52and54leading to the resistance heater42.

Located within the central axial hole50of the metal heater sleeve44is a fiber optic pressure sensor56laser welded into the hole at57and having a sensor diaphragm58. The entire assembly is supported by the glow plug shell46.

As above, the heater wires52and54and fiber optic cable62lead to a socket64at the glow plug end opposite the ceramic heater shell40.

Illustrated inFIGS. 3,3aand3bis a glow plug of another alternative embodiment having a metal sheath70enclosing a ceramic interior72and a coil69mounted on an electrode68. The metal sheath70is mounted on a heater sleeve74in turn separated from the electrode68by a ceramic insert66. The heater sleeve74, electrode68and ceramic insert66are formed with a plurality of radial pressure access holes78in communication with a central axial hole80also formed in the electrode. Located in the central axial hole80is a porous filter90of cylindrical shape.

Welded to the electrode68at82is an electrode tube84, and located in the electrode tube and central axial hole80is a fiber optic pressure sensor86having a sensor diaphragm88. The entire assembly is supported by the glow plug shell76. The electrode tube84and fiber optic cable92lead to a socket94at the glow plug end opposite the metal sheath70.