Abstract:
Sensor apparatus for a multiple layer steel (MLS) cylinder head gasket measures combustion pressures for detecting engine conditions. A membrane is positioned at one end of an elongated metal tube, and the membrane end of the tube engages a cylinder bore boundary. A fiber optical sensor apparatus is fixed within the tube, and communicates with cyclic combustion events via the membrane. In one disclosed embodiment, optical wires from sensor apparatus situated at each engine bore are bundled into a common groove machined into an extended spacer layer radially outwardly of the conventional boundary of the gasket. The tube protects the sensor apparatus from damage of sealing stress on the gasket, and particularly at the bore perimeter. Each tube lies in a separate groove in the spacer layer that terminates at the bore boundary. A converter changes optical signals received from the apparatus into electrical signals for transmittal to a controller.

Description:
RELATED APPLICATIONS 
     This application claims priority under Title 35, USC Section 119(e) of U.S. Patent Application No. 60/396,532 filed on Jul. 16, 2002 which is incorporated by reference in its entirety. This application also claims priority under Title 35, USC Section 120 of U.S. patent application Ser. No. 10/077,411 (now U.S. Pat. No. 6,701,775), filed on Feb. 15, 2002, of which the present application is a continuation-in-part, which is incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to an apparatus embedded in and or applied to gasket structures, and more particularly to a sensing apparatus applied to combustion gaskets of internal combustion engines. More specifically, the invention relates to a pressure sensing apparatus provided within structures of multi-layered steel combustion gaskets for measuring pressure levels of combustion gases within the cylinder bores of internal combustion engines. 
     2. Description of the Prior Art 
     It is known to employ electronic sensors in gaskets for sealing between engine components including, for example, the block and cylinder head of a multi-cylinder internal combustion engine. In one case, the gasket comprises a sealing plate having several combustion chamber orifices, with combustion chamber sealing elements situated on the edges of the sealing plate surrounding the combustion chamber orifices. The gasket includes sensor elements for cylinder-specific detection of sealing movements perpendicular to the plane of the sealing plate, caused by pressure changes in respective combustion chambers being measured. All of the sensor elements are arranged outside of the combustion chamber sealing elements, and can be piezoelectric and piezoresistive, as well as glass fiber light guide-style sensors. 
     In another example, a gasket enclosed sensor system is employed for measurement of combustion chamber parameters and delivery of signals to points external of the engine. The gasket includes a combustion opening substantially surrounding a combustion chamber, and includes an access opening extending from the combustion chamber to a point external of the engine. A metallic sensor terminal is positioned within the access opening, and insulating material substantially surrounds the metallic sensor terminal. 
     In yet another example, a fluid sensor and associated circuitry are used to indicate presence of oil flow in a multi-cylinder internal combustion engine. The oil sensor includes a heating element positioned within the oil line, directly in the oil flow path. A comparator measures the value of signals from upstream and downstream heat sensors, and triggers a switching circuit when the temperature at the sensors approach one another to indicate an adequate oil flow to the engine. 
     In still another example, a gasket formed in the shape of an exhaust flange includes a load sensor comprising a pressure sensitive electrically resistive material positioned between electrodes and conductors extending outwardly of the perimeter of the gasket. A seal provided between first and second layers of the gasket, and about the load sensor, provides a seal for the electrodes, which are positioned in a cavity to protect the sensor from fluids. 
     SUMMARY OF THE INVENTION 
     A sensor for a multiple layer steel (MLS) cylinder head gasket aperture boundary is adapted to measure combustion pressures occurring in internal combustion engines for detection and control of engine knock, i.e. predetonation conditions, among other purposes. The structure of the sensor includes a pressure sensitive membrane at one end of a metal tube, wherein the tube is positioned adjacent a cylinder bore aperture boundary. The membrane is affixed to the tube at its aperture boundary end, and an optical sensor structure is fixed within the tube downstream of the membrane. The tube protects the optical sensor from becoming damaged under high sealing stresses that occur at the cylinder bore. As disclosed, the sensor is placed into a spacer layer of the MLS gasket, in a groove formed in at least one spacer layer, and an optical fiber wire coupled with a sensor from each cylinder bore is bundled into a common groove of the spacer layer. Various methods for forming the groove are available. The groove may be located outside of the conventional component boundary of the gasket. Thus, the spacer layer may be extended radially outwardly of the conventional component perimeter at the convenience of the gasket designer. Finally, a converter is employed to change optical signals received from the optical wire into electrical signals for appropriate transmittal to a microprocessor of an engine control unit. 
     Where a plurality of cylinder bores is provided in the gasket, and to the extent that pressure sensing is provided at each bore, a real time quality engine management control opportunity based upon cylinder-by-cylinder measurement of combustion pressure is provided. The specific cylinder-to-cylinder data can be input into an engine control unit module that includes systems for optimization of engine performance parameters, including fuel economy and emissions levels, among others. 
     As the pressure sensor apparatus is designed to be applied to a protective tube positioned in a groove of a spacer layer, the apparatus may be positioned between beaded or active layers of a multiple-layered steel gasket without severe risk of being crushed or overstressed. Various alternative embodiments for positioning the tube are disclosed. The sensor may also be positioned relatively close to the flame front within the gasket structure, and as such can be particularly effective to measure pressure levels of cylinder-specific combustion gases in real time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a fragmentary plan view of one described embodiment of a cylinder head gasket that incorporates the combustion pressure sensor system of the present invention, each sensor contained within a protective cylindrical metal tube disposed within a surface groove provided in a spacer layer of the gasket, and adapted to be positioned at the edge of an engine combustion aperture. 
         FIG. 2  is an enlarged perspective break-away view of a portion of the gasket of the present invention to reveal details of a groove provided in the surface of an MLS cylinder head gasket spacer layer, showing the protective metal tube positioned in the groove, wherein the top layer of the gasket has been cut back to reveal the tube. 
         FIG. 3  is a cross-sectional view of a portion of the protective tube, shown separately and apart from the gasket, displaying the end of the tube adapted to be positioned nearest the engine combustion aperture, corresponding to the view of  FIG. 2 . 
         FIG. 4  is a cross-sectional view of an intermediate portion of the protective tube, also shown separately and apart from the gasket, displaying the pressure sensor apparatus contained within the metal tube. 
         FIG. 5  is a cross-sectional view of an end of the protective tube opposite the end positioned near the engine combustion aperture, displaying features related to the protection of the sensor mechanism. 
         FIG. 6  is a cross-sectional view of the entire length of the protective metal tube, including all sections of the tube as displayed in  FIGS. 3 ,  4 , and  5 . 
         FIG. 7  is a cross-sectional view of an alternative embodiment of the groove for positioning the sensor apparatus. 
         FIG. 8  is a cross-sectional view of another alternative embodiment of the groove formed in the spacer layer of the gasket. 
         FIGS. 9   a - 9   d  are alternative embodiments to achieve adequate sealing of the sensor tube adjacent to a combustion bore opening. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to  FIG. 1 , one described embodiment of the pressure sensor apparatus of the present invention is herein described in detail. A combustion, or variously called cylinder head, gasket  10  is formed as a multiple layer steel (MLS) structure, and is of a type now commonly employed as combustion gaskets of internal combustion engines. The gasket  10  is shown only fragmentarily, and includes a plurality of combustion apertures  12 , of which only one is shown and described herein. A plurality of bolt apertures  14 , along with a plurality of other apertures not identified, appear about the periphery of the gasket as shown. Finally, a plurality of grommets  16  are positioned so as to hold the plurality of metal layers together. 
     Referring now also to  FIG. 2 , the MLS gasket  10  includes at least a pair of layers  18  and  20 . The top layer  18  is a beaded active layer containing a metal bead  28 , as will be appreciated by those skilled in the art. Typically, the layer  18  has a counterpart mirror image layer (not shown) that defines a bottom layer, i.e. one positioned beneath the layer  20 , wherein the layer  20  acts as a non-beaded, non-active, spacer layer. 
     A protective metal tube  22  lies in a groove  24  of the spacer layer  20  in a manner such that the groove  24  completely encases the metal tube  22 , as shown. Alternatively, the grove  24  can be formed in both the spacer layer  20  as well as in the upper layer  18 . For example, referring to  FIG. 7 , instead of a single spacer layer  20  being provided with a single groove  24  deep enough for holding metal tube  22 , spacer layer  20  is split into two layers  20   a  and  20   b  that are positioned adjacent one another. Each of the layers  20   a  and  20   b  are provided with a groove  24   a  and  24   b  wherein the depth of each groove is preferably at least about half of the thickness of metal tube  22 . 
     An end  26  of the tube  22  is positioned near the boundary of the combustion aperture  12 . To the extent that only one end  30  of an elongated gasket  10  is depicted ( FIG. 1 ), references to apertures  12  will be understood to extend beyond the single combustion aperture  12  depicted in  FIG. 1 . 
     Referring now to  FIGS. 3 ,  4 ,  5 , and  6 , the pressure sensor apparatus  60  may specifically be described. Each of the  FIGS. 3 ,  4 , and  5 , displays only a partial section of the tube  22 , while  FIG. 6  shows the entire length of the protective metal tube  22 . It will be apparent that the combustion boundary end  26  of the metal tube  22 , shown in most detail in  FIG. 3 , is the end protruding toward the combustion aperture  12  in  FIG. 2 . On the other hand, an incoming fiber optic cable wire  34  is shown at the extreme opposite end of the tube  22  in  FIG. 5 . Intermediately positioned between noted ends of the tube  22 ,  FIG. 4  provides a detailed view of the sensor apparatus  60  that consists primarily of a silica tube  50  which houses a strand of reflective fiber optic cable wire  36 , spaced by a gap  38  from a reflective end  42  of the incoming fiber optic cable wire  34 . The cable wire strand  36  and the reflective end  42  are fused via high temperatures to the internal diameter of the silica tube  50  so as to fix the gap  38 . The respective spaced parallel ends  52  and  54  of the latter members are squared with respect to one another, as shown, so as to enable changes in intensity of light emitted through the incoming cable wire  34  to be measured with great accuracy. 
     Referring specifically now to  FIG. 3 , an interior bore  32  of the combustion end  26  of the tube  22  is adapted for receiving a metallic pressure diaphragm  40 , similar to an end cap, by which combustion pressure may be received and transmitted through a fluid medium, such as a column of oil  48 , to the sensor apparatus  60 . In the described embodiment, the diaphragm is manufactured of nickel alloy metal to provide appropriate characteristics of heat resistance and pressure transmission for the intended environment. Due to the miniature size of the pressure diaphragm  40 , the diaphragm is also referred to as a micro-bellows mechanism. For example,  FIG. 9   a  shows an enlarged view of tube  24  that is provided with a diaphragm  40  at combustion end  26 . Diaphragm  40  fits within a chamber  39  formed located adjacent to combustion opening  12 . Alternatively, diaphragm  40  may be press fit into groove  24  and onto end of tube  22  to properly seal metal tube  22  against the wall  41  of combustion aperture  12 . 
     Referring to  FIG. 9   b , in an alternative embodiment to use of diaphragm  40 , tube  24  may be provided with a trumpet type distal end  43 . In this embodiment, trumpet type distal end  43  engages the wall  41  of combustion aperture  12 . Ideally, distal end  41  is sized so as to be slightly larger than the diameter of groove  24  so as to seal around groove  24 . 
     In yet another alternative embodiment, referring now to  FIG. 9   c , a portion of groove  24  is proved with a plurality of “teeth”  45  or threads to provide localized contact pressure and create several pressure barriers around tube  22 . The teeth  45  are positioned adjacent to the combustion aperture  12 . 
     In yet another alternative embodiment, referring now to  FIG. 9   d , an end portion  47  of tube  22  may provided with triangular shape such that edges  49   a  and  49   b  extend away from one another. In accordance with this aspect of the invention, end portion  47  is press fit into groove  24 , thereby sealing tube  22  within groove  24 . 
     Referring now to  FIG. 5 , it will be noted that downstream of the sensor apparatus  60  is positioned a so-called wick stop material  44  installed during manufacture to arrest wicking of any high temperature adhesive material  46  into the oil entrained portion of the tube  22 . Thus referring specifically to  FIG. 6 , it will be noted that the oil-entrained columns  48  are both upstream and downstream of the sensor apparatus  60 . Those skilled in the art will appreciate that the high temperature oil  48  must be of a type not subject to significant thermal expansion. One such as choice is a so-called diffusion pump type of oil. Another is a silicone brake fluid such as that used in automotive brake systems, and subject to temperatures of up to at least 400 degrees Fahrenheit. The wick stop material  44  in the described embodiment is of a high temperature RTV elastomer, and is used because the high temperature adhesive material  46  is applied in a fluid state during the manufacturing process. 
     Referring now to  FIGS. 4 and 6 , it will be appreciated that the sensor apparatus  60  incorporates a silica tube  50  that floats in the oil column  48  within an intermediate portion of the tube  22 . In the described embodiment, there is no adhesion or attachment in the interface  56  ( FIG. 4 ) between the silica tube  50  and the metal protective tube  22 . The metal protective tube  22  is thus free to expand and contract in the engine environment relative to the apparatus  60 . 
     Finally, those skilled in the art will appreciate that the optical signals generated by means of the sensor apparatus  60  are created by virtue of fluctuating changes in the gap  38  caused by responses of the pressure diaphragm  40  to combustion activity occurring within the cylinders  12 . As appreciated by one skilled in the art, changes in pressure adjust the overall axial length of the silica tube  50 , thereby changing the distance of the gap  38  between the cable wire strand  36  and the reflective end  42  of the incoming fiber optic cable wire  34 . Such signals must ultimately however be converted into electrical signals for purposes of being read appropriately by an engine control module  62  ( FIG. 6 ) for providing real-time engine management, including optimization of fuel economy and emissions levels. 
     The process for manufacturing a spacer layer  20  having at least one groove  24  will be discussed. First, groove  24  is rough cut into spacer layer  20 . If groove  24  is only formed in a single spacer layer  20 , then at least one surface  61  of spacer layer  20  is preferably provided with a thin support layer  63 , as shown in  FIG. 8 . Thin support layer  63  may be attached to spacer layer  20  by spot welding or other suitable method. Once the rough cut groove  24  is formed, final shaping must be performed. Final shaping may be accomplished by either milling, saw blading a path, beading, or coining to the final shape. 
     It is desirable that an adequate seal is provided between the wall of groove  24  and an outer surface of tube  22 . Even if the tolerances are tightly controlled between metal tube  2  and the groove wall  24 , microsealing is desired. There are several different methods that are desirable to provide the sealant coating in groove  24 . One method includes applying sealant coating to a flat layer before the groove is formed. However, use of this method requires that groove  24  must be formed through use of a forming process as opposed to a machining process. Alternatively, the sealant coating may be applied after the groove  24  is formed, through use of a screen printing process. 
     In another alternative embodiment, the sealant coating may be applied directly to metal tube  22  prior to insertion of metal tube  22  into groove  24 . Due to the conformability of the sealant coating, once metal tube  22  is placed in groove  24 , the coating will seal any gap between the wall of the groove  24  and metal tube  22 . Many different types of coatings may be employed to affect the sealing between the groove  24  and the metal tube  22 . Suitable coatings include FKM based coatings, thermoplastic, cement (must be applied in a fluid stage and cured after sensor is assembled) and foam-like coatings. 
     It is to be understood that the above description is intended to be illustrative and not limiting. Many embodiments will be apparent to those of skill in the art upon reading the above description. For example, a gasket within the sensor elements and wires molded into the body of the gasket material would fall within the broader scope of this invention. Therefore, the scope of the invention should be determined, not with reference to the above description, but instead with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.