Abstract:
A method of detecting a gap between a valve seat insert and a port in a cylinder head may include heating the valve seat insert and the cylinder head and generating a thermal image of the valve seat insert and the cylinder head at an interface between the valve seat insert and corresponding port in the cylinder head housing the valve seat insert. The thermal image may be evaluated to determine the magnitude of a gap between the valve seat insert and the cylinder head based on a temperature at the interface between the valve seat insert and the cylinder head.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 61/158,888, filed on Mar. 10, 2009. The entire disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to assembly of internal combustion engines, and more specifically to evaluating engine valve seat gaps during assembly. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Engine assemblies may include valve seat inserts that are pressed into intake and exhaust valve ports. The inserts may abut a corresponding seating surface on the intake and exhaust ports. However, during assembly some inserts may not be completely seated within a port. As a result, gaps may exist between the insert and the seating surface defined by the port. Current methods of detecting these gaps may be time consuming and unreliable. 
     SUMMARY 
     An engine valve seat gap evaluation system may include a thermal camera assembly, a fixture having a first end coupled to the thermal camera assembly, and a mirror coupled to a second end of the fixture opposite the first end. The thermal camera assembly may include an infrared sensor. The mirror may be adapted to be located within an engine port to direct infrared radiation from a gap between a cylinder head and a valve seat insert to the infrared sensor. 
     A method of detecting a gap between a valve seat insert and a port in a cylinder head may include heating the valve seat insert and the cylinder head and generating a thermal image of the valve seat insert and the cylinder head at an interface between the valve seat insert and corresponding port in the cylinder head housing the valve seat insert. The thermal image may be evaluated to determine the magnitude of a gap between the valve seat insert and the cylinder head based on the thermal image at the interface between the valve seat insert and the cylinder head. 
     The thermal image may be generated by locating a mirror coupled to a first end of a fixture within the port at the interface and reflecting infrared radiation at the interface to an infrared sensor of a thermal camera assembly coupled to a second end of the fixture. The infrared radiation reflected by the mirror may provide a 360° image of the interface to the thermal camera assembly. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a schematic illustration of a cylinder head according to the present disclosure; 
         FIG. 2  is a schematic illustration of a portion of the cylinder head of  FIG. 1 , a valve seat insert and a thermal imaging system according to the present disclosure; 
         FIG. 3  is a schematic illustration of a portion of the cylinder head of  FIG. 1 , a valve seat insert and an alternate mirror for the thermal imaging system according to the present disclosure; 
         FIG. 4  is a first schematic illustration of the energy transfer between the cylinder head and valve seat insert; 
         FIG. 5  is a second schematic illustration of the energy transfer between the cylinder head and valve seat insert; 
         FIG. 6  is a schematic illustration of a thermal image of an interface between the cylinder head and valve seat insert using the thermal imaging system of  FIG. 2 ; and 
         FIG. 7  is a schematic illustration of an automated gap detection line according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     As seen in  FIGS. 1 and 2 , an engine cylinder head  10  may include intake ports  12  and exhaust ports  14 . The following description applies equally to the intake and exhaust ports  12 ,  14  and will be described with respect to the intake port  12  for simplicity. As seen in  FIG. 2 , the intake port  12  may include a valve seat  16  defining a stepped region  18 . The stepped region  18  may include an axial end surface  20  and an inner radial surface  22 . 
     A valve seat insert  24  may include an annular body  26  located within the stepped region  18 . The annular body  26  may include an outer radial surface  28  abutting the inner radial surface  22  of the valve seat  16  and a first axial end surface  30  facing the axial end surface  20  of the valve seat  16 . A second axial end surface  32  opposite the first axial end surface  30  may define a valve seating surface for an intake valve (not shown). 
     During assembly, the valve seat insert  24  is located within the valve seat  16  and the first axial end surface  30  is urged toward the axial end surface  20  of the valve seat  16 . However, after assembly the first axial end surface  30  may be offset from the axial end surface  20  of the valve seat  16 . The offset may form a gap (G) between the first axial end surface  30  and the axial end surface  20 . The gap (G) may be detected using an infrared (IR) thermal imaging system  100  discussed below. 
     The IR thermal imaging system  100  may include an IR transparent fixture  102  coupled to a thermal camera  104 . The fixture  102  may include a first end  106  fixed to the thermal camera  104  and a second end  108  having a mirror  110  fixed thereto. The second end  108  of the fixture  102  may have a diameter (D 1 ) less than a diameter (D 2 ) of the intake port  12 . Therefore, the mirror  110  may be located within the intake port  12 .  FIG. 2  illustrates the mirror  110  as an internal prism mirror (or optics). However, as seen in  FIG. 3 , an external prism mirror  210  may be used in place of the internal prism mirror  110 . The present disclosure applies equally to both internal and external prism mirrors. 
     The internal prism (internal reflection) mirror  110  may be made transparent to IR by using materials including, but not limited to, sapphire, quartz, NaCl, PtSi, or Ge depending on the IR detector wavelength selection (e.g. 3 to 5 microns or 8 to 12 microns). The external prism (exterior reflection) mirror  210  may be incorporated using a metal mirror. The metal external prism mirror  210  may be inserted in a fixture  202  ( FIG. 3 ) transparent to IR similar to the fixture  102  shown in  FIG. 2 . The metal external prism mirror  210  may be manufactured from aluminum, copper, stainless steel, or other metal materials. 
     The prism mirror  110 ,  210  may be used to reflect the emitted radiation from the gap (G) to the IR sensor (or detector)  114 . An included angle (α) of the prism mirror  110 ,  210  may be designed to amplify the signal (or the width of the gap (G)) so that at least one pixel is included within the gap (G) if the minimum pixel size of the IR sensor  114  itself is insufficient to separate the intensity of energy within the gap (G). By way of non-limiting example, the included angle (α) may be greater than ninety degrees. The thermal camera  104  may include a lens  112  at the first end  106  of the fixture  102  and aligned with the prism mirror  110 ,  210  and an IR sensor  114  located at the focal point of the lens  112 . 
     During assembly, the cylinder head  10  and the valve seat insert  24  may each be heated to a predetermined temperature. By way of non-limiting example, the predetermined temperature may be between thirty-two and forty-nine degrees Celsius (between ninety and one hundred and twenty degrees Fahrenheit). The predetermined temperature may provide repeatable IR radiation from the cylinder head  10  and the valve seat insert  24 , forming a reference for detection of the gap (G). Additionally, the cylinder head  10  and the valve seat insert  24  may be formed from different materials. By way of non-limiting example, the cylinder head  10  may be formed from aluminum and the valve seat insert  24  may be formed from steel. Therefore, the cylinder head  10  may have an emissivity (ε head ) that is lower than the emissivity (ε insert ) of the valve seat insert  24 . More specifically, the emissivity (ε head ) of the cylinder head  10  may be an order of magnitude lower than the emissivity (ε insert ) of the valve seat insert  24 . 
     With reference to  FIGS. 4 and 5 , the cylinder head  10  and the valve seat insert  24  may exchange radiation (or heat) through the gap (G). Since the cylinder head  10  and the valve seat insert  24  are formed from different materials, the radiant energy emitted from the axial end surfaces  20 ,  30  will be different from one another. The valve seat insert  24  may emit power (E 1 ) and the cylinder head  10  may emit power (E 2 ).  FIGS. 4 and 5  illustrate ray traces starting from the first axial end surface  30  of the valve seat insert  24  having power (E 1 ). 
     The ray  36  strikes the axial end surface  20  of the cylinder head  10  where part of the radiation will be absorbed and part will be reflected. The reflected ray will again strike the first axial end surface  30  where part of the reflected ray will be reflected again and the other part absorbed. This process continues among the two surfaces through the gap (G). Therefore, infinite exchanges between the axial end surfaces  20 ,  30  will occur resulting in an emissivity (ε GAP ) of the gap (G) being close to 1.0 due to the concentration of incident energy at the gap (G). 
     The diagrams of the radiation among two surfaces being either parallel ( FIG. 4 ) with a gap (G) or disposed at an angle ( FIG. 5 ) with gap (G) illustrate the concentration of energy. The high gap emissivity (ε GAP ) may produce a higher apparent temperature on the thermal camera  104  at the gap (G) relative to the cylinder head  10  and the valve seat insert  24 . Even if the temperature for the cylinder head  10  and the valve seat insert  24  are the same, the axial end surfaces  20 ,  30  will emit radiation across the surfaces within the gap (G) because of the difference in emissivity between the cylinder head  10  and the valve seat insert  24 . As discussed above, in the present non-limiting example, the emissivity of the cylinder head  10  is an order of magnitude lower than that of the valve seat insert  24  due to the difference in materials. 
     The increased concentration of incident energy discussed above will produce increased IR radiation, providing an indication of increased temperature (or higher pixel value) on the thermal camera  104  (even though the temperature may be the same as the predetermined temperature as discussed above). In machine vision vocabulary, the “pixel value” can be used instead of converting the IR radiation to a temperature reading. Just like a digital camera, a thermal image is built up by a number of individual pixels. The minimum size of the pixels produced is dependent on the IR sensor  114 . For example, the pixels produced by a Barium Strontium Titanate (BST) detector are 50 microns, while Vanadium Oxide or Amorphous silicon detectors can produce pixels as small as 15 microns. 
     The thermal camera  104  may therefore be used to provide an image of the interface  34  between the cylinder head  10  and valve seat insert  24  to detect the size of the gap (G). In the present non-limiting example, the fixture  102 ,  202  may provide a three hundred and sixty degree view of the interface  34 . However, the present disclosure is not limited to applications including the mirror  110 ,  210 . In alternate arrangements, a direct optics approach may be used where the thermal camera  104  is used without the prism mirror  110 ,  210  to provide images of portions of the interface  34  and is rotated relative to the interface  34  to provide a complete three hundred and sixty degree view of the interface  34 . 
     During operation, the prism mirror  110 ,  210  may be located within the intake port  12 . The prism mirror  110 ,  210  reflects the IR radiation through the lens  112  to the IR sensor  114  where an image may be formed as schematically illustrated in  FIG. 6 . The first region  116  represents the IR radiation from the valve seat insert  24 , the second region  118  represents the IR radiation at the gap (G), and the third region  120  represents the IR radiation from the cylinder head  10 . The included angle (α) of the prism mirror  110 ,  210  may provide an increased resolution for detection of the gap (G). The second region  118  may have a different pixel value than the first and third regions  116 ,  120  due to the higher apparent temperature resulting from the gap emissivity (ε GAP ). 
     In one implementation, illustrated in  FIG. 7 , a station may be located after the hot washer of the cylinder head  10  in an assembly line and may monitor the valve seat interface  34  with the IR thermal imaging system  100  prior to cylinder head assembly. The valve seat insert  24  may be secured to the cylinder head  10  before the cylinder head  10  passes through the hot washer. The hot washer may heat the cylinder head  10  and valve seat insert  24  may be heated to a predetermined temperature (both may be at approximately the same temperature). Alternatively, a different heat source may be used to provide the predetermined temperature. 
     Two IR thermal imaging systems  100  may be used for the inspection. The cylinder head  10  may travel under the IR thermal imaging system  100  or the IR thermal imaging system  100  may travel above the cylinder head  10  to view each of the valve seat interfaces  34 . In addition, the IR thermal imaging system  100  may be located on a robot arm to locate the prism mirror  110 ,  210  at the valve seat interface  34 . 
     IR thermal imaging systems  100  may be located on each side of the conveyor in a staggered configuration. A first IR thermal imaging system  100  may inspect the intake ports  12  and a second IR thermal imaging system  100  may inspect the exhaust ports  14 . The IR thermal imaging system  100  is insensitive to external light sources but an inspection chamber may be added to provide a shrouded area to eliminate external influence on the measurements. Additionally, inspection triggers may be provided by a series of photo-detectors positioned across the powered roller conveyor. As the component translates through the inspection chamber it may interrupt the photo-detectors and thus trigger a specific acquisition/inspection. 
     IR software with the imaging analysis tools may be used for real time monitoring capabilities to evaluate the pixel value (temperature) range and the pixel value (temperature) measurement zones for collecting and alarming valve seat gap data. Image calibration may additionally be included since the parts may have some temperature variation as they are exiting the hot washer. The cylinder head  10  and valve seat insert  24  assembly may be transported to and from the inspection station using standard line automation. 
     The system illustrated in  FIG. 7  may include two axes, one for the part travel and one for scanning. The system may utilize an image processing script that accesses the surface temperature and through further automation (i.e. conveyors, shuttles etc.) sorts the cylinder head  10  and valve seat insert  24  assemblies accordingly. 
     The image processing methodology may include separating pixel value (temperature) zones on the surface from actual part features using an image processing software script. The script may include a series of imaging algorithms that isolate the pixel value (or temperature) circular zones (illustrated in  FIG. 6 ) from the remaining image (i.e. surface). The tolerancing criteria may be defined based on pixel value difference (or a temperature difference) at the interface  34  between the cylinder head  10  and the valve seat insert  24 . The acceptability of a gap size at a given position may be determined based upon a predetermined difference in pixel value (or temperature difference). 
     Typically, pixel values may range from value 0 when an image is pure black, to pixel value 255 when an image is pure white. This produces 2 to the 8th power in pixel values (2, 4, 8, 16, 32, 64, 128, 256). When dealing with pixel values within a thermal infrared image (grey scale palette) simple threshold values can be used to eliminate all parts of the image that are under a certain pixel value. By way of non-limiting example, the resolution of the IR thermal imaging systems  100  may be set so that any temperature difference at the interface  34  indicates an unacceptable gap size. 
     An exemplary gap detection process may include first acquiring an original image from the IR thermal imaging system  100  to calibrate the system for proper positioning of the IR thermal imaging system  100 . A specific valve seat may then be located under the IR sensor. The adapter in  FIG. 2  may then be inserted in the corresponding porting section to acquire the emitted radiation or an image of the part surface as viewed under the IR camera. In pre-selected regions of interest, a pattern recognition algorithm may then be used to locate known features on the image to establish an orientation, a scaling factor, and a coordinate system that are all relative to the actual scanned surface. The image may then be scaled to appropriately set up the pixel resolution to the actual work-piece gap section of measure. This generally provides for defining the location of the gap (G) on the surface and also establishing the specification regions using different circular tolerance for control purposes. This may be achieved by establishing a Region of Interest (ROI) around an area of the image for which a search is performed for a specified range of pixel values. Next, the various regions of interest, such as the unique zonal tolerance requirements of a gap (G), may be specified relative to the previously defined coordinate system. 
     By way of non-limiting example, if all pixels of value 0 to 168 are changed to value 0 in the computer software, the resulting image will be just the gap itself if a gap exists. Since the gap is the best emitter in the image, it will have the highest pixel value that could be in the range of 172 to 255 in value. The computer can then change all of these bright pixels to a value, such as 240. The software can then add up the 240 value pixels to determine gap size. 
     While discussed with respect to gap detection between a cylinder head  10  and a valve seat insert  24 , it is understood that the present disclosure applies equally to gap detection between any variety of other engine components. Further, it is understood that the present disclosure has applications outside of engine assembly.