Abstract:
A method of detecting a fracture as it occurs in a component during a manufacturing process includes positioning an acoustic sensor in acoustic communication with the component. A manufacturing process is performed while the acoustic sensor remains in acoustic communication with the component. A signal indicative of acoustic emissions from the component during the manufacturing process is provided to a controller where it is determined whether the component has fractured based on the signal.

Description:
FIELD 
       [0001]    The present disclosure relates to a method of assembling a catalytic converter or other exhaust treatment device. More particularly, a method to detect ultrasonic acoustic emissions from a substrate is discussed. 
       BACKGROUND 
       [0002]    This section provides background information related to the present disclosure which is not necessarily prior art. 
         [0003]    Catalytic converters have been useful in motor vehicle exhaust gas systems to convert nitrous oxides, carbon monoxide and/or hydrocarbons to more environmentally friendly compounds. One type of catalytic converter includes one or more ceramic monoliths or substrates mounted inside of a sheet metal housing. The substrates typically contain a multiplicity of longitudinal straight-through-flow exhaust gas passages that are coated with a catalyst. 
         [0004]    In many instances, the metal housings used for commercially acceptable converters are formed as “pancake” or “clam shell” designs. These designs include stamped upper and lower shells which are substantially identical to each other. The shells have mating, peripheral side flanges that are welded together along a plane containing the longitudinal axis of the housing. Another commercial form of catalytic housing may be formed from three pieces including a tube with separate end cones welded at each end of the tube. 
         [0005]    Other more economically produced catalytic converters may include a singular open-ended metal tube in which the catalyst coated ceramic substrate is inserted. In one method of catalytic converter assembly, the metal tube is radially inwardly compressed around the substrate. In another process, the substrate is pressed into an undersized tube to a fixed position. Regardless of the manufacturing process, care must be taken to avoid damaging the relatively brittle ceramic substrates. Furthermore, substrates that have been cracked or otherwise damaged during assembly are relatively difficult to inspect once the catalytic converter assembly process has been completed and the metal housing substantially precludes access to the substrate. Non-destructive inspection of the completed assembly may not be as reliable as desired. The cost and time associated with post assembly inspection may also be very high. Accordingly, it may be beneficial to provide a non-destructive testing method for detecting substrate fracture during catalytic converter assembly. 
       SUMMARY 
       [0006]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0007]    A method of detecting a fracture as it occurs in a component during a manufacturing process includes positioning an acoustic sensor in acoustic communication with the component. A manufacturing process is performed while the acoustic sensor remains in acoustic communication with the component. A signal indicative of acoustic emissions from the component during the manufacturing process is provided to a controller where it is determined whether the component has fractured based on the signal. 
         [0008]    A method of detecting a fracture in a component of an exhaust treatment device as it occurs during a manufacturing process includes positioning an acoustic sensor in acoustic communication with the exhaust treatment device. A manufacturing process is performed on the exhaust treatment device while the acoustic sensor remains in acoustic communication with the exhaust treatment device. A signal from the acoustic sensor is output indicating acoustic emissions from the exhaust treatment device during the manufacturing process. The method includes comparing the signal output by the acoustic sensor to a predetermined value and determining whether the component has fractured based on the comparison. 
         [0009]    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 
         [0010]    The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
           [0011]      FIG. 1  is a schematic depicting a manufacturing process related to the assembly of an exemplary catalytic converter; 
           [0012]      FIG. 2  is a cross-sectional view of an acoustic sensor assembly for detecting fracture of a component during an assembly process; 
           [0013]      FIG. 3  is a graph depicting component insertion force versus displacement as well as acoustic sensor output for the process performed using the apparatus of  FIG. 1 ; 
           [0014]      FIG. 4  is a schematic view of another work station for performing a sizing operation on a catalytic converter; and 
           [0015]      FIG. 5  is a graph depicting machine operating characteristics as well as an acoustic output signal associated with a manufacturing operation using the apparatus of  FIG. 4 . 
       
    
    
       [0016]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0017]    Example embodiments will now be described more fully with reference to the accompanying drawings. 
         [0018]    With reference to  FIG. 1 , a catalytic converter assembly machine is identified at reference numeral  8 . Assembly machine  8  is arranged to at least partially assembly an exemplary catalytic converter  10 . Catalytic converter  10  includes a ceramic substrate  12  wrapped with a compressible mat  14  and positioned within a tubular housing  16 . 
         [0019]    Housing  16  is depicted as a hollow right circular cylinder having an open first end  18  and an opposite end  20 . Housing  16  includes an inner cylindrical surface  22  and an outer cylindrical surface  24 . It should be appreciated that other tubular shapes are also contemplated as being within the scope of the present disclosure. Accordingly, housing  16  may have any number of cross-sectional shapes including elongated slot, elliptical, square, polygonal, or other shape. 
         [0020]    Substrate  12  is shaped as a right circular cylinder having an outer cylindrical surface  26  and a first substantially planar end face  28  and an opposite substantially planar end face  30 . At the beginning of the assembly process, mat  14  is wrapped around substrate  12  in contact with cylindrical surface  26 . Mat  14  functions to support substrate  12  within housing  16  providing thermal and acoustically shielding, as well. It has been determined that mat  14  performs the above functions best when compressed to a predefined thickness. An outer cylindrical surface  31  of mat  14  defines an outer diameter greater than an inner diameter of inner cylindrical surface  22 . As such, radial compression of mat  14  is required to assemble catalytic converter  10 . 
         [0021]    One method of radial compression is combined with axially inserting the mat/substrate combination into housing  16  and includes using a stuffing cone, such as disclosed in U.S. Pat. Nos. 6,532,659 and 6,732,432. With the devices shown in these patents, an outlet of the stuffing cone is disposed adjacent to opening  18  of housing  16 . The cone structure has an inner diameter less than the inner diameter of the housing. As the mat and substrate combination moves through the stuffing cone toward the housing, the cone compresses compressible mat  14  about substrate  12  so that the subassembly can be axially translated into housing  16 . As the mat and substrate combination slide against the inwardly tapered interior of the stuffing cone, mat  14  compresses about substrate  12  until the combination has an outer diameter less than an inner diameter of inner cylindrical surface  22 . At this point, the mat and substrate combination is pushed or stuffed into housing  16 . In an alternate process, the mat may be compressed via a fluid bearing as disclosed in published patent application no. US2007/0148057. 
         [0022]    During the stuffing operation, substrate  12  may inadvertently contact housing  16 . During this contact, a portion, such as an edge, of substrate  12  may be chipped or the substrate may be cracked. The stuffing operation may also cause mat  14  to roll or bunch due to the shear forces generated between mat  14  and housing  16  during the stuffing process. As substrate  12  and mat  14  are further driven into housing  16 , stresses may increase to the point of fracturing or otherwise damaging substrate  12 . 
         [0023]    Assembly machine  8  performs the stuffing operation and includes a ram  32  fixed to a plate  34 . Ram  32  is coupled to a hydraulic press and is operable to move along the axis of ram  32 . A sensor assembly  38  is coupled to plate  34 . Sensor assembly  38  is depicted in  FIG. 2  to include a mounting block  42 , a spring  44 , a sensor  46  and a wave guide  48 . Mounting block  42  is preferably constructed from a plastic material such as Delrin® or an ultra high molecular weight material. Mounting block  42  is fixed to plate  34  and includes a pocket  50  in receipt of spring  44 , sensor  46  and at least a portion of wave guide  48 . 
         [0024]    Sensor  46  is an acoustical monitoring device operable to output a signal indicative of the magnitude and frequency of acoustic waves emanating from substrate  12 . Sensor  46  is in communication with a controller  54  ( FIG. 1 ) programmed to compare the signal provided by sensor  46  to a predetermined acoustical output and determine whether the substrate has been chipped, cracked or otherwise damaged. 
         [0025]    Wave guide  48  serves to protect sensor  46  from possible damage during the assembly process and may be constructed from a metal stamping sized to axially translate within pocket  50 . Wave guide  48  includes a recess  56  in receipt of sensor  46 . Spring  44  engages a wall  58  of mounting block  42  and biases sensor  46  and wave guide  48  away from mounting block  42 . Wave guide  48  includes a convex contact surface  60  that protrudes from a bottom face  62  of plate  34 . The amount of axial travel allowed between wave guide  48  and mounting block  42  exceeds the distance that convex surface  60  extends beyond surface  62  of plate  34 . In this manner, load provided by ram  32  is transferred through plate  34  to substrate  12  and not through the sensor  46 . Sensor  46  and wave guide  48  are only loaded against substrate  12  to the extent that spring  44  allows. 
         [0026]    To obtain an accurate acoustic signal, it may be desirable to minimize noise generated during the catalytic converter assembly process. One source of noise may occur when wave guide  48  moves relative to end face  28  of substrate  12 . To minimize this noise generation source, the shape of the end of wave guide  48  is curved as previously discussed. Furthermore, a lubricant or an acoustic couplant  64  may be provided between the interface of convex surface  60  and end face  28 . 
         [0027]    In an automated production process, it may be desirable to automatically dispense couplant  64  to surface  60  prior to engaging wave guide  48  with each substrate  12 . Couplant  64  may be stored within a container  66  and pumped or otherwise dispensed through a line  68  and a passageway  70  extending through wave guide  48 . Passageway  70  terminates at an outlet  72  positioned at or near the apex of convex surface  60 . By arranging sensor assembly  38  relative to plate  34  in the manner described, wave guide  48  will contact substrate  12  prior to the application of insertion force by ram  32 . Acoustic monitoring or crack detection may occur during the entire process for which a load is applied to substrate  12 . It should be appreciated that the axial load applied by ram  32  may be substantial because further compression of mat  14  may need to occur during the stuffing process. 
         [0028]    With reference to  FIG. 3 , a force versus displacement graph depicting an exemplary stuffing operation overlies a trace of acoustic output versus time representing a crack being formed in the substrate during the stuffing process. More particularly, a first trace  80  depicts the axial force provided by ram  32  during a stuffing operation. This trace may represent the axial force for a “properly installed” substrate and mat. It should be appreciated that a similar curve may result when an undesirable event such as rolling or bunching of mat  14  occurs. Accordingly, it may be desirable to utilize sensor  46  to determine if substrate  12  has been damaged during the stuffing process.  FIG. 3  also depicts a trace  82  showing radial pressure acting on mat  14  and substrate  12  during a desired or “normal” stuffing process. The maximum radial pressure remains below a radial pressure limit identified at line  84 . A trace  86  represents the radial pressure acting on mat  14  and substrate  12  during assembly of a defective catalytic converter  10 . As is shown in the graph, the radial pressure rapidly increases to a peak pressure  88  that is substantially greater than the radial pressure limit  84 . At the maximum radial pressure, substrate  12  cracks. The stress is relieved and the radial pressure decreases as the mat  14  and substrate  12  are continued to be stuffed within housing  16 . 
         [0029]    Another trace  90  of  FIG. 3  depicts an exemplary output from sensor  46 . A peak magnitude on the acoustic trace occurs at point  92 . Point  92  corresponds to the occurrence of a crack in substrate  12 . During the cracking event, sound is emitted from substrate  12 . Controller  54  may be programmed to output a signal corresponding to point  92  when the magnitude of acoustic emission measured is greater than a predetermined maximum. 
         [0030]    With reference to  FIG. 4 , another catalytic converter assembly machine is identified at reference numeral  100 . Assembly machine  100  is operable to radially inwardly compress housing  16  to further secure substrate  12  therein. Assembly machine  100  is operable to perform a sizing operation subsequent to the stuffing operation performed by assembly machine  8 . The sizing operation compresses mat  14  to the target predetermined thickness earlier described. A transfer apparatus  102  includes an upper clamp plate  104  and a lower clamp plate  106  operable to engage and capture tubular housing  16  therebetween. Sufficient load is applied through an upper rod  108  and a lower rod  110  to transfer the subassembly of substrate  12 , mat  14  and housing  16  created by assembly machine  8  into communication with radially moveable jaws  112  of assembly machine  100 . 
         [0031]    Jaws  112  are circumferentially spaced about a perimeter of a cavity  114 . The inner diameter of cavity  114  may vary based on the radial position of jaws  112 . At an open position, jaws  112  are retracted to a radial outward position thereby defining a maximum inner diameter. At this time, the substrate, mat and housing assembly is positioned within cavity  114  by axially translating rods  108 ,  110 . 
         [0032]    A retractable sensor head  116  is configured substantially similarly to sensor assembly  38  previously described. Accordingly, like elements will retain their previously introduced reference numerals. Retractable sensor head  116  is coupled to an axially moveable slide  118 . Slide  118  and retractable sensor head  116  pass through an aperture  120  formed in upper clamp plate  104 . Wave guide  48  is placed in contact with end face  28  prior to radial inward movement of jaws  112 . If desired, slide  118  may be actuated to place wave guide  48  in contact with end face  28  prior to engagement of clamp plates  104 ,  106  with housing  16 . 
         [0033]    Once the substrate, mat and housing assembly have been positioned within cavity  114 , upper rod  108  and lower rod  110  axially translate away from one another to retract upper clamp plate  104  and lower clamp plate  106  out of communication with jaws  112 . Jaws  112  are moved radially inwardly to contact outer cylindrical surface  24  and reduce the outer diameter of housing  16 . By moving the cylindrical wall of housing  16  radially inwardly, mat  14  is further compressed. Jaws  112  are controlled to move radially inwardly a desired amount to properly “size” housing  16  and compress mat  14  to the desired thickness. At the end of the sizing operation, jaws  112  are once again radially outwardly moved to maximize the inner diameter of cavity  114 . Assembly machine  100  causes upper rod  108  and lower rod  110  to move toward one another and engage upper clamp plate  104  with one end of housing  16  and lower clamp plate  106  with an opposite end of housing  16  to transfer the sized substrate, mat and housing assembly out of cavity  114 . 
         [0034]      FIG. 5  provides a trace  140  indicative of the radial position of jaws  112 . A trace  142  represents the radial pressure acting on mat  14  and substrate  12  during the sizing operation. A trace  144  represents the output of acoustic sensor  46  during a sizing operation. As jaws  112  move radially inwardly, as indicated by the downward sloping direction of trace  140 , the radial pressure illustrated by trace  142  increases. At or near a point of maximum radial pressure  146 , a crack occurs in substrate  12 . An acoustic emission emanates from the crack site. Sensor  46  detects the acoustic emission and outputs a maximum acoustic sensor signal output at a point  148 . Controller  54  determines whether the maximum detected magnitude of trace  144  exceeds a predetermined acceptable maximum. A fault signal is output when the actual magnitude exceeds the predetermined maximum value. 
         [0035]    From the above description, it should be appreciated that the present disclosure relates to crack detection and acoustic monitoring in a production assembly environment. It is contemplated that a number of acoustic sensor assemblies  38  may be positioned throughout the assembly process to collect acoustical data and detect cracks at one or more assembly stages. Furthermore, it is contemplated that additional acoustic sensor assemblies  38  may be positioned to contact substrate  12  before and during each transfer and/or handling step. In this manner, real time crack detection may be performed to greatly minimize and possibly eliminate the need for after-assembly catalytic converter inspection. At a minimum, it is contemplated that the assembly machines and processes described herein may be useful for identifying individual ceramic substrates that may require off-line inspection after the assembly processes have been completed. 
         [0036]    If further detail is required regarding crack initiation, three or more sensor assemblies  38  may be positioned in contact with a single substrate  12 . Controller  54  may be operable to compare the output of each sensor assembly  38  on a real-time basis in order to perform a triangulation method to locate the substrate crack in 3D space. Furthermore, while sensor assembly  38  has been shown for use in communication with ceramic substrate  12 , it is contemplated that acoustic detection for the handling and assembly of other components may be implemented as well. 
         [0037]    The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.