Abstract:
A method for determining which component of a multi-component product is responsible for a problem with the product features dismantling first and second products—one exhibiting the problem and one not. One different component from each of the original two samples is then used in building a plurality of new products. The new products are then comparatively tested to determine which component or components caused the problem.

Description:
RELATED APPLICATION(S)  
       [0001]     This application claims the benefit of Provisional Patent Application Ser. No. 60/504,812, filed Sep. 22, 2003. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The invention relates generally to product failure analysis. More specifically, the invention pertains to a failed component search technique where the original failed product containing a plurality of components must be at least partially destroyed in order to gain access to the plurality of components.  
         [0003]     Known techniques for identifying a cause of a multi-component product failure involve component swapping. One such prior method begins by identifying two samples of the product being analyzed—one exhibiting the problem (a “worst” product) and one that does not exhibit the problem (a “best” product sample). The “worst” and the “best” product samples are then disassembled, and a first component is swapped between the two samples. The samples are reassembled and tested for the previously observed failure in the “worst” sample. If the “best” product sample now exhibits the previously observed problem, then the component at fault has been identified. If the “best” is still failure-free, then the samples are again disassembled and a different component is swapped. This process continues until the “best” sample exhibits the problem, to identify the component or components at fault.  
         [0004]     This prior approach will not work, however, for products which are at least partially destroyed when disassembled. Such products typically employ non-mechanical fasteners such as welded seams or seals which are destroyed upon disassembly or dismantling.  
       SUMMARY OF THE INVENTION  
       [0005]     A method for determining which of a plurality N of components in a product are responsible for an observed problem of the product begins by identifying a first sample of the product not exhibiting the observed problem. A second sample of the product is identified which exhibits the observed problem. The first product sample is dismantled to obtain N separate first sample components and the second sample is also dismantled to obtain another N separate second sample components. N new versions of the product are then produced each containing a different one of the N first sample components, and another N new versions of the product are produced each containing a different one of the N second sample components. Which of the N second sample components is a source of the observed problem is determined by comparative testing of the N new versions containing a different one of the N second sample components and the N new versions containing a different one of the N first sample components.  
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0006]     The objects and features of the invention will become apparent from a reading of a detailed description, taken in conjunction with the drawing, in which:  
         [0007]      FIG. 1  is a combined perspective and exploded view of a vehicle shock absorber suitable for analysis in accordance with the principles of the invention;  
         [0008]      FIG. 2  is a spreadsheet showing how new products incorporate one component from the “worst” and the “best” product samples pursuant to the invention; and  
         [0009]      FIG. 3  presents an example comparative test protocol with results for identifying a component causing a product failure in accordance with the principles of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0010]     An example of a product suitable for failure analysis in accordance with the invention is an automotive shock absorber. A typical shock absorber  100  is shown in  FIG. 1 . Shock absorber  100  typically has ten main components, seven of which are not destroyed when the shock absorber is dismantled. These seven components are rod assembly  101 , oil seal  103 , spring  105 , rod guide  107 , check valve  109 , piston tube assembly  111  and piston valve assembly  113 . The three components of shock absorber  100  which are at least partially destroyed when the shock absorber is dismantled are the rod tube assembly, a cover seal and the oil used in the shock absorber.  
         [0011]     One type of problem with a typical vehicular shock absorber that is readily observable is “weepage”. Weepage comprises leakage of internal shock absorber fluid (oil) to an outside surface of the shock absorber housing. Experience has shown that the seven components shown in the exploded view of  FIG. 1  are the most likely causes of weepage.  
         [0012]     Hence, the problem becomes where weepage is observed to be unacceptable, which of the seven components or combination thereof have caused the problem.  
         [0013]     Prior component swapping techniques do not work with a vehicular shock absorber, because portions of the shock absorber are at least partially destroyed when dismantling a product sample exhibiting a weepage problem.  
         [0014]     Hence, in accordance with the invention, a “worst” shock exhibiting unacceptable weepage is used along with an identically designed shock, preferably from the same vehicle, which does not exhibit the weepage problem in order to determine which component or components are at fault. The spreadsheet of  FIG. 2  reflects the fact that in accordance with the invention, the “worst” product sample, in this case a shock absorber  100 , is dismantled and the seven components shown in  FIG. 1  are then used in producing seven new shock absorbers  200 , containing the components of columns  204 ,  206 ,  208 ,  210 ,  212 ,  214  and  216 . Likewise, the “best” shock absorber not exhibiting the problem is dismantled and its seven reusable components are distributed one at a time among seven new shock absorbers  202  to be built. Hence,  14  new shock absorbers are assembled where the “warranty” component comes from either the “worst” or the “best” original product samples which were dismantled. The distribution of the warranty parts for both the “worst” and “best” are set forth in the spreadsheet of  FIG. 2 .  
         [0015]     As previously discussed, the rod tube assembly  218 , the cover seal  220  and the oil  222  itself must be replaced with new components in the newly produced products for purposes of the failed component identification technique.  
         [0016]     The next step in the analysis is to take the 14 new shock absorbers and to perform appropriate comparative testing among the various new products in an attempt to identify a component or components causing the weepage failure.  FIG. 3  shows a protocol  300  for a series of cycling tests performed on the various shock absorbers for observing the degree of weepage with each product sample.  
         [0017]     The seven samples  200  containing a component from the “worst” original sample W 1 -W 7  and the seven new shock absorbers  202  assembled using components from the original “best” sample B 1 -B 7  are subjected to three rounds of cycling tests  308 ,  310  and  312  wherein the temperature (in degrees Fahrenheit) of various key components along with a “weepage rating” are determined. In the protocol of  FIG. 3 , there were 100 cycles per round and a stroke of 75 mm, a rebound velocity of 1 mps, a compression velocity of 0.1 mps and a side load of 0 were employed as the parameters for each cycle.  
         [0018]     The weepage rating is an indication of the observed amount of weepage over an outer surface area of the housing of the shock absorber and uses a rating scale of zero through five, zero being an indication of no weepage whatsoever while five is the “worst” case condition for weepage. A weepage rating indicates a shock absorber passes (P) if it is less than four, while a shock fails (F) with a weepage rating of four or higher.  
         [0019]     As seen from  FIG. 3 , the samples are identified in column  302 . The number of cycles completed for the three rounds was shown in column  304  and the weepage rating along with whether or not there was a pass (P) or failure (F) is indicated in column  306 . As seen from  FIG. 3 , sample W 2  at line  314  was the only sample having an unacceptable weepage rating of five. For the particular tests employed in this example, it will also be noted that sample B 2  at line  316  and B 5  at line  318  were indicated to have failed, even though these samples were produced using only components from the original “best” sample. Sample B 5  failed because it was determined that an internal defect did not allow it to perform properly, and therefore its test results were discarded. Sample B 2  failed, because it was determined that, although it was constructed from components from the “best” original sample, the component at issue was causing a delayed failure that would have been observed in time when the first and second original samples from the vehicle were being initially examined. In other words, over time, both the offending components from sample W 2  and sample B 2  would have ultimately caused a weepage failure.  
         [0020]     In any event, the tests of  FIG. 3  do demonstrate that only sample W 2  from the “worst” case grouping exhibited a failure. Hence, going back to  FIG. 2 , we note at column  206  that sample W 2  was built using the original oil seal  103  from the “worst” original sample. Hence, the offending component was oil seal  103 . Indeed, the result of all these tests demonstrates that, for this particular example, the oil seal would have failed in all cases given enough time. The actual detailed cause of the weepage would come from further analysis. The total cause could be due to a defect in the component itself, or in improper assembly of that component, or both.  
         [0021]     Hence, the technique of the invention may be summarized as follows. First, one takes two identically designed products, in the case of vehicular components preferably from the same vehicle, one of the two samples exhibiting the problem of interest and one not. The two samples should have similar use histories.  
         [0022]     Next, one picks from prior experience those N (an integer) components of the disassembled “worst” product that could possibly be the cause of the exhibited problem. Then a second N components are taken from the “best” case sample exhibiting no problem. The dismantled components are then distributed over 2N units, with one of the N components placed in each newly manufactured product.  
         [0023]     Finally, each of the 2N products are tested to determine which of the components from the “worst” case original sample product were causing the problem or failure.  
         [0024]     The invention has been described with reference to an exemplary embodiment. The scope and spirit of the invention are to be determined from appropriately interpreted claims.