Patent Number: 
Section: description

An exemplary embodiment of the present invention is a method for monitoring product performance. The term xe2x80x9cmonitorxe2x80x9d is intended to have a broad meaning and includes monitoring, diagnosing, inspecting, etc. During a design for six sigma (DFSS) design phase a database is created including a plurality of DFSS elements which may later be used to monitor product performance during a service phase. FIG. 1 is a flowchart of the process in an exemplary embodiment of the invention. The process is divided into two phases, namely the design phase and the service phase. In the design phase, the product is designed using design for six sigma techniques as shown at step 10. A number of DFSS elements, described in detail below, are generated during the design for six sigma process. At step 12, DFSS elements are stored in a DFSS database that will be used in the service phase to monitor product performance. Once the database is generated, it may be used in a service phase to provide for monitoring of product performance as shown at step 14. Accordingly, the product performance is monitored based on the engineering process used to design, build and first test the product. During the service phase, information about the product may be developed that is useful in designing second generation products. For example, monitoring the product in the service phase may yield information concerning the operating environment of the product which could be used to improve the design. Thus, information from the service phase may be used in subsequent design phases as represented by the dashed line 16. The database created in step 12 may include a number of DFSS elements. One DFSS element in the database may be DFSS design score cards. The DFSS design scorecards may list the key control parameters, their mean values, standard deviation, lower specified limit (LSL), upper specified limit (USL) and Z value. The Z value is a measure of how frequently the key control parameter is outside the LSL to USL range. A Z value of 6 indicates that the key control parameter is outside the LSL to USL range 3.4 times out of one million opportunities. The DFSS scorecard may include a Z value for each key control parameter and a total Z value for all the key control parameters representing how well the entire system meets all the LSL""s and USL""s. During the service phase, sensed key control parameters are measured and the mean and standard deviation are determined. The sensed key control parameter is compared to the as-designed LSL and USL to determine a sensed Z value. If the sensed Z value differs from the acceptable Z value by a predetermined amount (e.g. 5%), then service is recommended. It should be noted that not all key control parameters can be sensed during the service phase. Accordingly, transfer functions are used to determine critical to quality parameters during service. For example, the compression ratio may not be sensed during the service phase. Nevertheless, expected variation in the compression ratio is known from the design phase. The expected critical to quality parameter (e.g., SFC) can be expressed as a range of acceptable values. The derived SFC, based on a subset of sensed key control parameters, is compared to an expected distribution to determine if performance is acceptable. Another element in the DFSS database may be a list of key control parameters and the Z value for each key control parameter. In the DFSS process, key control parameters are defined for each level of the product. The key control parameters are those variables that need to be controlled in order to meet the CTQ""s. Referring to the diesel engine example, the key control parameters may include compression ratio, manifold air pressure and temperature, start of injection timing and fuel injection quantity in order to meet the EPA emission requirements. To monitor quality of a product, the values of the key control parameters are compared to sensed values to confirm that the product is operating under ideal conditions. For example, the compression ratio of the diesel engine may be sensed and the sensed value compared to the corresponding key control parameter design specification. If the sensed value deviates from the key control parameter design specification by more than a predetermined limit, this indicates that the CTQ""s may not be met and product service is required. Including the key control parameters in the DFSS database allows for simplified monitoring of product performance. Performance of a product may be determined on a predetermined result being obtained. In the diesel engine example, performance is acceptable if the engine meets EPA emission requirements. Using conventional techniques, testing an engine for compliance would require mounting a sensor to monitor the engine emissions. Such a sensor may be inaccurate or not be suited for the environment. Compliance with emission requirements can be confirmed by confirming that key control parameters are within certain levels. For example, if the key control parameters of compression ratio, manifold air pressure and temperature, start of injection timing and fuel injection quantity are within predetermined levels, then the emissions are deemed acceptable. Another DFSS element that may be in the DFSS database are the tools used to derive the key control parameters and CTQ""s. Exemplary tools include behavior scenarios, quality function deployment (QFD) and analysis results. During design, tools are used to simulate different scenarios (e.g., diesel engine operating at a high altitude) and the tools sort through hundreds of parameters to define a list of key control parameters for each scenario. During service, the service computer can determine which scenario is relevant and then locate the DFSS scorecard relevant to this scenario. The scorecard contains the key control parameters to be monitored for a given scenario. The specified key control parameters may then be monitored and compared to key control parameter limits as described herein. Another DFSS element that may be in the DFSS database are transfer functions that were used to determine the CTQ trade-off in the design phase. The transfer functions are mathematical equations that describe the product response to predetermined input data. The transfer functions may correspond to any level of the product including a component, an assembly, a sub-system or the entire system. The transfer functions can be used to monitor product performance by comparing actual product performance (e.g., measured with sensors) to predicted product performance (e.g., generated by transfer function). For example, diesel engine fuel consumption could be measured and compared to predicted fuel consumption generated by the engine transfer function. A difference between the actual fuel consumption and predicted fuel consumption indicates that the engine is not operating under ideal conditions and that service may be necessary. Another DFSS element that may be in the DFSS database are test results used to verify the transfer functions and CTQ verification assurance. The test results include measurements of key control parameters made during the design phase. The measurements are used to generate the mean and standard deviation in the DFSS scorecards described above. During service, the monitored key control parameters may be compared to the test results to determine normal or abnormal operation. For example, measured key control parameters may be compared to the list of test results. If the measured key control parameters do not fall within the distribution of test results, then service may be necessary. Monitoring product performance may be done in a variety of ways. One technique is to monitor the product remotely using sensors on the product and transmitting the sensed data to an off-board computer that monitors product performance. The sensed data should correspond to at least one key control parameter that would indicate whether the product is meeting CTQ""s. The drawback to total remote monitoring is that numerous sensors are needed and sensor reliability and accuracy becomes an issue. Alternatively, product performance could be monitored by service personnel during routine service checks. The service personnel would monitor key control parameters, through sensors, to determine if key control parameters are within specified limits. Yet another method may be a hybrid technique in which a limited number of sensors are used to monitor a subset of key control parameters. If one of the key control parameters in the subset exceeds a specified limit, then a notification is generated that the product needs service. The service may then be performed by service personnel during which all key control parameters may be evaluated. While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.