Logistic Model - Auto Transmission Example

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This example appears in the Reliability Growth and Repairable System Analysis Reference book.


The following table presents the reliabilities observed monthly for an automobile transmission that was tested for one year.

  1. Find a Logistic reliability growth curve that best represents the data.
  2. Plot it comparatively with the raw data.
  3. If design changes continue to be incorporated and the testing continues, when will the reliability goal of 99% be achieved?
  4. If design changes continue to be incorporated and the testing continues, what will be the attainable reliability at the end of January the following year?
Reliability data
Month Observed Reliability(%)
June 22
July 26
August 30
September 34
October 45
November 58
December 68
January 79
February 85
March 89
April 92
May 95

Solution

  1. The next figure shows the estimated parameters.
    Entered data and the estimated Logistic parameters.


  2. The next figure displays the Reliability vs. Time plot.
    Reliability vs. Time plot.


  3. Using the QCP, the next figure displays when the reliability goal of 99% will be achieved.
    When the reliability goal of 99% will be achieved.


  4. The last figure shows the reliability at the end of January the following year (i.e., after 20 months of testing and development).
    The reliability at the end of the following January (month=20)