Logistic Model - Auto Transmission Example

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This example appears in the Reliability growth reference.

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 entered data and the estimated parameters.
   
   

   
   

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

   
   

3. Using the QCP, the next figure displays, in months, 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).