Experiences on Combining Fault Tree Analysis and Failure Mode, Effects and Criticality Analysis for Fault Diagnosis of Hydrostatic Transmission

摘要

Detecting the failed component from an unhealthy hydrostatic transmission system is usually not a straightforward task. Failure in either main component (pump or motor) can cause similar effects to the whole system. Unnecessary component replacements can play remarkable role in costs. In addition, diagnosing time can be significant cause of downtime costs. Analytical analysis methods shorten the diagnosing time and prevent needless replacement of healthy components. The paper is concerned with combination of two different kinds of analysis methods. The most vulnerable components of the hydrostatic transmission are determined with the aid of Failure Mode, Effects and Criticality Analysis (FMECA). The FMECA analysis form is tailored to suit especially to the condition monitoring purposes. A disadvantage of the FMECA is that each component is analyzed individually and combinations of failures are not typically taken into account. The Fault Tree Analysis (FTA) is used for representing the interaction between failures and basic events of top failures. FTA can handle combination of failures, but it is not ideal when dealing with symptoms of failures in individual components. The combination of FMECA and FTA is used for creating troubleshooting charts for locating the failed component in the system. The charts are composed so that diagnosing is started from the failure that is the easiest to detect. The analyzing level of the related system is designed so that it reveals the smallest component or part of it that is replaceable in field conditions. The analysis methods can also be used for detecting the root cause for the malfunction and so to prevent future failures to occur. Finally, experiences from field of using troubleshooting charts based on FTA and FMECA are presented.