Reliability and Life Study of Hydraulic Solenoid Valve - Part 2 - Experimental Study

The current work studies the reliability of a solenoid valve (SV) used in automobile transmissions through a joint theoretical and experimental approach. The goal of this work is to use accelerated tests to characterize SV failure and correlate the results to new comprehensive finite element models (Part 1).

A custom test apparatus has been designed and built to simultaneously monitor and actuate up to four SVs. The test apparatus is capable of applying a controlled duty cycle, current and actuation frequency. The SVs are also placed in a thermal chamber so that the ambient temperature can be controlled precisely. The apparatus measures in real-time the temperature, current, and voltage of each SV. A series of tests have been conducted to produce repeated failures of the SV. The failure of the SV appears to be caused by overheating and failure of the insulation used in the solenoid coil. The current tests are run at a 100°C ambient temperature, 16.8V of average peak voltage, 50% duty cycle, and 60 Hertz actuation frequency. Upon failure, the solenoid electrical resistance drops to a significantly lower value due to shorting of the solenoid coil. This drop in resistance causes a measurable and noticeable increase in the average current. The insulation also melts and exits the SV. Hence, increasing ambient temperature and current is believed to cause a decrease in SV reliability.