1996-02-01

Dual Fan Alternator Design Analysis 960272

Component operating temperatures affect both the reliability and performance of automotive alternators. It is desirable to keep the rectifier bridge and regulator temperatures below 175 C because of the semiconductors contained in this area. At temperatures greater than this, expected lifespans have been observed to decay exponentially [1]. The air flow field surrounding an alternator and component temperature fields were investigated with Computational Fluid Dynamics (CFD) simulations. The objectives of the simulations were to examine the velocity field for the flow passage and the temperature fields for the components. Design proposals have been made to improve the air flow and to reduce the operating temperature.
An initial investigation was performed by setting an alternator in a test configuration and applying the appropriate heat generation for each component. The high temperatures in the alternator components occurred in the stator and the rectifier. These were correlated with the test results.
A more detailed analysis was subsequently conducted with the alternator located in an underhood thermal environment. Four cases have been analyzed, namely, baseline, reversed direction of the radiator electric cooling fans, an alternator without a rear fan, and additional shields. The additional shield which extended from the rear cover to guide air from the radiator cooling fan into the back of the alternator had the best (lowest) operating temperature and was therefore recommended in the design iterations.
We conclude that the present CFD approach with conjugate heat transfer can provide useful alternator design information (velocity, temperature, pressure) in a test box environment, and can be extended to include greater detail in an engine compartment analysis.

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