Low Profile Oil Deflector
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| background |
An electrical generator operates on the principles of magnetic induction to convert mechanical energy into electrical energy. As part of their broad range of products, Honeywell designs and manufactures electrical generators for numerous applications. One such application is the DeHavilland Q400 twin turboprop passenger plane. The generator in question uses input torque from a jet turbine to turn a rotor assembly, and a three-stage process beginning with a rare-earth magnet exciter priming induction coils finishes with the production of electrical current.
Electrical resistance generates heat in a conductive medium as a time-dependant function of current and resistance according to Joule’s First Law: The conductive copper coils in the final stage of the rotor assembly are sufficiently cooled by conduction to the posts around which they are wound. Unfortunately, the geometry of the coils in reference to their posts includes a free surface at the coil ends that must be convectively cooled. To solve this problem, engine oil flows over the coils at sufficient volumetric flow rate to ensure their proper function. The coolant choice is platform-specific, and the same Mobil Jet Oil II used for engine lubrication is also used as a working fluid for heat transfer. This oil is pumped into the rotor shaft at a constant pressure and flow rate and distributed to the coils through machined radial holes. The pressure driven jet-streams exit the shaft at high velocity sufficient to damage the coils, therefore a device has been designed to deflect and redirect this oil over the coils. A circular oil deflector mounted directly over the radial shaft holes serves to prevent the cutting-stream of oil from damaging the coils and to redirect the oil it collects over the coils to provide maximum cooling.
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Current Product:
The oil deflector is a vital part of the generator assembly. It is securely held in place between the rotor shaft, to which it is press fitted, and the stator housing. The deflector is responsible for protecting the coils from the high velocity oil jet streams that exit from the three shaft holes. The oil from these streams hits the outer ring of the deflector and loses virtually all of its kinetic energy. The oil accumulates and forms a lake between the outer ring of the deflector and the outer ring of the four slots. This lake overflows through the strategically placed slots to cool the coil ends. It is important that the oil is evenly distributed to the four coil ends to ensure that each section of coils remains at the same temperature and no part of the system overheats.
Honeywell’s current oil deflector was designed in the sixties. Since then there have been many advances in its field of application resulting in a need for an increased amount of power supply. The simple solution to producing more power in the generator has always been to add more coils to the system. Up until this point that solution has always been able to meet the power need. There is a limited amount of space available for the addition of the coils and that limit has been reached. Although there is no more space for additional coils, there is still a desire for more power.
In order to meet this need, Honeywell wants to redesign their current oil deflector.
The design process used for the current deflector was trial and error based. If a design failed during testing the concept was thrown out or modified; however, documentation is not available on any concepts or methods used. Once a design was tested and proved to be sufficient for the application it was put into action and the design process seems to have been forgotten. Due to the discussed method of design, very little detailed data or information is available on how the oil deflector truly operates.