This application relates to a housing structure that provides a cooling oil flow path between a stator housing, and a stator core.
Generators include a rotor which is driven to rotate, and carry magnetic features adjacent to magnetic features in a stator. The relative rotation of the rotor adjacent to the stator generates electrical power. The electrical power is utilized for various purposes.
One typical application for a generator is in an aircraft auxiliary power unit (APU). An APU is provided with a smaller gas turbine engine which is utilized prior to full start-up of the main gas turbine engines on an aircraft. The turbine on the APU is started, and drives a rotor to generate electricity for use by the aircraft prior to the actuation of the main gas turbine engines on the aircraft.
The generator in the APU requires cooling, and in particular cooling between a stator housing and the stator core to cool the stator winding and core. In known APUs, a complex heat exchanger is provided between the housing and the core, and includes a plurality of channels formed in the housing.
The housing is typically formed of a material that has a greater co-efficient of thermal expansion than does the stator core. The APU is subject to extreme temperature changes. As an example, the APU is typically operational on the ground, and can reach high temperatures. The cooling is particularly important at this operational point.
Conversely, when the aircraft is at cruise altitude, the APU is typically not operational. The APU is typically located in an unpressurized tail cone of the aircraft. During the cruise portion of a flight, this tail cone location of the aircraft is typically at extremely low temperatures at this point. The difference in co-efficient of thermal expansion between the housing and the core causes changing sizes of the housing and the core, and at the interface between the two. This results in compressive stress on the stator core caused by the stator housing, resulting in reduced fatigue life of the housing. In addition, for more electric aircraft, it may be required for the APU to start during the cruise portion of a flight. At such condition, the compressive load on the stator core may result in reduced electrical performance of the core. The existing cooling channels raise concerns due to this differing expansion rate.