Not sure what you mean by "stator case". Perhaps you can attach a labelled diagram of your specific idea and parts to your post to help us understand.
The air gap between stator and rotor typically is between the laminations and the magnets, and generally you don't want to interfere with the magnetic fields between them. I suspect you're not referring to this air gap but the wording of your post suggests this is the air gap you mean.
Are you instead referring to the rotor bell (not part of fhe stator) with the magnets on it, that spins around the stator, and then the air gap between that and the actual motor housing with spoke flanges, ring gear, etc.?
If so...I am not sure if reducing the distance between the two will noticeably change the heat flow between them, especially since the gap is already very small. Even though you dont' want to do this, it is more likely that replacing (at least part of) the air with a better heat conductor would have significantly greater effect (especially if there is enough of the conductor to also cause greater heat transfer from the stator itself to the rest of the motor, since the stator is where the vast majority of the heat is generated). You could test the add-on ring idea experimentally, with a before and after test of exactly the same instrumentation and conditions.
Other than zero (which would not allow the motor to operate), to get actual heat conduction from rotor bell to motor housing, I don't know a good way (short of thermal and physical modelling if you have all the characteristics of all the parts and materials of the system) other than actual experimentation to find out the best compromise between minimal gap forcing radiative / convective cooling (less effective than conductive) and ensuring no contact occurs between motor housing and rotor bell/conductor ring during any flexure or distortion of the parts during operation (from thermal expansion of parts or physical distortion due to wheel / spoke stresses, etc).
hias9 said:
On a G310 geared hub motor, there is a 1.6mm air gap between the OD of the stator case and the ID of the outer case.
I want to improve heat conductivity from the stator to the case without adding oil.
The plan would be to turn an aluminium ring, have it anodized in black and press it onto the stator case.
The air gap should be as small as possible, but the aluminium ring should never touch the case.
Does anybody have an idea what could be a solution to determine the minimum air gap width while riding?
