InRunner front Hubmotor for common 100mm wide forks
This is an Inrunner design, using the well known and above described planetary gearbox configuration. The space within the rotor of an InRunner BLDC motor, which is normally unused, encloses a speed reduction gearbox, having 9.33:1 reduction raio. This has great advantages in both space use and possible weight reduction.
The motor shown here is very similar to miles 90mm InRunner BLDC motor, having 18teeth and 10pole pairs. The major difference is that it has a thicker 40mm stator stack. Outer diameter of the gearbox is less than 55mm, when using module 1 gears. The inrunner BLDC motor used in the GNG Gen1 Kit, would also fit, but it has a shorter stator, so the gears would also have to be shorter to fit into the housing.
The motor is air cooled. The air enters the hub through axial holes and is forced to the radial exits by centripetal forces induced by the rotation of the hub. The InRunner motor is protected from dirt etc. by an own housing with fins for increased heat rejection.
Blue: Fixed parts, including stator, axle, stator housing and fixed gear (20teeth)
Orange: Rotor parts with Planetary carrier
Red: Planetary Gears (15 and 16teeth)
Green: Output Gear (21teeth)
These teeth counts where chosen since they offer both a very compact gearbox and a high reduction ratio. If the blue fixed gear is about 4/3 times the tooth count of the planets, this gearbox config becomes most compact for reduction ratios reasonable for hubmotors. It's the region between 5:1 and 15:1. It would be better to use hardened helical gears, for both lower noise operation and higher torque durability. For a prototype I would want to use straight gears, since they are cheaper. The three planetary double-gears (each consisting of one 15t and one 16t gear) have to be fixed in a special angle, which differs for all three planetary-double-gears. If they are not fixed to each other in the perfect right angle, it will be impossible to assemble the last two double-gears, after the first one was inserted.
Seals are still missing in this first design. It is proposed to keep abrasive parts inside the rotor, which are created due wear of the gears. To protect the magnet system of the BLDC motor from these magnetic particles, they just stay inside the rotor. This also keeps lubricant inside. Additionally it is suggested to use seals for keeping dirt out of the (blue) motor housing. For this purpose, common sealed bearings can be used. They are used in all common bycicle hub-motor as axle bearings.
There is a freewheel clutch, similar to the Stieber CSK-20 build into the hub, connecting the output gear (green) with the hub. It disconnects the motor while not using it, just like all known geared hub-motors use to do.
The stator winds are missing, just costs too much performance for my CAD computer. The phase wires will leave the unit through the right side, I used a oversized 20mm inner diameter axle bearing, to keep some space for those wires.