On Tue, 13 Dec 2016 11:44:51 +0000 (UTC), d wrote:

On Tue, 13 Dec 2016 04:24:59 -0600
wrote:
In article , d () wrote:

On Mon, 12 Dec 2016 13:11:03 +0000
Recliner wrote:
On Mon, 12 Dec 2016 09:39:45 +0000 (UTC), d wrote:
of the live axle, differential and half the prop shaft. Incidentally,
the units also include a reduction gearbox.

Christ, they must be heavy. Obviously a clever piece of engineering and
I'm trying to figure out how you can have a reduction gearbox with a hub
mounted motor because the whole point of the latter is the motor shaft is
fixed to the chassis while the rest of the motor is attached to the hub
and rotates.

AC electric motors are very light compared to axles and transmissions.

Not compared to a normal wheel though.

No, but a normal diesel bus also has the live axle, differential and
half the prop shaft as unsprung weight. The BYD site says:

"BYD's self-developed wheel-hub motor is adopted in the BYD ebus. It
is installed in the rear drive axle together with regenerative braking
technologies. Compared with a normal motor, the rear drive axle system
in the BYD ebus has no gear box, no transmission shaft, and no
differential mechanism. The power from the motor is directly
transmitted to the wheels, so that significant improvements are
achieved in transmission efficiency and reductions in noise and
vibration. In addition, the bus weight can be cut by 300kg, and
interior space is greatly saved."

http://bydeurope.com/innovations/tec...ndex.php#motor

I note that the reduction gear has a 17.7 ratio, and the bus has a
very low top speed -- 70 km/h (little more than 40mph) -- so the
unsprung weight isn't going to matter very much. You can see from the
illustration that the permanent magnet synchronous motor is inboard,
driving through the slim gear box that's between the motor and the
wheel.