Tesla makes three different models now with 3 motors, one for each wheel in the rear. They have a dedicated safety IC in both motors that monitors for a fault that could cause uncommanded torque, and if it's detected, it blows a pyrotechnic device that disconnects 2 of the 3 motor leads. So #2 is solvable. The unsprung mass issue is going to be much harder to fix!
On Fri, Jul 26, 2024 at 10:02 PM Bill Dube via EV <ev@lists.evdl.org> wrote: > Pretty much every highway-capable OEM EV company has tried, and > rejected, the hub motor design concept. Every one! > > Hub motors sound absolutely marvelous to anyone that has not gone down > that path before. (Like management that have not full thought out the > issues.) Then, once you actually have built a prototype, the plethora of > deal-killer issues become glaringly apparent. > > 1) >>> Unsprung weight << > > Any addition to the weight of the wheel assembly makes handling > suffer, and traction suffer. It also makes the ride more harsh. Not a > deal-killer, but a serious engineering challenge. This issue alone is > not enough to tip the balance away from the possible advantages of a hub > motor design. > > 2) >>> Uncommanded adverse wheel torque << > > This is the biggest single issue for an OEM passenger vehicle. If > (actually _when_) one of the wheels suddenly stops or reverses on the > highway, the passengers are doomed. ENORMOUS legal liability. > > There are a host of reasons why one hub motor wheel would exert an > adverse and sudden torque. When this happens, the vehicle will hurl > itself uncontrollably into the oncoming traffic, half of the time. The > other half of the time, it will hurl itself off the road into the ditch, > a bollard, a tree, or off a bridge. With a PM motor, you simply have to > short the stator in one motor for this to happen. There are a host of > other faults that will result in this sort of failure. > > Yes, it might be possible to address every possible adverse torque > fault scenario, but it is very time consuming and prohibitively > expensive. This issue typically torpedoes the design. > > 3) >>> Harsh motor environment << > > The hub motor feels every bump and railroad crossing full force > with only the tire for cushioning. It also gets every torque pulse from > these bumps with no damping. (Think of wheel hop.) These severe torque > peaks are really hard on the mechanical portions of the motor, but also > translate into voltage spikes and current spikes to the inverter. HUGE > engineering and maintenance headaches. (Also see above about uncommanded > adverse torque, which can often be the result of these failures.) > > >>> Move the hub motors inboard?? << > > This is the fix for issues #1 and #3, but doesn't address issue #2. > > Also, if you are going to use half shaft axles, and mount the > motors to the chassis, why not simply combine the two reduction > gearboxes into one, and use a conventional differential. Which is the > standard configuration for pretty much all OEM EV's. :-) > > Bill D. > > > _______________________________________________ > Address messages to ev@lists.evdl.org > No other addresses in TO and CC fields > HELP: http://www.evdl.org/help/ > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20240726/3d8588dd/attachment.htm> _______________________________________________ Address messages to ev@lists.evdl.org No other addresses in TO and CC fields HELP: http://www.evdl.org/help/
