Unsprung mass might be solvable with a completely active suspension, but even that will be easier to engineer with less mass.
Although the general idea and some variants have been around since at least the 1950s, few, if any, suitable active suspensions have been deployed beyond high-end or specialty vehicles. I suspect that this means it's one of those things that is more trouble than it's worth in a mass market vehicle. Adding mass to the wheel might make active suspension necessary, but it certainly won't make it easier or less expensive. On July 26, 2024 11:50:12 p.m. CST, "(-Phil-) via EV" <ev@lists.evdl.org> wrote: >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/ > -- Ron -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20240727/adcea9c2/attachment.htm> _______________________________________________ Address messages to ev@lists.evdl.org No other addresses in TO and CC fields HELP: http://www.evdl.org/help/
