Hello freebeard,
Quote:
Originally Posted by freebeard
Anything with dog clutches is not a Quaife. Quaife Limited Slip Differential I'm not prepared to explain how they work. ETVTV have them exclusively for the Tesla. |
Well, yes. That's why I talked about clutch-type limited slip or auto-locker. Both show the undesired characteristics in snow, though the limited slip may be more predictable because it starts "locked" and only differentiates when there's enough traction to overcome the clutch pack inside. The Quaife, Tor-Sen, TrueTrac and a few others I can't recall right now are the more desirable geared type that are "unlocked" first and bias torque once a wheel starts slipping. I'd have to read up more to see how much RPM differential/torque differential it takes to bind the gears and start the torque biasing process. The Torsen R series has clutches inside as well that provide a minimum amount of torque it can bias, even when one wheel is in the air. Not sure how they work on ice vs. a standard Torsen in terms of acting more like a clutch-type lsd or an open diff at first.
My point about the truetrac/torsen/etc geared limited slip between two motors was to see if the torque biasing it has would allow keeping the inside wheel loaded some once it lets go, by having the gearing in the truetrac bind up. Again, I need to do more reading to see how the ring gear affects the torque bias - does the diff case need to be locked to one axle for it to function properly without any ring-gear supplied torque.
Another potential idea: a number of the "CUV's" or "cute-utes", those little FWD biased car-based SUV type things with no low-range have a gerotor pump based clutch type differential. One axle shaft spins faster than the other, the pump builds pressure and applies it to the piston driving the clutches, jamming them together and applying torque to the slower axle. Very limited in power transfer, as the slower the speed differential, the less power it can transfer. They are available in the center position to drive the rear axles (only power rear axles when fronts are slipping fast enough to build pressure). This type might be best - no ring gear, generally. Put between the motor output shafts directly, or on the first stage of RPM reduction, the speed differential will be magnified between the two sides. There are sometimes double-pump units in the rear axle that basically do the same thing - each pump only applies power to its respective axle shaft when the ring gear is spinning fast enough to build pressure in them. That type would be less useful, as with 1 motor per corner you need no ring gear - unless you want to connect the front and rear axles mechanically so any given slipping wheel can transfer torque to the others that still have traction.
Hmm - interesting idea: Triple tor-sen/true-trac/quaife/other geared type limited slips. One each front and rear, and one in the middle. One BAS per corner, driving a pulley bolted between the CV shaft and the respective output shaft of the differential. You get your power at each corner, but if that corner lifts, it can transfer power mechanically as well as via more overload on the other motors.
All of these ideas might be too much complexity for too little gain, though. Just running one per corner could work fine. Kind of depends on the terrain thingstodo is looking to run on, and how light the vehicle is. Momentary overloads on the outer two motors during corners may work great. I only worry about performance on icy pavement in a corner, as I've heard a locker causes a higher probability of a spinout if you have to add throttle in the corner.
Also see final belt drives on Harley motorcycles that have replaced chains. No tensioner.
General:
I'm getting way off-topic with this mechanical stuff, I think. This thread is for control strategies per OP HaroldinCR, yes? I'll bow out on the mech side for now, unless HaroldinCR doesn't mind the digression.