I'm trying to figure out how Subaru can split the torque between front and rear axles in an amount other than 50:50? The only way I can think of decreasing or increasing torque is with gears, and whenever you change the torque, you also change the speed. If you had different torque splits between front and rear, wouldn't you also have mismatched speeds between front and rear?
Yousuf Khan
I can't answer your question but when I googled, "how Subaru can split the torque between front and rear axles", I got a lot of hits.
Thanks sometimes, getting the exact right google search term is all that's necessary. I found this site:
"Reading about torque split "under normal conditions" on this Web site lets you understand how the all wheel drive system is build from the mechanical point of view. The "default" torque split also indicates how a vehicle behaves when cornering. This depends on which wheels are favored and receive more torque. For example, a BMW with 36/64 front-to-rear split will have a rear-wheel-drive-like behavior when cornering. A planetary gear center differential is used to achieve asymmetrical torque split. A Volkswagen with Haldex, whose torque split is 95/5 front-to-rear, will understeer until you press the throttle and lock up the multiplate clutch."
Looks like I'm going to have to try again now.
Yousuf Khan
I'm not sure why you think this is not possible. Most cars on the road will the the engine torque split between front and rear wheels at 100% and 0%.
I got curious but did not want to spend time learning the details. Someone got me onto planetary gears the other day when he said that the average person does not know how an automatic transmission works.
Those are very easy splits, since they are part-time 4WD, they are usually 100:0 to 50:50, nothing in between. So it's easy to figure those ones out, they simply use clutches. But full-time 4WD is different, they should be 50:50 most of the time, with little adjustments due to turning circle which would possibly adjust it upto 51:49 or so.
Yousuf Khan
My VW Passat 4Motion has a 50/50 torque split most times because we don't g et many chances for a slick surface over here. The 4 wheel drive is not rea lly needed in the tropics but it sure has some wonderful stability when goi ng around bends. This is the best handling station wagon that I've ever had .
With the 4EAT for instance, the torque is varied with clutches in the tail section. The system detects slippage, and shifts torque away from the slipp ing axle towards the non-slipping axle. In a sense, it is specifically tryi ng to ELIMINATE a speed difference (slippage).
Yeah, that was due to frictional slippage. I would hope that more sophisticated torque splitters aren't relying on frictional inefficiencies to adjust torque splits.
Anyways, it looks like it's due to those accursed magical planetary gear sets to adjust torque splits, without affecting wheel speeds. I just never could wrap my head around how those planetary gear sets worked, couldn't keep the picture going in my head without a headache. ;)
Yousuf Khan
ail section. The system detects slippage, and shifts torque away from the s lipping axle towards the non-slipping axle. In a sense, it is specifically trying to ELIMINATE a speed difference (slippage).
You might try watching some of these videos;
Differentials aren't really a problem for me to understand, but planetary gearsets were. I did manage to locate an old 1950's US Army training video about it, which was one of the best explanations of it so far. However, it still puzzles me how one can obtain an asymmetrical torque split without also getting an attendant asymmetrical speed split too.
Watch the Torsen videos.
Actually, that Torsen video did help in understanding how torque splitting can occur. Basically a torsen gear is also using a form of frictional resistance, just like a clutch pack would. I sort of intuitively understood this for a long time, without really realizing the underlying principle, I just sort of glossed it over in my own head thinking it's not important. But the video did explain it properly. So no matter what mechanism you use, clutch packs, Torsen gears, etc., they all depend on friction to change torque distribution.
Yousuf Khan
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