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Better Weight Distribution in AWD Car

Put the engine back, put the front wheels forward
  (+1, -3)
(+1, -3)
  [vote for,

Many cars with AWD, such as Audis and Subarus, move their engines very far forward in order to preserve a symmetrical drivetrain, with the front axle about even with the back of the engine. This moves the weight distribution very far forward, however, making understeer a problem. It seems that you can either have a symmetrical layout, or good weight distribution, but not both.

My solution would be to move the engine backwards and the front wheels forward. To connect them, use some bevel gears in place of the universal joints on the halfshafts, and forward-facing trailing arms (or "leading arms," in this case) for suspension.

Since the suspension would swing up and down on the same axis as the front axle, only caged bevel gears would be needed instead of universal joints. The half-shaft would come out of the differential at a 45 degree angle (more or less), connect to the wheel hub, which would then turn another 45 degrees the other way to make to hubs align parallel to the front axle. A universal joint of some type might be needed in the hub to allow the wheels to turn.

I wish I could provide an illustration. This is basically just a way to move halfshafts at angles that ordinary universal joints cannot manage.

discontinuuity, Dec 14 2005

Rear Engine AWD http://lfpress.ca/c...x=articles&s=wheels
Production Version [jhomrighaus, Jul 05 2006]


       Four wheel drive trucks very rarely have symmetrical drivetrains. Afterall, the driveshaft has to get around the engine and into the front differential somehow.   

       The only method of having the front differential in front of the engine was achieved by Lamborghini with a driveshaft that ran through the engine's crankcase oil. Except that the entire system was backwards to fit in a mid-engined car.   

       Several other systems, like the one in some Cadillac sedans and most off-road trucks, uses an asymmetrical system with the front driveshaft coming out of the transmission about six inches to one side of the car's centerline, with the front differential also set to one side. The old Audi ur-Quatros worked similarly, I think, with the engine shifted over as well to make room for the front differential. This still works well, but gives a little torque steer and adds bulk and weight to the drivetrain.   

       I'm not sure if my idea would work very well. Lamborghini's idea might be best, but it also made for a slightly higher center of gravity and more complicated drivetrain.
discontinuuity, Dec 14 2005

       [rasberry re-tart], it sounds to me like you're proposing portal axles with bevel gears so that the CV shafts can point rearwards.   

       This is how I'm seeing your AWD concept car: It has a standard transaxle for the most part, except for forward-facing front outputs for front-corner mounted wheels. The CV driveshafts point backwards from the hubs at an angle, leading rearward to the transaxle.   

       Portal hubs would be heavy and kill handling by increasing unsprung weight. You could offset it a bit by inboarding the brakes, but that's probably still an overall detriment. You'd also need to keep the mounting of the CV flange on the hub towards pivot center so turning doesn't dramatically increase joint angles. The internal hub gearing I'm envisioning to allow that just isn't pretty.   

       Good idea (improve weight distribution) but via a means that seems horribly impractical. So I'm gonna hafta 'bone ya. Sorry.
Souse Mouse, Dec 14 2005

       Put sand bags in the trunk (boot). Problem solved.
whlanteigne, Jul 03 2006

       I was under the impression that Scoobies have near 50/50 distribution anyway. Or am I wrong?
Ling, Jul 03 2006

       See link for Alternative Layout. My Dodge Pickup has an Axle that runs just behind the front of the engine. This sounds like what you are describing.
jhomrighaus, Jul 05 2006

       Ling, you're right.
david_scothern, Jul 05 2006

       Scoobies cheat on the weight distribution by using a boxer engine layout. The advantage of a 180 degree arrangement is you gain a lot of design freedom in where you can mount the thing.
ed, Jul 05 2006


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