planitary gear sets at the axle hubs

[carnage1]

does anyone have any experience with mounting a transmission in the area of the rear axle and then elimination the ring and pinion gear and using a planetary gear set in each hub instead?

Luck is a difficult thing to verify and therefore should be tested often. - Me

 

[thruthefence]

might increase your unsprung weight a bit...................

 

[rmw]

How do you propose to convert the rotary motion of the drive shaft (regardless of how close the transmission is mounted) which is in line with the vehicle centerline to rotary motion in the direction of the wheels?

European truck tractor axles have favored hub mounted planetary reductions for as long as I can remember.

rmw

 

[GregLocock]

Have a look at Unimogs as well. You'll need a diff.

Cheers

Greg Locock

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[carnage1]

Actually I was considering a transversely mounted engine, so I don't have to move the line of action from down the center to across the back.
I'll look into what I can find on heavy trucks.
Does anyone ever use the hub mounted planetary to shift? like a two speed automatic?
Lastly unsprung weight should not be a huge issue as this will be a straight line exhibition car.

Luck is a difficult thing to verify and therefore should be tested often. - Me

 

[BrianPetersen]

What kind of scale of equipment are we talking about here.

On an earth-mover, it's quite likely that there will be enough space to do what you describe and I think at least some of them already use gear-reduction at the hubs. On a small car, that area has a lot of other stuff competing for space (brakes, wheel bearings, hub, suspension attachment points, CV joints in the case of independent suspension, etc).

It seems redundant to put a gear-change mechanism inside the hub. #1, space, weight, etc. #2, anything you do in this manner would have to be doubled (one on each side) compared to doing the same gear-change mechanism in front of the differential (in which case you only need one, and it can be integrated into the transaxle).

 

[carnage1]

Good point about having to do it twice, that would be quite a bit of extra stuff. the application is a small sports car.
The reason I was thinking about the planetaries to reduce torque on the axles reducing their weight and rotational inertia as well as being able to create a fully floating design so a failure would not be as catastrophic. Also if I have room I could sink the motor down between the axles lowering my center of gravity and reducing weight transfer to the aft.(possibly even set up in such a way as to pull power from both ends of the shaft)

Luck is a difficult thing to verify and therefore should be tested often. - Me

 

[Tmoose]

VW buses had reduction boxes at each axle. Not sure of the ratio, but I'm vaguely recalling (guessing) 1.2-1.6-ish according to year. They are offset, not concentric, so you could really lower or raise the axle CL.

Axle inertia would seem to be a minor contributor. When the engine gets closer to the ground a full sized flywheel can be the clearance limit.

 

[BrianPetersen]

The planetary reducer at the wheel will be unsprung rotating weight ... the worst possible kind of weight.

 

[carnage1]

but its ok as long as I don't turn and have a parachute for stopping

Luck is a difficult thing to verify and therefore should be tested often. - Me

 

[pontiacjack]

A couple of points-
1) Eliminating the ring/pinion gearset is one thing, but how would you implement the differential function?
2) Reducing polar moment of inertia of axles gets you nowhere if their speed is correspondingly increased.

Will axle torques be typical "small sports car" range, or is this a hot rod? If you're talking about relatively low torque values, I'd suggest you glance at the old DAF dual V-belt arrangement, which worked "okay".

 

[patprimmer]

If this is drag racing, differential action is not only not required, but is undesirable.

Regards

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[patprimmer]

Have you seen the overdrive gear boxes offered on some cars in the 60's. I think Studebaker, Jaguar and Austin Healy were some that offered it. A compact 2 speed planetary ox with electric shift so they should be near on simultaneous. Simultaneousness shift would be essential I think.

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[carnage1]

Actually I had forgotten about the old electric overdrive units, I know of some classic cars in the area that use them.
and yes it is drag racing.

Luck is a difficult thing to verify and therefore should be tested often. - Me

 

[modesign]

The overdrive was also used on Sunbeam Rapier for Race and Rally use as well as on the road cars. The main problem was that in standard form even in road cars the torque limit made it operational on 3rd and 4th gears only. The competition overdrives used a different spring arrangement and were used on all gears.They had a limited racing life.

Sandy

 

[BrianPetersen]

... but those electric overdrive units were all an add-on to the main gearbox, in front of the drive shaft and rear axle.

 

[carnage1]

they were but I would think I could use a pair of them and eliminate the gearbox altogether. I would have two speeds which should be enough and my entire powertrain would be engine---planitaries---tires. That should make for an extremely low loss system.

Luck is a difficult thing to verify and therefore should be tested often. - Me

 

[patprimmer]

A stronger option would be a pair of 2 speed Lencos but that is probably overkill.

I don't know of anything heavier duty than an old 60s OD unit but less than a Lenco.

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[carnage1]

Ill search for them, as I understand it we will have a large budget on this project as it is going to be used for advertising.

Luck is a difficult thing to verify and therefore should be tested often. - Me

 

[patprimmer]

The Lencos might be big and heavy as well as expensive

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