×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

planitary gear sets at the axle hubs

planitary gear sets at the axle hubs

planitary gear sets at the axle hubs

(OP)
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

RE: planitary gear sets at the axle hubs

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

RE: planitary gear sets at the axle hubs

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

RE: planitary gear sets at the axle hubs

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

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: planitary gear sets at the axle hubs

(OP)
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

RE: planitary gear sets at the axle hubs

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).

RE: planitary gear sets at the axle hubs

(OP)
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

RE: planitary gear sets at the axle hubs

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.
 

RE: planitary gear sets at the axle hubs

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

RE: planitary gear sets at the axle hubs

(OP)
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

RE: planitary gear sets at the axle hubs

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".

RE: planitary gear sets at the axle hubs

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

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
 

RE: planitary gear sets at the axle hubs

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.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
 

RE: planitary gear sets at the axle hubs

(OP)
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

RE: planitary gear sets at the axle hubs

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

RE: planitary gear sets at the axle hubs

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

RE: planitary gear sets at the axle hubs

(OP)
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

RE: planitary gear sets at the axle hubs

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.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
 

RE: planitary gear sets at the axle hubs

(OP)
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

RE: planitary gear sets at the axle hubs

The Lencos might be big and heavy as well as expensive

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
 

RE: planitary gear sets at the axle hubs

(OP)
hmm big and heavy isn't good.

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

RE: planitary gear sets at the axle hubs

Chevy power glide planetary gear sets may work in conjunction with an additional reduction set. Most transmission gear sets are narrow ratio and you would still need a reduction set to take the place of the ring gear and pinion. The final reduction set must be heavier than the transmission set. Some of the class 2B and larger truck automatic transmissions use planetary sets that may work.

Ed Danzer
www.danzcoinc.com
www.dehyds.com

RE: planitary gear sets at the axle hubs

As I remember the old planetary overdrive units, they could not be upshifted under power. You had to let off the throttle to let them upshift. To modify one to upshift under power, you'd wind up with a mini-automatic-transmission- with all the attendant systems- hydraulics, clutch pack, valve body, etc.

Dragrace motorcycles employ a unique gearbox design which allows upshifting without power interruption. I don't remember the details of the mechanism- read about it a few years ago, and remember thinking it was quite clever. You could look into building a two-speed manual transmission with this shifting design, for your "small" car.

Higher power drag race cars (such as Pro-Stock, over 1,000 HP) have used "clutchless" dog-ring-shifting manual transmissions, like the  four-speed Jerico.

A single two-speed Lenco unit is not very heavy, considering the torque capacity (1,000 ft.lb.?). It's maybe 7" diameter by about 8" long.

RE: planitary gear sets at the axle hubs

The drag-race motorcycle transmissions have the back-sides of all the engagement dogs machined to a taper, and relief cuts in the shift drum so that when upshifting to the next gear, it does not pull the shift fork for the previous gear out of engagement (which is what normally happens). What this does is allow the next gear's engagement dogs to be slid in under power without disengaging the previous gear, and then as soon as the next gear starts taking up the load, the reverse torque on the previous gear drives it up against the tapered backside of its engagement dogs and pushes it out of engagement.

Sounds fine at first, but there are some bad side effects to this. You can no longer downshift except at a standstill, but even worse, the gears for which this has been done can no longer transmit engine braking torque. Once you have applied load to the transmission in first gear you MUST upshift through all of the subsequent gears that have had this treatment done without ever backing out of the throttle to the point that the transmission is back-driving the engine (engine braking). If you do, the transmission smashes its internals to smithereens.

RE: planitary gear sets at the axle hubs

Thanks, Brian, for filling us in on the drag bike boxes. Even with the drawbacks noted, it seems to me that a two-speed version could possibly have application to the "small" drag race car being discussed here.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources