Liner Final Drive

[Flat54]

I am interested in feedback on a proposed liner final drive idea. The project involves a relatively slow revving (max 7000"rpm) engine, small drive wheels (23") and a record @ 302mph this would require rear end ratio of around 1.5 to 1. I was also trying to avoid overdrives in gearbox or diff to get around losses? is that a legitimate concern.  What I came up with is modeled off F1 final drives where they use a bevel gear set to change drive direction first and then use bull gears to drive the rear axle, the design proposed uses two sets of gears so that ratio changes can be done without pulling the final drive apart. I built a model to illustrate the idea (attached). The change gears and final drive gear set would use SCS ( https://www.scsgearbox.com/ ) gearbox change gears and shafts these are used in monster truck and other similar vehicles with an excellent record I believe. The change of direction gears are proving more problematic and I would really appreciate feedback about the gears I am proposing to use here. The proposal is for a miter gear set from Nissei https://www.khkgears.us/catalog/product/KSP132001GUL , what I would really appreciate is feedback on these gears in regard to their strength and whether or not a simple press fit shaft and key setup is capable of transmitting 670ft lbs of torque I talked to an industrial gear guy who believes they would be OK but interested in the special application on the salt. There is a larger miter gear set available but packaging becomes more difficult. Any ideas about other viable sources for the miter gears would be appreciated as these are pretty pricey. Any feedback appreciated any clarifications let me know.

[kiwi belly tank]

I did a bunch of searching when I started building my liner with the idea of using industrial bevel gearboxes. https://www.google.com/search?rlz=1C1CHBD_enUS788US788&biw=1008&bih=640&sxsrf=ALeKk01GPFAJAN-QB7RTmPneNYLVfH3V5A%3A1584900824237&ei=2Kp3XsKSDse3tAa47aLQCQ&q=bevel+gear&oq=rotating+sign+gearbox&gs_l=psy-ab.1.5.0i71l8.0.0..21425...0.3..0.0.0.......0......gws-wiz.uk7sSGftATY
I ended up not going that way due to having to rely on outsourcing specialized machining.
It might be good for you but I have gobbs of HP, 4WD & with overdrive have a final drive of .973 to 1.
  Sid.

[Rex Schimmer]

What a great project! Great concept and your "model" illustrates your thinking well. Now to just make it large enough to handle your power. As in most projects like this "the devil is in the details". One of the things you need to consider is that your engine is making 670 lb-ft of torque, I assume that you got this number from a dyno run. What dynos measure is the average torque that the engine makes which is quite a bit different than what the instantaneous  max torque that the engine develops. The reason that the instantaneous torque is important in your gear box design is that depending on the stiffness of the drive train your final drive may be seeing all or a big part of this torque level, which can be as much as several times the torque that is measured by a dyno. It all depends on the engine configuration, V12, V8, inline 4 etc. The more cylinders the less the instantaneous torque exceeds the average torque but on engines like an inline 4 cylinder the instantaneous torque can be as much as 3 times the average torque, a 90 degree V8 is about 1.5 times the average torque. This all means that you need to provide plenty of safety margin in your design to handle the "real" torque that your final drive could see. As Sid was saying there are some commercial right angle gear boxes that are available that may have spiral bevel 1:1 ratios that could be used. I would not depend on press fits and keys for driving the gears, there is a reason for splined shafts and gears on high speed and torque applications. Also you need to ensure that the bearings supporting the bevel drive gears are very robust and they should be, in my opinion, preloaded angular contact ball bearings with the one closest to the gear as large as possible to minimize deflection. Then there is getting the proper lubrication to the gears and bearings, you can not depend on a "splash and clatter" style system and have any level of efficiency. Again it is the details that will make this work.

Keep us informed on your progress!

Rex

[wobblywalrus]

Would an aluminum tube driveshaft dampen some of the shock?

[Jack Gifford]

Are the spiral bevel gears merely for convenience in the mockup? "Straight" bevel gears are more efficient, and I don't see any advantage for spiral in your application.
Another "devil is in the details"- although there's no need for bearings in your mockup, be sure to allow for bearing OD dimensions when designing the case. A "box" that appears to be very rigid will be less so with big holes for bearings.
I like your idea.

[Flat54]

Thanks for the feedback really appreciated!

Sid:I have looked at the sign gearboxes but found it hard to get real data the HP,rpm and torque ratings don't make much sense to me I know the Burkland liner used them but they looked enormous and no details seemed available on gears or setup. The Amo Steele liner used a Hub City 1050 I believe but with custom gears from what I could make out this only from the mention of Aero gears in a post on the forum. I understand the NB 3.5 uses some form of custom final drive using a semi truck spider or side gear unfortunately the photos from the post about the modifications have disappeared. If anybody has those photos it would be good to see them again.

Rex: Engine is 90 degree V8, the torque number is from modelling only at this point, the engine is a concurrent work in progress. I was proposing to use taper roller bearings on the bevel gears, (would angular contact ball bearings be a better choice?) with deep groove ball bearings on the spur gears. Oil supply is something I have mulled over the current decision was to use a pressure system squirters on gear engagements and I was also concerned about the fact that the bearings on the spur gears are shielded from much "splash and clatter" thanks for confirmation on this requirement. Thanks for feedback on the press fit and key scenario I was concerned about this hence the question, in trying to use a stock gear to reduce cost I struggled with a fit up that would allow good alignment on assembly to control run out, backlash etc. and how to do this with a splined gear that needs to be compact. Any ideas or suggestions about this would be greatly appreciated.

Wobblywalrus: No driveshaft a coupler direct off the end of a 6 speed trans is proposed. Just making it hard on myself. 

Jack: Went with spiral gears out of default essentially, from the stock gear lists that I could find, the Nissei Spiral Ground gears were the biggest tooth relatively small OD gears I could find with a reasonable tooth count. I don't understand the gear ratings they seem counter intuitive to what one sees in use i.e. the hp and torque numbers being transmitted in the real world. The proposed gears are only rated at 277 ft lbs given good steel and heat treatment and tooth size this doesn't seem sensible the same thing applies to the sign gearboxes very low ratings. Can anybody shed any light on these ratings please. My plan re bearings was to have back to back rollers on the bevels ( now being rethought due to Rexs input) and deep groove ball bearings on the spur gears, standard bearings on the SCS gearboxes are 209s 85mm x 45mm x 19mm.

Would a couple of truck diff side gears be a serious option??

Thanks again for the feedback and help.
Grant

[kiwi belly tank]

Truck axle gears are chunky but they don't have many teeth so not much tooth contact area. That's the usual fail point on a quickchange at the spur gears when you shove some HP up them.
A Rockwell top drive has something like a 2.4-1 so that doesn't help us.
We ran a 2.2-1 10-bolt Chevy gear in Al's liner with an overdrive 4th gear beyond 400.
  Sid.
 

[Rex Schimmer]

Grant,
I like ball bearings, specifically angular contact ball bearings, as they are very efficient especially compared to taper roller bearings. You can set up angular contact ball bearings with a set preload that will resist deflection and axial load and still provide a very efficient rolling action, where as tapered roller bearings are extremely sensitive to preload, to much (and to much might be as little as .001 inch to much preload) and the bearings will over heat and fail. You will need to calculate the axial thrust and also the radial loading of the bevel gears and this will pretty much set the bearing size.

I would suggest that you make both of the bevel gears to be assembled with their shafts and bearings in a cylindrical carrier with a flange on the end opposite the gear. The allows you to assemble the gears, bearings and shafts on the bench and then insert into a bore in your housing and use shims between the flange and housing to set the gear lash.

Regarding lubrication, do not squirt the oil between meshing gears such that the oil is going the same way as the gears are turning, this will force oil into the clearance gap between the gear teeth and literally make an oil pump, which will create lots of heat. If you spray the oil into the meshing teeth make it on the back side of the mesh where the teeth are disengaging. This will cool the teeth and provide lube for when they come around again to mesh. Also if possible get one of the gears with at least one extra tooth as this will prevent the same teeth from always working against each other which accelerates wear. You should also provide some sort of spray for the bearings but again do not flood them as this will cause them to heat up.

Regarding torque pulsations, which your V8 will have, ( If you happen to use a 180 deg flat plane crank the pulsations will be almost 2 times larger than a 90 deg crank) some of the things that you can do to reduce the peak of the instantaneous torque are to use a heavy flywheel/clutch combination, use a good crank dampener, use some sort of flexible(in torsion) shaft or coupling that will take the peaks off of the torque spikes.  Several years ago George Poteet's streamliner was using some very expensive 7 speed trannys and they were breaking them like they had a truck load of them. I do not know what they did to end the carnage but my guess is the they did one or several of my suggestions to reduce the shock load.

Rex


 

[manta22]

Rex & Grant,

Angular contact ball bearings are very efficient; the early '60s Ferrari front wheel bearings were double-row angular contact ball bearings. Back in the "Olden Days" FAG Bearing Co. published a very useful booklet with detailed technical data on various types of bearings. See if you can find a copy of that FAG manual. No snide remarks. 

[floydjer]

Then the axle(s) are driven by the spur gear at the top?

[wobblywalrus]

The 6Al4V titanium alloy is very strong and fatigue resistant.  It also has a low elastic modulus so it is springy and it absorbs shocks very well.  It is easier to machine than most stainless steel alloys based on my experiences using an old lathe, drill press, etc.

[Flat54]

Sid: Thanks had a look at diff gears after your post they are a bit short on teeth I agree. Based on your input and others I am still looking for a suitable bevel set.

Rex: Thanks great info on oil supply and construction duly noted will go to angular contact ball bearings. The engine has a 90deg crank.

Manta22: Found this https://www.farrellbearings.co.nz/site/farrellbearings/FAG%20Mounting%20Handbook.pdf does that look like the old one?

floydger: Yes attached a snip of the drawing on the SCS website for clarity. I have to load the output gear thru the top for constructability  reasons. i.e. no clearance on the side above the bevel box for a bearing housing separate to the box itself. The connection to the axles will be splined slide couplers or that's the plan at present anyway.

wobblywalrus:Thanks.

[manta22]

Well, the "FAG Mounting Handbook" is probably the later descendant of the "FAG Manual". Lots of good information there. I'm surprised that no one has made comments. 

[wobblywalrus]

Warped humor about the Bendix catalog?

[Dynoroom]

This is a custom built rearend from bevel gears. In this picture it is under repair BUT it made many passes at both El Mirage & Bonneville. Even has run over 400 mph...