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I've been trying to come up with an easy way to shoehorn an engine into a vehicle, situated directly on top of the rear wheels.
What I want to do is drop a vertical shaft from a downwards-facing tranny to an upwards-facing differential, but given that the differential will be bouncing up and down
and twisting it's not an easy task.
So I'm thinking if we use something like a short shock-absorber coil as a driveshaft we can allow both types of off-movement (within reason) without complicated mechanics. As a bonus there's a bit of torque energy absorption/release which protects both sides from the shocks of the other.
The problem of course is when you load up the truck you're going to be putting pressure on the differential (unless you have load-levelling) and driving on a rough road will introduce a varying flexing load.
The best spring of course would be one that's easy to compress/stretch, yet difficult to (un)ravel: a Slinky with torque-transmission capabilities.
How about this?
http://mgaguru.com/...shaft_1600_yoke.jpg
A sliding spline joint with universal joint [loonquawl, Mar 31 2009]
Flexible Drive
http://www.ondrives...cts.asp?subcatid=29
Don't expect it to last long though. [eight_nine_tortoise, Mar 31 2009]
Ultimate Hydro Drive
http://www.artemisip.com/index.htm
Made in Scotland, possibly near Stirling. [eight_nine_tortoise, Apr 02 2009]
Hydro CVT
http://auto.howstuffworks.com/cvt4.htm
A sort of anti HalfBaked website [eight_nine_tortoise, Apr 03 2009]
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FlyingT, if you can makes this work there is money in it. Although I suspect you need a spring material with different material properties in longditudinal and wound directions. Perhaps some sort of laminated CFC flat spring. [-] |
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The only way that works that I have seen of doing this it to have normal engine/transmission mounted horizontal, drop gear pair on back of transmission, prop then running in opposite direction back to diff under engine. |
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What's wrong with using a standard transverse engine? Is it a torque thing? |
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wouldn't a hollow shaft with internal teeth, and an outward-teeth shaft that slides freely up and down in it be sufficient to decouple the motor from the up-down of the differntial? |
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What you mean is a sliding spline joint loonquawl. I though this but I think FlyingT has a few other misalignments going on that this sort of joint cannot cope with by itself. |
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Mmm - I think FT said the differential would be twisting (I suppose this means if one rear wheel drops into a pot-hole?) - but couldn't you correct this with a "sliding spline" joint *and* a universal joint? - or with a horizontal loop of chain from the engine to the vertical drive-shaft? |
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//couldn't you correct this with a "sliding spline" joint *and* a universal joint? //
YES... that's actually the point of the post.... not using that. |
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//loop of chain from the engine to the vertical drive-shaft?//
hmm... if you mean a length of chain, sure but since you need a length equal to the longest extension of the suspension wouldn't that tend to bind up when the suspension is at it's shortest extension ? |
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Something from this [link] should so you. Suitibubly scaled up that is. |
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Why not make the differential static, and have an independent rear suspension where only the wheels move? Another, more complex option would be to let the whole engine move relative to the car body.
This idea is good, but it would require lots of engineering and I bet it would break pretty easily. |
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I'm also not sure why you want to use a standard format engine; why not a horizontally placed Wankel or better yet an old fashioned radial engine? |
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//wouldn't that tend to bind up when the suspension is at it's shortest extension ?// - well you'd have something to take up the slack on the chain, like the derailleur on a bicycle. |
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//The best spring of course would be one that's easy to compress/stretch, yet difficult to (un)ravel (if such a thing exists)// |
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//like a rubber CV joint?//
considering that the length of the join is going to vary by as much as a foot and a half or two I'm pretty sure a simple rubber rod isn't going to do much... unless you're referring to the rubber joint protector which doesn't actually do anything except keep dirt from the universal joint. |
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you need a PTO style drive shaft. It's going to be hard to find anything that can more than double in length. Most differentials, transmissions, and crankshafts, hate to have any extra thrust placed on the shaft, in or out. Also, a spring mounted at the center of the vehicle won't improve your handling very much. Have you considered mounting the engine to the axle itself? Not sure about the weight and suspension issues on a sold axle like that but it would certainly eliminate the need for a complicated drive shaft. |
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[DIYMatt] you're right, a 2 or 3 cylinder "I" on it's side, or opposed, or even a small radial is what I'm looking for. (I tend to want to poke Wankels with a stick to see if they bite so that's out). |
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[WcW] that would be [loon]'s spline/universal solution which would be standard, but even though I exaggerated the extension quite a bit, I'm not sure how much energy will be lost, or how robust that solution would be for driving a few hours on a rough road. |
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forget the energy the real concern is the thrust load it places on the the thrust bearings of the engine and differential when torque is applied or when the suspension moves. The end result would likely be severe crank walk or a differential that wears out very fast. |
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well the spring is just the main idea: if a spring with suitable "Slinky" properties couldn't be found we'd need endpieces with longitudinal-thrust-bearing bearings to fit onto the bodies of the transmission and differential. |
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what about my idea of mounting the engine to a cradle attached to the axle? this would be the cheapest most robust solution and it would eliminate flexing and reactionary torque as well. I guess a description of the application would help.... |
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well... unsprung weight is the issue with that I think. |
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APPLICATION:
Conversion of a RWD compact pickup truck to a PEV/CNG/EV AWD vechicle. Roughly:
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- bin the original engine and fill the underhood area with 100-200kg of traction-batteries (looking for a PEV range of 30 miles or so). 10hp wheelmotors in the front (or one motor for both, haven't decided). |
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- bin the original truckbed (convert to a flatbed) because of the room needed for the rear-engine: make storage compartments underneath wherever there's extra room. |
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- CNG tanks between the rails |
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- put a flat-as-possible engine/generatormotor (50hp/30kw) combination on(/in) the frame on top of where the rear differential is. Flat-as-possible to allow the new flatbed a low CG on the truck and on top of the differential to have the best energy transfer as well as the best weight (lack of)distribution, better traction than the original when lightly loaded and an increas in ground-clearance (since the differential has been turned to face upwards). |
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The current post is about the connection between the rear-engine and the rear-differential. |
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(note: this is a half-baked conversion because the used truck that was damned-near perfect for it got sold before I could get over there to buy it myself... take awhile to scrape up parts for the conversion too... a real project, but on "simmer") |
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why not put the rear engine between the frame rails under the bed and run a really short drive shaft? This would preserve the continuity of the bed and keep the install simple. Then you could use a cheap vw aircooled engine.... A high output vertical shaft engine is going to be pricy, are you planning to have a transmission? |
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... You could weld up a floating axle and VW axles and spindles with the VW tranny that would bolt straight up...... |
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Between the rails is optimum if everything will fit of course, but with a solid axle, the differential *will* move around... which is why I posted this in the first place :D |
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Ok, i don't think that a spring would make a very good drive shaft because of the thrust issues with thrust, harmonic and inefficiency issues but I AM really excited about the idea of a rear engined hybrid truck. You should seriously consider using the engine cradle and transmission from a VW which will fit nicely between the frame rails and sit happily under the bed without any hot rodding. Building a box beam that converts the IRS of the VW into a dead axle that mounts the VW drive train into a strong "trucklike" live axle would be easy as pie. This axle would be lighter than the stock pumpkin and utilize the stock springs and shocks. A 1800 vw will deliver barely adequate performance under a CNG carb which should be perfect for a hybrid while providing very respectable fuel economy. |
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k, you've almost sold me on the VW engine (air-cooled boxer 50'ish HP sounds perfect), but considering a pickup's gonna weigh >3,000lb dry, I'm not sure if a stock VW transmission would be even remotely capable (and at this point I note that my neighbour has 2 Transporters and I have a chainsaw...hmmm... nonono) but I still have to shoehorn a motor-generator in there somewhere *and* leave room for the tanks; don't want to put the engine behind the wheels either (I prefer to drive forwards, not sidewards)... what's wrong with using the stock axle ? (I don't know that much about old VW drivetrains) [edit] ah, I see....hmm.... we have slightly different ideas for hybrid powertrain... hmm... could go IRS on the rear-axle and tack the differential to the frame...but no clue how that would affect load capability |
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ok it's like anything else, you figure out what your goals are and you build up to meet the need. For instance a 50 hp engine could limp you home but it wouldn't be able to push a truck at highway speed. If you use a transporter drive train gear ratio is going to be a question for launching without battery assistance. A very good start for the application though. Reconsider placing the engine directly in the rear just as it mounts in the VW. This would maximize simplicity and still fit cleanly behind the rear bumper in most trucks where the spare tire sits between the frame rails. The VW tranny and diff and axles will be under the same loads that they experienced in the transporter because the engine is essentially unchanged. (DONT! lug the engine, make sure you make loading the engine at idle mechanically impossible, use the electrics to get rolling then load the engine) |
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This is a really really neat idea. |
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wouldn't consider loading the engine from a dead stop especially with a loaded truck... what I have in mind for this hybrid is: |
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unloaded:
- (sub)urban, <45mph, 30mi range : electrics only (FWD)
- highway <65mph : ICE supplemented by electrics for passing and hills(RWD/AWD)
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loaded:
- (sub)urban: ICE supplemented by electrics(RWD/AWD)
- highway: nope.
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bad road conditions: AWD and when the batteries run low, use the ICE to drive the rear wheels while charging the motorgen which runs the front wheels. |
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BUT... if we box the existing VW IRS into a solid axle then we have a couple hundred more pounds of VW engine added to unsprung weight... and tell me the engine won't fall off (and take the axle with it) after a few miles of potholed roads. |
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(the Transporter comment was a joke: if I had a VW pickup (already RWD), I'd just add batteries for 4WD) |
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This sounds like you want a hydraulic pump/motor system, effectively giving you a CVT into the bargain. |
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Strap the motor (and gearbox if required) to the diff input, and use whatever engine you like to power the pump! Just make sure you've got some good cooling for your fluid! |
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A [link] for your hydro drive. |
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Thanks [eight_nine_tortoise], I hadn't realized it was baked in anything other than farm/industrial machinery! My idea was to use the flexibility of the pipework rather than mechanical power transmission. |
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Yeah this is quite baked although not the most efficient drive. There is even a company in Ohio that makes them for busses (SuperDrive Inc.), the buses now do 10mpg instead of 7.4mpg. |
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okay, now I'm lost... hydrowhat ? |
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(the immediate problem that required the proposed solution(post) was to do an efficient (ie: 100'ish pct) transfer of power of up to 80-90hp between the end of a transmission and a differential, given that the distance might range between say 6" and 1.5', and the differential (being of a solid axle type) would be twisting (nomenclature?) as the wheels ran over stones and dropped into potholes... even including WcW's and mine aside the problem/hb-solution still remains) |
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FlyingT - you won't get anywhere near 100% with out a direct coupling, or a new chain in good alignment (which you cannot do because of all the freedom of movement you require). I think the hydrostatic drive is probaly the best may to go. Simply your motor drive a hydraulic pump (this can be fixed or variable displacement) that is connected by two hoses to another hydraulica pump on the nose of the diff (this can be fixed of variable displacement, but one end needs to be variable to give you a range of ratios) [link]. These thing are fairly common, cheep and robust in garden machinery and agrlicultural machinery. Any good tractor supply should have one that can take 90 bhp and there are probally plenty in scrap yards. |
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Keep away from toridal CVTs as if you don't have a PhD in the physics required you are unlikely to get one over 50% efficient. |
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How about a stack of rings that mesh each other
but give a few degrees of movement of the
universal joint type . On the outside of the rings
are bolted springs which to tie the rings together
but also spring any motion. Sort of like a locked
jewelery linked chain by adding springs. |
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Most of the time the teeth of the meshed rings
would be transferring the torque. Only in a
awkward position would the springs be taking
some strain. |
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//vertical engine//
In the original design I envisioned a diesel 2cylinder horizontally-opposed engine that could simply be rotated for vertical operation. (For some reason lubrication problems didn't occur to me.) |
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If the engine-fairy wants to drop in my lap a 2cyl 2stroke variableCR(for dual-fuel diesel/CNG) 40KW, air-cooled vertical crankshaft engine, I wouldn't say no. (.... I'd say "ow" and "thankyou") |
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you would still need a transmission of some sort unless you plan to run this only once you get up to highway speed. Don't immediately know of any high output vertical shaft diesels, especially not of the 40kw VCR type. |
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well, that was mostly a wishlist: might be able to get a complete powerband out of the diesel with no gearshifts from say 25-60mph's with electric assist but I still need (or want) to go engine> clutch> genmotor> clutch> differential. |
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