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I’m wondering if anybody can help me by critiquing my project idea of having a failsafe power train 4x4 for remote touring🙂.

Instead of having one big engine, I’m toying with the idea of running two small engines, parallel to each other, which would turn a mitre gearbox (90* bevel gears), which would both then have output shafts entering a differential to mate them into a single output.

I would run a differential lock so that I could disconnect a blown motor and drive turn the differential off a single engine (instead of just having the opposite side of the differential spin in reverse).

The only major hurdle I have thought of so far, is that the shafts would be spinning in opposite directions as they enter the diff which would be relatively ineffective and make me ever so slightly sad.

I’m thinking to overcome this I’ll need a 180* bevel bear to reverse the drive rotate of one of the shafts.

What say you?

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  • $\begingroup$ Why not have them drive hydraulic pumps? $\endgroup$
    – Solar Mike
    Jun 30, 2018 at 7:28

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While that which you propose is possible from a purely technical standpoint, each extra gizmo required to implement it introduces its own failure modes into the overall reliabililty equation for your vehicle: the more things that can break, the better the chances are that SOMETHING will break.

If your overall objective is to furnish redundancy in case of failure, then you would most likely be better off studying the existing failure modes of your 4X4 and their frequency of occurrence, and beefing up their weak points rather than doubling up on your drivetrain.

If on the other hand your objective is to get out your welding rig and a pile of tools and have fun, then by all means go for it.

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  • $\begingroup$ Honda is purportedly introducing a wicked tranny with two input shafts, one for ICE and one for electric, that allows not just separate clutching, but also multiple gearing combinations! (Please ping me if you find a teardown on Youtube) $\endgroup$
    – Phil Sweet
    Jul 1, 2018 at 12:51
  • $\begingroup$ seems Hyundai has at least toyed with the idea - patentimages.storage.googleapis.com/US7604565B2/… $\endgroup$
    – Phil Sweet
    Jul 1, 2018 at 14:02
  • $\begingroup$ Yep, I’ve got to a fair level of self sufficiency and preparedness for my vehicle’s weak points, but just like exploring new ideas! Thanks for your input 👌 $\endgroup$
    – Aussie Dave
    Jul 5, 2018 at 7:48
  • $\begingroup$ @AussieDave, in what part of aussiedom do you reside? $\endgroup$
    – niels nielsen
    Oct 1, 2018 at 4:21
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With just two normal gears, the direction of rotation can be reversed. That's not your major hurdle. Please understand that when using a diff, one engine can only bring you to half the speed, in comparison to using both engines. That's more of a problem, eg. when choosing the total gearing ratio's.

AFAIK, the Prius uses a planetary gear system to achieve what you're trying. It may be a better option. Otherwise, you could just have one main gear to the transmission, where two gears are driving it, one for each engine, and disconnectable from the main gear when one engine is shut off. The engines will run synchronised though, so the throttles have to be connected.

Another option is to go the Citroën 2CV way, use one engine for the front wheels, the other for the rearwheels. It has two engines, two transmissions, two fuel tanks... Typical French invention..

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  • $\begingroup$ Legend, thanks for sharing your thoughts! Very interesting points 👌 $\endgroup$
    – Aussie Dave
    Jul 5, 2018 at 7:46

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