Engine mount design

Guess the center of rotation. dispose the mounts as far from this point as practical. Find the torque needed to restrain the max engine torque with reasonable deflection. Specify the engine mounts to handle this torque AND the engine/transmission weight multiplied by a max bump acceleration (say 5g) multiplied by a design factor of say X1.5 That's it.

Brian W

Don't you have to account for gearbox reduction increasing the torque? One of the problems with a FWD setup is that the unit incorporates the final drive ratio so increasing the torque on the mountings. In a normal RWD the torque is split between the engine and the rear differential. In my experience, torque is one of the major killers of these mountings. Spread them as far apart as practical and don't try to make them too stiff. Large softer mounts seem to last longer.

John

Yep if the final drive is close coupled to the engine it sees a torque multiplier. Transverse engines with unit final drives typically use an anti-torque link to handle that final drive torque.

Brian W

You've gotten some good advice on applying pre- engineered mounts as components.

If you're interested in designing the mounts themselves, don't forget to include redundant load paths for when the rubber rots away. Having your engine slide out through your radiator at a stoplight is embarrassing.

At least one book exists about race car dynamics, that explains, for instance, how jounce bumpers prevent frame failures. It probably covers engine mounts, too, but the kinetics of automobiles are not real simple. Look at

-Mike-

Thanks for all that. I'll investigate further. I f any of you guys can reccommend a good book on the subject of designing engine mounts or a similar product were vibration will be a factor i'd appreciate the isbn and name.

Good answers, on the right track, but (a) you'll never see 5g on an engine in normal use , an additional 1g is more like it (after all how many times have you been crushed to your seat by an additional force of your own weight? - the engine is pretty much a passenger for road loads). Also (b) even a normal gearbox gives you a torque multiplier, at a maximum in first gear. Actually the shock loads are a factor of two or so worse than that in a manual, and think about a torque converter's effect as well.

Although it is nice to spread them apart as wide as possible, there are good refinement type reasons not to do so. For a home build project I'd stick them far apart.

I agree that torque is more likely to kill the mounts than road inputs.

I can think of three cars whose launch was delayed by one-two years because they couldn't figure out how best to mount the engine - so if I were you I'd find a similar car to your design and copy their mounting system!

Is this a FWD or a proper car?

Cheers

Greg Locock