A 50 kg spring could get a 1,000 kg vehicle up to 15 mph.
Instead of using a high HP motor with a lot of rare earth materials driving up the cost of an electric vehicle it might be better to just use a spring for some of the regenerative braking and use a lower hp motor.
This approach would get you through intersections. On the down side getting up to freeway speeds might take longer than a diesel Rabbit.
It's not clear exactly what you propose. I gather you are trying to capture braking energy for subsequent use in acceleration. How does the spring interact with the brakes? You mention "ratchet"; are you proposing brake calipers that (somehow) totally grab the wheel and then as the wheel turns a bit that winds the spring a bit, then the ratchet releases the calipers and they re-grab the wheel in another spot? Sounds like a jerky ride!
Similar questions about how you'd transfer the spring energy back to the wheel later. Seems like the key to this whole idea is a special transmission of some sort, which would be the *real* invention here!
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That'll eventually improve but it's a lousy round trip efficiency right now.
That's why it's desirable to keep the number of energy conversion components down.
There's no question that for freeway commuting situations it wouldn't work. Either you would have to use a 1600 kg spring to get the same car up to 100 kph or you'd have to get DoT to lower the speed limits near ramps and intersections.
There may be some niche markets where 100% of the driving is in city traffic or rural. If you want to get on the freeway you'd want to wait until traffic is very light.
I think that pursuing a mechanical system for bicycles is a dead end. The overall amount of energy is small and smoothness of capture & release is even more critical than a car. It needs clutches, gearboxes, things to grab onto the wheels...that all sounds big, heavy and inefficient to me.
Even assuming 50% efficiency the shove you'll get from braking at a stop/start intersection just doesn't seem worth it.
As a rider I don't see stop/start intersections as much of a problem anyway, not compared to going up hills.
I think a much better idea would be a small dynamo which charges up a capacitor as you ride. This would be connected to an electric motor which can provide boost when you press a button on the handlebars.
The dynamo could even have a 'high charge' mode which you could activate to increase the amount of energy being captured when you're going down a hill. Dynamos produce drag when they're active so it would act like a brake to slow you down as well as storing the energy - double win!
A fully charged supercapacitor could easily launch you away from an intersection and provide a lot of help for going up a short hill.
There is at least one patent for a spring mechanism for a bicycle. The spring fits inside the hub. Assuming the dimensions of the hub in the drawing are similar to conventional, there is no way the spring could weigh anywhere near the 5 kg that would make it worthwhile.
Some work has been done on carbon nanotube springs as "batteries" which weigh 3 orders of magnitude less than steel springs but cost 3 orders more. As a replacement for a gas tank and/or batteries for motor vehicles the weight may be ok but the cost would be over $5 million.
It would be better to use carbon nanotubes for regenerative braking but even then it would be hundreds of dollars for a bicycle and thousands for a motor vehicle. This is just to scoot through the intersection.
To get a 1 ton motor vehicle up to freeway speeds might take $100,000 worth of nanotubes. The round trip efficiency is good but you can buy a lot of rare earth magnets and supercaps with 100K.
What we need is a material that is somewhere in between steel and carbon nanotubes in price as well as energy density.