I always fancied myself an amateur inventor, in the sense that I generally welcome the idea of inventing things, but don’t have the foresight, patience, scientific or mechanical knowledge to put any of my ideas into motion.
For years I wondered why no one had ever used a highly wound spring as an energy storage medium in a car. Converting mechanical energy to mechanical energy is more efficient than converting chemical energy (gas or a battery) to mechanical, is it not?
There’s a lot of dreamers and thinkers out there with the same idea as me, and googling “Spring loaded cars” or “torsion spring cars” bring up a long of the same ideas. I’ve also been introduced to the concept of flywheels, which I’ve only encountered in person from my Spincycle classes. Apparently they’re a similar form of energy store, only perhaps a bit more sturdy or reliable.
Is there any way to either have a wind-up car or flywheel car that would be practical as a means of transportation? I know we have a few science and engineering people on here, so I’m hoping someone can fight my ignorance in nice small words.
IIRC the problems are too much mass, not enough power, and a tendency towards catastrophic failure. The more you spin up a flywheel, the more prone it is to act rather like a bomb if something goes wrong. And while you can put it in an armored shell such a shell is massive and reduces the range of the vehicle. And only spinning it up to more reasonable levels leaves you with less stored energy to tap.
There’s been more work on using flywheels as short term kinetic storage for things like regenerative braking.
Dig up some Popular Science magazines from the mid 1970’s and if memory serves, you’ll find some sort of flywheel or whackadoodle 100 MPG car engine design on the front cover every three months or so. Maybe not quite that often, but it just seemed like there was an endless parade of concepts that never saw the light of day back then.
the concept of a flywheel for energy storage is not woo (see the link about buses above, or the Chrysler Patriot; not to mention pretty much every metal stamping press in existence) but it’s not really feasible to use it as the primary source. 'cos you either have to have a flywheel so massive that you’ve pretty much screwed yourself from the get-go, or it has to spin so fast that it’s not likely one could even be manufactured to stay in one piece.
as for springs, I’d think they have the same limitation. you’d have to put them under so much stress to get any useful energy storage that they’d probably break. Not to mention that you’d have to do it over and over and over and over again; if the spring didn’t have a yield fracture, fatigue would probably get it. And think about this- people have been injured or killed just trying to remove the spring from the strut on their car’s suspension. The amount of stored energy in a “propulsion” spring would be extremely hazardous.
The gyroscopic effect of a massive flywheel in a moving vehicle would make cornering… interesting. (Or traversing hills, depending on the axis of rotation).
Rather than use mechanical springs, another option is to use hydraulic accumulators. Instead of batteries and electric motors, the driveline uses hydraulic pump-motors and accumulators. During decel, hydraulic fluid is pumped into the accumulators, compressing nitrogen gas on the other side of a piston or bladder. The energy is stored in the compressed nitrogen.
It works pretty well. One of the key advantages over electrical hybrids is power density: a hydraulic system is able to absorb and deliver energy faster than an electrical system of the same weight.
It’s not feasible to store enough energy in the accumulators for a hydraulic-only trip, so the system doesn’t particularly improve highway fuel economy. But for city driving, it allows recovery of a greater fraction of braking energy than a comparable electrical system, which means it really boost city fuel economy. That’s perfect for urban delivery vehicles: UPS trucks, mail trucks, buses, garbage trucks, and so on.
This is true of every non-chemical energy storage option. Chemical energy storage does not rely on the physical integrity of the container, the chemicals themselves are relatively stable and will only release their energy under specified conditions.
Physical/electrical energy storage, like a flywheel, spring or supercapacitor, relies on the physical integrity of the storage device, break the device and all the energy is released immediately. When you talk about the amount of energy required to move a car a significant distance that’s a ton of energy. 1 gallon of gasoline has about the same energy as 60 pounds of TNT. So, if your storage device holds the energy equivalent of 1 gallon of gasoline, and you get into a serious wreck that damages the storage device… big boom.
As supplemental storage, such as saving your braking energy, it can work, but not as primary storage.
I suppose in a roundabout (snicker) way, pretty much every car stores some energy in the flywheel every time we use the engine to brake.
Or perhaps not exactly “stores energy” as such (seeing as a normal ICE isn’t set up to make use of that energy input)…but some kinetic energy of the vehicle ends up as kinetic energy in the flywheel.
Besides the problem with failure modes (which is a pretty big problem), there’s also the fact that for a vehicle, actual working efficiency has to account for not only the output of the engine compared to energy stored, but the weight of the engine and energy storage. A spring might return most of the energy stored in it, but if it’s very heavy, the vehicle will use a lot more energy, meaning actual useful working efficiency is going to be low.
And gasoline (including diesel and other fuels) is a huge winner in energy density (energy stored divided by weight), even when you add in the weight of the engine, too. That’s why serious model airplanes use gasoline (or whatever similar fuel they actually use) rather than wind-up springs.
Of course, for a full-sized passenger vehicle, the safety issues with mechanical storage mean the weight has to go up even more, so it’s even further behind.
I believe there is a pickup truck that uses this method to drive additional fluid through an automatic transmission when starting out with a heavy load. It might be the Ford F-350.
I’m suprised it hasn’t been been mentioned but it is very difficult to couple the energy into or out of a driveline to/from a flywheel without resorting to electrical or hydraulic means:
You need to speed the flywheel up when the vehicle is decelerating, and you need to speed the car up while decelerating the flywheel.
If you are going to have hydraulics or electrical stuff to couple the flywheel to the driveline, then hydraulic accumulators or batteries compete nicely with the flywheel for less weight and complication.
This new system uses magnetic coupling to the flywheel. They claim that it will provide regenerative breaking at a fraction of the size of a battery powered system.
