Regenerative shock absorber

[night9]

Thanks for the info guys! I knew there had to be more info out there on these types of systems. Hopefully we will see more of this type of tech in our future.

[shovel]

A while ago, I'm pretty sure here on Ecomodder, I presented the idea of using bass shakers bolted to the jiggly bits under the car, and connected through a simple bridge rectifier to charge a vehicle. No idea if it would actually work or last, but it's an idea.

[Blue Angel]

Originally Posted by NeilBlanchard

Normal tires absorb most of the small bumps, so having a rigid tire (similar to the Energy Return Wheel) that had lower rolling resistance, and it would pass more motion through to the shocks. So, the ride would be similar, but the dampening work would be mostly done by the shocks, so you could regain more energy, as well.

This is the second stage of efficiency improvement that I hope to be able to try on my CarBEN EV5 project: rigid airless tires combined with regenerative shock absorbers.

Using rigid tires would definitely transfer more energy to the suspension for recovery, but doing so would increase NVH (Noise, Vibration, Harshness) to dramatically unacceptable levels for a passenger car.

A car's suspension system has areas of compliance (assuming rigid road surface, hard parts and body mounting locations), listed in order of greatest to least:

1. Spring/Shock assembly
2. Tire Sidewall/Tread
3. Bushings/Isolators

Reducing/eliminating the compliance of any of these without compensating somewhere else will increase NVH.

Also WRT rigid tires, contact at the road surface will be drastically reduced as the tire gets more and more rigid. This is evident even when over-inflating a standard car tire. The stiffer the tire the more it will rebound off of road imperfections, increasing your energy recovery potential but reducing contact with the road and traction.

The tire is the car's most critical "suspension system" and is far more efficient at absorbing small high frequency road imperfections than the rest of the suspension system, since it's unsprung "mass" is extremely low (measured in grams instead of kilograms). For a car that travels on anything other than perectly smooth testing surfaces (any real road) I think your efforts would be better spent using a traditional tire and experimenting with inflation pressures to find an acceptable balance between all of the inevitable compromises.

I'm sure you and many others on the forum are well aware of everything I have posted above. I posted this specifically for those who may not be aware that all of these compromises exist and must be dealt with.

Having said all that...

The very act of compressing a car's suspension system requires energy, because dampers generate heat (resist motion). The more we reduce suspension movement the less energy we waste.

Remember that a large part of LRR tire design is efficient sidewall flexing, or compliance without generating heat. Compared to a suspension damper, tires generate very little heat as they compress.

The moral of this story is, the more suspension "work" you can do with the tires, the less you need to do with the dampers/springs, and the more efficient the suspension "system" will be at travelling over a given road imperfection.

Making the tires more rigid would be creating inefficiency for the sake of recapturing some % of the energy wasted with an EM shock absorber.

[Blue Angel]

Originally Posted by shovel

A while ago, I'm pretty sure here on Ecomodder, I presented the idea of using bass shakers bolted to the jiggly bits under the car, and connected through a simple bridge rectifier to charge a vehicle. No idea if it would actually work or last, but it's an idea.

I'm absolutely sure it would work. Making it last might require a bass shaker specifically designed for the loads placed on it.

This EM shock absorber is basically the same concept as what you're describing, except that the bass shaker idea would intentionally add mass to an existing system. The EM shock absorber would be much more efficient, for sure, but the bass shaker experiment would be cool to try out!

[RedDevil]

Originally Posted by Blue Angel

... The very act of compressing a car's suspension system requires energy, because dampers generate heat (resist motion). The more we reduce suspension movement the less energy we waste. ...

That's close but the culprit is the damping, not suspension travel per se.

Compressing a car's suspension system require energy both to overcome the spring load and the resistance from the shock absorbers.
The spring will release most of that energy when the wheel moves down again. The damper will resist the outgoing movement and waste more energy doing that.

The reason reducing suspension movement wastes less energy is by and large just because of the shock absorbers. Lose the shocks, then the suspension can travel without adding (much) resistance.
The Australian solar racers had a working suspension system with springs, just no dampers.

Obviously, that compromises safety and comfort. Having no shocks is no option for real cars. That's why Ferrari, Audi and many others use shocks with variable resistance; low when dealing with minor bumps (where the shocks added friction would reduce comfort) and stiffer when the road or the handling roughens.
By operating the shocks in a smart way they can prevent energy from getting wasted instead of trying to gain some of the wasted energy back.

Just varying the rigidity irrespective of the actual movement of the wheel and car is a bit crude.
Those systems should switch rigidity quickly enough (maybe by using a solenoid switch in the damper fluid channels) to dampen just those movements that would increase body roll etc. while allowing for the adverse movements.
That would be a kind of holy grail; better comfort, lesser resistance, better handling all marching together while no outside power is required (apart from operating the switch).

A full active suspension would go even further than that; actively pulling the wheels in at the upstroke and pushing them down on the recurve, such a system could work as a propulsion system on its own as long as the road is choppy. But it would be a very expensive way of propulsion.

Going back to the original idea of reducing travel in the suspension system; that's what stiffer springs would achieve.
Unfortunately, stiffer springs always come with bigger rims, wider tires with tiny sidewalls, tons of carbon decals and >2000W audio sets, making it hard to measure any gain in FE.
And maybe the stiffer springs would also require stiffer shocks.

Another approach is to make sure the wheels are as light as possible. While the spring load stays the same (as the rest of the car keeps the same weight) the lighter wheels make that lighter shocks may provide enough damping where they would underdampen the OEM wheels.

Maybe combining the two would be best; e.g. stiffer springs, lighter wheels, original shocks travelling less. Obvoiusly such a setup would reduce the effect of regenerative shocks, though the combination might still work.

My favourite remains the solenoid operated shocks; while not producing power they would reduce resistance to an extent that cannot be topped by regen shocks, and improve other characteristics to boot. Building the logic to operate that solenoid and its fail safe system make it a project for the experts only.

[Blue Angel]

Originally Posted by RedDevil

Those systems should switch rigidity quickly enough (maybe by using a solenoid switch in the damper fluid channels) to dampen just those movements that would increase body roll etc. while allowing for the adverse movements.
That would be a kind of holy grail; better comfort, lesser resistance, better handling all marching together while no outside power is required (apart from operating the switch).

You have just described the magnetorheological shocks GM has been using in the corvette since 2005:

Magnetorheological damper - Wikipedia, the free encyclopedia

They work very well and are used in many more cars now. Basically, an electric current changes the viscosity of the damper's fluid in real-time.

[RedDevil]

Am I right in thinking that those dampers make regenerative shocks all but obsolete?

[NeilBlanchard]

The whole point of regenerative shocks *is* to regain some of the energy that would otherwise be waste heat. Don't forget that flexing in the pneumatic tire also produces waste heat in the tire itself.

My earlier suggestion does two things to increase the efficiency of a car - the rigid wheels would have the lowest rolling resistance possible, and with most of the motion caused by bumps and swells in the road surface being dampened by the regenerative shocks, they would produce a greater amount of reclaimed energy.

Other advantages of using airless tires: they never need to have their pressure checked, and they would never leak and lose efficiency. Also, you would not need to carry a spare, or a jack, and full wheel skirts don't have to be removed to change a flat. You would never have a blowout, either.

I'm pretty sure that the ride quality and handling could be tuned to provide normal characteristics. The Energy Return Wheel is close to what I would expect, though it needs to be aerodynamically smoothed and it doesn't need to be tuned to mimic a standard tire. And the Levant Power regenerative shock would need reworking to account for the small rapid motions that a more rigid wheel would generate in the suspension.

[Blue Angel]

Originally Posted by RedDevil

Am I right in thinking that those dampers make regenerative shocks all but obsolete?

No. The MR dampers do not allow the capture of any wasted energy due to suspension movement. They simply adjust their damping rate to accommodate changing requirements in real time, blending comfort with dynamic performance better than a damper with a single damping rate.

[Blue Angel]

Originally Posted by NeilBlanchard

The whole point of regenerative shocks *is* to regain some of the energy that would otherwise be waste heat. Don't forget that flexing in the pneumatic tire also produces waste heat in the tire itself.

You are correct, but comparing the bump absorbing efficiency of a tire and the rest of the suspension, the tire will win every time.

The ideal tire/wheel/suspension system would be zero mass and ride on a frictionless air spring. The frictionless air spring would return darn close to 100% of the energy it absorbed when encountering a bump, and zero mass parts means no need to damp the suspension, the tire would just follow the road. The only reason a car requires dampers when encountering a bump is to control the inertia of the moving parts. The less mass, the less inertia, the less damping required.

A tire absorbing a bump is FAR closer to the ideal zero mass suspension system than the actual suspension is, as it does ride on an air spring and its moving mass is extremely small. Since the moving mass is so small it requires very little damping, and yes that little bit of damping generates a little bit of heat. The physics are unavoidable, and favor the tire strongly over the suspension.

Of course, since the tire has very limited "travel" and is relatively stiff, as the bump gets larger a higher percentage of the bump is absorbed by the suspension system.

And before someone else says it, yes dampers are required to control roll and pitch dynamics. This conversation is about absorbing bumps and the related energy, not handling related dynamics.

Originally Posted by NeilBlanchard

My earlier suggestion does two things to increase the efficiency of a car - the rigid wheels would have the lowest rolling resistance possible, and with most of the motion caused by bumps and swells in the road surface being dampened by the regenerative shocks, they would produce a greater amount of reclaimed energy.

I believe the #1 priority in gaining efficiency should be lowering the rolling resistance; on most roads under most conditions the greatest efficiency gains would be found there. Compared to rolling resistance, wasted suspension energy is a FAR lesser concern and this is more and more true when traveling on roads that are in good condition. If making the tire more rigid shows gains in rolling resistance then this would be a good direction to go.

Having said that, if making the tire more rigid was done purely to increase suspension activity and showed no real gains in rolling resistance, the overall vehicle efficiency will go down for the reason I mention above; a tire is more efficient at dealing with small road irregularities than the suspension system is. The higher the % of the bump absorbed by the tire, the less energy the car will lose.

I should have included that in my initial response.

Originally Posted by NeilBlanchard

Other advantages of using airless tires: they never need to have their pressure checked, and they would never leak and lose efficiency. Also, you would not need to carry a spare, or a jack, and full wheel skirts don't have to be removed to change a flat. You would never have a blowout, either.

All very good points.

Originally Posted by NeilBlanchard

I'm pretty sure that the ride quality and handling could be tuned to provide normal characteristics.

I'm not sure about this. Making the tire more rigid might mean adding more bushing compliance at the suspension mounting points to compensate, and then you are taking the energy "gained" at the tire and wasting it in the bushings, maybe? All else equal, stiffening the tires will reduce the ride quality...