Suspension energy recovery system

[godlameroso]

As the topic title implies, does anyone think that this technology could find it's way into F1, or perhaps sports car racing.

Apparently the technology exists

http://www.engadget.com/2013/09/01/zf-l ... sion-cars/

[Jersey Tom]

Spring = suspension energy recovery system

[godlameroso]

Indeed it is, however the rest of the suspension puts a damper on the party. I'm speaking in terms of using the suspension to harvest energy that can be used later.

[Jersey Tom]

Oh for sure, I get it. Interesting idea. Wonder how much it amounts to, though. How much energy is actually dissipated over the course of say.. a commute. A reasonable amount, or a trivial amount?

[RideRate]

JT,
Probably a reasonable amount. P=F*v for 4 corners... Integrated over the commute. Haha.



I think there is merit to the idea and I expect it may one day be implemented on road cars. Free energy, however little it may be, is free energy forgetting the weight and initial cost penalty which tend to wash out in the long run on passenger cars. I don't think it'll catch on until the efficiency is very very high and I'm not sure converting the energy to electrical is the way it'll go.

I think the question is not how much energy is dissipated by the shock, but how efficiently can you capture what is dissipated. I don't think it'll ever be enough for a racecar since there is much more effective ways to alternately get the energy that would be captured. Plus whatever you do will carry a weight penalty. It would probably only show up in racing like KERS did, under the dictation by some set of rules.

[Robbobnob]

Indeed this technology does exist.

For my honours research project I looked into a model for approximating the potential recoveries of such a system.
Without going into too much detail the jist of our findings can be shown in this plot



In a simplistic 2DOF model there are two modes which are responsible for the majority of the power being dissipated across the damping unit. Of course in a real vehicle there will be additional modes due to the added behaviour of any roll, heave, and pitch controlled by a spring unit.

In order to assess the potenial for excitation of the modes the input excitation of the system, i.e. the road profile, needs to contain or excite frequencies in these ranges. This can be quantified by a function known as the Power spectral density, a measure of the frequency content of a signal. As a road is a spatial waveform the Power spectral density is a direct function of vehicular speed.



The above PSD was formulated to represent a 'typical' new zealand highway at a vehicle speed of 80 Kmh.

Therefore for a given power spectral density we can then predict a expected response of a model and given the relitive displacements and velocities across the damping unit derive an expression for the power dissipation across such unit.




Where the Power is directly proportional to the damping co-efficient multiplied by the relative velocity across the damper.
Depending on the values for the models masses and spring rates, energy dissipation can vary from 10 W to 122 W across a single unit.

The real trick is the construction of a unit which can harness that energy.
Attached is an article comparing different units in development

http://www.iaeng.org/publication/WCE201 ... 9-1892.pdf

[xpensive]

Errhh...I'm not certain if I'm being taken for a ride or just totally misunderstand the concept here, but energy is always force times distance, 2 tons of vertical load with 2 inches of travel is only 1 kJ, the equivalent of less than 0.03 cc of gasoline.

If you jump around 1000 times over one lap however?

[tok-tokkie]

I remember it was done on motorcycle shocks some years ago. Google doesn't find that but it finds me this which predicts 256W on a car. http://www.gizmag.com/regenerative-shoc ... ber/14564/

I don't understand the final graph from robbobnob - Wm^2. What is that area?

[Tim.Wright]

I too think the idea is a waste of time. The gains are just not worth the cost in weight and complexity. Going by the analysis above we can expect a peak of 122W which is nothing (0.1kW to put it in engine terms). Assuming that the complete system weighs 20kg (5kg/whl) you will need about 200W to accelerate its own mass at 0.2g from 20km/h. So its not even providing enough energy to accelerate itself! i.e. you will accelerate faster without it.

Also, its likely that the system will have to run below its peak recovery mode in order to not disturb the tyre forces (this system will be acting like an active ride element in parallel with the spring). On road cars you will have ride comfort constraints too.

So in reality, once you detune it so it doesn't disturb the tyre forces and the ride comfort, its not going to be giving you any useable power at all.

I realy can't see any advantages to such a system on a road car. Maybe a rally car though...

[xpensive]

Now that I have thought about it, what you can gain is really nothing but the hysteresis in the springs, isn't it?

[Tim.Wright]

Well if the system was perfect it could replace the dampers. This way it would harvest all of the energy that would otherwise be dissipated by the dampers.

The problem is, we are talking of recovering a few hundred Watts maximum. Good for nothing...

[xpensive]

There you go, we would be talking about the power lost in the dampers, speed times force, which is not much.

[RideRate]

Now that I have thought about it, what you can gain is really nothing but the hysteresis in the springs, isn't it?

No, not at all. You get all the energy dissipated across the suspension, ideally. So normally the stored spring energy is 0.5*k*x^2. That energy with no dissipation would be continually converted from accelerating the mass to being stored in the spring and vice versa. The damping dissipates all that. How much is done by the damper and how much is inherently in the system is gonna be a big component of your total recovery efficiency.

Thinking about it quickly, the spring hysteresis is actually energy lost through the spring, so it's lowering your possible efficiency. It represents energy that can't be captured across the damper.

[MOWOG]

I read somewhere about a night club that harvests the energy of the customers stomping around the dance floor to supplement its electricity needs. So the concept is plausible.

The only question is, is the effort worth the reward when it comes to automotive suspensions, either road cars or race cars? The non-technical answer to that appears to be a resounding "No!"

[xpensive]

Just like the idea of recovering energy from methane xhausted by different mammals perhaps?