Engineers invent way for cars to harvest energy from bumps in the road

August 4, 2015 by Eleanor Nelsen, Virginia Tech
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Credit: Scott Meltzer/public domain

The 255 million cars on the road in the United States account for 40 percent of the country's fuel consumption. Most of that fuel is wasted.

Lei Zuo, an associate professor of mechanical engineering in Virginia Tech's College of Engineering, may have a partial solution: harvesting from the car's suspension.

Zuo explained that only 10 to 16 percent of the fuel a car consumes is actually used to drive—that is, to overcome road resistance and air drag. Most of the rest is lost to heat and other inefficiencies.

With clever engineering, however, that deficit can be reduced.

Three major opportunities exist for recovering or generating energy while driving: the given off by the engine, the kinetic energy absorbed during braking, and the dampened by the shock absorbers, he said.

Zuo estimates that a car's shock absorbers should be able to provide between 100 and 400 watts of energy on normal roads and even more on rougher roads. By comparison, the average cell phone call uses about 1 watt. That corresponds to an increase in between 1 and 5 percent, which would add up to an annual fuel savings of $13 billion to $19 billion.

His energy-harvesting shock absorber works by translating the vertical vibrations of the suspension into rotational motion that turns a generator. The generator delivers electricity directly to the car's battery or electrical devices, reducing the demand on the alternator.

This system has solved a major challenge in harvesting vibrational energy: converting bidirectional, up-and-down motion into the unidirectional motion needed to drive a generator. A unique combination of gears allows motion in both directions to be converted into electricity, essentially doubling the amount of energy that can be recovered.

Zuo, who is affiliated with the Institute for Critical Technology and Applied Science, explains that this innovation allows the generator to work at a steady speed and reduces the load on the gear teeth, making the system more efficient and reliable. Moreover, the generator keeps rotating even after the vibration has stopped, maximizing the amount of energy recovered.

He and his students have tested the on campus roads. Their current model, which the students have built using off-the-shelf components, can harvest about 60 percent of the available energy—a substantial improvement over other designs.

Zuo said he is confident that with precision components and manufacturing the system could reach 85 percent efficiency.

Moreover, he said, the device is entirely retrofittable in terms of space and function, and "can be integrated in the car directly without changing anything in the car." Zuo and his team have created other types of energy-harvesting shock absorbers, including linear electromagnetic and hydroelectric absorbers.

Zuo, who recently received an award for this work from the Governor's Commonwealth of Virginia Research Commercialization Fund, said he plans to focus next on the commercial viability of the energy-harvesting system.

He said he hopes to address the concerns of both drivers and automakers—who have different priorities.

"When we present this to drivers, they ask, how much can you improve the fuel efficiency? How soon can I get my money back?" Zuo said.

"From the car manufacturer's side, they ask another question: Can you replace my commercial shock absorbers? Can you give me better suspension performance?"

Zuo said he plans to tackle both cost and performance in the next round of development. Currently, the system wouldn't be cost-effective for owners who drive less than an hour or so a day, so Zuo will focus on applications for large commercial vehicles while working to reduce the cost.

To improve performance, Zuo said he wants to adapt his design using a strategy called self-powered semi-active control: A microprocessor senses vehicle conditions and adjusts the suspension settings accordingly, delivering the smoothest ride while harvesting the greatest amount of energy.

Zuo also is working on the two others areas for energy recovery in cars: waste heat and regenerative braking. Regenerative braking is already in use for hybrid vehicles, but those make up only about 3 percent of the cars on the road; Zuo wants to develop a system that will work for conventional vehicles.

Energy-harvesting research often focuses on milliwatts and microwatts; Zuo focuses on systems that can yield hundreds or even thousands of watts. "I'm particularly excited about the opportunities in large-scale energy harvesting, which may help solve the global energy crisis," he said.

Explore further: Energy-harvesting shock absorber that increases fuel efficiency wins R&D 100 award

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31 comments

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MR166
4.5 / 5 (8) Aug 04, 2015
If he is able to generate 400 watts average on the campus the school need to seriously consider repaving their roads.
MR166
3 / 5 (4) Aug 04, 2015
Second of all why should scientifically illiterate people be able to post and article on Physics.Org. A Watt is not a unit of energy. Watts*Time is, IE watt-second or watt-hour.
gkam
2.1 / 5 (7) Aug 04, 2015
He used the term for power instead of energy.

So what?

I think most of this energy harvesting will be with thermoelectric and piezoelectric systems.
MR166
3.4 / 5 (5) Aug 04, 2015
"He used the term for power instead of energy. So what?"

So, 400 watts is very deceptive. You can discharge a capacitor in microseconds and generate headline making peak wattages but the actual energy discharged in watt-seconds is tiny. This article was designed to be deceptive. It is nothing more than green propaganda.
gkam
1.6 / 5 (7) Aug 04, 2015
" This article was designed to be deceptive. It is nothing more than green propaganda."
----------------------------------

Is that what you would do? Why do you think others would have your character?
MR166
4.4 / 5 (7) Aug 04, 2015
Simple Gkam,,,, I would disclose how many watt-hours the new shock absorbers generated in a one hour trip and equate that to the amount of gasoline saved. But they did not do this for fear of being discovered as the charlatans that they are.
gkam
1.7 / 5 (6) Aug 04, 2015
Again, why would you assume they would cheat?
MR166
3 / 5 (4) Aug 04, 2015
"Again, why would you assume they would cheat? "

Simple, because a "Professor" who knows better chose to describe the output of the device in peak watts instead of watt-hours!!!

"Fund Me Fund Me"
gkam
1.6 / 5 (7) Aug 04, 2015
The professor probably did not write those words. And I still cannot figure out why you think others cheat normally. In what field do you work? Is that standard procedure there? Why?
MR166
3.4 / 5 (5) Aug 04, 2015
You know Gkam it takes a real man to admit when he is wrong. I can only assume that you are a Caitlyn Jenner type of guy.
fay
3.7 / 5 (6) Aug 04, 2015
Again, why would you assume they would cheat?

because attention and resulting funding - in short, money
gkam
1.6 / 5 (7) Aug 04, 2015
fay must work in some other field than science, since he/she seems to not understand how science works.
gkam
1.7 / 5 (6) Aug 04, 2015
"You know Gkam it takes a real man to admit when he is wrong. I can only assume that you are a Caitlyn Jenner type of guy."
------------------------------------

Emote much? This is a science site, and assumptions are not invited.
MR166
4 / 5 (4) Aug 04, 2015
"Emote much? This is a science site, and assumptions are not invited."

Ah yes, and that is exactly why my post questioned the use of Watts instead of Watt-hours!
gkam
1.7 / 5 (6) Aug 04, 2015
And I explained those were the words of the writer, not the researcher.
MR166
3.7 / 5 (3) Aug 04, 2015
"And I explained those were the words of the writer, not the researcher. "

So you are claiming that the writer did not interface with the researcher properly and is incompetent.

Well doesn't that make P.O. an unreliable website for posting the article???
MR166
5 / 5 (5) Aug 04, 2015
One of the favorite responses of the AGW crowd on this site is "Show me the paper that proves your statement." Yet the content of articles that promote new sources of "Green Energy" are never questioned.

Yup, the green movement is not too political!!!!
gkam
1 / 5 (6) Aug 04, 2015
Why do you make wild extrapolations into the ridiculous?
TheGhostofOtto1923
1 / 5 (5) Aug 04, 2015
The professor probably did not write those words. And I still cannot figure out why you think others cheat normally. In what field do you work? Is that standard procedure there? Why?
Well if the person is a psychopath then one assumes that everything they say is a lie, because it is a symptom of their disease.

Its like a college dropout who claims to have an MS, or a tech who claims to be an engineer.
gkam
1.7 / 5 (6) Aug 04, 2015
"Well if the person is a psychopath then one assumes that everything they say is a lie, because it is a symptom of their disease."
-------------------------------

Oh, . . the cowards who hide behind pseudonyms and advertise their fixation on others in public?
TheGhostofOtto1923
2.3 / 5 (3) Aug 04, 2015
"Well if the person is a psychopath then one assumes that everything they say is a lie, because it is a symptom of their disease."
-------------------------------

Oh, . . the cowards who hide behind pseudonyms and advertise their fixation on others in public?
You display your pathological lying in public along with your real name.

This indicates just how sick you are.
gkam
1 / 5 (5) Aug 04, 2015
"This indicates just how sick you are."
----------------------------------

Hey, Goober, you are the one with the fixation on "getting even" with me for letting you make a fool of yourself.

But you are not real: Get over it.
TheGhostofOtto1923
1 / 5 (4) Aug 04, 2015
"This indicates just how sick you are."
----------------------------------

Hey, Goober, you are the one with the fixation on "getting even" with me for letting you make a fool of yourself.

But you are not real: Get over it.
'Getting even' is not the reason you have so much trouble here. That is just an excuse you made up in that sick little mind of yours.

In reality the people here are not going to let you post lies and fabrications and pretend to be who and what you clearly are not.

And it is NOT going to stop until you do.

Is that clear?
gkam
1.7 / 5 (6) Aug 04, 2015
"Is that clear?"
--------------------------------

Well, . . it's certainly funny, . .
dustywells
5 / 5 (3) Aug 05, 2015
" I would disclose how many watt-hours the new shock absorbers generated in a one hour trip and equate that to the amount of gasoline saved."
That too would be meaningless since the results would depend on the surface covered and the speeds maintained. Obviously a rough country road at 30mph would generate more electricity and save more gas than a smooth highway at 60mph.
MR166
3.7 / 5 (3) Aug 05, 2015
"That too would be meaningless since the results would depend on the surface covered and the speeds maintained. Obviously a rough country road at 30mph would generate more electricity and save more gas than a smooth highway at 60mph."

Dusty I alluded to that same problem of road surface in my first post. Just because the actual savings are hard to average and quantify this does not mean that the energy output of the system should be left out of the article.
MR166
2.3 / 5 (3) Aug 05, 2015
If you look at the bottom of the page it seems that the article was authored or provided by Virginia Tech so you can't even blame an ignorant reporter for the lack of clarity. Until I see some real numbers I can only conclude that this is little more than grant bait.
docile
Aug 05, 2015
This comment has been removed by a moderator.
nignolo92
3 / 5 (2) Aug 09, 2015
I know very well Zuo's work. I made my graduatio thesis about this topic. Unfortunatly energy harvesting from suspension is not that useful for little mass vehicles.
Power haverstable (not considering losses) is directly proportional to the mass of the vehicle, the car's velocity and the street's roughness.
Street roughness is classified in 8 Classes: from A (the smoothest) to H the most wrinkled. The class considered in Zuo's study was C but I found a mistake in his calculations and I thought he took the values of D class.

I found that the power harvestable (with the same parameters) was 25 to 100W. Not 100 to 400 W. Anyway this is very little compared to the power needed to move the car.
gkam
2.3 / 5 (3) Aug 09, 2015
If you really want to generate power you would magnetize the stroke of the shocks to produce the power, and can then tune the resistance with an exciter.
Lord_jag
not rated yet Aug 17, 2015
Where does this power come from?

Wouldn't this slow the vehicle down more than if it wasn't used? Isn't that like putting a windmill on the roof to create electricity for propulsion?

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