MIT students adapt regenerative braking principles to shock absorbers

[PaperclipGod]

From Ars: http://arstechnica.com/science...st-from-road-bumps.ars

Students at MIT have developed a novel shock absorber system that allows vehicles to regenerate lost energy in a manner analogous to the regenerative braking used in the majority of hybrids on the road today. They calculate up to a 10 percent boost in overall fuel efficiency.

Wouldn't any system which recovers energy from the shock absorbers make those shocks inherently less absorbent? Your car hits a pothole, and the perceived impact is reduced by the giant spring next to your wheel which spreads that "impact energy" out over a longer period of time than if there were no spring. That energy eventually dissipates as heat. If you're putting any type of energy recovery device on the spring, though, that energy is going to be recovered by putting some sort of resistance on the springs motion, which can capture that otherwise "wasted" energy. So, if you had a 100% effective energy recovery device on the spring, the spring wouldn't even budge when it hit that pothole - all the energy would be "recovered" by your device. Great for fuel savings, but not so great for New England roads. Besides, the guys who invented the wheel already came up with a more efficient "energy recovery" device - no shocks at all. If they still want something that won't break the drivers coccyx, why not just use stiffer springs, and skip all the extra "energy recovery" doodads?

I realize the guys mentioned in this article are using hydraulics, sensors, and all sorts of other highly-engineered stuff... but it still reminds me of a perpetual motion machine. I mean, they state themselves that their generator will monitor road conditions to provide the optimal resistance for ride comfort - any resistance at all is going to reduce ride comfort from that of a shock absorber which isn't providing extra resistance.

So... what am I missing? I know I'm not smart enough to get into MIT, so what am I not understanding?

 

[Schadenfroh]

The DailyTech article's comments are rather amusing

new "pickup" line:
hey baby.. want to help me recharge my car??

 

[sandorski]

I don't know what you're missing, but I highly doubt they'll make shocks so stiff that your teeth will rattle going over cracks in the road. There might be some compromise, ut if they can recoup some Energy and provide an acceptable ride, bring it on.

 

[jackschmittusa]

Don't see a problem with the idea.

Hydraulic shocks work by transferring fluid from 1 chamber to another through a port (valve) to a resistance device (spring, gas). Putting an impeller in the path of the fluid will affect the transfer rate of the fluid, but the desired level of damping can be achieved by various means: port size, number of ports active, design of the fluid return mechanism (spring tension, air/nitrogen pressure, etc.).

Active suspensions have already been in use for a while now, so controlling this new system on the fly shouldn't be a problem either.

 

[frostedflakes]

It's not like this technology doesn't allow the shock absorber to dissipate energy. It's just that waste energy is being converted into electricity instead of heat or sound. Depending on the control system it may affect ride quality, but that's something they can (and probably already have) tweak for the best compromise between comfort and performance.

This is actually a pretty ingenious idea, wish I had thought of it first.

 

[JEDIYoda]

Originally posted by: PaperclipGod
From Ars: http://arstechnica.com/science...st-from-road-bumps.ars

Students at MIT have developed a novel shock absorber system that allows vehicles to regenerate lost energy in a manner analogous to the regenerative braking used in the majority of hybrids on the road today. They calculate up to a 10 percent boost in overall fuel efficiency.

Wouldn't any system which recovers energy from the shock absorbers make those shocks inherently less absorbent? Your car hits a pothole, and the perceived impact is reduced by the giant spring next to your wheel which spreads that "impact energy" out over a longer period of time than if there were no spring. That energy eventually dissipates as heat. If you're putting any type of energy recovery device on the spring, though, that energy is going to be recovered by putting some sort of resistance on the springs motion, which can capture that otherwise "wasted" energy. So, if you had a 100% effective energy recovery device on the spring, the spring wouldn't even budge when it hit that pothole - all the energy would be "recovered" by your device. Great for fuel savings, but not so great for New England roads. Besides, the guys who invented the wheel already came up with a more efficient "energy recovery" device - no shocks at all. If they still want something that won't break the drivers coccyx, why not just use stiffer springs, and skip all the extra "energy recovery" doodads?

I realize the guys mentioned in this article are using hydraulics, sensors, and all sorts of other highly-engineered stuff... but it still reminds me of a perpetual motion machine. I mean, they state themselves that their generator will monitor road conditions to provide the optimal resistance for ride comfort - any resistance at all is going to reduce ride comfort from that of a shock absorber which isn't providing extra resistance.

So... what am I missing? I know I'm not smart enough to get into MIT, so what am I not understanding?

well your name on these forums says it all.......
Would you be complaining if the story was-- MIT students adapt regenerative braking principles to paperclips???

 

[Harvey]

Originally posted by: PaperclipGod

Wouldn't any system which recovers energy from the shock absorbers make those shocks inherently less absorbent?

No, and you almost came up with the right answer in your own question.

Your car hits a pothole, and the perceived impact is reduced by the giant spring next to your wheel which spreads that "impact energy" out over a longer period of time than if there were no spring. That energy eventually dissipates as heat.

In current systems, once the stored energy is in the form of heat, it is dissipated as wasted energy into the ambient environment. All that would be needed would be a means to convert that wasted thermal energy to electricity that could be stored through the same system that charges the car's battery. The energy recovery happens after the shock absorber has smoothed the mechanical motion of the car so it would have no impact on the previous smoothing action of the shock absorber.

If you're putting any type of energy recovery device on the spring, though, that energy is going to be recovered by putting some sort of resistance on the springs motion, which can capture that otherwise "wasted" energy. So, if you had a 100% effective energy recovery device on the spring, the spring wouldn't even budge when it hit that pothole - all the energy would be "recovered" by your device.

There's the flaw in your argument. The system would not stop the spring motion. It would recover some portion of the otherwise wasted energy produced by the action of the spring.

Don't expect 100% recovery. Not all of the energy is "wasted." Some of it is used in producing the desired smoothing of the mechanical motion of the car, and no recovery system will be 100% efficient in recovering the rest if for no other reason than the recovery system, itself, would require some energy to operate.

The bottom line is, any system that recovers more energy than it uses to operate the system will produce a net gain. The remaining questions are whether such a recovery system could be easily and effectively integrated into vehichle designs and whether they could be produced and sold at a price that would result in a net economic advantage.

 

[theeedude]

Do they not teach physics in school anymore?

 

[MovingTarget]

Looks to be a good idea. However, they are certain to be quite a bit more expensive than conventional shocks if they are ever produced. We will see. Hopefully something like this will become commercially available as we begin to switch to electric propulsion.

 

[DrPizza]

Originally posted by: senseamp
Do they not teach physics in school anymore?

They do at MIT. However, it's not a requirement for posting in P&N.

 

[PaperclipGod]

How is this an improvement over simply stiffening the suspension, then? Less energy stolen by a cushy spring = more energy left to the cars momentum.

I mean, with hydraulics you can design any combination of port and impeller size you want, but to recover any energy you still need to trade dampening effect for energy recovery. Less energy used for dampening = more energy recovered, and vice versa.

This just looks like an attempt to "double dip" in the energy pool, using the same amount of energy to both absorb bumps and propel the car forward (better gas mileage). Doesn't this totally ignore the principle of entropy??

 

[PaperclipGod]

Originally posted by: Harvey

In current systems, once the stored energy is in the form of heat, it is dissipated as wasted energy into the ambient environment. All that would be needed would be a means to convert that wasted thermal energy to electricity that could be stored through the same system that charges the car's battery. The energy recovery happens after the shock absorber has smoothed the mechanical motion of the car so it would have no impact on the previous smoothing action of the shock absorber.

If you're putting any type of energy recovery device on the spring, though, that energy is going to be recovered by putting some sort of resistance on the springs motion, which can capture that otherwise "wasted" energy. So, if you had a 100% effective energy recovery device on the spring, the spring wouldn't even budge when it hit that pothole - all the energy would be "recovered" by your device.

There's the flaw in your argument. The system would not stop the spring motion. It would recover some portion of the otherwise wasted energy produced by the action of the spring.

Don't expect 100% recovery. Not all of the energy is "wasted." Some of it is used in producing the desired smoothing of the mechanical motion of the car, and no recovery system will be 100% efficient in recovering the rest if for no other reason than the recovery system, itself, would require some energy to operate.

The bottom line is, any system that recovers more energy than it uses to operate the system will produce a net gain. The remaining questions are whether such a recovery system could be easily and effectively integrated into vehichle designs and whether they could be produced and sold at a price that would result in a net economic advantage.

That's not what the MIT guys designed, though. They're not re-using waste heat, they're using the actual force of hydraulic fluid through an impeller to "recover" energy. Yes, if they were actually using waste heat to recover energy, I'd agree with you... but I'd also say they'd have better luck using the engine block.

 

[Brainonska511]

Originally posted by: PaperclipGod
How is this an improvement over simply stiffening the suspension, then? Less energy stolen by a cushy spring = more energy left to the cars momentum.

I mean, with hydraulics you can design any combination of port and impeller size you want, but to recover any energy you still need to trade dampening effect for energy recovery. Less energy used for dampening = more energy recovered, and vice versa.

This just looks like an attempt to "double dip" in the energy pool, using the same amount of energy to both absorb bumps and propel the car forward (better gas mileage). Doesn't this totally ignore the principle of entropy??

It's not double dipping; that's impossible.

It's using energy that is wasted by heat or by absorption into the suspension to drive a small generator. It's not going to make the shocks worse.

Could you explain how it would "totally ignore the principle of entropy"?

 

[Brainonska511]

Originally posted by: PaperclipGod

Originally posted by: Harvey

In current systems, once the stored energy is in the form of heat, it is dissipated as wasted energy into the ambient environment. All that would be needed would be a means to convert that wasted thermal energy to electricity that could be stored through the same system that charges the car's battery. The energy recovery happens after the shock absorber has smoothed the mechanical motion of the car so it would have no impact on the previous smoothing action of the shock absorber.

If you're putting any type of energy recovery device on the spring, though, that energy is going to be recovered by putting some sort of resistance on the springs motion, which can capture that otherwise "wasted" energy. So, if you had a 100% effective energy recovery device on the spring, the spring wouldn't even budge when it hit that pothole - all the energy would be "recovered" by your device.

There's the flaw in your argument. The system would not stop the spring motion. It would recover some portion of the otherwise wasted energy produced by the action of the spring.

Don't expect 100% recovery. Not all of the energy is "wasted." Some of it is used in producing the desired smoothing of the mechanical motion of the car, and no recovery system will be 100% efficient in recovering the rest if for no other reason than the recovery system, itself, would require some energy to operate.

The bottom line is, any system that recovers more energy than it uses to operate the system will produce a net gain. The remaining questions are whether such a recovery system could be easily and effectively integrated into vehichle designs and whether they could be produced and sold at a price that would result in a net economic advantage.

That's not what the MIT guys designed, though. They're not re-using waste heat, they're using the actual force of hydraulic fluid through an impeller to "recover" energy. Yes, if they were actually using waste heat to recover energy, I'd agree with you... but I'd also say they'd have better luck using the engine block.

But they are using waste heat. Instead of the energy being converted to heat in the first place, it is instead being used to drive a small generator.

 

[frostedflakes]

Originally posted by: MovingTarget
Looks to be a good idea. However, they are certain to be quite a bit more expensive than conventional shocks if they are ever produced. We will see. Hopefully something like this will become commercially available as we begin to switch to electric propulsion.

That's probably the big thing. Will the extra cost of the system be worth a 10% increase in fuel economy. I can only assume that it isn't, or else this technology would probably already be used in hybrid vehicles. I mean it's not a radical idea, I can't believe that somebody wouldn't have thought of and tried to implement something like this already.

 

[Brainonska511]

Originally posted by: frostedflakes

Originally posted by: MovingTarget
Looks to be a good idea. However, they are certain to be quite a bit more expensive than conventional shocks if they are ever produced. We will see. Hopefully something like this will become commercially available as we begin to switch to electric propulsion.

That's probably the big thing. Will the extra cost of the system be worth a 10% increase in fuel economy. I can only assume that it isn't, or else this technology would probably already be used in hybrid vehicles. I mean it's not a radical idea, I can't believe that somebody wouldn't have thought of and tried to implement something like this already.

It's entirely possible that someone could have had a similar idea, but just tossed it out for the lack of knowledge on how to implement it effectively.

 

[PaperclipGod]

Originally posted by: Brainonska511

Originally posted by: PaperclipGod
How is this an improvement over simply stiffening the suspension, then? Less energy stolen by a cushy spring = more energy left to the cars momentum.

I mean, with hydraulics you can design any combination of port and impeller size you want, but to recover any energy you still need to trade dampening effect for energy recovery. Less energy used for dampening = more energy recovered, and vice versa.

This just looks like an attempt to "double dip" in the energy pool, using the same amount of energy to both absorb bumps and propel the car forward (better gas mileage). Doesn't this totally ignore the principle of entropy??

It's not double dipping; that's impossible.

It's using energy that is wasted by heat or by absorption into the suspension to drive a small generator. It's not going to make the shocks worse.

Could you explain how it would "totally ignore the principle of entropy"?

The energy absorbed by the suspension is not wasted, it's used to cushion the impact of one rigid object (the car frame) to another (the pothole). The energy of a car hitting a pothole would normally be transformed almost entirely to waste heat. Think of what happens when you hit a nail with a hammer. All the force of your swing is transferred to the head of the nail. If there's nowhere for the nail to go and no way for it to deform, all that energy turns to heat. The suspension in a car is like a nail that deforms under the hit of a hammer -- instead of all the energy turning to heat (and a jarring impact), the energy is used to deform the spring. The spring captures the energy and allows it to dissipate as heat over a much longer period of time, decreasing the initial impact force and giving you a smoother ride.

So, any energy you remove from that equation, short of harvesting the heat after it's radiated off of the spring, is going to reduce the ability of that spring to cushion the ride. I said it ignores the principle of entropy because it's claiming to use the same amount of energy to produce two power two different actions - first it uses this energy to cushion the cars ride, and then it uses it to charge a battery with.

I agree that they can design a system that might use half of the energy to recharge a battery, and half to cushion the cars ride, but then that negates the entire purpose of this device anyway.

 

[PaperclipGod]

Originally posted by: Brainonska511

But they are using waste heat. Instead of the energy being converted to heat in the first place, it is instead being used to drive a small generator.

You can't say it uses "waste heat" before it actually becomes waste heat.

 

[frostedflakes]

Originally posted by: PaperclipGod
How is this an improvement over simply stiffening the suspension, then? Less energy stolen by a cushy spring = more energy left to the cars momentum.

I mean, with hydraulics you can design any combination of port and impeller size you want, but to recover any energy you still need to trade dampening effect for energy recovery. Less energy used for dampening = more energy recovered, and vice versa.

This just looks like an attempt to "double dip" in the energy pool, using the same amount of energy to both absorb bumps and propel the car forward (better gas mileage). Doesn't this totally ignore the principle of entropy??

Why would stiffening the suspension increase fuel economy? The energy absorbed by the suspension should be independent from the energy used to move the car, because the forces due to bumps in the road will be normal to the forces moving the car. Any energy harvested from the suspension system would be "free energy", it doesn't come from energy used to move the car forward.

And the idea of this technology is to harvest some of that energy created by bumps in the road. I don't know why this is so hard to understand, I think it makes sense at least.

 

[Brainonska511]

Originally posted by: PaperclipGod

Originally posted by: Brainonska511

But they are using waste heat. Instead of the energy being converted to heat in the first place, it is instead being used to drive a small generator.

You can't say it uses "waste heat" before it actually becomes waste heat.

Yes you can.

In a normal shock system, that excess energy is either distributed via vibrations in the suspension/shocks, as heat, or transfered back into the road.

Instead of it becoming heat and as many vibrations in this system, it is instead used to drive a small turbine.

This thread just makes me want to burn my physics and thermodynamics textbooks because you've opened up my eyes to how this system is complete bullshit :roll:

 

[PaperclipGod]

Originally posted by: frostedflakes
Why would stiffening the suspension increase fuel economy? The energy absorbed by the suspension should be independent from the energy used to move the car, because the forces due to bumps in the road will be normal to the forces moving the car. Any energy harvested from the suspension system would be "free energy", it doesn't come from energy used to move the car forward.

And the idea of this technology is to harvest some of that energy created by bumps in the road. I don't know why this is so hard to understand, I think it makes sense at least.

The car uses fuel as energy to push the mass of the car forward. Unless you attach a sail to your roof, all the energy in this equation is coming from the fuel. When you hit a bump, some of that linear momentum is deflected... ideally into the suspension system, where it can dissipate without impacting ride quality.

 

[PaperclipGod]

Originally posted by: Brainonska511

Yes you can.

In a normal shock system, that excess energy is either distributed via vibrations in the suspension/shocks, as heat, or transfered back into the road.

Instead of it becoming heat and as many vibrations in this system, it is instead used to drive a small turbine.

This thread just makes me want to burn my physics and thermodynamics textbooks because you've opened up my eyes to how this system is complete bullshit :roll:

Those vibrations are what mitigates the shock of the impact. If you remove those vibrations, you're essentially removing the suspension.

 

[Zenmervolt]

Originally posted by: PaperclipGod
From Ars: http://arstechnica.com/science...st-from-road-bumps.ars

Students at MIT have developed a novel shock absorber system that allows vehicles to regenerate lost energy in a manner analogous to the regenerative braking used in the majority of hybrids on the road today. They calculate up to a 10 percent boost in overall fuel efficiency.

Wouldn't any system which recovers energy from the shock absorbers make those shocks inherently less absorbent? Your car hits a pothole, and the perceived impact is reduced by the giant spring next to your wheel which spreads that "impact energy" out over a longer period of time than if there were no spring. That energy eventually dissipates as heat. If you're putting any type of energy recovery device on the spring, though, that energy is going to be recovered by putting some sort of resistance on the springs motion, which can capture that otherwise "wasted" energy. So, if you had a 100% effective energy recovery device on the spring, the spring wouldn't even budge when it hit that pothole - all the energy would be "recovered" by your device. Great for fuel savings, but not so great for New England roads. Besides, the guys who invented the wheel already came up with a more efficient "energy recovery" device - no shocks at all. If they still want something that won't break the drivers coccyx, why not just use stiffer springs, and skip all the extra "energy recovery" doodads?

I realize the guys mentioned in this article are using hydraulics, sensors, and all sorts of other highly-engineered stuff... but it still reminds me of a perpetual motion machine. I mean, they state themselves that their generator will monitor road conditions to provide the optimal resistance for ride comfort - any resistance at all is going to reduce ride comfort from that of a shock absorber which isn't providing extra resistance.

So... what am I missing? I know I'm not smart enough to get into MIT, so what am I not understanding?

All shocks provide extra resistance. That's what a shock absorber does, it resists the spring's movement.

Your confusion seems to come from the fact that the North American term "shock absorber" is not an accurate description of what the part actually does. In the UK, the same part is called a "damper", which is a more accurate term. The part actually plays no role whatsoever in absorbing shocks; the springs do that work. The shock absorber exists to counteract a coil spring's inherent lack of damping, which would otherwise result in the awful "floaty" feeling associated with cars that have blown shocks.

Using a larger-diameter orifice in the shock absorber while incorporating an impeller would provide the same net resistance to flow while still recovering energy.

ZV

EDIT: Stop thinking about the heat generated by the springs. This system would use energy from the shocks that would otherwise be turned into heat. The net energy absorption of the shocks is still the same, it's just being turned into electrical energy instead of heat energy.

 

[PaperclipGod]

Originally posted by: Zenmervolt

All shocks provide extra resistance. That's what a shock absorber does, it resists the spring's movement.

Your confusion seems to come from the fact that the North American term "shock absorber" is not an accurate description of what the part actually does. In the UK, the same part is called a "damper", which is a more accurate term. The part actually plays no role whatsoever in absorbing shocks; the springs do that work. The shock absorber exists to counteract a coil spring's inherent lack of damping, which would otherwise result in the awful "floaty" feeling associated with cars that have blown shocks.

Using a larger-diameter orifice in the shock absorber while incorporating an impeller would provide the same net resistance to flow while still recovering energy.

ZV

EDIT: Stop thinking about the heat generated by the springs. This system would use energy from the shocks that would otherwise be turned into heat. The net energy absorption of the shocks is still the same, it's just being turned into electrical energy instead of heat energy.

Ahhh... sweet, thank you! You're right, I was mixing up shocks/dampers/absorbers/etc. Now I see how it works.

 

[Harvey]

Originally posted by: PaperclipGod

How is this an improvement over simply stiffening the suspension, then? Less energy stolen by a cushy spring = more energy left to the cars momentum.

"Simply stiffening the suspension" is not the objective. It's intended to soften the ride for the passengers. If the system produces more energy than it uses, and it can store that excess energy for later use, the system is producing a net gain in efficiency.

That's not what the MIT guys designed, though. They're not re-using waste heat, they're using the actual force of hydraulic fluid through an impeller to "recover" energy. Yes, if they were actually using waste heat to recover energy, I'd agree with you... but I'd also say they'd have better luck using the engine block.

So they're not going through the wasteful transition from mechanical energy to heat. It's still using the energy that would otherwise be wasted as heat to drive their system. If it's not used, that same energy would otherwise eventually be wasted as dissipated heat.

Think of it in more macro terms. Roads are not infinitely smooth so a car travelling down a road WILL produce mechanical shock energy. This shock absorbing system extracts more energy from the vibration than it requires to operate, and converts the excess to a usable, storable form.

It's a law of physics know as the law of conservation of energy.

Conservation of energy

The law of conservation of energy states that the total amount of energy in an isolated system remains constant. A consequence of this law is that energy cannot be created or destroyed. The only thing that can happen with energy in an isolated system is that it can change form, that is to say for instance kinetic energy can become thermal energy. Because energy is associated with mass in the Einstein's theory of relativity, the conservation of energy also implies the conservation of mass in isolated systems (that is, the mass of a system cannot change, so long as energy is not permitted to enter or leave the system).

Another consequence of this law is that perpetual motion machines can only work if they deliver no energy to their surroundings, and also that devices that produce more energy than is put into them without losing mass (and thus eventually disappearing), are impossible.

Einstein's theory of relativity expands the concept to address the equivalency of mass and energy.