Kinetic energy recovery system

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Hi.
To this day, in cars with gasoline engines, the kinetic energy under braking is simply wasted.
What i wonder is, is it really difficult or unnecessery to recover that enegry and use under acceleration ?
It would especially be useful while driving in heavy traffic.
 
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Certainly it would, but then there's another few thousand dollars worth of stuff on top of he car, plus the weight.

electrical would require motor generators somewhere in the drive train plus batteries of some sort.

I've seen it done hydraulically on rigs, where a bit of the braking effort is stored to push it off next start.
 
Originally Posted By: NICAT
Hi.
To this day, in cars with gasoline engines, the kinetic energy under braking is simply wasted.
What i wonder is, is it really difficult or unnecessery to recover that enegry and use under acceleration ?
It would especially be useful while driving in heavy traffic.



You are describing hybrid cars such as the Toyota Prius, one of the first ones. Braking causes the on board battery to get charged and the pressing the accelerator releases energy to the motor/generator and helps accelerate the car.
 
Originally Posted By: Shannow
Certainly it would, but then there's another few thousand dollars worth of stuff on top of he car, plus the weight.

electrical would require motor generators somewhere in the drive train plus batteries of some sort.

I've seen it done hydraulically on rigs, where a bit of the braking effort is stored to push it off next start.


Sir, You are right. If it is done at electrical level, it would be more complicated, even though it would have more and easily upgradable storage capacity.
But if the energy can be saved mechanically, wouldn't it be more simple and useful enough?
 
Originally Posted By: NICAT
To this day, in cars with gasoline engines, the kinetic energy under braking is simply wasted.
My Ford C-Max Hybrid does it all the time, and it has a gasoline engine. It does improve MPG by quite a bit.
Now for non-hybrids, Mazda uses a fat capacitor to recover kinetic energy (its very limited as to how much it can soak up!!):
technology_env_i-eloop_en_2nd-row_img.ts.1602150248478130.jpg
 
Originally Posted By: NICAT
But if the energy can be saved mechanically, wouldn't it be more simple and useful enough?

Hydraulic Hybrids were big a few years ago. Hardly hear about them anymore. They recover braking energy in things like stop-start garbage trucks and city vehicles, and store it in an accumulator. Limited storage, but they work OK.
Flywheels can be used, but they need shafts to spin them up, and you hope they don't fly apart.
 
Originally Posted By: NICAT

But if the energy can be saved mechanically, wouldn't it be more simple and useful enough?


A big ole flywheel bolted to the chassis might screw up the crash safety, and how about the geartrain to drive it? Impracticality for days
 
Originally Posted By: oil_film_movies
Originally Posted By: NICAT
But if the energy can be saved mechanically, wouldn't it be more simple and useful enough?

Hydraulic Hybrids were big a few years ago. Hardly hear about them anymore. They recover braking energy in things like stop-start garbage trucks and city vehicles, and store it in an accumulator. Limited storage, but they work OK.
Flywheels can be used, but they need shafts to spin them up, and you hope they don't fly apart.


If flywheels are used, how long can they store the energy ?
smile.gif
 
You are talking about hybrid. Depends on the kind you have some pros and cons: battery if you want to store your energy for a long time (hours to months), flywheel if you want minimal loss but not much waste, and then other exotic stuff like pneumatic if you want something in between.

In the end it is about cost and benefit. Prius and other similar hybrid has a good compromise between cost and benefit (that's why cabbies and delivery guys use them), flywheel is good for racing, etc. For some vehicles you don't have much space for these devices so you just let it burn fuel and waste them (most minivan and pickups).

The question is whether it is even better if you make it a battery EV and use the savings from the engine for a bigger battery pack.
 
2009 was KERS. A heat recovery system with its own motor was later combined in addition to the kinetic recovery system. An explanation is available at formula1.com. Cannot post link for some reason.
 
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With battery energy storage, much of the original energy gets lost in the transitions from mechanical to electrical to electrical at a different voltage to chemical energy, and then back.

All modern electric cars recover braking energy, and have much more battery capacity than "regular" hybrids.
 
Originally Posted By: PeterPolyol
Originally Posted By: NICAT

But if the energy can be saved mechanically, wouldn't it be more simple and useful enough?


A big ole flywheel bolted to the chassis might screw up the crash safety, and how about the geartrain to drive it? Impracticality for days


Not to mention the gyro effects!
 
Originally Posted By: SteveSRT8
Not to mention the gyro effects!


My understanding is they worked around that (and the packaging issue) by having even number of flywheels and spin them in opposite direction.
 
Most modern cars already have a small KERS system in the form of a variable voltage ECU controlled alternator that aims to charge as far as possible on the overrun. It's not much but better than nothing and the implementation cost will have been low. This has been going on for 10 years.

The next relatively low cost step has recently been taken by Mercedes and perhaps others. The incorporation of the alternator into the flywheel allows kinetic energy recovered on the overrun to be fed back into the flywheel under acceleration.
 
Originally Posted By: PandaBear
Originally Posted By: SteveSRT8
Not to mention the gyro effects!


My understanding is they worked around that (and the packaging issue) by having even number of flywheels and spin them in opposite direction.


Popular mechanics had articles on these back in the 1980s. City buses were the application. Even with opposing flywheels, I don't think they were really able to get passed the forces and bearing loading on each flywheel itself. It takes thousands of RPM vs HEAVY weight, and a combination of both, to store anything useful. I don't think it every really saw feasibility at the time.
 
There's no "nett" gyro effect when dual flywheels are used, but each still tries to wrench it's mountings off when pitches and yaws take place.

When I watch manual cars do hig speed spins on the burnout track, the forces that the bolts are experiencing maskes me shudder.
 
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