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Prototype Volvo Flywheel Tech Uses Car's Wasted Brake Energy 262

cartechboy (2660665) writes "Sometimes we get carried away with sexy moonshot car tech--whereas most everyday gains are about reducing inefficiencies, piece by piece. Volvo's flywheel energy-recovery prototype is a great example of the latter--not to mention similar to one used in Formula 1 racing. The system recaptures energy that would be wasted in braking, like a hybrid does, to reduce fuel consumption by up to 25 percent. When you hit the brakes, kinetic energy that's usually wasted as heat is transferred to a "Kinetic Energy Recovery System" mounted to the undriven axle. It spools up a carbon flywheel that turns at 60,000 rpm to store the energy. When the driver hits the gas, some of the stored energy is transferred back to power the wheels through a specially designed transmission, either boosting total power to the wheels or substituting for engine torque to cut fuel consumption."
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Prototype Volvo Flywheel Tech Uses Car's Wasted Brake Energy

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  • by Gothmolly ( 148874 ) on Thursday March 27, 2014 @04:04PM (#46595681)

    This seems great for high or nearly-sustained speed driving, but what I really want is an electric only option from 0-15 mph, a "parking garage" or "traffic jam" mode that I can put my car into.

    • by raymorris ( 2726007 ) on Thursday March 27, 2014 @04:10PM (#46595751) Journal

      It briefly stores energy from braking and uses it to accelerate a moment later. If you don't hit the brakes, it does nothing. If you hit the brakes and stay at a low speed for five minutes, it does nothing.

      When it works is when you stop (which stores energy), then go (which uses the stored energy). In other words "stop and go" traffic is EXACTLY what this is designed for.

      • by gnick ( 1211984 ) on Thursday March 27, 2014 @04:29PM (#46595939) Homepage

        That seems to make sense and seems like an interesting idea. Can you express it using a car analogy?

        • by Anubis IV ( 1279820 ) on Thursday March 27, 2014 @05:23PM (#46596593)

          Actually, yes, I think we can, strangely.

          Imagine you're coasting your way to the top of a hill and stopping at the top of it, with the brakes doing very little of the work in stopping you. By cresting to the top of the hill, we've effectively converted the kinetic energy you had into potential energy that can later be reclaimed when you go down the hill, and we've lost very little of that energy to heat from the brakes. That is, we can reclaim that stored energy to get a good chunk of the way back up to speed for a fraction of the fuel cost that it would have taken had that energy been lost.

          In much the same way, a flywheel is capable of converting forward momentum into a form that can then be used later. You can think of it as an invisible incline under the car every time you hit the brakes, helping to bring you to a stop while storing that energy for later, and an invisible declination under the car every time you follow the braking with the accelerator, helping you get back up to speed without having to consume as much fuel.

          (I'm now eagerly awaiting corrections, since I'm sure I misused terms and explained things poorly)

      • by kyrsjo ( 2420192 )

        According to the article, it holds the energy for ~20 minutes.

  • " “some form of KERS” would be inevitable on production cars after 2020."

    I'm hoping that by then, electric cars (with regenerative braking) are starting to become the norm.

    Really, 2020? With the pace technology develops, this might as well be Star Trek.

  • by hubie ( 108345 ) on Thursday March 27, 2014 @04:08PM (#46595723)
    Since you are spinning up a high-speed gyroscope, if you are braking through a turn I wonder if it effects handling in any significant way.
    • by Anonymous Coward on Thursday March 27, 2014 @04:19PM (#46595851)

      This was discussed when flywheel KERS was added to formula one. The forces involved are not significant, and on a heavy vehicle (as opposed to an F1 car) would have even less effects.

      Ultimately it is just a stop gap. Electric is so much more flexible than the complex CVT and fundamentally limited flywheel used in this. Which is why F1 all went to battery based systems.

      • by necro81 ( 917438 ) on Thursday March 27, 2014 @05:22PM (#46596583) Journal
        The F-1 flywheel systems have a vertically oriented axis, so that the gyro forces are reduced.

        The model demonstrated by Volvo has a horizontal axis, so the gyro forces will be greater and must be dealt with. Thankfully, it's pretty easy to quantify. If you get the flywheel spinning in the correct direction, you can even make the forces work in your favor to reduce roll during a turn.
    • by Anonymous Coward on Thursday March 27, 2014 @04:25PM (#46595915)

      The Chrysler Patriot prototype in the early 90's had this problem. This was a vehicle that was being designed for the 24 Hours of Lemans. It had a gas turbine that ran a alternator, which powered an electric motor driving the wheels. Instead of a battery pack it used a composite flywheel to store energy. Initially the flywheel caused too much of a gyroscopic effect and it was found that you couldn't turn the car. The solution was to make the flywheel gimbaled so it could rotate as needed while the car maneuvered.

    • by kyrsjo ( 2420192 )

      I would guess the effect would be very much smaller if it is mounted so it's rotating in the horizontal plane (vertical axis), than if it's mounted with a horizontal axis.

      • by Lumpy ( 12016 )

        going up or down a hill when you brake hard will be entertaining.... Mommy, why is that car standing on it's nose?

      • by steveg ( 55825 )


        You're going to get this effect (under braking or acceleration) no matter what orientation the flywheel is using. In one case it will be precession, in the other it will be a straightforward angular acceleration. The vertical axis might work better when your speed is constant.

        When you apply the brakes with a vertical axis flywheel, you are accelerating that flywheel which means an application of torque. The frame of the car will experience the opposing torque, providing a twisting force in one directi

  • Brake Pedal (Score:4, Interesting)

    by lgw ( 121541 ) on Thursday March 27, 2014 @04:08PM (#46595725) Journal

    I love this idea (and why has it taken so long to come to consumer cars), but please don't screw up the basic UI of a car the way some hybrids do! The brake pedal is for braking, dammit; simply lifting off the gas pedal should result in nearly coasting, unless I've deliberately put the car into a low gear for engine braking.

    The hybrid I test drove (and I understand this is normal) would do regenerative braking up to the limits of that system on a simple lift-throttle, where the brake pedal was just the brakes. Talk about leaking the implementation details through to the UI! Don't do that!

    For all I complain about UI designers, engineer-designed UIs are worse still.

    • by gnick ( 1211984 )

      Engineer-designed UIs are damned near perfect. As long as you're the engineer that designed them. And it hasn't been too long since you used them.

      Yes - I am an engineer. And yes, I have outsmarted myself more than once. Go back to a 3-year-old project and think, "What was this person thinking??? Oh wait, that person was me..."

      • by lgw ( 121541 )

        Engineer-designed UIs are damned near perfect. As long as you're the engineer that designed them. And it hasn't been too long since you used them.

        Ain't it the truth! It's hard to tell from modern software, but you really can make a UI that's easy to learn without being expert-proof! But now the sad trend is to simply remove every seldom-used control entirely - I'm sure "UI designers" will eventually achieve the same degree of uselessness as an unfamiliar engineer-designed UI.

    • by steveg ( 55825 )

      I haven't seen this. My hybrid (Ford Fusion) bleeds a little off the speed when I lift the throttle, but somewhat less than a regular ICE drivetrain would. The brakes, on the other hand, extract speed energy into the battery as fast as the battery can take it -- if I'm braking harder than that, it simultaneously applies the friction brakes. From a "user interface" perspective, I can't tell which part of the brake system is being used until I've come to a stop, when it gives me a "braking score" that show

      • by lgw ( 121541 )

        That's a great design on Ford's part. They really have gotten their act together on most things (if only they'd stop with the deliberately-cheap interiors, a holdover from Mercury and Lincoln still being different brands instead of different trim levels).

    • I don't know what model you drove, but my Fusion Hybrid does not behave that way. The only time it'll do regenerative braking without the brake pedal down is if its coasting downhill and would otherwise be gaining quite a bit of speed, and frankly in that situation I don't mind it applying a tiny bit of brake for me since I'd end up having to do it myself anyway.

      • Same for the Toyota Prius: unless you press the brake, regenerative braking is not engaged. So with neither pedal depressed, the car is just coasting. In fact, because the Prius is so aerodynamic, it coasts 'faster' (by which I mean it slows down due to air friction more slowly) than most other cars, so you can coast for quite awhile before needing to touch the gas again. In fact, I've actually been in situations where I was over-taking other cars while coasting...
  • mass in motion (Score:5, Interesting)

    by RichMan ( 8097 ) on Thursday March 27, 2014 @04:09PM (#46595733)

    The big factor is mass. To store energy you need to spin up and down the mass. However to drive in general you want to carry less mass on the vehicle.

    Factor #1: A more massive flywheel can store more energy at slower spin rates.
    Factor #2: A more massive flywheel is going to be more of a load in general driving.

    The optimium point of flywheel mass is going to depend on driving conditions. Really you should have at least 2 interchangeable fly wheels that you physically replace in the vehicle. One flywheel for city driving one for highway driving.

    Factor #3: A spinning flywheel is one hell of an energy store. Having a stopped vehichle with a fully spun up flywheel hit could release the spinning flywheel to the detriment of pedestrians in the neighborhood.
    Factor #4: Starting from a stop and attempting to corner, left or right, having a spinning flywheel is going to do gyroscopic things to the vehicle.

    There are all sorts of tradeoffs and safety considerations here.

    • by raymorris ( 2726007 ) on Thursday March 27, 2014 @04:16PM (#46595815) Journal

      It would seem to me that at 60,000 RPM, the rotational momentum is so much higher than the linear momentum that 1) and 2) aren't really a problem.

      3 and 4, on the other hand, could be a problem.

      • by raymorris ( 2726007 ) on Thursday March 27, 2014 @04:24PM (#46595903) Journal

        It occurs to that this is basically a larger copy of the "friction motor" that was used in toy cars. The ones you'd spin up by rolling them on the floor , then you let go and they speed away. If you ever played with those, you know that the spinning flywheel has WAY more than enough rotational energy than required to accelerate its own mass. Those aren't going nearly 60,000 RPM either. (I think, I've never measured their flywheel speed.)

      • by houghi ( 78078 )

        What if you take two flywheels that each rotate in a different direction? The total mass can be the same, but the individual mass would be half.
        The devided mass should be easier and lighter to protect the outside world from.
        The two rotating directions should lift up the gyroscope effect.

        Or am I missing something here?

    • by danlip ( 737336 )

      If the flywheel spins parallel to the road I don't think it would affect turning left or right - except it would resist the car leaning to the side on a sharp turn, which might be a good thing.

      • ... having a spinning flywheel is going to do gyroscopic things to the vehicle.

        Isn't this usually addressed using counter-rotating flywheels? Or does that not apply to the issue here?

    • Yeah, I'm not liking number 4 there.
      If you you try to turn the flywheel around its vertical axis, it will try and twist around the horizontal axis, effectively trying to make the car roll over while it turns a corner.
      The harder you brake coming in to a corner, the faster the flywheel spins, the slower you can take the corner.
      It's also going to slow down the flywheel. That energy required to slow it down is going to come from the engine.

      • We have formular one cars that run with 400km/h ... using fly wheels.
        I assume the engineering challange to scale that down to 200km/h is done.
        Hint, the company we right now talk about is Volvo, that should ring a bell.

    • Not much sense having a separate flywheel for highway driving - highway driving involves minimal braking, and so offers minimal opportunity to recover energy while doing so. Energy recovery systems are targetted specifically at stop-and-go driving at reasonable speeds, even "mobile parking lots" rarely involve high enough speeds to offer much kinetic energy for recovery - the vast majority of wasted energy is in idling the engine without using it.

    • Re:mass in motion (Score:4, Insightful)

      by Matt_Bennett ( 79107 ) on Thursday March 27, 2014 @04:53PM (#46596233) Homepage Journal

      Counter-rotate the flywheels and #4 isn't an issue, no matter what the orientation is.

    • Car makers need to think outside the box. An average American car-driver is a fat-ass. Just figure out a way to convert all the potential energy stored in drivers fat ass/belly and convert it to kinetic energy, it will kill 2 birds with one stone
    • by kyrsjo ( 2420192 )

      The mass of the flywheel is 13 pounds (~6 kg), while the whole device weighs 130 pounds (~60 kg). A lot of that is going to be shielding in case the rotor grenades.

    • Factor #3: A spinning flywheel is one hell of an energy store. Having a stopped vehichle with a fully spun up flywheel hit could release the spinning flywheel to the detriment of pedestrians in the neighborhood.
      Factor #4: Starting from a stop and attempting to corner, left or right, having a spinning flywheel is going to do gyroscopic things to the vehicle.

      You do know that cars already have a flywheel in them...

      • This flywheel is spinning at 60,000 RPM.
        Energy = mass * velocity^2 if I remember correctly, so this flywheel has a like million times as much energy and therefore potential danger.

        Engineers please feel free to correct me, or actually do the math.

    • by Lumpy ( 12016 )

      The problem is the "engineers" are trying to break laws of physics. the extra mass of the flywheel will soak up all the power gained from spinning it up.
      A flywheel is Power Output = Power input - losses, You will not have any gains from the flywheel only losses. it will conserve some energy, but not as much as an electrical regeneration system does.

    • by mspohr ( 589790 )

      "There are all sorts of tradeoffs and safety considerations here."
      Thank you for your insightful comments. I am sure that the Volvo engineers haven't considered any of this and will be very grateful for your valuable input.
      This is why /. is such a valuable resource for engineers the world over.

    • by odie_q ( 130040 )

      It doesn't have to be at all heavy, the article mentions 6 kg. Remember that kinetic energy is proportional to the square of the velocity, so doubling rotational speed lets you cut weight by three quarters. Also, gyroscopic forces won't be a problem, you just mount the wheel horizontally.

      Containing the stored energy in case of an accident likely requires some engineering thought, however. I suppose you would design the system so that it brakes the flywheel if it gets busted, converting the energy into heat

  • So what happens when the flywheel shatters at high speed?

    • No shatter. It's spun carbon fiber. You end up with a big bowl of carbon spaghetti.

    • Same thing that happens when you spin a CD at 60,000rpm in a CDROM drive. It shatters into a million pieces and destroys anything delicate inside the drive.
      You'll be fine if you're not in the car when it happens.

    • Two thoughts:

      1) How fast do your wheels spin now?
      2) How often do they shatter?

      • 1) How fast do your wheels spin now?

        Not very fast at all. Most engines turn less than 7,000 RPM and the wheels turn notably slower. The overdrive gear ratio will be just over 1, and the highest rear end ratios in common use are around 2.7:1. There's nothing whatsoever in most production cars which spins as fast as KERS.

      • by Lumpy ( 12016 )

        At 70 miles per hour a tire with a rim 15 inches wide will spin about 129 times per minute.

        Call me when you invent a car that the wheels spin at 60,000 rpm, I want to watch you drive it.

        • Call me when you invent a car that the wheels spin at 60,000 rpm, I want to watch you drive it.

          I just invented one. It needs very smooth road though, for its tiny wheels.

    • by Matheus ( 586080 )

      thousands of babies across the globe suddenly die in their sleep...

  • . . .for this to be in a production car. Back then, I read an article in Discover (?) Magazine about Mercedes working on this technology. Then nothing until today. Sounds great, to me.

    Also a really interesting tech I read about at that time was smaller motors at the wheels. No need for transmissions and shafts and gears.

    Pie in the sky tech I heard about then, too, was instead of brush and coil motors, having charged plate motors.

    Still nothing on those last two.

    • My father's been involved in alternative energy research since the 70's, I'm pretty sure I heard about regenerative braking with flywheels in the early 80s. (This is what happens when you're related to mad scientists whose idea of fun involves steam engines, solar panels and ocean thermal energy, preferably at the same time...)

      Here's a patent filed in 81 and granted in 85 [].

      This stuff is like clothing fashions, just wait long enough and they'll all come back, hopefully with the patents expired.

      • by steveg ( 55825 )

        When I was in school (mid 70s) there was work being done on "super-flywheels," both for automotive use and for fixed energy storage. Flywheels can deliver (or accept) virtually unlimited power -- not unlimited energy, but if you need a burst of power in a very short time, your limitation is not going to be the flywheel.

        One of the applications I read about then was for a university particle accelerator. The local city got upset at having the lights dim all over the city when they fired it up, so they spent

    • by Bomarc ( 306716 )
      The 90's ???? This concept was proposed in the back in August 1970 in Popular Science. [] article "Super Flywheel to power Zero Emission Car" [].

      I also remember a same concept article talking about buses (mass transit) when I went to school (don't remember the magazine though).
    • Also a really interesting tech I read about at that time was smaller motors at the wheels. No need for transmissions and shafts and gears.

      Motors at the wheels are actually pretty lame, because they increase unsprung mass which negatively impacts handling. A motor for each wheel is a nice way to go, though. Modern CV shafts rarely fail until the boots do. Go inspect your CV shaft boots and have them replaced if they appear to be leaking.

    • Brush and coil motors are old tech now. It's transistor and coil now

  • by Virtucon ( 127420 ) on Thursday March 27, 2014 @04:20PM (#46595861)

    Williams F1 has been working on this technology for quite awhile now. It's definitely fascinating. This video shows [] the technology applications.

  • by Animats ( 122034 ) on Thursday March 27, 2014 @04:35PM (#46596013) Homepage

    This isn't a new idea. It's been tried several times since 1950 for city buses, which are constantly stopping and starting. In 2009, one was developed for use in London. In the 2009 model, the linkage to the flywheel is mechanical, through a continously variable transmission [], not electrical. Although this has been in test for several years now, it's only one bus.

    That's the same technology Volvo is using. Putting this in a car seems marginal. It makes more sense for buses and delivery vans.

    • It really does not make sense for buses/vans. Far better to move those to electric.
    • 50 years, yeah, and the rest. Flywheels were widely used in the 1930s and 1940s to store energy and cut fuel consumption.. The first car I remember (a 1945 Rover 75) had one.
    • by Locutus ( 9039 )
      It was also done more recently as the late 1990s when the Rosen brothers created Rosen Motors and built a turbine and flywheel based system for cars. When they could not get any old school auto companies to buy into it they folded the company. I believe Capstone Turbines is the only remaining element of the company. It was created to make the compact turbines used in their auto system.

  • this concept has been used for awhile in UPS (battery backup) systems with a giant heavy flywheel on a generator-type spindle, which is kept spinning by electric motor power until the power goes off and then the rotating energy is put out into a generator to output AC power to critical electronics
  • I'd prefer air power (Score:2, Interesting)

    by Ken_g6 ( 775014 )

    This air-hybrid system [] uses nitrogen, hydraulic fluid, a hydraulic motor, and a couple of high-pressure tanks. I imagine it shouldn't cost much more than this flywheel, and it should store energy much longer.

  • by WindBourne ( 631190 ) on Thursday March 27, 2014 @04:45PM (#46596103) Journal
    Seriously, rather than focusing on a much cheaper saner approach of a simple electric car, these car makers continue to make more and more complex systems, which will have maintenance issues down the road.
    This is why tesla, and I think Nissan, will become major players in the car making business.
    • Not Really - (Score:2, Interesting)

      by Anonymous Coward

      All Tesla proves is that it's easier and quite possibly cheaper to send payloads into space and back than it is to make a reliable, affordable electric car. Recall that Tesla and SpaceX were founded by the same guy.

      Flywheels are old, old technology. They're very well understood and very reliable. Practically all of the gyroscopic problems can be resolved just by dividing the system into two wheels rotating in opposite directions - the forces cancel out. Mass producing sophisticated, relatively massive, vacu

  • by tomhath ( 637240 ) on Thursday March 27, 2014 @04:47PM (#46596125)

    Early tractors had the power take-off geared directly to the final drive. So if you were using a big rotating implement like a mower which was driven by the PTO you needed to be very careful when you got to the end of the field because the mower had so much energy you had no chance of stopping the tractor with the brakes.

    To get over that they added a coupler that would let the machine freewheel. I've been on a tractor without that coupler and it's pretty scary. Not stop and go, just go and keep going.

  • So what happens if you come to a stop and then want to turn right? You have a flywheel spinning real good and you're trying to change its axis. Either it's going to twist and bust its bearings and do considerable mayhem, or your car is going to go around the turn on two wheels. Fun times!

  • My 2005 Prius already have this technology as does many other hybrid vehicle.

Statistics are no substitute for judgement. -- Henry Clay