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."
Gyroscopic precession (Score:4, Interesting)
Brake Pedal (Score:4, Interesting)
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.
mass in motion (Score:5, Interesting)
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.
1) & 2) solved by 60,000 RPM (Score:4, Interesting)
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.
Re:Gyroscopic precession (Score:5, Interesting)
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.
http://www.allpar.com/model/patriot.html
I'd prefer air power (Score:2, Interesting)
This air-hybrid system [popsci.com] 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.
Kinda like an old tractor (not) (Score:4, Interesting)
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.
Re:energy from BRAKING - best for stop-and-go (Score:5, Interesting)
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)
Re:I'd prefer air power (Score:4, Interesting)
Compressing gas has a fairly lousy energy return. The air heats up when being compressed, and that heat is wasted unless you insulate the tank.
Not Really - (Score:2, Interesting)
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, vacuum-packed flywheels doesn't require the kind of industrial and technological leaps that most people assume. Many appliance manufacturers already have the necessary facilities and experience. Intriguingly, so do hard drive makers. Making things spin extremely fast in environmentally sealed compartments while aided by self-balancing technology is kind of what their engineers do.
Flywheels also charge and discharge far faster than batteries (their specific power can be absolutely gigantic) and flywheels made from modern composites have energy densities that compare favorably to batteries. These materials also tend to turn into powder when the wheels shatter. The worst case failure mode for one of these things breaking is nothing an inch or two of kevlar can't reliably stop, so flywheel explosions should only be a concern in designs lacking some pretty basic safety features.
Batteries are attractive for a lot of reasons but as far as I'm concerned, battery chemistry is a dead horse. I've been following this subject for a very long time - it's not getting better anytime soon and given the research climate there's no reason to even assume that most of these 'breakthroughs' that get trotted out every month or so are even real. (A decade of watching and waiting has shown me that almost none of them make it to market.) The specific power and charge rate problems aren't going away. I think Volvo is ahead of the curve on this one.
Re:Fuck Hypermilers (Score:5, Interesting)