Why Can't Plug-In Prius Recharge Its Larger Battery?

How about a flywheel that then turns a generator??? Woooooo.

Yes, no matter how light, medium, or hard you brake, that flywheel gets cranked up to thousands of rpms, but then while you sit there at the red light, that fly wheel turns a small generator that charges your battery. Woooooo. Did someone just have a LIGHTBULB light up!!!

(Toyota, feel free to use my idea*
*just send me one of your cars when it's available )

Update: I just read wwest40's comment, and I think he got it in the last sentence. Nice.

 

Fast charging and high regen can both be solved with better chemistries that allow higher charge currents (and also a larger traction motor, the prius could never capture more than 60kw of regen power, the volt would be able to capture 112kw) so it's only a matter of time.

Yes, there should only be one large battery. the larger the battery, the lower the current per cell when charging/discharging. It's possible they've used two high energy desnsity (but low power density) batteries for the plugins, with a lower energy density (and higher power density) for the normal traction battery.

 

I'm no engineer, but one of the benefits of the Prius is its reliability and surely any type of flywheel, being a moving part, will require more maintenance/replacement. I know from having had turbo diesel cars in the past that turbo's have an expensive habit of going pop when you least want them to.

Perhaps your average Porsche owner is happy to pay for expensive replacement parts such as these fast spinning flywheels, but your average Joe who buys a Prius probably isn't.

 

Ken@Japan shared the answer last year and it comes down to battery chemistry and design:

• High energy storage - these battery types provide energy at a relatively low rate but a lot of it. These are the high kilowatt hour batteries needed for range. But they don't last long at higher rates of charge and discharge.
• High energy rate - these batteries provide peak power, a surge capability and tolerate rapid charge. These are often the ones most likley to be replaced or augmented with an ultra-capacitor storage device.

Hybrid means a heat engine and a second power system which is not limited to electric. I remain hopeful that we'll see practical hydraulic hybrids someday for utility trucks and pickups. Hydraulic power systems handle very high energy rates but for short periods such as acceleration and stopping. However, they tend to have a lot of moving parts and that hurts reliability.

The flywheel systems have the advantage of one moving part, the energy storage flywheel and high rates. From a moving parts count, it is simpler than the hydraulic hybrids and a practical alternative to hydraulic power systems.

Bob Wilson

 

Dan, do you have the percentage numbers that go with the words "percentage" and "some" in the first and second sentences quoted above? I only ask because I've always wanted to know the efficiency of the recapture and reuse features of the regen system in our cars. (I.e., does regen recapture 85% abd do you lose 10% converting back?)

Thanks, Larry

 

Toyota cars already have hundreds of moving parts. Toyota has been dealing with moving parts since the 1930s. I don't see why this would be any different.

 

Indeed they do, but battery charge hybrid systems like the Prius don't compared to a flywheel. I tried to answer this by refering to turbos which spin at very high rpm. I'm guessing as I'm no engineer, that a flywheel system would spin at very high rpm also and high rpm's mean wear and expensive (relative) replacement. I've had many turbo diesel cars (approx 50% of cars here are) and turbo's do go bang expensively despite following manufacturers service intervals.

A flywheel is still a very interesting idea though.

 

Yes, I agree with the ideal hybrid braking. Unfortunately, both regen systems we are talking about are limited to one axle. That way is impossible to achieve total braking relying on regen. But if you put not 2 but 4 electric motors for regen, you put more weight...and Porsche would not have that in mind...
Please be reminded that, in fact, regen is limited to a minimum speed of rotation, which Prius does deal very well with, PSD has gearing to still achieve that in a slower speed. When coming to a stop, hydraulics is needed.

 

IMHO it won't recharge, not can't recharge.

My guess is Toyota just does not know how much/fast recharge they can do while still maintaining battery life. They have separated the packs to use a maximum of 2 so they do not have the maximum power density. My guess is that much higher regeneration power density could be done with the addition of super-caps and recharging of all three packs. This would require additional weight and additional electrical parts to provide similar energy storage.

Flywheels would be my second choice if super caps aren't practical. It is a well understood technology and very reliable. While increasing the regen rate, attention needs to be paid to the abs and vsc and redesign to have them work properly.

There is always that problem when adding a new system, you give it so much attention to what is new that you forget the strain it puts on the rest of the car.

 

But first you must have the AVAILIBILITY, OPPORTUNITY of having excess recharge capability, beyond the need of the base system. If you were to even get, consistently get, to the point wherein the MAIN hybrid battery has a full charge only then would it be appropriate to use REGEN to recharge the GRID batterys.

The HSD system already sacrifices coastdown distance, ABSOLUTELY FREE forward motion, in favor of regen (to simulate engine compression braking...??) in order to come up with "more" (ENOUGH..??) regen capability.

And yes, a REAL break-through (BRAKE-through..?) would be to use regen to a higher level rather than as quickly transitioning to frictional braking, partial frictional braking.

Until then.....