2015 Toyota Prius Will Be Lighter, More Slippery

Re: improvements and wishlists, there is Summary of proposed improvements for future versions of Prius | PriusChat...

 

Too bad Michelin has discontinued the Energy Saver in the Prius size...

 

hands off cruise doesn't mean let the car take over while taking your eyes off the road. You still gotta be there to take over in case anything happens.

 

Lots of good ideas, but most cost something. I wonder what, if money was no object, a hybrid of the prius' size and performance could get for mileage with current technology.

 

Infinite if it was a plug in with large battery

Larger lithium battery with some kind of electric pulse glide could improve city milage 20%. Dropping cd to .20 with a 20% reduced frontal area would drop drag 36%, that could increase highway mileage by 21%. The ICE with current tech could jump from 38% to 43% peak efficiency that's 13%. Lower rolling resistance tires could drop rolling resistance by 10%. That is about a 35% improvement, 67mpg, without exotic materials for weight loss.

 

The heavier the car the more difficult it is to hypermile in stop and go traffic jams - so at some point a heavy battery becomes a liability. What the Prius needs is a lighter battery with a higher energy density - possibly a nano-tech lithium polymer variant battery pack. One of the major challenges with these newer and more powerful battery tech is heat dissipation.

The bigger the engine/catalytic converter the more energy it takes to warmup during the first 5 minutes (to reduce its emissions) and the bigger the warmup MPG penalty - so a bigger engine would probably need to be driven longer just to get to the rated EPA MPG levels.

 

This has not been confirmed by Michelin. I sent them an email and the response was that the tires were not being discontinued in that size. However, the people who answer those emails may not really know what's going on. If Toyota wanted a tire like the ESAS then Michelin would build it for them.

 

IRRC the prius battery only weighs about 100lbs. A lithium battery will be lighter and more powerful, but its not going to make a huge difference. Toyota does have its limh batteries in the prius+ for weight and smaller volume, but rumors have been they are sticking to nimh for at least for now. Lower rolling resistance tires are the biggest improvement for hyper miler at low speeds although weight reduction helps and a lighter battery is in that direction.

The rumor for the NS4 has been 2L, but we don't even know if that is being built. 2L is not significantly larger than 1.8, and I would not expect it to appreciably affect warm up. The bad thing about the article is it did not point to anything in the ice department. Toyota supposedly is getting 42% efficiency out of a di ice in the lab. That would allow them to get more power out of a smaller engine. DI stratified charge, along with early exhaust valve closing allows an engine to warm up quicker. They also will have had time to improve exhaust heat recover or use other techniques. One thing toyota said was they were having a little trouble combining DI and atkinson mode. I'm sure they have time to overcome that, but they could also do a port + direct injection atkinson engine as they have in the new scion 2L. A turbo DI small displacement engine (1.33L?) might be the most efficient and have quick warm up, but it would cost more and be more complicated.

 

What's killing my Prius' MPG right now in the summer is when I over shoot on the acceleration and either use too much gas (>=1.40 GPH) or if I overshoot on speed by 5mph to 10 mph too fast. It normally happens when I have to go uphill immediately from a dead stop at a traffic light that has just turn green where I am first in a long line of vehicles. I don't need to accelerate to 60 or even 40 mph in 8 seconds but I do need to get up to 25mph to 35 mph quickly. One hypermiling technique NICE is illegal in the DC area ( if Toyota could automate this - that would be great).

 

more possible ways of losing more extra weight:

1) replace interior plastic panels and carpets with a lighter weight carbon fiber panels padded with embedded water proof sound proofing matting.

2) replace 12VDC auxillary battery with a voltage regulator and start the Prius with the HV battery instead (25 pounds).

3) create/develop/invent Run-Flat Low Rolling Resistant tires and skip the spare tire (30 pounds).

 

How they gonna know if you're doing it?

 

I like number one, but first it won't shave much weight, and toyota is unlikely to use more expensive materials.

The reason for a 12VDC battery is so the HV battery can sleep. Getting rid of it would require a physical switch instead of smart key or discharge of the traction battery. Porsche allows the replacement of the 12V battery with a Lithium one, which holds its charge a long time. If the battery is only used for minimal duty this could be very small.

The trend is to simply drop a fix a flat kit. Run Flats add mass to the tires, which more than offsets the cost and fuel gains from getting rid of the spare. You really just want a no spare/fix a flat option.

What does NICE stand for and why is it illegal?

Easiest weight savings from current prius is lithium battery, carbon fiber roof, no spare simply fix a flat. That would allow less volume from the battery and spare so car could shrink slightly with interior volume. I don't think any of that will happen though. 200lbs lighter might improve city by 1mpg and less on the highway.

 

NICE is neutral coast, engine one

Its illegal in some locals to have the car free wheeling and moving. The lack of immediate engine braking is felt to be a safety hazard. There was a time (decades ago) when some did cars did automate this in order to save gas. Between the heavy car and no power brakes, the car could become unstoppable going downhill. So it was outlawed and remains on the books in some areas.

 

Early 90's Chevy Lumina with automatic trans had engine assisted coasting. I remember renting an automatic Lumina Z34. On the way to Vegas I let off the gas pedal. The car would coasts with barely decreasing speed. I shift to neutral and the RPM revved up for half a second then dropped down to idle speed. The vehicle speed decreased faster than with the car in gear and coasting.

 

Damn, the '90s would be decades ago now.
The feature I was thinking of was around the '50s.

I don't know if it could called engine assisted, but our 2001 Sable would coast about as well in drive as in neutral. The only difference is when the decelerating fuel cut off(DFCO) kicked in and engine braking came into play.

More aggressive DFCO is being used for increased economy. Without some type of valve modulation, like the Prius closing them with ICE off, the engine braking will reduce coasting.

 

I've been thinking of ditching the spare tire in my v5. If you do the research you will find a lot of cars come with no spare. With TPMS on every car, if you pump your tires up above what the manufactuer recommends, then the TPMS will give you a signal when your tires are still near "normal". Also, do a "back of the envelope" calculation of how often you think you will have a catastrophic tire failure AND be out of cell phone service. That probability is pretty low. Of course, when it happens you REALLY need that tire!

 

I've used fix-a-flat a couple of times, it works well if the tire is not shreaded. I did need a flat bed for my prius when two tires were destroyed by stuff in the road. I'm not sure if anyone has done the experiment, but I doubt you get close to 1 mpg better by pulling the spare. The reason they do it is to free up cargo volume. In the phv they do it for room for the battery.

 

For those of us who don't know, how do you define "frontal area" for aerodynamics?
Also, I got the impression from discussions a while ago that, because it is tall, the Prius is subject to greater resistance in side winds than, say, a Corolla. Am I right about that? If so, is there anything that can be done.

I still think the biggest change the Prius needs has nothing to do with economy--by far its worst feature is the terrible rear visibility.

 

What about the new Lithium batterys that Panasonic is supposed to be developeing that are just as good as the ones Envia are doing for GM. 125$/kwhr and 60% more energy. I won't replace my 2004 prius with Hymotion plug-in pack until the next Gen Batterys are out.