Theoretical Max MPG revisions question

[ChrisY]

I've been trying to figure out what modifications would be required to provide the max possible FE. My thoughts are below, for comment.

The goal would be to get the car to recycle its kinetic energy as close as possible to the theoretical max, presumably 95%. (I believe electric motors can be 95% efficient. I don't know if they can do that in regen mode.) That means if the car always recaptured 95% of it's kinetic energy, MPG could go well into the hundreds (at least at non-highway speeds).

I'm ignoring for the moment wind loss issues, and also cost and technology issues. Billions are being spent on hydrogen and fuel cells, which are much less efficient and are decades away. So why not focus on something that is dramatically more efficient and available much sooner? From what I read about global warming, we don't have decades.

Problems & Solutions:
1. Engine drag
This is a huge issue: run the engine only when essential. Allow it to shut down anytime the throttle is released by adding a sprag clutch between the engine and electric motor.

2. Maximize regen
a. Change the settings so regen kicks in any time the throttle is released. (MIMA style, perhaps)
b. Make friction braking unnecessary except for emergencies. Increase the power capacity of the regen system so it can slow the car much more forcefully. This presumably would require an energy control and storage system that could accept much higher current rates than batteries can. (Maybe capacitors in parallel with batteries? Maybe add a second regen system?)

Perhaps some sort of skunk works is possible to work on this?

[Insightful Trekker]

I think that the required brain surgery (yes you read that right ) for 90% of drivers out there will be the cost limiting factor.

Look at the MPG differences in attributable to driving style. Its the "loose nut" behind the wheel that needs torquing. And while you could "program" performance limits for maximum MPG there would be a serious safety issue since a little bit of scoot in some situations can make all the difference.

[ChrisY]

Originally Posted by Insightful Trekker

for 90% of drivers out there cost will be the limiting factor.

I've had trouble understanding how Honda developed the original Insight concept at anything close to what the car costs.

However, they did it, so it seems plausible that the incremental cost wouldn't be that bad to build one that hi-milers could push to well over 200 mpg! And ordinary mortals could count on for 100+...

[b1shmu63]

I've had trouble understanding how Honda developed the original Insight concept at anything close to what the car costs.

The answer is simple.....the research costs came from the profit on other models.

As for the profitability of the Insight, the words gift and write-off come to mind. The Insight will pay back but not in direct sales of Insights. Honda and Toyota have decided to put billions into research instead of advertising in the belief that the advancements will eventually create brand loyalty. Time seems to be vindicating their strategy.

[Insightful Trekker]

Ahh,

The old 100MPG and drive it anyway I'd care to concept. Well my old Honda CL100 motorcycle could _almost_ achieve that.

Just remember that there's is only so much energy in a gallon of gasoline. And there are _huge_ percentage losses in the conversion of energy forms. Physics and the physical properties of matter come into play here. Yes its "doable" with technology now available. And an Insight in comparison will drive and feel like a "luxury" car. But with the Insight's abysmal sales figures I doubt any auto manufacturer will mainstream anything like it soon.

[ChrisY]

Originally Posted by Insightful Trekker

... I doubt any auto manufacturer will mainstream anything like it soon...

Sorry-I wasn't expecting anything to come on the market like that.

I was thinking about building it. Or at least trying to figure out what it would take.

As for the physics, it seems to me that if regen efficiency could be made to approximate electric motor efficiency, you'd have something approximating a pendulum-a system that is constantly starting and stopping with only a little boost energy required.

[b1shmu63]

Chris, most of the losses are in the control electronics, not the batteries. We're talking really big chunks of silicon switching about 50,000 times a second. The other problem is engine drag, as you mentioned. A second clutch would help, but often when you have the brakes on a little engine drag saves wear on the brakes. Doubling the sise of the IMA motor, controll circuit and battery pack would cost more than any gasoline savings for the forseeable future. Would be nice though.

Question 2.a. is easily done with two parts. PM me.

[Dougie]

I think the best way to approach this is to look at the compromises the Honda engineers had to make in order to make this a daily-driver car. For example, they had to take into account snow and mud, so the clearance around the tires is much more than it should be. Similarly, the suspension has lots of travel, so the aerodynamics of the undertry aren't optimal. The tires could undoubtably be improved from the MPG viewpoint if you would accept a much harsher ride and less capability in the wet.

Take a look at the solar car crowd to see what's possible in the area of drag reduction.

[ChrisY]

A different way to look at this might be to think of today's electric tools that have electric brakes (chop saws, circular saws, drills). They use the motor as a brake, and can stop a high speed tool almost instantly. That's pretty powerful braking! Problem is, this energy is not stored for reuse, it is dumped as heat. But at least it proves the power of electric braking.

I would like to see the regen system in my Insight be that effecient, but store the energy for reuse rather than dump it. If that could be done, once it got going initially, the car could stop and start over and over many times. Then there'd be little if any need for friction brakes' dumping the kinetic energy as waste heat. And to keep the car going, only small amounts of energy would be required to keep the process going.

For the moment, this is primarily a concept exercise-a thought experiment-just to get the thinking straight. Then I would consider trying to build it.

[clett]

Hi Chris, the energy from braking really doesn't contribute that much to improved mpgs over most driving cycles. Only in very heavy, stop-start urban traffic will it make a big difference. Most of the energy goes into pushing the car through the air and overcoming rolling resistance - at highway speeds only a tiny proportion is used for acceleration (and hence lost during braking).

Nevertheless, improvements to regen could be made by installing a bigger motor. The Insight has a 10 kW motor, but braking from 60 to 50 in 2 seconds yields about 46 kW, so a 10 kW motor can only capture about 20% of the available braking energy. However even putting in a 50 kW motor to get more regen, the gains to real-world mpgs would still be small.

Assuming you won't touch the engine itself (where 75% of the energy in the gasoline is lost as heat and as such is by far the best place to make improvements), mpg gains are much easier had elsewhere, such as reducing weight further and improving aerodynamic coefficient.

Daihatsu did this with their UFE-II and got about 140 mpg US, with a CD of 0.19, in a 4 seater car.

http://www.daihatsu.com/motorshow/to...fe2/index.html

The UFE-III got CD of 0.168 and 170 mpg US.