[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. :!: :shock:

 

[ChrisY]

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]

... 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/tokyo03/ufe2/index.html

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

 

[Infidel]

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.

Hmm... I don't think you're right here.... IIRC, the eletronics on the insight draw around 5A or so on the 12V system, the DC-DC converter is supposed to be drawing directly from the IMA motor, and is supposed to be over 90% efficient. Also, you're only looking at 1-way conversion losses to get from the motor to powering the electronics. I'd call this insignificant.

Even if the DC-DC were always pulling out of the batteries, at 60% efficiency, you're only talking about storing charge at less than an Amp @ 144V.

Looking at it another way, the electronics only burn around 60 Watts or so, and 750W == 1hp at 100% efficiency. No matter what efficiency figure you want to use for a "back of the envelope" calculation, you're talking about an order of magnitude less than anything that is significant.

 

[ChrisY]

That's about what I was thinking.

My goal in this is simply to address the fact that in my car, a huge amount of energy loss seems to come from changes in velocity. These changes are subtle, but happen almost constantly-rarely am I able to keep my foot locked steady on the gas pedal. There's always either a turn in the road, a hill, an approaching car, or whatever.

This means energy is constantly being bled off by the engine, which sucks it up because of compression whenever I let up on the gas even a little bit without stepping on the clutch. And if I do step on the clutch, I often overrun whomever I'm following because the car rolls so effortlessly. This forces me to let the clutch back out or use the brakes, both of which dump relatively huge quantities of energy compared to what's recaptured by the regen.

Taking this to it's extreme, around town driving would be almost the same as constant driving at the average speed, with the engine off line much of the time. My experience and calculations say this could be very high indeed if it were done right.

 

[Insightful Trekker]

ChrisY,

Reads to me like your describing driving technique. Now you know what the limits of traffic and terrain can do to the Insight's hyper MPG potential.

Not as much improvement is available through improving regen efficiency. And it fact the _best_ MPG has been proven to be achieved in Honda hybrids with techniques that virtually eliminate IMA usage.

Your "if you could" statements don't allow for thenlimits of physics.

 

[b1shmu63]

No folks, I wasn't talking about 1 amp at 12 volts, I was talking about 50 amps at roughly 170 volts. That regenerating power is handled by solid state junctions. About 100 amps at roughly 144 volts is handled by another set of junctions on its way back to the motor. Now that's what I'm talking about.

For technical reasons beyond what most folk here would probably want explained, the efficiency of ferrite transformers and silicon junctions decreases as the ratio of on to off times of a switching converter increases. For this reason the varying voltage on a charge storing capacitor requires a less efficient control scheme than a relatively constant voltage of a battery. Thus most of the assumed gains from using capacitors is eaten up by the silicon and ferrite in the control circuitry.

Sorry to be the bearer of bad news. As a power conversion designer I struggled against the laws of physics for years and from time to time won a small battle.

 

[ChrisY]

Oh well-looks like I may have to leave such dreams to the research labs.

It's just that the urge to tinker was upon me, and I thought I saw a possible opportunity...

 

[clett]

If you're looking to tinker for max mpgs, the best thing to do (other than altering your driving style) is to increase the tyre pressures. Maybe 45 psi to start, should see a noticeable improvement.

In terms of other easy tinkerings, perhaps you could try to reduce the weight further? Or improve the aerodynamics? Nobody has tried the project described in this previous thread, as far as I can tell.

If you want greater than 150 mpg though, best to talk to Mike Dabrowski!

 

[b1shmu63]

I have tried a larger aero cover under the engine and I'm working on an improved model. Preliminary tests seem to indicate that it works, especially at achieving better lean burn at higher speeds. I have no quantitative results to share and I'm sure there is room for further improvement, so I have not announced results here. This is a good fall project for me, with accurate road tests next summer.

 

[Mike Dabrowski 2000]

Kip is correct about losses in the conversion electronics, but we are forgetting the batteries them self have serious losses when charging, and at higher rates that loss is greater in both the controller and batteries.
ChrisY
Your urge to tinker can be easily satisfied if you drop down to CT and lend a hand with some of the things I am tinkering with.
8)

 

[ChrisY]

ChrisY
Your urge to tinker can be easily satisfied if you drop down to CT and lend a hand with some of the things I am tinkering with...

Mike- Be careful what you wish for! :shock: :roll:
I'm on the way...

 

[Mike Dabrowski 2000]

Thats good, better wait till next week when I am back from Up Your Volts 2, where I will make a point to snap some photos of the IMA/clutch assembly.
I would welcome some help.