[b1shmu63]

Actually John a lean burn engine can produce as much power as the same engine throttled back in normal mode. If to maintain a constant speed you only need only 7 HP (for example) the engine will put out exactly the same amount of power in lean burn or out of lean burn as long as your speed is constant. Yes, an engine running lean burn will always put out less maximum HP. The Insight cycles rich burn to clear the Nox storage cat. When it cycles rich the car will accellerate then decellerate as it cycles back to lean burn. You can see this cyclical action on the IMPG gauge, and that is one indication you are in lean burn.

Others here may take issue with some of the other statements you have made, for example, studies have found that engines running a small percentage of alcohol can get better mileage despite its lower energy content. Nevertheless this off topic discussion will have to end here otherwise the topic will have to be split, heavily moderated, or locked. We are trying to determine the amount of power required to maintain a given constant speed.

 

[retepsnikrep]

OK, a lively discussion but why did I pose the question "How much power to maintain speed?" :shock:

Answer. I've been looking at a rear wheel motor idea for a pure EV drive for low cruising speed. 8)

Now I know a few people have looked at this, and Mike has his third rear wheel idea.

I recently built a Savonius wind turbine using a direct drive washing machine motor.

http://www.thebackshed.com/Windmill/FOR ... D=889&PN=3

I bought them from scrap machines.

Why not use them as they were designed, an effcient low rpm high torque 3phase motor. They are about 1.5kw each and one on each rear wheel may give enough power to maintain low speed in a pure electric mode in good conditions. Engine in neutral and even FAS so minimal transmission losses. I offered one up to an insight wheel on my bench and low and behold it's a pretty good fit. Yes the motor rotor diameter is about 20mm smaller than the inside of an insight alloy wheel but I think that can be got round. The stator coils could fairly easily be attached to the rear drum back plate assembly.

To match the insight wheel inner diameter and reduce it 20 mm a nylon magnet holder could be machined and even neodynium magnets fitted to it and then it could be bonded in place inside the wheel hub. We could have some neodynium magnets made up with the profile reqd to fit the Insight wheel and the stator, they could just be bonded directly to the inside of the alloy wheel like a balancing weight. We could leave the rotor as it is but remove/machine the inside of it and attach it to a flat place which fits onto the wheel studs. a 2mm plate sandwiched between the brake hub and wheel on the wheel studs would make very little difference to the Insight setup IMO.

I'm away on hols for a couple of weeks now but just thought I would throw this into the pot. A few pics now to give you an idea of what i'm talking about.

You can see here rotor magnets are about 10-20mm away from inside of Insight wheel.

Yes it would add a couple of Kg to the unsprung weight but no big deal IMO.

Regards Peter

PS I havent even thought about the motor power control issues yet

 

[IamIan]

So I think from what I've seen we have generally 3 answers.

Mathematics of rolling resistance + Aerodynamics +Gravity gives about 1 to 2 HP.

ScanGuage gives about 5 to 6 HP.

Test driving and the "Feel" of horsepower says under 15 HP.

So I think we can all agree it is under 15 HP...
A compromise would seem to be around 2 to 4 HP.

The exact number will require a very controlled experiment... one that can not be done easily... any outdoor test is immediately ruled out as being controlled... and very few roads are flat and level enough to have a consistent incline to be able to measure the incline to a small margin of error.

In short I doubt we will have an exact answer short of a massively expensive controlled experiment... but we still know the answer is around 2 to 4 HP.

just my 2 bits.

 

[clett]

If we're thinking about recycling what we already have, an alternative approach could be to simply use an old 2 kW hand held battery powertool. It would be placed so that a small cog would fit inside the Insight rim which would have rack-like teeth welded to its circumference on the inside. You'd need high rpms at the cog, so probably some gearing up required, and possibly also a bendy flexible shaft to transmit the power from the drill to the cog, but it would also be a low cost, low weight solution. One on each side and you could have up to 4 kW.

I'd been thinking about this approach for a while in a different way, as in order to PHEV retrofit a vehicle it would be quite simple to bolt a motor onto the crank bottom pulley and pump in some power in a "blended power" mode. I realised that the easiest (although not the cheapest!) way to get the long cycle life / high power / safe lithium-iron-phosphate batteries from A123 would be to buy several of the 36 Volt DeWalt drills and batteries. This would give me not only several kWh of batteries, but also some small, high power motors to play with. 20 kg of DeWalt batteries holds 2 kWh, so at 50% blended power input it should be able to give double mpgs for the first 16 miles of any trip (using 80% DOD). Expensive though at £2,500 per kWh when buying packs this way! Lead acid to 36V would probably be much cheaper and in combination with a secondhand drill cheaper still.

Here is a link to some charts in a previous discussion of rolling and aerodynamic power requirements to push the Insight along. They suggest about 2 kW for 30 mph at ambient temperature.

 

[james]

"So, how many people think a V8 with 4 cyl fueled is "just as powerful" as the full V8?
Don't tell me it's not the same. It is mechanically different, but SAME IN FUNCTION and end result."

At the risk of irritating the moderators, I'll point out that you're confusing an engine's maximum power output with the power needed to maintain a constant speed. Now we have a figure for how much power it takes to move the Insight on a level road at constant speed, which is the power needed to overcome wind resistance and rolling friction. Say that figure is 15 horsepower at 65 mph. It's going to take that same 15 hp regardless of engine type or its operating mode. Convert it to pure electric: it will take 15 hp. (Assuming of course that we have magic batteries to keep the total weight the same ) Replace the engine with your V8, it will still take 15 hp. Drop in a 1000 hp gas turbine, and it will still take only 15. Take the engine out and convert it to a Soapbox Derby racer. If it reaches a terminal velocity of 65 mph, then you'll find the slope is such that you're using 15 hp of gravitational potential energy.

 

[Mike Dabrowski 2000]

Peter,
The windmill looks nice, and what a nice clean shop you have. My shop was like that for a month after I built it, now I have to move stuff to find a space to work on the benches :?
No question that you would be able to push the insight with two of those motors. May not have the torque to do much hill climbing though.
Clett,
In principal the drill motor could push the car, but from my experience the small sintered gears in the drills planetary reducer would not make it more than a few miles before wearing out.

 

[gpsman1]

OK, a lively discussion but why did I pose the question "How much power to maintain speed?" :shock:
Answer. I've been looking at a rear wheel motor idea for a pure EV drive for low cruising speed. 8)

Well that's what I figured all along which is why I tried to give you "real world" numbers with all the losses included!


The ScanGuage, while some believe reads high, included those losses. If it tells me 6 HP at 30 MPH, and reads even 20% high... ( doubt it's that far off, but lets assume it is ) that means you are really going to need 5 HP in all likelyhood.

Good luck with your projects, they sound like fun to me!
-John

 

[IamIan]

Good luck with the e-wheel motor... that is no small undertaking.

 

[Dougie]

Lean burn is not unlike cylinder deactivation... you know... those large cars/trucks with a V8 that can run on 4 when cruising. That is, in a way, the same as lean burn.

In those V8, you feed air/fuel to 4 cylinders, and just air to 4.
Thus, really, taken each full Revolution at a time, you have just changed the A/F ratio to 28:1.

That's not actually how cylinder deactivation works. What you do is close both the intake and exhaust valves, and stop injecting fuel. So the calculated A/F ratio isn't any different from regular operation...

 

[Mike Dabrowski 2000]

I ran across this Prius site with some interesting calculations of the effects of wind, rain, and areo drag that may relate to this question.
http://privatenrg.com/#Bill_Moores

 

[b1shmu63]

Thanks Mike. That is a very interesting site with a lot of really usefull information.

 

[james]

Very interesting site. I really want the rear-wheel steering: from flying small planes, I'm quite familiar with the way ground track & relative wind relate, and how much extra drag you can create with a bit of "slip".

 

[mrbill]

IamIan,
Impressive physics with a slight math-o.
From your post:
=====================
= ~ 1.3245 kW
1kW = ~1.34 HP

So it takes a minimum of ~0.9884 HP ( just about 1 HP )
==========================================
It would be hp= 1.34 times 1.3245, not divided by.
Or abou 1.7 hp.

thanks for the in depth answer.

 

[3-Wheeler]

MrBill,

Thanks for digging this up from the archives...

I have been doing coast down testing with the Insight for some time now, and Ian's calculations are a good check next to mine.

Thanks, Jim.