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Discussion Starter #1
Curious - shouldn't a low displacement engine be able to rev much higher?

Am I correct in assuming our revs are limited due to eco-factors, because the engine isn't making power beyond 6k RPM? Or are there other limiting factors, such as the IMA motor doesn't like to spin faster or...? :confused:

Another thought... would there be oil starvation of some type at higher RPMs maybe? We only take 2.x quarts of oil where my 599 motorcycle takes 4 (with 60% of the Insight's displacement). Also note, it uses the same oil filter! ;)

Just curious, hopefully someone has some insight on this.
 

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My guess: it's an inline triple (inherently unbalanced) with no balance shaft. Balancing comes from applying assist and regen alternately during engine rotation. Perhaps beyond a certain point this is unable to balance the engine???

I rarely go to redline anyway so it's not a problem.
 

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Curious - shouldn't a low displacement engine be able to rev much higher?
Easy question, Complex answer.

More than just "eco" factors, the overall design of the engine comes into play, although eco factors prefer low revving engines. In the Insight the short piston skirts and the low friction rings are one of the major concerns. There is a significant durability issue with these parts. Higher RPMs always means more heat: Friction & greater amounts of fuel burning in the system. At some point no matter what the choice(s) of materials, lubricants, cooling systems, much more wear.

Another major design factor applicable to any engines redline is the camshaft design paramaters; lift, duration, timing, and overlap of the exhaust / intake stroke. These all combine to set an engines horsepower and torque characteristics. The engine will either be more "powerful" at low engine RPM's and run out of breath at higher RPM's, or develop more power which requires higher RPM's. Unless your a VTEC and "switch" cam profiles on the fly, then you can blend 2 different engine horsepower & torque curves. ;)

In all piston internal combustion engines the ultimate limiting factor is the maximum linear velocity of the pistons. At some point, no matter what, pistons will begin to weld themselves to the cylinder walls due to friction. Shorter stroke engines can rev higher than longer stroke engines all other things being equal.

HTH! :)
 

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... Longer stroke engines can rev higher than shorter stroke engines all other things being equal...HTH! :)
I think you meant that the other way around...

Formula 1 engines have incredibly short strokes to allow the 19,000 rpm's they typically run to.

The short stroke in addition to the high revs, means that the piston velocity in feet/second is still very high.

The old Norton 750 on the other hand, had a relatively long stroke and only revved to about 8000 rpm or so, if I recall correctly. Longer stroke combined with lower rpm's still means high piston velocity.

___________________________________________________

Just an aside note: the highest I have spin the Insight is about 3500 rpm's. That's it. Have had no reason to run higher for my driving style and route to work.

Jim.
 

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Discussion Starter #6
In this case, would these limiting factors cause the engine to be immediately damaged if it were (for some reason) accidentally downshifted into too low of a gear? It doesn't seem to be the case if it were to somehow hit 8,000RPM for a second.

Whereas in the S2000, for instance, it'll blow up in a heartbeat if you accidentally drop it into second at too high of a speed.
 

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In this case, would these limiting factors cause the engine to be immediately damaged if it were (for some reason) accidentally downshifted into too low of a gear? It doesn't seem to be the case if it were to somehow hit 8,000RPM for a second.

Whereas in the S2000, for instance, it'll blow up in a heartbeat if you accidentally drop it into second at too high of a speed.
I bet it would grenade in a second. With a redline of 6000rpm, there's no sense in having a valvetrain that would endure higher speeds. And what happens when you spin the IMA rotor that fast?

Which makes me wonder... what's the redline of the 2010 CRZ?
 

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In this case, would these limiting factors cause the engine to be immediately damaged if it were (for some reason) accidentally downshifted into too low of a gear?
In the case of an Insight (and most other cars) the weak link in the chain is probably in the valve train. Specifically the strength of the valve springs. High RPM engines _require_ stronger springs to snap the valves closed quickly, proportionally to how fast their popped open. As you might guess stronger springs are a significant wear factor (overall higher loads on all the related parts). For most engines the "weakest" spring needed is chosen.

So guess what happens at high RPM's if you haven't snapped a valve sufficiently closed quickly enough?

HTH! :)
 

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Discussion Starter #9 (Edited)
Good thinking on the weaker springs. That's probably the case. The weaker they are the less resistance. I wish I knew what RPM would give valve float. I misshifted the first day I had my Insight, so a very brief stint won't kill it, that I know.

And what happens when you spin the IMA rotor that fast?

Which makes me wonder... what's the redline of the 2010 CRZ?
Dumb question, but can't the motor rev without the rotor - as in, are they completely linked? I assumed they were on some kind of a clutch system, probably magnetic like most A/C compressors, and other belt-driven devices that can be turned off.



...but it looks like the CR-Z only redlines at 6200, so maybe the IMA motor is the limiting factor?
 

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Dumb question, but can't the motor rev without the rotor - as in, are they completely linked? I assumed they were on some kind of a clutch system, probably magnetic like most A/C compressors, and other belt-driven devices that can be turned off.
See InsightCentral.net - Encyclopedia - Honda Insight IMA Motor

"The IMA motor is located between the internal combustion engine (ICE) and clutch. One end of the IMA motor rotor is bolted to the ICE crankshaft, and the other end of the rotor is bolted to the flywheel."
 

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Maybe I'm missing something?

What possible reason / benefit would there be to go to higher RPMs?

1st gear doesn't reach ~6,000 RPMs until about ~34 MPH
2nd gear doesn't reach ~6,000 RPMs until about ~71 MPH
3rd gear doesn't reach ~6,000 RPMs until about ~112 MPH
4th gear doesn't reach ~6,000 RPMs until about ~143 MPH
5th gear doesn't reach ~6,000 RPMs until about ~173 MPH

http://www.insightcentral.net/_images/ratios.jpg

You'd hit the speed governor before even reaching red line in 3rd gear.
 

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Discussion Starter #12
It's not that I want to rev higher (because it wouldn't be making any power up there), but rather, I was just puzzled as to why it was limited so low when my 2.2L S2000 can rev past 8K, and my old Integra could rev to 7k. Usually 6k redlines are for beastly V6s.
 

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red1dr, That only captures half of the description. The two halves of the rotor are permanently connected(unless physically unbolted) and move at the same speed as the engine, always. The stator with the magnets do not move and is attached permanently to the engine block. It's a brushless DC motor that has quite a lot of power for it's size.

So we have no magic way of disconnecting the engine and running just one, it's why when retepsnikrep runs his PHEV vehicles, especially the 40Ah one, he runs it with just enough throttle to prevent the engine from leaving him dragging the compression behind. From that point, he adds more throttle during warm up, as appropriate for acceleration, hill climbing when needed, and to meter out the electric power to last the duration of the trip.

EDIT: The redline wouldn't have anything to do with the IMA, it's a small rotor so edge speed would be no issue and if the motor couldn't provide power, it simply wouldn't do it and would shut off if that was the case. Peak power on the IMA is at 3,000RPM I believe. If I hit 20 bars and want to burn off a little power under acceleration to be able to regen the next time I slow down, I'll shift between 2500 and 3000rpm depending on which gear I'm in before shifting if I feel like putting the hammer down on the throttle.
 

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Discussion Starter #14
Here's one thing I don't understand: Don't electric motors make power everywhere? Or is that a completely different beast?

And on that note, does the Prius electric motor have the same type of torque curve, or is it more like a normal electric motor - because it's outside of the main motor, right?
 

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Don't electric motors make power everywhere?
Yes, but their maximum torque occurs at 0 rpm and decreases with speed. This makes an electric motor a good match for an internal combustion engine whose torque is 0 at 0 rpm and increases with speed up to its torque peak.

And on that note, does the Prius electric motor have the same type of torque curve, or is it more like a normal electric motor - because it's outside of the main motor, right?
I assume that the two Prius electric motors have torque curves similar to the IMA motor, all of which behave like "normal" electric motors. The Prius electric motors are in the planetary gear transaxle, not attached directly to the internal combustion engine crankshaft. The Prius design is very clever in that it eliminates all friction components (e.g., clutch, CVT belt) and a conventional mechanical transmission, and allows the larger electric motor to propel the car for short distances and low speeds with no help from the internal combustion engine. There must be a lot of energy conversion loss in the Prius system with its two motor/generators continuously converting electrical to mechanical energy and back, but these energy losses must be offset by the ability of the computer control systems to keep the internal combustion engine operating in very efficient modes.
 

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No, they don't make power everywhere, at least not all motors unless they have enough voltage for it. The Insight seems able to produce power everywhere but has its peak power point where the amount it provides will drop off. They make their max torque based on the maximum amperage that is pushed through them. In the case of the I1 it is 100 amps which I think is the limit to the motor. If it's the limit from the battery then it's even more torque, especially from starting but this typically isn't the case, but for the sake of the battery, maybe it is limited on battery current and more capable than 100 amps, as far as I know, it isn't. If I had MIMA I'd know that for sure as I'd know which wire the hall sensor is on, someone will chime in quickly, I'm sure.

So motor 100 amps would provide it's peak torque rating. Then as voltage rises to the motor as the motor spins faster, there is more power produced because volts and amps is watts. Wattage is power. From the specs I've come across, this peaks out at 3000rpm for maximum power. Once you get past a certain point, the motor can't produce more power since the voltage is limited by the source voltage, the batteries, due to the motor producing a generator effect because it's a hunk of magnetic energy spinning which cancels out the power so more amperage can't flow as the "motors voltage" is now higher. It's a bit more complicated with these brushless DC and AC motors that car manufacturers are using since their current is varied and fed in through 3 phase wires and pulsed based on the position of the motor, being able to time those pulses adds efficiency, removes the maintenance requirement of swapping brushes every 50k-100k miles or so, which isn't really that hard but it's still work that could be avoided.

There are other advantages, if something shorts out in the system and the power goes full on to the motor, the car doesn't take off like an uncontrollable rocket or grenade the motor from overspeed. Instead it locks up the phase which turns the motor into a giant brake, at least until it gets demagnetized. There is only so much amperage you can put through the motor before the magnetic force developed is powerful enough to demagnetize the magnets and render your motor useless, so depending on how much power gets shoved through, the braking affect might end quickly and there might be some smoke from the wires getting way too much power. If you are really lucky, the 100 amp fuse will blow fast enough to stop everything and save things but demagnetization doesn't take much time at all. This is where people start to see the benefits of AC motors, no magnets. Brushless DC motors can be noisy as you can hear their pulses, they aren't a sine wave like AC motors and motors are basically speakers in many respects and depending on how you toss those pulses in and how much variation and how quick you make them, they can be noisy. The Insight is quite quiet, nothing that anyone would likely ever complain about. The E-Bike and RC community uses some terribly loud motors since they are pumping tons of amperage through those motors and running them on the ragged edge of their limits. If I made an electric car I'd go with AC or brushless DC if it could be had for cheap enough, but will probably go with brushed DC since the power vs price is extremely attractive. I've got the plans laid out in my head of how I would convert my Insight to an electric car but instead have decided that PHEV is a far cheaper way to go both in the short term and the long term and is what I plan to go with as it doesn't involve extensive modifications involving lots of time and money, not to mention the increased cost of adding loads of batteries, adding more weight than I would otherwise need, and dealing with losing the limited cargo space I already have as the trunk area available isn't quite enough for the range I want without cutting into the space above the deck of the trunk.

...I went on for awhile on motor theory, I hope I answered your question somewhere in there and provided a little extra info.
 

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So we have no magic way of disconnecting the engine and running just one,
Maybe not magic ... but ... there are times when I toy with ideas ... You know for that imaginary time when I have nothing better to do with my time or money. ;) ... I especially like,

A Practical Hybrid 6 page paper ( MS Word ) which outlines a simulation of using a 2nd clutch between the IMA motor and the ICE... it's one of the files I put a link to , toward the bottom of the:

http://www.insightcentral.net/forums/modifications-technical-issues/15146-honda-insight-gen-i-resource-library.html
 

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Curious - shouldn't a low displacement engine be able to rev much higher?

Am I correct in assuming our revs are limited due to eco-factors, because the engine isn't making power beyond 6k RPM? Or are there other limiting factors, such as the IMA motor doesn't like to spin faster or...? :confused:

Another thought... would there be oil starvation of some type at higher RPMs maybe? We only take 2.x quarts of oil where my 599 motorcycle takes 4 (with 60% of the Insight's displacement). Also note, it uses the same oil filter! ;)

Just curious, hopefully someone has some insight on this.


RPM limit is set usually by the rpm that is less than 2500 feet per minute piston travel. using better materials can raise that of course but it usually means shorter times between rebuilds. The Insight stroke is 81 mm, or 3.18". tHAT MEANS EVERY crankshaft revolution THE PISTON TRAVELS 0.53 FT. aT 5000 RPM THATS 2657 FEET PER MINUTE. Thats fast enough for a long life engine with low internal friction. The bearing loadson something accelerating that fast is horredous (zero to 1.6" in less than 3 thousands of a second; whats that 44,444 feet per second per second. pore old earth gravity accelerates at only 32.4 fps2.)
F1 engines routinely exceed 8000 fpm (19,000 rpm) but then of course don't last very long between rebuilds either. NASCAR exceeds 4000 fpm but thenthey are rebuit virtually between races of 400 - 600 miles.. Neither engines are inexpensive either.
PS go back a decade or two and see how many domestic engines had redlines over 4800 rpm.
 

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There is a lot of good technical info here, but I never considered 6000 rpm that low of a redline.

Most engines (until recently) were redlined in that range. Performance cars have recently seen higher rev limits with technology. BMW's, for example, rev into the 8000 range, where the higher revs produce more power, but consume copious amounts of fuel.

The s2000 was a little unique, a smalll displacement motor with a high redline, but it was designed to be a sports (sporty?) car. Good power, but only at high revs and very low torque, hence the need to spin the motor to get any acceleration. Not bad for a race car always in the high rpm band, but not so good on a street car going from traffic light to traffic light. Even the later generations traded some rpm at redline for better mid range torque. Redline went from something like 9000 to about 8600.

In an economy car(after all, the insight may look like a sports/sporty car and feel like one from behind the wheel at 6/10 driving) high revs really don't make sense. Revs eat fuel, so it wouldn't make a lot of sense to have an ecomomy car with a "high" redline anyway.

If you are maximizing mpg, how often do you even go over 2500? And if you are in a hurry, the insight scoots along ok if you wind it out to 5500 or so.

Regards,
Jerry
 

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I know this is necro posting, but I thought it would be good to mention that in the post where people mentioned things that would make the ECA1 not rev well is actually the opposite. The Insight motor actually has good things going for it to rev higher. I'm not saying that it can or should, just that things like shorter piston skirts, light weight connecting rods, etc are good for higher revving. That's because the engineers were trying to reduce friction, like in F1 engines they have really really short piston skirts to reduce friction and piston weight to rev higher.

The ECA1 also employs the offset crank to reduce side loading of the piston which is commonly used on motorcycles to help improve top end power.

Additionally a 3 cylinder layout is actually great for higher rpms since it's got great primary and secondary balance characteristics due to its 120 degree crank, it's just at low rpms it wants to rock back and forth due to the layout being unbalanced from end to end. This is why inline 6 motors are extremely smooth because it can eliminate the rocking since it's basically two inline 3 motors mirrored to cancel out the rocking from end to end. 4 cylinders actually have more secondary vibrations that's why a lot of them have balance shafts. They just don't have the rocking motion because nearly all inline 4s use a flat-plane crank which makes it like you have mirrored parallel twins joined together.

And a fun tid bit is that some of the valve train components are shared with the D-series motors and because of that a person could purchase some lighter valve train components like the valve spring retainers.

Rod ratio is another determining factor. That is the connecting rod length in relation to the piston stroke. For reference the S2000 it has a connecting rod length to stroke ratio of something in the order of 1.8, which makes it much more ideal to rev easier. K20 is around 1.6. I think most commuter engines are around 1.5.
 
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