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#90 of 139 Re: Driving on Battery Only ... Does this help mileage [midnightcowboy]
Sep 20, 2005 (9:14 pm)
First, you grossly misspelled my name.
Second, that reasoning is based on common assumptions... not how the system actually works.
There are far more efficiency savings opportunities in city type driving than there are when cruising on an open highway. The HSD system takes full advantage of them by preventing the inefficiencies that would normally occur, hence the MPG observation.
And where the heck did that "fully charged" claim come from? That isn't even close to correct. The Multi-Display very clearly shows 6 bars (68.57%) almost all of the time. I've personally only seen it up to 8 bars (80.00%) briefly 3 times over the past 40,600 miles. That's not full by any definition.
#91 of 139 Regenergative Braking
Oct 22, 2005 (12:11 pm)
Here's a newbie question for you:
How does regenerative braking actually work?
I've heard again and again that it converts kinetic energy, but I don't know by what means. Where on a hybrid vehicle is the actual mechanism that converts braking energy, and how does it do so?
#92 of 139 MG1 spins needlessly ??
Oct 23, 2005 (1:12 pm)
on post # 88 you stated the following
" One wonders why the little motor generator MG1 spins and spins needlessly converting ICE to electrical at the penalty of energy conversion loss when the traction battery is fully charged!
It is first necessary to to have a clear idea of what the Toyota HSD is. It is a power split device and takes the form of a planetary gearbox except that unlike conventional planetary gears where the the outer ring gear is fastened to the gearbox casing and is therefore stationary, in the HSD this gear is allowed to rotate (upto 6000rpm 100mph) and is connected to the drive wheels via a 5:1 ratio.
MG1 is connected to the central sun gear and though it may appear to be spinning needlessly to midcow and others, it is in fact splitting off some power which it must do (about which more later )
The engine is connected to the planetary carrier and of course provides the power which gets split. The three planet gears are distributed and held symmetrically around the carrier and make contact with the internal teeth of the ring gear. Clearly (I'm hoping it's clear!) if the sun gear was removed there would be nothing for these three gears to 'bite' on and the engine would be rotating easily while those three planet gears would be spun around by the internal teeth of the ring gear as they passed by. So almost no torque would be imparted to the ring gear and the car would sit still. If now the sun gear and MG1 assembly is mounted there would still be no torque if the sun gear with MG1 were allowed to start flying off in the opposite direction. At this point the engine cannot put any useful power into the system so there is no power to split and MG1 would - in midcow's words - spin needlessly.
But supposing the electronics to MG1 are turned on. And the electronics says "I am going to continue to allow MG1 to be pushed backwards at 6000rpm but I will not allow it to be pushed backwards at 6001rpm." Of course with a little more engine throttle you know this is bound to happen. But the electronics are probably measuring the shaft speed about 100 times/sec with great accuracy at this time and when this tries to happen will change the electrical conditions to make MG1 start to regenerate probably as much 22kw. This will have the effect of applying a restraining force of up to 20lb-ft on the sun gear. The planet gears will pass this force on from the sun gear to the ring gear which due to the 2.6 ratio between sun and ring will exert a torque of 50lb-ft. This example pertains close to full throttle. It shows how quickly torque can be generated and it attempts to explain the power splitting process and how a small torque at the sun gear can control a much larger torque from the HSD output. It should be mentioned that the engine is effectively supplying both these torques . At lower throttle openings the same strategy applies with MG1 always extracting power from the sun gear in order for the HSD output (the ring gear) to be able send power to the wheels.
So MG1 never spins needlessly.
BTW where does the generated power go?, it goes to the electronic inverter which powers MG2. MG2 is made to devour all the electrical energy brought in by MG1 unless the battery happens to need charging in which case it cuts back to allow the battery to absorb the excess. MG2 happens to be conveniently connected to the ring gear where it drives the wheels by the same 5:1 reduction as previously mentioned.
Why is MG2 twice as big as MG1 ? The answer is because during acceleration MG2 not only has to absorb all the power from MG1 but also absorb up to 20kw from the battery as well.
But what's the point of all this ? A very good question, I'm glad I asked !
The Prius is capable of a lot more things than has been mentioned here. To get through everything would take half a dozen posts at least. And some involve speculation because not many people play with synchronous motors and inverters. And, I might add, those that do utilise industrial servos do so without needing to understand the why. Getting two servos with the same inverter bus when either can be called on to motor or generate under a wide range of speeds particularly when mechanically coupled with a planetary gear and with the addition of a prime mover in the mix is something that needs a write up from the designers themselves. And this is what we are not getting.
The real point of a spinning MG1 is to form a CVT function. The so called Continuously Variable gear ratio Transmission. Toyota chooses to use an electro-mechanical implementation while Honda have chosen to use a wholly mechanical implementation as found in the 2006 HCH. I have to say that now that Honda have dispensed with the manual transmission option on the Civic hybrid it is to be hoped they can concentrate their resources to really nail this device and improve its reliability. Something that industrial CVTs were lacking when they were discarded years ago.
The reason for the CVT was originally for it to be an alternative to automatic three speed transmissions which were no more efficient than now particularly on subcompact cars. Today the reason is to allow a much smaller engine perform as if it were a larger engine when needed but to have that fuel consumption of the smaller engine most of the time.
When using a manual transmission, the power profile of a constant torque engine is triangular, power increases with rpm. The area under the curve represents the energy delivered over time.
The power profile of the output after an engine goes through a CVT, however is closely rectangular - at low revs the torque is much higher than in the previous case dropping slowly until at high revs the torque will become the same. The area under the CVT's rectangular profile will be almost double that area found under the manual transmission therefore the CVT will have delivered twice the energy in the same time.
This can be played two ways by doubling the road performance of an existing engine or accepting the same performance from a weaker engine.
The Toyota Prius and HCH obviously go for the latter and the fuel economy it brings. I would say that CVT's can provide fuel economy approaching double that of the manual transmission car and then that's it folks ! There will have to be another shift in thinking.
#93 of 139 Re: Driving on Battery Only ... Does this help mileage [john1701a]
Oct 23, 2005 (6:34 pm)
"Civic-Hybrid and the other IMA vehicles are hybrids with *PASSIVE* electrical systems. With them, the regenerative braking is the primary source of electricity"
Regen accounts for 5-10% recharge, the other 90% comes from the gasoline engine.
Either you don't know the IMA system or are just spreading misinformation about it.
Hybrid vehicles don't need more misinformation spread about than already is.
#94 of 139 Re: MG1 spins needlessly ?? [toyolla2]
Oct 24, 2005 (8:47 am)
Wow that was pretty interesting explanation but it still didn't explain why the MG1 keeps on providing a charge even when it is not needed. It you could put a centrifical electric operated cluth on MG1 then it would have to dump excess power when the MG2 didn't need it the PSP didn't need it and the battery was at it optimum charge ( 80% according to JOHN).
It seems to me that the wider the CVT range the better. With the palnetray CVT concept is is practical to be able to get a very low equivalaent first gear and a very high evivalent high gear. Typically a apread of 5-6 is considered very wide. This afford the best acceleration and the best no load mileage. However, with the torque of the electric motor the lwo end is already sufficient.
Actually you are really trying to simplify it too much to call the torque cure triangular and the power outpiut profile retangular.While it might approxiamte to that on an occiliscope it is actually closer to a standard bell curve and inverted "U" . Actually an ideal engine would always run at the most efficient output maxiumm torque , WOT. The with CVT you just adjust the effective gear ratio to the desires speed. But once you have charege the battery and are at the desired speed what do you do with the excess power. You could back off the engine speed but then you reduce the eficiency of the engine, which an ICE has low effciency to start with or you could pulse the engine, but there is a startup lag time.
I am sure you realize the torque curve of an electric brushless motor , It is almost maximu torque from 0 to approximately 1000 rpm after that is significantly falls off. The HSD system effectively extends this by mutiplying the efective rpm through gearing.
If you need more explanation please let me know, but you have pretty well written most of the information written in the Prius technical manual. Let me guess, you are an engineering student just getting ready to graduate. Good luck with your futre job search. Again thanks for your efforts to explain the Prius CVT system.
#95 of 139 Re: MG1 spins needlessly ?? [midnightcowboy]
Oct 24, 2005 (9:14 pm)
too bad you couldn't follow my explanation. I tried hard to put up the best post I could. I even used spell check, something that you could use also if you don't mind my saying.
Perhaps this is the bit that you, or the person reading for you, may have missed.
MG1 is always extracting power from the sun gear in order for the HSD output (the ring gear) to be able send power to the wheels.
So MG1 never spins needlessly.
BTW where does the generated power go?, it goes to the electronic inverter which powers MG2. MG2 is made to devour all the electrical energy brought in by MG1 unless the battery happens to need charging in which case it cuts back to allow the battery to absorb the excess. MG2 happens to be conveniently connected to the ring gear where it drives the wheels (through the 3.95 : 1 reduction)
Of course when the cruise speed is reached, accelerating torque will no longer be needed and power will drop considerably. MG1 must still act as a generator albeit at a much lower level in order to maintain control of the sun gear speed. Remember the car still needs torque transfer from the engine's planetary to the ring gear and it can only do that with an (dare I use this word with you midcow) "obstinate" sun gear. If a sun gear were to offer no resistance you may as well not have it there at that time. Now in that circumstance can you tell me where the torque would be coming from to continue to propel the vehicle. ?
BTW If you going to reply spare me the remarks that appeared in the last paragraph of your previous post please and thankyou.
#96 of 139 Re: MG1 spins needlessly ?? [midnightcowboy]
Oct 25, 2005 (11:47 pm)
Just because MG1 is spinning doesn't mean it's generating power.
By the way, this is NOT an electric brushless (DC) motor. It's a permanent-magnet, 3-phase AC motor. Same for MG2. IMA uses a brushless DC motor. Easier to wire but more complicated mechanically and electrically.
The rate of rotation of MG1 is controlled by the computer to deliver the ideal "effective gear ratio" for the ICE. Depending on conditions that could mean that MG1 is acting as a generator, acting as a motor, or being forced back-EMF to provide a braking effect against it's input shaft. When acting as a generator, the power from MG1 can go to either MG2, the battery, or both.
Oh, and internal combustion engines have their maximum POWER at or near redline, not their maximum TORQUE.
I would not dismiss John out of hand, he's probably more knowledgable about THS and HSD than most Toyota dealership staffs.
#97 of 139 Re: MG1 spins needlessly ?? [toyolla2]
Oct 27, 2005 (8:47 am)
You didn't like my spelling; sorry I didn't go back an spell check or reread! I am bad about that sometimes and yes I am a crummy typist and I don't always spell the words correctly. It is just that the spell check on Edmunds doesn't suggest the correct spelling and sometimes I am too lazy to look it up.
Let's see you didn't like my last paragraph but yet you said "...or the person reading for you." Actually, you don't know anything about my intelligence, experience or abilities or if I read it myself or had someone read it too me. My implication was that you gave a rather long drawn-out engineering oriented answer that really didn't answer the question. Maybe, it would have been appropriate in the "advanced engineering" thread. But assuming that I was a Newbie, it was out of place, too complicated of an answer, but interesting to me! That was the intent of my point, sorry if it offened you.
The MG1 spins all of the time. Sometimes it supplies the MG2 and sometime it supplies the battery when acting as a generator. And sometimes receives power form the battery and acts as a motor. It is debatable whether or not it spins needlessly. But let me explain further ....
When one form of energy is converted to another, there is always a loss of efficiency. No conversion is 100% efficient. I think it is a poor design to always spin the MG1. Why in the world would someone design something where the ICE power is converted into electrical power of the MG1 which is immediately converted into supply power for the MG2. Then the MG2 acts as a motor further converting power with additional energy loss. Why not use the power directly from the ICE? Double and triple conversion of energy is just not an efficient design.
Lets look at two designs the Honda Insight 5-speed and the Prius
The Insight doesn't needlessly spin a MG1 and double/triple convert nenrgy and it has an EPA rating of 60 City and 66 highway. The Prius always spins the MG1 ( it is up in the air whether it is needless or not) and it has an EPA rating of 60 City and 51 highway.
In my higher math, before calculus of several variables, I thought that 66 was greater than 51. Why is the highway mileage of the Prius less than the City mileage while the Insight is higher ?
Okay, some would save the HSD full hybrid uses electric power to gain City efficincy and higher City EPA. Perhaps a ICE only Prius would have mileage in the range 35/48 with a gain of 25 mpg City and 3 mpg Highway because of HSD. Man that sounds like a whole lot of regenerative braking to get that +25 City. I just don't by it.
True is could be the CD. However the Prius has a low CD of 0.29 which isn't htat much higher than the Insight's 0.25. There there is the weight difference, but then we digress ...
Back to my hypothesis: The Prius has lower highway mileage than city becuase the MG1 spins needlessly and wastes energy by double/triple converting enegy and/or charging fully charged batteries.
P.S. Oh by the way you notice I did not mention anything derrogatory about you driving an Echo
P.S.S. - I was a member of Eta Kappa Nu and Sigma Tau. Then later with my MBA, Beta Gamma Sigma. But, hey who's counting.
#98 of 139 Re: MG1 spins needlessly ?? [midnightcowboy]
Oct 27, 2005 (11:05 am)
Did you know that Einstein was not a good speller. If someone doesn't spell right it is RUDE to point it out to them. Hope your feelings weren't too hurt.
Oct 27, 2005 (11:52 am)
Let's drop the personal comments and stick to the topics please.