wondering how the Prius ECVT works?

Heuristic mode might be a good name for it (Of or relating to a usually speculative formulation serving as a guide in the investigation or solution of a problem).

Personally, I can see MG1 being supplied with a counter force (reversed voltage polarities on the stator) that would put a stopping force on the sun gear that would, in turn, force ALL of the internal combustion engine's shaft rotation power to be transferred via the planet carrier and planets to only the ring gear during 'ICE only' drive mode.

But during deceleration or coast mode I can see (heuristically) MG1 in 'help charge the battery mode' resulting in both ring gear rotation (turning due to the car's momentum), and the engine's power (if the engine's running), going primarily to the sun gear (because the sun gear becomes the path of least resistance - a very light load compared to the ring gear).

Sorry, but this old retired engineer has a real problem with virtually all of the Prius ECVT writeups found so far. They seem to have been accepted as gospel (most are several years old) but it also seems that no one has actually tried to follow them, detail by detail, and have them work out based on the laws of common physics. In reading them, you might note that whenever the logic of their explanation get's tough, they introduce the words microprocessor, microcontroller, computer, or ECU into the explanation as if these gadgets were capable of doing some kind of magic beyond the scope of their capabilities).

 

Still confused

I've seen many descriptions of how the power is split between the ICE and electrical motors, but I think they're all leaving one step out. If the electric motor is starting the car with the engine off, what forces the power to go to the wheels rather than spinning the engine backwards? Is there some braking mechanism on the ICE? Similarly, what about when the ICE is supplying power and the motors are not? Does the system use electrical power to force the motor to stay in one place, fighting against the ICE? Would they really waste power like that?

 

Re: Still confused

It takes little power to do that: energy is the integral of force times distance, and if the distance is zero (that is, if the object doesn't move) then the energy is zero. Similarly, your desk uses very little power while suspending your computer monitor above the floor :_> It's not really zero in a Prius or in your muscles because those mechanisms use power to dynamically create force (moving magnetic fields, moving myosin heads, respectively), not statically like the desk does it.

 

Re: Still confused

Remember, when power is supplied to motor/generator (MG2) stator windings, that MG acts as a motor that drives, or helps drive the car.

When the ICE is driving the car and when MG2 is NOT driving or helping to drive the car, the rotor on MG2 turns at the speed that the ICE powered ring gear is spinning, and, because no power is supplied during that time to MG2's stator windings, MG2's rotor spins freely with virtually no resistance to the ICE.

Remember too that the ICE is also driving the smaller MG1's rotor (when MG1 is acting as a generator) supplying power from its stator windings to either help power MG2 or to charge the battery.

Keep in mind too that when the ICE is off and the computer want's to turn it on, the computer tells the battery to supply power via the inverter to MG1's stators causing it to be a motor. Now the rotor on MG1 is already spinning (mechanical transfer of spin from the final drive connected ring gear via the planetary gears to the sun gear which is tied to the rotor of MG2). The power from the battery (via the inverter) simply causes that rotor to spin even faster. Then .. the difference in the speed of the fast spinniing sun gear and the slower turning ring gear has to go somewhere - so the planet carrier starts spinning to make up the difference. The planet carrier being tied directly to the ICE's drive shaft get's that shaft turning, starting the ICE (the internal combustion engine).

Once the ICE is started, the computer takes power off MG1's stators and MG1 is reverted back to being a generator.

 

htmlspinnr, It sounds like you're pretty well convinced that it makes sense that the sun gear should be stopped or rotated in the direction it doesn't normally rotate in order to start the engine.

I presume you visualize the planetary gear set as a ring gear linking with planet gears linking with the sun gear. And if the rotation speed of the sun gear doesn't match its ratio equivelent speed of the ring gear, the planet carrier must be spinning.

I also presume you see the momentum of the drive on the ring gear as the force that starts the engine, relying on the sun gear being forced electrically to slow or reverse in order to assure sufficient rotation speed difference between sun and ring spin speeds in order to make the planet carrier spin at a rate sufficient to start the engine.

That could work, just as speeding up the sun gear would work to meet the same end. Your input doesn't match with the research I've done but, then again, as I've mentioned in earlier postings, I haven't found a paper on the subject yet that suggested full understanding by any of the writers on the subject.

 

Thank you htmlspinnr! I'll order it.

By the way, would you please look in this Toyota resource you mention and share with us what the maximum allowed RPM is for MG1 (I'm not sure why I would be interested in knowing what the maximum reverse RPM is though, at least from the perspective of its relationship with the power split device).

Also, does the $10 cost for this NFC Guide include the subscription fee refered to on this TIS site (see quote from its lead-in page below)?

"Thank you for your interest in the Toyota | Lexus Technical Information System or TIS. To start your subscription, please complete the following simple, three-step process to create your own personal account. For your reference, the progress meter below will display your current status.

Step 1: Register your User Name and Password and provide the necessary Personal Information to create your account.
Step 2: Select your preferred subscription type and duration and also enter your billing details.
Step 3: Your payment is processed and your account is activated and ready for use. An email will also be sent to your registered email address to confirm the transaction. "

 

Rather than IIRC, would you be so kind as to quote directly what the NFG guide says is the max RPM for the 2004 Prius MG1.

Also, would appreciate it if you would also quote directly what it states about MG1, in conjunction with the power split device, on starting the 2004 Prius ICE.

Thanks in advance,
Ken

P.S. insightcentral has some very good descriptions of hybrid technology. Here's what that site says about starting the Prius:

"When power demand becomes higher, usually between 13 and 25 mph, the Prius's gasoline engine will be started. This is done by directing energy from the battery to motor/generator "G", to increase its speed. This, in turn, will cause the gasoline engine to start moving. When fuel supply and spark are turned on, the engine will then be running."

Other sourses that I haven't yet located (but will) also say the same thing about starting the car, some in more detail.

Sorry to sound like such a skeptic, but I've just become a bit frustrated by all the misinformation that's out there on the subject of the Prius ECVT.

Oh by the way, there are some very sophisticated writeups written back in the early days of the Prius that even include math and nomographs. Please note though that if you use the most commonly referenced of these (even discusses the backward running MG1), at the bottom there's a very clear "no liability" statement. Just like everything else on the web, one must never take anything as gospel.

 

Hey Rick,
I've always understood you to say that the limit of the MG1 is 10,000 rpm. In your last post it says it's rpm range for maximum power output has been increased from 6500 to 10000 rpm. I don't read that to mean that MG1 would be damaged by spinning faster than that, only that it's output would be limited above that speed. Have you seen somewhere else that MG1 can be damaged by turning faster than 10000 rpm under no load? That would be the case, I believe in a neutral or deadband condition above 42 mph. I achieve this condition regularly, and have mused about the possibility of damage. Thanks for your commitment to the car and this forum.
Ray

 

It's moot Ray. As Rick now states, MG1 is spinning in the forward direction when starting the ICE. As he said in his last posting: "As for starting - they only show a nomiograph which shows that the speed is reversed (-) before starting, and then forward with forward torque applied when actually starting." So, as it stands, the highest RPM for the sun gear, and thus MG1, is going to be 2.6 times (planetary gear ratio) the ring gear speed when the car is at it's maximum speed.

 

I found the following link to be most helpfull when trying to unserstand the power split device.

Grahams Prius site

It has a few animations and is clear.

 

Rich, this is an EXCELLENT link. I sincerely wish I had found it before. It would have saved a lot of trying to figure out the errors or ambiguity in other PSD description postings I had come across. Also, I notice it postdates Graham's referenced link noted in an earlier posting (I think he hadn't quite mastered some of the details of operation when he wrote the earlier explanation).

If you don't beat me to it, in the future when I see a question here on the operation of the power split device I'll answer simply by posting this link.

Thanks again,

Ken

 

Not the moderator; however, the answer is to check the "Delete this Post" box below the message composition window after clicking "edit".

 

Thanks 10132003, looks like the moderator responded with his delete of my duplicate post before I got a chance to follow your advice to do it myself.

Ken