Mountain driving

Cowgomoo, you made my day with that offer. If I put it up on blocks in the Waffle House parking lot, can I get a $20 gift card? Or maybe I’ll take it to a port of entry and ask the Customs guys to X-ray it like they do shipping containers. Or maybe we need a mass sit in/protest at Honda HQ: No, no we won’t go, till we know what makes it go!!!!!

In my earlier post I linked to a Honda page that said it has an eCVT and it also listed fixed fear ratios. Rather a mixed message from Honda wouldn’t you say.

 

May be we should define what the term 'eCVT' means. Does different manufacturers have different definition for this 'technical' term?

 

Good point, iluvacuba.
Honda may be calling it an e-CVT when it may just be a fixed gear planetary system. After all they listed both on one page! Based on all the posts, I’m now leaning towards this, but who knows for sure?

We really don’t know what their definition is with any more certainty than we know what the ”transmission” (or lack there of) is exactly.
Hey Fizdio, could we both be right; could it be a non conventional transmission for efficiency but with fixed gear ratio (as Honda states) and implemented through a planetary gear set up?? So I guess technically speaking it may not be continuously variable and functions only to blend all the modes of power transfer. So I see your point in not calling it a transmission per se, but again who really knows?

So now I can say with total and absolute certainty that I am somewhat confused. Now let’s see anyone prove that wrong.

 

Even if it doesn't use a traditional planetary gearset directly, what they have is essentially the same thing with 1 sun, 1 planet and 1 "ring" gear, Looking at the Honda PR video I see two places where power can be put into the gear set and one place it can come out (or it could have 1 input and two outputs). Whatever they have there is effectively a planetary gear set (just with the ring gear being replaced with a normal gear).

Even if it doesn't have a traditional planetary gearset, it still is a transmission no matter what. If it had a single gear reduction that would be the transmission. Look up the definition of transmission.

CVT means continuously variable transmission. Although traditional CVTs used belts and pulleys, to be called a CVT it only needs to be able to continuously vary the engine RPM vs the wheel speed, which the Honda transmission can by loading the motors differently. Just as with a traditional planetary arrangement, the gears are always linked directly to the wheels unless they are clutched out. Again, the Clarity transmission appears to be a planetary transmission in function with 1 sun, 1 planet, and ring gear that doesn't loop around the other planets, since there is only 1, so can have the same variability in continuously controlling the drive ratio from the engine by how they load the two motors.

There is plenty of documentation on the web about how Toyota twin motor planetary CVT works, and this is effectively the same thing, even if the gears are not arranged in your typical planetary setup.

 

Thank you Viking79, my head was spinning. If I had to bet my life on it ( and I hope I don’t have to) I would have to go with the eCVT being a planetary gear set that efficiently blends the all the power modes and has a fixed? ratio. Would the fixed ratio explain why the ICE can’t directly physically power the wheels except at higher speeds.

 

I might be using the gear names wrong, as I am no expert of epicyclic gears, but if you look you will find weird variations with 2 planets and 2 suns with no ring, etc, and this appears to be one of those variations.

 

I still don't have a great grasp on how twin motor planetary (epicyclic) gears act as CVT. The motors can either drive or be driven by the gear (in either direction) difference in RPM allows the engine to turn at different speeds to make up the difference.

For engine only mode, I think you are right, you essentially disconnect the motors and let the engine drive the wheels directly with very little mechanical loss between the motor and the wheels, this can only happen at certain RPMs based on the gear ratio in this mode, which happen to be highway speeds. I think some european semi trucks do this to get high efficiency; bypass the gear box cruising on the highway and run the engine directly to the wheels (through minimal amount of gearing).

 

I've always found this article helpful. http://eahart.com/prius/psd/

 

The eCVT in the Prius actually drives a component of the planetary set with the ICE and gets the CVT effect by backdriving a motor as a generator and directing that power to a motor to drive the axles in parallel.
I wouldn't be surprised to see something similar in use in the Clarity when the clutch from the engine is engaged.

 

Thanks goes to Viking79, jdonalds (as always), and css28 for the great info.
I’ll restate what I said in another thread:
I think we’re doing the same thing the Volt community has been doing for years in that we are accumulating and sharing knowledge until we get this figured out. Too bad Honda and GM won’t put out a tech manual for us.

 

The drive system used in the Clarity is nothing like the very well designed drive system in the Prius. Using two drive motors an engine and a very elaborate set of planetary gears, Toyota was able to create a CVT transmission without using the traditional belt drive system.
The Clarity uses the same I-MMD (intelligent Multi Mode Drive) two motor hybrid system that was originally used in the 2017 Accord. The best explanation of that system I have found is the caranddriver article Fidzio indicated in post #15.
The Clarity has two motors both can also be used as generators. The first motor is the propulsion motor which is connected thru gears to the front wheels. It is the only motor use to propel the vehicle. It is used when decelerating or breaking as a generator to put power back into the battery. The second motor is the starter/generator motor which is used to start the engine when needed and to provide power to charge the battery or to power the propulsion motor when the engine is running.
There is no CVT transmission on this vehicle. The gear ratio is always fixed. In hybrid mode with the clutch not engaged between the engine and the propulsion motor there are two separate systems. The engine is generating power to charge the battery or to provide power for the motor, but the two systems run independently from one another. At speeds above 45 mph in hybrid mode, the clutch may be engaged and the engine is directly connected to the wheels through a set of fix gears.
The Clarity also has no planetary gears in the drive train. There is a planetary gear in the grey are of the caranddriver article, but it is used to allow the two front tires to turn at different speeds when the vehicle is turning. (Same reason there are planetary gears in a differential)

 

I found a cutaway view of the Accord's i-MMD system and added labels based on my understanding of the system. I believe the one unlabeled gear in the back transfers power from the drive-motor or the clutched engine to the differential. I don't see any planetary gears. I welcome any corrections.

 

Yes, this is what I understand it to be. There are some cutaway images of this engine, they show the shaft to the generator more clearly.

The idea, at least to me, is kind of like turning a Merry go Round. If you have two people turn it, they can both add rotation, or one can slow it down and draw some of the rotation for another purpose (charging the battery).