[Ziyang]

Hi, just want to share a newly uploaded video on YouTube describing how Honda’s e-CVT ‘transmission’ works.

I know, I know, it is not a traditional transmission with varied gear ratios; from a broader perspective it serves the same purpose of diverting engine power to the front axle just as a traditional transmission does.

Some interesting points I picked from this video:
1. An additional 2.455 reduction gear is there from motor to front axle, making the motor to final gear ratio 8.398. I wasn’t aware of this reduction gear before.

This puts 232 lb ft of motor torque amplified to 1948 lb ft if I do the math right.

2. A permanently applied clutch is there on the flywheel for safety breakaway. This is something good to learn.

3. This e-CVT ‘transmission’ needs ATF similarly to a traditional transmission. The ATF serves the purposes of cooling, engaging clutch, and lubricating gears.

It seems no much fluid will be left inside during ATF change since the inside structure is so much simpler than stepped ATs.

 

[jackpine]

Excellent post, Ziyang! That's a beautifully thought out design, isn't it? I love the way the axle gets power from any of the three inputs seamlessly. I agree, it's a simple, straightforward design.

- Jack

 

[zroger73]

The power of these hybrid and EV motors relative to their size is incredible. To put things into perspective, a typical, general purpose, 150 HP motor weighs nearly a ton, is two feet in diameter, and sells for over $14,000.

 

[OG1]

Great find! Thank you.

 

[JeffJo]

Hi, just want to share a newly uploaded video on YouTube describing how Honda’s e-CVT ‘transmission’ works.

Thanks. I had been waiting for Prof. Kelly to post one on i-MMD; he is quite renowned for his videos on hybrids, but anything recent was only about Toyotas.

A couple of points I noticed:

• He called the transaxle an "e-Drive." I had never heard that name applied to iMMD before, and it sounds like it should belong to the electric-only cars.
• He implies he calculated that the HAH switches to Engine Drive at 100 kph (62 mph) and uses it up to top EV speed of 140 kph (87 mph). We know that isn't right from experience. I saw a Car & Driver review that put it between 44 and 75 mph, which sounded specific enough to have been from a better calculation. I don't know for sure what it is, but those numbers correspond almost exactly to where the fuel efficiency exceeds 210 grams per kilowatt (it's best is 208.1 g/kW). See the efficiency map below.
• That error may be because he also doesn't seem to understand what Engine Drive does. He claimed that both motors are uninvolved when the clutch is engaged, and seems to think it is driven by where the engine is more efficient.

But overall it was a good reinforcement what I already knew, with some specific numbers for the gears.

 

[InTotalAccord]

Yeah, the professor makes a number of incorrect statement, both about the speed, above which the engine can be coupled to the electric drive motor. (Which is above about 42 mph, not 60-some mph.) He is also incorrect in saying that there is a gas-engine-only mode of operation. The electric drive motor is always attached to the wheels.

His analysis of the effective gear ratios from drive motor to wheels, and from gas engine to wheels, seems right.

The generator motor is always "connected" to the gas engine. And as I understand it, the coupling of the gas engine to the wheels, is actually made to happen by locking up the generator motor to the drive motor.

 

[JeffJo]

The generator motor is always "connected" to the gas engine. And as I understand it, the coupling of the gas engine to the wheels, is actually made to happen by locking up the generator motor to the drive motor.

Close, but not quite. The clutch locks the engine with the traction motor.

This cartoon illustrates it best. It's the whiteboard behind Jason Fenske in his "Engineering Explained" Youtube video about the 2017 HAH.

I have yet to compare it to the Weber State video to make sure it includes everything, but I think it does.

The engine is connected directly (i.e., by the input shaft, not a gear) to one end of the clutch.This is drawn in black.

That shaft is also geared to the rotor of the generator (purple). This is the only thing the generator is ever connected with, and it is always connected. What may be confusing is that motor shaft is a tube, and the generator shaft rotates inside of it without a connection.

The other end of the clutch is geared to the rotor of the traction motor (green). Which, in turn, is geared to the countershaft (brown) and then the differential (blue).

 

[zroger73]

One tiny little omission from Jason's illustration is that the power flow between the battery and the generator is actually bidirectional - the generator also serves as the starter.

Has the engine-only speed changed from the 2017 to 2018? This chart indicates 62 MPH. The presenter states "at around 60 MPH depending upon conditions, the lockup clutch engages and the engine is driving the wheels".

 

[JeffJo]

One tiny little omission from Jason's illustration is that the power flow between the battery and the generator is actually bidirectional - the generator also serves as the starter.

True - you are correct, and it is a tiny point. But that can't contribute to driving, so one could claim the illustration correctly displays all driving modes.

Has the engine-only speed changed from the 2017 to 2018?

No. The most important speed to include in Engine Drive (it isn't engine-only). is 54 mph = 2000 rpm in Engine Drive.

This chart indicates 62 MPH.

No, that chart indicates that it can be in EV or Hybrid drive while cruising at 37 mph, in Hybrid Drive in "powerful acceleration" up to 62 mph, and then EV or Engine Drive when it begins cruising at 62 mph. The same would happen if it cruised anywhere between about 45 and 75 mph.

Think of Engine Drive as equivalent to overdrive in a gas car. The gearing is too short to operate below about 45 mph, and the efficiency drops below that of Hybrid Drive above about 75 mph.

+++++

But there is another mistake, that I made by making assumptions about Jason's illustration. The OD gear is connected directly to the countershaft, not through the motor gear. The illustration is two-dimensional, and can't show that this connection is "behind" the motor gear. The lower-right portion that shows the gear ratios is correct (I thought it represented the effective gear ratio in the double connection.)

Here's where the components show up in the Weber State video, using Jason's colors:

 

[mtts60]

One thing I've never understood is why we don't make diesel-electric cars. We've been making diesel-electric railroad locomotives since the 1930's, so the technology is well-known.

A small diesel engine to power an electrical generator, which then powers the electric motors at each wheel. No 'range anxiety' with this setup as diesel pumps are everywhere.

 

[JeffJo]

One thing I've never understood is why we don't make diesel-electric cars. We've been making diesel-electric railroad locomotives since the 1930's, so the technology is well-known.

A small diesel engine to power an electrical generator, which then powers the electric motors at each wheel. No 'range anxiety' with this setup as diesel pumps are everywhere.

You do realize that the technology you talk about is called "Hybrid Mode" in the Accord Hybrid? The exceptions being that it uses a gas engine instead of a diesel, and it adds a battery to make it more efficient?

 

[mtts60]

If that's the case, why does it have a transmission? A true diesel-electric vehicle would not have one.

 

[JeffJo]

If that's the case, why does it have a transmission? A true diesel-electric vehicle would not have one.

It switches between parallel hybrid mode and serial hybrid mode (what a diesel-electric locomotive uses) when efficiency warrants. In parallel mode, it uses a fixed-gear transmission system, not what is traditionally called a "transmission."

In serial mode, it does not use it. You have a small gas engine powering a generator, and the equivaent of one motor driving one pair of wheels. Pretty much what you asked for, with specific differences how a car is different than a locomotive.

 

[nickandre]

That's really cool. That transmission is going to last ages -- only one clutch. It's a nifty idea to rely exclusively on gas-electric in lieu of a CVT with a single lockup clutch.

 

[mikemargolis]

One thing I've never understood is why we don't make diesel-electric cars. We've been making diesel-electric railroad locomotives since the 1930's, so the technology is well-known.

A small diesel engine to power an electrical generator, which then powers the electric motors at each wheel. No 'range anxiety' with this setup as diesel pumps are everywhere.

I came from a Mercedes 6 cylinder diesel (OM-642) engine to my HAH, and I promise you, you do not want diesel. The cost of oil changes, fuel filters, DEF heaters, and the raw cost of diesel fuel vs regular gasoline makes me SUPER happy that Honda didn't go there.

 

[Hudouc]

One thing I've never understood is why we don't make diesel-electric cars. We've been making diesel-electric railroad locomotives since the 1930's, so the technology is well-known.

A small diesel engine to power an electrical generator, which then powers the electric motors at each wheel. No 'range anxiety' with this setup as diesel pumps are everywhere.

Probably packaging and emission treatments. If you look at the new tier 4 (and tier 3) compliant locomotives and their older ancestors, you'll notice that the new tier 3/4 locomotives have significantly larger cooling system to help reduce emission. That alone will create packaging issues. Not to mention the more complex exhaust treatment and having more components.

 

[.167026]

Hi, just want to share a newly uploaded video on YouTube describing how Honda’s e-CVT ‘transmission’ works.

I know, I know, it is not a traditional transmission with varied gear ratios; from a broader perspective it serves the same purpose of diverting engine power to the front axle just as a traditional transmission does.

Some interesting points I picked from this video:
1. An additional 2.455 reduction gear is there from motor to front axle, making the motor to final gear ratio 8.398. I wasn’t aware of this reduction gear before.

This puts 232 lb ft of motor torque amplified to 1948 lb ft if I do the math right.
View attachment 526425

2. A permanently applied clutch is there on the flywheel for safety breakaway. This is something good to learn.
View attachment 526426

3. This e-CVT ‘transmission’ needs ATF similarly to a traditional transmission. The ATF serves the purposes of cooling, engaging clutch, and lubricating gears.

It seems no much fluid will be left inside during ATF change since the inside structure is so much simpler than stepped ATs.

Please explain quoted sentence would you?

Please explain quoted sentence would you?

It seems no much fluid will be left inside during ATF change since the inside structure is so much simpler than stepped ATs.
Did you mean “it seems NOT much fluid...”? And why? I mean the drain and refill spec in manual is 2.3 quarts so?? I’m wondering how much fluid in TOTAL is in this e-cvt? Anyone know?

 

[UnknownJinX]

Probably packaging and emission treatments. If you look at the new tier 4 (and tier 3) compliant locomotives and their older ancestors, you'll notice that the new tier 3/4 locomotives have significantly larger cooling system to help reduce emission. That alone will create packaging issues. Not to mention the more complex exhaust treatment and having more components.

That, and diesel has some nasty emissions. Particulates are a big issue and Europe has pretty much demonstrated the effect from going all diesel. Not to mention, you need to remember to fill up DEF once in a while to keep NOx emission at bay. Yet another extra maintenance item. I know GM's diesel engine also needs Dexos 2 oil to improve the emissions, which is much harder to come by.

There is also issues like weight and cost, as diesel engines have to be sturdier to handle the higher compression. Diesel engines also benefit greatly from a turbocharger, so now you have to package the turbo, intercooler and all the ducts appropriately.

Diesel pumps are also less common than gas pumps, and usually gas stations will have 2 diesel pumps at most(one is more common) compared to 8 gas pumps. Oh, and pray that there wasn't a semi just before you that sucked up all that diesel...

If that's the case, why does it have a transmission? A true diesel-electric vehicle would not have one.

Having worked with Komatsu haul trucks that are diesel-electric, it's not at all like a consumer car. As mentioned before, those are usually a serial hybrid only. Only the electric motor is used to drive the wheels.

Those haul trucks use the diesel engine at all times and have no batteries or capacitors(their cost is as crazy as it is, now imagine putting literal hundreds of tons of batteries on it), so any extra energy a diesel engine generates goes through a lot of resistors and gets dissipated as heat. Not efficient at all for a consumer vehicle.

Sent from GM1917, technology or something like that.

 

[Ziyang]

It seems no much fluid will be left inside during ATF change since the inside structure is so much simpler than stepped ATs.
Did you mean “it seems NOT much fluid...”? And why? I mean the drain and refill spec in manual is 2.3 quarts so?? I’m wondering how much fluid in TOTAL is in this e-cvt? Anyone know?

If you have ever watched a tear town video of modern ATs, you’ll understand what I mean. There are so many oil channels inside the transmission making it impossible to drain all out by the bottom plug. That makes ATF change less effective if you can only drain 60-70% of all fluid inside.

I meant the structure of this e-CVT case seems less capable of hiding fluid here and there.

 

[.167026]

If you have ever watched a tear town video of modern ATs, you’ll understand what I mean. There are so many oil channels inside the transmission making it impossible to drain all out by the bottom plug. That makes ATF change less effective if you can only drain 60-70% of all fluid inside.

I meant the structure of this e-CVT case seems less capable of hiding fluid here and there.

Yes. I also understand that this transmission does not have a torque converter and would also mean IMO anyway that it would hold a lot less fluid. Taking that in consideration and basically why I’d like to find out how much in total fluid it actually holds because if it’s less then the other 6-10 speeds typically using this DW-1 fluid one could assume MORE drain and refills at the 2.3 quart change would certainly be better and recommended to keep the fluid clean. I’m unsure of the filtering also with this trans and wondered what if any it had AND whether it’s serviceable? If not certainly another reason to keep it clean! Found this and thought it explains this system pretty well.