[Sheldon]

https://gm-volt.com/2015/02/20/gen-2-volt-transmission-operating-modes-explained/
https://www.youtube.com/watch?v=kCdUwUCLPB8

The gen2 transmission has two planetary gears, and is continuously variable. In CS1 (and CS3 mode) the ICE transmission "gear" is magically controlled by the speed of the electric motor which allows the ICE gearing to be continuously variable. They call this "eCVT" since the gear is being electronically controlled rather than a mechanical CVT. In CS2 mode ICE is directly coupled to the wheels for maximum efficiency to minimize transmission losses.

Ignoring the two electric motors which are the cost of having an EV, how much more complicated and/or more expensive is the two planetary gear transmission setup in the Volt than a convention automatic transmission in say a Chevrolet Cruze? Which would be expected to last longer, conventional transmission or Voltec eCVT?

Also, what other hybrids use two planetary gears? Honda? I think the Prius uses one planetary gear for their hybrids, but maybe that changed with the gen4 Prius.

 

[jcanoe]

By now GM has produced XX million 6 speed transmissions like the one in the Chevy Cruze. The unit cost has been driven down to the lowest possible cost for this transmission design. The Voltec transmission is only used in the Gen 1, Gen 2 Volt and the Malibu Hybrid, probably still less than 200,000 units total so the unit cost is relatively high.

Vehicles such as the Bolt do not need a traditional automatic transmission or a CVT. EVs have 30% fewer parts and cost up to 30% less to manufacture. Once the cost of the EV battery has fallen to ~ $100/kWh this will steer more consumers to purchase EVs. Businesses that are based around performing oil changes, engine tuneups and repairing transmissions will need to find new services to offer consumers or they will not be in business for long. Certainly within 20 years but the impact of EVs on the automotive industry will be felt much sooner.

 

[Tommy_D]

I'm guessing the actual cost to build the transmission is not that much more, or possibly equal, to that of a standard 6 speed automatic transmission. However, the R&D for this type of transmission (and the motors, the battery, etc) is likely still being paid for, which is why Volts cost a lot more than a Cruze. In the end its all just gears, clutches and electrical programming. As jcanoe says, the per unit cost of a regular transmission is very small because they are in just about every vehicle, but the Volt's transmission is still in its early days so per unit costs are high.

 

[hellsop]

By now GM has produced XX million 6 speed transmissions like the one in the Chevy Cruze. The unit cost has been driven down to the lowest possible cost for this transmission design. The Voltec transmission is only used in the Gen 1, Gen 2 Volt and the Malibu Hybrid, probably still less than 200,000 units total so the unit cost is relatively high.

Gen 1 and ELR uses 4ET50, Gen 2 and Malibu use 5ET50. They're different enough, IMHO, to be considered as separate developments.

 

[Loboc]

Gen 1 and ELR uses 4ET50, Gen 2 and Malibu use 5ET50. They're different enough, IMHO, to be considered as separate developments.

I just got a CT6 PHEV. It seems to operate way differently than these two. Is it the same as 5ET50 but with different software? The operation is more demand-based (if power is needed the ICE kicks in.) rather than drain-the-battery first before using the ICE.

 

[!arry4pyro]

A general rule of thumb is one planetary gear set and at least one clutch is needed for every two speeds. So a conventional 6-speed needs three planetary gear sets and three clutch packs. Automatic transmissions also need a torque converter which also has a clutch. So if you exclude the motors either the first of second Voltec transmissions should be significantly cheaper. Even if you include the two motors I would be willing to bet the costs would be comparable.

The big difference between the Volt and a conventional car is the battery. However battery costs are falling quickly. In my opinion I think the cost difference between a Voltec and a conventional drivetrain will be similar soon. So Voltec type plugins may appear in more future models, on the other hand cheap batteries makes BEVs even cheaper.

 

[jcanoe]

A general rule of thumb is one planetary gear set and at least one clutch is needed for every two speeds. So a conventional 6-speed needs three planetary gear sets and three clutch packs. Automatic transmissions also need a torque converter which also has a clutch. So if you exclude the motors either the first of second Voltec transmissions should be significantly cheaper. Even if you include the two motors I would be willing to bet the costs would be comparable.

The big difference between the Volt and a conventional car is the battery. However battery costs are falling quickly. In my opinion I think the cost difference between a Voltec and a conventional drivetrain will be similar soon. So Voltec type plugins may appear in more future models, on the other hand cheap batteries makes BEVs even cheaper.

A pure EV skips having a conventional transmission or CVT, also skips having ICE. The EV only needs one or possibly two electric motors if AWD. That has to result in significant savings.

 

[Sheldon]

A general rule of thumb is one planetary gear set and at least one clutch is needed for every two speeds. So a conventional 6-speed needs three planetary gear sets and three clutch packs. Automatic transmissions also need a torque converter which also has a clutch. So if you exclude the motors either the first of second Voltec transmissions should be significantly cheaper. Even if you include the two motors I would be willing to bet the costs would be comparable.

The big difference between the Volt and a conventional car is the battery. However battery costs are falling quickly. In my opinion I think the cost difference between a Voltec and a conventional drivetrain will be similar soon. So Voltec type plugins may appear in more future models, on the other hand cheap batteries makes BEVs even cheaper.

So far, the the Malibu hybrid is the only other car that uses the 5ET50 but it sells pretty poorly. It seems like only the Voltec like PHEV will get any volumes, but those batteries are much bigger and more expensive than the hybrid's batteries. But one can imagine someday 10kwh/20-25 mile batteries might be compact and cheap enough to make sense for a brought range of products.

 

[hallcp]

I'm no expert, but the CVT in the Prius only had about 8 moving parts, far, far less than a real transmission. I've read up on the Voltec system, and I think it's pretty similar. They did add some tidbits to let the gas motor connect directly to the drive wheels at highway speeds.
Parts count-wise, I don't think there's any comparison between the Voltec system and a conventional automatic transmission, we're talking 10's versus 100's of pieces.
The fact that the Prius and Voltec use a planetary gear system is not similar to how a conventional transmission operates.
That's my 2-cents.
Like others have said, a pure BEV takes the part count down to a whole new level!

 

[hellsop]

I just got a CT6 PHEV. It seems to operate way differently than these two. Is it the same as 5ET50 but with different software? The operation is more demand-based (if power is needed the ICE kicks in.) rather than drain-the-battery first before using the ICE.

I don't know what they're calling it, but the CT6 Hybrid's transmission has THREE planetary sets and five clutches to the 5ET50's two and three. Still only two MGx though -- I haven't puzzled out how that all works yet, but it may be to help decouple the relationship of speed between the two MGx while the ICE is also turning so that the ICE can stay at an efficient RPM and vary the power drawn off of it without changing speed (kind of like an e-governor) while the MGA generates and the ICE and MGB drives the wheels at speed independent of both ICE and MGA speeds.

 

[9G-man]

Of the three,

An eCVT is the simplest, most reliable, with the least maintenance.

A mechanical (belt) CVT is least reliable and least durable.

A traditional (torque converter) ATF is most complex, requires the most maintenance, yet, is very tried-and-true reliable.

eCVT is probably most efficent.

Hybrids (VOLT included) require some sort of coupling of two power sources (ICE, MG) thus a planetary gears and/or clutches.
EV don't require a transmission because they are direct drive and electric motors are powerful at low RPM.
ICE cars need a transmission because and ICE is NOT powerful at low RPM and across it operating range.

A transmission (shifting) kills the (hybrid) EV experience IMHO.
A CVT helps the hybrid seem EV-ish

Toyota and Chevy made the right choice with eCVT, as did FORD in their Energy line of PHEV's

I have grown to really dislike transmissions that shift. The whole experience is so crude. I can't believe they are making 8 speed automatic transmissions now. They are constantly shifting- up up up up up up up up then down down down down down down down down. I had a BMW that i got rid of because it shifted too damn much !

 

[Sheldon]

Of the three,

An eCVT is the simplest, most reliable, with the least maintenance.

A mechanical (belt) CVT is least reliable and least durable.

A traditional (torque converter) ATF is most complex, requires the most maintenance, is very tried-and-true reliable.

eCVT is probably most efficent.
...
I have grown to really dislike transmissions that shift. The whole experience is so crude. I can't believe they are making 8 speed automatic transmissions now. They are constantly shifting- up up up up up up up up then down down down down down down down down. I had a BMW that i got rid of because it shifted too damn much !

Once an EV owner, an ICE seems old technology. The Volt is a gateway drug.

Anyway, even if an e-CVT is maintenance free and efficient, it does have a lot of complicated software behind it. Especially for a PHEV. I suspect some sort of machine learning optimization was involved in the Volt's software too.

The driver's foot on the accelerator has to adjust the two electric motors to optimally combine, and regenerate electricity when braking and gliding as needed. When the car switches to CS mode, you have to adjust the amount of fuel going to the engine depending on the battery charge state, and the accelerator pedal and the brake and the current speed ... as well as decide how much additional battery power to add in. And then's there's which CS/CD mode is appropriate ...
CS1 at low speeds with the engine creating extra power that simultaneously flows in and out of the battery
CS2 direct coupled at higher speeds
CS3 for the highest speeds which I think uses overdrive gearing, or under drive gearing when less torque is required than CS2.
CD mode for when the battery buffer has filled up and the ICE engine is temporarily off.

mechanically simple, efficient and reliable? probably. but the software is complicated.

 

[9G-man]

You're right.
I was going to add this earlier,

The eCVT is control complicated
The (belt) CVT is design and execution complicated.
The ATF is mechanically and hydraulically complicated.

 

[martik777]

Weberauto has very detailed explanations of how these transaxles work.

Volt Gen1 4et50: https://www.youtube.com/watch?v=dqM3YXEf1js

2nd gen Prius eCVT: https://www.youtube.com/watch?v=ZmHpSyTsfm0

He has a 5ET50 (Volt G2) but has not yet released the video.

 

[hellsop]

They got an eFlite (Pacifica hybrid) one up now too. Sure sounds like it works exactly like 5RT50 but the design doesn't seem quite as pretty.

 

[Loboc]

The CT6 PHEV seems to allow full ICE power instead of limiting it in any way. The RPMs follow the throttle IOW. Even if there is available EV power. The total available power is way more than ELR.

I wish someone would do a mode vid to show how it works.

 

[gbergman14]

Depending on which CVT you refer to, you may be asking the wrong question...
The original Prius CVT (Power Split Device) is as simple as you can get. It has more in common with a differential gear than a transmission. My Camry Hybrid had 2 planetary gears. One served as the CVT and other served as a reduction gear. Far far simpler than any other transmission. No clutches, no latches, no shifting mechanism, just the unavoidable bearings as with any rotating device. The Volt CVT is far more complex but, my understanding is it doesn't use a friction or fluid clutch. The clutch engagements are computer synchronized to virtually eliminate the wear and tear that plague traditional transmissions. You won't feel any "shifts" as you do with a traditional vehicle.

Hope this helps,
Gary

I'm not an engineer but, I play one on TV.

 

[samotlietuvis]

eCVT is probably most efficent.

The eCVT (aka planetary gear transmission) friction losses are higher than manual transmission and higher than automatic transmission. The higher friction losses have to do with more gear surface having contact at any time than the other two transmission types.
As a transmission, from friction point of view, planetary gear transmission is the least efficient out of the three.
However, eCVT allows infinite gear ratio and in this way the ICE engine operate in a most efficient rpm band.
In addition, 1 planetary gear transmission allows "smoothly" combining two power producers (engine + 1 electric motor).
The biggest advantage of the planetary gear transmission is that per weight it can handle the most torque when compared to manual / automatic transmission. It is the most "weight/(max torque)" efficient transmission out there.
Given how the double planetary gear transmission works very well for Volts, it would work even better for large vehicles, like trucks or SUVs, where higher torque is needed.

I have a feeling that Gen II transmission would have no issues combining both 2 electric motors and gas engine at the same time, assuming clutch #2 holds (see bottom link).

I saw the cutout of the Gen II Volts transmission 3 (4) years back in LA Auto show and it actually was very compact when compared to the T56 transmission I am very familiar with (4th Gen F-body…).
Since Gen II Volt transmission volume wise is smaller than the equivalent manual / automatic transmission, it is reasonable to assume it cost less to produce.
However, the engineering cost to design newly architected transmission, and # of lines of code that were written for the 5-mode operation probably make it quite expensive, unless GM sells a lot of them (which it is not…)

The Gen II Volt transmission is a piece of engineering art, limited only by short vision of GM leaders to not deploy it to trucks and SUVs...
https://gm-volt.com/2015/02/20/gen-2-volt-transmission-operating-modes-explained/