The Beauty Of The Chevrolet Volt’s New Gen 2 Transaxle


Some know that I am a kind of a gear head. I’ve followed the Volt since its early development days. We would spend countless hours reading Lyle Dennis’ (co-founder of InsideEVs and daily articles and speculating on how the Volt worked. Was it pure series? Did it have a mechanical link to the wheels in CS Mode?

After I got my Volt I got a DashDaq data acquisition device and took a lot of data and published many articles on the Volt’s transmission. I also wrote a computer program that modeled its behavior. The Volt’s transmission is truly a work of art.

Here are the articles if you are interested:

It’s no surprise then that I am totally blown away by GM’s new transmission, the 5ET50. The new transmission is now 5 modes soon to be announced but all but verified by our GM rep Wop on Tour that the 5th mode is where we link the 2 motors together in EV mode for more acceleration.

There is an excellent SAE article out about the new transmission. In the article there is a great cutaway of the trans.

Figure 1

Figure 1

The new transmission is much more compact than the Gen 1 transmission. They have integrated the inverter assembly into the transmission itself instead of it being a separate module with heavy electric cabled connecting the two as shown in figures 2 and 3.

Figure 2

Figure 2

Figure 3

Figure 3

In figures 4 and 5 one can see how much more compact the gear sets are in the new transmission. The old transmission used spur gears in the reduction gear set downstream of the power split planetary.

Figure 4

Figure 4

I am speculating that the new transmission uses a planetary gear reduction set much like the spark coaxial gearbox as shown in figure 5.

Figure 5

Figure 5

Some publications have said that the new gearbox has TWO planetary gear sets in it compared to only 1 in the original transmission. This second PG set may be for gear reduction so we still only have 1 PG set used for the power split device.

Figure 6

Figure 6

My labeling in figure 6 is speculation also. Some things are fairly certain though: one PG set for the power split device, 2 MG’s that are more nearly the same size ie a slightly larger MGA and a smaller MGB traction motor. The larger MGA allows more 2 motor operation and less series operation increasing MPG in RE mode. The 2 motors are linked together in EV mode for more power. There probably are some gear ratio changes as well.

Also shown in figure 6 are what I am speculating are clutch sets. Two are fairly obvious because one can see the clutch friction plates. The other two are not so obvious but they appear to be dog gears with no friction plates. The clutch at the ICE output is the most obvious dog gear assembly. No friction plates are needed as the Volt synchronize speeds prior to shifting as I detailed in the first of my articles above.

Could there be 4 clutches in the new gearbox? We do need another one to engage the 2 motors in mode 5. We shall find out in January at the Chevy’s official debut at the NAIAS in Detroit.

Cheers Volt Heads!

Categories: Chevrolet


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44 Comments on "The Beauty Of The Chevrolet Volt’s New Gen 2 Transaxle"

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Optioning up the Cruze to the Volt, is well, not possible.
To try to get close to the Volt, you need the Cruze LT2, Enhanced Safety package ( which is much more extensive on the Volt, it does not have the collision warning system ), MyLink Radio and Nav, with only 6 speakers. And it totals $25,720. So, the Volt + options + the Federal Tax Credit, is only $3000 more expensive.

In other words, You Will Save the $3000 difference from a Cruze, with More Options in the Volt.

I think I read something that seemed reliable that said the new transmission had 2 clutches, not 4. But then many people assumed the would have a 3 cylinder engine. Nothing is certain other than what GM has stated directly.

I’m less certain about the 2 motors being closer to the same size (power). I’m kinda guessing the larger motor still needs to be a full 115 kW or so but I’m not at all sure.

Interesting… GM themselves claimed only two clutches for cost reduction. Perhaps they only referred to the friction clutches and omitted the dogs.

Refer to the GM animation video previously posted a coupe of weeks ago.

Hmmm… After looking at the cutaway and associated pictures, there are some obvious things to note.

The MG1 is connected to the planet carrier and final drive (via the morse chain), just like before. What is noted as clutch 1 is not, it’s the parking dog (you can see the pawl). And there is no clutch 4, that’s a bearing carrier.

The ring gear has a clutch/brake to the body, also like before. What is not clear is the left hand side configuration. First instinct is the engine drives the ring gear through the 2nd clutch, and MG2 drives the sun gear. That supports all 5 modes, but it doesn’t seem to align with the cutaway.

Regardless, I still think there are only two clutches, no more.

“The MG1 is connected to the planet carrier and final drive (via the morse chain), just like before.”

Huh? How is that just like Volt 1.0?

I was pointing out the wheels are driven from the planet carrier, as was the case in 1.0 Volt. Apologies for poor wording.

OK, after a few more hours studying the cutaway, parts pictures and the animation, I think I’ve worked it out. The key is the presence of a conventional one way overrun clutch at the engine in addition to the two friction clutches, and the sun gear is reversed from what it appears to be in the cutaway. The MG1 drive the sun gear. The planet carrier is connected to the wheels via the chain drive. The ring gear can be braked to the body, and is also connected to the 2nd clutch in the left compartment. The MG2 is connected to the engine via the one way overrun clutch located on the engine, and can be connected to the ring gear by the 2nd clutch. I’ve made a nice diagram, but don’t know how to attach it. So, here are the modes: – MG1 only, ring gear braked – MG1 + MG2, ring release, clutch 2 engages, note the overrun clutch prevents engine turning – MG1 + MG2 + Engine, Engine starts and drives MG2/ring via overrun clutch – MG1 + Engine + Generating, same as above but MG2 is generating rather than motoring – Engine + MG2 generating, clutch… Read more »

Article needs a better introduction as in context setting. Like what is the status of gen 2 volt. I feel like I’m diving into a conversation not knowing what has been discussed.

Much complexity here, more weight, more repairs…
KISS and go all electric, more batteries and the same result…without gasoline.

To each their own. I prefer the range extender over more batteries.

you prefer to use and waste gas when you dont need to?

i hate running out of electric and switching over to gas when im only a few miles away from home.

cannot wait until i can get a tesla

Correct. I don’t want to pay for and lug around a huge battery that I don’t need on a daily basis. Plus I don’t want to be dependent on finding a charging station. Not JUST a charging station, but one that is nearby, NOT broken, NOT ICE’d or in use by another EV. I don’t know where you live, but in my part of the country charging stations are far and few between.

That is how complicate the volt system can be instead of a simple completely separated generator that can then be optimized for Electricity production instead of circular motion production. The Toyota direct free piston generator would be much better than this crap.

Prius, the beauty of the Volt is that it is complicated on the inside but simple on the outside. You get in and drive and it is like an ICE, you can drive all day with no worries about charging, fast or otherwise. With just 38 miles of AER I am up to 644 mpg, plus 50 cents of electricity a day. My monthly fuel bill is just $4 of gasoline and $15 worth of electricity, and I don’t have a 75 mile range limitation.
With more AER, the Gen II Volt should be even better.

The result is nice but the price gets to 34345$ and the EV range remains too low.
An EV with a 100 miles battery and a completely separate APU could make a simpler car in the 25000-30000 $ range with better ev range and less maintenance.

BMW made this product. It costs $11K more than the Volt, only has a 180 total range, and only 90 miles on gas. In CS mode, it’s limited by the 25kW ICE.

Since GM patented the free piston many moons ago, I’m sure they have looked at that option, LOL.

Dr. Kenneth Noisewater

They had modern fuel injection and ECU technology many moons ago?

Here’s some details of GM receiving a patent for a plug-in hybrid using their free piston design. It was filed in 2009, awarded in 2012. That was 5 years ago, so not sure why they would want to use something from Toyota.

Here’s an interesting paper from the GM Research Lab in 1988, talking about using a free piston system to move a car.

And here’s a paper from back in the 50’s looking at 5 different free piston designs.

(getting moderated… swap 0 and o)

Here’s s0me details 0f GM receiving a patent f0r a plug-in hybrid using their free pist0n design. It was filed in 2009, awarded in 2012. That was 5 years ag0, s0 n0t sure why they w0uld want t0 use s0mething fr0m T0y0ta.
Here’s an interesting paper fr0m the GM Research Lab in 1988, talking ab0ut using a free pist0n system t0 m0ve a car.
And here’s a paper fr0m back in the 50′s l00king at 5 different free pist0n designs.

Hopefully the folks that designed the Spark’s hood latch that just got recalled, didn’t design this part of the Volt…

Being a Volt owner, I share your excitement about the next Gen Volt! I am really looking forward to knowing what “better in every way” will be in hard numbers. I think more awards are in the Volt’s future.

Dr. Kenneth Noisewater

Very cool, now stick it in an Equinox already!!!

George. I read your article on regen and just thought I would share my experience with regen in our Volt when descending our mountain here in Hawaii. It’s possible to descend 9500′ in about 30 miles from Mauna Kea visitor center to my house here in Hilo. I’ve not tried that yet, but I done the climb and descent from 5900′ to 200′ elevation on about 8 occasions. I’ve been able to recapture anywhere from 30% battery all the way up to about 45% battery depending on a bunch of factors. It’s fascinating to be sure. I really really wanna try the 9300′ descent to see if I can get close to 100% battery back. That would be way cool pulling in my driveway after a 2 hour drive with a FULL battery. I suspect I would have to summit Mauna Kea to get more than 80% but YA never know til you try. 🙂 stay tuned.

All I see is an incredibly complex car with lots that can wrong. Already my co-worker had to take their new Volt in twice for “clutch problems”.

In many ways, the Volt seems to be the worst of both worlds… an EV that has to drag around an ICE and its gasoline, and an ICE that has to drag around a heavy battery. And all of it twice as complex.

I prefer the simplicity of a pure “motor-to-wheels” EV. These cars will prove to be extremely reliable and maintenance-free.

Foo, anecdotal tales are useful, but in the real world Volt owners are some of the happiest car buyers out there according to JD Powers, three years in a row. The award list Jeff Cobb compiled pretty much sums it up: The List o The Detroit News invites 100 readers at NAIAS to select their favorite vehicles in a variety of categories: Chevrolet Volt named Most Earth Friendly for being the greenest vehicle at the show (1/15/10) o Named “Best of Show” at the 2010 Chicago Auto Show – Best Green Vehicle (25 percent of vote) o The Volt makes the 2011 North American Car of the Year Short List. o Popular Mechanics October issues names Chevy Volt a 2010 Breakthrough Technology Winner o Popular Mechanics also salutes the Volt as a “Brilliant Idea” o Popular Mechanics names Volt on list of top ten vehicles for 2011 (11/11/10). o Chevrolet Volt Named Motor Trend 2011 Car of the Year (11/16/10) o Automobile Magazine recognized Chevrolet Volt as its 2011 Car of the Year on its Facebook page (11/16/10) o Volt Named Automobile Magazine 2011 Automobile of the Year (11/17/10), and Technology of the Year award o Chevy Volt Named 2011… Read more »

And now for 2016 …. the same lame hybrid and still no good all electric car from GM

GM is the principal shill of Big Oil ans their pressure on the medis is tremendous. Half of your awards are exagerated. Here in Snowland the Volt start his ICE whenever it is a little cold.
Yesterday somebody wrote about his brand new 2015 Volt that start the ICE after 15 miles..
Another that his hybrid mysteriously stops anywhere by itself…

LOL, an old Jalopnik article from 2010 that basically has everything wrong. Not a very good link to try to make a point with. I’m not really sure what point you are trying to make anyway. Is it that you are just anti-GM? If you don’t understand how the car works, don’t blame anyone else but yourself. Get educated. Look at what George S. has done, and even shared his information. There’s lots of sources.

I thought the same thing to kdawg. What a joke. BusinessInsider and a blog that looks like someone middle school kid homework assignment.

You can seek out and find negative information about pretty much anything. It looks like what he tried to do, and it funny that those were the best two things he could come up with!

I have an all-electric Nissan Leaf. When I leaserd it two and a half years ago. It was the car of my dreams, but I have since realized that my life and my driving habits are too unpredictable to have a car like the Nissan Leaf. The Chevy Volt is what I need. It may not be for you, but don’t knock it. I believe one day I’ll be able to charge the Volt in 5 minutes with a range of hundreds of miles. Until then, bring on generation 2.

You can find anecdotal tales and stories about problems with any vehicle regardless of the drive train. Google Tesla reliability, Leaf battery degradation or Leaf brake fluid to see not 100% of BEV owners are satisfied with reliability or maintenance costs. Half of what you find is exaggerated, just plain false (like inaccurate trashy stuff Lustuccc tried to share), or may not even apply to your situation. They are still great cars and I wouldn’t hesitate to own one if they fit my needs better. The fact is owner satisfaction of the Volt has been outstanding.

Just because concepts seem complex to you does not mean they result in unreliable results.

“All I see is an incredibly complex car with lots that can wrong”

That is what an “average” person who doesn’t know any techical details about engineering would say…

The Voltec system is actually incredible simple. Planet gearsets are compact and simple and that is why every transmission class would cover it first.

In a way, it is far simpler than a 6-speed automatic transsmission. The complexity is not much different than a manual 5-speed.

Prius has been making similar system for decades without major quality issue.

So, your concern is overblown by lack of understanding. Sure, a single speed powertrain would be simpler, but the complexity of owning a limited range BEV is in the ownership experience of planning out every long drives and searching for charging station while worrying about the availability of station when you get there…

I call that major “complexity”, especially when you end up calling a diesel tow truck whe you run out of range…

Hopefully in ten years the word hybrid will be thought of as mostly in crops and vegetables.

Sorry George, The fact that you confuse a spur gearset with an obvious helical gearset calls into question your whole article, and shows unfortunately, you’re not conversant with this stuff.

I call ’em like I see ’em.

Where are your articles?

That would be a fair gripe except for one thing, I’m not paid to be here, and as far as I know, George is a professional writer and is compensated.

Its like this: I’m a lousy piano player, and wouldn’t dream of being paid to do it. It would be quite another thing to hear a professional pianist and criticize his playing ability. Once you’re a ‘professional’ you automatically operate on a different plane, and therefore open yourself moreso to constructive criticism.

As far as this topic goes, QCO’s blog above is ‘helpful’.

No. You write a post like that, you make it a fair gripe.

Also, there is more than one reason why people may contribute an article to this site. They might have a strong interest in cars and technology, or a serious concern about global warming, or they might just want to share a recent adventure they took in their EV. Many contributors aren’t professional writers. Even if someone happens to get compensated, it doesn’t make them a ‘professional’ writer.

Bill, you ‘call ’em like (you) see ’em’ depending heavily upon your mood. Many things might explain the transposition here.

Frankly, it ‘calls into question’ some of your negative experiences reported here, as Tone can have a seriously negative effect upon the listener’s reaction to your difficulty(s).

I believe we used to say, “who pissed in Your wheaties?”

I humbly offer that I have expressly described something as Blue when it was inarguably Red.. I mis-spoke. I have then appreciated the fact that the corrector did not feel the need to call what little intellect I have remaining into question

Anybody who gets paid for a service is in the employ of someone else.

The concept is a decent demarcation point.

I’m not picking on George. As a professional writer his articles are more readable than others on here and I was just offering up apparently some unwanted criticism, especially since he specifically called himself a ‘gear head’..

To George’s credit, he’s one of the more accurate writers here, usually. As a matter of fact it was rather strange to see him make the mistake that he did since he is usually so accurate.

But the original comment was directed to him, actually.

You can get compensated to do something outside of your occupation or profession. If I helped my friend move and he bought me some drinks for it, it does not make me a professional mover. If I watch my brother’s kids and he pays me for it, it does not make me a professional child care provider.

Two clutches and five modes: Engine only; electric only both torque transmitting mechanisms disengaged and the motors adding torque through the planetary gearset (power split); electric only both torque transmitting mechanisms engaged and the second planetary gearset (ratio changing) supplies reactive torque for the two motors; electric variable torque with no torque multiplication; electric varialbe torque with multiplication.

One other thing about MG1 and MG2. I believe I read that use the same stators and therefore are the same physical sizes, but use different rotor materials. MG2, the larger HP motor/generator, has some rare-earth magnetic material. MG1, the smaller HP motor, uses ferrite material.

We’ll see the inner working detail when the SAE technical papers are finally released next spring.

Yes, common stators was assumed based on GM’s early comments, but the cutaway clearly shows different widths so they are not the same.

In retrospect the commonality referred to by GM was in diameter, so the same stampings can be used for each motor core. But each stator is built up to a different width and wound separately.

And yes they minimized the use of expensive rare earth materials in the rotors by precisely optimizing each motor for their respective torque needs. They still needed some rare earths for the larger motor, which provides most of the torque, but were able to eliminate rare earths completely in the smaller motor.

This and the other changes show that the most significant achievement by far in Volt 2 is cost reduction to make it commercially viable. It’s a very important statement of support for mass market vehicle electrification compared to some other manufacturers.