Exclusive Video: Want to Know EXACTLY How the Chevy Volt Powertrain Works?

· · 7 years ago

Thought you had enough of the Chevrolet Volt powertrain? The debate about whether or not the Volt is an electric car, an extended range electric car, or a plug-in hybrid vehicle still seems to be taking up an inordinate amount of tech-related blogosphere energy these days, even though general fatigue seems to have set in on the topic.

Although PluginCars.com published an interview with the Volt Chief Engineer, Andrew Farah, last week that essentially put the issue to rest, there was still enough vagary that the following series of three videos should completely satisfy any remaining questions you may have.

In an extremely detailed walkthrough—including a slick animation—Pamela Fletcher, Chief Chevrolet Engineer for Global Voltec and Plug-in Hybrid Systems, elucidates the entire drive system, including the inner workings of the Volt's oft-misunderstood drive unit. If you like these videos, then you should also check out our walkthrough of the Volt's battery from the same series of presentations.

Part 1 of an extensive walkthrough highlighting how the Chevy Volt powertrain works, presented by Pamela Fletcher, Chevrolet Chief Engineer for Global Voltec and Plug-in Hybrid systems.

Part 2 of an extensive walkthrough highlighting how the Chevy Volt powertrain works, presented by Pamela Fletcher, Chevrolet Chief Engineer for Global Voltec and Plug-in Hybrid systems.

Part 3 of an extensive walkthrough highlighting how the Chevy Volt powertrain works, presented by Pamela Fletcher, Chevrolet Chief Engineer for Global Voltec and Plug-in Hybrid systems.

Seriously, after all that what is there left to say? You should now be fully armed to have an educated discussion about what kind of vehicle the Volt is... but in the end only us car geeks care what label it gets. I think we should call it an extended range half double hybrid half plug-in (with a twist of lemon) and leave it at that. ERHDHHPI... Now doesn't that just roll off the tongue?


· · 7 years ago

I finally had a chance to listen to parts 1 and 2 and offer the following comments.
1) Clearly, they like to build gears. There are many gears and clutches in this Rube-Goldberg arrangement. But then the speaker is a power-train engineer so that's what she does and probably won't like to admit that she might as well be a buggy whip designer when it comes to EVs.
2) The EV section (motor+inverter+battery) is too wimpy. Therefore, it didn't work efficiently at high speeds. Therefore, they used the tool they really wanted to use (ICE) and connected the ICE to the wheels, trying to prove that it is best. A larger motor would be plenty efficient at high speeds but that clearly isn't want they wanted to prove.
Notice how carefully the engineers choose their words when they are trying to spout the party line to explain things.
More when I have time to listen to part 3.

· Anonymous (not verified) · 7 years ago

ex-EV1 driver:

It appears you allege a conspiracy of all engineers, technicians, marketing people, and suppliers who would have access to this. Do you have supporting technical information upon which to base your statements?

Tesla tried to use a 2-speed transmission to improve efficiency but removed it due to durability issues (or so I have read in the press). Why is it so difficult to believe that GM has tried to apply the same optimization to this vehicle?

Much Appreciated.

· · 7 years ago

It's not conspiracy, it's engineering. Granted, I can't prove the motivations but they are not exploiting what an electric motor can do while throwing in nearly all parts of a traditional ICE kit that I allege are not important technically. We can draw our own conclusions as to the motivations. I'll offer that they do conveniently employ various folks in important parts of an ICE car company that would otherwise not have a role in a world of electric vehicles .
Tesla actually considered using a 2-speed transmission in order to get low speed torque and high top-end speed. They are actually very open about exactly what they did, how they did it, and what the performance is (http://www.teslamotors.com/blog/roadster-efficiency-and-range and http://www.teslamotors.com/blog/roadster-efficiency-and-range)
The 2-speed transmission was originally a risk reduction approach in fear that the electric motor couldn't handle the low-end torque. In reality, however, the transmission ended up being a mistake and the electric motor proved itself capable of handling the load by itself. (caveat, they did reduce the top-end speed but that was mainly because of the PEM cooling system, not running out of available power)
Look at those torque and efficiency curves for the Tesla's electric motor. The drivetrain efficiency curve (wH/mile -vs- speed) is fairly straight, even at the high end. The main losses at speed are in Aero drag, not the drivetrain. I see no reason to switch away from the electric motor based on Tesla's graphs. Perhaps GM's motor isn't as good as Tesla's? Does that excuse them for solving this problem with the ICE?
I've worked in software-oriented companies that tend to lean towards software to solve their problems and I've worked for chip companies that always tend to lean towards hardware solutions. Why is it surprising that an ICE company retreats to it's comfort zone of ICE and transmission when the road starts to get a bit tough? Not a conspiracy but not acceptable for a company that want's to compete against the likes of Tesla in a world with rising gasoline prices.

· Anonymous (not verified) · 7 years ago

If you read between the lines, you see that engineering this platform as a BEV takes relatively little effort for the drive train...mostly removing the ICE components and adjusting the control circuits. It will be interesting to find out how they hand the other systems without the ICE installed, i.e., PS, AC/Heater, PB, etc. They have the benefit of the ICE to power those systems in a conventional way. In the Nissan Leaf BEV, the 12v lead acid battery is still retained and charged by an inverter which runs the lights, radio, and power for the brakes. These are exciting time in the engineering of automobiles and I look forward to GM's evolution into building long-range BEVs and I consider the Volt an interim car toward that goal.

· · 7 years ago

ex-EV1 driver said in the first comment above: "The EV section (motor+inverter+battery) is too wimpy."

As far as I understand, the Volt does not use the ICE in the electric mode at all, and still goes as fast as 100 mph and has a decent 0-60 time. Does it mean that the EV section is actually strong enough?

· · 7 years ago

Does it mean that the EV section is actually strong enough?"
not if it isn't strong enough to be efficient at high speeds.
This is the difference between torque and power output of an electric motor.
The torque affects the low-speed acceleration while the power affects the efficiency at high speeds. It could have good torque, hence "decent 0-60 time" and go 100 mph. But the electric motor is allegedly not very efficient at high output power.
Remember that Power = Torque X Speed. The torque of an electric motor is simply a function of the amount of current running through it, up to a certain speed. This is limited by the amount of heat that can be carried away from it before doing heat damage and the size of the motor. Generally, the larger the motor, the more torque.
At some speed, however, the Back-EMF starts to limit the amount of torque produced and we see a drop-off in the motor's torque.
This means there is a speed range over which an electric motor can run efficiently. With the Tesla Roadster, it is from about 0 to 7,000 rpms (I can't find the link). That means that above around 7,000 rpms, the motor starts to lose efficiency. If the gearing is high enough, you can be going pretty quickly at that motor speed. Unfortunately the trade off for the high gearing is that the low-end acceleration will be less.
There are 2 ways to get high speed out of an electric motor:
1) put in a gear box to shift to a higher gear ratio at high speeds
2) put in a bigger motor
Note that with an electric car, the bigger motor actually will run more efficiently overall than the smaller one. It also doesn't make the car a lot more expensive since the motor is a small part of the cost of the whole electric car.
Tesla made a mistake originally by trying to put in a gear box but realized that was too expensive when it was so easy to just get more power out of the motor.
I can understand how GM engineers, with their ICE-centric legacy would not see anything wrong with putting in a direct mechanical connection to the engine, rather than putting in a bigger electric motor. After all, all of their cars have direct mechanical connections between the ICE and the wheels.
It would be great if Tesla would publish torque and power plots for their electric motors. Then we could see the exactly what is happening - but that's probably hoping for way too much.

· Jim1961 (not verified) · 7 years ago

Before I comment on this I'd like to say a little about myself. I was wrenching on cars before I was old enough to drive. In high school I took a three-hour-a-day two year long vocational auto mechanics class. I never worked as professional mechanic but I've done everything from brake jobs to complete engine rebuilds. In college I majored in electrical engineering and graduated with honors. Among other things I studied electric motors and generators in great detail. In my engineering career I did some work in the automotive industry and also some other industries. At one point I worked on a project which involved the design of a battery charging circuit. I did research on various types of battery technologies including lead-acid, lithium-ion, and nickel-metal-hydride. I'm not trying to brag about my accomplishments but I'd like people to know this is an area in which I have some knowledge. I'd like to make three points.

1. The whole GM-killed-the-electric-car-as-part-of-a-conspiracy meme is laughable. The EV-1 was a great design. GM put more effort into the EV-1 than all other car companies combined at the time. There were several reasons why the EV-1 was not successful and forgive me making this into a long post but I feel I must go into detail. The only battery technology available at the time which was economically feasible was lead-acid batteries. Lead-acid batteries are heavy. The battery pack in the EV-1 weighed 1200 lbs. To make up for the weight of the batteries GM constructed the EV-1 mostly of aluminum. This added much cost to the vehicle. Another way to reduce weight was to make it a two-passenger car. So the car could only carry two people, it had limited range, and it was expensive. At the time gasoline was really, really cheap and very few people wanted to buy an EV-1. It was a money loser plain and simple. The producer of the documentary "who killed the electric car" does not have a clue that the average Joe like me can't afford to purchase such and expensive car when gasoline was dirt cheap.

2. The Chevy Volt power train is absolutely brilliant. I feel sorry for anyone who does not understand how a planetary gear set works and can't appreciate the genius of the design.

3. I suspect the people who are the most critical are the ones who have never designed or built anything of any complexity. I'd be willing to bet most of the Volt critics could not even do something as simple as a brake job.

· Jim1961 (not verified) · 7 years ago

I understand now why GM says there is no direct mechanical link between the ICE and the wheels. The way the planetary gears are used it's equivalent to using the ICE to turn the body (not the shaft) of the electric motor. Imagine a cordless electric screwdriver. Now imagine you twist the body of the screwdriver while the motor in the screwdriver is also turning. I think it's a clever way to combine an ICE and an electric motor. Not only does the ICE effectively turn the body of the traction motor but in "mode 2" the smaller electric motor also effectively spins the body of the main electric motor. Instead of being harshly critical of the engineers I believe they deserve admiration for doing something innovative for the sake of improved efficiency.

· · 7 years ago

ex-EV1 driver, thanks a lot for the detailed explanation.

· Jim1961 (not verified) · 7 years ago

In another post it was mentioned that the Volt drivetrain looks a lot like the Toyota Hybrid Synergy Drive. I had always been curious about how the Toyota HSD worked. I was also curious if there might be some patent infringement issues for GM. So I finally googled it and found the wikipedia.page for Toyota Synergy Drive. The Toyota HSD is just as interesting as the Volt drivetrain but different so there doesn't seem to be any patent infringement problems. I must be a hopeless techno-geek because these planetary gearset "transmissions" combining ICEs and electric motor/generators totally fascinate me. I'm glad I found this website. Everyone here seems to be very knowledgeable and passionate about green technology. I look forward to reading more articles and posts here.

· Anonymous (not verified) · 7 years ago

To start with, thanks for these videos. As an engineer, I love to see the details.

I just wish the videos were of a higher quality. Can't you zoom out so we can see all 4 edges of the slides? Panning around the slides is awful. And please don't pan over to an unlit presenter that we can barely see.

The presenters (this and the battery one) are not that great either. Even if your primary job is real engineering, you should be able to give a smooth, well-spoken presentation. I'm not sure why they are so unsure and unpracticed.

Still, thanks very much for the cool info!

· · 7 years ago

Anonymous, I really wish you would at least put in some kind of pseudonym so I don't have to keep answering these responses to "anonymous." :) So you want better video, eh? I'm a one man show who's mostly devoted to writing. I've got a pocket video camera that I keep basically for when something comes up for which words just won't suffice. The screen was huge and I was sitting up front for an unobstructed view. So I choose the situation that had he least amount of trade-offs. I honestly feel that I did the best with what I had. This is some of the only footage of this out there and they weren't allowing professional videotaping of it, so I feel lucky to have even gotten this. I hope that helps you and others to view it in the context of the bigger picture.

· Kirk_Lucky (not verified) · 7 years ago

Nick Chambers - thank you for capturing this and presenting it. I agree with Anonymous #whatever that the panning was a bit too much - but considering the situation, I think you did a good job.

I would have liked to have heard some comparisons from GM on tradeoffs between configurations - in real numbers, not just better or worse. I have always heard that an ICE could be made much more efficient if it ran at a fixed RPM. I wonder what the comparison of efficiencies would between a fixed RPM ICS just charging the battery when needed, and the Volt approach with its combined mortor extended range driving mode. This efficiency comparison should also include weight considerations.

I hope GM explains this more fully to the technical community. The tradeoffs between various configurations is probably where GM applied its best and brightest engineers, and those stories could really sell the concept to the technical community. Though the technical community is not normally considered part a traditional marketing effort, if the technical community beleived that this is a great solution, there would be a powerful voice and grass roots marketing effort behind the Volt.

· · 4 years ago

The video links are down !?

· · 4 years ago

Also, the audio in this page, "Exclusive: Chevrolet Volt Chief Engineer Explains Volt Drivetrain, Says "Volt is an Electric Vehicle"" , the audio interview is down.

· · 3 years ago

I've driven my Volt over 14,000 miles of hard city driving here in Pittsburgh. Potholes , -16F in winter, Hills and more hills, stop sign every 100' it seems like.
Bottom line... it's costing me 3cents per mile for gas+elec+maintenace. I have a wattmeter on the charger which tells me exactly how much electricity I'm paying for... which is about the same as one of my refrigerators.. about $20 per month... for my 19mpg city Buick I was spending $120+ per month.
I've only used 17.9gallons of gas and changed the oil once in 20 months.... saving over 60 trips to the gas station.. and at least 4 oil changes. The acceleration is better than any V8 I've ever driven and I do like my V8's. This car does everything totally effortlessly. No ICE comes close to the smooth quiet acceleration of this Chevy Volt.
273lbs of torque any speed any time.

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