Comments on: Chat Live with Andrew Farah, Chevy Volt Chief Engineer Right Here: 4PM EDT

By: Rick Hightower

Rick Hightower — Tue, 18 Aug 2009 03:12:17 +0000

Hey all, this all fascinating, and maybe even practical. But all I see here (in the Volt) is lithium ion batteries. If you recall Porsche, (yes that Porsche) designed a car called the Lohner-Porsche very nearly 100 years ago that used electric motors at both front wheels and an on-board generator to keep the batteries charged. He later added motore=s to the rear wheels for 4 wheel drive! He even had moderate racing success withe this car. The decline of electrics due to the limitations of batteries led him to copy Hans Ledwinka’s masterful rear drive Tatra to develope the volkswagen, Don’t be so busy looking forward that you forget to look back. How does burning fuel to run a generator to feed batteries increase the efficiency of the vehicle? perpetual motion? I see technology in the Prius, but what does the Volt have besides the ability to dance among the tallies and produce drastic “mileage” figures?

By: kaiyum

kaiyum — Tue, 30 Jun 2009 02:10:38 +0000

hi i am kaiyum from bd

By: Cab Driver

Cab Driver — Sun, 28 Jun 2009 06:14:38 +0000

Dave, I agree with you that we’re just making educated guesses. The housing which contains the generator also contains the traction motor. The 2 sets of 3 orange high voltage cables are all that we see between the Power Electronics Module and the Motors housing. If all 6 were used for the traction motor that would leave none for the generator. That doesn’t seem right to me, but, as you say, it’s all guessing.

If you look at this photo from AutoblogGreen’s coverage of the battery lab opening you can see all the connectors on the nose of the battery pack:

http://www.autobloggreen.com/photos/opening-of-the-new-gm-battery-lab/2069279/

In particular, the 2 orange rectangular connectors at the top are for the high voltage cables to the PEM and the charger. You can see that there are 2 contacts in each of these connectors. Presumably the 2 contacts are for the signal and return. All this is just to support the guess that the two sets of three orange cables between the PEM and Motors housing also have a signal and a return in each cable. I don’t know that, but it would explain how just one cable is provide for each of the 3 phases for the generator and the traction motor.

Time will tell how all this really works, but it is fun to try to puzzle it out from limited info. Thanks for sharing in the process!

Here’s a side note to that battery photo and Herm’s posting above “The Volt has a 400VDC power bus, this is connected to the battery.” There is a label shown in the photo which reads “360V”. I haven’t seen any pronouncement by GM of what the pack voltage actually is. Do you or Herm (or any other poster) have a clue what the pack voltage is?

By: koz

koz — Sat, 27 Jun 2009 13:07:32 +0000

Your point is well made and a glorified golf cart or ultra low Cd design like Aptera would have been too niche and too compromised IMO. I do believe GM mis-interpreted the public in assuming that the Volt HAD to be more mainstream to project a Green halo. While I am ecStatik the Volt will be built in any form, I do believe they would have been better served to do a Converj-like or EREV Camarro first. The Volt is mainstream in every non-EREV aspect, except cost. The current state of the tech just fits the higher performing, higher end market better. Mainstream Volt for gen 2 would have been perfect.

Regardless, I have been and will continue to strongly support GM in it’s Volt development.

WJGTVWOTR! Now let’s get them on the showroom floor.

NPNS! Start your own stimulus program, BUY NORTH AMERICAN!

By: koz

koz — Sat, 27 Jun 2009 12:10:44 +0000

Very clear, concise description but I disagree about the design complexity. I think the control software and algorithms to take best advantage of average power efficiencies while meeting other design constraints (customer experience, battery longevity, etc) is one biggest engineering challenges of the Volt.

By: Dave G

Dave G — Sat, 27 Jun 2009 10:51:12 +0000

The 150hp induction electric motor has 3 coils in the stator. Each coil has 2 electrical connections. So my guess is that’s what the 6 wires are for.

I guess you could tie one end of each coil to a common ground, but that might not give the motor controller the same amount of control/feedback as separate connections.

But we are all just making educated guesses here, so I could very well be wrong on this. The bottom line is that GM has provided very few details on the the generator, except that it generates 53kw max.

By: Cab Driver

Cab Driver — Fri, 26 Jun 2009 20:29:52 +0000

DaveG and Herm, you guys make a good point about the lack of DC / DC converters in conventional cars so I’ll bow to your wisdom that the rectified voltage of the generator is compatible with the battery.

I also agree that in conventional cars the rectifier diodes are mounted internal to the generator housing and the output of the generator assembly is DC. However, I ask you to check out this photo of the Volt power electronics module and motor housing:

http://ftp.wieck.com/2009/GMC200901/GMC2009011084015_PV.jpg

It clearly shows that there are two sets of THREE orange high voltage cables connecting the PEM to the generator/traction motor/differential housing (one set for the generator plus another set for the traction motor). I think the only reasonable conclusion is that GM chose to put the 54kw rectifier in the PEM, presumably because of space and/or cooling considerations.

I could be wrong, but the photo seems inconsistent with the generator having the usual integrated rectifier. What do you guys think?

By: Monroe

Monroe — Fri, 26 Jun 2009 18:38:46 +0000

I’m quite sure that with a peak power of 110 kW and a top speed of 100 mph, you will have no problem passing on a highway. I heard that it only takes around 20 kW to maintain a constant highway speed.

By: Monroe

Monroe — Fri, 26 Jun 2009 18:36:54 +0000

Getting stuck in traffic is not actually a problem with EVs, because there is no idling. You don’t waste any fuel waiting in line, except possibly if you do “stop and go” rapid acceleration.

By: Herm

Herm — Fri, 26 Jun 2009 18:15:58 +0000

GM has not confirmed too many details.. I would assume the generator would need its own controller to operate at maximum efficiency at different RPM levels, but that is only an assumption since 53kw controllers are expensive. Also an asumption is that the generator is brushless.

Perhaps there is a second motor on the generator shaft, just for starting the ICE.