Volt Transmission? [Archive] - GM-Volt: Chevy Volt Forum

WopOnTour

09-11-2008, 10:59 PM

How bout this?

2009 2 Mode FWD Hybrid Transmission ( MK3 )
● New Applications: Saturn Vue
● All-new Transmission Designed For Front Wheel Drive
● Hybrid Two-Mode Design
● Electrically Variable Transmission With Two Integral Electric Motors
● Matched To 3.6L LCS engine V6
● Engine-Off Operations
● Fuel Efficiency Dramatically Improved
● Towing Capability Maintained
● Increased Performance

Full descriptions of new or changed features
NEW APPLICATION: Saturn VUE
The 2-Mode transmission’s case size is nearly the same as the GM 6-speed front wheel drive transmission, minimizing the impact to vehicle packaging.

ALL-NEW DESIGN FOR FRONT WHEEL DRIVE
The 2-Mode Hybrid Transmission contains two electric motors, 2 planetary gear sets, and 5 wet-plate clutches (including mechanical damper). The hybrid transmission can operate in multiple modes including propelling the vehicle electrically with the combustion engine off. Two continuous ratio modes of operation are attained with the electric motors, one with the combustion engine supplying torque, and the other with an electric motor supplying torque. Since the continuous ratio ability is attained with one of the electric motors, these modes are described as Electrically Variable Transmission modes or “EVT” modes. Three 300 volt A/C cables are connected to each of the two motors, these cables attach to the transmission housing via a rigid conduit around the transmission and are connected to an inverter which drives the motors.

Four fixed ratios of 3.24:1, 1.88:1, 1.0:1 and 0.62:1 may be chosen for balancing performance and fuel economy. The fixed ratios also let the transmission save battery power that would otherwise be used to control range of the variable ratios to keep the engine in its optimal rev range. Fixed ratios also allow overdrive, for faster overall total speed of the vehicle. Fixed gear changes are accomplished with clutch-to-clutch control, where an oncoming clutch is engaged and an “offgoing” clutch is released in a precise manner to achieve the ratio change.

MATCHED TO 3.6L V6 LCS
The two-mode hybrid is mated to an optimized direct injection gasoline engine, which takes advantage of higher compression ratio enabled by direct injection technology as well as optimized late intake valve closing (LIVC) using dual independent variable valve timing (VVT) to reduce pumping losses.

ENGINE OFF OPERATION
In typical operation, an acceleration will be initiated with the engine off and utilize only electrical power. As the acceleration continues, the electric motors will simultaneously propel the vehicle and start the engine. With the engine running, the control system will blend the electrical energy with the engine energy operating in the most efficient range to maximize fuel economy.

In a 2-mode system, one electric motor controls the speed ratio using the sun gear of a planetary gearset as the input from the gasoline combustion engine and a second motor generates electricity to power the first motor, or to supply torque to the output shaft. The hybrid design therefore has two power sources, the gasoline/ethanol combustion engine and the electric motor, and either can supply torque independently to the output shaft and final drive.

An internally mounted oil pump supplies oil pressure for the hydraulic clutches, and for cooling the electric motors with the combustion engine running or turned off.

TOWING CAPABILITY MAINTAINED
Under higher load drive cycles the control system will directly clutch the engine through the transmission, effectively locking the first electric motor between its input and output, enabling full V6 engine torque with electric motor assist torque.

Overview
Model year 2008 interim is the debut of the two-mode M99 electrically variable hybrid transmission. It was developed from the years of experience GM has gained from designing large passenger buses with single-mode hybrid drive systems.

Electrically Variable Transmissions (EVT) have been used since the 1930s, and are most prevalent in locomotives. These are one-mode operations, with the combustion engine driving a generator which powers electric motors at the wheels. This requires very large electric motors to enable variable speed ranges.

GM began building passenger buses with two-mode EVTs, the first mode using an input-split EVT mode and the second being a compound-split EVT mode and production began in 2003. The two-mode systems reduce the size of the electric motors necessary, allowing them to be used in smaller vehicles.

In addition, to optimize the size of the electric motors for a private passenger vehicle, the 2 Mode FWD Hybrid Transmission uses four fixed ratios, added with the addition of two additional planetary gearsets. The fixed ratios in addition to the EVT continuously variable ratios were developed for the full-size SUVs to improve fuel efficiency and meet all requirements for acceleration, towing, top speed, driveline refinement, and emissions.

Locking the first motor keeps the output shaft operating at the same speed as the input shaft, which is called “input-split” mode. This is a single-mode system such as is used on the commercial vehicles. For passenger vehicles it can have high fuel efficiency or high power, but not both. That is why the two-mode, or “compound-split”, system with two electric motors was developed for the Saturn VUE.

The clutches in the 2-mode EVT are wet hydraulic clutches, similar to those in a conventional automatic transmission, and require a pump to activate.

The fixed ratios are operated by synchronous “clutch-on, clutch-off” timing, which allows smooth shift events between modes of fixed and variable ratio operation. The fixed ratios were added to the EVT design to allow superior towing capability without requiring larger electric motors. This required two additional clutches and two additional planetary gearsets, which with the electric motors can be packaged inside a case that fits in the existing platform package of the Saturn Vue application.

In layman’s terms, the 2-Mode EVT can be thought of like two transmissions connected inline: One transmission is continuously variable by way of using an electric motor to vary ratios, and the other is a conventional stepped-ratio transmission. The fixed gears take over when power demand from the combustion engine is higher than the electric motor’s ability to maintain a ratio.

The fixed gears are used in high-load situations. When the fixed gears are in use, the electric motors then can generate electricity rather than consume it, or they can also be used to add torque to the output shaft for better performance. Coasting and braking also allow the electric motors to generate electricity.

Low maintenance
DEXRON® VI is used as a lubricant and to cool the electric motors. For normal use there is no fluid change scheduled. DEXRON® VI was developed to have a more consistent viscosity profile; a more consistent shift performance in extreme conditions; and less degradation over time. Internal GM tests have demonstrated DEXRON® VI delivers more than twice the durability and stability in friction tests compared to existing fluids.

The 2009 2 Mode FWD Hybrid Transmission (MK3) is produced in Ramos, Mexico.

PatrickfromMd

09-19-2008, 04:32 PM

I thought that due to the performance characteristics of the electric motor versus a gasoline engine the Volt wouldn't need a conventional multi-gear or continuously variable transmission. That makes the design simpler, lighter and less costly to build.
.... :D

I had several questions for Bob Lutz during the centennial online blog session. He got to about 3 of them so I consider myself lucky. On the transmission (my favorite subject)
I have been pursuing more info in this as I believe it’s the last major unknown area of the drive train that can make a noticeable difference on how the car will behave. I was the one that posed this question to Bob as well as several others along the same lines. The fact that he chose to answer this particular version of the question (I had some more longwinded ones as well) plus responding to my follow-on question about Tesla, does lead me to believe this transmission will feature some sort of torque multiplication via either fixed ratios, or variable. Their challenge will be how to do this with the least amount of geartrain losses and still make the transition to direct drive smooth given the high torque output of the motor. In his later response where he confirmed that Tesla would be the one inspired this time,… I also think this supports gear multiplication because Tesla originally designed a two speed transmission of apx 1.6/1 for its first gear, but had to abandoned that idea due to design and manufacturing issues. Some people claim an electric does not need a transmission which I can agree to, but the math is clear, some gear multiplication (even on a motor with a totally linier torque) curve is advantageous.
I think if they choose a 2 speed transmission, that 1.7/1 would be ideal.
Let me illustrate the point another way, a typical 4 cyl engine with a hypothetical peak of 150 ftlbs torque has a transmission that provides apx 4/1 between its highest and lowest gear. That equates to 600 ftlbs torque to the differential in 1st gear. Even off its peak (i.e. gas engines do not have a linear torque curve), the motor still probably makes 100ftlbs which equates to 400 ftlbs to the diff in 1st gear. If the Volt is to have decent off the line get up and go with its strong apx 250 ft/lbs motor, a 1.7/1 will give it 425 ftlbs to the Diff and probably be able to stay in that gear up to 75mph, where as the traditional 5 speed 4 cyl car world have to shift out by 35 mph. These numbers are not suggested to be what the volt will be, but only to illustrate the point. Another thing to consider is that a little modest gearing will allow the motor to spin up with less current draw due to the torque multiplication, and therefore less taxing of the battery. To achieve the range GM wants on the EPA test profiles (I mean they cannot state range based upon a steady state speed, they will have to adopt the test profiles the EPA uses, and that means a lot of varied driving), they will likely want to take advantage of mechanical torque multiplication through fixed or variable. gearing. (I’m willing to bet that you stant to pick up 3-6 miles of range if the transmission is efficient enough as opposed to a direct drive.

I doubt Bob would have used the term "top secret" and something no one has done before had they just adopted a direct drive. That’s really more of a gearbox, than a transmission. I think they have come up with something really cool. I cant wait to see it.

DonC

09-19-2008, 04:45 PM

I doubt Bob would have used the term "top secret" and something no one has done before had they just adopted a direct drive. That’s really more of a gearbox, than a transmission. I think they have come up with something really cool. I cant wait to see it.
Dynamically changing the motor windings?

Do you have a transcript of the chat? Usually they post it pretty quickly but it's still not up.

PatrickfromMd

09-19-2008, 05:36 PM

Dynamically changing the motor windings?

Do you have a transcript of the chat? Usually they post it pretty quickly but it's still not up.

I screwed up by not copying. I went over to the next chat (on the interior) and lost the ability to cut and paste. I have not found them on the GM Next site.
For what its worth, below are all the questions I sent pasted up for Bob to Answer. The 3 in bold he answered for everyone.

1) I have heard that some of your inspiration for industry being ready to tackle a car like to volt, came from Tesla.
Is GM able to inspire Tesla with was it was unable to design and manufacture,. Namely a world class transmission that is suited for the special characteristics of an 100% electrically propelled car? As you probably know, Tesla had to abandon their efforts for a two speed transmission and incorporate a single speed gearbox due to unforeseen manufacturing and reliability difficulties, and try and make up for the performance penalty elsewhere. Its well know GM and its partners have the ability to develop and manufacture such a transmission that can tap the full potential of an electric car. What did you build us for the Volt?

2) Any plans to modularize future versions of the volt or other variants of the Eflex family? I mean like the ability to slide in additional battery modules to further extend range, or swap out extender modules for say diesel, natural gas, hydrogen, or fuel cell. (Or if you are a base thumping stereo head, has there been any thought given to aux accessory battery modules so the cars range is not hit by the annoying thumping of those subwoofers you hear at stoplights) Maybe even a weel hub addon to create an on demand AWD option (and an extra kick in the pants when needed)

3 )Knowing the liner nature of the electric motors toque curve does not require gears like a traditional car, but what sort of transmission was developed to optimize the full potential of the Volt?

4) Regarding the engine options of the Camaro, has any thought been given to a 4.8 liter direct injection variant of the Camaros/ Cadillac 3.6 motor? Its seems to me that that would be a more technically refined alternative to the LS3 V8

5) I’m sure your new top secret transmission will be an inspiration for Tesla who was unable to bring one to market. Without giving away all the secrets, does it provide torque multiplication beyond a 1/1 gearbox (like tesla had to fall back to)?

6) With most the part already built in, can I take my volt camping and power my campsite? (or perhaps some items in my house the next time one of these tropical storms roars through)

7) How about a V8 version of that 3.6 liter direct injection motor that’s in the base Camano. Are there ideas to add 2 more cylinders for a estimated 400hp and 4.8 liters? Add cylinder deactivation, and it would surly get far better mileage than the LS3 V8

If anyone finds a transcript, please post.
I reacall his answer to my #5 to be something line I certainly agree with the 1st part of yoru statement.

Regarding his answer to #6, he said yes, you would be able to power your camp site and home devices from the volt, but it would deplete battery charge.

PatrickfromMd

09-19-2008, 05:50 PM

Dynamically changing the motor windings?

No, I’m thinking mechanically changing the gear drive ratio, like in a conventional transmission, but perhaps by unconventional means.
Motor windings are fixed, perhaps you are thinking about energizing different sets of windings depending if you want low speed torque or high speed. If you are talking DC motors you can change the motor timing to do this and the effect is noticeable (but I have no idea how it works in A/C motors).

PatrickfromMd

09-19-2008, 05:56 PM

Dynamically changing the motor windings?

Do you have a transcript of the chat? Usually they post it pretty quickly but it's still not up.

I screwed up by not copying it before I went over to the next chat (on the interior) and lost the ability to cut and paste. I have not been able to find it on the GM Next site.
For what its worth, below are all the questions I sent pasted up for Bob to Answer. The 3 in bold he answered for everyone.

1) I have heard that some of your inspiration for industry being ready to tackle a car like to volt, came from Tesla.
Is GM able to inspire Tesla with was it was unable to design and manufacture,. Namely a world class transmission that is suited for the special characteristics of an 100% electrically propelled car? As you probably know, Tesla had to abandon their efforts for a two speed transmission and incorporate a single speed gearbox due to unforeseen manufacturing and reliability difficulties, and try and make up for the performance penalty elsewhere. Its well know GM and its partners have the ability to develop and manufacture such a transmission that can tap the full potential of an electric car. What did you build us for the Volt?

2) Any plans to modularize future versions of the volt or other variants of the Eflex family? I mean like the ability to slide in additional battery modules to further extend range, or swap out extender modules for say diesel, natural gas, hydrogen, or fuel cell. (Or if you are a base thumping stereo head, has there been any thought given to aux accessory battery modules so the cars range is not hit by the annoying thumping of those subwoofers you hear at stoplights) Maybe even a weel hub addon to create an on demand AWD option (and an extra kick in the pants when needed)

3 )Knowing the liner nature of the electric motors toque curve does not require gears like a traditional car, but what sort of transmission was developed to optimize the full potential of the Volt?

4) Regarding the engine options of the Camaro, has any thought been given to a 4.8 liter direct injection variant of the Camaros/ Cadillac 3.6 motor? Its seems to me that that would be a more technically refined alternative to the LS3 V8

5) I’m sure your new top secret transmission will be an inspiration for Tesla who was unable to bring one to market. Without giving away all the secrets, does it provide torque multiplication beyond a 1/1 gearbox (like tesla had to fall back to)?

6) With most the part already built in, can I take my volt camping and power my campsite? (or perhaps some items in my house the next time one of these tropical storms roars through)

7) How about a V8 version of that 3.6 liter direct injection motor that’s in the base Camano. Are there ideas to add 2 more cylinders for a estimated 400hp and 4.8 liters? Add cylinder deactivation, and it would surly get far better mileage than the LS3 V8

If anyone finds a transcript, please post.
I reacall his answer to my #5 to be something line I certainly agree with the 1st part of yoru statement.

Regarding his answer to #6, he said yes, you would be able to power your camp site and home devices from the volt, but it would deplete battery charge.

DonC

09-19-2008, 11:17 PM

WopOnTour

09-19-2008, 11:42 PM

No, I’m thinking mechanically changing the gear drive ratio, like in a conventional transmission, but perhaps by unconventional means.
Motor windings are fixed, perhaps you are thinking about energizing different sets of windings depending if you want low speed torque or high speed. If you are talking DC motors you can change the motor timing to do this and the effect is noticeable (but I have no idea how it works in A/C motors).
I can't see changing a gear drive ratio as being something no other car manufacturer has thought of. I'd think something with the windings because electric motors for EVs is a very new field and there are probably a lot of things that haven't been thought of yet. So I'm thinking the windings.FYI- Varying the speeds of the electric motors in combination with planetary gearsets and clutches form the basis of pretty much ALL EVTs- Electronically Variable (Ratio) Transmissions. From the simplest configuration (like the Prius) that uses a single gearset in an "input split" configuration to more complex transmissions such as the GM 2-mode transmissions which add variable ratio "compound split" capability as well as the potential availability of fixed mechanical gear states.
HTH
WopOnTour

igotzzoom

09-20-2008, 12:00 AM

PatrickfromMd

09-20-2008, 08:38 AM

I believe the Volt has a single-ratio transmission. As stated, electric motors can "rev" up to about 12,000 rpm or more. If GM wanted to go with a powerful enough electric motor, they could make the gear ratio tall enough to allow for a higher top speed than 100 mph.

But considering most current pickups are governed to about 100 or less, I don't think it's that big a deal. To me, 85 is "fast." I rarely, rarely go faster than that.

I keep hearing "under 9 seconds" for 0-60. I personally hope it's closer to 8 flat, but even 9-ish is OK.

No denying that 12,000 RPMs sure is a wide powerband,.....Well, we both have out logic backing what we think GM will do. I’ll stick with mine that says they WILL use some form of gearing (mechanical of varable ratio) at lower speeds. Perhaps if the top speed were 60 or so, I might lean to a single sped setup, but for a car with 100 mph, I’ll go on record that they will have at least 1.5 – 2.0/1 in the lower range. If they spent so much time in the wind tunnel trying to coax every bit of range out of the car, I bet they use a transmission to fine tune its ability to run the EPA courses with the least amount of current draw for a given driving characteristic. A brisk acceleration to say 0- 40 should be done with less current draw then using some gearing , then direct drive. (no real fact to back this up just my dwindeling understanding of physics and Engineering,.. of and yes, playing with electric R/C race cars when in college) I bet 0-60 is at least a second better with a tranmission and the same overall power (kw/h) Just my opinion.

Rooster

09-20-2008, 12:24 PM

No denying that 12,000 RPMs sure is a wide powerband,.....Well, we both have out logic backing what we think GM will do. I’ll stick with mine that says they WILL use some form of gearing (mechanical of varable ratio) at lower speeds. Perhaps if the top speed were 60 or so, I might lean to a single sped setup, but for a car with 100 mph, I’ll go on record that they will have at least 1.5 – 2.0/1 in the lower range. If they spent so much time in the wind tunnel trying to coax every bit of range out of the car, I bet they use a transmission to fine tune its ability to run the EPA courses with the least amount of current draw for a given driving characteristic. A brisk acceleration to say 0- 40 should be done with less current draw then using some gearing , then direct drive. (no real fact to back this up just my dwindeling understanding of physics and Engineering,.. of and yes, playing with electric R/C race cars when in college) I bet 0-60 is at least a second better with a tranmission and the same overall power (kw/h) Just my opinion.

Patrick,

I agree with you. Lutz has made several off the cuff comments about gearing that has caused much debate (it’s buried somewhere in forums) as to what he meant. It also makes sense that GM would want to take advantage of what they have in their 2-mode EVT if it could be applied advantageously between the Electric motor and drive wheels.

Tom created a fairly detailed model of the Volt drive train to estimate the vehicle’s range at highway speeds.

http://www.gm-volt.com/forum/showthread.php?t=719
http://www.gm-volt.com/forum/showthread.php?t=454&page=2 (http://www.gm-volt.com/forum/showthread.php?t=454&page=2)

He has run his model of the Volt through the EPA drive cycles, and it predicts around a 41 mile range in the city cycle, but only 32-34 mile range in the EPA highway cycle using the new, more aggressive driving schedules. I understand his model assumes a single fixed drive ratio. It would be very interesting if he could model these cycles using 3-4 gear ratios. I too agree that it should increase the range, by reducing the amount of current required to quickly reach and maintain a desired speed.

DaV8or

09-20-2008, 12:26 PM

I have advocated a two speed transmission for the Volt for a long time. When I was at Volt Nation, I asked one of the engineers about a transmission for the Volt, and his response was, "Why would you want one?" We then discussed the Tesla and he admitted that they were doing that for performance reasons. That is my answer. That is why I want one. Better 0-60 and better hill climbing. The Volt doesn't need a transmission, but should it have one?

The claim about the Tesla transmission is that it couldn't handle the 10k+ RPMs at high speed and would break down. Never mind that race cars and race motorcycles run at those RPMs with multispeed transmissions. I get that this is a car that has to go 150,000 miles with not tranny failure. So here's my proposal, put a reduction gear ahead of the transmission to get the RPMs down before going into the transmission. We know that a simple reduction gear is possible because that's exactly one of the functions of the differential and the Volt will have one of those.

The engineers told me flat out to my face, that the Volt will have no transmission. However, I still hold out for the dream of an E-Flex variant that is built for performance in the future. I believe that this future car will have a transmission.

Mohsen

09-20-2008, 07:25 PM

1- There is no transmission (anymore) on the Tesla (i.e. it is single speed drivetrain). This is because the AC induction motor has extremely high torque when needed.

2- Same with Volt. No transmission needed and it has none.

3- Transmission mechanics and transmission cooling people -- go find another job. The customer rules.

WopOnTour

09-20-2008, 08:32 PM

MikeKO

09-20-2008, 09:00 PM

WopOnTour

09-20-2008, 10:11 PM

I'm not nit picking here, but am I correct in assuming you are referring to the electric motor being bolted to the trans axle?

Assuming the above, how do you know it's a trans axle and not just a differential? This is a question, not a disagreement. Yes of course it has a differential.But it also has final drive gearing and additional planetary gearsets with members meshed (some directly, some through clutching) to the 2 PMSM motors that are also INSIDE the transaxle. (Actually both are on the same centerline as the range extender engine) You can disagree with me if you wish :D
WopOnTour

MikeKO

09-20-2008, 10:41 PM

I have no idea how they've laid some of this stuff out. I know a lot about serial hybrids in general, but not, necessarily, about the Volt. I have many faults but refusing to shut up and listen on subjects I am ignorant of isn't one of them.

I what goes on there documented anywhere I can get to?

Mohsen

09-20-2008, 11:56 PM

You can only lead a horse to water...
I don't know anything about the Tesla but I can tell you the Volt definitely has a transaxle.
In fact the range extender engine is bolted to it in such manner that it "looks" very similar to the 2-mode transaxle in my post above. ;)
Although realize it is definately NOT exactly the same internally,but it still allows control of the speeds of the various rotating assemblies though motors speed control and by connecting and disconnecting various planetary members.This permits the extention in the efficiency of the electric motor/s as delivered TQ and output speed can then be controlled throughout a variable ratio.

WopOnTour

Tesla may have a single reduction gear - but CERTAINLY not a transmission changing gears (anymore).

The point is that an AC induction electric motor can produce CONSTANT TORQUE over a huge range of RPM (from almost 0 to thousands). You do NOT need a variable gear ratio, CVT or transmission.

Now if the Volt has a transmission, transaxle or not, it has not been reported anywhere.

Mohsen

09-21-2008, 12:02 AM

Yes of course it has a differential. But it also has final drive gearing and additional planetary gearsets with members meshed (some directly, some through clutching) to the 2 PMSM motors that are also INSIDE the transaxle. (Actually both are on the same centerline as the range extender engine) You can disagree with me if you wish :D
WopOnTour

Where has this been reported - has GM announced this transmission? And is this a semi-automatic without a torque convertor?

If so, heavens save us, as GM aint smart enough to figure a semi-automatic. I hope what you say is not the case, especially that if they choose the right elec. motor, they can do away with the transmission for most of us.

BTW what is PMSM motor?

zeksteve

09-21-2008, 12:39 AM

It should have a 1 speed gear box with a ratio of about 10:1

Mohsen

09-21-2008, 01:00 AM

It should have a 1 speed gear box with a ratio of about 10:1

That is what I am thinking. Why would they need an automatic or semi-automatic transmission when there is sufficient torque in the electric motor?

Unless WapOnTour can produce some links, I do not believe there is a transmission - just a simple gear reduction.

If there were a transmission, the acceleration times would be much higher than the official numbers given.

WopOnTour

09-21-2008, 02:04 AM

Where has this been reported - has GM announced this transmission? And is this a semi-automatic without a torque convertor?

If so, heavens save us, as GM aint smart enough to figure a semi-automatic. I hope what you say is not the case, especially that if they choose the right elec. motor, they can do away with the transmission for most of us.

BTW what is PMSM motor?PMSM stands for Permanent Magnet Syncronous Machine.
GM isn't smart enough? Does that suggest you or someone else is?
Links?, like I said before it's OK if you disagree!
WopOnTour

Mohsen

09-21-2008, 02:28 AM

GM isn't smart enough? Does that suggest you or someone else is?
Links?, like I said before it's OK if you disagree!
WopOnTour

I am not disagreeing for its sake. I assume you know something that I don't. So I am happy to learn. But without backup, I know you don't expect others to take you seriously.

If GM was smart enough, it would not be going begging for the taxpayer's purse. Looks like you work for them because of your visceral reaction and personal attack retort (always a sign of defeat in debates).

So if you work for GM, then you must know something, and therefore you are probably right.

If so, what a tragedy for GM having to employ a whole slew of old fart gearheads to build another transmission that will fail or have to be serviced, simply to keep them busybodies who have driven it into the ground around.

Tesla, with much higher performance, does not have a transmission (just a gear reduction) and GM was not smart enough to figure it out -- was it?

WopOnTour

09-21-2008, 03:04 AM

Tesla? Oh please.
Talk about "vaporware"! A company building a few expensive electric "kit-cars" doesnt account for much.
Good luck with that.
WOT

Mohsen

09-21-2008, 03:54 AM

Tesla? Oh please.
Talk about "vaporware"! (building a few electric "kit-cars" doesnt account for much)
Good luck with that.
WOT

Tesla is the one with dozens on the streets with 500 orders on book and its price is going up.

GM has none on the streets and nobody is allowed to look inside it and they dont want you to know about the battery. And it will become a 2012.

WHO exactly is vaporwear???

Besides the Nissan and the Mitsubishi will whip GM's ass in EV and the busybodies will probably go back to hydrogen??? (wink wink)

WopOnTour

09-21-2008, 04:04 AM

Tesla is the one with dozens on the streets with 500 orders on book and its price is going up.
GM has none on the streets and nobody is allowed to look inside it and they dont want you to know about the battery. And it will become a 2012.
WHO exactly is vaporwear???You were being serious? Wow
Well I'm not sure 27 delivered units (ALL recalled for transmission issues) contitutes "dozens" but...
By the time Magna International and 26 former employees (over 10% of their entire workforce) get through with them in the courts, I predict they'll be nothing more than a wet-spot on the pavement.
But like I said...
Enjoy! and good luck!
WOT

zeksteve

09-21-2008, 11:21 AM

Neither are vaporware. They both have the unfortunate job of developing a car in the public eye.
This is why companies normally don’t even mention a new model until a few months before its rolled out.

Tesla made the mistake of overstating their goals. They had such a tight timeline allowing no room for mistake. They have parts coming from all over the world which is now the worlds largest assembly line. Batteries from Malaysia frame from England body from Norway. Transmission from Canada.

Their transmission engineer warned them about using a 2 speed tranny if they wanted to make their time line and they ignored him.

If your going to really change things from the norm its usually best to keep it out of public view until its working perfect that way you wont spoil the preconceived notions of what it will be.
Tesla has been screwing up more than GM. They did almost zero chassis development.
The majority of Teslas work is Systems not Structure. Hell they even subcontracted everything out all tesla really is the final assembler. Yes its going to be a great product. I hope the screw ups from the roadster will allow for a much smoother transition into other cars.

GM in my opinion 21 months from a concept which had a golf cart motor and no gas engine with no systems engineering To a running car. You’ll see 10 a week on the roads for the next few months and ever increasing numbers. If they pull this off by late 2010 they will have done the automotive equivalent of the Manhattan project in under 4 years While Tesla is using off the shelf “although highly customized” components . Both cars are great.

DaV8or

09-21-2008, 12:04 PM

Tesla is the one with dozens on the streets with 500 orders on book and its price is going up.

GM has none on the streets and nobody is allowed to look inside it and they dont want you to know about the battery. And it will become a 2012.

WHO exactly is vaporwear???

Besides the Nissan and the Mitsubishi will whip GM's ass in EV and the busybodies will probably go back to hydrogen??? (wink wink)

If GM were building $100k + two seat roadsters for the elite and years after taking people's deposits had only actually produced and delivered two dozen and they only had an order log of 500 and they were going to raise the price... THEY WOULD BE CRUCIFIED IN THE PRESS!! As it stands, Tesla is a joke. I hope they can pull it together, but I think that they will be lucky to even be in business in 2012.

I did a Google search for a fan site or forum like this one for the Mitsubishi Miev and could find nothing dedicated to it. I did the same for the Chevy Volt and four different dedicated sites popped up right away. Which car do you think will be more popular on the American road? As for Nissan, they've got nothing but words at this point.

zeksteve

09-21-2008, 12:49 PM

As for Nissan, they've got nothing but words at this point.

Nissan has adopted the ZAP business model for their EV business

Mohsen

09-21-2008, 02:07 PM

Never underestimate the enemy. Nissan is probably the biggest danger to the Volt. Just remember, Li-Ion batteries are dropping like a rock in price. Before you know it, it will become a pricing game and GM will find itself in the red on the Volt, due to people like Nissan.

An SEV (GM calls it EREV) is even less complex than a motorcycle. Do you think GM can compete in this market? How about in the golfcart market ey? Now imagine half the auto market becoming a golfcart market plus a genset market where the genset is getting smaller and smaller. GM will be history, unless they change their identity. The best they can do is outsource all their manufacturing (just like Tesla) and milk the public with their command of market share. That is all. Unless of course they start becoming entrepreneurial - which they have with the Volt, like a, heavens forbid, Tesla!

PatrickfromMd

09-21-2008, 05:46 PM

Tesla is the one with dozens on the streets with 500 orders on book and its price is going up.

Mohsen, I believe we have some common ground on the Tesla story. I believe they have done a remarkable job for a startup. They will not compete with GM on volume, or designing a vehicle from ground up given that GM is hundreds of times bigger, but they sure made a lot or people sit up and take notice, and Bob Lutz is one of them. Some have suggested they bought a lotus chassis and retrofitted it, but that is not true. Sure they avoided reinventing the wheel and borrowed from some of the best designs available to help them achieve their goal. I understand much more of the chassis is unique then many people give them credit for, though no one argues it was the lotus that they used as the basis, and adapted much of it work in the Tesla.
I do believe however had Tesla had the R&D budget, and the transmission partners GM does, … I personally believe they would have stayed with the original goals to have mechanical gear multiplication for the Tesla. You have to give them credit for Engineering al alternative solution to make up for the performance loss by going to a single speed design.
My hats off to Tesla for embarrassed all those big automakers that presumed it was too far of a reach. At least Bob Lutz and company got a good start, they may come to the game in the 4th quarter. But their coming.

Now on the issue of predicting GMs Trans vs. Gearbox approach.... well, I'll continue to work on converting you hehe :) more tt follow

zeksteve

09-21-2008, 05:53 PM

GM will have more volts on the road by years end than tesla will ever build for their roadster

PatrickfromMd

09-22-2008, 06:36 PM

Letterman’s Top 3 reasons GM will build the volt with a single speed gearbox
3) An extra string section added to your favorite classical tunes: While cruising the freeway in Bobs new Volt the other day, he introduced me to new aspect of Vivaldi on his stereo. What I thought was an extra violin accompaniment that shrilled as a constant high note, Bob later told me was his Volt motor poking along at a modest 7800 RPMs! (in traffic no less)
2) Because GM It outsourced their electric drive assembly to their subsidiary that builds golf carts.
1) So GM can brag about its powerful 120 KW electric motor, (but failing to tell people it only makes that much power between 98 and 100 mph)

A little sarcasm ...

Where has this been reported - has GM announced this transmission? And is this a semi-automatic without a torque convertor?

Mohsen, I had expected GM to post the results of theChat Sept 16 session with Bob Lutz at this link, but so far nothing.
http://www.gmnext.com/Pressroom.aspx

I can say that the following 2 questions where picked up by Bob and responded to them. I’m hoping they will publish the responses.

1) Knowing the liner nature of the electric motors toque curve does not require gears like a traditional car, but what sort of transmission was developed to optimize the full potential of the Volt?

2) I’m sure your new top secret transmission will be an inspiration for Tesla who was unable to bring one to market. Without giving away all the secrets, does it provide torque multiplication beyond a 1/1 gearbox (like tesla had to fall back to)?

I can give you the essence of his response 1) he said it is Top Secret, but that it would do things no one else has done before. 2) Bob replied that he agreed with the 1st part of my question.
I had sent up other questions that were more lengthy in nature that gave comparisons to the Tesla transmission and why GM should have the resources to do what Tesla was unable to do. They were long winded questions, but when I shortened them up and reposted (above) he replied immediately.

Analysis: His responses are not conclusive of an announcement of a transmission, but I interpret them to be 90% the car will have a transmission that will have gear multiplication. Why else would he say its top secret, why else would he say Tesla would be inspired (I’m sure he follows the Tesla ups and downs quite closely, as he’s betting GMs reputation on bringing the concept to market,. and in mass production). Why else would he say it will do things no one else has done? I do not think these statements relate well to a single speed gearbox.

The point is that an AC induction electric motor can produce CONSTANT TORQUE over a huge range of RPM (from almost 0 to thousands). You do NOT need a variable gear ratio, CVT or transmission.

Agree on the constant torque over a huge range. This should reduce the need for a transmission, but not necessarily negate it. With a linier torque curve, peak HP will occur at max RPM (in this case I think people have been using the figure of 12,000 RPMS) this is a simple math formula. One can also deduce that the electric motor will produce nearly twice the HP at 12,000 as it does at 6000 RPMS therefore for max acceleration, the more you can keep your motor where it makes max HP the better you will accelerate (ask any drag racer this one).
In the scenario of a single speed gearbox, one would assume you would gear it so you achieve 12,000 at 100 mph. Therefore it will be only when you approach this speed will the motor be achieving max HP (not an ideal place for a 4 seat grocery getter).

It should have a 1 speed gear box with a ratio of about 10:1
Assuming a gearbox design, logically GM will set it up so that it tops out at an RPM where it makes max HP/KW power or above (if not they probably would not be allowed to use that rating if the motor never sees it) Let’s assume 12,000 RPMS at 100 mph. Simple math will show the motor turning at 7800 at 65mph. I do not have any personal experience with riding in electrics, and I acknowledge that they should be many times smoother than a gas engine, still it would seem to be a bit of a high pitched whine to me (maybe I’m wrong). I just seems more logical that they would allow the motor to drop down to a more moderate RPM, especially just to hold the car at constant speed.

Interested in what I think would be the ideal solution? (I thought so,.. but you will get it anyway :) )
A variable ratio trans that has very little gear train losses. When the driver pushes down on the gas…opps, mean the accelerator pedal, the computer computes the perfect gear ratio to achieve the selected acceleration level optimized to use the least amount of current from the battery. As the car accelerates the computer keeps adjusting the gear ratio to maintain the optimum balance. The selector switch that appears in the interior images of the car might be for selecting computer profiles that emphasize 1) acceleration with the least current draw, or 2) acceleration irrespective of current draw that would probably allow higher RPM of the motor as the car accelerates.
Perhaps if very modest acceleration is being requested from the driver, the computer may hold it in a more direct drive mode, where as if the driver needs to perform a quick pass, the computer will incorporate some gearing to allow the motor achieve more RPMs whereby more total HP/KW is available. It would then dial the gearing out as the driver lifts back up on the accelerator pedal,… perhaps to the point that overdrive is incorporated to lower the electrics RPM it its is just in constant speed sustaining mode.
…Just another opinion from a guy whose interested is what GM will do here… take it for what its worth.

Rooster

09-22-2008, 10:21 PM

Patrick,

I agree with you. Lutz has made several off the cuff comments about gearing that has caused much debate (it’s buried somewhere in forums) as to what he meant. It also makes sense that GM would want to take advantage of what they have in their 2-mode EVT if it could be applied advantageously between the Electric motor and drive wheels.

Tom created a fairly detailed model of the Volt drive train to estimate the vehicle’s range at highway speeds.

http://www.gm-volt.com/forum/showthread.php?t=719
http://www.gm-volt.com/forum/showthread.php?t=454&page=2 (http://www.gm-volt.com/forum/showthread.php?t=454&page=2)

He has run his model of the Volt through the EPA drive cycles, and it predicts around a 41 mile range in the city cycle, but only 32-34 mile range in the EPA highway cycle using the new, more aggressive driving schedules. I understand his model assumes a single fixed drive ratio. It would be very interesting if he could model these cycles using 3-4 gear ratios. I too agree that it should increase the range, by reducing the amount of current required to quickly reach and maintain a desired speed.

Ah, finally found it in the Old Forums -- we had this discussion back in Jan, when Lutz commented that the mules', “0 to 60 mph acceleration will be 60 seconds because the step gear ratios are not setup.”

That comment caused much debate and speculation as to what he meant. You can read the discuss we had at the link below. Based on the EVT information in this post, perhaps the Volt will have variable “step ratios” between the electric motor and drive wheels?

http://gm-volt.com/volt-discussion/?forum=1&topic=289&search=1&value=transmission%251&ret=all

WopOnTour

09-24-2008, 12:23 PM

The transaxle shown in the Volt pictures below (from the GM media site) looks VERY similar to the 2MT70 as used in the 2-Mode VUE (at least on the exterior) as per the details I posted above.
The 6 empty bores you see on top of the case are the entry points for the 3-phase (U-V-W) motor cables from the PIM-Power Inverter Module.(for whatever reason, shown unpopulated) All that would really be required then are larger motors (at least MG2) as compared to the 55kW units sued in the VUE-2M and then revised software to correctly control the transmission using infinitely variable ranges properly matched for the Volt's EV operation. And of course to create the desired charging modes (variable ratio as well?) thru MG1 via the range extending ICE. This trans design also provides positive pressure fed oil cooling directly into galleries within the electric motor stator assemblies.

While simple single speed gearing may seem adequate, it is always a compromise- favoring either low, mid or high speed operation depending on the chosen ratio. Through the use of an EVT the ratios can be more closely matched to driver demand and the terrain creating the most efficient motor speeds. i.e. you will get the best range when you are creating the neccessary torque using as little power (i.e. electrical current leaving the battery) as possible.
I suspect the Volt will have a variant of this transmission. Bob???
JMO
WopOnTour

willdryden

10-03-2008, 02:00 AM

1) So GM can brag about its powerful 120 KW electric motor, (but failing to tell people it only makes that much power between 98 and 100 mph)

A little sarcasm ...

Agree on the constant torque over a huge range. This should reduce the need for a transmission, but not necessarily negate it. With a linier torque curve, peak HP will occur at max RPM (in this case I think people have been using the figure of 12,000 RPMS) this is a simple math formula. One can also deduce that the electric motor will produce nearly twice the HP at 12,000 as it does at 6000 RPMS therefore for max acceleration, the more you can keep your motor where it makes max HP the better you will accelerate (ask any drag racer this one).

Since when did they change the rules on electric motors? Peak torque is produced at motor stall. HP as related to electric motors is the maximum amount of power consumed without burning up the windings in the motor which also occurs at motor stall also known as 0 RPMS.

PatrickfromMd

11-11-2008, 09:47 AM

Since when did they change the rules on electric motors? Peak torque is produced at motor stall. HP as related to electric motors is the maximum amount of power consumed without burning up the windings in the motor which also occurs at motor stall also known as 0 RPMS.

I was referring to the old hot rodders formula that’s based on torque and engine RPM. If the torque is linear across the RPM band (as people are often stating), then the peak horsepower has to be achieved at max RPM. HP = (RPM x Torque)/5252. Now I have since seen some motor toque graphs that shows linear torque across the RPM band, but drops off as it reaches its peak. I would like to see the motor graphs for the Volt Electric Motor

Xzlon

11-11-2008, 11:53 AM

Willdryden
You are right it is a simple math formula. HP at zero RPM is Zero.

IamIan

11-11-2008, 01:04 PM

Willdryden
You are right it is a simple math formula. HP at zero RPM is Zero.

kind of...

my overly long 2 bits follows:

There are technically different kinds of work.

The unit of work is the joule ... which measures heat , electrical , and mechanical work...

In mechanical terms:
One joule is the work done, or energy expended, by a force of one newton moving one metre along the direction of the force.

In electrical terms:
One joule is also the work required to move an electric charge of one coulomb through an electrical potential difference of one volt.

So with or without movement work is done... it is only a question of what type of work... is it mechanical work , electrical work, or thermodynamic work?

Now Power is the rate at which work is done.
Power is measured in watts for metric ... or HP for English... both watts and HP are measuring the same thing.

Watts are electrically defined as Volts * Amps... so if there is a voltage and amperage is electrically flowing which happens any time the electric motor is consuming electrical energy ... than work is done and the rate of the work is the power in watts ... can be converted to the HP being done even at zero RPMs ... 746 watts = 1 HP.... even if this is electrical power and work ... and not mechanical power and work... it is still HP at zero rpms.... also the peak HP or Watts from an electric motor is when it consumes the most Volts x Amps... it doesn't matter what the RPMs are.

-----------------

I haven't done the math yet... but it seems like we almost know everything we would need to know to determine with math if it will be required a single gear ratio or not...

Given the known torque and known power of the electric motor... and the known wheel size... in order to have the proposed acceleration 0-60 time there would have to be at least a specific gear ratio of the electric motor to the wheels.... if we also know the vehicle weight ( or a reasonably close guess ) we can calculate the required gear ratio in order to achieve that acceleration.

given the gear ratio determined above what would be the top speed when the electric motor gets near the known RPM limits ~12,000...

If the electric motor has to spin faster than its known RPMs than there has to be more than one gear.... if the electric motor has not topped out yet at that required acceleration gearing ... than it is not required for GM to be using more than one gear ratio....

This is not guaranteed as even if GM does not need the gearing they might still choose to put it in... but if it is needed given what is known than it kind of forces them to put it in ... unless they lower the top speed or add seconds to the 0-60 acceleration time.

Xzlon

11-11-2008, 01:32 PM

Thanks IamIan

You are more ambitious than I was. Generally however motors and engines are rated on useful power out at the shaft, not power in. One is the fun factor and the other is MPG rating.

PatrickfromMd

11-11-2008, 06:59 PM

IamIan

11-11-2008, 09:21 PM

IamIan,

Good explanation. I know you had to do it, but adding into the mix electrical power and mechanical power to an already complicated discussion….. oh well. If nothing else, you sure showed your knowledge on the subject
So, I see you were not on any of the previous post on this thread, so I have to ask the question, do you think a single speed gearbox, or something with some gear multiplication in it? In my post (#45 I think) I’d like you opinion.

I was just lurking/reading ... I figured I would add my 2 bits to try to show how the two camps of HP at zero RPMs were both correct... it just depends on what type of HP you are talking about... and the Volt uses both mechanical and electrical... so they are both correct.

as for my prediction...

while a single gear is viable... I expect GM to use some type of multiple gear ratio system.

In order for the Volt to get the ~9 sec 0-60 time there will have to be a gear reduction in order to get enough torque to the wheels from the electric motor that we have been told about... I figure at least around ~2.0 gear ratio... but they may lean a bit higher or lower depending on a world of variables/data I do not have access to.... but I don't see a need to go more than 3.0 for the gear ratio to accelerate.

At ~2.0 gear ratio I would expect to be getting near the RPM limit very near ~100 MPH.

Of course while the electric motor might be operational at those higher RPMs there is a thing called back EMF... and it will be more efficient not to run it into those higher RPMs... and it would be much hard to control the switching of a electric motor at those higher RPMs... figure the Electric motor will have a frequency at least twice the RPMs and more likely 3 or 4 times the RPMs.. so at 10,000 RPMs you have to be switching all those volts and amps on and and off at over 20,000 times per second... maybe as high as 40,000 times per second... it is doable... but add additional complexity and cost to the drive control system.

While a single gear ratio can fit the acceleration and the top end... it is only by a narrow margin ... That might be a large enough margin... but, I expect GM will want the wider margin of more than one gear ratio... for many reasons... not the least of which is that, as you discharge the batteries to a lower SoC you get less and less cranking power available from them... in order to still have the same level of 0-60 acceleration time when the battery is down to to less than full SoC you will need a larger gear ratio for acceleration ... something above 2.0 and closer to 3.0... but a higher ratio means you will hit the RPM limit before 100 MPH... thus another benefit of multiple gear ratio system.

A side not... I think many people over look... at full power with the pedal floored the Volt will drain the fully charged 16 kWh battery pack in about ~7 minutes.... although I doubt anybody would really keep the Volt at full power for a full 7 minutes. ;) You would be at 100 MPH long before that, and then power demand should drop off, unless you are climbing a steep hill and going 100 mph , with the AC running at max , and the radio thumping, etc... :cool:

I see how it can go either way... but I expect more than one gear ratio... and they have many different methods to get that if they want it.

PatrickfromMd

11-11-2008, 11:41 PM

I was just lurking/reading ... I figured I would add my 2 bits to try to show how the two camps of HP at zero RPMs were both correct... it just depends on what type of HP you are talking about... and the Volt uses both mechanical and electrical... so they are both correct.

as for my prediction...

while a single gear is viable... I expect GM to use some type of multiple gear ratio system.

In order for the Volt to get the ~9 sec 0-60 time there will have to be a gear reduction in order to get enough torque to the wheels from the electric motor that we have been told about... I figure at least around ~2.0 gear ratio... but they may lean a bit higher or lower depending on a world of variables/data I do not have access to.... but I don't see a need to go more than 3.0 for the gear ratio to accelerate.

At ~2.0 gear ratio I would expect to be getting near the RPM limit very near ~100 MPH.

Of course while the electric motor might be operational at those higher RPMs there is a thing called back EMF... and it will be more efficient not to run it into those higher RPMs... and it would be much hard to control the switching of a electric motor at those higher RPMs... figure the Electric motor will have a frequency at least twice the RPMs and more likely 3 or 4 times the RPMs.. so at 10,000 RPMs you have to be switching all those volts and amps on and and off at over 20,000 times per second... maybe as high as 40,000 times per second... it is doable... but add additional complexity and cost to the drive control system.

While a single gear ratio can fit the acceleration and the top end... it is only by a narrow margin ... That might be a large enough margin... but, I expect GM will want the wider margin of more than one gear ratio... for many reasons... not the least of which is that, as you discharge the batteries to a lower SoC you get less and less cranking power available from them... in order to still have the same level of 0-60 acceleration time when the battery is down to to less than full SoC you will need a larger gear ratio for acceleration ... something above 2.0 and closer to 3.0... but a higher ratio means you will hit the RPM limit before 100 MPH... thus another benefit of multiple gear ratio system.

A side not... I think many people over look... at full power with the pedal floored the Volt will drain the fully charged 16 kWh battery pack in about ~7 minutes.... although I doubt anybody would really keep the Volt at full power for a full 7 minutes. ;) You would be at 100 MPH long before that, and then power demand should drop off, unless you are climbing a steep hill and going 100 mph , with the AC running at max , and the radio thumping, etc... :cool:

I see how it can go either way... but I expect more than one gear ratio... and they have many different methods to get that if they want it.

IamIan,

Very informative, and also supports my arguments that gear multiplications will produce a more efficient running car (I was incorrect, it was my post #22 where I made my predictions). I studied back EMF in one of my engineering classes, but do not remember enough to get into that area.
The controller requirements, I am not an expert on controllers, but it sounds logical that those high of frequencies would require complex electronics
Well, I’m anxious to see what GM comes up with. Bob Lutz said the transmission was top secret and was doing things that had not been done before , so should be interesting.

WopOnTour

11-12-2008, 12:08 AM

Insider

12-25-2008, 08:03 PM

jscott1000

11-12-2009, 02:25 PM

hermperez

11-12-2009, 03:32 PM

It seems almost certain to me at this point that the Volt will use a variant of the 2MT70 if not identical to the one previously planned for the Vue hybrid. All they needed to do was beef up MG2, (which we all they can do) and tweak the software to allow the 40 miles AER.

It's going to disappoint the purists to realize there is a mechanical connection between the engine and wheels, but with software you can use an infinitely variable amount of ICE and electric motor combinations. I like this architecture if this is in fact what GM has done.

It probably will be a variant of the 2MT70, but with all 5 clutches and many gears removed.. there will be no mechanical connection between the traction and generator motors.. there is no need for one, keep it simple and all that. GM has stated many times its not a hybrid but a serial configuration EV with a range extender.. Perhaps a variant of the Volt with a smaller battery pack could go back to a true 2-Mode transmission.

Mohsen

11-12-2009, 04:20 PM

It probably will be a variant of the 2MT70, but with all 5 clutches and many gears removed.. there will be no mechanical connection between the traction and generator motors.. there is no need for one, keep it simple and all that. GM has stated many times its not a hybrid but a serial configuration EV with a range extender.. Perhaps a variant of the Volt with a smaller battery pack could go back to a true 2-Mode transmission.

Kudos to WapOnTour who predicted the 2MT70 variant back in September 2008. (#47 in this thread).

Hermperez - the consensus is that there IS indeed a mechanical connection between the ICE and the wheels. See the other thread in this section.

The ICE which is permanently connected to the Generator which then have a mechanical clutch that is connected to the Universe (annulus) of a planetary balancing transmission.

In other words, the Volt is NOT a pure serial. It can run in series mode (probably at low speeds - inner city), but at high speeds (highway) where HP is required, the ICE directly couples to the transmission and the wheels, and even the Generator becomes a motor (after all its the starter for the ICE) and all 3 are DIRECTLY connected (through the planetary balancing mechanism) to the wheels.

Another let-down by GM.

Now go and service/repair such a beast. GM is not exactly Toyota, you know.

That is why this thing is so expensive and is taking so long.

hermperez

11-12-2009, 04:41 PM

we will see who is right..

Altazi

11-12-2009, 04:45 PM

we will see who is right..
It surely wouldn't take much effort for GM to clear up the confusion on this. Lyle? GM? Some clarification, please?

Mohsen

11-12-2009, 05:27 PM

we will see who is right..

Lets make sure the semantics are clear. By "Direct Connection" which I claim, I mean through a gearbox (such as a planetary balancer) that includes a mechanical or hydraulic clutch. I do not mean a simple shaft from the ICE to the Traction.

So maybe we are both saying the same thing.

"Direct Connection" == some form of mechanical coupling in addition to an electrical coupling, as opposed to just an electrical coupling.

The Volt is poth parallel and serial - its a Mongrel EV!

Mohsen

11-12-2009, 05:35 PM

It surely wouldn't take much effort for GM to clear up the confusion on this. Lyle? GM? Some clarification, please?

Are you kidding? Lyle only asks feely-goody questions, like:

"how does it feel to you when driving the Volt the range extender turns itself off at the stop sign - does that cause you an adrenalin rush?"

Lyle is not engineering/science-centric. Lyle is a poet dealing more with humans than machines.

As a top power electronics engineer, you should know that!

BTW - I asked you this a long time before: what is the voltage drop across the best MOSFET or BTSG or whatever its called. Like if your source voltage is 300 V., what is the least drop you can get away with in your 100 A controller?

Also: is an AC induction motor synchronous by definition?

Thanks

Altazi

11-12-2009, 06:29 PM

BTW - I asked you this a long time before: what is the voltage drop across the best MOSFET or BTSG or whatever its called. Like if your source voltage is 300 V., what is the least drop you can get away with in your 100 A controller?
Sorry, I must have missed your previous question. Statically, a MOSFET in the "on" state looks like a resistor. The spec you are looking for is called Rds-on (Resistance, Drain-to-Source, on-state). The voltage drop across the MOSFET is proportional to the drain currend (Id) and the Rds-on spec for that MOSFET. Typical Rds values for power MOSFETs are in the low milli-ohm range, so the I^2 R losses across the device are minimized. You can find single MOSFETs with Id (drain current) specs in the low 100's of amps. Drain-source voltages can be as high as low kV range. Of course, handling high current AND high voltage is tricky and expensive. High voltage handling requires thicker oxide layers to avoid breakdown. High current handling requires many MOSFET cells in parallel (power MOSFETs consist of multiple cells in parallel). Paralleling all of the gate lines increases the overall gate capacitance, which requires higher current drive at a given switching frequency. For exceptionally high drive current, MOSFET devices may be wired in parallel, as long as proper attention is paid to the design of the driver circuitry.

Also: is an AC induction motor synchronous by definition?

Thanks
From Wikipedia:

The basic difference between an induction motor and a synchronous AC motor is that in the latter a current is supplied onto the rotor. This then creates a magnetic field which, through magnetic interaction, links to the rotating magnetic field in the stator which in turn causes the rotor to turn. It is called synchronous because at steady state the speed of the rotor is the same as the speed of the rotating magnetic field in the stator.

By way of contrast, the induction motor does not have any direct supply onto the rotor; instead, a secondary current is induced in the rotor. To achieve this, stator windings are arranged around the rotor so that when energised with a polyphase supply they create a rotating magnetic field pattern which sweeps past the rotor. This changing magnetic field pattern induces current in the rotor conductors. These currents interact with the rotating magnetic field created by the stator and in effect causes a rotational motion on the rotor.

When I used the term "synchronous" in my discussion of the switching regulator, this referred to the replacement of what would normally be a Schottky "catch" diode with a MOSFET that is driven synchronously with respect to the switching MOSFET (series with inductor for buck, inductor to ground for boost). The Schottky diode maintains the current flow in the output capacitor when the inductor is charging. The diode is simple, but has a voltage drop (~0.3V-0.5V) which can seriously degrade the efficiency of a switching regulator. Using synchronously-switched MOSFETs to replace the diode improves efficiency.

Mohsen

11-12-2009, 08:44 PM

Thanks Altazi. I wasn't aware that MOSFETs had no reverse voltage and am just familiar with junction devices where 0.6 volt base to emitter drop is an immutable law written in the Bible which you have to live with.

So my next question is, for an individual discrete MOSFET device, what is the highest source to drain device that is reasonably commercially available? I think you said 300 A? Would that be a discrete device (i.e. no parallelism inside)? So can I assume that a 500V 200A MOSFET does not cost an arm and a leg? Like what would be the cost?

Finally, how difficult is it to convert a DC source into a variable AC current in order to run an induction motor (induction motors by definition have to be AC)?

Also, how different is a Schottky diode from a regular diode (the breakdown voltage is adjustable and non-destructive?)

Its been a while since I had that 6.02 course.

prowler

11-12-2009, 09:47 PM

Its been a while since I had that 6.02 course.
enough of that secret beaverspeak.

Altazi

11-12-2009, 09:59 PM

Thanks Altazi. I wasn't aware that MOSFETs had no reverse voltage and am just familiar with junction devices where 0.6 volt base to emitter drop is an immutable law written in the Bible which you have to live with.
To get more detailed, MOSFETs have a substrate diode that conducts in the opposite direction of the switched drain-source current flow. You need to exercise care to avoid any unintentional reverse current paths when using MOSFETs as power switches.

So my next question is, for an individual discrete MOSFET device, what is the highest source to drain device that is reasonably commercially available? I think you said 300 A? Would that be a discrete device (i.e. no parallelism inside)? So can I assume that a 500V 200A MOSFET does not cost an arm and a leg? Like what would be the cost?
Virtually all MOSFETs are parallel devices, having hundreds of MOSFET transistor cells wired in parallel on the die to reduce the overall Rds-on resistance. Doing a quick search at DigiKey (my FAVORITE!) gives us a 180A device (http://www.microsemi.com/datasheets/APTM50DAM17G-Rev2.pdf) (I know you said 200A, but I liked this datasheet). My DigiKey search results show six devices having Vdss (drain-source voltage, like Vce for bipolar transistors) of 500V - 1kV, and drain currents (Id, like Ic) of 180A to 497A. These are not cheap, costing $200 - $500/each in unit quantities. I'm not sure where you're "costing an arm and a leg" threshold is. (It would be really sad to ruin one of these after you bought it . . .) :(

Finally, how difficult is it to convert a DC source into a variable AC current in order to run an induction motor (induction motors by definition have to be AC)?
DC-to-AC conversion is simple. Generally, you start with a high-voltage DC source, use variable PWM to chop it into a sinewave approximation, filter the results with an inductor and capacitor, and you have an AC sine wave at the output. This is standard for driving BLDC motors, for example. Of course, high voltage and high power complicate the circuit a bit, and definitely drive up cost.

Also, how different is a Schottky diode from a regular diode (the breakdown voltage is adjustable and non-destructive?)

Its been a while since I had that 6.02 course.
Schottky diodes are used for their low forward voltage (Vf) to minimize conduction losses compared to standard silicon diodes. They also have high switching speeds (switching from forward conduction to reverse blocking). Breakdown voltages tend to be lower, but DigiKey has Schottkys for 1200V @ 15A.

G35X

11-12-2009, 10:46 PM

From Wikipedia:
Quote:
The basic difference between an induction motor and a synchronous AC motor is that in the latter a current is supplied onto the rotor. This then creates a magnetic field which, through magnetic interaction, links to the rotating magnetic field in the stator which in turn causes the rotor to turn. It is called synchronous because at steady state the speed of the rotor is the same as the speed of the rotating magnetic field in the stator.By way of contrast, the induction motor does not have any direct supply onto the rotor; instead, a secondary current is induced in the rotor. To achieve this, stator windings are arranged around the rotor so that when energised with a polyphase supply they create a rotating magnetic field pattern which sweeps past the rotor. This changing magnetic field pattern induces current in the rotor conductors. These currents interact with the rotating magnetic field created by the stator and in effect causes a rotational motion on the rotor.

I think the above explanation needs a little bit further explanation…

1) Role of the rotor and stator is interchangeable. Therefore, explanation from their function can cause confusion.

2) AC synchronous motors, such as hysteresis, reluctance, 3-phase types, are basically induction motors. The difference is that ordinary induction motors with closed-loop basket coils need “slippage” between the stator and rotor to create torque, whereas strong and steady magnetic attraction between the rotor and stator of the synchronous motors locks the speed on to the rotation of the magnetic field.

3) You cannot turn closed-loop basket (to create magnetism by induction current) type common induction motor in its basic form into a generator, whereas synchronous motors with permanent magnets or some other means to excite rotor coils can become a generator when rotational force is given from the outside.

4) You can control speed of induction or synchronous motors by varying frequency of the supply electricity.

5) You can control torque of induction or synchronous motor by changing the voltage of the supply electricity.

Judging from the above the Volt’s drive motor, which is said to be of 3-phase induction type, needs variable voltage, variable frequency power supply (inverter). If it has the function of a generator, then it must have some means to magnetise the rotor. Slip rings?

Mohsen

11-12-2009, 11:20 PM

enough of that secret beaverspeak.

Heh heh :D

Mohsen

11-12-2009, 11:29 PM

Thanks Altazi and G35X for your contributions. Maybe I will design my own controller for the ultralight amphibian I will be converting. As you may guess, the batteries are A123.

WopOnTour

11-20-2009, 09:21 PM

Judging from the above the Volt’s drive motor, which is said to be of 3-phase induction type, needs variable voltage, variable frequency power supply (inverter). If it has the function of a generator, then it must have some means to magnetise the rotor. Slip rings?
Ouch! Wiki quotes?? etu GX35X??? LOL j/k ;)
FYI-There are no slip rings in the Volt's motor system. In "motoring" modes the motor drive voltage/pulse-width/current is directly applied to high-density* armature field coils hard-wired to the power inverter/drive controller and the highly magnetized** PM rotor, rotates at an RPM/TQ in direct response to that.

*To improve motor energy density GM is using a technique where the armature coil windings are created through an extrusion process that creates a square shaped wire of high copper, low oxygen, purity. When laid out in the winding pattern there is virtually zero wasted space such as those that occur with traditional round wire windings.

** Also to maximize motor energy density, GM is utilizing permanent magnet materials based on their "Magnaquench" technology, that has essentially revolutionized man-made permanent magnet technology over the past 20 or so years. (It's the primary reason why a conventional 12V starter/cranking motor is now the size of a beer can as opposed to the diameter of a football only 20 years ago.) GM eventually spun-off the Magnaquench company, but still maintains much of the intellectual rights to its use.

HTH
WopOnTour