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I read about the Tesla roadster being delayed due to it's planned two-speed transmission. OK. I'm not sure why, but I guess that proved difficult to implement. So I have two questions:

What type of transmission will the Volt have?
If not CVT, why not?

I don't understand the mechanics of limiting a fully electric engine to two gears versus the infinitely variable nature of a CVT.

Thanks!

-jay
 

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I read about the Tesla roadster being delayed due to it's planned two-speed transmission. OK. I'm not sure why, but I guess that proved difficult to implement. So I have two questions:

What type of transmission will the Volt have?
If not CVT, why not?

I don't understand the mechanics of limiting a fully electric engine to two gears versus the infinitely variable nature of a CVT.

Thanks!

-jay
My understanding is that neither the Volt nor the Tesla needs a multi-speed transmission for normal highway speeds. They both use three-phase induction motors (using technology from the EV1), and motors like this can handle up to about 12,000 RPM. Given normal acceleration needs, that gives the cars a top speed of about 100MPH.

100MPH is OK for the Volt, so I don't think you'll see any transmission there. The designers for the Tesla thought that this was too slow for a 2-seater sports car, so that forced them to put in the 2-speed transmission - one speed for up to 100MPH and another for faster. However, the transmission apparently isn't production-ready yet, so the first Teslas will be limited to about 100MPH until they complete the transmission and install it (at company expense).

To their credit, Tesla has been completely open and honest about this situation. Given their high public profile, I have to hand it to them for this.
 

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I read about the Tesla roadster being delayed due to it's planned two-speed transmission. OK. I'm not sure why, but I guess that proved difficult to implement.
That's an interesting quote...

Perhaps Tesla should have found a 55 Chevy and just used its Powerglide transmission. That was a rock solid two speed automatic. I mean, for chrying out loud, how much engineering is involved in a 2 speed automatic?
 

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I think the problem was shifting at 12,000rpm. The electric motor is a different animal. They have a really good post on their blog about the issue and the single speed solution to fix it.
 

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Powerglie? Hahaha! Yes, that was a very robust transmission. But, maybe it’s too heavy and bulky. I think there are two possible reasons why Tesla wanted to use a two-speed transmission… One is to keep the motor from frying itself because of too much heat at low-speed, high-torque situation such as when starting from standstill on an uphill grade. However, this should not be a problem if you properly design the PWM system to limit the max current, although it slows down the car, or simply use a more powerful motor.

Another is to limit the max rpm. Because:
1) Energy required to spool the motor increases at the rate of the square of rpm, although some of the energy can be recovered when coasting and braking you lose energy in heat nonetheless.
2) At high rpm the magnets embedded in the rotor might spin out destroying the motor.
3) The counter-electromotive voltage becomes too high to maintain the required torque.
4) The flywheel effect of the rotor compromises driving dynamics.
 

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I read somewhere that the Tesla no longer needs the transmission becuase of changes to the motors (IIRC). I have no idea where I read this. Autoblog Green maybe.
 

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GM EVT Patents

GM has been issued US Patents for what they are calling an Electrically Variable Transmission (EVT). It can be adapted to either series or parallel hybrid operation. I think the first issued is "Two-mode, compound-split, electro-mechanical vehicular transmission," Michael R. Schmidt, US patent # 5,558,589 (1996). Take a look, it even has cross-sectional engineering drawings.

There are many citations to this patent up to April 2008.

IMHO, this is the basis for the Volt transmission design.

Seems that GM has been busy building a patent portfolio. There are some interesting control system patents issued to GM also (USPat7024299).

Marc
 

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GM has been issued US Patents for what they are calling an Electrically Variable Transmission (EVT). It can be adapted to either series or parallel hybrid operation. I think the first issued is "Two-mode, compound-split, electro-mechanical vehicular transmission," Michael R. Schmidt, US patent # 5,558,589 (1996). Take a look, it even has cross-sectional engineering drawings.

There are many citations to this patent up to April 2008.

IMHO, this is the basis for the Volt transmission design.

Seems that GM has been busy building a patent portfolio. There are some interesting control system patents issued to GM also (USPat7024299).

Marc
This looks like it's for the 2-Mode Hybrid system they're using in SUVs and trucks. It seems way more complex than what they'd need for the Volt.
 

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This looks like it's for the 2-Mode Hybrid system they're using in SUVs and trucks. It seems way more complex than what they'd need for the Volt.
I agree, the SUV 2-mode is probably based on this patent also. This patent is the earliest I could find from GM for this tech.

It is a complex machine. However, it provides a series hybrid transmission capable of the Volt's attributes. One specifically, constant ICE RPM operation over a wide vehicle speed range. GM has also improved on this design over the last 12 years as evidenced by the patent literature.

They would also have production and reliability data on similar designs with the current 2-mode. There is also all that capital invested in the factories.

These factors lead to my opinion that the Volt will have an EVT.
 

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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.

The gas engine isn't connected to the wheels. :D
 

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A transmission of this type can be designed to be either a parallel or series hybrid. Series meaning that the ICE is not mechanically connected to the wheels.

This patent is a concrete example of a design from GM. There are also many other patents that derive/improve on this description.

Could you provide a description of a simpler, lighter and less costly design so we could compare the two?
 

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How bout this?
GM Powertrain Division said:
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.
 

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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.
 

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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.
 

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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.
 

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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).
 

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More on Transmissions and Bob Lutz comments

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.
 

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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.
 

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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
 
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