Does this patent app describe the Volt transmission?

[Cab Driver]

I found the following patent application from GM titled "Output Split Electrically-Variable Transmission with Electric Propulsion Using One or Two Motors": http://www.freepatentsonline.com/20090082171.pdf. (The file is a pdf so you'll need the free Adobe reader to view it.)

I believe that it describes the Volt's transmission (what GM has elsewhere called the Power Electronics Module or PEM).

Back in June I proposed in post #8 of the following thread http://gm-volt.com/forum/showthread.php?t=4745 that the Volt transmission consists of a planetary gearset and three clutches connecting the input from the ICE with Motors A and B to the output to the final drive. Here is the drawing I made for that posting: .

If you compare figure 1 of the GM patent application to my drawing you'll see that they are functionally the same. What I called Motor A and B are called M/G A and B. The clutches I called CBRing, CAOut, and CAIn are called C1, C2, and C3. The only significant difference is that GM's figure shows an alternate optional configuration where C3 is eliminated in favor of a full time connection between the Engine and M/G A.

Of course, there is no proof that the Volt's transmission is what this patent application describes, but the timing (filed September 10, 2007) is right and it fits the statement by GM public relations guy Rob Peterson that the Volt has a planetary gearset and a number of clutches. It also fits the statements Volt powertrain engineer Alex Cattelan made in her interviews with Lyle last November. In addition, several people who've ordered Volts have posted the following description from the myvolt.com order tracking site:

"Powertrain
TRANSMISSION AUTOMATIC, ELECTRONIC RATIO SELECT, GM, STRONG HYB RID, EVT, PLUG IN
ENGINE FLEXIBLE FUEL, (GAS/ALC), 4 CYL, 1.4L, MFI, DOHC E-FLEX, FAM 0"

If the patent application does describe the Volt's transmission it means that the Volt is NOT a single speed only transmission. It is an Electrically Variable Transmission (EVT). In addition, if the clutches C2 and C3 are engaged simultaneously there is a mechanical power path from the engine to the wheels. It may be that GM has chosen to never engage C2 and C3 simultaneously, but they could if they wanted to. (I don't know if that would be an infringement of Toyota's Hybrid Synergy Drive patents; I'm an engineer, not a patent lawyer.)

[Shaft]

Nice find. I'll bet this is it. Now more speculation can begin!

My bet, consistent with my previous posts: C2 and C3 are never simultaneously engaged.

But that suggests that CD mode has a CVT but CS mode has one or at most two gears.

Seems weird, and may also be inconsistent with GM's claim that CS and CD modes perform the same.

Is there any way that C2 and C3 are simultaneously engaged, but the ICE only drives M/G 1 to produce electricity and control the CVT, but does not formally "drive" the wheels?

I guess reverse is solved by just having M/G 2 run backwards.

[BillR]

Well, Cab Driver, I think you have solved the problem.

Note that this patent describes 6 basic operating modes:

1) 1 Motor Electric Only
2) Series
3) Output Split
4) Neutral
5) Neutral / Battery Charge
6) 2 Motor Electric Only

At paragraph [0041], the authors describe the basic system operation. The vehicle starts from rest in mode 1. As the M/G B speed increases, it becomes less efficient, so M/G A can be engaged (mode 6) to use the EVT to keep the motors at their optimum speed.

In mode 2, series mode, the ICE drives M/G A as a generator, but does not couple to M/G B. It is noted that M/G B can provide all of the vehicle's power.

"For cruising conditions", Mode 3, output split, gets propulsion power from M/G B and the ICE.

So "IF" this is the Volt's transmission (which I believe it to be), then it can operate as both a series and a parallel arrangement.

Great find!!

[ChrisC]

Very interesting. Elimination of clutch C3 (CAIn) ... means that M/G A (Motor A) would be used exclusively as a generator, right?

[Marty]

I don't think that this is it. GM has repeatedly said that there is no mechanical connection between the ICE and the wheels. The ICE/generator have been described as an integrated unit. The patent may indeed be used in other GM hybrids and perhaps future Volts but if we're to believe the GM description of Volt operation to date there is absolutely no mechanical coupling between the ICE and the vehicle transmission.

[Rooster]

if I understand things correctly, for an EVT, you'd have to have M/G 1 (aka the generator) rotate the ring gear to vary the ratio for M/G 2 (aka, the drive motor) right? So that would mean in CS mode, the ICE would rotate the ring gear via M/G 1--thus there would be a mechanical connection between the ICE and the ring gear.

Our inside guy (WOT) has stressed that there is never a mechanical connection between the ICE and drive wheels, and I have no reason not to believe him. Thus, I don't see how the Volt could have an EVT -- it would need a 3rd electric motor. It could have a CVT between M/G 2 and the wheels, but that would be adding a lot of complexity.

However, with the PG, you could clutch between the sun gear and ring gear, whereby the planets allow a simple 2-spd gearing function to keep M/G 2 in it's optimal efficiency band. I'm thinking the Volt may do something like this to "keep it simple". Course, I'm just guessing, it is also quite possible gearing isn't required at all.

[Cab Driver]

Nice find. I'll bet this is it. Now more speculation can begin!

My bet, consistent with my previous posts: C2 and C3 are never simultaneously engaged.

But that suggests that CD mode has a CVT but CS mode has one or at most two gears.

Seems weird, and may also be inconsistent with GM's claim that CS and CD modes perform the same.

Is there any way that C2 and C3 are simultaneously engaged, but the ICE only drives M/G 1 to produce electricity and control the CVT, but does not formally "drive" the wheels?

I guess reverse is solved by just having M/G 2 run backwards.

I believe that the EVT is used in CD mode to optimize the efficiency of M/G A and B to get the best possible All Electric Range, rather than to get better performance than the single gear ratio available in CS mode.

If C2 and C3 are simultaneously engaged then the power of the ICE plus or minus the power provided to or taken from M/G A will determine the speed of the ICE, M/G A, and the Ring gear. The speed of the Ring gear will determine the gear ratio from M/G B and the Sun gear to the planet Carrier and the Final Drive at a given road speed.

Putting it differently, you cannot take all the ICE's power away with the M/G A and still force the Ring gear to your preferred speed to select the M/G B torque multiplication.

Finally, yes: reverse would be achieved by just running M/G B backwards.

[Cab Driver]

Very interesting. Elimination of clutch C3 (CAIn) ... means that M/G A (Motor A) would be used exclusively as a generator, right?

Regardless of whether C3 is present, M/G A is the starter motor for the engine as well as the generator.

In addition, the Power Split mode would be available with or without the presense of C3, though GM may have chosen not to use Power Split mode for some reason. In Power Split mode M/G A would work as a motor with its torque added to that of the engine in driving the Ring gear whose torque would be blended with the torque of M/G B applied at the Sun gear. This blended torque would go from the planet Carrier to the Final Drive.

Be aware in all this that I believe the Volt's transmission would have the C3 clutch present. It would be too inefficient to suffer the drag of spinning the unpowered engine any time we want to run M/G A.

[Cab Driver]

I don't think that this is it. GM has repeatedly said that there is no mechanical connection between the ICE and the wheels. The ICE/generator have been described as an integrated unit. The patent may indeed be used in other GM hybrids and perhaps future Volts but if we're to believe the GM description of Volt operation to date there is absolutely no mechanical coupling between the ICE and the vehicle transmission.

I understand your concern but as long as they choose not to engage C2 and C3 simultaneously there is no mechanical coupling between the ICE and the Final Drive.

We will just have to wait until GM shares the specifics of the Volt transmission to know for sure.

[hermperez]

"I believe that the EVT is used in CD mode to optimize the efficiency of M/G A and B to get the best possible All Electric Range, rather than to get better performance than the single gear ratio available in CS mode."

You still think that the EVT is also used during regen to maximize energy recovery and thus AER?

Alex did say their goal was the best efficiency in the CD mode, not CS mode.

My contribution is that this also makes the Volt a quieter car during CD mode, by maintaining the inverter's switching frequency in the supersonic range, or at least higher than the 1000hz at which human hearing is most sensitive. There have been reports that the Volt does not have the usual motor whine of many electrics.