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.

[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.

[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.

[Cab Driver]

"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.

Yes, I think the EVT is used in CD mode regenerative braking to maximize recovered energy and thus AER. You said it well.

Your suggestion about inverter frequency and motor whine is intriguing. I don't know enough about inverter design to have a useful opinion.

[BillR]

I see this as being a modified FWD 2-mode, as I have mentioned in the past.

For operation, I see a larger motor for the MGB and smaller unit for MGA.

Some time ago, GM mentioned that energy consumption went in this order:

1) Aero drag
2) Accessories
3) Weight
4) Rolling resistance

Note the surprise that accessories takes more energy than weight. This is likely due to the regen, that captures the kinetic energy of the car.

So I see that in urban driving, where you are starting and stopping in traffic, the accessories like cabin heat, AC, power steering, radio, etc., put a constant draw on the vehicle, even though you may be sitting still for extended periods of time.

This is the ideal time for the series mode (2) in CS mode. This is where the ICE is connected to MGA, but is not connected to MGB. So the Volt can produce power to replenish the battery buffer, but yet not be providing torque to the drive. Also, MGB provides all the drive power without the benefit of EVT, but this is okay at low speeds. At this point, the Volt may only need 3 or 4 kW on an average basis.

At higher speeds in CS mode, the Volt switches to output split mode (3) so that some torque from the ICE is transferred to the drive. This is more efficient than doing the conversions from AC-DC-AC and taking the motor and generator losses. Here the ICE may operate at 15 kW, and most of that is directed to the drive system, while a few kW is absorbed by MGA to generate power to replenish the battery buffer.

For a review of a planetary gear system, see this video:

http://www.youtube.com/watch?v=a1JAW...eature=related

Now imagine the large outer ring gear housings to actually be part of an electric motor. See this link to a motor family by Remy Int'l that contains a performance curve.

http://www.remyinc.com/docs/HVH410R2.pdf

Note that this motor is most efficient at moderate torque loads between 1000 and 3000 rpm. I believe this is indicative of the performance curve for the Volt's MG's.

However, I think the motor that seems the most likely for the Volt is the HVH250, shown in this catalog.

http://www.remyinc.com/docs/HVH250R4.pdf

I would guess that the FWD 2-mode has something close to 2 of the std HVH250's. However, I would guess that the Volt has replaced MGB with the High Torque model (note that 2 of these models are for a 650 volt power supply, so they don't apply).

So MGA is a 60 kW std HVH250 at 60 kW (rated 55 kW by GM) and MGB is still ~55 kW, but with a peak power of 87 kW. Peak torque is 440 NM or about 324 lb-ft. Slightly more than the 273 in the Volt's specs.

So in CD mode, MGB provides power initially at launch. This torque and power is adequate in most circumstances. Since this motor has a maximum speed of 10,600 rpm, MGB could be geared such that 100 rpm equals 1 mph (just for discussion). Referring to the performance curve, the best efficiency is thus between 10 and 30 mph. So the Volt operates in transmission mode 1 in these circumstances.

As speed increases, or more power is needed, the Volt goes to mode 6, which is 2-motor electric only. Now MGA works in conjunction with MGB to vary the gear ratio to keep MGB in its optimum speed range. Also, more total power is now available. I believe sport mode may actually just put the Volt into this mode so that all this power is available at any instant.

So in summary, normal mode is mode 1, MGB drive only at lower speeds and power inputs. This will switch to mode 6 depending upon speed and power demands.

Once in CS mode, mode 2 (series) is used at lower power demand and speed such as urban driving.

When traveling at higher speeds, or when more power is demanded, it switches to mode 3, the output split mode so that torque from the ICE is directly transmitted, and also the EVT effects of MGA can be utilized.

I believe that this fits the Volt's mission, which is to be as efficient as possible in all modes of driving.

[George S. Bower]

CabDriver,

My apologies for not commenting earlier.

I have stated that I believe the primary purpose of the planetary gearset is to maximize regenerative braking. Your proposal does that as it is a power split device able to sent power to both MG1 and MG2 in a seemless manner. It also provides an EVT in AE mode. CS mode is just one speed the way you have sketched it. However, Roosters suggestion would make it a 2 speed if req'd. Perhaps w/ a gradual engagement of Rooster's added clutch the GM engineers can make it a fairly smooth shift.

I still think the Volt is series not parallel but would like to see the connection added to improve CS mileage. my driving cycle would have me in CS mode almost 1/2 of the time. The point about Toyotas patents may also have something to do w/ it. ----and I love Herm's suggestions about all the hacking that can be done to make it so.

I definitely think your proposal here is a better one than mine that I posted in the other thread "Volt has planetary gearset."

This has been a very productive thread indeed!!!! And a great example of what Rooster coined as "group think". (with Cabdriver getting most of the credit of course.)

[Cab Driver]

Bill,

Thanks very much for your comment. Most of what you suggest seems quite plausible to me.

I particularly like the planetary gearset tutorial video you linked to. It seems like a much more understandable explanation than the HowStuffWorks link I provided.

I think you're right that the Volt transmission is philosophically a descendant of the FWD two mode hybrid transmission. The main difference is deleting the first planetary gearset and the clutch brake on the sun of the remaining planetary gearset. We lose the four fixed mechanical gear ratios and the compound split EVT range, but retain the six modes described in this patent app. In particular, I think the control software for the Volt transmission was derived from the two mode hybrid control control software by deleting the software for the deleted modes and re-tuning for the Volt "feeds and speeds". Having spent 30 years developing software for embedded systems, I think this is a very elegant approach.

I also think you're right that the Volt motors are sourced from Remy and that they use the hairpin windings. I believe that M/G B has an inductive rotor even though both motors in the 2 mode hybrid have the permanent magnet rotors. I also believe that M/G B is significantly longer and more powerful than the 2 mode hybrid M/G B. If you look at the photos of the Volt transmission and the 2 mode hybrid transmission it is clear that the rear cover of the Volt unit is much deeper to allow space for the bigger M/G B.

Again, thanks for a great comment!

[Shaft]

From Lyle's post today:
"I am also scheduled to go back on October 11th when GM themselves will lay bare the details of how the drivetrain truly operates, finally answering burning questions about the transmission and whether at any point the engine can turn the driveshaft (they still say no)."

[Cab Driver]

From Lyle's post today:
"I am also scheduled to go back on October 11th when GM themselves will lay bare the details of how the drivetrain truly operates, finally answering burning questions about the transmission and whether at any point the engine can turn the driveshaft (they still say no)."

In case I turn out to have been clueless, do any of you have seasoning recommendations for humble pie?