GM Volt Forum banner

1 - 20 of 181 Posts

·
Registered
Joined
·
211 Posts
Discussion Starter #1 (Edited)
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.)
 

·
Registered
Joined
·
350 Posts
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.
 

·
Registered
Joined
·
695 Posts
You've Found It!!

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!!
 

·
Registered
Joined
·
1,208 Posts
Very interesting. Elimination of clutch C3 (CAIn) ... means that M/G A (Motor A) would be used exclusively as a generator, right?
 

·
Registered
Joined
·
471 Posts
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.
 

·
Registered
Joined
·
706 Posts
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.
 

·
Registered
Joined
·
211 Posts
Discussion Starter #7
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.
 

·
Registered
Joined
·
211 Posts
Discussion Starter #8
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.
 

·
Registered
Joined
·
211 Posts
Discussion Starter #9
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.
 

·
Registered
Joined
·
1,791 Posts
"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.
 

·
Registered
Joined
·
211 Posts
Discussion Starter #11
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.
My belief is that the Volt has EVT functionality in CD mode but not in CS mode. The EVT is used to optimize All Electric Range. CS mode efficiency is a lesser concern since GM's data says 75% of Volt drivers won't encounter CS mode on a typical day's drive.

I don't believe that there is a two fixed gear ratio setup since none of the test drivers have ever reported the sense of a shift occurring.
 

·
Registered
Joined
·
1,791 Posts
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.
Of course if hackers break the security then we could see Volts with ICE coupling enabled, plus opened up DOD range on the battery to 95%, high temp limits on the battery modified (a hotter battery produces more hp), high temp limits on the inverter/motors bypassed.. recharging of the battery by ice allowed and so on. Cats and Dogs living together..
 

·
Registered
Joined
·
211 Posts
Discussion Starter #13 (Edited)
"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.
 

·
Registered
Joined
·
695 Posts
More Speculation

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=a1JAWoAvK-E&feature=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.
 

·
Registered
Joined
·
2,707 Posts
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.)
 

·
Registered
Joined
·
211 Posts
Discussion Starter #16
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!
 

·
Registered
Joined
·
211 Posts
Discussion Starter #17
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.)
Thanks for the kind words. I couldn't agree more that a number of people all bouncing ideas off each other can come up with good results!

It is the nature of the 2 Motor Electric-only mode to allow improved efficiency for both drive and regenerative braking by optimizing the rpm of the 2 motors for a given road speed. This is a classic "twofer" and is the main justification for the expense, weight, and complexity of this transmission versus a one speed transmission.
 

·
Registered
Joined
·
706 Posts
My belief is that the Volt has EVT functionality in CD mode but not in CS mode. The EVT is used to optimize All Electric Range. CS mode efficiency is a lesser concern since GM's data says 75% of Volt drivers won't encounter CS mode on a typical day's drive.

I don't believe that there is a two fixed gear ratio setup since none of the test drivers have ever reported the sense of a shift occurring.
Certainly possible, but I would think there would be a noticeable performance difference between CS and CD mode, none have been noted. Also, if you already have the inherent capability to clutch between M/G A and the PG in CD mode (for an EVT function), then why the heck wouldn't you take advantage of it in CS mode also? WOT has clearly stated there is no connection between M/G A and the PG in CS mode.

Would you notice an electric motor stepping down via a slight gear change? An electric motor doesn’t have the inertia, vibration or sound associated with an ICE.
 

·
Registered
Joined
·
211 Posts
Discussion Starter #19
Certainly possible, but I would think there would be a noticeable performance difference between CS and CD mode, none have been noted. Also, if you already have the inherent capability to clutch between M/G A and the PG in CD mode (for an EVT function), then why the heck wouldn't you take advantage of it in CS mode also? WOT has clearly stated there is no connection between M/G A and the PG in CS mode.

Would you notice an electric motor stepping down via a slight gear change? An electric motor doesn’t have the inertia, vibration or sound associated with an ICE.
Alex Catellan said that using M/G A combined with M/G B would not involve an increase in total power past the 110 kW. Thus the performance impact of the 2 Motor Electric-only mode would be relatively subtle. The mode is there to optimize CD mode efficiency (AER), not performance.

As to why GM wouldn't choose to use the Output Split mode, the only reason I can think of is concern about infringing Toyota's Hybrid Synergy Drive patents. This one puzzles me too.

With regard to the possibility of using additional clutches to reconfigure the gearing of M/G B through the planetary gearset in Series mode, it certainly could be done. Would the shift be noticible? I suppose the combination of a fairly small change of ratio and some progressive action of the clutches might make the effect subtle. I can't prove GM hasn't done this, but I'm still betting that the Volt transmission is configured as this patent app describes.

Time will tell how the Volt transmission is actually configured. In the meantime, it's fun to speculate.
 

·
Registered
Joined
·
706 Posts
Alex Catellan said that using M/G A combined with M/G B would not involve an increase in total power past the 110 kW. Thus the performance impact of the 2 Motor Electric-only mode would be relatively subtle. The mode is there to optimize CD mode efficiency (AER), not performance.

As to why GM wouldn't choose to use the Output Split mode, the only reason I can think of is concern about infringing Toyota's Hybrid Synergy Drive patents. This one puzzles me too.

With regard to the possibility of using additional clutches to reconfigure the gearing of M/G B through the planetary gearset in Series mode, it certainly could be done. Would the shift be noticible? I suppose the combination of a fairly small change of ratio and some progressive action of the clutches might make the effect subtle. I can't prove GM hasn't done this, but I'm still betting that the Volt transmission is configured as this patent app describes.

Time will tell how the Volt transmission is actually configured. In the meantime, it's fun to speculate.
The speculation is fun, and we are both puzzled on why GM wouldn't use the split output mode in CS mode -- initially I too was convinced this is what they were doing. The the patent infringement argument just doesn't hold water with me. I would think it's akin to try to sue GM because the Malibu has a 5 speed tranmission like in the Camry.

I also agree S/W could keep the acceleration performance the same.

WOT, can you throw us a bone yet?
 
1 - 20 of 181 Posts
Top