Volt Drivetrain Patent and info

May I ask where you have found that "fact", please?
And also, please explain in which it represents a "fact", as you said earlier, and I quote:

"Indeed .... the drivetrain in the Prius is much more likely to destroy itself due to

computer failure than the transmissions in a conventional vehicle. "

Source: http://priuschat.com/forums/chevrolet-volt/85572-volt-drivetrain-patent-info-4.html#post1249676

 

I love the technology in the Prius and do tell people how cool it is, but I'm not a purist.

Toyota chose the maximum-simplicity design, no question. No clutches to wear out. This involved some compromises though.

One is the residual drive torque when the engine starts. You can't feel it at speed, but you can at rest. The car rocks when the engine starts. As a result, engine start is disabled in N (neutral). Since the engine can't run in N, they also disable (relay-open) the hybrid battery. This leads to issues with the small battery in car washes.

Another is the speed limit of 46 (III) MPH in electric. Faster than that and MG1 can't compensate to hold the ICE still.

Also, MG1 cannot be used to help propel the car in electric. With the ICE off, it's only used to hold the engine still (no net power out), so it's 20 kW potential goes to waste.

The traction control / ABS system has to monitor/control the rate of change of the HSD output, since too much rate of change = too much torque through the HSD to MG2 = breakage. Some of us believe this led to more compromises in the traction control/stability control/ABS programming. There's no torque limiting component between the brakes and the gears/motors. A clutch pack would/could be this limiter.

As far as I can see, the Volt design eliminates the need for these compromises, granted, at the cost of added complexity.

As for all 3 clutches engaging at the same time...well, that's a red herring. If the wrong clutches lock in most any automatic (or DSG), you get a lockup. This basically never happens. If anything, the clutches slip as they get old. I'm not worried about this at all. The clutch packs will need to be replaced as they wear out though.

As an engineer, I think the topology choices GM made in the Volt transmission are very interesting, and I can see why they did what they did. It's not a step back, it's a step in a different direction, for valid reasons.

I've always believed that the long-run equilibrium would be a true dual-"fuel" vehicle, where it's efficient at using both energy sources. Enough battery would be provided for the commutes of 75-90% of buyers, but no more than that. 100% electric is simpler, but way too many other compromises come into play that limit the utility of the car.

I think the Volt is closer to that equilibrium than the Prius.

Imagine a spectrum from conventional gasoline, to mild hybrid (Honda), to hybrid (Prius) to extra battery hybrid (Prius PHEV), to medium-battery dual source (Volt), to large battery dual source (??), to electric. By dual-source, I mean the ability to perform at 100% on either source (no compromises running on battery).

I think either extreme of that spectrum involves too many sacrifices, and that we'll see more in the middle, like the Prius PHEV and Volt. Maybe the next player will have a full dual-source design, but with more battery (like 80 to 100 miles).

 

MG1 can handle up to 62 MPH with ICE moving as seen in the PHV Prius.

I think MG1 should be able to act as a motor in reverse direction, like MG2. Do you have any document that said it cannot? After experiencing PHV Prius accelerate in EV mode, it is hard to believe only MG2 with 60kW is doing all the EV propulsion.

 

Ok, 62, but it's still a limit.

If MG1 applies torque, there's a fraction (don't know the exact number) that will act on the ICE through the planetary gears. No, I can't document it.

In a non-plug Prius, MG2's maximum power on battery is limited by the (single) battery. In the PHV, there are 3 batteries (more power), so MG2 can be powered closer to it's 60 kW rating.

 

Volt's speed limit is 100 mph and Leaf's limit is around 90 mph. Prius' top speed is 112 mph.

The energy loss due to the aero drag above 55 mph becomes a major portion anyway. Starting the gas engine beyond that speed only make sense (think synergy). HSD focuses on doing more with less with KISS principle.

This is from Volt's owner manual:

I also understand the plus and minuses of Volt's drivetain. It is not "superior" like MotorTrend claimed to be. I think we both agree on that.

 

Not sure what your last sentence means...

Indeed.
I've been saying that for a while in this forum amidst claims of grenading clutches and the wonderful Prius TC system.

 

Two things:
The car rocks, but it does not move a bit, even with the crawl mode (no brakes acting). MG2 does the accomodation of the "impact".
MG1, when putting ICE still, is doing just only its own friction (motor), since there is no output, I can't see those 20kw wasted!

 

+1

I think the key here is the speed limit in 49 states is 65mph or above. The volt and leaf do have a lower maximum speed than the prius but both are well above the highest US speed limit of 80mph.

I think wasted is a confusing word. MG1 can not provide power in ev mode, so that extra power is wasted. In the volt the generator can be used in ev mode. I don't think this is really a waste, MG1 is just extra weight in ev mode, it is very effective in HV mode. I do think that adding a clutch to the prius would make it a cleaner design for ev, which would remove the parasitic losses of the ice and mg1 spinning.

 

The discussion above of the pluses and minuses of both transmissions is very interesting. However, what would worry me more if I was inclined to purchase the very expensive Volt, (even with the gov't subsidy the price hovers around 33K) is GM's commitment to the whole project. I could easily see them drop the current system in the Volt in a nano second if it isn't either making them "enough" money or something comes along that is the slightest bit different that might be less expensive to produce. Then what anyone who was an early adopter would have is a white elephant when it comes time to trade it in or sell it. At least I know Toyota is commited to the HSD system and the improvement of the current system, rather than the wholesale dumping. GM's record of staying with something for along time and developing it to it's fullest potential is not good. Just look at what they did with the first electric vehicle.

 

I'll keep posting this ad-nauseae, that is, until someone understands what is wrong with the approach from you.

MG1 is the key to provide "gear ratio" during ICE work and when in EV, provide zero rpm to the ICE. So simple. Calling its nominal power as underused is a mistake, because load changes, is part of the game in this case (any case in transportation actually)
There is no extra power wasted, and it does not release heat more than a fraction of its work being done. It is called efficiency, which a MG is very good at, even with almost no power delivered.

Cleaner design? Depends, clutches releasing small debris to the transaxle oil seems dirtier to me.

And smoothness might be in stake also, when performing clutch action. HSD has shown how possible that is without one, and what silent/silky on board urban trips has given to 2 million users so far.

For the Prius PHEV it has not changed very much, because ICE is still to work in some journeys. I personally would not change what is perfect for purpose.
If Prius PHEV was a BEV, there would be no HSD needed.

 

what? the tahoe has been around forever!

 

I was saying it IS NOT wasted in HV mode, so I do not consider it a waste. You may want to notice that I was actually agreeing with you. Then again since you think I have the wrong approach are you going to change your mind;-)

I guess my use of cleaner was confusing. I mean a better design from an engineering point of view removing losses in EV mode. The prius has done much to remove parasitic losses. I believe it is likely that they will do something in the Gen IV to remove these extra losses of the ice and mg1 turning at normal US highway speeds. The volt does this now, hence a cleaner, er um I mean IMHO superior design.

Clutches have been around a long time and I doubt that these are going to cause a large amount of debris. The engine in the volt does however pollute more than the one in the prius, when we are in CS or HV mode.

 

Sorry, my choice of words left open a possibility for misinterpretation.

With the ICE off, the 20kW MG1 does not waste 20kW of energy (power). In fact MG1 is barely using any power, just enough to overcome it's own drag and that from a few spinning gears transferring no net torque.

What I meant was that the 20kW motor isn't helping accelerate the car. As such, the motor itself is "going to waste". It would be nice if both MG1 and MG2 could propel the car with the ICE off. In the Prius, only MG2 can propel the car with the ICE off. In the Volt, the clutches allow both motors (whatever they call them) to propel the car with the ICE off...better performance if the battery can supply the amps.

The Prius design is more elegant (I won't use the word clean), but the Volt's design is more flexible.

 

Prius doesn't need to use MG1 to propel since MG2 already out muscle the HV battery already.

In PHV Prius, it may be a different story. I have felt how the PHV accelerates. It is really strong and I cannot believe MG2 is the only one propelling.

MG1 can act as a motor in the hierarchy mode so it may just be a software upgrade, I do not know.

 

There is a mathematical relationship between speed of the car and speed of the motor generators.

MG1 = 3.6 * ICE - 2.6 * MG2

Keeping the ICE rpm at 0 reduces to
MG1 = -2.6*MG2 with the motor generator supplying no power to forward movement.

If you allow the ICE to rotate, MG1 can contribute, but IMHO this is not a good design for an EV mode. I can not confirm that toyota will not do this, but must say it is unlikely. In HV mode, MG1 can supply power.

At low speeds MG2 provides plenty of power to the car and this is what you are feeling.

 

That's the formula to find the RPM, not power. If ICE is 0 RPM, and the car is moving, MG2 would have positive RPM. MG1 at the same time would have negative RPM. We know MG1 can act as a motor in negative RPM. It would be like this.

 

power = torque X rpm
If the rpm is negative the power can be 0 or negative.
RPM needs to be positive if it is powering the car forward.

When the ice is kept at 0 and the car is going in a positive direction the mg1 is really providing 0 forward power, only power to overcome losses and hold the ice in place. Mg2 is powering the car. How do you get negative torque here while hold the ice speed at 0?

 

Can anyone confirm if what I have here is correct:

C1
Clutched - Locks Ring Gear to Case
Unclutched - Unlocks Ring Gear to Case

C2
Clutched - Connects ICE/MG[A] to Ring Gear
Unclutched - Disconnects ICE/MG[A] to Ring Gear

C3
Clutched - Connects ICE to MG[A]
Unclutched - Disconnects ICE to MG[A]

Also from diagram, it looks like there are no clutches for the big motor, MG (Sun Gear). Unlike HSD where the ICE and MG1 spin different elements in the planetary gearing, the Voltec ICE always goes through MG[A] before connecting via the ring gear to the transmission. The output is the planet carrier. MG free spins in neutral.

If my assumptions are correct, nothing immediately bad will happen if all three clutches are engaged. It will simply lock the ring gear, MG[A] and ICE to the case.

For the engine, this which is no worse than stalling a high-reving engine in a manual transmission.

For MG[A], depending on how fast it was spinning, or how much torque is suddenly placed on it, it is probably the one that will experience the worst part of this scenario, and by extension, the electronics.

However, if MG[A] and ICE are spinning and suddenly locked to the case, there are at least two or three different clutches which will slip, so mechanically, nothing too bad should immediately happen. You might destroy the powertrain, but the wheels can still spin so it will coast to a stop.

And assuming the electronics aren't fried, with three clutches engaged, you can still use MG in battery-draining mode to drive around with.

Can anyone tell me if I read the diagrams correctly?

 

Perhaps my assumption is incorrect. I thought ICE is parked / locked so MG1's negative torque could move the car, even without power from MG2.

 

I could be wrong but this is what I think happens:

When MG2 is providing torque, and the ICE is off (0 RPM): since MG2 is connected to the the wheels by fixed ratio, it is actually pushing against the ground through the tires. So, MG2 doesn't have to push against the ICE or MG1. MG1 just spins backwards, but not providing any torque. It is driven only only overcoming its own friction and match the speed of MG2 by another ratio. I believe the ICE is locked by keeping all valves closed.

When the ICE is allowed to spin forward to slow down MG1, I'm not 100% sure what happens, whether the ICE passively spins by opening some valves or something, or MG1 is powered, etc.