Volt Drivetrain Patent and info

http://gm-volt.com/2010/09/27/gm-patent-application-may-be-for-the-chevrolet-volts-transmission/

This is confirmed to be the patent for the drive train. Planetary gear but it has three clutches. The traction motor can be directly coupled to the wheels with ICE and generator disengaged completely.

Generator is coupled over 70mph to allow 101mph in EV mode probably by lowering the effective ratio for the traction motor to the wheels.

ICE can run the generator decoupled from the planetary gear which pumps power into the traction motor as needed to help run the car when the battery is low but apparently sometimes the ICE/Generator is also coupled directly to the wheels to aid in propulsion.

It is confirmed that going up steep hills with the battery discharged yields a 40mph top speed.

 

It is crazy to think all it takes it all 3 clutches to engage at the same time and something will break. Also if Clutch 1 isn't working I don't think you're going to be able to move at all as the generator probably cannot counteract the high torque needed to get the car moving.

The one benefit to this system (over Toyota HSD) is mode 6 basically allows ECVT for the traction motor. On the Prius, MG2 is coupled directly to the final drive so once you go over 62mph insufficient torque is available due to MG2's RPM. The Volt can engage C2 and disengage C1 (and keep C3 disengaged) and that would allow it to control the traction motor RPM to keep it producing torque then can engage C3 to allow the ICE to contribute power. I don't think the system can charge in this mode, though. C2 needs to be disengaged to allow the ICE to charge the battery... Of course, the ECU can direct generator power to traction as needed while still in series mode.

This drivetrain is certainly catering to EV mode operation over ICE... It's all very interesting. People are pissed it's not a true series setup with no PSD or clutches at all ... but this system is pretty neat and certainly very flexible.

You just sacrifice economy while the ICE is running as the system is not optimized like HSD after multiple generations.

 

We do know one thing: if the battery is totally depleted, it seems your maximum speed is 40mph. It seems the ECU does its best to prevent this condition but Motor Trend activated it while driving hard in the hills. It's a pretty lame limitation and it shows that the ICE/Generator are undersized for the car and if you are placing continual high demand on the system, it will max out and you are physically speed limited due to insufficient power.

You push the hill climb button to start charging the batteries even while on flat ground -- and GM says that'll get you up any grade in the US... that works in that case (if you hit the button.)

But conditions outside of that like going flat out at 100mph for an extended time would probably cause the same problem and you would end up being speed limited once the battery drained.

This is clearly not an issue on the Prius as the ICE/MG1/MG2 combo have more than enough power to motivate the car even without help from the battery pack.

 

It would be interesting to see a Prius top speed test when SoC gets to 40%.... I wonder how much it would be reduced?

I did a very spirited drive from California Central valley (just above sea level) to about 7000ft in Sequoia National Forest (in PWR mode) on curvy mountain roads, very hot day with A/C running and the car maintained a normal SoC without any issue, so I would say the Prius has enough.

I've never seen the car pulling amps from the battery to maintain a steady speed up a hill before. 75mph up the 6% grade of the I5 was trivial on my last drive.

100+ amps from the battery during high speed passing maneuvers, for sure....

 

It's more than that. Without it, it would not be possible to run the ICE through the generator to the wheels... But they do use it for neutral too for a true total disconnect. I suppose the benefit if you can run in neutral ICE off until any speed.... and with C3 connected but not C1/C2 you can charge in neutral too.

Oh ya ... that is true. i was stuck in a terrible traffic jam on I5 and the ICE kept cycling to charge up the batteries because it was 100F and I was blasting the A/C. When I finally pulled off I5 and headed up the hill to palmdale I didn't notice any problem getting back up to speed, but perhaps the battery pack was charged up a bit.

With A/C on, the ICE comes on around 40% SOC and then stops somewhere around 45-47%. ~60% is normal for highway driving... 80% is the absolute top limit.

Around 25% is where the error message to put the car in PARK comes on. (Like when in a carwash in neutral.)

 

Good point. The latest Tesla iteration has now gone back to a single speed transmission and they said it's more efficient and reliable.

I assume GM looked at using a true series system where the ICE/Generator are truly mechanically isolated from the traction motor. I wonder why they went with this complex setup versus that simplicity?


On a different subject, what is interesting to me is it seems the most intelligent conversations about the Volt are happening on Prius forums. Seems none of the GM Volt fans have any understanding of hybrid drive trains or PSD.... The amount of misinformation is staggering, even among the automotive press.



If you add clutches, it becomes more flexible and also add complexity, cost and extra maintenance. It is all trade-offs. I prefer simplicity and elegance of HSD.


Yup, because it has EVT in mode 6, it lacks EVT in mode 3 (with ICE directly powering the wheels). Mode 2 has EVT for the ICE but not for the electric motors and mode 2 has 10-15% conversion loss.

For the Prius, it is the opposite. Prius ICE has EVT functionality (can run at any speed despite of Prius speed) but the MG2 doesn't.

Electric motors are pretty efficient already. Volt is said to gain 1-2 EV miles from mode 6 EVT. I question if it is worth taking the hit (35 MPG in CS mode) without EVT functionality.[/QUOTE]

 

I think the point is the HSD system used in the Prius uses no clutches at all. With no parts that actuate, there is less room for failure.

I also don't think he was talking about clutch failure. If there is a software glitch or electrical glitch which causes all three clutches to engage at the same time, bad things will most likely happen... at the minimum total lock up of the front wheels. If the speed is high (and depending on the clamping forces of the clutches and component strength) components may break.