Power Split Device

try the knowledge base articles forum.

 

• MG1 - starts the engine and there after, provides 'counter torque' to force the engine power to pass through the mechanical part of the Power Split Device. Without MG1, even if the engine is running, nothing happens.
• MG2 - provides reverse and it also absorbs or generates power from MG1. At slow speeds, less than ~25 mph, the counter torque comes from MG1 working like a generator. That power is sent to MG2 which feeds it back into the drive gears to the wheels. At speeds over ~25 mph, MG2 generates power that it feeds to MG1 so it can provide counter torque for the engine. That power takes the mechanical path through the Power Split Device and on to the drive gears.

Don't feel bad, it took a couple of years before I finally understood it:
http://hiwaay.net/~bzwilson/prius/pri_PSD.html

Bob Wilson

 

Whoa! I suspect you meant to say " At speeds over ~25 mph, MG2 generates power that it feeds to MG1 so it can provide counter torque ... ".

Actually there's nothing magical or significant about the specific speed of 25 mph. Whether MG1 acts as a generator feeding power to MG2, or vice versa depends on the ratio of speeds of the engine and wheels. Generally the former tends to occur at low wheel speeds relative to the engine speed (i.e., simulating "low" gear ratios), and the latter at higher wheel speeds (simulating "high" gears). The PSD follows the same simple algebraic rules as every other single-stage planetary gear set.

 

I don't remember why I was thinking 25 mph. This data shows the power flow reversal.

Bob Wilson

 

As I understand the Gen4 version, M/G2 is now where you show it, although the chain is now gears.

 

Correct. The Gen-1 and Gen-2 have a 'silent chain' and the Gen-3 and Gen-4 have gears. I was trying to show the power flows through the power split device.

Bob Wilson

 

This is the clearest explanation I have seen, and you get a feel for the way Chevrolet handles the device in the Volt. I finally just gave up and built a planetary gear set on my 3D printer and then used it to simulate the various modes. It is quite ingenious.



Study it, but realize that the power can move through more than just the single center shaft. The ring gear is MG2's rotation, the planet carrier rotating is the ICE's output, and the sun gear with the central shaft is the rotational force from MG1.

 

Well done!

I used a similar approach: PSD Model

Having a mechanical model in hand, you can feel the torque which otherwise is not so easy to visualize.

Bob Wilson

 

Toyota Prius - Power Split Device

Play with this interactive website. It is very instructive. The fun thing about the 2016 Prius is that they have somehow tweaked it so the motor can be at 0 rpm up to 73 mph (in my 2016 in fact, and have not attained or heard of a higher speed) All previous ones had to engage the gas motor above mid 40's mph.

 

Note that the illustration shows how the 1st generation Volt (model years 2011-2015) works. The 2nd generation Volt has a completely different design.

If you want to read more about the new Volt design (shared by the 2016 Malibu hybrid) see:

Second-Generation Volt Transmission Operation Explained

plus a video explainer based on the above article:

and

2016 Chevrolet Volt Powertrain: How It Works In Electric, Hybrid Modes

 

American Engineering vs. Japanese Engineering

Always a good read

 

I managed to have the Gen4 in EV mode at 80-90km/h but 117km/h (73mph) never... it sticks using the ICE - I think you need a full battery for that...

 

I see 73 mph only on sustained downgrades which are plentiful here in central Colorado. I have to wonder if the Li Ion battery vs NiMH battery might be a factor. Also for some reason the EV icon is more prone to lighting up when cruise control is NOT engaged, even when the energy monitor indicates no output from the ICE.

 

Awesome explanation. You should summarize how the battery comes to play during the process you talked about, like how the SOC of battery affects the process, and when the battery is low and the car is actively charging the battery.

I have been always curious in what extend has the battery assisted in acceleration when the engine is on. I suppose it will assist in acceleration when the car is driving under 25mph by feeding power to MG2. But what about above 25mph.

 

Traction battery roles:

1. Powers MG1 to start engine.
2. Absorbs excess engine power when vehicle, drag-load, is low and SOC is low
3. Provides power when engine is off and the vehicle needs power to move
4. Absorbs vehicle kinetic energy during regenerative braking
5. Powers 12V inverter for vehicle electronics and lights
6. Additional power when demand exceeds ICE power (Thanks @ChapmanF )

Bob Wilson

 

6. Contributes power when engine is running and accelerator demand has momentarily exceeded engine output. You can see this on the MFD 'car' display; with a ScanGauge you can see how many amps are being contributed.

Sometimes 'momentarily' means more than just momentarily, too ... a year ago I was in my Gen 1 as a passenger while my sister drove up through Rockfish Gap and she was maintaining about 80 mph all the way up. I was watching the scangauge and the battery was supplying 10 to 20 amps or more pretty much the whole way up the mountain. I was watching the state of charge count down through the 40s, expecting that the instant it reached 39.5 my sister would suddenly find herself driving a much slower car. Our exit came just before that happened.

-Chap

 

Interesting. I have never seen this behavior except when the SOC of traction battery is high and the ECU wants to get rid of excess battery charge to make room for regen.

 

You've never let my sister drive your car.