Still Scratching My Head About My '16 Two Eco

Yes, my Scangauge shows RPM=0 whenever the EV icon is illuminated.

As for your second question, I have been wanting to know the same thing. I looked in the reviews and could not find anything describing how Toyota changed the HSD in the Gen 4.

 

Ring to sun ratio now is 2.8/1, so you can achieve higher speeds before MG1 reaches max rpm. This allow you to maintain higher speeds using only MG2.

Nexus 10 ?

 

In this video they mention 1/1.05.

I don't know yet about the PiPP, but I think it should have a more powerful MG2 or use a bigger reduction to get more torque to the wheels as it is supposed to stay in ev as long as you have enough battery charge. Regular gen4 uses a smaller and less powerful MG2 than gen3, but has a reduction connecting to the ring gear and goes up to 17000rpm, so you basically get the same torque and acceleration.

Nexus 10 ?

 

Source?

Toyota has given the name P610 to the new gen4 transaxle. According to the P610 thread here, Toyota's New Car Features documentation says that the power-split planetary gear has the same gear ratios as every previous Prius -- 78 teeth on the ring and 30 on the Sun giving the ratio 2.6:1, not 2.8. If the new ratio actually were 2.8 instead of 2.6 that would be bad since it would cause MG1 to spin faster and reach its max rpm sooner thus reducing the maximum EV speed with the ICE off.

P610 transaxle

Something that did change was the final fixed gear ratio right before the differential that sends power to each of the front wheels. The old final gear ratio was 3.267 in gen 3 and is now 2.834 in gen 4. The lower ratio means the output of the power-split unit spins about 15% slower at the same vehicle speed in gen 4 versus gen 3 and that means that MG1 also spins 15% slower when the gas engine is off than in gen 3 at the same vehicle speeds.

Another possible part of the story is the maximum allowed rpm of MG1. Over the generations, Toyota has increased this max rpm by making design changes to MG1. It is possible they have done this again in gen4 but I haven't seen any specs for this yet in gen 4.

 

According to the spec page at the Toyota Global website, the Prius Prime has the same motor specs as the regular gen 4 Prius. I assume for now that the gear ratios are also the same as the regular gen 4. However, they did change the transaxle in the Prime to add a one-way clutch to the planetary carrier that the gas engine is hooked up to. This allows MG1 to help push the vehicle without spinning the gas engine during EV driving so now MG2 and MG1 can be used together to provide up to about 95 kW of output instead of just the 53 kW of MG2 alone.

The battery is also part of the context here. The small regular hybrid battery only puts out up to about 25-30 kW (not sure of exact gen 4 number) so MG2 alone can handle that and the one-way clutch is not needed. On the Prime, the larger 8.8 kWh pack can output more than MG2's 53 kW capability so the one-way clutch is needed so MG1 can help out. Toyota does not seem to have published the Prime maximum battery output yet but it is probably around 70-80 kW.

So, the small regular hybrid battery in the gen 4 Prius can't put out enough power to maintain highway speeds up to the transaxle's actual inherent EV speed limits and it can't store much energy anyway so it would quickly run out. The much larger battery in the Prime has enough power capability to take the car up to and maintain its maximum EV transaxle design speed of 84 mph.

A very similar story plays out between the 2016 Volt and the 2016 Malibu hybrid from GM. They share essentially the same hybrid transaxle except that the Volt, with its large battery, gets a one-way clutch where it's engine hooks up to the power-split planetary gears (the Malibu also gets a customized "MG1" motor). Other recently introduced plugin hybrids that play the same basic engine braking clutch game are the Cadillac CT6 and the Chrysler Pacifica minivan.

 

I guess I confused the final gear ratio with ring to sun ratio. I saw it precisely in the p610 thread, but it's a lot of information in few days. Thanks for making it clear.

I read too that MG1 and MG2 have been redesigned. Now they are smaller with less torque but higher rpm. Final new gear reduction and this modification allows to stay in ev mode with ICE off up to 112kmh, almost 70 mph.

Nexus 10 ?

 

From what I have read, and I I understood it correctly, the main enabler was that the new P610 transaxle has the MG1 and MG2 on separate shafts.