Poor ev milage on 24 prime

Going a set speed, an EV/PHEV will use X amount of power. How "powerful" the motor is doesn't matter. Electric motors are efficient like that.
Your right foot controls the energy usage and speed.

I find it curious that the Prime is up there in efficiency when it has to spin two motors to propel the car.
MG2 rolls the car forward. MG1 must then spin in the opposite direction to keep the Gasser stationary, correct?

 

The PHEV models have a clutch between the engine and MG1.

 

MG1 and MG2 both drive the car. This is made possible by the one-way clutch, which prevents reverse operation of the engine by locking the engine into the transaxle case if it tries to turn in reverse. So, the one-way clutch is not really between the engine and MG1 but between the engine and transaxle case, and its function is to lock the engine into the transaxle case when it tries to turn in reverse. The engine and MG1 couple as the planetary and sun gears, respectively, and there is no clutch in between.

Advancement of Toyota Hybrid System II (THS-II) | Toyota Motor Corporation Official Global Website

From the Gen 4 Prius Prime new-car features manual:

By installing a one-way clutch between the engine and transaxle [case] to prevent reverse operation of the engine, torque from the generator (MG1), which conventionally only generates electricity, can be transmitted to the output shaft and adds the torque of the generator (MG1) to that of the motor (MG2) improving drivability and the feeling of acceleration when the vehicle is driven by motor.

The one-way clutch prevents reverse operation of the engine when the generator (MG1) is used as a motor. The torque from the generator (MG1) in addition to that of the motor (MG2) is transmitted to the counter driven gear when the motors are operated at maximum output.

 

And on top of the correction about the 'clutch', that exists only in the G4 PHEV. The G5 reverted back to only MG2 pushing in EV operation.

 

Is MG1 spinning? Is the clutch just in a different location?

 

For my (US) Prime XSE Premium-In switching to the LE/SE Prime wheels and 205/60R17 Turanza 005 (so maintined the same overall rolling diameter as stock for XSE/XSE Premium) (with the LE/SE Prime wheel covers) I am now getting 55-61overall mpg in HV only mode versus 46-50 before the change (this is over 1700 miles since the wheel/tire change in varied driving conditions/mix freeway and city/stop-go traffic). One thing I did notice versus the Gen4 Prime is the slight hiccup (don't know what else to call it) or hitch you feel when pressing on accelerator pedal from a start rest position and that the gas engine appears to be more engaged versus Gen 4 which felt a lot smoother starting from rest (due to more reliance on the electric motor?)-Gen 5 appears to want to switch to gas at the slightest provocation (at least that is how it feels for me) If I do press the accelerator pedal ever so softly then it does feel like the Gen 4 ...until you reach higher speeds/slopes when the gas engine does come on. Essentially starting from rest, Gen 4 (in HV) felt like an EV up to a point, whereas Gen 5 (also in HV) does not feel that way (gas engine more involved)

 

MG1 is always spinning backwards if the car is moving forwards and the engine is stopped, in all Priuses.

If you're driving in EV mode, MG2 is pushing forwards and MG1 is normally free-wheeling backwards. It's easier to push than the engine is, so the engine stays put and MG1 just spins along mirroring whatever MG2 and the wheels do. If MG1 pushes forwards (or resists the backwards spin), it starts the engine.

The distinction of the G4 PHEV is the engine "anti-reverse" sprag clutch which means MG1 can push backwards rather than freewheel to contribute motive power.

MG1 pushing backwards in other Priuses would start the engine spinning backwards - the transaxle being symmetrical, MG1 could spin the engine ether way - but in the G4 PHEV the sprag clutch makes the engine lock in position if pushed backwards, letting MG1 transmit all its torque to push the wheels forward.

There's no replacement mechanism in the G5 PHEV - it just has a bigger more powerful MG2 so doesn't need an assist from MG1.

 

And the lack of the one-way clutch in Gen 5 PHEV is probably resulting in a lower fuel efficiency and BEV range, as MG1 is freewheeling and losing energy without providing torque to the wheels. It seems to be a cost-saving measure by Toyota. Gen 4 PHEV might have the best fuel economy in the BEV mode among all cars out there.

 

So you are seeing Zero power at MG1, if you have instrumentation that displays this, (Torquepro, etc.)?
Isn't there an RPM redline for this smaller motor and that's what limits top EV speed?
That poor little MG and associated planetary gears are near Redline while the Prius is at what top EV speeds on the Gen4 and Gen5?

 

That would be an interesting chart to see!
'Fuel' economy on BEV and PHEV.
Of course we have an EPA rating, but showing actual power usage at a few different speeds would be a great comparison chart!

 

Yes, the MG1 rpm is what limits the EV speed, but it was increased along with the MG2 in the gen5.
Even with MG1 not moving, the gears are in motion. Appears Toyota kept that in mind when designing them.

 

Haven't got anything wired up, but yes, it will be zero power flow to/from MG1. Just a bit of mechanical drag.

Precise numbers on MG1 speeds haven't always been given in every verison, but the general outline from some notes I have. These figures will have had gaps filled in using gearing ratios which are known.

G1 had a 6500rpm MG1 limit in either direction. That limited EV speed to 44mph / 70km/h or so.
G2 boosted the forward MG1 speed to 10,000rpm, permitting faster engine revving at lower speeds, boosting system output. Backwards remained at 6,500rpm, or at least they didn't increase the EV speed limit beyond 44mph.
G3 had other gearing changes, which seem to have lowered the backwards rate to 5,500rpm based on the 47mph / 76km/h EV limit.
G4 took that up to 6,800rpm, with a 68mph / 110km/h limit.
G4 PHEV seems to have a 9,500rpm backwards limit corresponding to 84mph / 136km/h in EV.
G5 PHEV has basically the same EV speed limit, but that's now 10,000rpm backwards on MG1 due to minor gearing changes.

MG1 doesn't really see anything significantly different between G4 and G5, except that it's not allowed to push in G5 any more.

MG2 speed limit remains at 17,000rpm afaik, as it has been since G3, setting the overall top speed.

 

Maybe that's it then. The extra power from MG1 probably gave a little boost to the efficiency of the Gen4 on a distance per kwh basis. The gen 5 is also heavier so the extra weight is likely also a contributing factor.

 

Gen 5 SE PHEV is 96 lb heavier than Gen 4 Limited PHEV, and Gen 4 Limited PHEV could be a little more aerodynamic than Gen 5 SE PHEV as well.

Edmunds got only 33.7 miles of BEV range on Gen 5 PHEV. Thye mention using the maximum regenerative braking. I hope they didn't use the B mode, which would have lowered the fuel efficiency. The other day, I was wondering why my fuel efficiency was bad, and I realized I had accidentally switched to the B mode when my hand had hit the shift lever. I then accidentally switched to the N mode, and I had to pull to the shoulder in panic, only to realize that it shows on the display how to switch back to the D mode (the same way when you start). That said, I do easily far exceed the 25-mi EPA BEV range on my Gen 4 Prius Prime.

2023 Toyota Prius Prime doesn’t live up to its electric range | Edmunds

 

The rated distance is around 75km, and I get 90 *with* AC