ICU behavior at high-speed gliding/coasting

That is the way it was designed. The "ICE" will spin above about the speed that you mention to prevent overspeed of MG1.

 

Unlike a CVT (continuously variable transmission), the synergy drive is a direct drive. The planetary gears use a combination ICE speed and MG1 to create a final drive ratio per se. The system is always connected unless in neutral.
I personally wouldn't shift into neutral on hills. I can't remember where but I read something akin to it being a bad thing due to the fact that shifting back to D would put MG1 at risk of overspinning. I'll have to test that theory out with the Scangauge.
Coasting is the ultimate fuel saver - DWB (driving without brakes). With that being said, there are hypermiling techniques that will optimize throttle positions such as pulse and glide and DWL (driving with load). If you do a search you can find dozens of tips.
Happy driving!

 

In Neutral, only the electric fields that drive the MGs are disconnected. All the parts are still physically or mechanically connected, and must still spin. The gearing is such that if the ICE crankshaft is stationary, MG1 must spin very fast. Spinning up the ICE to idle speed allows MG1 to slow to a safe RPM.

When your foot is off the throttle pedal, the car is using a small bit of regeneration to create synthetic drag, similar to (but weaker than) the engine compression drag of a non-hybrid. This greatly helps drivability for people accustomed to the feel of non-hybrids. But any regeneration creates some conversion loss, so this does not make for the most efficient operation.

To truly coast in D gear, without this synthetic drag, press the throttle just a little bit. On a Gen2 Liftback, adjust the throttle until the energy flow arrows disappear. On a Gen3 Liftback, bring up the HSI display and adjust until the CHG bar disappears. Your 'c' has different displays (my aging brain refuses to remember all the details), but does have something similar for guidance.

Be extremely cautious about using Neutral downhill, or just avoid it altogether. In gear (D and B), the car can protect itself from MG1 overspeed. In Neutral, it cannot, and there are ways for the driver to unintentionally destroy it.

 

The hypothesis of overspeeding MG1 has been discussed since the era of Gen1. However, starting from the Gen3, PiP, v & c, the introduction of SRU has lowered the speed of MG1 and very close to MG2.

For Gen1 & Gen2,

MG1 rpm = -2.6 * MG2 rpm when Engine stopped

For Gen3, PiP, v & c,

MG1 rpm = - ( 143 / 145 ) * MG2 rpm when Engine stopped

At 50 mph, MG2 is about 5954 rpm and MG1 could be commanded to spin at -5872 rpm if the engine were to be stopped but instead Toyota chose to spin MG1 at about -2272 rpm. 5872 rpm is hardly the maximum rpm or unsafe rpm so does the overspeed of MG1 hypothesis still hold?

The PiP has the same PSD & SRU and yet it can run EV up to 62 mph, so why MG1 does not overspeed?

Vincent

 

This is the explanation I have always seen given for the reason that the Gen 3 ICE will run above 46 mph. If this is not the reason then why would you think Toyota would run the ICE above this speed?

I always wondered why the PiP could run up to 62 mph in EV too. Hopefully someone can come along and explain this to us.

 

A lot of power would be drawing from the HV battery above 46 mph. It would put more stress (charge/recharge cycles) on the battery and may not reach 10 years / 150k miles warrenty. That's my speculation.

I bet the engineers figured that is also when gas engine can be very efficient.

PiP battery was design to handle up to 62 mph.

 

Just let it glide. If you throttle a little, gas engine makes about 5-7 kw. Per the BSFC engine map, that is not an ideal efficiency. Ideal is only reached at min of 10 kw.

That's my observation on my PiP. C maybe the same or slightly different.

 

This is incorrect. The system is always connected. In Neutral no electrical power is applied to M/G1 or M/G2, but the gearing is still connected. There is no clutch in the Prius, so the mechanical gears are always connected.

This simulation shows the relation of M/G1, the engine, and M/G2. M/G2 is linear with the speed of the tires.

Toyota Prius - Power Split Device

The Prius being emulated is a Gen 1, not a c, so some numbers will not be exact, but you will see the same effect of the engine rotating being mandatory in the 40s.

 

Good catch jimbo.

Nothing gets disconnected, even in Neutral. No clutch and very simple.

 

The HSI in the c is prettier and in colour, but it is functionally identical to the HSI in a Gen III, so the advice is the same - adjust pedal input until there's no charge bar (or positive bar).

 

FWIW, how fast the car will go before the ICE comes on is subject to SOC of the traction battery. With a high SOC, the highest speed I've attained without ICE is 82 km/h (51 mph). You must accelerate slowly up to that speed. If decelerating, the ICE won't kick out until you're going quite a bit slower.

 

If you're going above 42 mph and take your foot off the gas, fuel will be cut off but the ICE will continue to "run (pump air), hence no "EV" light. The energy flow meter will confirm this. In the same scenario, you can lightly press the gas pedal to do a "true coast" (no regen or propulsion). If you very gently push the pedal beyond that, the energy flow diagram will show power from the battery but no ICE power.