High'ish engine-off EV speeds in N.

The issue of over-revving the MG2 applies in the same way to the Gen III. The Gen III has different gearing than the Gen II, and thus the 62mph limit in the Gen III rather than 40mph in the Gen II, but the mechanical issues are the same.

I haven't seen it mentioned here how fast you have to be going in N to actually damage the MG2. I don't think anyone want to do the experiment.

 

Are you not confusing between Gen 3 and PiP?
PiP limit is 62 mph (USA) or 85 km/h (EU). I thought Gen 3 limit is 70 km/h (43 mph).

 

Shifting to N does a lot more than you might think. It disables the regeneration systems as well as a lot of the control and protection systems. If the engine is off, it will not come back on and you can definitely over-rev the engine.

 

N is always a bad idea.
It is M/G1 at risk, M/G2 is locked to wheel speed.
The engine CANNOT start or stop in N.

 

Recall the the PiP is essentially a Gen III with a bigger traction battery and a charger. As I understand it, the mechanical parts of the transaxle are the same. When a PiP is in HV mode, then it behaves like an regular Gen III Prius with respect to when it starts the ICE. So a PiP in HV mode, or a standard Gen III Prius, turns on the ICE at around 43 mph. (Note that there is a difference between the speed at which the ICE will turn on in normal driving, and the speed at which the ICE is forced on to protect the MG1, like on a downhill.) A PiP in EV mode starts the ICE at about 63 mph. The Gen II has a lower speed threshhold to force on the ICE. In the Gen III, they added a gear reduction component that spins the transaxle slower for given car speed.

And right, we are talking about the MG1 over-revving here, not the hard-linked MG2.

 

I have been wrong in my previous comments about using N to exceed engine off coasting speeds.

Today I did some lower speed coasting in N and noticed that both MG1 and MG2 were reporting RPM proportional to speed. N does not disconnect them from spinning. That would suggest to me that it isn't a good idea to go much faster than 63 MPH in N.

What is the maximum rated speed for both MG1 and MG2? It would be a simple matter to setup an alarm on Torque.

It seems odd that Toyota doesn't mention avoiding excessive N speed in the manual. I've gone up to at least 70, and perhaps even 75 MPH in N with the engine off.

 

N only refuses to power M/G2 and M/G1, they do still spin, but they spin freely so no engine power gets to the wheels.

 

A bit more detail: there are no clutches in the Prius transaxle. All of the gears are are always connected. But depending on how MG1 and the ICE is powered, the various components will spin at different speeds with respect to each other. In N, the ICE will not be turned on (if it is already on, I think that it would be idling) and neither MG are powered. With the ICE off, MG1 speed will be in a fixed ratio to the MG2, which is in a fixed ratio to the tire rotation speed, which in turn is in a fixed ratio to the speed of the car.

In many states, it is against the traffic code to be moving with the transmission in N. It is considered a safety issue.

 

MG1/MG2 speed at 50MPH is ~6000 RPM, so about 1200 RPM per 10MPH

 

The problem is that MG1 doesn't start the engine when in neutral. MG1 and MG2 speeds have a linear relationship with the vehicle speed when operating in EV mode (engine off). That means they will both spin faster and faster with increasing vehicle speed.

Assuming Tracksyde's data is accurate, the motors spin 120 RPM for every MPH. If the operating limit for MG1 is 10,000 RPM, dividing that by 120 gives us a top speed of 83 MPH. Beyond that speed, MG1 will be spinning beyond engineered limits.

I'm fairly confident I've never exceeded that speed in N. I want to verify the information roflwaffle and Tracksyde have provided before I resume coasting in N again, but it looks like there is no harm in it. As a reminder to everyone, regen doesn't work when the gear selector is in N. The only useful time to shift to N on a downhill is when you want to exceed 62 MPH with the engine off, but won't need to do any braking.

Toyota isn't able to engineer the car to re-engage D and start the engine when exceeding 83 MPH because there is a legal requirement for N to always be easily and reliably accessible. That means no over-riding a user initiated N setting.

 

Every generation, every model, M/G2's RPM is ALWAYS linear with speed. It is geared directly to the wheels. 0 MPH = 0 RPM, R means negative RPMs. D means positive RPMs, always and forever in sync with wheel speed. It never 'kicks in'.

In N neither M/G1 nor M/G2 gets electrical power, so the Prius cannot start the engine in N nor can it stop the engine in N. (It also can't charge the battery in N, avoid N at all costs. Toyota is required by law to provide an N, it is a 'compliance gear'.)

When not in N, to avoid over reving M/G1, the Gen 1 & 2 spins up the engine at just over 40 MPH even if not needed to propel the car. My understanding is that Gen 3 and PHV it is 62 MPH that is crucial. No idea about c and v.

 

In the Gen III (including the PiP) there is a reduction gear that reduces the speed of the MG1 for a given vehicle speed. This was specifically done to allow the car to go faster without turning on the ICE, presumably in anticipation of the PiP.

 

I read the entire referenced thread. Peef says that in a Gen II in Ready mode, even if starting from a stop in N and rolling down a hill completely in N, above a critical speed (about 52mph in a Gen II), that the MG1 will be energized and turn the ICE, albeit without fuel and with valve timing set to minimize compression braking, to prevent over-revving of the MG1. It is not clear how this would apply to the Gen III (including the PiP), with the gear reduction specifically put in to reduce the speed of MG1 with respect to that of MG2. 62 mph is the maximum speed where the PiP will let you drive in pure EV, but that that doesn't tell us what the maximum speed is before the controller would want to force the ICE to spin to protect the MG1. In the Gen III (including PiP), the rotational speed of the MG1 and MG2 with the ICE off are very close to each other (within about 10%), and, as in all Prius's, the ratio between vehicle speed and MG2 rpm is fixed, which suggests that even if you can slow down the MG1 by spinning the ICE, there would be no point, since the MG2 would also be hitting its limit at the same time. (Unless one of the mechanical engineers here chimes in and tells us that the maximum rpm rating for MG2 is greater than for MG1.) Edit: JeffN confirms that 13,500 is the max rpm of MG2 which allows the car to travel at its max speed of about 112 mph. With the ICE not spinning, MG1 reaches its max rpm of 9,800 at 83 mph.

It would be nice of some of the engineers here could run experiments to put this question to rest.