Regenerative braking

FWIR it does not

 

Toyota was legally required to have a Neutral, but you almost NEVER want to be in it.

You can't generate any charge for the HV Battery in N.
It is dangerous to the Motor/Generators to go from a speed below 40ish to a speed above 45ish in N (exact MPH number varies by model)
You can't use regenerative or engine braking in N, only friction braking.

On the other hand, should you ever suffer the semi mythical Sudden Unintended Acceleration*, N is the right gear.

* I have, in a Ford minivan

 

What is the harm to the motor/generators (aren't they disconnected in N) from coasting and why is it more harmful above 40 MPH?

 

The engine cannot start in N*, so M/G1 can rev to over 10,000 RPMs. Normally this is not an issue, as the engine always starts up to prevent this.

Nothing is ever disconnected mechanically in the Prius transmission, there are no clutches at all. In N, the M/Gs get/produce no electricaity, so freewheel.

* M/G1 starts the engine and neither M/G uses or generates electricity in N.

 

you need a pip for that decline.

 

I have no clue what a "pip" is but I can't imagine that you are gaining a whole lot in neutral compared to being off throttle for the decline. Whether or not it is damaging to your vehicle, I think it's a waste of effort.

 

In this context, he is referring to the Plug-in Prius, or "PiP". Some of us call each mark on the fuel guage a "pip."

 

While I am not the one to judge, you do need to know this is illegal in CA


V C Section 21710 Coasting Prohibited



Going 75, the engine has to be on, and so long as you have the engine on at the start, there is no risk of over reving the Motor/Generators. You still can't charge the HV Battery, but at 75 MPH, 4 miles is not a long time. I do not think you are harming anything, although I don't see any advantage.

Hitting the brakes while in N, is wasting energy as you can't be getting any regen.

 

If you start over the hybrid threshold speed, 42 mph for the older 1.5L Prius and 47 mph for the 1.8L Prius, there is no risk. The engine will already be running and the engine speed will adjust up as needed to keep MG1 in a safe range. However, if the engine is NOT running and you exceed 47 mph, it is possible MG1 might destructively over speed.

Now two of us, Good Prius Friend Hobbit and I have both 'tickled the monster' and exceeded the hybrid speed in "N" with the ICE off. I went up to ~50 mph and he has done something similar. However, I do not recommend it unless you are prepared to accept the risk.

When descending a hill large enough to significantly over speed MG1, I will briefly shift into "D" as I pass through the hybrid threshold speed to get the engine running. Then I can shift back into "N" without risk.

Bob Wilson

 

I would like to suggest getting a Scangauge II and programming in some XGAUGEs to monitor key metrics. Built-in, you'll get ICE rpm, engine coolant, and gallons/hr fuel consumption. But you can add XGAUGEs to see MG1 and battery metrics, to see what is going on. Regardless, welcome to the world of Prius experimenters. <GRINS>

What is your area of study?

Bob Wilson

 

Thank you, JimboPalmer and PriusChat! I learn new thing about our Prius on this site regularly.

 

One reason I enjoy Priuschat is that everyone is trying to help. I sure hope I got that right!

 

I'm not sure asking Toyota will be useful, as the owners manual already forbids this maneuver. For liability reasons -- it is both illegal, and potentially damaging if you botch the speeds and overspeed MG1 -- they really cannot give it their blessing.

I also don't see it as being all that useful. By carefully controlling the gas pedal and watching the HSI display, you can get rid of the synthetic 'engine compression drag' and effectively get a neutral coast. And if the car rolls up a bit too fast, regenerative braking is available both from the gas pedal and from the brake pedal.

But practicing shifting to Neutral is a good step in training how to respond to the semi-mythical Sudden Unintended Acceleration. Manual transmission drivers reflexively know what to do, but many people who drive only automatics don't know, especially under stress.

 

Correct me if I am wrong, but I do remember something in my vast readings on this site that 62 mph is the threshold for riding in neutral. Any higher speed than that and you have to make sure the engine is rotating.

I did a quick search:

ICE 'running' is ambiguous, because the ICE can turn over with or without burning gas in the HSD drivetrain.

Label however you want, but
No petrol, no ICE turn -- up to 62 mph
No petrol, ICE turning -- no speed limit, the ICE spin is powered by either kinetic or battery energy.

Read more: http://priuschat.com/threads/maxim-plug-in-prius-glide-speed.102023/#ixzz29OjpgBzd

 

I know others have made this point in other posts, but wouldn't popping the car in neutral (especially at higher speeds where the engine would basically shut off the gas intake and use the wheels to keep it going) and "gliding" that way be more fuel INefficient as opposed to keeping light pressure on the gas pedal to keep the artificial "drag" from taking over?

Or does the Prius operate differently? As in it'll still shut off gas intake into the engine even when gliding in N at high speeds?

 

That thread is for the Plug-In, not the regular Prius. Many of us have the regular Liftback equipped with an engine monitor (ScanGauge, Torq, and others), and I don't recall anyone reporting RPM=0 for speeds above 46 mph.