Engine Braking, is it possible to over rev the engine?

1) No, the computers will not overrev your engine.
2) Avoid N at any time, neither M/G1 nor M/G2 has any power in N. No charging happens in N, the gas engine cannot start in N.

There are odd conditions where N can hurt your MG/1 motor, in Gen1 and Gen2, coasting in N from bellow 42 MPH to above 42 MPH would over rev MG/1 as the gas engine cannot be started in N. This limit SHOULD be 62 MPH in Gen 3 but I have never seen a test of that.

 

I'm still enjoying tripling my MPGs in going from a pickup to the Prius, so I can't vouch personally, but I understand the correct technique for max MPG is to feather the as pedal so that no bars appear in the regeneration part on the left of the upper dash display.

 

Real Neutral is a wonderful tool in traditional manual transmissions, but unnecessary on a Prius. It is OK on mild slopes where you don't speed up. Uncle Wayne has students use it so that they can quickly get the feel of a true glide. But they are supposed to practice achieving the same thing by just putting light pressure on the gas pedal and not shifting into Neutral, saving time and hand motion and avoiding risk. His lessons just don't have enough time to gain proficiency at it, so on a Prius, Neutral is a stopgap to help pack in more lesson in the brief time available.

The Hybrid system is more complex than that. MG1 is typically a generator, passing some of the propulsion power on the electrical path to the motor MG2. The rest of the power flows through the mechanical path. But there are several other operating modes, and each MG gets its turn both as a motor and as a generator.

Toyota warns to not shift to Neutral while moving, but doesn't go into detail about what the risks really are. (Whatever they write, someone will misunderstand and botch it, damaging the transaxle.) Some of us do it on occasion anyway, believing we know how to avoid the risky spots, but mostly nudge the gas pedal to achieve essentially the same result. Neutral is also an important tool to know in case of a real runaway engine, something that has been alleged on numerous car models over the decades, but in the modern era is mostly caused by pilot error instead of true mechanical problem.

 

Motor/Generator 2 is linearly attached to the wheels, if they are stopped, it is stopped, it is always going the same speed at 60MPH (or any speed) regardless of load. Viewed from the perspective of M/G2 your Prius has a one speed transmission with no clutch.

Motor/Generator 1 has a function as your car's starter, and, frequently, as your car's alternator, but is used by the computers to help adjust engine speed. By spinning plus or minus zero to 10,000 RPM, it can force the engine RPM to be what the computers believe is ideal for current conditions.

The ratio between M/G 1, the internal combustion engine (ICE), and M/G 2 is fixed (no gears ever shift) and there is no clutch. (the gears always turn when moving) Yet Federal law requires a N gear, and there is not one. Toyota emulates Neutral by cutting power to both M/Gs (with nothing to push against, the engine can never move the car)

Since neither M/G has power, no electricity is being generated in N.

Toyota Prius - Power Split Device
Down the page, is an emulator that allow you to change M/G 2 RPM (and so Prius speed) and engine RPM. If the line connecting M/G 2, the ICE, and M/g 1 goes red, you have chosen an impossible combination. (Try leaving the engine off and traveling more than 42 MPH)

 

I am finding it almost impossible to just nudge the gas pedal to achieve the equivalent of neutral for more than just a second or 2. Once all arrows have disappeared what are you supposed to do next?

 

Try to keep your foot in that position as steadily as you can (it's easier in ECO mode). For Gen3 (and Prius-v) the Energy display often doesn't show no arrows for very long, but the consensus from those with scangauges seems to be that even 1 bar above zero on the HSI generally works out to a glide.

 

In a GenIII liftback (sorry, I'm not familiar with the 'v' displays), don't bother with the arrows. (It actually is impossible at some speeds.) Instead, use the HSI display, and aim to cut the HSI bar close to zero. Close is good enough, there is no need for 0.01% accuracy.

The 'no arrows' display is useful in the GenII, where it is easily achievable. But for some unknown reason, Toyota cut the 'close enough' window in the GenIII display down to a very impractically narrow spread.

 

On my v, two green bars is about right. It is not worth my life to study if that is precise.

 

When you take your foot completely off the gas, there is a little bit of regen braking applied to help simulate engine drag as on a non-hybrid car. The HSI will show one pip in the charge area. You're applying just enough pedal pressure to override that regen. At highway speed in this situation, the ICE will be turning (because it has to prevent the MGs from spinning too fast) but no fuel is burning.

 

There is only one gear. It is engaged ALL the time. There is no clutch.
P adds a pawl not to let the gear move.
R is electric only, with the Motor/Generators turning 'backwards'.
N does not send or accept electricity from the Motor/Generators
B adds real engine braking, so gets lower MPG.
D allows the Motor/Generators and the Engine to be blended to achieve the best MPG.

If you imagine a manual 'stuck' in 3rd, with no clutch, you will see that the computers do an excellent job.

 

When applying light throttle take your cue about gas usage from the instantaneous mpg reading. As long as it's displaying 99.9 mpg no gas is being used.

 

Don't you have the picture with the arrows on down on the Nav screen, press the CAR button.

 

At lower speeds that's true. Somewhere above 70 km/hr though, the engine HAS to run. The car will persist in showing infinite mileage, but in fact it's idling, albeit using very little gas.

It's too bad the Prius doesn't display rpm; you can see this with a ScanGuage.

 

If you have the radar cruise control you can set the cruise and when you need to brake, say for a bend, you drop the speed setting down the 5 mph increment. The cruise will hold you at the set speed with regenerative braking, no foot brake needed. We live in Colorado and come down some very steep canyon roads, almost 100% without using the brakes.

 

The magic speed is 42 MPH or 67.6 KPH. If you go to this link you can see the relationships between ICE and MG2. You can use the MG2 slider to verify the 42 MPH

You will discover later on in this thread that the link I have provided is for Gen II and that due to gearing changes the speeds are now different.

 

It certainly was in the Gen 1. I suspect it varies in the Gen 2, Gen 3, c, v, and PHV.