Hello, I was wondering when you guys are pulsing and gliding with your prius (classic or new). Do you use just enough accelerator pedal to stop regen of the batteries or do you shift the shifter to N to coast? Is there any noticeable differences between the two? Or is it just a matter of different ways to do different things?

Thanks!

 

From the Alabama driving code:

"Section 32-5A-57
Coasting prohibited.

(a) The driver of any motor vehicle when traveling upon a down grade shall not coast with the gears or transmission of such vehicle in neutral or the clutch disengaged.

(b) The driver of a truck or bus when traveling upon a down grade shall not coast with the clutch disengaged.
(Acts 1980, No. 80-434, p. 604, §11-108.)"

http://www.legislature.state.al.us/C...5/32-5A-57.htm

My understanding is most states have simular laws against "coasting."

The "Pulse and glide" articles indicate they had additional instrumentation to help them 'feather' the accellerator:

". . .
In order to achieve extreme fuel economy, the team primarily used a gas-saving technique called pulse and glide. It's a form of coasting that involves releasing the gas pedal, then pressing it slightly again to disengage the electric motors. And as they glide, the drivers glance at a built-in screen displaying vital statistics like average miles per gallon.
. . ."
http://www.post-gazette.com/pg/05220/550484.stm

The Prius is a computer controlled car which makes such instrumentation easy.

Bob Wilson

 

Are there any laws against speeding? Considering I see many more people speeding on the highway than I do using a neutral cost I would assume there isn't such a law.

Neutral coasting is no more dangerous than speeding. The only difference between the two is that police can't tell if you are neutral coasting but they can certainly tell if you are speeding.

 

I just use the light touch on the pedal that you mentioned. As touchy as that pedal is I find it easier than reaching for the shifter. Sometimes my glides are quite short and I would not want ot be going in and out of gear that much.

 

The statute predates hybrid electrics. In the days of model A Fords and less effective, mechanical brakes, they wanted to keep speeds going down hill moderated by engine braking. Having driven a model A Ford in high school, this was a real problem. Putting a low-rolling resistance, hybrid into neutral on a down grade and the original problem of over speeding returns. In the case of the Prius, going into to neutral also disables the electrical generation circuity and that might put the battery at risk.

A better approach is an assisted cruse control. This keeps the vehicle 'in gear' at all times while keeping the target speeds within a narrow and safe range. Thus having set the 'top speed', the assistant cruse control would decrement the setting as needed to keep the car in glide until some lower threshold, 5 or 10 mph lower, was reached. When power is needed at the lower speed, it would then accellerate the cruse control back to the original speed. Once the power demand levels out, it would restart the glide. With this approach, the existing vehicle ICE, battery and hybrid vehicle ECUs would continue to work just as designed.

This type of modification is straight forward in computer controlled cars like the Prius. All of the computer controls and sensors for the ICE, MG1, MG2 and speed sensors are built-in. Adding a single-board computer and software for this function is straight forward.

Bob Wilson

 

I glide by working the accelerator pedal. The biggest safety advantage is that acceleration is immediate in case of the need for a collision avoidance maneuver.

 

I find it depends on the engine temperature and velocity of the car. When just starting out on a cold morning it is almost impossible to use the accelerator pedal to achieve a drifting mode. Neutral is the way to go here.

Another time when using neutral is clearly best is at highway speeds.

When the engine has warmed up somewhat and speeds are, say, less than 40 mph, it is easy to simply use the accelerator pedal. So I find myself doing it that way "around town." It also feels more appropriate for short drifts. When I can anticipate a significant drift, even at low speeds, I simply hit the shifter and put her in neutral.

storm petrol
'05 Prius/package 5

 

But you can certainly tell if you suddenly need to accelerate to get out of danger and the gas pedal doesn't do anything but revv the engine.

 

I throw it in neutral at cold temperatures and low speeds. I glide, everywhere else.

Is there a risk to the transmission, if you throw it in neutral, at high speeds? I don't fully understand the CVT, but I'm concerned putting it back in "gear" at highway speeds could mess up the transmission.

 

There's nothing mechanical happening when you put a Prius in neutral, it's really just setting a mode for the computer to be in that disables the electric motors, although I don't know to what extent, it may have to run one of them above 40 to keep the engine spinning to protect itself... I'll try to remember to check that out on the CAN-View.

Bottom line: there's absolutely no danger in re-engaging back to D mode at higher speeds in the eCVT type transmission.