Pulse and Glide question

[sonyhome]

Originally Posted by RoadWarrior

Cruising at "max mpg" speed has the motor in a very inefficient operating region, and you're just doing the "least worst" you can with it, efficiency may be as low as 15-20%

Hmmm...

CR-V's should have a flat torque curve from 2K to 6K with the VTec engine design. If that's the case I should be better off cruising at 2000K RPMs, right? Peak torque is at 4500 RPMs I believe. Impossible to find a CR-V dyno...

How about doing P&G staying in drive, not going to Neutral? You pay the extra drag from the engine in G. That might be acceptable for highway driving... I don't have DFCO on the CR-V.

P&G trades off the cost of accelerating vs staying at constant speed, for usage of the engine at a higher efficiency for short intense work bursts, and low consumption for the glide.

[theholycow]

Originally Posted by Jay2TheRescue

I've noticed that my truck will P&G all by itself on a level road w/ the cruise set @ 60 MPH. Every time the cruise lets off the throttle for 3 seconds it will DFCO for a moment.

Originally Posted by sonyhome

How about doing P&G staying in drive, not going to Neutral? You pay the extra drag from the engine in G. That might be acceptable for highway driving... I don't have DFCO on the CR-V.

You've both described what I call "Pulse & DFCO". It's not gliding if you're not in neutral. If your torque converter doesn't stay locked then you are actually at a hybrid of glide and DFCO.

Pulse & DFCO does not work with a manual transmission*, but with a torque converter that unlocks during highway speed engine braking I imagine it could partially work.

I'm amazed that a CR-V doesn't DFCO.

*: It's even worse than just cruising; I gained 3mpg by using cruise at 70mph instead of Pulse & DFCO. I believe that this is because you're still subject to the same amount of engine friction, same amount of drivetrain loss, same everything; and it all adds up to the same energy used to get to your destination, but may be made less efficiently. I'm not sure why it would be made less efficiently, though, since when the engine is making power it's doing so at increased BSFC efficiency.

[Jay2TheRescue]

Hmmm, Hybrid glide... I like the sound of that... so its extending the "glide" by not letting the full momentum of the vehicle get eaten up by the compression of the engine... Anyway, like I said earlier, I would like to be able to reproduce my 30 MPG highway trip again.


-Jay