Delay ICE fire until after 15mph? (Prius)

F8L · #1 06-20-2012, 09:48 PM

It is generally considered more efficient to accelerate briskly from a stop, reach your desired speed then lift off the throttle then reapply gentle pressure to maintain speed. But I noticed in one of Wayne's videos he was instructing a driver to delay ICE startup until 15mph by using EV power only until that point then forcing the ICE to fire. I think I understand the mechanics of how this could possibly be more efficient despite going against common opinion but I would like to know more about this practice and why 15mph vs. 25mph (EV Mode speed limit).

Can anyone help me understand this concept a little better?

ALS · #2 06-21-2012, 09:24 AM

You're using the battery to get the car from a stop and up to fifteen miles per hour. Thus you have eliminated the biggest drain on the engine moving the car from a dead stop to a set speed. It's easier to optimize fuel mileage accelerating from 15 to 35 mph with the engine when you already have the vehicles momentum on your side.

Harold · #3 06-21-2012, 10:03 AM

This can only be done when in stag 4 , right? Or after ICE is at operating temp warmed.H

ksstathead · #4 06-21-2012, 10:14 AM

Harold, I think it would work in stage 3 as well, but have not looked back at that.
Definitely a no go in stage 1.

F8L, I think by 15 mph the ICE can add enough torque to make it worthwhile, and it also gets you going more tolerably for those behind.

F8L · #5 06-22-2012, 01:25 AM

Thanks guys.

I have been doing this off and on but I'm not consistent with it so I have not been able to determine how effective it is. I was hoping to hear your thoughts and get a more solid answer so I can decide if it is worth the effort or not.

Now that I am starting to see 60mpg tanks more regularly I am interested in putting a little more effort into keeping them over 60.

F8L · #6 06-24-2012, 09:36 AM

Here is one of the videos in which this technique is used.

http://www.youtube.com/watch?v=7fzLp...e_gdata_player

groar · #7 07-16-2012, 07:13 AM

The MG have lot of torque as soon as they turn, while the ICE has to turn rather quickly.
At low speed, without too hard acceleration (ie in golf cart), the MG doesn't consume a lot, so it may be useful to use wasted energy stocked in the HV battery than to use the ICE.

In S1, the Prius is mainly in golf cart, while the HV battery is full enough.
After S1, while the HV battery is full enough, try to accelerate in golf cart up to 15mph.
The 2nd rule is : never go under 15mph, but before all (except safety and courtesy)
the 1st rule is : never stop.

Staying between 18 & 31mph seams ideal : I was over 70mpg until yesterday and reached 72 over 500mi of daily commutes 12 days ago. I'm using golf cart to accelerate up to 15-18mph.

Have fun,

Denis.

PS Wayne, when are you coming in France to give us your number ?

Harold · #8 07-16-2012, 09:55 AM

If Wayne uses this method I would not bet against the benefits F8L. H

herm · #9 07-16-2012, 12:04 PM

Denis, I'm going to start calling BEVs Golf Carts

groar · #10 07-16-2012, 12:48 PM

"golf cart" is to differentiate with the EV mode.
The EV mode is with the EV button : you can have stronger acceleration but up to a lower speed.
The "golf cart" mode is without the EV button : you have lighter acceleration but up to an higher speed.

The EV mode is definitely EVil as it can consume a lot : don't use it, maybe except for a few very rare useful situations, per example to switch off the ICE in S3 or to beat a trip record.

Denis.