Maybe driving style doesn't matter?

[plus 3 golfer]

At highway speeds, I've found (via scangauge) that it's best to use the brakes moderately hard for max regen (max brake scores) and not coast.  Too much kinetic energy is lost to wind resistance and tire friction while coasting that could be going into the battery.

 

Coasting further not only allows for more charge of the battery but often means longer periods with no gas being used, the best driving for low mileage you can have.  I have not used scangauge but the harder the stop the more difficult it becomes to stay out of friction braking which shortens the life of your brakes.  

The question though is how efficient is the capture and reuse of the kinetic energy.  In my research and testing, I believe the following to be realistic:  the traction motor is likely between 90 - 93% efficient, the inverter efficiency is likely 90-95 % efficient, the battery is likely around 90% - 95% efficient.  So how much of the KE at the wheels can be captured and returned to the wheels.

 

wheel to wheel efficiency might be as low as = 0.90 * 0.90 * 0.90 * 0.90 * 0.90 = 60%

wheel to wheel efficiency might be as high as = 0.93 * 0.95 * 0.95 * 0.95 * 0.93 = 74%

 

So then, if losses in the regeneration process might be between 26 -40%,  is it better to use the losses even at higher speeds to offset road load by coasting or is it better to brake harder at higher speeds to store more of the KE to slow the car down quicker and reduce road load quicker?  I have modeled this before but am looking at it again.

 

Also, my guess is that when slowing down to a stop, many are seeing the PE of a slight drop in elevation also being captured.  Here's a quick chart showing the KE and PE of the C-Max. So, at 70 mph exiting an interstate down a 1/4 mile ramp with an elevation change of 10 meters, the C-Max has 0.25 kWh of KE and around 0.05 kWh of PE or 0.30 kWh of total energy.  So, what's the best course of action to capture the most energy in this 1/4 mile?  Or should one back off the throttle at 1/2 mile or more and coast in gear to scrub speed?  We know coasting adds time but it also saves fuel for 1/4 mile.

 

Edited January 18, 2015 by Plus 3 Golfer

[fotomoto]

  We know coasting adds time but it also saves fuel for 1/4 mile.

 

It's your last sentence that's the most significant for me (and I suspect most others).  I split the difference and use moderate braking from high highway speeds and coasting for lower speeds.   Coasting down from highway speeds with highly inflated tires isn't practical in most of my traffic situations as it takes too long (which is a GOOD thing from an efficiency standpoint).   The difference between the two at city speeds is usually only a tenth or two of a percent on the SGII; so a wash.  

 

So, I've found that banking the most regen I can in a short time frame (and thus not holding up traffic) is the best compromise in my Energi. NOTE:  It can bank more regen than the hybrid.

[plus 3 golfer]

It's your last sentence that's the most significant for me (and I suspect most others).  I split the difference and use moderate braking from high highway speeds and coasting for lower speeds.   Coasting down from highway speeds with highly inflated tires isn't practical in most of my traffic situations as it takes too long (which is a GOOD thing from an efficiency standpoint).   The difference between the two at city speeds is usually only a tenth or two of a percent on the SGII; so a wash.  

 

So, I've found that banking the most regen I can in a short time frame (and thus not holding up traffic) is the best compromise in my Energi. NOTE:  It can bank more regen than the hybrid.

Yes, I've said similar before - traffic constraints and my time dictate what I do.  It simply takes too long to coast in gear from 70 mph to the exit ramp for it to be practicable for me given the traffic conditions I drive in.  So, I do brake fairly hard once I hit the exit ramp and then  apply moderate braking once speed is reduced trying to achieve a good score.  In suburban and city driving where speed limits are generally in the 35 - 45 mph range with lights every 1/2 to 1 mile, it's a lot easier to coast and time lights plus the amount of KE is so small (that would not be captured by coasting) that it matters little on braking technique. Increasing braking score amounts to very little additional energy captured. 

 

Bottom line: I'm not going to alter my braking techniques - that's why I quit trying to develop a regeneration model after Ford got the RLHP coefficients correct.  Also, we don't know the exact algorithm used in regenerative braking but can guess at the max regen kW  and the coasting regen kW to simulate ICE braking (difference between my coast down runs in gear vs in N).  Anyways it's fun to try to understand the physics behind regenerative braking.

 

Tying this back to the topic, regenerative braking style / technique IMO matters little to FE given traffic constraints most drive in.  Decrease ones overall driving speed and watch FE soar. :)

Edited January 19, 2015 by Plus 3 Golfer

[SnowStorm]

At highway speeds, I've found (via scangauge) that it's best to use the brakes moderately hard for max regen (max brake scores) and not coast.  Too much kinetic energy is lost to wind resistance and tire friction while coasting that could be going into the battery.

I can believe your scangauge will show more energy but I don't think that is the goal.  The goal is to use the least amount of total energy going from point A to B.  It is better to have kinetic energy go directly towards pushing the car rather than loose some through the regen process.

 

So, what's the best course of action to capture the most energy in this 1/4 mile?  Or should one back off the throttle at 1/2 mile or more and coast in gear to scrub speed?  We know coasting adds time but it also saves fuel for 1/4 mile.

 

Goal should be to waste the smallest amount of energy.  That means no friction brakes and the smallest amount of regen practical.  The 1/4 versus 1/2 mile comparison is nice - you burn no fuel for an extra 1/4 mile.  But then your average speed is slightly less so you have to cruise a tiny bit faster!  Probably offsets the whole thing.

Anyways it's fun to try to understand the physics behind regenerative braking.

 

Tying this back to the topic, regenerative braking style / technique IMO matters little to FE given traffic constraints most drive in.  Decrease ones overall driving speed and watch FE soar. :)

Agree - agree - agree.  Still think the simplest, most natural and "best" is:

1. "Coast" down from high speeds for a bit.  It just seems "wrong" to hit the brakes at 70 mph (friction or regen).
2. Brake the rest of the way so as to get a high score (80% to 90% or above).  Experience, available distance and grade dictate when to start braking.  I suppose the goal is to use max available regen without friction brakes.  I'm not obligated to do a panic stop just because a tailgater wants to save 2 seconds.
3. If you have a choice on exits, choose those that are uphill.  Converting kinetic to potential energy is essentially 100% efficient.
4. Otherwise, don't worry about it!

[fotomoto]

 The goal is to use the least amount of total energy going from point A to B.  

 

My goal is to get from point A to B in the most efficient manner in regards to both energy and time.  I can do my daily commute via two routes; one is more energy efficient and the other more time.   I choose the time route and try to manage it with the least amount of energy I can.  When I got my 894 mile tank, I chose the more efficient route but it cost me a whole lot of time (approx. 30 minutes per day).

Edited January 23, 2015 by fotomoto

[ptjones]

Back to the OP, you don't go 920mi on 13.5gal averaging 68mpg by accident, driving style is everything! :) 

 

Paul