Braking best techniques

[SnowStorm]

Yes this really sucks. I just downloaded the 2014 manual and did a search for the word  lifetime and came  up with nothing :(

They probably removed it as many didn't know how to reset it and early driving miles by the owner learning how to drive  Hybrid led to early poor mpg numbers and then people complaining about it getting less than advertised mpg and then  posting bad reviews on the net and suing Ford.

Horrors!  So lifetime EV, Regen and Breaking Score are gone too?  :rant2: We love seeing that we've gone over 12,000 miles with the engine OFF!  Its our favorite way to "brag" on the car!

[salsaguy]

Not sure what else is gone since I didn't read the entire manual just looked up that 1 page from the Ford downloads site.

[jestevens]

Don't just tap the brakes - learn to look at the traffic flow ahead of your car - see if there are any red lights coming up, and what the other drivers in front of you are doing..if someone is making a turn back off the throttle slightly or if you will have to stop apply a slow steady pressure to the brakes in order to brake the car so that it slows down gently behind the car in front of you.  The longer you can brake (within reason), the more regen is going into the battery. 

 

This is of course subject to safety.  I also look in the rear view to see just how much hypermiling is going to frustrate the other drivers and try to adjust my driving style accordingly.  If I know that they are ALSO going to have to stop with me I take that into account and sometimes will gently slow down several MPH to try to meet the other cars' acceleration curve as they are pulling away at a stop light.

 

I usually get a very good brake score, unless I am caught off guard by a traffic light or a "merging" motorist.  It's the acceleration score I have a hard time with, I just love the extra torque and I hate the idea of a bunch of people sitting behind my car while I slowly throttle up to speed seems tedious.  I prefer briskly accelerating to crusing speed and then trying to "cruise" as much as possible around town.

[SnowStorm]

I agree with "briskly accelerating" but that's a relative term.  Here's a suggestion for establishing an acceleration rate we can all compare to:

1. Set cruise control to Eco mode
2. Go to 55 mph and "set" the speed
3. Slow to just above 20 mph (minimum speed for cruise to work)
4. Tap Resume and keep foot off accelerator

The car will accelerate smoothly at about "2 bars" all the way back up.  Call this rate "Eco Acceleration" which I would call "moderate".  Some would call it "slow", others may call it "brisk" - suit yourself.  At least its a point we can all replicate for comparison purposes.

 

I feel that "Eco Acceleration" is a good rate for normal driving - one that shouldn't annoy any reasonable driver behind you.  It should still be quite efficient - it is "Eco" after all!  One variant though is to accelerate harder when you have a low SOC in order to keep the HVB from charging (up arrow) while accelerating.  I'll just "step on it" until the up arrow is gone - but no more.  The inverse process with a high SOC, however, is rather out of the question.  That is, slowing your acceleration to prevent discharge is not practical - the rate will be too slow.  So, my summary would be:

• Accelerate with Eco Cruise if practical
• Accelerate harder if necessary to prevent up arrow
• Don't use EV for acceleration (as many have said before)
• Don't accelerate past 3000 rpm (if watching the Tach) as that is likely beyond the peak efficiency point.

[scottwood2]

 

I agree with "briskly accelerating" but that's a relative term.  Here's a suggestion for establishing an acceleration rate we can all compare to:

1. Set cruise control to Eco mode
2. Go to 55 mph and "set" the speed
3. Slow to just above 20 mph (minimum speed for cruise to work)
4. Tap Resume and keep foot off accelerator

The car will accelerate smoothly at about "2 bars" all the way back up.  Call this rate "Eco Acceleration" which I would call "moderate".  Some would call it "slow", others may call it "brisk" - suit yourself.  At least its a point we can all replicate for comparison purposes.

 

I feel that "Eco Acceleration" is a good rate for normal driving - one that shouldn't annoy any reasonable driver behind you.  It should still be quite efficient - it is "Eco" after all!  One variant though is to accelerate harder when you have a low SOC in order to keep the HVB from charging (up arrow) while accelerating.  I'll just "step on it" until the up arrow is gone - but no more.  The inverse process with a high SOC, however, is rather out of the question.  That is, slowing your acceleration to prevent discharge is not practical - the rate will be too slow.  So, my summary would be:

• Accelerate with Eco Cruise if practical
• Accelerate harder if necessary to prevent up arrow
• Don't use EV for acceleration (as many have said before)
• Don't accelerate past 3000 rpm (if watching the Tach) as that is likely beyond the peak efficiency point.

 

I don't understand why you would want to keep the battery from being recharged while accelerating if the SOC is low?  That is when I try to accelerate slower if I can so I can charge and get up to speed at the same time. 

[raadsel]

I don't understand why you would want to keep the battery from being recharged while accelerating if the SOC is low?  That is when I try to accelerate slower if I can so I can charge and get up to speed at the same time. 

 

Because you don't necessarily want the battery charged. Remember that charging the battery is using extra gasoline. The idea behind a hybrid is to recapture lost energy (regenerative braking) and, to a lesser degree, to run the ICE as efficiently as possible. So, for example, when running at a steady rate of speed on the highway, Ford knows what RPMs the engine runs most efficiently -- for example, bumping the engine speed from 2000 to 2200 RPMs might use little, to no, additional gas (this is merely a demonstration, I don't know the efficient points of the engine); so it it is more efficient to run the engine at 2200 RPM and use that slight increase in power to charge the battery.

 

By contrast, when you are accelerating, you are above the RPMs where the engine is its most efficient. Slowing down, so you can charge the battery, tends to make your acceleration even more inefficient; any charge you are adding to your battery is costing you MPG because of how hard the engine is working. Instead, the idea is that accelerating faster, so the battery does not charge, runs the engine harder for a shorter length of time and, while you are using more energy, short term, to get to speed, you are saving energy because the engine runs efficiently for longer. 

 

At least one argument made by hypermilers is: since all battery charge is created by use of gasoline, and you are losing some energy by converting the power to electricity and then charging your battery, you want to charge the battery as little as possible. It can be debated how true that is, but it is worth remembering that you want the best fuel efficiency, which isn't always the same as running in EV mode as much as possible.

Edited April 28, 2015 by raadsel

[ptjones]

To me it seems like the computer wants to accelerate at two bars which ends up in the range of 2k-3k rpm . For maximum mpg you need to have the minimum ICE (28% for me on best mpg's).

 

Paul

[SnowStorm]

I don't understand why you would want to keep the battery from being recharged while accelerating if the SOC is low?  That is when I try to accelerate slower if I can so I can charge and get up to speed at the same time. 

That comment is in the context of maximizing "fun" without sacrificing efficiency.  I'm not so much trying to avoid charging - just trying to accelerate using all available energy that's being generated at the ICE's peak efficiency point.  If I accelerate more slowly, the control algorithm will run the ICE on up to the peak efficiency point anyway, using the excess energy to charge the battery.  You can use all energy to accelerate quickly (and then charge at steady speed) or accelerate slowly while charging at the same time.  If the ICE is always at its peak efficiency point, you should burn the same amount of fuel either way.  Somewhere down the road you will have stored the same amount of kinetic and battery energy using the same amount of fuel.

 

But I got just a little more "fun per gallon"! 

[scottwood2]

Because you don't necessarily want the battery charged. Remember that charging the battery is using extra gasoline. The idea behind a hybrid is to recapture lost energy (regenerative braking) and, to a lesser degree, to run the ICE as efficiently as possible. So, for example, when running at a steady rate of speed on the highway, Ford knows what RPMs the engine runs most efficiently -- for example, bumping the engine speed from 2000 to 2200 RPMs might use little, to no, additional gas (this is merely a demonstration, I don't know the efficient points of the engine); so it it is more efficient to run the engine at 2200 RPM and use that slight increase in power to charge the battery.

 

By contrast, when you are accelerating, you are above the RPMs where the engine is its most efficient. Slowing down, so you can charge the battery, tends to make your acceleration even more inefficient; any charge you are adding to your battery is costing you MPG because of how hard the engine is working. Instead, the idea is that accelerating faster, so the battery does not charge, runs the engine harder for a shorter length of time and, while you are using more energy, short term, to get to speed, you are saving energy because the engine runs efficiently for longer. 

 

At least one argument made by hypermilers is: since all battery charge is created by use of gasoline, and you are losing some energy by converting the power to electricity and then charging your battery, you want to charge the battery as little as possible. It can be debated how true that is, but it is worth remembering that you want the best fuel efficiency, which isn't always the same as running in EV mode as much as possible.

 

 

That comment is in the context of maximizing "fun" without sacrificing efficiency.  I'm not so much trying to avoid charging - just trying to accelerate using all available energy that's being generated at the ICE's peak efficiency point.  If I accelerate more slowly, the control algorithm will run the ICE on up to the peak efficiency point anyway, using the excess energy to charge the battery.  You can use all energy to accelerate quickly (and then charge at steady speed) or accelerate slowly while charging at the same time.  If the ICE is always at its peak efficiency point, you should burn the same amount of fuel either way.  Somewhere down the road you will have stored the same amount of kinetic and battery energy using the same amount of fuel.

 

But I got just a little more "fun per gallon"! 

Interesting.  I will have to play around with that technique.  I guess it does make sense as there is always a loss when converting energy. 

 

I mainly try to use ICE to accelerate and charge the battery.  I use that to get above the speed limit and then go to elec mode just so it gives a little power .  The pulse and glide technique.  In the city I can get 50 to 60 or more MPG with this.  Now if I have a high SOC then I accelerate quickly to get to a point I can glide again. 

 

It will be fun to try this new technique to see how it compares for my driving style.  

 

Thx for the explanation of this technique.

[fbov]

 

To me it seems like the computer wants to accelerate at two bars which ends up in the range of 2k-3k rpm . ...

I got a ~15% improvement in mileage when I stopped doing that.

 

When I got the car, the conventional wisdom was to accelerate as fast as would keep the battery charging. Keep that ^ visible, which allowed full 2-bar acceleration if SOC was low.

 

Last year, I tried lower throttle settings, about 1.5-bar, so the car accelerated more slowly, and spent more time charging the battery (and warming coolant in winter). I soon realized that lower throttle settings increased the charge rate as well. I've since set My View up with a tachometer so I could watch RPM. Keeping it under 2,000 RPM most of the time has made a huge difference, as I can still accelerate and climb what pass for hills around here while charging the HVB - win-win-win.

 

You may have to open this is a new browser window to see it, but in the lower chart, "baseline" was using 2-bar, and the "Spring" and "Summer" were more like 1.5-bar acceleration (when prudent, of course)

 

Have fun,

Frank

Edited April 29, 2015 by fbov

[ScubaDadMiami]

 

 

I got a ~15% improvement in mileage when I stopped doing that.

 

When I got the car, the conventional wisdom was to accelerate as fast as would keep the battery charging. Keep that ^ visible, which allowed full 2-bar acceleration if SOC was low.

 

Last year, I tried lower throttle settings, about 1.5-bar, so the car accelerated more slowly, and spent more time charging the battery (and warming coolant in winter). I soon realized that lower throttle settings increased the charge rate as well. I've since set My View up with a tachometer so I could watch RPM. Keeping it under 2,000 RPM most of the time has made a huge difference, as I can still accelerate and climb what pass for hills around here while charging the HVB - win-win-win.

 

You may have to open this is a new browser window to see it, but in the lower chart, "baseline" was using 2-bar, and the "Spring" and "Summer" were more like 1.5-bar acceleration (when prudent, of course)

 

 

Have fun,

Frank

 

This sounds like what I do. Also, things depend on your intended speed and your current SOC.

 

If my HVB is low while my intended speed is city speeds, 30-45 MPH, I tap to engage ICE, bring the pressure down to just enough to keep ICE engaged, and I do a slow burn that keeps me going at the same speed (or slowly speeding up) while charging. Once I get to a good SOC, I do another "soft" tap, engaging HVB and turning off ICE, and I either keep going at the same speed, or I am slowly slowing down somewhat, and I glide until back down to a low SOC. I make changes to technique based upon the road conditions, such as areas with known hills, places where I have to stop for signals, etc.

 

If I have a low SOC and I need to speed up from a dead stop, such as from a red light, I start rolling with EV up to about 15-18 MPH, then I do a brief (as brief as I can get away with, given traffic flow--usually for about 5 to 7 seconds, something like that) two bar burn with ICE. This keeps me moving with the traffic flow, or even better than that. I back off of the throttle pressure but keep ICE engaged, and I try to maintain about 1.125 bar pressure to continue to speed up. After checking with My View many times, this works out to the 2,000 RPM figure.

 

If I have a high SOC, I start rolling in EV up to about 15-18 MPH, then I do a two bar burn to get up to intended speed ASAP. The reason: ICE uses less gas by making a higher burn for a shorter time than it does with a lower burn for a longer time. Once at speed, I glide using EV.

[fbov]

...: ICE uses less gas by making a higher burn for a shorter time than it does with a lower burn for a longer time.

I've come to question this, with very positive results, as this is exactly what I changed.

 

The "higher burn for a shorter time" approach leaves me with lower SOC compared with "lower burn for a longer time." Believe me when I say I was skeptical, but watching the tank average MPG, I realized that at 1.5-2K RPM, the car seems to use much less gas than at 2.5-3K RPM. A low burn that drops the average 0.1MPG is a lot longer than a high burn with the same MPG drop, and you gain SOC and WT (a critical advantage in winter).

 

Conversely, SDM, I'm finally getting the hang of EV'ing from a stop, a technique you once suggested that I had a hard time achieving.

 

BTW, the low burn approach has an interesting affect on following traffic. Invariably, the conventional drivetrain is on my bumber coming out of the intersection, because they're in a low gear putting lots of torque to the road. As their tranny shifts to higher gears, their accelaration rate slows. They invariably end up many car lengths behind because they stop accelerating when they hit high gears. Our little CVT will keep the ICE RPM constant the whole time, so my slow acceleration has continued past their achieved cruising speed. They may catch up, but I've still only been passed once in 21 months driving the car.

 

Have fun,

Frank

Edited April 30, 2015 by fbov

[scottwood2]

I tried the new technique last night.  I did 5 stops (trips) and tried to keep the car from charging the battery while I was accelerating.  It felt really strange and kind of the opposite from what I have been driving.  So this produced much shorter bursts of power keeping ICE off a whole lot more but my battery was not being charged much.  The recharge mainly came from decel and braking.  Once I was up to speed (above speed) I would go to elec and try to just keep the down arrow on.  This works pretty well most of the time and I am always surprised how this little amount of power pushes the car.  If the speed would drop too far down I would use ICE to quickly bring the speed back up.  Usually after 10 MPH drops.   This depends on traffic too. 

 

I almost stopped doing this about half way to my 1st stop as it just did not feel right.  I really thought my FE was going to suck but I decided to stick it out to see what happens.  To my surprise i did almost 56 MPG.  I mainly get upper 40's /  low 50's going home and this was a totally different route so I had no comparison but I did not expect anywhere near this FE. 

 

I continued the other legs of the trips and did even better.  Some in the 60's and even one at 72 MPG (short trip 2 miles). 

 

Coming into work this morning I did 55 MPG.  My old technique would do this and sometime into the 60's but there is not much traffic but a lot of lights so avg speed is way lower. 

 

I really did not focus on the RPM much other than to try to keep the battery from being charged by ICE.  It was hard to do sometime and would still charge at over a 3 bar burn but again at this acceleration ICE is not on very long.  I was also surprised by how much the decel and braking recharged the battery.  My SOC gauge was low on the scale most of the time but it was enough to keep the car moving most of the time without starting ICE to charge. 

 

Thx for the tip and my other half appreciates the speedier drive as well  :)

[SnowStorm]

This discussion sent me back to one of my OBDII data logs.  I found an extended period cruising along at 54 mph with several cycles of EV versus ICE.  First, when ICE is on it goes to about 85 ft-lbs and 2000 rpm which is 32 HP or 24 kW.  Looking back through the graph you can see an obvious "preference" to run the ICE near these values so, having no BSFC map :sad: , I'll take that as the most efficient point.  Second, the limit for ICE charging of the HVB is 35 amps (it never goes higher) which is about 10 kW.  So for peak efficiency with a low SOC (HVB charging at 10kW) you need to use 14kW (17 HP) to run the car.  If you don't need that much power, the ICE is forced to run below the peak - no way out.  As SOC goes up, the charge rate starts to drop off.  I can see an earlier point where, after an extended ICE run at 55 mph, the HVB current was near 0 and the ICE was at 60 ft-lbs and 1550 rpm (13kW).  So much for steady speed.

 

When accelerating, we still want to stay on top of the magical BSFC mountain!  But its quite a balancing act between SOC, car speed, traffic, hills and fun!  Forgetting traffic and hills for the moment, below are some observations/suggestions (all subject to peer review!).

1. If you accelerate too slowly with ICE on, you may not use all 24kW of peak efficiency power.  Not good.
2. Accelerate too hard and you will push the ICE past peak and/or pull battery power to help.  Keeping RPM below 2500 certainly seems advisable.
3. Keeping SOC low in stop/go driving seems good since it gives a place for any excess ICE power to go (you can't always use 24kW) and helps prevent negative split mode.
4. It seems good (as several have suggested) to start in EV for a bit.  Helps keep SOC low.
5. Once ICE comes on, push it to the "no charge" point but no further.  Its more fun!  Might be more efficient as well.

We don't have any regular daily commute to do comparisons on so must leave that to others.

 

(P.S. I think this post about "braking techniques" is feeling hijacked!)

[ScubaDadMiami]

The "higher burn for a shorter time" approach leaves me with lower SOC compared with "lower burn for a longer time." Believe me when I say I was skeptical, but watching the tank average MPG, I realized that at 1.5-2K RPM, the car seems to use much less gas than at 2.5-3K RPM. A low burn that drops the average 0.1MPG is a lot longer than a high burn with the same MPG drop, and you gain SOC and WT (a critical advantage in winter).

 

Conversely, SDM, I'm finally getting the hang of EV'ing from a stop, a technique you once suggested that I had a hard time achieving.

As to the first point, that is correct. I only use that technique (2 bar burn) when I already have a high SOC. If I have a low SOC, I get rolling in EV, then I tap to engage ICE but at a low RPM, usually well below 2K RPM (I never checked, but it corresponds with about .5 bar), charging up while driving from between 20 MPH to about 35 or so. The long, slow burn is usually for more than a minute, whereas the 2 bar burn is for usually only about 5 to maybe 9 seconds, depending on upper speed.

 

Glad to hear that you have learned to chase the bar! ;)

[jestevens]

I never bother with trying to control whether the ICE is charging the HV battery or not..the battery NEEDS to be charged and eventually it will be regardless of how "ginger" you try to be with the throttle.  Trying to monitor the SoC all the time using just the factory gauges seems like it takes too much time away from concentrating on actually driving the car.  Even if the car is in warm up I still get to use that energy later on in the trip driving around the 25MPH area at work on pure EV.

 

Sure, it's exciting to try to max out the MPG but you still can't change the laws of physics..or the patterns of other drivers..I have noticed my coach score go way down as I react appropriately to sudden changes in traffic - it's not worth an extra 1 or 2 MPG to me to not treat this thing like a car..  The beauty is with both this car and the prius sedan, you can get very good fuel economy with only a few modest changes in driving style.

Edited May 1, 2015 by jestevens

[fbov]

...The long, slow burn is usually for more than a minute, whereas the 2 bar burn is for usually only about 5 to maybe 9 seconds,...

Clearly, in any tradeoff scenario, there are points of diminishing returns. I believe a 10x different in burn duration is well past that point. I'm suggesting more like 1.5x duration, 8 to 12 second burns instead of 5 to 9 seconds. The goal is lower RPM, not the lowest.

 

To Snow's point, I see the 2K-2.2K RPM sweet spot a lot, but also one at 1.5K RPM, and a couple scenarios that run more like 1-1.1K RPM. Of course, I'm drving mostly with a 35 MPH speed limit, so I'm not surprised I see lower ICE RPM modes.

 

And you've got the BSFC map link, right?

http://ecomodder.com/wiki/index.php/Brake_Specific_Fuel_Consumption_(BSFC)_Maps

 

Viewing several BSFC maps, I see a common thread... peak efficiency is a plateau of high load in the 1.5K-3KRPM range for Atkinson (Toyota) and many conventional gas engines. In Snow's example, I expect the 24kW@2000RPM running point would shift lower as road energy needs, or charging needs, diminished without leaving the optimum efficiency plateau region. At 1.5K PRM, you might get 18kW, which assuming 10kW charge, leaves only 8kW for the road, which is at the low range of the power needed to maintain speed.

 

If nothing else, it points to the benefit of using ICE uphill, where gravity adds load, so you crest it with high SOC, and extend the EV glide even farther with some downhill slope. If you live in hilly country, where you fill the battery going downhill, the reverse may be true. There's a lot to be said for knowing your route!

 

Have fun,

Frank