My 2c: EV driving

[DaveofDurham]

Very good posts in this thread.

 

This is from Ford tech service regarding hybrid driving philosophy:

 

The Hybrid is optimized to run the engine during acceleration from a stop, and to stop

the engine during moderate speed cruising and during deceleration.

 

Trying to accelerate the vehicle slowly in EV mode tends to drain the HVTB (high

Voltage Traction Battery) which forces the engine to run during cruise, lowering fuel

economy.

 

Interesting info from Ford, but it seems to me to contradict Frank's (fbov's) explanation for 0-15mph above: 

 

"- accelerating to 0-15 MPH requires 1/4 the energy of accelerating 0-30 MPH.

- accelerating to 15 MPH doesn't put enough load on the ICE to reach the minimal BSFC operating region

- accelerating from 15-30 requires 3x the energy of 0-15

- the higher load pushes the ICE closer to the BSFC minima, increasing ICE efficiency"

[jeffkruse]

Wow, thanks for the explanation. 

 

This makes sense:

- accelerating to 15 MPH doesn't put enough load on the ICE to reach the minimal BSFC operating region

- the higher load pushes the ICE closer to the BSFC minima, increasing ICE efficiency

The gist of the hypermiling advice is to run the ICE as little as possible, and then with the highest load achievable without discharging the battery, to minimize fuel consumption.

 

 

But it conflicts with the following post:

The Hybrid is optimized to run the engine during acceleration from a stop, and to stop

the engine during moderate speed cruising and during deceleration.

 

Trying to accelerate the vehicle slowly in EV mode tends to drain the HVTB (high

Voltage Traction Battery) which forces the engine to run during cruise, lowering fuel

economy.

 

 

 

And then you mention the issue of torque for big-motor/small ICE.  So if I comprehend this correctly the small motors and batteries in these cheaper hybrids don’t have the torque a small ICE has but the bigger more expensive EV’s have torque that blows away most ICE’s.?

[jeffkruse]

 

Or maybe it’s just a matter of semantics.

 

Both are correct, the 0-15 doesn’t reach the minimal BSFC operating region but accelerating past this point charges the battery back up and moves the car up to cruising speed.?

 

0-15 takes some energy from the battery, so how long do you need to accelerate to put all that energy back.  I assume the sweet spot of the ICE can accelerate the car and charge the battery at the same time.?

[MI C-max]

 I assume the sweet spot of the ICE can accelerate the car and charge the battery at the same time.?

 

Driving at what I described as "2 white ticks" on the the display gauge, while running under ICE power, does allow the vehicle to accelerate while recharging the battery.  And somewhere below that range, once you're up to speed, you can maintain forward momentum while recharging the batteries if you're not ready to kick into EV mode.  I recently made a trip to Cleveland - on the way there I was able to keep it on ICE while cruising around 68MPH - the EMPOWER display was showing under 1 white tick which means I was probably on a slight downhill grade, and the instantaneous MPG gauge was showing I was hitting somewhere between 45-50MPG while using the ICE to cruise and recharge the battery.  Obviously on the way home, the grade was slightly uphill, and I couldn't get into that range again.  

 

The ICE "2 white ticks" range provides ample acceleration to keep up with the pack.  Trying to feather the EV mode to stay in EV when accelerating from a dead stop results in little or no acceleration beyond 20MPH - and thus lots of people freaking out in your rearview.  I was pushing it a little this morning - running 0 - 20MPH in EV mode - I was starting to fall behind the pack a little before I would kick in the ICE at 20MPH, but it wasn't enough to start driving people behind me insane.  I ended up with a 58.6 MPG for a 10 mile trip.

Edited August 30, 2013 by MI C-max

[Jus-A-CMax]

MI, we call it bars.

 

Look, theres no right or wrong - just preferences. Some people prefer ICE from 0-15 whilst hypermilers like Matt and I (for Jeff who does not know who Matt aka Recumpence, he's done over 30,000 miles on his CMax, 1st to break the 700 mile barrier per tank), we prefer EV because our bottom line is the gas used.

 

In a real start stop, city driving we never know (but we can anticipate) when the light ahead will go off so using gas to go from stationary means we did a ICE burn when we really didn't have to because the light ahead has gone red. That's a 0.02 for 4 second burn at 2 bars (to give u an idea, my morning work cummute had 21.7 miles using 0.26 gas used, resulting in 17.3EV and 82.6MPG :headspin: ).....so if we start on EV, we can choose mid-road to kick in ICE or not based on whats the traffic and lights are doing ahead.

 

In those driving conditions and using 2 bar or 1 3/4 bar conditions, charging is never an issue. Don't forget, there are 3 ways to charge (for Jeff): coasting with no pedal input, braking and ICE between (0.4 and 2.1) bars.

 

I find it funny that my views would differ from Ford Support, but thats OK  :jump_earth:

Edited August 30, 2013 by Jus-A-CMax

[fbov]

Wow, thanks for the explanation. 

 

This makes sense:

- accelerating to 15 MPH doesn't put enough load on the ICE to reach the minimal BSFC operating region

- the higher load pushes the ICE closer to the BSFC minima, increasing ICE efficiency

The gist of the hypermiling advice is to run the ICE as little as possible, and then with the highest load achievable without discharging the battery, to minimize fuel consumption.

 

But it conflicts with the following post:

The Hybrid is optimized to run the engine during acceleration from a stop, and to stop

the engine during moderate speed cruising and during deceleration.

 

Trying to accelerate the vehicle slowly in EV mode tends to drain the HVTB (high

Voltage Traction Battery) which forces the engine to run during cruise, lowering fuel

economy.

 

And then you mention the issue of torque for big-motor/small ICE.  So if I comprehend this correctly the small motors and batteries in these cheaper hybrids don’t have the torque a small ICE has but the bigger more expensive EV’s have torque that blows away most ICE’s.?

Remember the part about energy required to achieve speed?

 

The example I gave used EV for the first 15 mph, ICE after that. It's using EV for only 25% of the energy required to get to 30 mph, and only 6% of the energy to 60 mph. That's perfectly consistent with what Ford is saying, if you add in:

- the hypermiling technique of never stopping completely when driving ICE

- the idea of returning EV re-gen energy from the brakes back to kinetic energy.

 

I also update the energy flow with energy capacities... very enlightening! (I'll list assumptions below; can anyone check my math?)

 

Orders of magnitude variation in energy capacities!

13.5gal gas tank contains 1747MJ (mega joules)

C-Max @ 60mph has 0.63MJ

Hybrid HV battery capacity is 5MJ

A rolling down a 10m hill gains only 0.15MJ, but that's 30mph.

 

Clearly, the battery can't accelerate the car to 60!  yes, it can.

- reaching 30MPH from stop is 0.15MJ, so that would drain the battery at 100% charge, 2/3 utilization.

- reaching 60mph is only 0.63MJ, so well within EV capability.

 

BIG caveat: I've ignored parasitic losses, like rolling resistance, drag and ICE inefficiencies which along absorb 2/3 of the fuel's energy content per the EPA.

 

Have fun,

Frank

 

Assumptions

- Wikipedia has correct data for gasoline and Li-ion battery energy densities

- Wiki also has accurate unit conversions

- car weighs 3600 lb., has a 1.4kWh HV battery and 13.5gal tank

- gravitational acceleration is 9.8m/s^2

- potential energy is mass x grav. accel. x height in meters

- kinetic energy is 1/2 x mass x velocity^2

 

CORRECTION

Ah ha! I found it! Now th enumbers make sense... a 10m drop gets you to 30mph, and you don't kill the battery getting to 60! Does this fit more with what you see Jus?

Frank

Edited August 31, 2013 by fbov

[Jus-A-CMax]

Erh...I can accelerate from zero to 45 mph in EV and I lose approx. 1/3 charge from about 80% SOC, using 2 bar to max EV burn. No tried the EV from 0 to 60 mph though...gotta find that  :airquote: road. 

[ceemax71]

I think the decision on how to accelerate from a stop depends greatly on the terrain ahead.

 

I accelerate in EV mode from a stop in the following conditions:

• When I know the road ahead is downhill and can use the hill to recharge the battery
• Will be cruising less than 45-50mph
• Stop-and-go traffic
• When there is a stop sign, red light, or sharp turn just ahead

I accelerate in ICE mode from a stop in the following conditions:

• When the road ahead is uphill
• Accelerating to over 50 mph (on-ramp to highway)
• When it safer than accelerating in EV (traffic approaching from behind)
• When the HV battery state-of-charge is low

I think the Ford advice on accelerating from a stop might be over-simplified. 

 

[MI C-max]

MI, we call it bars.

 

Oops - old Test Engineer terminology ("ticks") rearing it's head again!

 

BTW - we tend to avoid "bars" while driving in these parts ... 

[fbov]

Please note corrections to post 81.

[fbov]

Erh...I can accelerate from zero to 45 mph in EV and I lose approx. 1/3 charge from about 80% SOC, using 2 bar to max EV burn. No tried the EV from 0 to 60 mph though...gotta find that  :airquote: road. 

With the corrected values for KE (and I'd still like someone to verify...), 0-45 is more like 8.8% of an 80% discharge depth. The most straightforward way to test would be a 10m free-roll test. With losses, you should end up around 25mph, and no more than 30.

(link to diagram)

 

Again, I'm just trying to get some idea of relative energy content, so folks see how much energy they have in variouis forms. High gas mileage is a simple matter of tapping on the chemical side as little as possible by managing energy among the other three. I'm hoping it helps to see their relative capacities.

 

Have fun,

Frank

Edited February 5, 2014 by fbov

[Jus-A-CMax]

I'll make notes next time, it wasn't as high as 80% from what I recall but next time I'll let you know. LA roads are always busy....gotta find one that is flat as well....hmmmh.

[hybridbear]

Jeff,

My background is Physics, so I see the system's energy balance a little differently. My mental model looks like this:

Energy Flow Diagram.jpg

 

Chemical energy is gasoline, one-way transfer to either battery or drive wheels

Electrical energy is battery charge, one-way charge from ICE or two-way charge/discharge to drive wheels

Potential energy is gravitational - being on top of a hill - so you store or use this energy based on terrain.

Of course, Kinetic energy is motion...

 

Reduced fuel consumption comes from only using the ICE in a very efficient mode, as measured by "brake specific fuel consuption" (BSFC) mapping. BSFC maps show contours of equal fuel consumption on a specific torque vs. RPM axes. Most ICE's are most efficient at low RPM (low pumping loss) and high load (so open throttle).

(This link has a lot of data in the attachment to the first post, and it's an interesting read.)

 

Hybrid are efficient to the degree that they allow the ICE to operate infrequently but efficiently, and store/use the excess energy efficiently. Minimum fuel consumption is achieved by only running the ICE in BSFC region of maximum efficiency. The control system sets RPM, the driver set the load by selecting a throttle position and terrain (road choice).

 

To your specifc question, motion (kinetic energy) is proportional to speed^2 (speed squared).

- accelerating to 0-15 MPH requires 1/4 the energy of accelerating 0-30 MPH.

- accelerating to 15 MPH doesn't put enough load on the ICE to reach the minimal BSFC operating region

- accelerating from 15-30 requires 3x the energy of 0-15

- the higher load pushes the ICE closer to the BSFC minima, increasing ICE efficiency

 

The gist of the hypermiling advice is to run the ICE as little as possible, and then with the highest load achievable without discharging the battery, to minimize fuel consuption. Make sense now?

 

As to the big-motor/small ICE approach, I see it as an issue of torque - ICE has lots more than any comparable EV. I find myself using ICE to get moving (see above) and to climb hills (see attachement). I'd need a larger battery and traction motor to achieve the same drive wheel torque, which is doable (Tesla) at a price. The current ICE/EV balance is likely a result of practical tradeoffs. The link talks a little about the ICE size range found in the hybrid market today - 1.5l to 2.0 for Prii and Ford.

 

Have fun,

Frank

Frank,

 

Is it ok if I quote your posts on the Fusion Hybrid Forum? They're great information that will surely benefit Fusion Hybrid owners too.

 

I'll make notes next time, it wasn't as high as 80% from what I recall but next time I'll let you know. LA roads are always busy....gotta find one that is flat as well....hmmmh.

Don't forget that the bottom of the battery symbol on the dash isn't actually 0% SOC and a full symbol isn't actually 100% SOC. Like the Prius, Ford doesn't allow the battery to be fully discharged or fully charged. it's hard to judge actual SOC and kWh based on the dash icon because it doesn't actually represent the entire kWh capacity of the battery. I recently bought a ScanGauge and I'm working on figuring out XGauge codes to try to get more information out of our Fusion which would likely apply to the C-Max too.

[fbov]

As long as you quote corrections as well, yes, quoting anything I post is fine with me, as long as it leads to greater accuracy. Since you grabbed one I got right the first time, no issues.

 

Just saw my first Fusion Hybrid...

 

Thanks, Frank

Frank,

 

Is it ok if I quote your posts on the Fusion Hybrid Forum?

[fbov]

Well, I live on a slight hill... the hockey stick is my street.

 

Turns out it's almost a 30' drop (10m = 32.5')' so I tried the free roll test. Stopped near the top of the hill, put the transmission in N and let it roll down to the cul de sac.

 

Just hit 25 mph. The Potential Energy numbers appear to be in the ballpark.

 

Frank

 

... The most straightforward way to test would be a 10m free-roll test. With losses, you should end up around 25mph, and no more than 30.

[salsaguy]

Jus

do you try and keep the battery in the 1/2 to 7/8 range and never get all the way 100 % charged and not down to 25% low either?

if it starts getting too high on SOC do you let off the gas and go into EV to drain some? since once u reach 100% SOC it cant charge more and u are wasting more gas using the ICE to charge with no added benefit?

right?

 

If its youtube, just simply copy and paste the link.

 

While I understand the eco-cruise, I still don't think its that efficient - however, next Monday, I will do my morning route to work in eco-cruise and see but driving conditions with morning traffic will vary.

Edited May 25, 2014 by salsaguy

[salsaguy]

have u considered going back and adding in notes as the video is playing to tell us what is going on in each stage of the vid?

you can add real comments embedded in the vid that pop up for a length of time u decide and show it when the note needs to show up and where

its cool

i think it would help new folks learn better about the techniques

 

I can't figure out how to embed the video, but I'm doing something similar in the video below. The only difference is I use eco cruise rather than feathering the throttle.

 

http://www.youtube.com/watch?v=L-DeoP7__DQ

[Jus-A-CMax]

Jus

do you try and keep the battery in the 1/2 to 7/8 range and never get all the way 100 % charged and not down to 25% low either?

if it starts getting too high on SOC do you let off the gas and go into EV to drain some? since once u reach 100% SOC it cant charge more and u are wasting more gas using the ICE to charge with no added benefit?

right?

I don't go for the 100% charge, makes no sense and here's why:

 

1. In City mode, you waste too much gas trying to keep the SOC high, the Lemon does very well in the 25mph to 38mph range and needs little EV to maintain the speed with traffic plus u regen with the traffic lights. I try to keep it low unless I know theres up slope that I need more EV. Also, I find routes that are downhills and I let the Lemon ride to naturally regen, I don't burn gas to regen as some here do, but it all depends..well, let me re-state that, I try not to run too many "regen with ICE".

 

If I get a high enough SOC (ala coming down from 118 to Tampa) I then will use a EV acceleration as much as possible, sometimes I floor it as the engine will suck the extra juice from the battery saving a ton of gas and then I get a really nice long pulse (traffice and LAPD permitting).

 

2. Freeway. I try to keep it around 90% only for me to run the eco-cruise. In the old days I would work the P&G but it gets tiring after a while but its a fact, my MPG is better on my Mammoth trips with P&G vs just eco-cruise but I work my butt off to squeeze out the MPGs...and then my wife turns on the AC...wtf....ppppff...jus eco it after that. I also use eco cruise to charge but never to 100%. Only time I get 100% is going south of the Sherwin Grade, north of Bishop, or leaving Mammoth town to the 395...or going down Agua Dulce to Via Princessa on the 14. 

 

Hving a high SOC is an advantage, of course but only when it's free - thanks to the downslope. By the way, I also get a high SOC going down Box Canyon from the 118 to Valley Circle (I pay a bit to climb but its well worth the returns).

[Jus-A-CMax]

The Rapier vidoe is excellent. My only suggestion is to let the Lemon ride a wee bit after ICE to get some regen and then kick in the minimal EV. He's running it too high in my experience (assuming his road was flat). I got 104MPG going from San Fernando to North Hollywood for my Gym, something like 12 odd miles of which 10 miles were EV, thru many traffic lights etc. Summer is back, and Jus is back...saw a lot of CMaxs too...wonder how they are doing in the MPG department.

 

PS this was a "semi" new route. Using the terrian will sure add MPGs for sure.

Edited May 26, 2014 by Jus-A-CMax

[salsaguy]

On a long down slope do you tap the brake a little ( not enough to hit the real fraction brake but just the regeneration brake) to get the SOC up or does it do it by itself on a downgrade?

 

I don't go for the 100% charge, makes no sense and here's why:

...

 

If I get a high enough SOC (ala coming down from 118 to Tampa) I then will use a EV acceleration as much as possible, sometimes I floor it as the engine will suck the extra juice from the battery saving a ton of gas and then I get a really nice long pulse (traffice and LAPD permitting).

 

....

 

Hving a high SOC is an advantage, of course but only when it's free - thanks to the downslope. By the way, I also get a high SOC going down Box Canyon from the 118 to Valley Circle (I pay a bit to climb but its well worth the returns).

[Jus-A-CMax]

No, on the long downgrade, just let her roll. I just let it roll and it will build charge naturally. Remember, the CMax does charge by itself if you let it glide, no need for brakes. Adding brakes increase the charge. Just as in the morning, the ICE warms up & I also tap the brake a little as I come down the hill and pretty soon I am at 90% (I started with like 30%).

 

If you recall, coming back from Vegas, there is a super long 10+ mile downgrade....just let the CMax ride at 70mph and she will roll sweetly. Let all the buffoons in their 4x4 trucks & SUV fang by. @$4+ a gallon, I am sure ALL of them made enough money from the tables to pay for their gas they are wasting hooning down this super long downgrade. By the way, this is the same grade that, going up, caused an overheat warning to come on using the full Grill Covers. Not a good idea, as I found out...

Edited May 27, 2014 by Jus-A-CMax

[salsaguy]

Cool thanks for the info Justin

[weebee]

Great read here! One question, I'm probably overlooking it in the manual. But Ecodrive and cruise are the same thing? I keep bouncing back from page 184 to 171 and I believe it is. Thankfully my learning curve isn't as bad as others since this is my third hybrid. But, wow, this car is like a computer on wheels.  The things it can do are awesome. I've learned from the Escape hybrid that a gentle touch is needed to keep the EV mode engaged. Not to mention the Escape was not meant to run in electric over 40 by itself anyway.I'm going to try the tricks listed here. I drove the C-max about 45 miles yesterday and I was seeing around 43mpg. In November we're going to N.C. for a vacation. It'll be interesting to see what it does on a long haul. We're going to Maine in about two weeks for vacation, I'm tempted to use it then. But I prefer it to have more miles on it first. Plus my Subaru will come in handy for some of the roads we'll be on.

 

Anyway, hats off to all that gave this info. Very much appreciated!

[fbov]

Eco-cruise is a separate cruise control mode you select in the "settings" screen on the left dashboard display, under Driver Assist.

 

The idea is to allow speed to vary a few MPH around the set point, depending on terrain. You run slower uphill and faster downhill, reflecting the relative contribution of the terrain to vehicle motion. Drives my wife crazy trying to follow me with her conventional cruise control...

 

Have fun,

Frank

[RobMax]

Great read here! One question, I'm probably overlooking it in the manual. But Ecodrive and cruise are the same thing? I keep bouncing back from page 184 to 171 and I believe it is. Thankfully my learning curve isn't as bad as others since this is my third hybrid. But, wow, this car is like a computer on wheels.  The things it can do are awesome. I've learned from the Escape hybrid that a gentle touch is needed to keep the EV mode engaged. Not to mention the Escape was not meant to run in electric over 40 by itself anyway.I'm going to try the tricks listed here. I drove the C-max about 45 miles yesterday and I was seeing around 43mpg. In November we're going to N.C. for a vacation. It'll be interesting to see what it does on a long haul. We're going to Maine in about two weeks for vacation, I'm tempted to use it then. But I prefer it to have more miles on it first. Plus my Subaru will come in handy for some of the roads we'll be on.

 

Anyway, hats off to all that gave this info. Very much appreciated!

 

I totally agree with you on how awesome this car is regarding the ability to feed the driver great information and enable us to use that info to obtain great MPGs. My '08 FEH (Ford Escape Hybrid) is like an analog modem and The Max is like fiber. I always thought the less-than-40mph EV restriction on the FEH was a nuisance, as there were plenty of times when a steep downgrade could've greatly improved my MPGs. At least The Max allows running in EV past 40mph, and I was surprised to find myself in EV during portions of my hwy cruise this AM, which could never have happened in my FEH.

 

I will definitely be trying more of the techniques Justin mentions regarding the 0-15mph EV runs with up to 2 bar ICE burns when traffic patterns allow. Up till tonight, I used the FEH driving style, which is to say I just tried to stay off the gas pedal to squeeze out a bit more EV mode, but it seems the lithium-ion batteries and increased electronic nannies improve ICE efficiency to a point where a slightly different driving style is necessary. Even with that old FEH style I was amazed I eeked out a 49mpg run home (according to the key-off readout) with mostly 70mph fwy driving with some 20-40mph slow-and-go mixed in. This is on a car with less than 100 miles total on the odometer. Hell, on the city streets near the end of my commute I was in EV mode far more than I ever was in the FEH. Awesome improvements, Ford.

Edited August 19, 2014 by RobMax