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Mountain Driving Help


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54 replies to this topic

#21 OFFLINE   Noah Harbinger

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Posted 10 August 2013 - 01:38 PM

A few weeks ago, I drove down a long, steady downhill grade from 6000'. The battery filled up quickly, but the whole rest of the way, the little regen arrows kept spinning, and the ICE did not turn on except for the brief period when I turned on hill hold assist (I didn't like how fast the engine was spinning (4000RPM), so I went back to manually [pedially?] braking). I did not check to see how hot the brakes were, but I did not smell anything when I stopped on the way down.

 

I turned the AC to "LO", just to feel like I was getting some benefit from all that potential energy - it was a hot day :) 

 

I was wondering if engine braking puts any exceptional strain on the engine? 


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#22 OFFLINE   HannahWCU

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Posted 10 August 2013 - 07:17 PM

I have reported this (don't know if I was the one you were referring to).  The ICE will engage once the battery reaches 100% charge, but ONLY if hill decent is on.  

 

And it is my experience that the friction brakes do no engage unless you press the brake pedal.

 

 

Someone on this forum reported that the ICE spins for engine braking on a downgrade once the battery is full, but I don't remember where it was.

 

I don't think the friction brakes will ever grab in any mode unless you press the brake pedal.  But, you can press the brake pedal to some unknown threshold and only get regen (no friction brakes).


Edited by HannahWCU, 10 August 2013 - 07:19 PM.


#23 ONLINE   Plus 3 Golfer

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Posted 10 August 2013 - 07:47 PM

I have reported this (don't know if I was the one you were referring to).  The ICE will engage once the battery reaches 100% charge, but ONLY if hill decent is on.  
 
And it is my experience that the friction brakes do no engage unless you press the brake pedal.

If Ice only engages when hill descent is on, how does the algorithm simulate engine braking when the battery is full and hill descent is OFF? I doubt there's enough load on the HV battery to allow MG2 to generate to simulate normal engine braking especially on steeper hills. Something has to provide engine braking otherwise in effect the car is free wheeling and it wouldn't take much of a hill to rapidly increase speed.

#24 OFFLINE   HannahWCU

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Posted 10 August 2013 - 08:26 PM

If Ice only engages when hill descent is on, how does the algorithm simulate engine braking when the battery is full and hill descent is OFF? I doubt there's enough load on the HV battery to allow MG2 to generate to simulate normal engine braking especially on steeper hills. Something has to provide engine braking otherwise in effect the car is free wheeling and it wouldn't take much of a hill to rapidly increase speed.

 

I have no answer for this.  But I will tell you my experience on a mountain of a hill.  First a little about the grade I am descending.  It is on I-40 East out of Asheville, NC (near Black Mountain, NC).  Here is a note I found online about the grade:

 

By law, all trucks except pickups and vans are required to stop at the top of this hill and read the information posted about the eastbound descent ahead.  The top of the hill is near milepost 67 just east of Black Mountain.  The grade is posted as 5 miles of 6%.  It is a strong 6%.  There are three runaway truck ramps, all of which are short sand beds with sand piles at the end.  There is about a mile of grade left after the last escape ramp.   The westbound descent is about 1¼ mile of 6%.

 

I have descended this grade with hill decent on and hill decent off.  With hill descent on, when the battery gets very close to 100% (I have a scangauge to monitor this) the ICE will kick in and rev very high (as Noah Harbinger pointed out above). While the ICE is engaged, it does not use any fuel.  I left the hill descent on for the length of the grade.  The ICE does a very good job of holding back the car during the descent and I used very little brakes.  The last time I descended this mountain I did so with hill decent off.  Normal regen (foot off both the gas and brake) does NOT hold the car back at all on a hill this steep.  When I would press on the brake pedal to slow the car, the regen symbol (blue circle) would come on until the battery hit 100%.  Once the battery was at 100%, sometimes the display would show regen sometimes it would not.  But I do not think the friction brakes engaged by themselves with the hill descent off.  If they had, my brakes would have been smoking by the bottom of the grade.  I have seen where drivers have dragged their brakes the whole way to the bottom and you can smell the brakes burning by the bottom.  I could be wrong though.

 

I will point out that even with hill descent on, regen alone did not keep the car from accelerating on this grade.


Edited by HannahWCU, 10 August 2013 - 08:26 PM.

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#25 OFFLINE   salsaguy

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Posted 10 August 2013 - 09:18 PM

noah, you are mixing up two terms/names of two different techs in the cmax.

 

 

hill **hold** is what you engage when you are on a hill facing *up* the hill at a stop light and don't want to have the car roll back when you let your foot off the gas (like if someone was driving a stick on a hill and didn't know how to drive clutch and guns the gas when the light turns green to overcome gravity.) with this tech, the car "holdsl without rolling back.

 

hill **decent** is what you use when going DOWN a hill to prevent you from going to fast, like cruise control for downhill, as someone hereput it so well.

 

A few weeks ago, I drove down a long, steady downhill grade from 6000'. The battery filled up quickly, but the whole rest of the way, the little regen arrows kept spinning, and the ICE did not turn on except for the brief period when I turned on hill hold assist (I didn't like how fast the engine was spinning (4000RPM), so I went back to manually [pedially?] braking). I did not check to see how hot the brakes were, but I did not smell anything when I stopped on the way down.

 

I turned the AC to "LO", just to feel like I was getting some benefit from all that potential energy - it was a hot day :)

 

I was wondering if engine braking puts any exceptional strain on the engine? 



#26 OFFLINE   fotomoto

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Posted 10 August 2013 - 10:23 PM

 I'm leaving tomorrow morning and will report back what I find.   I'll use hill assist and if the grade gets really steep I'll put it in L.  I want to see how well the car handles things with as little brake pedal as possible.  Should be a welcome diversion from traveling the straights around here!  Thanks.



#27 OFFLINE   fotomoto

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Posted 20 August 2013 - 06:36 PM

Update:  grade assist work VERY well.  I rarely needed to touch the brakes and only dropped it into L twice (first time just out of curiosity).  The highest rpm I saw with grade assist activated was 4,500.   I think folks who drive through steep terrain will see economy gains with the new software update.  Since the system wants to burn off a really full battery, the higher EV speeds now available can be put to more use going up the next hill.  

 

null_zps68517abf.jpg



#28 OFFLINE   DaveofDurham

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Posted 20 August 2013 - 09:24 PM

I have no answer for this.  But I will tell you my experience on a mountain of a hill.  First a little about the grade I am descending.  It is on I-40 East out of Asheville, NC (near Black Mountain, NC).  Here is a note I found online about the grade:

 

By law, all trucks except pickups and vans are required to stop at the top of this hill and read the information posted about the eastbound descent ahead.  The top of the hill is near milepost 67 just east of Black Mountain.  The grade is posted as 5 miles of 6%.  It is a strong 6%.  There are three runaway truck ramps, all of which are short sand beds with sand piles at the end.  There is about a mile of grade left after the last escape ramp.   The westbound descent is about 1¼ mile of 6%.

 

I have descended this grade with hill decent on and hill decent off.  With hill descent on, when the battery gets very close to 100% (I have a scangauge to monitor this) the ICE will kick in and rev very high (as Noah Harbinger pointed out above). While the ICE is engaged, it does not use any fuel.  I left the hill descent on for the length of the grade.  The ICE does a very good job of holding back the car during the descent and I used very little brakes.  The last time I descended this mountain I did so with hill decent off.  Normal regen (foot off both the gas and brake) does NOT hold the car back at all on a hill this steep.  When I would press on the brake pedal to slow the car, the regen symbol (blue circle) would come on until the battery hit 100%.  Once the battery was at 100%, sometimes the display would show regen sometimes it would not.  But I do not think the friction brakes engaged by themselves with the hill descent off.  If they had, my brakes would have been smoking by the bottom of the grade.  I have seen where drivers have dragged their brakes the whole way to the bottom and you can smell the brakes burning by the bottom.  I could be wrong though.

 

I will point out that even with hill descent on, regen alone did not keep the car from accelerating on this grade.

 

I'm still looking forward to my first C-Max drive to Asheville and back.

 

Two weeks ago we drove from Charlottesville VA to Parkersburg WV.  This was 5+ hours of uos and downs with minimal interstate over the Skyline Drive and through two national forests.  We used grade assist on most of the 6% downhill grades.  Once the battery was full, the vacuum cleaning/sewing machine noise was interesting.



#29 OFFLINE   ScubaDadMiami

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Posted 20 August 2013 - 11:25 PM

In September, I will be driving from Miami to the mountains of western North Carolina, then driving all around that area for about a week, and finally driving back to Miami.  So, I guess I will be finding out about the mountain driving, soon enough! 

 

If I understand correctly, we can put the C-MAX into L at any speed?  When do you go with L versus Grade Assist?  Would I start by using Grade Assist, and then shift to L if Grade Assist is not enough to stay within the speed limit?



#30 OFFLINE   HannahWCU

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Posted 09 September 2013 - 01:28 PM

Here is a graph of the mountain of a hill I drove to get my information on how the CMax works on hills.  As you can see the total incline is just over 1300' over a distance of 5 miles.  MPG is really sucked down going uphill, but on the downhill run ...

 

BlackMountain.png

 

Here is a view of my total drive (going uphill), from my house to my parents house.  Total distance is just over 103 miles and altitude gain is almost 1900' (peak to peak)

 

HometoAsheville.png

 



#31 OFFLINE   fbov

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Posted 09 September 2013 - 02:04 PM

Is that the the fall line of the Piedmont? we're seeing in your route?

 

HAve fun,

Frank



#32 OFFLINE   ScubaDadMiami

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Posted 09 September 2013 - 06:17 PM

I have been driving the mountains since arriving in western North Carolina for the past four days. Surprisingly, I find it to be very easy. There aren't many choices about where to go EV. When you are going uphill, it is too steep to do any kind of realistic EV driving. When you go downhill, EV is a no brainer.

Where land is flatter, you have to decide and plan for when you go ICE or EV. That has been harder to learn, especially at highway speeds (given my limited highway driving experience).

#33 OFFLINE   bigalpha

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Posted 09 September 2013 - 06:19 PM

Hannah, how did you record that data?



#34 OFFLINE   obob

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Posted 09 September 2013 - 07:27 PM

I recently drover a 3 mile, 800 ft ascent route straight up, followed by 3 mile 600 ft decent and the return trip.

 

On the way up I decided to go about 47 mph to keep the engine cool and the SOC was about 3/4 on the top, and was full on the decent pretty quickly.

 

On the way back I went up 2-3 pixels over two bars(about 3200 rpm) so there was no regen to keep the SOC lower before the descent, but now I am thinking it was not worth it. Once again the SOC was 100% pretty quickly.  If the car was geeked out there would be a switch to prevent regen up the hill before a long decent.

 

I was impressed with the power of the engine though.  It never seemed like it was stressing.

 

By the way, since the software update, my sense is that when in hill assist the car goes into ICE slowing on any pretty steep hill, even without a full SOC sooner than before the update.

 

I liked the idea that was presented to turn the A/C up (if it is hot) on the downhill to use up some electricity and store the energy as a cool car.


Edited by obob, 10 September 2013 - 04:37 PM.


#35 OFFLINE   obob

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Posted 09 September 2013 - 09:25 PM

Hannah, how did you record that data?

http://fordcmaxhybri...route-altitude/



#36 OFFLINE   HannahWCU

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Posted 10 September 2013 - 03:16 PM

http://fordcmaxhybri...route-altitude/


Yes that is what I used. And no that isn't the Piedmont. Its a mountain near Asheville. The route I mapped is actually I-40. So it is a road that ALOT of people use.

#37 OFFLINE   HannahWCU

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Posted 10 November 2014 - 03:27 PM

I wanted to add a little to this discussion.  I finally remembered to take a few pictures on my mountain descent:

 

Here I have Hill Control on. I am running 55MPH, the battery is fully charged (State of Charge 100%), ICE is engaged (4296RPM), no fuel burning (0.00GPH), and a slight charge into the battery (-1.28 AMPs).

 

Attached File  old fort 2.jpg   68.47KB   0 downloads

 

 

This is 1.5 miles later. Same conditions, but as you can see the car has accelerated to over 60MPH now (STEEP hill!  LOL)

 

Attached File  old fort 1.jpg   66.28KB   0 downloads

 

Now where is that 1+ amps going?  Well the AMPs fluctuates from +1.?? to -1.??. My assumption is that those amps are what the car uses to keep everything running (i.e. radio, fan on HVAC, electric steering, electric brakes, charging 12v battery, etc.)

 

Anyway, just thought I would post a little more information for everyone.



#38 OFFLINE   stevedebi

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Posted 10 November 2014 - 05:01 PM

I'm not sure I understand some of the questions about "L" mode. The generator is spinning the engine to bleed off the excess energy once the battery is full. That is where the "extra" energy is going.



#39 ONLINE   Plus 3 Golfer

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Posted 12 November 2014 - 10:26 AM

I'm not sure I understand some of the questions about "L" mode. The generator is spinning the engine to bleed off the excess energy once the battery is full. That is where the "extra" energy is going.

MG1 (the generator) is not spinning to bleed off excess energy.  It's using energy to control engine speed - in negative split to more efficiently run ICE (like up-shifting a conventional transmission to a higher gear) and when in "L" mode to increase engine speed perhaps for engine braking or because the driver wants ICE to run in an effective lower gear. 

 

Speed up MG1 and the engine slows down (assuming car speed hasn't changed).  Slow down MG1 or reverse MG1 rotation and engine speed increases - "L" mode (like downshifting to a lower gear in a conventional transmission).   De-fuel the engine (take foot off accelerator) in "L" and engine becomes a load on the drive train (engine braking) which can help in controlling / reducing vehicle speed especially going down hill.  

 

 If the battery is not full, the PCM will use MG1 as a generator to increase engine load requirements and ICE will increase rpm / fuel to meet the additional load.  ICE should be operating in an more efficient range (than without the additional load) similar to when the battery if full but at decreased load and rpm.  The PCM should control MG1 and thus rate of charge for best efficiency.

 

There is no benefit to simply bleed off energy. Once the battery reaches its threshold capacity for hybrid operation, the traction motor (MG2) can act as a generator at the same time the generator (MG1) can act as a motor. The PCM should effectively use MG1 and MG2 to minimize input energy (fuel) effectively changing the gear ratio for best overall efficiency. Sometimes, one might see the battery being charged and sometimes one might see the battery being discharged.   The net effect as I've stated before in monitoring change in battery energy in negative split was a slight increase in state of charge of 2% points over 4 miles.  Going down hill for several miles using regenerative braking can increase the state of charge up to it's limit of about 70% SOC given a long enough down grade  But there's nothing one can do about that.  Just like a convention vehicle, one may lose some of the available potential energy going down hill because there is no room to store any more energy.  



#40 OFFLINE   stevedebi

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Posted 12 November 2014 - 01:22 PM

Plus 3,

Let's not get another thread off topic again. The car is causing the engine to spin because it has to slow down the vehicle, and the generator cannot store any more energy in the battery due to high SOC. It is a high level description, not an in depth discussion of the internal workings of the hybrid system.

 

I read your former posts, and watched the video. I prefer to think of it the way I do, and I don't think most folks care that much about the semantics.








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