Mountain Driving Help

[fotomoto]

I live along the coast and have no experience yet with mountain driving in my 4 month old CMax.  We will soon be taking a trip to the mountains up to 9,000 ft. and will, of course, experience significant downhill grades.

 

Manual says:

 

 

In prolonged mountainous driving, you may see the engine tachometer changing without your input. This is intentional and maintains the battery charge level. You may also notice during extended downhill driving that your engine continues to run instead of shutting off.

During this engine braking, the engine stays on, but it’s not using any fuel. You may also hear a slight whine or whistle when operating your vehicle. This is the normal operation of the electric generator in the hybrid system. 

 

Should I keep grade assist on all the time?  When or will I ever need to use L gear if using grade assist?  

 

I want to #1) not overheat friction brakes (safety) and #2) strive for best mpg.

 

 

Edited August 6, 2013 by fotomoto

[mtb9153]

I have found that I can maintain good fuel usage and economy by staying in the slow lane and watching the left screen where the Average MPG is displayed.  As I climb a hill I apply pressure on the gas pedal but keep the white line on the left side of the screen so that it never exceeds the 2-bar line.  This seems to give me better fuel economy.

Edited August 6, 2013 by mtb9153

[DR61]

 

Should I keep grade assist on all the time?  When or will I ever need to use L gear if using grade assist?  

 

I want to #1) not overheat friction brakes (safety) and #2) strive for best mpg.

 

 

I think actively managing your car is best in mountain driving.  I use D on upgrades, so if I let off the pedal some momentum is retained.  I use L on very twisty sections so I can get high regen when backing off to slow for corners, hopefully without having to engage friction brakes.  I use L or grade assist on downgrades, depending on how curvy it is.  On some downgrades that are straight and lead to long flat sections or upgrades, I shift to D or N (if speed is safe) to maximize momentum for the upgrade.

[BIG ROCCO]

How does L differ from Grade Assist?

[Ryan McEachern]

Grade assist will use regen to try to maintain your speed when being pulled downhill by gravity. If you engage it at 50 miles per hour, it will apply progressively more are more regen as you speed up past 50 rolling downhill. It will not apply the friction brakes though. In one sense it is like a reverse cruise control for downhills. I like it very much.

 

Using low gear, is just forcing the regen to maximum as soon as you let off the gas pedal. It is useful for slowing down the car as fast as possible without using the friction brakes, however, once you drive the car for a while, you will get a feel for how much you can push the brake pedal to get max regen, without using any friction brakes. The problem with using low is that coasting is always more effecient that regenerating power and then burning it again, so for downhill driving, it is better to use "D" and engage hill assist to hold your speed down, because then it will let you coast more once the speed drops below the hill assist threshold. (yes, I know there is still a little regen all the time in "D", but it is much closer to coasting than "L")

[zhackwyatt]

I believe L also does Engine braking.

[wab]

Are you planning to hypermile up and down or just drive up and down safely?

 

 

I don't hypermile but have found that I can touch the brake just enough to regin and not use the friction pads.

 

You're battery will be at 100% quickly.

 

 

I use the hill descent but turn it off when our speed starts to drop.

When our speed builds I briefly use the friction pads.

Haven't used L.

 

 

Short version:

 

I drive it like a normal car but the people behind are probably thinking

:lol2:

 

" there goes another flat lander burning up his brakes."

 

[bigalpha]

I made the mistake of using only brake while going down a mountain grade and I stopped for a break and I could smell the brakes - they were HOT.  At the same time, I don't like using the downhill descent control.  I feel like it uses way too much regen/transmission braking.  It was almost maxed out.

[plus 3 golfer]

With my C-Max once the battery level is virtually full, I "downshift" / "upshift" between "L" / "D" to help control speed going down long, steep grades and thus limit the use of the friction brakes and potentially overheating the brakes.

[wab]

Plus 3

 

The car will continue to regin after the bat is at 100%, what does it do with the juice? Heat Sink?

[plus 3 golfer]

Plus 3

 

The car will continue to regin after the bat is at 100%, what does it do with the juice? Heat Sink?

 

That's a good question.  Because once the battery is full how does the algorithm simulate "engine braking" of a conventional car when coasting.  

 

My guess is the engine begins to spin once the battery is full. I doubt there's a heat sink (although I suppose the algorithm could use the friction brakes). I really never monitored engine rpm going down a long steep hill. In a few weeks I should be able to test this out. I also don't know whether my battery was completely charged in prior uses of "L" as the hills were not that long just steep.

 

When you shift the hybrid to "L", the generator MG1 must supply holding torque to the sun gear so that ICE begins to spin if ICE were stopped or spins faster if ICE were already spinning.   The increase in rpm of the spinning engine (no additional fuel supplied) acts as additional load on the final drive to slow the car down. So there is energy being used by MG1 to increase ICE rpm, slow down MG1 and slow down the car when one shifts to "L".  The traction motor could also be used to help simulate this shifting into a lower gear by generating energy that then is directly used by MG1 to keep ICE spinning.  So the net affect might be near zero change in electrical energy but for MG1 and MG2 losses.

 

The more I think about it, I believe ICE has to start spinning when the battery is near 100% full.

[slampro]

The more I read from +3, the more I am :confused:  :headscratch:  By the time I get done I feel like :twister:  hit me.

 

I love how technical you get, even if it mostly goes over my head. It has led to much learning, for many others as well, I am sure.

 

:worship:  :worship: 

Edited August 7, 2013 by slampro

[ScubaDadMiami]

Is there a max suggested safe speed for shifting to L?

[plus 3 golfer]

Is there a max suggested safe speed for shifting to L?

I don't believe there needs to be since the PCM controls MG1, MG2, and ICE. It's not like "L"is a fixed gear ratio like in a conventional transmission.

[MtnMarty]

I wish I could use downhill assist but it doesn't work on my car. Dealer put in a query to Ford for me and they're supposed to fix it next week when I go in for the headliner. When I push the button on the side of the shifter, nothing happens.

[fotomoto]

Is there a max suggested safe speed for shifting to L?

 

From page 209 of the OM:

 

 

L (Low)

• Provides maximum engine braking.

• The transmission may be shifted into L (Low) at any vehicle speed. 

[viajero]

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).

[stratosurfer]

Are you planning to hypermile up and down or just drive up and down safely?

 

 

I don't hypermile but have found that I can touch the brake just enough to regin and not use the friction pads.

 

You're battery will be at 100% quickly.

 

 

I use the hill descent but turn it off when our speed starts to drop.

When our speed builds I briefly use the friction pads.

Haven't used L.

 

 

Short version:

 

I drive it like a normal car but the people behind are probably thinking

:lol2:

 

" there goes another flat lander burning up his brakes."

Question: 

Is the brake light on when in regen braking??

I guess so huh?

Folks probably think I'm always riding my brakes.

 

Mark

[wab]

Question: 

Is the brake light on when in regen braking??

I guess so huh?

Folks probably think I'm always riding my brakes.

 

Mark

 

Brake light switches are usually adjustable.

 

 

I'll crawl under there and see.

 

Would be good to regin and NOT have the light on.

[fotomoto]

Brake light is NOT on during regen nor is it required to be. 

[Noah Harbinger]

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? 

[HannahWCU]

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 August 11, 2013 by HannahWCU

[plus 3 golfer]

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.

[HannahWCU]

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 August 11, 2013 by HannahWCU

[salsaguy]

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?