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Mountain Driving Help


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54 replies to this topic

#41 OFFLINE   bigalpha

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Posted 12 November 2014 - 01:37 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.

 

That's a pretty snotty reply.


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#42 OFFLINE   stevedebi

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Posted 12 November 2014 - 01:48 PM

That's a pretty snotty reply.

Sorry, I didn't mean it to be. We both got warned in another thread to get back on topic, and I didn't want this discussion to wander off again.

 

EDIT: I don't think it would be beneificial to the average reader...


Edited by stevedebi, 12 November 2014 - 01:49 PM.


#43 OFFLINE   BIG ROCCO

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Posted 12 November 2014 - 04:33 PM

We go up and down a lot of long steep grades going to our cabin in the AZ White Mountains and so I have had a lot of practice and have tried a lot of things.  I don't like how high the engine revs in downhill assist mode...4,000+ RPM.  I try to keep the revs to no more than 3,000 RPM going uphill (or sometimes 3,500 RM at the most, if necessary), so 4.000+ seems, and sounds, really high to me.  OK, maybe I'm wrong to be concerned about that, but one thing I noticed is that if I am going downhill and I put the hill descent mode on and the engine revs up higher than I would like, turning the hill descent mode off does not actually disengage the hill descent mode.  The ICE is still engaged and revs, but not quite as high as when the hill descent mode light is on.  It's kind of like shifting to a higher gear when engine braking/decelerating...maybe like going from 3rd gear to 4th gear or 4th gear to 5th gear in a conventional car with a 6 speed automatic.  So it's like hill descent "light".  The only way to actually turn the hill descent off and disengage the ICE is to accelerate slightly by pressing on the gas pedal



#44 OFFLINE   stevedebi

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Posted 12 November 2014 - 05:41 PM

We go up and down a lot of long steep grades going to our cabin in the AZ White Mountains and so I have had a lot of practice and have tried a lot of things.  I don't like how high the engine revs in downhill assist mode...4,000+ RPM.  I try to keep the revs to no more than 3,000 RPM going uphill (or sometimes 3,500 RM at the most, if necessary), so 4.000+ seems, and sounds, really high to me.  OK, maybe I'm wrong to be concerned about that, but one thing I noticed is that if I am going downhill and I put the hill descent mode on and the engine revs up higher than I would like, turning the hill descent mode off does not actually disengage the hill descent mode.  The ICE is still engaged and revs, but not quite as high as when the hill descent mode light is on.  It's kind of like shifting to a higher gear when engine braking/decelerating...maybe like going from 3rd gear to 4th gear or 4th gear to 5th gear in a conventional car with a 6 speed automatic.  So it's like hill descent "light".  The only way to actually turn the hill descent off and disengage the ICE is to accelerate slightly by pressing on the gas pedal

Well, at least the engine is not straining when it does that - there is a fuel cutoff and it is simply spinning rather than the hard work that an uphill 4K RPM would indicate.



#45 OFFLINE   Plus 3 Golfer

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Posted 12 November 2014 - 09:04 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.

Describing how L mode works in mountainous driving in not off-topic as I use it all the time descending steep, curvy mountainous roads to control speed when grade assist can't adequately control speed regardless of the SOC of the HVB so I don't have to use the friction brakes very often if at all.   

 

Your high level description above (highlighted in red) as what is happening in L mode when the battery is full (knowing full means about 70% SOC) is not technically correct except if  you mean MG2 not MG1 the generator. The traction motor MG2 provides regenerative braking slowing the car down when the battery is not full with ICE off.  This is to simulate ICE engine braking when coasting.  When regenerative braking is not sufficient to slow the car down, shifting into L aids in braking the car. L mode  causes the engine to engage and spin even if the battery is not full.  As I've said before, negative spit starts when the battery is around 56% SOC. So, positive spit mode ceases (MG1 charging the HVB). The HVB will continue to be charged via MG2, regenerative braking up to around 70% SOC

 

What I care about is that posts are representing conditions correctly and are not ambiguous.  There's a big difference between MG1, the generator and MG2 the traction motor.  Wording (semantics) is extremely important.   ;)


Edited by Plus 3 Golfer, 12 November 2014 - 09:21 PM.

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#46 OFFLINE   stevedebi

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Posted 13 November 2014 - 12:56 PM

Describing how L mode works in mountainous driving in not off-topic as I use it all the time descending steep, curvy mountainous roads to control speed when grade assist can't adequately control speed regardless of the SOC of the HVB so I don't have to use the friction brakes very often if at all.   

 

Your high level description above (highlighted in red) as what is happening in L mode when the battery is full (knowing full means about 70% SOC) is not technically correct except if  you mean MG2 not MG1 the generator. The traction motor MG2 provides regenerative braking slowing the car down when the battery is not full with ICE off.  This is to simulate ICE engine braking when coasting.  When regenerative braking is not sufficient to slow the car down, shifting into L aids in braking the car. L mode  causes the engine to engage and spin even if the battery is not full.  As I've said before, negative spit starts when the battery is around 56% SOC. So, positive spit mode ceases (MG1 charging the HVB). The HVB will continue to be charged via MG2, regenerative braking up to around 70% SOC

 

What I care about is that posts are representing conditions correctly and are not ambiguous.  There's a big difference between MG1, the generator and MG2 the traction motor.  Wording (semantics) is extremely important.   ;)

Plus 3,

I hope you didn't take offense at my other post; none was intended!

 

The engine does not always spin in L. I thought that too, at first, but someone pointed out I was wrong, and subsequently I discovered them to be right.



#47 OFFLINE   stevedebi

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Posted 13 November 2014 - 01:06 PM

I need to clarify my last post - the Energi C-Max does not always spin the engine in "L". But it has a larger battery, and would have more capacity.

 

For all I know, the C-Max Hybrid, with it's smaller battery may very well always end up in the condition where "L" will spin the battery.

 

I try and make sure my posts apply to both vehicles, but in this case I thought I'd clarify a bit.



#48 OFFLINE   ptjones

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Posted 13 November 2014 - 01:20 PM

When possible I try to use up the HVB before I get to the top of a hill so I can get the maximum of regen braking and use down hill assist If I need to. That way you get the most for your EV miles. :)  :shift:

 

Paul 


Edited by ptjones, 14 November 2014 - 10:08 AM.


#49 OFFLINE   BIG ROCCO

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Posted 13 November 2014 - 07:37 PM

Well, at least the engine is not straining when it does that - there is a fuel cutoff and it is simply spinning rather than the hard work that an uphill 4K RPM would indicate.

I think you are correct...there may be some small difference between acceleration and deceleration (or I suppose more properly, negative acceleration), but even just spinning the engine at high speed does still subject all the parts to the same or similar forces as when when it is actually running.  I will admit that the Ford engineers probably decided that 4,000 or 4,500 RPM is not an unsafe speed, or they would not have programmed the car to permit that, but I like to keep my cars for >10 years/100K miles, so I try not to always push the car to the limit...sometimes, you can't help it, but I try to avoid beating on the car on a daily basis.



#50 OFFLINE   Plus 3 Golfer

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Posted 13 November 2014 - 08:22 PM

I need to clarify my last post - the Energi C-Max does not always spin the engine in "L". But it has a larger battery, and would have more capacity.

 

For all I know, the C-Max Hybrid, with it's smaller battery may very well always end up in the condition where "L" will spin the battery.

 

I try and make sure my posts apply to both vehicles, but in this case I thought I'd clarify a bit.

Yes, I do recall there's a difference between the two using Low.  I forgot that you have an Energi. There were discussions on this in the past.  For those with Hybrids, it's easy to see that shifting to L starts ICE spinning.  Put RPM in MyView and drive shifting in and out of L.

 

I don't recall anyone who has documented / described the hybrid mode operation in the Energi.  I would think the hybrid mode algorithms are the same except perhaps threshold levels in the Energi might be increased  - but why? running ICE just to charge the big HVB (in positive split mode) even now with low gas prices would likely cost (in Phoenix with about $2.64 / gallon) over twice as much to charge the HVB with gas vs electricity.   But when descending a hill in the Energi, it makes sense to maximize regeneration whether the car in in D or L.   So, ICE should not spin in L to slow the car down like in the Hybrid. 


Edited by Plus 3 Golfer, 14 November 2014 - 07:21 AM.


#51 OFFLINE   ScubaDadMiami

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Posted 13 November 2014 - 11:55 PM

even just spinning the engine at high speed does still subject all the parts to the same or similar forces as when when it is actually running.  I will admit that the Ford engineers probably decided that 4,000 or 4,500 RPM is not an unsafe speed, or they would not have programmed the car to permit that, but I like to keep my cars for >10 years/100K miles, so I try not to always push the car to the limit...sometimes, you can't help it, but I try to avoid beating on the car on a daily basis.

I don't live in the mountains, but I've traveled there in my C-MAX. I know that it sounds scary when you hear ICE turning without firing, but I just don't sweat it. When I was just in New England, I ran down 15 percent grades with Downhill Assist on and a maxed out HVB. All I could think was: "What a waste of regen!" After all, once the HVB is fully topped off, the rest just goes bye-bye.

 

Honestly, I wouldn't worry about it. It has to be softer on the engine to turn without the heat from the combustion happening than it is with running ICE, even if everything is turning at a high rate of speed. My guess would be that lubrication is provided to the cylinder walls, or that enough is already there, to allow extended high RPM.



#52 OFFLINE   ptjones

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Posted 14 November 2014 - 10:15 AM

Looking at the Smart Gauge Tack It looks like 6,000rpms is the red line for the ICE, no reason to sweat 4,500. BTW the ICE still makes some heat from compressing air in the cylinders so the ICE doesn't cool off totally going down hill. You wouldn't want to waist gas heating up the ICE again. :) 

 

Paul 



#53 OFFLINE   stevedebi

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Posted 14 November 2014 - 11:43 AM

I think you are correct...there may be some small difference between acceleration and deceleration (or I suppose more properly, negative acceleration), but even just spinning the engine at high speed does still subject all the parts to the same or similar forces as when when it is actually running.  I will admit that the Ford engineers probably decided that 4,000 or 4,500 RPM is not an unsafe speed, or they would not have programmed the car to permit that, but I like to keep my cars for >10 years/100K miles, so I try not to always push the car to the limit...sometimes, you can't help it, but I try to avoid beating on the car on a daily basis.

I had an Escape Hybrid, and on a trip to New Mexico, on secondary roads with a lot of uphill / downhill (about 200 foot hills), I saw the RPM go up past 6000 on the uphills. I didn't sweat it, since Ford designed the computer parameters to protect the engine as needed. I don't really worry about it myself. On my Energi, I don't usually even have the RPM guage up on the left hand MyView.

 

I also hope to have mine well past 100K.



#54 OFFLINE   stevedebi

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Posted 14 November 2014 - 11:50 AM

...

 

I don't recall anyone who has documented / described the hybrid mode operation in the Energi.  I would think the hybrid mode algorithms are the same except perhaps threshold levels in the Energi might be increased  - but why? running ICE just to charge the big HVB (in positive split mode) even now with low gas prices would likely cost (in Phoenix with about $2.64 / gallon) over twice as much to charge the HVB with gas vs electricity.   But when descending a hill in the Energi, it makes sense to maximize regeneration whether the car in in D or L.   So, ICE should not spin in L to slow the car down like in the Hybrid. 

A bit off topic, so for those who don't care about the Energi - just skip this!

 

From what I can tell, the Energi uses the same (fairly small) range of battery that the conventional C-Max uses, when it is in what I call "highway mode", which means the larger part of the battery is depeleted, or the owner has set EV Later (which reserves the larger battery for later off highway use). I think Ford just copied the algorithms between the two. It makes sense, as you note, because there is no point in charging the HVB past a certain point - it is just burning gas.

 

The only difference I can tell is that the Energi will often not spin up the engine in L, because it has more capacity to store energy, and that it can recover extra energy on large downhill slopes, which it then burns off in either EV or just assisting the engine. After any excess is used, it reverts to that same highway mode.

 

I follow this forum because there is a lot of stuff the same between the two models. I try to think twice before posting, to make sure my Energi doesn't operate differently than the C-Max. I don't want to waste people's time reading stuff that doesn't apply.


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#55 OFFLINE   fbov

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Posted 14 November 2014 - 03:31 PM

When possible I try to use up the HVB before I get to the top of a hill so I can get the maximum of regen braking and use down hill assist If I need to....

My technique is the opposite:

When possible I try to charge up the HVB before I get to the top of a hill so I can get the maximum glide range on the way down.

 

I know... spoken like a true flat-lander. I can accelerate up most hills with less than 2-bar throttle, so I'm still charging. You may not, and it may be one reason your mileage eclipses mine.

 

Regarding fuel-off engine RPM, consider that, without fuel, the engine's using pumping losses to dissipate energy, and not experiencing a power stroke, so internal stresses are much, much less than if you were running under load at that RPM. It just sounds terrible compared with the relative silence of normal operation. 

 

HAve fun,

Frank


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