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Guest Message by DevFuse

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Can I use Low Gear and/or the Downhill Button for Better MPG?

mpg low gear downhill button

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12 replies to this topic

#1 OFFLINE   stlouisgeorge

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Posted 03 February 2017 - 08:19 AM

I see this topic here and there but not on the Hybrid Driving discussion.

I understand I can shift into L any time.
I can shift into reverse or park at 75MPH if I want to.
Does car ignore L like it does R and P when on highway going flat or uphill?

1. How can I use the L (low) button to boost my MPG?

2. Should I use the downhill button at anytime other than going down a mountain or pulling a motor home (yeah right..)?

From the 2017 FFH manual page 147

Low:
Low (L) is designed to mimic the enhanced engine braking available in 
non-hybrid vehicles.  Low gear will produce high engine speeds to provide 
necessary engine braking.  This is normal and will not damage your vehicle. 
In low gear, the gas engine will remain on more often than in drive (D).

Edited by stlouisgeorge, 03 February 2017 - 08:21 AM.








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#2 OFFLINE   ptjones

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Posted 03 February 2017 - 11:47 AM

In theory you could run in Low all the time, but I don't think it helps your MPG's.  Down Hill Assist only works going down hill, not on the level. I only use DHA when I'm going down hill, turn off when I'm not. Very rarely use Low, use regen braking instead. :)

 

Paul


163299.png 600 Club

Current Record:  12/30/2014  902.2 mi.  63.8 mpg  14.13  gal. (Actual GPS:  922 mi.  68 mpg  13.5 gal.


#3 OFFLINE   talmy

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Posted 25 February 2017 - 11:40 AM

The car will regeneratively brake, providing the HV battery is not at 100%, when you use the brake pedal. This recovers energy that can be used for acceleration or cruising and is thus most efficient and will increase gas mileage.

 

Using low gear with the foot off the accelerator will use the engine braking to slow the car. That's non-recoverable energy. Using the downhill button will use engine braking to attempt to maintain the current speed. Again that's non-recoverable energy.

 

When driving downhill, use the brake pedal to regeneratively brake until the battery has reached 100%, then use the downhill button to save wear on the convectional, friction brakes. There is never any reason to use Low unless you want the car to seem like it has a conventional automatic transmission. Low won't save on gas or give any increased torque over Drive.

 

Regenerative braking not only increases gas mileage, it also cuts down on brake wear. Work to get high braking scores by smoothly slowing down to prevent the friction brakes from being applied.  Latest report has our Fusion's brake linings at >90% at 58000 miles so the brakes will be good for half a million miles. Similarly our Camry hybrid at 140,000 miles hasn't needed any brake work.



#4 OFFLINE   ptjones

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Posted 25 February 2017 - 09:21 PM

DHA does charge HVB until 100% usable charge w/Smart Gauge(65% actual using scangaugeII). :)


163299.png 600 Club

Current Record:  12/30/2014  902.2 mi.  63.8 mpg  14.13  gal. (Actual GPS:  922 mi.  68 mpg  13.5 gal.


#5 OFFLINE   stlouisgeorge

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Posted 25 February 2017 - 11:57 PM

Using low gear with the foot off the accelerator will use the engine braking to slow the car. That's non-recoverable energy.

Are you saying coasting (with engine braking) does not recover energy (from your momentum or gravity)? I have read (but not noticed) that coasting doesn't slow you down as much when the battery is charged.

Is there anywhere on the FFH you can see a percentage charge on the HVB?
(I am sure the Energi owners just look at their Apple watch or its in their view all the time).

I saw on this Ford "grade assist" video that if you want to you could leave your hill grade assist on all the time.
The car is smart enough to know when to (and when not to) engage the feature.

#6 OFFLINE   bdginmo

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Posted 26 February 2017 - 09:55 AM

If you get Torque Pro and an OBD dongle or a ScanGauge you can see the actual HVB state of charge.

 

In my Energi L generally transfers 100% of the kinetic energy back to the HVB. I've never had it engine brake, but I'm sure there are scenarios where it will use the engine to brake (HVB full or overheating).

 

As a test...get up to 45mph or so and then let off the throttle to get the ICE to turn off. Then switch to L. If the ICE kicks on then it's probably engine braking. If it stays off then it is probably regeneratively braking (at least partially).


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#7 OFFLINE   talmy

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Posted 26 February 2017 - 11:22 AM

DHA does charge HVB until 100% usable charge w/Smart Gauge(65% actual using scangaugeII). :)

 

Nice to know! I didn't realize it was that smart, so only turned it on when HVB reached 100%. 

 

Are you saying coasting (with engine braking) does not recover energy (from your momentum or gravity)? I have read (but not noticed) that coasting doesn't slow you down as much when the battery is charged.

Is there anywhere on the FFH you can see a percentage charge on the HVB?
(I am sure the Energi owners just look at their Apple watch or its in their view all the time).

I saw on this Ford "grade assist" video that if you want to you could leave your hill grade assist on all the time.
The car is smart enough to know when to (and when not to) engage the feature.

 

When you coast with DHA off and in "D" there will be energy recovery without applying the brakes. This is done to mimic the engine drag one would get with a conventional automatic transmission. Somewhere here I read that the amount of recovery applied has been increased in more recent models (perhaps 2016 or 16, we have a 14)  to help slow the car down faster to get better braking scores -- braking effectively starts earlier. 

 

Since the DHA only purpose is to maintain the existing speed using engine braking going downhill, it does nothing on level ground or going uphill. If it indeed will do energy recovery if the battery is not fully charged then it probably wouldn't hurt to leave it on all the time. I know I've hit the button occasionally and didn't realize it!

 

If you get Torque Pro and an OBD dongle or a ScanGauge you can see the actual HVB state of charge.

 

In my Energi L generally transfers 100% of the kinetic energy back to the HVB. I've never had it engine brake, but I'm sure there are scenarios where it will use the engine to brake (HVB full or overheating).

 

As a test...get up to 45mph or so and then let off the throttle to get the ICE to turn off. Then switch to L. If the ICE kicks on then it's probably engine braking. If it stays off then it is probably regeneratively braking (at least partially).

 

Don't have an Energi, but I would find it strange when running electrically for it to fire up the engine just to slow the car down. Disturbing! Turn on Downhill Assist, go down a steep hill, and report back!



#8 OFFLINE   Texasota

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Posted 26 February 2017 - 01:21 PM

 

Don't have an Energi, but I would find it strange when running electrically for it to fire up the engine just to slow the car down. Disturbing! Turn on Downhill Assist, go down a steep hill, and report back!

This is normal operation and not peculiar to just the FFH. Many cars have done this for years. When the ICE and transmission go into this "compression braking" mode the fuel injectors are not operating (no fuel is being injected) and no combustion is occurring. The ICE is merely acting like an air compressor. My 2012 Ford Focus did this while descending hills with cruise control on.



#9 OFFLINE   bdginmo

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Posted 26 February 2017 - 07:29 PM

Exactly. That's what you want a car to do to control downhill speeds (like in the mountains). The HVB is going to fill up in hurry for hybrid-only models so you want the engine to run to apply resistance on the forward motion. This reduces the amount of real braking that has to be applied. Like Texasota said, the computer cuts the fuel off in this situation.


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#10 OFFLINE   talmy

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Posted 26 February 2017 - 10:17 PM

This is normal operation and not peculiar to just the FFH. Many cars have done this for years. When the ICE and transmission go into this "compression braking" mode the fuel injectors are not operating (no fuel is being injected) and no combustion is occurring. The ICE is merely acting like an air compressor. My 2012 Ford Focus did this while descending hills with cruise control on.

 

Indeed true. My old 1983 VW Vanagon did the same. But what would be unusual in the Energi case is that the ICE isn't normally spinning at all but when you turn on the DHA or shift to "L" the engine starts spinning. Might be shocking!.

 

A similar oddity happens in our Camry hybrid. When in "B" going down a hill, as you press on the gas the ICE slows down. The further you press the slower it runs. Now that's strange!



#11 OFFLINE   mwr

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Posted 26 February 2017 - 11:04 PM

 

A similar oddity happens in our Camry hybrid. When in "B" going down a hill, as you press on the gas the ICE slows down. The further you press the slower it runs. Now that's strange!

I get the same effect in my 2015 FFH when descending a steep mountainous road, which I've done a few times. The HVB gets fully charged quickly and then to keep from using the friction brakes I set cruise control to the lowest possible speed (20 mph) then go faster by pressing on the "gas pedal". The more I press the less engine braking occurs (and engine revs are less) as the car speed increases. To slow down I release pressure on the gas pedal and the engine revs more for more engine braking. Works for me :-)


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#12 OFFLINE   Sky14FFH

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Posted 19 August 2017 - 10:45 AM

It's too bad the L doesn't use a more steady form (than your foot can) of regenerative braking.  On a long trip through mountains I found that it doesn't.  Question, once the battery is charged to the max what happens to the energy from the regenerative brakes? This has happened to me a couple times in some mountain situations.



#13 OFFLINE   murphy

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Posted 19 August 2017 - 12:23 PM

When the battery is full regenerative braking is turned off and the engine spools up without feeding any fuel to the engine.  It provides the braking and is similar to an air compressor in this mode.


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