Fuel Mileage Root Cause Analysis

[gultim]

About a half an hour prior to taking the 3 pictures, I descended a mile long 10% grade hill and use the down hill decent control (which is a fantastic feature).  I left the down hill decent control on as it makes no difference either way in my car.  Maybe that is a clue?  When driving on the flats, do you notice lower engine revs when you turn off this feature and higher revs when turned on?  I know I read something in the manual last year pertaining to it and tried many times since to see if there was a difference in engine rpms but never witnessed any RPM or MPG changes after selecting either mode.  To me, this button only does one thing and that's limit the speed going down a hill.

[drdiesel1]

About a half an hour prior to taking the 3 pictures, I descended a mile long 10% grade hill and use the down hill decent control (which is a fantastic feature).  I left the down hill decent control on as it makes no difference either way in my car.  Maybe that is a clue?  When driving on the flats, do you notice lower engine revs when you turn off this feature and higher revs when turned on?  I know I read something in the manual last year pertaining to it and tried many times since to see if there was a difference in engine rpms but never witnessed any RPM or MPG changes after selecting either mode.  To me, this button only does one thing and that's limit the speed going down a hill.

DHA limits downhill speed by using MG1 as a brake. MG1 recharges the HVB battery. It has zero effect on the engine or rpm's, unless the HVB is full. When the HVB is full on a downhill grade with the DHA on, the system will spin the engine in decel/fuel cut mode to reduce vehicle speed. It uses the engines drag while off to control speed.

The manual states not to use the DHA (down hill assist) all the time, so make sure to turn it off when not driving in hilly areas.

Edited October 28, 2013 by drdiesel1

[hybridbear]

Yes, that sounds correct.  I am not experiencing the necessary load on my engine. 

 

Regarding Ford's "Preliminary 2013 MY OBD System Operation Summary for Plug In and Hybrid Electric Vehicles" it states that our C-Max's should enter negative split mode under certain conditions.  Other publications have explained negative split in the following manner:  "§ 1.3.5 Negative split mode - In this mode the power in the transmission flows the other way around. The electric motor delivers power via the generator and the planetary gear set to the engine. This is done to keep the engine running at low speeds and thereby optimizes the fuel economy."  Another described it as follows " Negative split mode – Forced engine lugging to optimize fuel economy" 

 

I also found LOAD explained as follows: "You want to maximize the amount of load on the engine at the lowest RPM, so a higher load at lower RPM is better than lower load at higher RPM. It is more fuel efficient to have more load at lower RPM than at a higher RPM, as you are getting more bang for the buck at that point.” A driver from the Ford Fusion Hybrid Forum stated the following about his car: “The car often shows 95-99% LOAD when accelerating slightly more aggressively such as accelerating onto the freeway, when accelerating in the city it often shows only 80-85%.” 

 

I believe the C-Max has the same Hybrid Drivetrain as the Fusion.  It appears that my C-Max is never entering the negative split mode.  The attached 3 pictures show the engine load, which was captured today on that ideal flat stretch of highway I described earlier in this post.  My Engine LOAD was 66%. It looks like it should be around 85% (Prius LOAD is 82 to 83%).  In order to raise this LOAD percentage, I need my car to lug its' motor RPMs down by entering the negative split mode.

 

For those of you with the ability to measure engine LOAD and Hybrid Battery AMPS, what is your engine LOAD around 0 AMPS on the flats at 60 MPH and no wind?

 

Also, since the C-Max can do 85 MPH in electric, I think that translates to 10,000 to 12,000 RPM that both the motor and generator can  safely operate at.  At this speed, negative split can be entered at very high driving speeds...much higher than what this link indicates http://eahart.com/prius/psd/ as that older eCVT drivetrain was based on the first Generation Prius. 

 

Please share your engine LOAD pictures. Thanks in advance :yahoo:   

I'm glad you've found my ScanGauge observations on the FFH Forum of value! Thanks!

 

We have observed the same as you in our Fusion. I just added a bunch more information to that ScanGauge thread about the HVB and when charging the HVB. Once the HVB reaches 60% of the useable SOC it stops using the ICE to charge the battery as you observed in your pictures above. When this happens the LOD value drops into the 60s since the car usually uses MG1 as a generator charging the battery to artificially load up the engine to be more efficient.

 

About a half an hour prior to taking the 3 pictures, I descended a mile long 10% grade hill and use the down hill decent control (which is a fantastic feature).  I left the down hill decent control on as it makes no difference either way in my car.  Maybe that is a clue?  When driving on the flats, do you notice lower engine revs when you turn off this feature and higher revs when turned on?  I know I read something in the manual last year pertaining to it and tried many times since to see if there was a difference in engine rpms but never witnessed any RPM or MPG changes after selecting either mode.  To me, this button only does one thing and that's limit the speed going down a hill.

Having this turned on has no impact on flat ground. Its function is to prevent the car from gaining speed when you aren't pressing the accelerator pedal. That is the only thing it looks for. It will thus increase regen as needed to prevent the car from gaining speed when you aren't pressing the accelerator. If the gravitational energy acting on the car is more than what the electric motor can convert to electrical energy stored in the battery then engine braking will begin even if the HVB isn't full.

Edited October 28, 2013 by hybridbear

[drdiesel1]

I've never had mine use the engine unless the HVB was full.  I guess it makes sense that it could use the engine in decel mode anytime it requires added drag to reduce downhill speeds beyond MG1's capability to control it.

 

I've been on some steep hills too ;)

Edited October 28, 2013 by drdiesel1

[gultim]

Can anyone share contact information regarding any Engineers at Ford who work on the C-Max Hybrid Power Train?  I would like to ask them about my unusually low engine loading at highway speeds and why my car's engine is not being lugged down by going into negative split mode to optimize MPGs.  Thanks!