Fuel Mileage Root Cause Analysis

[gultim]

Why C-Max Hybrids are getting low MPGs
Tim Gulden 7/23/2013

Introduction - It appears that the majority of C-Max owners are experiencing 20 to 25% lower MPGs than the rated 47/47.

While 90 miles into a 110 mile trip, a 2013 C-Max experienced a MPG/RPM anomaly while traveling on a sunny 65 degree day. The C-Max entered the bottom of a long level straight stretch after descending a minor slope along the Mississippi river. The RPM remained low at 1589 on the flats while traveling 65 MPH with a slight tail wind. The instant MPG meter went a little over 60 MPG and stayed there (while slightly fluctuating up and down) for about 15 seconds while the RPM remained just under 1600. During this time the battery was neither charging nor discharging and the Engage Graphical Display did not indicate any blue. Normally at 65 MPH on the flats this 2013 C-Max experiences an instant MPG meter reading hovering slightly below or spot on 40 MPG. After the above 15 second time period elapsed, the RPM went back to around 2000 RPM and the instant MPG meter went back to around 40 MPG. This above anomaly prompted the following investigation.

History - Ford Motor Company independently developed a system with key technologies similar to Toyota's HSD (Hybrid Synergy Drive) technology in 2004. As a result, Ford licensed 21 patents from Toyota in exchange for patents relating to emissions technology.

Theory - Ford obtained CVT transmission firmware from Toyota that was mapped to the higher revving 1.5 liter engine and used it in the new 2.0 liter Ford Hybrids without remapping the transmission to operate at the much lower and more efficient RPM range of the 2.0 liter displacement engine.

Data - The following data points are based on a level stretch of road with negligible wind at 70 to 73 degrees, samples taken in both road directions, with no accessories operating, windows rolled up, and/or industry known test data was used and is noted at the end of that bullet item. The driving duration prior to the test run was of a sufficient length as to stabilize the battery pack charge so the computer neither tried charging the battery nor was discharging the battery during the time the measurements were captured. (If any battery current did happened to be flowing at this time it would have been negligible.)

• 
  Maximum MPG is attained when Engine RPM is close to its lowest.
• 
  Gen II Toyota 1.5 liter operates at 1900 to 2000 RPM at 55 to 60 MPH (taken from online source)

• 
  Gen III 1.8 liter measured around 1248-1300 RPM at 55 MPH @82% engine load, and achieved 60 to 65 instant MPG.
• 
  Gen III 1.8 liter measured around 1000 RPM at its lowest at 45 MPH and 1600 RPM at 65 MPH.
• 
  Maximum engine efficiency is when the engine is loaded close to 100%.
• 
  2013 C-Max 2.0 liter engine measured 65% loaded at 65 MPH.

• 
  2.0 Liter C-Max engine should have its best MPG around 1100 to 1200 RPM.
• 
  2013 current C-Max engine RPM operates at 2000 RPM at 65 MPH and achieves an instant 40 MPG.
• 
  230 g/kWh Brake Specific Fuel Consumption efficiency for the 1.5 liter starts at 2,000 RPM.
• 
  230 g/kWh Brake Specific Fuel Consumption efficiency for the 1.8 liter starts at 1200 RPM.
• 
  Brake Specific Fuel Consumption maximum efficiency for the 2.0 liter RPM should be at or lower than the 1.8 liter's lowest RPM.
• 
  Running an engine at a higher than needed RPM results in high parasitic pumping losses.
• 
  Running an engine at less than its maximum efficient load results in lower thermal efficiency.

Conclusion – The 2.0 Liter Ford Hybrid engine is not currently operated in its' most efficient RPM or MPG range. The C-Max Transmission Firmware needs to be modified to allow the 2.0 liter engine to operate at its' lowest efficient RPM (somewhere between 1,000 and 1,200 @ 45 MPH and 1,500 to 1,600 @ 65 MPH) while maintaining its Brake Specific Fuel Consumption maximum efficiency, high engine loading percentage, and smooth engine operation. As a side note - Lower engine RPM might also result in slower traction battery charging which will help extend the battery's lifespan.

 

Note - See the attached file for more details.

Why C-Max and Fusion Hybrids are getting low MPGs 2 Printed.pdf

Edited August 27, 2013 by gultim

[zhackwyatt]

The engine will turn in the C-Max w/o using fuel sometimes.  Usually when the battery is fully charged.

[hybridbear]

Great analysis that applies to the FFH too! How did you do your C-Max tests at different RPMs when the computer controls all that?

[fotomoto]

Interesting!

 

The 2014 will come with a new transmission ratio.  Maybe this will support your theory.

[plus 3 golfer]

Do you have the BSFC for the C-Max?  If so please post it.

[gultim]

The transmission is continuously variable and already has the ability to vary its ratio by altering the firmware settings that operate the motor and generator RPMs.  If you set the electric motor RPM to 2650, set the engine RPM to 1100, set the generator RPM to -2820, the car should then go 45 MPH on the flats and obtain phenomenal MPGs.  The maximum engine output power at 1100 RPM is around 12 kW (16 HP).  This is sufficient to propel the car 60 MPH on the flats with no wind.  The CVT can be programmed to operate the engine at 1100 RPM by setting the electric motor RPM to 3500 and by setting the generator to -5070 RPM...this will give you 60 MPH.  To operate in this mode would require close to full wide open throttle (most efficient engine thermal operation), again you would receive phenomenal fuel mileage.  Should you not want to operate the engine close to its maximum torque at these low RPMs then raise the RPMs roughly 10%.  I would like to see a 2.0 Liter C-Max reprogrammed to allow the engine RPMs to be 1200 at 45MPH, 1400 at 55 MPH and 1600 at 65 MPH.  Maybe have an Eco button that would remap the RPMs lower to the following for even better MPG's -  engine RPM 1000 at 45MPH, 1200 at 55 MPH and 1300 at 65 MPH. All these RPMs would be on the flats with no wind, no accessories, windows rolled up, 70 degrees F, and while the battery was neither charging nor discharging (purely engine driven).  The lower you force the engine RPM, the higher the MPGs will be.

[plus 3 golfer]

As far as the "anomaly", it sure appears that you were in negative split mode where MG2 (traction motor) is generating, MG1(generator and starter) is using power and thus is reducing ICE rpm.  The torque requirements of ICE haven't changed. But ICE rpm have been reduced and thus ICE is operating at a higher efficiency point on the BSFC.  This usually result in higher FE - many time around the 60+ range.  The chevrons may not be displayed if the net effect on the HV battery is zero (in essence, MG2 electrical energy produced = MG1 electrical energy used). 

 

Generally, one needs a virtually full HV Battery (see description below) and to be going slightly downhill or on level ground.   I would see this alot pre PCM update as about every mile on the local freeways there are either over passes or underpasses with gradual slopes.  I might see the chevrons disappear for about 2 - 3 seconds or so but never for 15 seconds as a slight change in torque requirements usually means that the net HV energy is not a net zero and thus the HV battery is either being charged or supplying energy.  After the PCM update my HV battery is rarely near full charge at 65 - 70 mph cruising on the freeways as it would have been pre PCM update and thus I now rarely see the chevrons "disappear". 

 

 

Negative Split Mode

 The engine is on and the generator motor consumes electrical energy to reduce engine speed

 

 The traction motor can operate as a motor or a generator to make up the difference between the engine power and the desired power

 

 Typical highway mode

 

 Occurs when the engine needs to be on, the system can not be operated in parallel mode and the battery is charged near its upper limit

 

[plus 3 golfer]

The transmission is continuously variable and already has the ability to vary its ratio by altering the firmware settings that operate the motor and generator RPMs.  If you set the electric motor RPM to 2650, set the engine RPM to 1100, set the generator RPM to -2820, the car should then go 45 MPH on the flats and obtain phenomenal MPGs.  The maximum engine output power at 1100 RPM is around 12 kW (16 HP).  This is sufficient to propel the car 60 MPH on the flats with no wind.  The CVT can be programmed to operate the engine at 1100 RPM by setting the electric motor RPM to 3500 and by setting the generator to -5070 RPM...this will give you 60 MPH.  To operate in this mode would require close to full wide open throttle (most efficient engine thermal operation), again you would receive phenomenal fuel mileage.  Should you not want to operate the engine close to its maximum torque at these low RPMs then raise the RPMs roughly 10%.  I would like to see a 2.0 Liter C-Max reprogrammed to allow the engine RPMs to be 1200 at 45MPH, 1400 at 55 MPH and 1600 at 65 MPH.  Maybe have an Eco button that would remap the RPMs lower to the following for even better MPG's -  engine RPM 1000 at 45MPH, 1200 at 55 MPH and 1300 at 65 MPH. All these RPMs would be on the flats with no wind, no accessories, windows rolled up, 70 degrees F, and while the battery was neither charging nor discharging (purely engine driven).  The lower you force the engine RPM, the higher the MPGs will be.

In theory, it makes it sense but it's likely not practicable given the degrees of freedom.  One can likely tune for better performance or better FE. The ECO button makes sense. There have been many papers written on the subject of optimizing the Hybrid Power Split Transmission.  Ford will likely continue to tweak the C-Max over time.

 

The real question though is how much FE improvement would one expect to see in the C-Max for such change and how would such change affect performance.  The C-Max weighs about 600 pounds more than the Prius, has a Cd that is 20% higher and likely has a larger frontal area.  That likely accounts for nearly all the FE difference we currently see between the two vehicles.  

[gultim]

Anyone have luck connecting an Engine Tuner/Flasher to download, alter, then upload a new C-Max engine/transmission map with the newly altered lower CVT RPM parameters?  Opening up the CVT ratio to allow the engine to spin at lower RPMs for better MPGs under light throttle conditions will not alter the total engine HP or motor HP output thus the performance would not be altered as the engine and motor RPM and torque are allowed to operate as they do now under hard acceleration.  I've seen 55 to 60 MPGs under brief but ideal conditions.  I believe that by lowering the RPM we would all experience 55 to 60 MPGs at 65 MPH under the ideal conditions I described prior.  I have also experienced the chevron showing charging and discharging while the instant MPGs were close to 60.  I included these two pictures.  All I ask is...Ford, please change my RPMs as I indicated earlier, and I'll report my findings for free...also, you can then keep the $550 check that you will be sending me due to the low MPGs...I am that confident regarding this MPG increase.  Also, it would put the C-Max back in the news with a huge positive spin.  Besides the current lower MPG's, I love this car! 

[hybridbear]

Anyone have luck connecting an Engine Tuner/Flasher to download, alter, then upload a new C-Max engine/transmission map with the newly altered lower CVT RPM parameters?  Opening up the CVT ratio to allow the engine to spin at lower RPMs for better MPGs under light throttle conditions will not alter the total engine HP or motor HP output thus the performance would not be altered as the engine and motor RPM and torque are allowed to operate as they do now under hard acceleration.  I've seen 55 to 60 MPGs under brief but ideal conditions.  I believe that by lowering the RPM we would all experience 55 to 60 MPGs at 65 MPH under the ideal conditions I described prior.  I have also experienced the chevron showing charging and discharging while the instant MPGs were close to 60.  I included these two pictures.  All I ask is...Ford, please change my RPMs as I indicated earlier, and I'll report my findings for free...also, you can then keep the $550 check that you will be sending me due to the low MPGs...I am that confident regarding this MPG increase.  Also, it would put the C-Max back in the news with a huge positive spin.  Besides the current lower MPG's, I love this car! 

How did you get the car to go to a lower RPM under these conditions to momentarily get the high instant fuel economy? I'm kind of doubtful that the Ford engineers wouldn't have implemented this already if it were possible. They no doubt extensively studied the Prius and TCH powertrains to figure out the engineering behind them and then tried to improve upon it. They also have surely analyzed the BSFC charts for the 2.0L Atkinson cycle engine in our cars to make it run most efficiently as often as possible.

[gultim]

Experimenting with my 2003 Jetta Diesel revealed different MPGs going up a mile long 10% grade hill while using different gears at a constant speed of 30 MPH in each of these gears.  The car attained 9 MPG @ 30 MPH in 2nd gear (very high reving engine), 15 MPG @ 30 MPH in 3rd gear, and 22 MPG @ 30 MPH in 4th gear (which had to have the accelerator pedal almost pushed to the floor and had a very low RPM).  The take away is that you have to lower the Engine RPM and make it work harder to increase your MPGs. Fuel use was the main determining factor with transmission efficiency between the gears following a distant second.

 

Here is some math to substantiate why the C-Max should achieve around 58 to 61 MPGs at 60 MPH.

C-Max Curb Weight - 3,600 lbs

My weight 170 lbs

Total weight - 3,770 lbs

C-Max average coast down time from 65 MPH to 55 MPH - 17.7 seconds

Grams of Gasoline per Gallon - 2,721 g.

Horse Power required to maintain 60 MPH on the flats with no wind - 15.52 HP

Horse Power required to maintain 60 MPH on the flats with no wind and factoring 91% transmission efficiency - 17.06 HP

15.52 HP converted to kW - 11.6 kW

17.06 HP converted to kW - 12.7 kW

RPM needed to attain 11.6 kW - 1,250 RPM (see attached. The Ford 2 Liter Atkinson engine should have slightly lower RPM values)

RPM needed to attain 12.7 kW - 1,400 RPM (see attached. The Ford 2 Liter Atkinson engine should have slightly lower RPM values)

To drive for 1 Hr at 60 MPH will consume 11.6 kWh

To drive for 1 Hr at 60 MPH will consume 12.7 kWh (this has 91% transmission efficiency factored in)

BSFC fuel consumption at 1250 RPM to attain 11.6 kWh - 230 g/kWh (see attached. The Ford 2 Liter Atkinson engine should have slightly lower values)

BSFC fuel consumption at 1400 RPM to attain 12.7 kWh - 220 g/kWh (see attached. The Ford 2 Liter Atkinson engine should have slightly lower values)

Total grams of fuel per hour consumed while traveling at 60 MPH at 11.6 kWh - 2,663.4 gr./hr

Total grams of fuel per hour consumed while traveling at 60 MPH at 12.7 kWh (this has 91% transmission efficiency factored in ) - 2,799.5 gr./hr

Calculated MPG for 11.6 kWh - 61.3 MPG @ 60 MPH

Calculated MPG for 12.7 kWh (this has 91% transmission efficiency factored in) - 58.3 MPG @ 60 MPH

 

Conclusion - Actual MPGs for the C-Max should be around the calculated values of 58.3 MPG to 61.3 MPG with the engine RPM of 1,400 @ 60 MPH. 

 

Note - due to the nature of a CVT, I doubt that there will be much if any added transmission losses when shifting into neutral at 60 MPH thus I believe the higher MPG figure of 61.3 MPG is the more accurate of the two.

 

 

 

 

[Noah Harbinger]

I have a very, very difficult time imagining that either of the components of your proposed theory could be true, particularly on the C-Max and Fusion that use Ford's Gen-II hybrid system (which uses an in-house built transmission, larger motors, and is powered by a higher-current capable lithium-ion battery). 

 

Secondly, I find it ridiculous for someone to delude themselves into believing BOTH that this firmware is apparently so hard to change that Ford hasn't touched it IN TEN YEARS, and that independent tuner could poke in the dark and tweak it to magically discover huge fuel economy gains.

 

I'll be the first to eat my words if someone actually gets out there and does it. Heck, it could be a fun bit of work… But color me skeptical. 

Edited September 12, 2013 by Noah Harbinger

[gultim]

My math substantiates my test condition findings.  Should I have made a mathematical error, please let me know.  If I hear nothing then I can assume it must be correct.  Also, you are right...I will keep this strictly factual and leave out any conspiracy theories.  I reiterate, the C Max should be getting around 61 mpg at 60 mph...the math proves it.  Ford...if your reading this...please lower my RPMs in the next firmware release!  I will also volunteer to test your beta version for free.  Thanks in advance :victory:

[fotomoto]

Interesting!

 

The 2014 will come with a new transmission ratio.  Maybe this will support your theory.

 

 

The transmission is continuously variable and already has the ability to vary its ratio by altering the firmware settings that operate the motor and generator RPMs.  I

 

Sorry, I meant the 2014 will come with a new final drive ratio.  IIRC, it will match the current Energi model.

Edited September 23, 2013 by fotomoto

[GaryM]

I am a science and mat person as well, but I think you are over simplifying this a bit. 

 

I have tried to picture the way the ratio splitting works, and it is a very clever balance between the mechanical ratios and the two MG units balancing out the torque produced by the engine and delivered to the wheels. The ratios in the Ford C-Max trans are very different from the Prius. The so called final drive ration on the Prius is 3.70:1 and the C-Max is 2.57:1 so there is no chance they are using any of the old Prius programming.

 

My "normal" comute from Santa Clarita to Burbank and back is far from straight and level. I drop about 600 feet going to work, and have to climb it back coming home. There is a bit that is close to level, and I watch the instant numbers, maybe a bit too much on my drive. I have now put over 7,000 miles on the car, all with the original programming. My 13B07 update is not going to happen until Oct 25. I average about 70 mph on the most level stretch. When the HV battery is close to full and I feather the accelerator, I can get it to where the battery is not charging or discharging, no chevrons. At that point, the instant MPG graph is floating above the 60 mpg mark on the down side and and just under the 60 mpg on the up side. This is with the window open at 70, so I think the car really does do a steady state near 60 mpg like it should from the math. I was not able to read the engine rpm at that moment. I ran the same stretch in cruise control so I could switch the display to the tach. It was fluctuating from discharge to charge. The rpm was hard to read, but was just under the 2000 mark, I would say maybe as low as 1800. On my way to work today, I am going in later so traffic will be light, I will try and get a more accurate read. Just changing the programming could move the rpm some, but I think the efficiency is more bound by the balance between the 2 MG units and that can only really be moved by either different ratios or windings in the motors. Permanent magnet rotor brushless motors do have a very wide operating range, but they do have a fixed relationship to the current in to torque out and the voltage in to rpm out, and of course, the opposite, torque in to current out and rpm in to voltage out when being used as an alternator. And yes, it does create AC that is converted back to DC in the control unit. The control unit does use high speed switching to be able to trade voltage for current but that process is not 100% efficient. forcing the MG1 to turn backwards to lower engine rpm is likely to start using more energy than the MG2 is generating. I am willing to bet, Ford has done a lot of testing to determine what balance between MG1 and MG2 consumes the least fuel at any given level road speed. Adding in the hills and acceleration/deceleration adds a ton more complexity and could take much more testing to get to the ideal points. To move the rpm points much will require changing mechanical gear ratios just like in a conventional transmission. 

 

This may nt be rocket science, but, it may actually be more difficult because newtons laws work perfectly in space, not so much on the I5 in traffic.

[fbov]

...The control unit does use high speed switching to be able to trade voltage for current but that process is not 100% efficient. forcing the MG1 to turn backwards to lower engine rpm is likely to start using more energy than the MG2 is generating. ... (emphasis added)

 

This may n(o)t be rocket science, but, it may actually be more difficult because newtons laws work perfectly in space, not so much on the I5 in traffic.

 

Why?

 

Electric motors are marvelous devices, capable of performing diametrically opposed operations with a simple change in connections. Motors can run forward and backward (or clockwise/counterclockwise). A set of coils around a magnet can make the magnet move, or turn magnet motion into electricity.

 

Calling both units "MGs" in the Toyota-based series/parallel design is a bit of a misnomer as only one is attached to the drive wheels, and it simplifies the explanation. C-max has a generator (GEN, aka MG1) and a motor/generator (MG aka MG2). MG is attached to the drive wheels, so it always turns in the direction of car motion (D or R). GEN can turn both ways (neat sim), and can generate power with equal efficiency in either direction. The only thing that changes going from CW to CCW is output voltage polarity, which will not challenge the power control unit (may even be switched in the GEN). There is no systematic energy loss, per se, in the GEN step, as you seem to imply.

 

As to Newton's Laws, it's only in space that we see his theory's shortcomings... Newton got us to the Moon just fine, but gravity as a force does not exist. Space-time is curved. Einstein got it completely right, as best we can tell.

 

Have fun,

Frank

[ptjones]

I am a science and mat person as well, but I think you are over simplifying this a bit. 

 

I have tried to picture the way the ratio splitting works, and it is a very clever balance between the mechanical ratios and the two MG units balancing out the torque produced by the engine and delivered to the wheels. The ratios in the Ford C-Max trans are very different from the Prius. The so called final drive ration on the Prius is 3.70:1 and the C-Max is 2.57:1 so there is no chance they are using any of the old Prius programming.

 

My "normal" comute from Santa Clarita to Burbank and back is far from straight and level. I drop about 600 feet going to work, and have to climb it back coming home. There is a bit that is close to level, and I watch the instant numbers, maybe a bit too much on my drive. I have now put over 7,000 miles on the car, all with the original programming. My 13B07 update is not going to happen until Oct 25. I average about 70 mph on the most level stretch. When the HV battery is close to full and I feather the accelerator, I can get it to where the battery is not charging or discharging, no chevrons. At that point, the instant MPG graph is floating above the 60 mpg mark on the down side and and just under the 60 mpg on the up side. This is with the window open at 70, so I think the car really does do a steady state near 60 mpg like it should from the math. I was not able to read the engine rpm at that moment. I ran the same stretch in cruise control so I could switch the display to the tach. It was fluctuating from discharge to charge. The rpm was hard to read, but was just under the 2000 mark, I would say maybe as low as 1800. On my way to work today, I am going in later so traffic will be light, I will try and get a more accurate read. Just changing the programming could move the rpm some, but I think the efficiency is more bound by the balance between the 2 MG units and that can only really be moved by either different ratios or windings in the motors. Permanent magnet rotor brushless motors do have a very wide operating range, but they do have a fixed relationship to the current in to torque out and the voltage in to rpm out, and of course, the opposite, torque in to current out and rpm in to voltage out when being used as an alternator. And yes, it does create AC that is converted back to DC in the control unit. The control unit does use high speed switching to be able to trade voltage for current but that process is not 100% efficient. forcing the MG1 to turn backwards to lower engine rpm is likely to start using more energy than the MG2 is generating. I am willing to bet, Ford has done a lot of testing to determine what balance between MG1 and MG2 consumes the least fuel at any given level road speed. Adding in the hills and acceleration/deceleration adds a ton more complexity and could take much more testing to get to the ideal points. To move the rpm points much will require changing mechanical gear ratios just like in a conventional transmission. 

 

This may nt be rocket science, but, it may actually be more difficult because newtons laws work perfectly in space, not so much on the I5 in traffic.

You need to get a SCANGAUGE so you can see RPM's etc. I believe I currently can get 55mpg at 60mph drafting and 53mpg without. It looks like I should get to 55mpg without drafting with additional aero  Mods including my Grill Covers.  Paul

[GaryM]

Why?

 

Electric motors are marvelous devices, capable of performing diametrically opposed operations with a simple change in connections. Motors can run forward and backward (or clockwise/counterclockwise). A set of coils around a magnet can make the magnet move, or turn magnet motion into electricity.

 

Calling both units "MGs" in the Toyota-based series/parallel design is a bit of a misnomer as only one is attached to the drive wheels, and it simplifies the explanation. C-max has a generator (GEN, aka MG1) and a motor/generator (MG aka MG2). MG is attached to the drive wheels, so it always turns in the direction of car motion (D or R). GEN can turn both ways (neat sim), and can generate power with equal efficiency in either direction. The only thing that changes going from CW to CCW is output voltage polarity, which will not challenge the power control unit (may even be switched in the GEN). There is no systematic energy loss, per se, in the GEN step, as you seem to imply.

 

As to Newton's Laws, it's only in space that we see his theory's shortcomings... Newton got us to the Moon just fine, but gravity as a force does not exist. Space-time is curved. Einstein got it completely right, as best we can tell.

 

Have fun,

Frank

I have seen that simulation for the Prius a few times, but the ratios are wrong for the C-Max. I would love to find out the speeds of each part in our cars and see what is going on at the 50 mph to 85 area where they can now go EV only. What is the RMP limits of our MG units? I have had my C-Max over 90, but obviously, it was not in EV mode with the old software and all.

 

I race very high performance electric 1/8 scale RC cars. The motors are the exact same technology as the ones in our cars. They have very strictly defined characteristics. Any given wind / rotor combination will have a specific RPM / Volt rating and a torque / amp rating. These do not change unless the magnet starts to lose strength, which does happen from over heat and/or large over current events. When the magnet gets weaker, the rpm for a given voltage will go up, but the torque for a given current will go down. The result is the power drops a bit until the magnet is way too weak, then the efficiency goes to crap. So many new racers gear way too high to go faster, and when the motor is fresh, they seem to run great, but kill the rotor fast. This is only dealing with about 1400 watts or just under 2 HP in an 8 pound car. In the C-Max, we are shoving around 3,600 pounds with 33,000 watts of electricity. The electronics need to monitor the rotor and winding temps and make sure they don't demagnatize it in a few second if something goes wrong. The voltage limit is the battery pack at full state of charge. This limits the rpm the motors can produce any torque out. In theory, you could spin them faster and still use it as a generator for charging, but the system will have to throw away some of the power as the batteries can't accept the charge too fast or at too high of a voltage.I know the cells are just under 5 amp hour each, and even the good high current racing cells can only be charged at 5 times the amp hour, most are limited to 1 or 2 times. The pack in the C-Max hybrid it 76 cells in series, for a nominal terminal voltage of about 245 volts, and a max voltage at full charge could hit about 310 volts. Good race cells can dump out up to 30 times amp hour current, but I doubt highly our cars would ever even try to do that. Most cells are more in the range of 5 to 10 times for long life. so the battery can theoretically put out around 300 volts at 50 amps for 6 minutes, that works out to 1,500 watt hours, the spec says 1400 wh, so I am pretty close with the simpler numbers. The problem is the battery can't accept current at near that rate, which is why you need to brake gentle to get a 100% recovery score. Most of the power MG1 generates, has to go straight to MG2 to help push the car. The Battery is only seeing at most 1/2 of the power at any time. The charge rate, even at 5C is 25 amps at 300 volts, or 7500 watts, or only about 10 hp of braking force. Under maximum acceleration, they do claim 33 KW out of the 1,400 wh battery. Wow, that is about 24C rate discharge, right up with the racing RC cells that last just 300 charge cycles. And that amount of power will only last 2.5 minutes going from 10% to 0%, and the C-Max will only do 80% tops down to 30 or 40% at the bottom. So figure you get that power for just 1 minute. Well, that is plenty to get up to 80 mph accelerating onto the freeway. By the way, 33KW is almost 44 hp with a 98% efficient electric motor. So our ICE engine is also making 144 hp to get the 188 rating to the wheels. Not too shabby.

 

My whole point of all this, the math all works, the battery, motor, gearing, etc. all has to be carefully chosen to get this kind of performance. You can't just say program this motor for more rpm and change physics. If the data Ford is gettign off real world cars in use shows an issue, they could maybe get a little better with software alone (13B07) but to make any bigger change will require different gearing and/or motor(MG1 MG2) windings to move the rpm ranges much at all. And yes, BOTH MG units can act as motor or generator depending on where in the power range the car is. MG1 is mostly generating and MG2 is mostly a motor, but the roles do change with conditions. Any time the MG1 is trying to reverse to make the engine turn slower, it is consuming energy, and adding it to the wheels through the PSD. This energy either has to come from the battery, or use the MG2 as a generator, dragging that power from the wheels, making the efficiency seems pretty weak. Without knowing all the ratios involved, I can't calculate how efficient the trasfer would be, but trying to force a big over drive sounds like a losing proposition. 

 

The goal when in this mode is to not be using any battery power. So all the power used by MG1 will be coming from MG2. When the engine is turning faster, doing a low gear, the opposite is true. The MG1 is only acting as a generator, slowing the inner gear of the PSD and therefore producing output torque to the wheels at the outer gear of the PSD. This generated power can charge the battery, or feed to MG2 to add even more torque to the wheels. This mode makes for an incredibly efficient torque converter. The fact that under drive is more efficient than over drive explains Ford going to the 2.57 final drive ratio. But I still need to figure out the PSD gear ratios to make much use of that simple ratio number. I assume they mean if the ICE and MG1 are turning the same speed, such as the PSD al turning as a single unit, then the wheels are turning just ICE speed / 2.57 ??? or is this a max ratio, with any PSD induced overdrive added in ?? I have no idea at this point. Using the Toyota PSD diagram, you can see if the engine and MG are at the same speed, the final drive to the wheels (assuming the tires roll 6 foot per revolution) works out to about 4.0, the book says 3.7, so maybe the tires are a bit smaller on that model. Doing the math backwards, I get a tire roll out of  5.45 feet per revolution, that seems really small, a 185 60 14 is 6.4 feet per revolution. Maybe they do use some of the overdrvie in the PSD to get the final ratio, or this PSD simulator is based off of a different gearing in an older Prius??

 

Sorry for the ramble on, I really want to use my engineering thoughts to understand how the power is being used and if it can be improved on.

[fbov]

I have seen that simulation for the Prius a few times, but the ratios are wrong for the C-Max. ... And yes, BOTH MG units can act as motor or generator depending on where in the power range the car is. MG1 is mostly generating and MG2 is mostly a motor, but the roles do change with conditions. Any time the MG1 is trying to reverse to make the engine turn slower, it is consuming energy, and adding it to the wheels through the PSD. This energy either has to come from the battery, or use the MG2 as a generator, dragging that power from the wheels, making the efficiency seems pretty weak. Without knowing all the ratios involved,...

 I don't think so.

 

The traction motor, MT is connected to the wheels. It only goes in reverse when you select R. It generates in re-gen mode, drives when requested, but always in the same direction in D. I don't see how you can see it otherwise. Looking at the simulation, one side (traction) only turns in one direction, consistent with connection to drive wheels. I'm sure you're aware that a turning rotor in the traction motor can apply driving and braking forces by changing only electrical inputs to the device, and that it can freewheel with no force imparted as well. I can also see the power split system allowing torque to pass into and out of the ICE/GEN pair, but I don't see all the stuff you do...

 

To me, the specific rations don't matter, it's the understanding conveyed ignoring the axis labels, save for the 0 points.

 

I'll also note that a lot of your experience with small-scale motors may not scale up linearly.

- You can magnetize small magnets far stronger than large ones.

- You're not trying for 900HP electric motors (4 lb/hp for your cars?)

 

Beyond that, I'm not an RC hobbyist; you have a far better grasp of the details in that arena. I'm just asking if you think everything transfers (lots sure does... much of what you say is reasonable, I just think you're off in this respect.)

 

HAve fun,

Frank

[jdbob]

Scattered throughout this document are some interesting descriptions of how things work:

 

http://www.motorcraftservice.com/vdirs/diagnostics/pdf/OBDSM1303_HEV.pdf

[gultim]

If it has to do with physics, and if it was designed by humans, then it can be substantiated with math...that is how Engineering works.  And, if you understand engine fuel consumption at different horse powers, horse power needed to maintain a specific vehicle speed, and distance traveled, then you can calculate the energy needed to propel that vehicle at a given speed over a specific distance. It is undisputable and industry known that to achieve the best MPGs you need to operate a gasoline engine at it's lowest RPM while producing enough horse power to maintain the vehicle at the desired speed which then will reveal the quantity of fuel consumed.  Again, all this can be calculated.  Toyota has figured this out.  My testing using a Scan Gauge II revealed that their engine revs at 1,200 rpm at 45 MPH and achieves 75 MPG, at 55 MPH it revs at 1,400 RPM and achieves 65 MPG, and at 65 MPH the engine revs at 1,600 RPM and achieves 55 MPG.  My C-Max revs at 2,000 RPM at 65 MPH under the same driving conditions as the Prius and achieves only 40 MPG. If I set the C-Max transmission to Low then the engine revs to 4,400 RPM and the car achieves 25 MPG.  Yes, the Prius has a better C/D and is lighter.  I bet that if you add parts to the Prius body to lower its' C/D to that of the C-Max, and add the difference in weight to the Prius, the Prius will still far surpass the C-Max MPGs.  Would any of you Prius owners like to try this experiment?

 

Here is a high revving engine analogy...try pedaling a 5 speed bike on the flats with no wind at 10 MPH in 1st gear for a few miles.  You might attain 10 MPH for a few blocks and at this rate of speed you will notice your legs are spinning the pedals at an extremely high rate.  You will then notice that you will tire out very quickly.  Most of your energy is spent as parasitic energy which is being expended in your legs trying to keep them peddling at this high rate...as a result, very little energy is making it to the wheels.  Shifting to a higher gear will allow for more efficient energy transfer to the wheels and reduces these parasitic leg losses.     

 

Here is a quick test you can perform to demonstrate the relationship between MPGs and engine RPM.  While driving your C-Max with a stabilized battery at 60 MPH on the flats with no wind, take note of your instant MPG gauge then downshift to Low and you will notice your MPGs drop significantly while your engine revs up high (this is totally safe as the computer limits the RPM to a safe range).  The power needed at the wheels (load) has not changed, only the engine rpm has (input power and fuel consumption has increased).  This reveals the extra parasitic energy being consumed by the higher revving engine.  Now imagine what would happen to the MPG meter if you could lower the engine RPM further than it's current value when in Drive?

 

The C-Max has demonstrated (by myself and others) that it can achieve 60 MPG just as the calculations predicted.  These conditions are happening when the motor, generator, and engine are all in their safe, efficient, and designed operating parameters.  The motor and generator speeds are all firmware controlled.  Now we need Ford to alter the C-Max firmware to maintain this high efficiency operation at all times. 

 

Also, I am hoping that we can prevent other discussions that appear to be derailing us from trying to find a solution as to why the C-Max MPG's are so low.  I hope we can exchange factual information that can help resolve this issue and help drive us to root cause.  What pertinent data do you offer in helping to resolve this issue?  Thank you in advance for your help in submitting this data and helping find a solution. 

[hybridbear]

If it has to do with physics, and if it was designed by humans, then it can be substantiated with math...that is how Engineering works.  And, if you understand engine fuel consumption at different horse powers, horse power needed to maintain a specific vehicle speed, and distance traveled, then you can calculate the energy needed to propel that vehicle at a given speed over a specific distance. It is undisputable and industry known that to achieve the best MPGs you need to operate a gasoline engine at it's lowest RPM while producing enough horse power to maintain the vehicle at the desired speed which then will reveal the quantity of fuel consumed.  Again, all this can be calculated.  Toyota has figured this out.  My testing using a Scan Gauge II revealed that their engine revs at 1,200 rpm at 45 MPH and achieves 75 MPG, at 55 MPH it revs at 1,400 RPM and achieves 65 MPG, and at 65 MPH the engine revs at 1,600 RPM and achieves 55 MPG.  My C-Max revs at 2,000 RPM at 65 MPH under the same driving conditions as the Prius and achieves only 40 MPG. If I set the C-Max transmission to Low then the engine revs to 4,400 RPM and the car achieves 25 MPG.  Yes, the Prius has a better C/D and is lighter.  I bet that if you add parts to the Prius body to lower its' C/D to that of the C-Max, and add the difference in weight to the Prius, the Prius will still far surpass the C-Max MPGs.  Would any of you Prius owners like to try this experiment?

 

Here is a high revving engine analogy...try pedaling a 5 speed bike on the flats with no wind at 10 MPH in 1st gear for a few miles.  You might attain 10 MPH for a few blocks and at this rate of speed you will notice your legs are spinning the pedals at an extremely high rate.  You will then notice that you will tire out very quickly.  Most of your energy is spent as parasitic energy which is being expended in your legs trying to keep them peddling at this high rate...as a result, very little energy is making it to the wheels.  Shifting to a higher gear will allow for more efficient energy transfer to the wheels and reduces these parasitic leg losses.     

 

Here is a quick test you can perform to demonstrate the relationship between MPGs and engine RPM.  While driving your C-Max with a stabilized battery at 60 MPH on the flats with no wind, take note of your instant MPG gauge then downshift to Low and you will notice your MPGs drop significantly while your engine revs up high (this is totally safe as the computer limits the RPM to a safe range).  The power needed at the wheels (load) has not changed, only the engine rpm has (input power and fuel consumption has increased).  This reveals the extra parasitic energy being consumed by the higher revving engine.  Now imagine what would happen to the MPG meter if you could lower the engine RPM further than it's current value when in Drive?

 

The C-Max has demonstrated (by myself and others) that it can achieve 60 MPG just as the calculations predicted.  These conditions are happening when the motor, generator, and engine are all in their safe, efficient, and designed operating parameters.  The motor and generator speeds are all firmware controlled.  Now we need Ford to alter the C-Max firmware to maintain this high efficiency operation at all times. 

 

Also, I am hoping that we can prevent other discussions that appear to be derailing us from trying to find a solution as to why the C-Max MPG's are so low.  I hope we can exchange factual information that can help resolve this issue and help drive us to root cause.  What pertinent data do you offer in helping to resolve this issue?  Thank you in advance for your help in submitting this data and helping find a solution. 

Basically what you're saying has to do with the load on the engine. Your hypothesis is that when cruising on the highway the RPMs are too high and thus the load % is too low to be efficient. Possibly this isn't within the limits of the Ford system. Here you can see a simulation of the relationship between MG1 RPM, MG2 RPM & ICE RPM. There are certain scenarios that are not possible. For example, if you're going 70 MPH the ICE RPM must be at least 1432 for MG1 to not be spinning in excess of its limit, more likely in this situation the Prius ICE would be close to 2000 RPM to slow down MG1. The Ford system also has limits. It's possible that the MG1 max RPM requires the ICE to spin faster than you would like. The design can quite likely be improved, but not just with software. Some improvements will require different sized electric motors.

[gultim]

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:   

Edited October 27, 2013 by gultim

[ptjones]

I have had this happen several times that I can remember, RPM's around 1200-1300 and the EV mode helping.  It feels like the ICE is bogged down and having a hard time accelerating. I don't remember if it has done it since the up date, but I think so.  I have a ScanGauge.

Paul

[grggwlkr]

Gultim- do you keep the hill assist engaged all the time? The yellow icon just under the instant MPG gauge in your posted pics is lit and you are traveling 60mph, or are you going downhill. I thought hill assist increased ICE rpm to act as a brake.