Saw this blog post about why the C-Max doesn't get good MPGs

[kyledamron1]

Hi everyone! like the title says, I saw this blog post shared in the thread about the new Escape hybrid. Was wondering if anyone ever remapped the car's computer to where it would run the more efficient power band?

 

http://www.winonarenewableenergy.com/uploads/5/3/6/7/5367335/why_c-max_and_fusion_hybrids_are_getting_low_mpgs_2_printed.pdf

 

If so, what was the process like?

[plus 3 golfer]

The above data was posted a long time ago by the author.  Bottom line is that the 2013 Prius has a Road Load HP that is lower than the C-Max by around 32% at 20 mph dropping to around 23% at 80 mph as shown on the attached graph.  So, one would expect the Prius to get around 25 to 30% better FE under normal cruising conditions than the C-Max all other things being equal.  But according to the data by Tim, this is not the case as indicated by the table of Tim's data below.  This suggests that the software algorithm for the C-Max is "tuned" to achieve FE and "beats" the Prius tuning or perhaps the Toyota M/G set can't operate in negative split mode (generator reducing ICE rpm by speeding up to keep rpm to wheels / vehicle speed constant) like the C-Max can due to operating limitations.  There is a physical connection between ICE, MG1, and MG2.  At 65 mph and likely higher, the Prius apparently can achieve an equivalent FE based on its lower RLHP as shown in the table below.

 

	Fuel Economy (mpg)
MPH	45	55	65
2013Prius	75	65.1	57.5
C-Max	74.7	57.5	48
% diff	0%	13%	20%

 

Here's the link to the old thread on this.  At that time, most were unaware of how Ford "blew it" on the EPA fuel economy estimates and how the RLHP coefficients from coast down measurements changed.  So, the natural assumption was that tuning was off or final drive ratio was wrong.  Tim's post below was prior to the final correction of coefficients in 2014.  Tim also did not record data for analysis to help understand how both cars were operating.  All we see are four points at a specific time (scan gauge) and he doesn't have the BSFC curve for the C-Max.  

 

Edited April 18, 2020 by Plus 3 Golfer

[plus 3 golfer]

Also, one must remember that that the rpm of ICE, generator, motor and wheels have a physical relationship:

 

When ICE is spinning, 3.55 = (motor rpm + generator rpm) / ICE rpm

When ICE is not spinning,  -0.995 = generator rpm / motor rpm

For stock wheel / tires and 2.57 final drive ratio, 9 = wheel rpm / motor rpm 

 

So, when driving, these physical relationships must hold true with respect to rpm.  But, the torque relationship among the physical components may not follow these physical relationships.  Torque demand changes based on driver input and road conditions (up / down, surface, and weather).  Torque demand is met by ICE and the motor.  So, the algorithms determine how best to match demand with supply taking into account physical limitations mentioned above plus the HVB.

 

The easiest way to get a vehicle to operate at a more efficient point on the BSFC is to shift to a higher gear or reduce the final drive ratio on a conventional car.  Thus, ICE will spin at a lower rpm and presumably at a more efficient point on the BSFC curve for a given torque demand.  However, it's not quite that easy for the C-Max or Prius because of the physical relationships.  Could a numerically lower gear ratio improve C-Max fuel economy at higher speeds where one could hold the generator at zero rpm? Probably but what happens at slower speeds with that lower gear ratio.  But, the C-Max does have the capability to in essence, shift to a higher gear.   For example at about 72 mph (motor rpm about 9000 rpm), the algorithms do via software effectively lower ICE rpm to achieve an effective final drive ratio of 2.0:1 from the fixed final drive ratio of 2.57.   ICE would normally spin at around 2500 rpm (gen rpm =0) with the ratio fixed at 2.57.  But by spinning the generator around -2000 rpm, ICE rpm drop to around 2000 rpm.  From the first equation (relationship above),   

 

ICE rpm = (motor + gen)/3.55 = (9000-2000)/3.55 = 1972 rpm

 

This would be akin to an overdrive gear in a conventional vehicle of 0.8:1 or a 20% reduction (1-500/2500) in the final drive gear ratio.

 

Attached is a graph I did several years ago showing the above.  

 

Edited April 18, 2020 by Plus 3 Golfer

[ptjones]

5 hours ago, Plus 3 Golfer said:

The above data was posted a long time ago by the author.  Bottom line is that the 2013 Prius has a Road Load HP that is lower than the C-Max by around 32% at 20 mph dropping to around 23% at 80 mph as shown on the attached graph.  So, one would expect the Prius to get around 25 to 30% better FE under normal cruising conditions than the C-Max all other things being equal.  But according to the data by Tim, this is not the case as indicated by the table of Tim's data below.  This suggests that the software algorithm for the C-Max is "tuned" to achieve FE and "beats" the Prius tuning or perhaps the Toyota M/G set can't operate in negative split mode (generator reducing ICE rpm by speeding up to keep rpm to wheels / vehicle speed constant) like the C-Max can due to operating limitations.  There is a physical connection between ICE, MG1, and MG2.  At 65 mph and likely higher, the Prius apparently can achieve an equivalent FE based on its lower RLHP as shown in the table below.

 

	Fuel Economy (mpg)
MPH	45	55	65
2013Prius	75	65.1	57.5
C-Max	74.7	57.5	48
% diff	0%	13%	20%

 

Here's the link to the old thread on this.  At that time, most were unaware of how Ford "blew it" on the EPA fuel economy estimates and how the RLHP coefficients from coast down measurements changed.  So, the natural assumption was that tuning was off or final drive ratio was wrong.  Tim's post below was prior to the final correction of coefficients in 2014.  Tim also did not record data for analysis to help understand how both cars were operating.  All we see are four points at a specific time (scan gauge) and he doesn't have the BSFC curve for the C-Max.  

 

I would think the aero drag coefficient would be the big part of the difference between the two.  I believe I gain 6 mpg from having Grill Covers and wheel covers to close the gap in mpg's.

 

Paul 

[plus 3 golfer]

20 hours ago, ptjones said:

I would think the aero drag coefficient would be the big part of the difference between the two.  I believe I gain 6 mpg from having Grill Covers and wheel covers to close the gap in mpg's.

 

Paul 

Exactly, the CdA of the Prius is significantly lower than the C-Max. Also, the additional weight of the C-Max contributes significantly to the C-Max RLHP at lower speeds.   You’ve shown that lowering  the Cd of the C-Max, the CdA does significantly lower the C-Max RLHP and significantly improve FE.  Even with your aero mods, the C-Max CdA is still likely greater than the Prius. 
 

The bottom line is that there is no evidence that the C-Max algorithms are inferior (as Tim suggests used Prius software for larger C-Max engine) to the Prius with respect to the hybrid systems and are  the causal factor of “why the C-Max doesn’t get good  MPG”.

 

Edited April 19, 2020 by Plus 3 Golfer

[fbov]

It would be interesting to see how the Escape fits. With its 2.5l ICE and liquid-cooled HVB, one might expect Ford has re-optimized algorithms. Charging certainly seems to replenish a low HVB SOC very quickly. There's no standard tach access, but I don't hear the engine rev until I'm asking for more than 10kW. Very throaty above there as RPM rises, and I haven't floored it yet. 

 

We won't talk about CdA.

 

Stay well,

Frank

[plus 3 golfer]

There has to be reasons the city EPA rating of the Escape (44 mpg) is higher than the C-Max rating (42 mpg).  Even the AWD Escape (43 mpg) is rated higher than the C-Max which weighs slightly more than the C-Max. 

 

I think the 2.5L ICE has about 10 HP more than the 2.0L.   So, at the same given rpm for both Escape and C-Max, the Escape would likely be able to charge the HVB quicker and keep it cool. This might allow more EV operation and enhance FE. 

 

Also,  one would think that in both that the algorithms would be optimized for efficient charging.  Given the extra HP, the Escape could be charged more efficiently by lowering rpm slightly while still charging the HVB similar to the C-Max and taking advantage of a more efficient point on the BSFC curve and thus enhancing FE.  Add the higher CdA FE penalty of the Escape to the FE comparison and Ford certainly enhanced something to increase city FE.  Perhaps the Escape electric motors and HVB are also more efficient.

 

 

[fbov]

My one disappointment with Ford is the lack of simple things like engine specs. Power and torque @ RPM used to be ubiquitous, now we guess and estimate. 10 HP isn't a 25% increase, so I'm expecting a big bump in torque, especially at low RPM, but can't find a bit of data. I also haven't seen anything to indicate the EV side has greater capacity than in C-Max. I think HF35 and HF45 share electric motor specs; it certainly drives like it. 

 

I think the big difference is HVB cooling, allowing a more aggressive charging strategy without exceeding thermal limits. I can't see engine charging rates, but have noticed that regen maxes out at 35kW if you're going fast enough. I have also noted that on long downhills, with Hill Assist ON, the car no longer turns the ICE to limit speed once the HVB is full. I see it limit regen to 20kW, max, with resulting reduction in regen score. I wonder if there are resistive loads in the cooling loop with 20kW short-term power dissipation capacity. 

 

Given the Escape is a high-volume product, I expected Ford to tell us a lot about it. Not the case....

 

Stay well,

Frank

[plus 3 golfer]

Ford Specs

2018 C-Max --- Engine torque =129 ft-lbs @ 4000 rpm;  Total HP = 188 HP @6000 rpm

HVB - Charge Limit = 35 kW, 1.4 kWh;  Motor - 88 kW, 177 ft-lbs @ 6000 rpm;  Generator 64 kW

 

2020 Escape - Engine Torque = 155 ft-lbs @ 4500 rpm; Total HP =  200 HP @ 6250

HVB - 1.1 kWh;  Motor - 88 kW (Autoblog);  Generator ???

 

So, it looks like the 2.5L Escape ICE has 26 ft-lbs more peak torque at 500 more rpm than the 2.0L C-Max. So, the HVB charge limit of the Escape is 35 kW - the same as the C-Max.

[fbov]

This is what I've been able to find. It's consistent with yours, save for one comment. 

1 hour ago, Plus 3 Golfer said:

Motor - 88 kW, 177 ft-lbs @ 6000 rpm

I think this is properly stated "88 kW @ 6000 rpm, 177 ft-lb" torque (@ 0 to ~2000 RPM). Motors are current limited at low RPM. 

 

And the system torque spec of 155 lb-ft is from the brochure, but less than either ICE or EV alone makes no sense! The Hybrid fits between the 1.5 and 2.0L EBs, so between 190 and 280 lb.-ft. makes sense, 255 lb-ft maybe?

 

Stay well,

Frank 

 

PERFORMANCE	C-Max	Escape
Engine horsepower	141 hp	168 hp
Engine torque	129 lb.-ft.	170 lb.-ft.
Total system power (sustain)	188 hp	200 hp, 155 lb-ft.
ELECTRIC MOTOR/GENERATOR
Type	Permanent magnet AC synchronous motor	same as C-Max?
Output	118 hp@6,000 RPM/88kW@6,000
Torque	Torque 177 lb.-ft./240N

Edited April 22, 2020 by fbov