OBD II Data for ICE

[larryh]

The following plot shows the preferred operating regions for the ICE for a recent trip obtained driving on highways by recording OBD II data from the car.  The x-axis is engine RPMs.  The y-axis is Absolute Load (Volumetric Efficiency), i.e. the percentage of maximum airflow into the engine.  Absolute Load is linearly correlated with brake torque (force) of the engine.  Engine power is then proportional to torque x RPMs.  One would expect the car to operate in the regions where it is most efficient. 

 

While the ICE is warming up, it operates at a constant 1500 rpm.  Only the load varies.  The electric motor makes up any difference in required power.  At highway speeds, it likes to operate at around 2000 rpm and vary the load between 45% and 75% as needed to supply the required power.  The ICE runs the generator at times which increases the load on the engine.  Only when power demand is very high (for example accelerating to pass), does the engine speed exceed 2300 rpm.   The results may be different for city driving. 

 

It would be nice to also show normalized fuel consumption at each operating point (such a map for a Prius can be found here: "http://fordfusionhybridforum.com/topic/6775-what-is-an-ecvt-how-does-it-work-here-is-the-answer/?p=74047").  But that would require a lot of data.  The OBD II measurements are not synchronized.  There may be more than a second difference in time between when each of the measurements (rpms, load, fuel rate) are taken.  A lot can happen in one second.  This following chart has errors due to this issue.

 

Edited March 16, 2014 at 02:03 PM by larryh

[larryh]

The following plot shows the operating region of the ICE similar to the one above with data from several trips.  I added a solid black line that estimates the maximum Absolute Load at a given RPM.  Note the ICE does not normally operate below 1900 RPM.  It only operates at 1500 RPM while warming up.  It is difficult to estimate the maximum Absolute Load.  The OBD II data contains Calculated Load and Absolute Load.  When the Calculated Load Value is 100%, the engine is at maximum output at a given RPM.  So I can look at the OBD II data to find points where the Calculated Load Value is close to 100% and extrapolate what the corresponding Absolute Load Value would be if the Calculated Load Value were 100%.  Unfortunately, the relationship between Calculated Load Value and Absolute Load Value is non-linear, so there is lots of room for error in the solid black line showing maximum engine output.  I also made the assumption that the maximum absolute load is typically 95% (know as volumetric efficiency).  The specs for the ICE indicate that the maximum torque is 175 Nm at 4000 rpm.  So I drew the line through 95% at 4000 rpm.  The specs also indicate that the maximum horsepower of the ICE is 141 hp at 6000 rpm, or about 165 Nm of torque, or 165/175 = 94% of maximum torque.  So I drew the line through 89.5% at 6000 rpm. 

 

I don't have much data for RPMs greater than 2700.   The ICE would operate there only during heavy acceleration.  I don't want to ruin my driving score. 

 

 

Edited March 23, 2014 at 08:14 AM by larryh

[larryh]

The chart below shows the ICE Engine Map that I have constructed from several recent trips (mostly highway/freeway driving).  It shows the fuel consumption in grams per kWh of energy output by the ICE for various RPMs and loads.  The horizontal axis shows ICE RPM.  The vertical axis shows Absolute Load, which is linearly correlated with torque (I determined that this is not true--I have corrected the chart for the non-linear relationship between Absolute Load and Torque).  I estimate from the data that I have recorded and information available about Absolute Load that the maximum Load is about 95%, which should correspond to the maximum torque of the ICE which is 175 Nm. 

 

The colored contours show the fuel consumption per unit of energy.  The most efficient region, the least amount of fuel consumed per unit of energy output by the ICE, is the red region in the center followed by the green region surrounding it (ignore the blue region--the values in this region is not significantly smaller than the red region--Excel arbitrarily decided to split the contour here even though there is no significant difference).  The curved white lines are lines of equal power output.  If the ICE operates anywhere on the line in the upper right corner, it is produces about 35 kW of power.  Power roughly correlates with the vehicle's speed on a level road. 

 

The light blue markers are actual operating points that I have recorded on my trips.  These show the regions in which the ICE actually operates.  Note that the contours are only valid in regions containing red markers.   The contours in other regions are computed by extrapolating the data from regions which do contain data.  For example, the efficient red region in the upper right corner was computed by extrapolating the observed measurements from the other regions.  (Note that does not mean the car uses least amount of fuel in this region.  It uses the most fuel in this region.  However, it also produces the most power in this region.  The net result is that it uses the least amount of fuel per unit of energy produced in this region).  Since I have no fuel consumption measurements for that region, I can't be sure that it is really one of the most efficient operating regions.  (That region no longer exits in the updated chart).

 

The least efficient regions are the lower right and upper left.  The ICE can't actually operate at the top left corner--that would exceed the maximum torque that the ICE can produce at a given RPM.

 

You can see from the data that the ICE mostly operates in the efficient red and green regions at the lower left between 20 kW and 25 kW of power.  The points that exceed 25 kW were most likely recording during accelerations/decelerations or going up hills.  When more power is demanded, the ICE cannot always operate in the most efficient regions for driveability reasons.  I would not be happy if the car prioritized operating in an efficient region and totally disregarded my desire to quickly increase output power for acceleration--I would perceive the car has having very weak acceleration.

 

I had to make a lot of assumptions to generate this data, so it may not be entirely accurate. 

 

Edited March 24, 2014 at 02:02 AM by larryh

[larryh]

If the above data is correct and the ICE consumes 270 g of gas for each kWh of mechanical energy produced, then the efficiency of the ICE is about 30%.  The remaining 70% of the energy from the combustion of gas is lost as heat warming up the engine and as exhaust through the tailpipe.  Looking at the power consumed by the electric motor vs. its output power, the efficiency of the electric motor is around 87%.  Thus the EV MPGe should be about 2.9 times the ICE MPGe. 

Edited March 22, 2014 at 11:36 AM by larryh

[viajero]

I like your graphs.  Checking your numbers by comparing your end results to some researched numbers, it looks like your assumptions are pretty good.

 

The FFE is rated at 43 mpg combined and 100 mpge, or 2.32 times more efficient using electricity.  I think the EPA uses electrical energy from the wall, so allowing for 80% round trip charging efficiency, 100 mpge would be 125 mpge from the battery, or 2.91 times more than 43 mpg.  That's awfully close to your 2.9.

 

Looking at this web site with some BSFC graphs people have scrounged up, most gasoline engines can achieve between 215-250 g/kWh at their sweet spot.

 

http://ecomodder.com/wiki/index.php/Brake_Specific_Fuel_Consumption_%28BSFC%29_Maps

 

This Wikipedia article got some data from an SAE paper I'm not going to pay for, but they say the 2nd generation Prius engine, which should be similar to the Energi's Atkinson cycle 4-cylinder, does 225 g/kWh, for a peak efficiency of 37%.

 

http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption

 

Of course they can't keep the ICE right at the sweet spot all the time, so average efficiency is lower.

Edited March 23, 2014 at 03:59 AM by viajero

[larryh]

I updated the chart in post #3 above to correct for the fact that Absolute Load is not linearly correlated with Torque as I had previously assumed.  I have determined the correlation between Torque produced by the ICE and and Absolute Load and attempted to correct for the non-linearity.  The ICE appears to consume about 220 grams of gasoline for every kWh of energy produced when operating in its most efficient region (rather than 270 as indicated in my previous post).  If that is really the case, the efficiency of the ICE is about 37%.  Note that these measurement should really be done at 70 F rather than in the middle of the winter when it is 0 F.  That may be impacting computations since I am not adjusting for the cold. 

Edited March 24, 2014 at 02:03 AM by larryh

[larryh]

 

The following plot shows hybrid operation of the Fusion Energi, with the ICE on, driving on a freeway at 65 mph. Initially, the ICE is off.  The ICE turns on around 3:36:43 pm. 

 

The purple line is the electrical power output from the HVB.   When the power is positive, the HVB is discharging to provide power to run the motor/generator/accessories.  When the power is negative, the HVB is charging from electrical power generated by the motor/generator.    At the start, the electric motor and generator are consuming up to 28 kW of electrical power.  Shortly after the ICE turns on, the electric motor and generator produce about 10 kW of power to charge the HVB. 

 

The blue line is the mechanical power output by the electric motor, which comes from the HVB.  The red line is the mechanical power output by the generator, which also comes from the HVB.  When the power is positive, the motor/generator is drawing power from the HVB to power the wheels.  When the power is negative, they are providing power to the HVB. 

 

When the ICE turns on, the motor power and HVB power turn negative.  The motor is charging the HVB.  The generator power also becomes negative a little while later.  Now both the generator and motor are charging the HVB.   The Power Flow screen in the car now displays Charging HV Battery.  Gradually, the generator power turns positive and hovers around 0.  It is now drawing power from the HVB battery.  The Power Flow screen now displays Hybrid Drive.  The HVB is still being charged by the electric motor.  The electrical power to charge the HVB remains about the same as before when the generator was also generating power to charge the HVB. 

 

Gradually, the generator consumes more and more electrical power to provide mechanical power to the wheels (the remaining power comes from the ICE).  Near the end of the plot, the mechanical power output of the generator is about 6 kW.  The electric motor is consuming about 8 kW of mechanical power to produce electricity.  The total power to the HVB is around 0.  The HVB is no longer being charged.  The Power Flow screen still displays Hybrid Drive.  I assume the goal here is to lug the ICE to force it into a more efficient operating region.  The electric motor is increasing the load on the ICE by 8 kW and the generator is reducing the ICE's load by 6 kW, so the overall additional load on the ICE is 2 kW.  Hopefully, the ICE now uses less fuel with the additional 2 kW load.  I believe this is the negative-split mode of hybrid operation.

 

The generator generates very little power.  It comes mostly from the electric motor.  Instead, it appears the generator is used to power the wheels along with the ICE.

 

Edited April 7, 2014 at 12:40 AM by larryh

[larryh]

I observed the following power measurements this morning for my commute on the Freeway going about 65 mph in EV Later mode with the power flow screen showing Hybrid Drive:

 

Mechanical Power Consumed

Average power applied to wheels:  19.1 kW.

Average power applied to motor:  7.4 kW

Total: 26.5 kW

 

Mechanical Power Generated

Average power output from ICE:  21.0 kW

Average power output from generator:  5.4 kW

Total:  26.4 kW

 

Electrical Power Consumed

Average power consumed by accessories:  0.5 kW

Average power applied to HVB:  0.6 kW

Total:  1.1 kW

 

I don't know how to measure the electrical power generated by the motor or consumed by the generator.  The SOC of the battery increased slightly by about 0.69% during this 10 minute segment.  The motor is generating electricity which is consumed by the HVB, generator, and accessories.  The ICE is generating slightly more power than is required to drive the wheels.

 

When in hybrid mode, after the HVB was depleted, I observed the following going about 50 mph with the power flow screen displaying Charging HV Battery:

 

Mechanical Power Consumed

Average power applied to wheels:  18.0 kW

Average power applied to motor:  10.4 kW

Average power applied to generator: 1.4 kW

Total: 29.8 kW

 

Mechanical Power Generated

Average power output from ICE:  31.1 kW

 

Electrical Power Consumed

Average power consumed by accessories:  0.6 kW

Average power applied to HVB:  10.5 kW

Total:  11.1 kW

 

This was for about a minute, so the measurements are not as accurate as above.  The ICE is generating significantly more power than required to drive the wheels.  So the question is, which is more efficient?  "Hybrid Drive" (the first mode of operation above) which slightly increases the load on the ICE, or "Charging HV Battery" along with "Electric Drive" in hybrid mode (the second mode of operation above), charging and discharging the HVB battery, which places a significantly higher load on the ICE when charging the HVB and the ICE is completely off when discharging the HVB.   Am I better off depleting the HVB as soon as possible, or saving it for later?  The car does not seem to charge the HVB much during EV later mode--the power flow screen usually shows only Hybrid Drive.  Note that Hybrid Drive is displayed when either the generator, the motor, or both are consuming electrical power.  Charging HV Battery is displayed when both the generator and motor are generating electrical power.

Edited April 11, 2014 at 07:13 PM by larryh

[Russael]

I think ideally at higher speeds, like above 50MPH, it's better to 'float' the HVB and just use the ICE to propel the vehicle... EV Later and Hybrid mode do the same thing.  Letting it go in to EV mode, then having the ICE come on to charge the battery again probably introduces additional losses (how efficient is that generator when it's putting juice back in to the battery when driven by the ICE?) and this would be less efficient.  While going uphill, you'll probably go in to charge assist mode, but when going back downhill, it can recapture that expelled energy, and then start floating the HVB again while back on flat ground.

 

We know the AC to DC charging system is around 80some odd percent efficient thanks to your calculations... I can't recall if you calculated the efficiency of the generator when putting energy back in to the battery.

 

Well, we do know that the ICE is about 37% efficient, again thanks to your calculations... so I guess in a way the generator is less than 37% efficient at putting energy back in to the battery.  The generator itself may be high, but it isn't 100%... probably closer to around 90 (Regen is specified to be around 90%... I'd assume the generator is identical).

Edited April 11, 2014 at 07:27 PM by Russael

[larryh]

Actually, the first mode of operation at 65 mph on the Freeway doesn't look too bad.  The ICE is generating an extra 1.9 kW more power than required to drive the wheels.  We need about 0.5 kW of additional power for the accessories.  So that leaves the ICE generating about 1.4 kW more power than required.  From that extra power, we are getting about 0.6 kW of electrical energy from the motor/generator to charge the HVB.  In addition, it is probably forcing the ICE to operate at more efficient rpm/load operating point. 

 

The second mode of operation at 50 mph is probably not typical of what would be seen in hybrid mode driving at constant speed.   I will have to collect more data to see what happens.  The theory is that we can use the excess power generated by the ICE when we force it into a more efficient operating region to charge the HVB.  And then when the HVB is full, we can turn off the ICE and use the electric motor to power the car.  But in the example above, I think the ICE is being pushed far beyond its most efficient operating point.  I believe the efficiency of the generator/motor runs around 75% to 90%.  I will have to produce a Generator/Motor map that shows their efficiency. 

[larryh]

The following plot is a Motor/Generator Map that shows the efficiency of the motor/generator for various RPMs and Torque.  Generally, the efficiency is from 60% to 90%, i.e. if 1 kW of electric power is applied to the motor/generator, the motor/generator will produce between 0.65 and 0.90 kW of mechanical power.  This map is a rough approximation of the true map.  I am unable to get the measurements that are required for an accurate map and have to make several assumptions/approximations.  The efficiency increases with increasing Torque and RPM.   The blue markers show actual operating points of the motor/generator during my trips.  The plot is only reasonably accurate in regions where there are markers.   The remaining regions are computed by extrapolating the existing data and may not be correct.  The power output required for the upper right portion of the map is beyond the capabilities of the motor/generator. 

 

The curved lines in the map show the mechanical power generated by the motor/generator.  The lines range from 5 kW to 40 kW from left to right.  A motor speed of 8400 rpm corresponds to about 60 mph.   Note I can't isolate the generator from the motor, they both work together to power the vehicle. 

 

Going 30 mph, the efficiency is around 60%.  Going 60 mph, the efficiency increases to 75%.  You get significantly better efficiency during acceleration. 

 

Edited April 18, 2014 at 08:56 PM by larryh

[larryh]

The generator/motor efficiency for regenerative braking also seems to be around 90%.  So if we assume that the HVB efficiency is 97% for charging and for discharging, we get:

 

Efficiency in capturing energy by HVB during regenerative braking:  90%*97% = 87%.

Efficiency in recovering energy from HVB after regenerative braking:  90%*97% = 87%.

 

So I estimate the overall efficiency of regenerative braking is about 87%*87% = 75%, i.e. you recapture about 75% of the kinetic energy lost by braking.

Edited April 12, 2014 at 11:54 AM by larryh

[Russael]

You mean 75% efficient from capture to re-usage, not just capture.  If that's the case, using the ICE to charge and discharge the battery (cycling in and out of EV mode on flat ground), seems wasteful, and the way the car can float the HVB at speeds 45MPH or greater while in hybrid mode seems to support that (although, when I was able to make it do that, I was running heat).  It could potentially be more efficient at some speeds, but that's a lot of energy loss to somehow still be more efficient.

 

When you mentioned you were on the freeway at 65MPH, were you also running climate at all?  The ICE may have been producing a smidge of extra energy more than required to propel the car... I kind of wonder if that was to overcome some mechanical loss, or if you were possibly on a slight incline/decline.  I don't think it'd ever be completely balanced, but that is as close as it's going to get. 

[larryh]

I meant 75% recapture efficiency to imply the amount of kinematic energy restored through regenerative braking, i.e. if you are going 60 mph, come to a full stop, and then accelerate back to 60 mph, 75% of the kinematic energy required to accelerate back to 60 mph is provided through regenerative braking (ignored friction, aerodynamic drag, etc.).  The remaining 25% of the kinetic energy must come from plug-in energy stored in the HVB or from the ICE. 

 

Similarly, when the ICE charges the HVB, only 75% of that energy is actually used to propel the car.  The rest is lost as heat by the generator/motor converting mechanical to electrical energy, the HVB storing the electrical energy, the HVB then recovering the stored energy and converting it to electrical energy, and finally the motor/generator then converting the electrical energy to mechanical energy. 

 

If you look at an accurate Engine Map for an ICE, you will see dramatic differences in the efficiency of the ICE at different operating points.  It is entirely possible, by running the generating/motor to charge the HVB, the ICE is able to operate at a more efficient operating point and the overall ICE fuel usage is less with charging/discharging the HVB than simply only driving the wheels.  The differences in efficiency at the various operating points is far greater than 25%.  According to documents I have seen, the preferred mode of operation on the Highway at higher speeds is to not charge/discharge the HVB.  But at lower speeds, it will start charging/discharging the HVB in addition to powering the wheels.  I think the first mode, at highway speeds, is referred to as, negative split mode of operation.  And the second mode, at lower speeds, is referred to as positive split mode of operation.  Both modes attempt to force the ICE into a more efficient operating point.

 

The outside temperature was about 50 F.  I didn't use any significant energy from climate.  If you are referring to balancing the mechanical power that was generated and consumed, you also need to account for friction.  Not all of the mechanical energy can be transmitted to the wheels.  In addition, the power at the wheels that I showed is not the measured power at the wheels, but the desired power at the wheels.   All the other quantities were measured power. 

Edited April 12, 2014 at 12:44 PM by larryh

[larryh]

This is what I observe in Electric Drive going with cruise control set to 55 mph on a relatively level road (GPS speed was 54.3 mph):

 

Mechanical Power Consumed

Average power applied to wheels:  14.3 kW.

 

Mechanical Power Generated

Average power output from motor:  11.6 kW

Average power output from generator:  -1.8 kW

Total:  9.8 kW

 

Electrical Power Consumed

Average power consumed by accessories:  0.6 kW

Average power consumed by motor and generator:  14.6 kW

Total:  15.1 kW

 

The generator seems to be generating electricity rather than propelling the car along with the motor.  The motor is consuming electricity to generate mechanical power and the generator is consuming some of that mechanical power to convert it back to electricity.  The power provided by the motor and generator to power the wheels is 11.6 - 1.8 = 9.8 kW.  The efficiency of the motor/generator seems to be:  9.8 / 14.6 = 67%. 

 

Note that the car reports the wheels are being supplied with 14.3 kW of power.  There a big gap in power produced by the motor/generator of 9.8 kW to power the wheels and what the car reports for power at the wheels of 14.3 kW.  The reported value of 14.3 kW cannot be right.  If I plot the reported power at the wheels and the HVB power, they are equal.  It is impossible to convert 100% of the electrical power from the HVB to mechanical power and transmit all that power to the wheels.  In a normal car, the loss in power in the transmission alone is between 15% and 20%.  In addition, a motor/generator is not 100% efficient. 

 

The other power measurements seem to be correct.  Note that I would expect the motor/generator to use less power to power the wheels than the ICE.  The ICE needs to use the transmission to power the wheels.  I think the electric motor has a more direct route to the wheels which will be more efficient in transmitting power to the wheels.

.

Edited April 19, 2014 at 09:53 PM by larryh

[larryh]

I attempted to measure the efficiency of regenerative braking.  I started at 54 mph, placed the drive in Low, and removed my foot from the accelerator.  The total mechanical energy generated by the motor/generator was 0.115 kWh.  The total electric energy supplied to the HVB (accounting for power required to run the accessories) was 0.110 kWh.  If these numbers are correct, the efficiency was about 96%.

 

The motor/generator started out generating about 30 kW of electrical power, which gradually decreased when speed fell below 50 mph.  The efficiency seemed greatest around 20 to 40 mph.  Below 20 mph, efficiency dropped off rapidly. 

 

I am revising my estimate for regenerative braking to range from 80% to 95%.

 

The car's speed dropped from about 54 mph to 8 mph.  I estimate the total change in kinematic energy to be about 0.143 kWh.  So the motor/generator only received 0.115 / 0.143 = 80% of the kinetic energy.  The remaining energy must have been lost due to aerodynamic drag, rolling resistance of tires, and friction. 

Edited April 19, 2014 at 01:47 PM by larryh

[Energitic]

I think you are in the right ballpark. For comparison: The Opel engineer who was responsible for the development of the regenerative braking system of the Chevy Volt/Opel Ampera claims that they are able to recover about 80% of the kinetic energy (which he says is industry-leading efficiency).

 

http://www.opel-blog.com/2011/07/21/maximale-rekuperation/

[larryh]

I observed the following power measurements this morning for my commute on the Freeway going about 65 mph in EV Later mode with the power flow screen showing Hybrid Drive:

 

Mechanical Power Consumed

Average power applied to wheels:  19.1 kW.

Average power applied to motor:  7.4 kW

Total: 26.5 kW

 

Mechanical Power Generated

Average power output from ICE:  21.0 kW

Average power output from generator:  5.4 kW

Total:  26.4 kW

 

Electrical Power Consumed

Average power consumed by accessories:  0.5 kW

Average power applied to HVB:  0.6 kW

Total:  1.1 kW

 

I don't know how to measure the electrical power generated by the motor or consumed by the generator.  The SOC of the battery increased slightly by about 0.69% during this 10 minute segment.  The motor is generating electricity which is consumed by the HVB, generator, and accessories.  The ICE is generating slightly more power than is required to drive the wheels.

 

If I assume 90% efficiency for the generator and motor, then we have:

 

The motor converting 7.4 kW of mechanical energy to 6.7 kW of electrical energy.

The generator producing 5.4 kW of mechanical energy by consuming 6 kW of electrical energy.

There is a 0.7 kW net surplus of electrical energy which closely matches the 0.6 kW of electrical energy being supplied to the HVB.

 

So both the mechanical and electrical power produced/consumed by the ICE, motor, generator, and HVB all balance out.

Edited April 13, 2014 at 01:06 AM by larryh

[larryh]

I am confused by the power measurements for the generator that I am getting.  The sign of the generator power seems to be different when the ICE is off versus when the ICE is on.  When the ICE is on, a negative power measurement seems to only make sense if the generator is converting mechanical power into electrical power.  When the ICE is off, a negative power measurement seems to only make sense if the generator is converting electrical power to mechanical power.  In EV mode, I infer from the data that I am getting that both the electric motor and generator are consuming electricity to propel the vehicle.  The electric motor power is positive and the generator power is negative. 

 

The generator has several modes of operation, including modes called Torque, Speed, various types of Engine Start, and Engine Stop.  In the Torque mode, the generator and motor rotate at the same speed.  In the other modes, their rotation speeds differ.  The Torque mode is used during EV operation.  The Speed mode is used when the ICE is on.  The definition of the torque output by the generator (positive or negative torque) seems to depend on the generator mode. 

Edited April 13, 2014 at 12:28 PM by larryh

[larryh]

The following are the relationships between the rotations of the motor, generator, ICE, and wheels:

 

(motor rpm + generator rpm)

------------------------------------   = ICE rpm

               3.55

 

10.39 * wheel rpm = motor rpm
 

Usually, the motor rpm and generator rpm have opposite signs.

 

So in order to prevent the ICE from spinning (EV mode), the motor and generator must have equal, but opposite RPMs.

Edited April 13, 2014 at 06:57 PM by larryh

[larryh]

If you look at an accurate Engine Map for an ICE, you will see dramatic differences in the efficiency of the ICE at different operating points.  It is entirely possible, by running the generating/motor to charge the HVB, the ICE is able to operate at a more efficient operating point and the overall ICE fuel usage is less with charging/discharging the HVB than simply only driving the wheels.  The differences in efficiency at the various operating points is far greater than 25%.  According to documents I have seen, the preferred mode of operation on the Highway at higher speeds is to not charge/discharge the HVB.  But at lower speeds, it will start charging/discharging the HVB in addition to powering the wheels.  I think the first mode, at highway speeds, is referred to as, negative split mode of operation.  And the second mode, at lower speeds, is referred to as positive split mode of operation.  Both modes attempt to force the ICE into a more efficient operating point.

 

 

Today, I left the mode set to EV auto for my entire 60 mile highway/freeway (55-65 mph) commute home, rather than reserving the HVB for the slower segments of my route.  It was 39 F.  I got 23 EV miles before the battery depleted (That's about the best range I got last summer.  I haven't seen any degradation in range of the HVB after one year).  The remaining miles were then in hybrid mode.  I achieved 68 MPGe.  The previous high MPGe at that temperature was 60 MPGe.  One data point is certainly not conclusive.  I will have to investigate further the efficiency of EV Later mode vs. Hybrid mode. 

Edited April 13, 2014 at 11:04 PM by larryh

[larryh]

I looked at today's data to see what was happening in "Hybrid Drive" vs "Charging HV Battery".  This is traveling at 66 mph on the freeway.   I observed the following data in each of the modes:

 

"Hybrid Drive"

Avg. Fuel flow:  0.0276 gal/min

Power to HVB: 2.56 kW

ICE output power:  19.9 kW

Power to Wheels:  16.1 kW

 

"Charging HV Battery"

Avg. Fuel flow:  0.0414 gal/min

Power to HVB: 10.55 kW

ICE output power:  28.0 kW

Power to Wheels:  18.1 kW

 

Apparently, the freeway is not level.  It required more power to the wheels in the "Charging HV Battery" segment. 

 

It requires about 16.7 kW of power in EV mode to travel this same speed.  Assuming 90% of the energy stored in the battery can be retrieved, that means for the different modes, that the ICE generated enough power to power the car in EV mode the following percent of the time:

 

"Hybrid Drive"

0.9*2.56/16.7 = 14%

 

"Charging HV Battery"

0.9*10.55/16.7 = 57%

 

So the ICE could be off 14% of the time in "Hybrid Drive" mode vs. 57% of the time in "Charging HV Battery" mode.  So the effective fuel consumption in each mode is:

 

"Hybrid Drive"

(1-0.14)*.0276 = 0.024 gal/min

 

"Charging HV Battery"

(1-0.57)*.0414 = 0.018 gal/min

 

The "Charging HV Battery" mode uses 75% of the fuel of the "Hybrid Drive" mode.  This simplistic analysis suggests that you want the ICE to charge the HVB and then when it is full, discharge the HVB with the ICE off.  The Hybrid Drive mode may, in fact, be less efficient.

Edited April 14, 2014 at 02:07 AM by larryh

[Russael]

You could try experimenting with coaxing the car into an EV mode while at speed... let off the gas, let it drop in to EV, and then resume your speed without exceeding the ICE threshold.  Requires a lot of effort and finesse, but that'd be away to see if cycling the ICE is better than just letting it float the HVB.

[Hybridbear]

I looked at today's data to see what was happening in "Hybrid Drive" vs "Charging HV Battery".  This is traveling at 66 mph on the freeway.   I observed the following data in each of the modes:

 

"Hybrid Drive"

Avg. Fuel flow:  0.0276 gal/min

Power to HVB: 2.56 kW

ICE output power:  19.9 kW

Power to Wheels:  16.1 kW

 

"Charging HV Battery"

Avg. Fuel flow:  0.0414 gal/min

Power to HVB: 10.55 kW

ICE output power:  28.0 kW

Power to Wheels:  18.1 kW

 

Apparently, the freeway is not level.  It required more power to the wheels in the "Charging HV Battery" segment. 

 

It requires about 16.7 kW of power in EV mode to travel this same speed.  Assuming 90% of the energy stored in the battery can be retrieved, that means for the different modes, that the ICE generated enough power to power the car in EV mode the following percent of the time:

 

"Hybrid Drive"

0.9*2.56/16.7 = 14%

 

"Charging HV Battery"

0.9*10.55/16.7 = 57%

 

So the ICE could be off 14% of the time in "Hybrid Drive" mode vs. 57% of the time in "Charging HV Battery" mode.  So the effective fuel consumption in each mode is:

 

"Hybrid Drive"

(1-0.14)*.0276 = 0.024 gal/min

 

"Charging HV Battery"

(1-0.57)*.0414 = 0.018 gal/min

 

The "Charging HV Battery" mode uses 75% of the fuel of the "Hybrid Drive" mode.  This simplistic analysis suggests that you want the ICE to charge the HVB and then when it is full, discharge the HVB with the ICE off.  The Hybrid Drive mode may, in fact, be less efficient.

This is my theory as well based on observation. Before the PCM update to the hybrids, the ICE never shut off above 62 MPH. This meant that at 65 MPH you would spend most of the time with the ICE not charging the HVB, but just powering the wheels through one path or another. After the PCM update the ICE will turn off at higher speeds which has increased highway MPGs.

 

This is also my theory as to why the Energi is less efficient than the hybrid. I've observed in my parents' C-Max Energi that it rarely uses the ICE to charge the HVB when in hybrid mode. This leads to lower overall fuel economy and less miles in EV mode.

 

You could try experimenting with coaxing the car into an EV mode while at speed... let off the gas, let it drop in to EV, and then resume your speed without exceeding the ICE threshold.  Requires a lot of effort and finesse, but that'd be away to see if cycling the ICE is better than just letting it float the HVB.

Pulse & glide is a great way to show this too. I can get better MPGs pulsing from 65-60 MPH than I can with the cruise set at 60 MPH and I can also get to my destination more quickly. Cruise control on the freeway won't shut the ICE off very much which leads to lower fuel economy.

[larryh]

I looked at today's data to see what was happening in "Hybrid Drive" vs "Charging HV Battery".  This is traveling at 66 mph on the freeway.   I observed the following data in each of the modes:

 

"Hybrid Drive"

Avg. Fuel flow:  0.0276 gal/min

Power to HVB: 2.56 kW

ICE output power:  19.9 kW

Power to Wheels:  16.1 kW

 

"Charging HV Battery"

Avg. Fuel flow:  0.0414 gal/min

Power to HVB: 10.55 kW

ICE output power:  28.0 kW

Power to Wheels:  18.1 kW

 

Apparently, the freeway is not level.  It required more power to the wheels in the "Charging HV Battery" segment. 

 

It requires about 16.7 kW of power in EV mode to travel this same speed.  Assuming 90% of the energy stored in the battery can be retrieved, that means for the different modes, that the ICE generated enough power to power the car in EV mode the following percent of the time:

 

"Hybrid Drive"

0.9*2.56/16.7 = 14%

 

"Charging HV Battery"

0.9*10.55/16.7 = 57%

 

So the ICE could be off 14% of the time in "Hybrid Drive" mode vs. 57% of the time in "Charging HV Battery" mode.  So the effective fuel consumption in each mode is:

 

"Hybrid Drive"

(1-0.14)*.0276 = 0.024 gal/min

 

"Charging HV Battery"

(1-0.57)*.0414 = 0.018 gal/min

 

The "Charging HV Battery" mode uses 75% of the fuel of the "Hybrid Drive" mode.  This simplistic analysis suggests that you want the ICE to charge the HVB and then when it is full, discharge the HVB with the ICE off.  The Hybrid Drive mode may, in fact, be less efficient.

Sorry, but my math is incorrect here.  The "Hybrid Drive" mode is more efficient than the "Charging HV Battery Mode".  The correct computation is as follows:

 

In the "Hybrid Drive" mode, rather than going 1 minute using 0.0276 gallons of gas, you can can now go 1.14 minutes (14% longer) on the same amount of gas.  After you have gone for one minute, you now have stored enough energy in the HVB to go another 14%*1 minutes = 0.14 minutes in EV mode.  Similarly, in "Charging HV Battery" mode, rather than going 1 minute using 0.414 gallons of gas, you can now go 1.57 minutes (57% longer) on the same amount of gas.  So, the effective gas consumption rate is:

 

"Hybrid Drive"

0.0276/1.14 = 0.0242 gallons/min

 

"Charging HV Battery"

0.0414/1.57 = 0.0264 gallons/min

 

"Hybrid Drive" is more efficient. 

 

If I look at the instantaneous gas mileage in "Hybrid Drive" going 66 mph, I see 38.8 MPG.  But it is also generating power that is stored in the HVB that can be used to later power the car in EV mode.  Taking that into account, the effective MPGe is actually 44.4 MPGe. 

 

Similarly, if I look at the instantaneous gas mileage in "Charging HV Battery" mode going 66 mph, I see 26.7 MPG.  The effective MPGe is actually 41.7 MPGe.

 

The instantaneous MPG displayed on the car's console can be deceiving.  The ICE may be generating power being stored in the HVB which can be used later in EV mode.   You may see 26.7 MPG, but you are really effectively getting 41.7 MPGe. 

Edited April 16, 2014 at 01:48 PM by larryh