Efficient EV Mode Driving Techniques

[larryh]

This plot is similar to the plots in the previous two posts, except this time I am going up the hills.  The car starts at the right at distance 1.72 miles and travels to the left at distance 0.0 miles.  This time the excess energy loss is slightly greater--the motor had to provide additional energy to climb the hills and motor efficiency is not 100%.  The final Excess Energy Loss when going up the hills is 0.044 kWh vs. 0.039 kWh when going down the hills. 

 

As before, there is a 21% energy loss providing the kinetic energy to get up to 45 mph.  However, the loss associated with providing the 0.22 kWh of potential energy appears to be minimal.  Accelerating is a significant source of energy loss.  Climbing hills is not.  Most of the extra energy consumed from the HVB by the motor to climb hills is converted to potential energy.   The motor is probably around 92+% efficient converting electrical energy to potential energy.   I'm not sure if that would be true for steeper hills or only moderate hills. 

 

You can lower the energy loss climbing hills by allowing the car to slow down as it goes up the hill, converting kinetic energy to potential energy (100% efficient).   

 

 

Edited October 26, 2014 at 12:44 AM by larryh

[rbort]

So from reading this the best way to climb a hill is:

 

a) disengage cruise and allow the car to slow from 35 for example to 25,

  or a1) use eco cruise which allows the car to slow from 35 to the low 30's and is that enough?

 

b) at the top of the hill, let the car speed back up on its own before re-engaging cruise while in D,

  or b) shift the car to N to speed up quicker with no regen before going back to D and re-enabling cruise.

 

Inquiring minds want to know!

 

-=>Raja.

[larryh]

If you are only going 30 mph, you don't have much kinetic energy to work with and slowing down/speeding up isn't going to help much.

 

Eco cruise does slow the car down some when going up a hill.  You can see that in post 77.  I used cruise control for the trip.  The kinetic energy fell (speed slowed) some from distance 1.6 to distance 1.35 miles.  But you can do even more by disengaging cruise control and letting up on the accelerator.  The more you slow down, the less the loss.

 

At the top of the hill, I would disengage cruise control and control regen via the accelerator.  See post 74.  Try to stop regen.   But don't press the accelerator too hard (the bar in the Empower screen goes above 0).  Shifting into neutral on a downgrade is illegal.  But you can achieve the same effect by controlling the accelerator so that the power into/from the HVB is 0.  You have a wider range of control if you shift into Low. 

Edited October 26, 2014 at 12:05 PM by larryh

[larryh]

As before, there is a 21% energy loss providing the kinetic energy to get up to 45 mph.  However, the loss associated with providing the 0.22 kWh of potential energy appears to be minimal.  Accelerating is a significant source of energy loss.  Climbing hills is not.  Most of the extra energy consumed from the HVB by the motor to climb hills is converted to potential energy.   The motor is probably around 92+% efficient converting electrical energy to potential energy.   I'm not sure if that would be true for steeper hills or only moderate hills. 

 

 

As I suspected, the energy loss associated with climbing a hill is dependent on the length and grade of the hill.  The hill in the previous post was only a relatively small hill.  The average grade was about 2% and the loss was minimal.  Doing the same analysis on a larger/steeper hill with average 4% grade, the loss was much more at 13%.  For a steep 8-9% grade hill, the loss was 12%.  So for a moderate or large hill, about 12-13% of the potential energy is lost. 

Edited October 26, 2014 at 05:13 PM by larryh

[rbort]

Ok so basically all you're saying there is accelerate back up to speed as slowly as possible with the gas pedal until you run out of hill or until the speed comes back then re-engage cruise at that point.  If lots of hill still remains, from previous tests we found that you need to use HA or L at that point to prevent the car from overspeeding as you will get better MPGe results over the same distance if you don't overspeed and lose more energy due to friction.

 

-=>Raja.

[larryh]

Yes--use the accelerator to accelerate, but try to make sure that you the blue indicator bar on the empower screen remains at or below 0 so you aren't using energy from the HVB.   When back up to speed, then reengage cruise control and Low, or grade assist.  The faster you go down the hill, the more energy you will lose.

Edited October 26, 2014 at 02:26 PM by larryh

[Hybridbear]

One situation I frequently encounter is approaching a stop sign at the top of a hill. What's the best way to approach this scenario?

Edited October 28, 2014 at 01:28 PM by Hybridbear

[larryh]

One situation I frequently encounter is approaching a stop sign at the top of a hill. What's the best way to approach this scenario?

 

I think the sooner you begin slowing down, the better, as long as you make it to the stop sign.  There appears to be three primary sources of energy loss:

 

1.  Friction from aerodynamic drag, tire rolling resistance, etc is the largest source of energy loss. 

2.  Acceleration is the second largest source of energy loss. 

3.  Finally, climbing hills is the last significant source of energy loss.

 

To minimize energy loss, you want to slow down as soon as possible and you want to minimize the energy required from the HVB to climb the hill.  It might be better to gradually reduce power well before the stop sign, slowing down more slowly, rather than maintaining full power to climb the hill and then let off on the accelerator and coast to the stop sign.  I would have to try it out. 

Edited October 28, 2014 at 11:38 PM by larryh

[larryh]

I analyzed a recent commute to work to determine the source of the energy losses during the trip.  The distance is 8 miles.  The electrical energy loss due to friction was 1.41 kWh.  An additional 0.26 kWh was lost when accelerating.  The total loss was 1.67 kWh.   This is essentially the amount of energy consumed from the HVB for the trip.  The actual amount was 1.57 kWh.  The destination is at a lower elevation which accounts for the 0.10 kWh difference. 

 

The amount of energy consumed for my commute is basically determined by the friction (mostly average speed and outside temperature) and the amount of acceleration (and maybe a little from climbing hills).  Very little else matters, provided I get good braking scores. 

 

To reduce the friction losses, I would have to drive slower.  To reduce the acceleration losses, I would have to maintain more constant speed throughout the trip, which is hard to do with stop lights.  Acceleration losses were 16% of the energy consumed from the HVB. 

 

As mentioned in the previous post, friction, acceleration, and climbing hills are the main things one needs to concentrate on to improve mileage.  That is where the majority of the energy losses are occurring. 

Edited October 29, 2014 at 12:29 AM by larryh

[rbort]

friction, acceleration, and climbing hills are the main things one needs to concentrate on to improve mileage

 

And thanks to your testing and data analysis, the answers are:

 

Friction: Take it slow

Acceleration:  Take a long time to do it

Climbing hills: Lose some speed on the way up

 

I'm banging 99 driving scores now one after the other with city driving :)

 

Hybridbear, my answer to your question would be get off the gas at the moment the car will roll to a stop at the stop sign without any braking because:

 

If you keep going and hit the brake, then you wasted too much energy and regen has losses you won't get it all back.

If you slow down too early, then you waste energy accelerating again to make it to the top of the hill.

 

Best scenario, that perfect timing where knowing from your speed and the incline angle when to coast to make it to the stop sign with no brake needed but to hold the car there from rolling back.

 

-=>Raja.

Edited October 29, 2014 at 04:03 AM by rbort

[Hybridbear]

Quite often what ends up happening is that I shift to neutral while going up the hill and then the car slows down too much and I have to shift back to drive and use the accelerator pedal to not stop too early.

[stevedebi]

That is pretty much what I do as well. Ease off the accelerator with the goal to be very near to stopped at the top of the hill. It is fun to watch the battery charging on an uphill...

 

I also vary my route so as to not encounter that particular hill unless I absolutely have to.

[larryh]

The following chart shows electrical energy loss when ascending a hill.  The red line is the potential energy, i.e. elevation profile of the hill.  The darker blue line is the kinetic energy of the car when using cruise control to maintain speed of 50 mph.  The lighter blue line is the kinetic energy of the car when I allowed the car to slow down as I ascending the hill by letting up on the accelerator.  Note there is a dip half way of the hill, so in both cases the car speeds up during the downgrade. 

 

The green line is the energy loss associated with ascending the hill using cruise control and the purple line is the energy loss when allowing the car to slow down going up the hill.  You can see the green line immediately begins to increase when starting to ascend.  The purple line remains steady, i.e. no loss, until well up the hill.  In this example, about 0.02 kWh less electrical energy was lost by not maintaining speed when ascending the hill, i.e. the loss was half as much.  Note that the lines do not start at 0 because they included acceleration losses prior to ascending the hill.

 

Edited October 29, 2014 at 10:16 PM by larryh

[larryh]

This plot shows the electrical energy consumed during my 8 mile commute to work.   The red line and darker blue line are the potential and kinetic energy, respectively.  The orange line shows the energy consumed from the HVB.  The light blue line is the total electrical energy loss.  The purple line is the energy loss from friction and the green line is the energy loss from acceleration and ascending hills.  The friction loss, purple line, is a function of speed.  The green line, acceleration/ascent losses, increases when I accelerate to increase speed (or climb hills) and levels off once I have reach cruising speed and during regenerative braking. 

 

The relationship between the lines is as follows:

 

HVB Energy = Kinetic Energy + Potential Energy + Total Energy Loss

Total Energy Loss = Friction Loss + Acceleration/Ascent Loss

 

The electrical energy loss due to friction at the end of the commute was 1.41 kWh.  An additional 0.26 kWh was lost when accelerating and ascending hills.  The total energy loss was 1.67 kWh.  See post 84.

 

Edited October 29, 2014 at 11:07 PM by larryh

[larryh]

Quite often what ends up happening is that I shift to neutral while going up the hill and then the car slows down too much and I have to shift back to drive and use the accelerator pedal to not stop too early.

I think the goal for stopping at the top of a hill is to avoid regen and convert the maximum amount of kinetic energy to potential energy. If you allow regen to occur, you would have been better off not using that energy to propel the car in the first place--it wasn't necessary. Let the hill do all the work slowing the car down. Otherwise, it should be similar to stopping on a level road.

Edited October 30, 2014 at 01:03 PM by larryh

[rbort]

I did pretty good yesterday, check out the photo below.  Drove to Cambridge during the day from home, 199 MPGe.  On the way back driving at night with headlights and vent got only 151 MPGe.  There is some loss there due to extra power needed at night as well as that dreaded hill most likely that I posted about 2 miles from home.

 

-=>Raja.

[Hybridbear]

I think the goal for stopping at the top of a hill is to avoid regen and convert the maximum amount of kinetic energy to potential energy. If you allow regen to occur, you would have been better off not using that energy to propel the car in the first place--it wasn't necessary. Let the hill do all the work slowing the car down. Otherwise, it should be similar to stopping on a level road.

Sounds good, that'll be my focus, shift to neutral and let the hill slow the car down and use as little regen as possible. This only works though if no one is behind me. In traffic people can get rather mad since most people like to race to red lights and brake at the last moment.

[Hybridbear]

I did pretty good yesterday, check out the photo below.  Drove to Cambridge during the day from home, 199 MPGe.  On the way back driving at night with headlights and vent got only 151 MPGe.  There is some loss there due to extra power needed at night as well as that dreaded hill most likely that I posted about 2 miles from home.

 

-=>Raja.

I don't see a pic, Raja.

[rbort]

Wouldn't let me add the picture here, says its limited to 500mb only too big to fit.  I posted it here:

 

http://fordcmaxenergiforum.com/topic/3261-im-getting-better/

 

Note that I never used N on this drive, only D, hill assist on shallow hills and L on steep ones to hold the car from going over 40mph.

 

My thing is that I don't want to go to the extra step to shift to N back and forth unless it means the difference between starting the engine or not.  If I have enough charge to get to a charger then I'm going to forget about that its not worth it for me with all this extra shifting stuff.  Just CC sit back, relax and enjoy the ride.  The savings you get from N are probably going to be very negligible.  

 

-=>Raja.

Edited October 30, 2014 at 02:52 PM by rbort

[stevedebi]

I think the goal for stopping at the top of a hill is to avoid regen and convert the maximum amount of kinetic energy to potential energy. If you allow regen to occur, you would have been better off not using that energy to propel the car in the first place--it wasn't necessary. Let the hill do all the work slowing the car down. Otherwise, it should be similar to stopping on a level road.

Raja, neutral is illegal here in CA, so I can't use that technique. While I understand what you mean, I should point out that you are storing kenetic energy in the battery during regen, just not as much, and that once at the top of the hill, you automatically have the potential energy represented by the higher elevation. I get your point that you are storing energy that you had to achieve by using the battery.

 

But around here and on the particular hill (that I usually avoid), I could not travel slow enough to make that work anyway - it would interfere with traffic.