Driving in L

[Tree63]

Friend and I shared driving on a 15 hour trip recently.  When she took over on one switch at a gas fill up, I went to sleep.  A couple of hours later when I woke up, happened to see that fuel efficiency was down quite a bit --- and that she had been driving expressway speed in ... oops ... L not D gear!  

 

Temp and noise levels were both ok and manual says we can switch to (and stay in?) L at any speed ... so some immediate relief was had by all. And C-Max returned to normal fuel efficiency for hwy and matched city FE just fine when back home.

 

Any suggestions on things to keep an eye on?  I am guessing an earlier tranny fluid change may be worthwhile. 

 

PS - Thank goodness for Trip meters - reset Trip1 after the fill-up and that's where I first noticed something was off.  Otherwise there was no whiny noise as with usual trannies.

 

 

 

 

[JAZ]

I've carelessly been in Low a couple of times, but the engine noise when accelerating promptly told me I wasn't in Drive.

[RachelnLa]

Sorry, but after reading this post I know keep singing... apple bottom jeans, boots with the fur, the whole club was looking at her.. shorty got LOW LOW LOW LOW......

 

I think I need to put some more music on my jump drive LOL

[Laurel]

We had one episode of my husband driving our C-Max in low for about a mile, but immediately he was questioning that something was wrong with the car due to the engine noise being so loud.  He then noticed that he was in low gear.  Another reason for them to have lighted indicators for the gears on the console.  I'm not sure how I would handle this situation with the dealership i.e. if something goes wrong due to the high rpm's will the warranty still cover you?  Maybe our warranties cover us even when we do something like this and problems come up as a result--does anyone know the answer?

[ArizonaEnergi]

Unless the Hybrid L is different from the Energi, the only difference in L vs D is the amount of regeneration while decelerating. A thread on this is here, with a general conclusion that at steady speeds it is less efficiency as coasting gives better MPG than regen.: http://fordcmaxenergiforum.com/topic/748-low-gear-regen-ive-heard-its-more-aggressive-but-how-much-any-links-and-my-experience/

Edited May 19, 2013 by ArizonaEnergi

[Laurel]

Our car in low sounded VERY loud, and I immediately said "something is wrong with the car".  So one has to think that L and D are very different gear ratios even in a hybrid.
 

[armoredsaint]

I prefer driving backwards, it saves gas 

[Jus-A-CMax]

I prefer driving backwards, it saves gas 

I prefer gas, it saves driving backwards

[homestead]

I think you just figured out the accelerated breakin procedure.  In the 1960's my dad worked at

a Dodge dealership in AZ and when someone would bring back their new car that was burning oil because

the owner had been babying the car,  he would take the car on the hiway and put it in low gear and go as fast

he dared go until the rings would seat in the cylinders.

[viajero]

Our car in low sounded VERY loud, and I immediately said "something is wrong with the car".  So one has to think that L and D are very different gear ratios even in a hybrid.

 

There are no changeable gear ratios in a C-Max.  In theory, shifting to L has no effect while accelerating or driving at a constant speed.  It only increases the regenerative braking when you let off the gas.  I drive in L almost all the time with the same "fuel" economy as D.  It gives me more precise control of my speed.

 

The reason I do it ALMOST all the time is because there's a strange quirk in the Energi where if you start out in L with a full battery the engine will turn on and rev up like you're stomping on the gas.  It can be kind of scary.  Once you've burned just a little bit of charge, it doesn't happen any more.  I and some other people on the Energi forum have experienced this.

 

Since all the discussion I've seen was on the Energi forum, I'm not sure what might set off this issue in a non-Energi C-Max.  But it sounds like you're experiencing some variation of this theme.

[Laurel]

Viajero when in L by accident it sounded like an engine rev'ing very high and loud.  So not sure what that is about.  Next time we take the car out, we will drive it in L for awhile and see what happens.  I'll let you know the outcome.  It was so loud that we both though we had a big problem.

[plus 3 golfer]

There are no changeable gear ratios in a C-Max.  In theory, shifting to L has no effect while accelerating or driving at a constant speed.  It only increases the regenerative braking when you let off the gas.  I drive in L almost all the time with the same "fuel" economy as D.  It gives me more precise control of my speed.

 

The reason I do it ALMOST all the time is because there's a strange quirk in the Energi where if you start out in L with a full battery the engine will turn on and rev up like you're stomping on the gas.  It can be kind of scary.  Once you've burned just a little bit of charge, it doesn't happen any more.  I and some other people on the Energi forum have experienced this.

 

Since all the discussion I've seen was on the Energi forum, I'm not sure what might set off this issue in a non-Energi C-Max.  But it sounds like you're experiencing some variation of this theme.

This couldn't be further from the truth with the Hybrid (can't speak to the Energi).  If the engine is on, the rpm increase significantly if one shifts to L.  If you continue to drive in L, the rpm remains higher than in D.   If the engine is not running and one shifts to L, the transmission engages the engine and rpm goes from zero to XXXX depending on speed.  L is for "engine braking" not "regenerative braking". 

 

Also, CVT transmissions can be held in fixed set point gear ratios which in effect changes the gear ratio.  Many CVT transmissions employ this with "manual shift mode".  This is what is happening when on shifts to L in the Hybrid.

 

The workshop manual shows no difference for L  for the Hybrid or Energi:

 

 

 Low

The range selector LOW position provides:

• engine braking.

• improved traction on slippery roads.

 

I suggest you set up MyView to rpm and watch and listen to the engine to see if rpm increases when you shift to L in your Energi.  

[plus 3 golfer]

Unless the Hybrid L is different from the Energi, the only difference in L vs D is the amount of regeneration while decelerating. A thread on this is here, with a general conclusion that at steady speeds it is less efficiency as coasting gives better MPG than regen.: http://fordcmaxenergiforum.com/topic/748-low-gear-regen-ive-heard-its-more-aggressive-but-how-much-any-links-and-my-experience/

I perused this thread and don't buy L increases regeneration while decelerating.

 

The engine remains engaged in L when decelerating and thus uses kinetic energy that would otherwise be available for regeneration. So, how can one get more regeneration energy when in L then in D when the engine is not spinning and disconnected from the driveline when decelerating. There is less energy available to be regenerated using low when decelerating. To me it's physics.

[viajero]

Ford's documentation (owner's manual and marketing brochures) can be kind of confusing if you're trying to understand the workings of the C-Max.  They use terms like "CVT" and "engine braking"  because many people are familiar with those ideas, and the C-Max often behaves as if it has a CVT or does engine braking.  But, there is no CVT in the traditional sense, and the ICE is never "engaged" or "disengaged".  There's one planetary gearset, and a second, smaller electric motor to take up the difference in rpm between the ICE and the wheels.

 

This thread on the Energi forum has links to three sites which are very helpful in understanding how the whole thing works.  Y'all can check these out while I go do some driving experiments...

 

http://fordcmaxenergiforum.com/topic/531-powersplit-ecvt-hybrid-transmission-video/

[plus 3 golfer]

I completely understand how the transmission works. Engaged = spinning, disengaged = not spinning. CVT=eCVT. The fact is the engine is spinning when in low. So, how does the spinning engine increase regeneration when decelerating?

Edited May 21, 2013 by Plus 3 Golfer

[viajero]

OK, you made me question my own memory for a bit, so I went for a drive around the neighborhood.  I'll have to believe you on how the hybrid behaves, since I don't have one to experiment with, but here's how the Energi behaves:

 

When the ICE is running, and my foot is on the gas, shifting from D to L or vice versa does absolutely nothing.  The engine rpm stays exactly the same, according to the tach and to my hearing.

 

When I let my foot off the gas, the engine goes silent and the tach goes to zero rpm.  Shifting between D and L makes the regen weaker or stronger.  It's a pronounced effect and very easy to feel the difference.  But in either D or L, the engine is not turning at all when my foot is not on the gas pedal.

[viajero]

I completely understand how the transmission works. Engaged = spinning, disengaged = not spinning. CVT=eCVT. The fact is the engine is spinning when in low. So, how does the spinning engine increase regeneration when decelerating?

 

The engine is not always spinning while in low, at least not while decelerating.  Go to the power split animation and play with the sliders.  You can set the ICE to zero rpm and the MG2 to something other than zero.   In this case the power electronics turn on switches allowing current to flow from the electric motor/generators to the battery charger, which creates a reverse torque on the motor/generators, slowing the car down.  It feels like engine braking, walks like engine braking, and quacks like engine braking, but it's not engine braking.  It's regeneration.

 

The C-Max's eCVT is not equal to a CVT.  In a traditional CVT, there is a belt or chain that slides along cone-shaped gears to change the ratio of engine rpm to wheel rpm.  In a C-Max, the MG2 is connected directly to the differential to create a single-speed electric car, and the MG1 allows the ICE rpm to vary relative to the wheel rpm, mimicing the effect of a CVT.  There are no clutches or bands, no engaging or disengaging.  All the gears are always meshed, all the time.  The magic of the system is the computer, which feeds electricity into or out of MG1 and MG2 as necessary to keep everything turning smoothly at the proper rpm.

 

It took me a while to get my mind around this.  It made my brain hurt at first.  It is very different from how any traditional automotive drivetrain works.  Play with the sliders on the animation, play with your car on the road, sleep on it, and repeat.  The system is really very simple and elegant once you come to appreciate it.

 

Of course, for most car buyers this information would probably either bore them to tears or scare them away, so the manual just says "CVT" and "engine braking" because it feels exactly like those things when you're driving.

Edited May 21, 2013 by viajero

[viajero]

I did read somewhere, but can't find it now, that if your battery is full and can take no more charge, or you're going down a really steep hill and the regen would produce power faster than the battery could take it, then if you're in L the computer will move the MG1 to make the ICE start turning and you'll get real compression braking from the engine.

 

I suspect that the computer (rightly or wrongly) thinks this might be about to happen when driving in L with an almost full battery, causing the engine to rev wildly, like Laurel and I and others on the Energi forum have observed.  I'm just speculating here - there may be a different reason, and maybe even two different reasons between the hybrid and the Energi.  They may never tell us the root cause, but I know the workaround for the Energi.  Maybe the hybrid is different...

[plus 3 golfer]

That's hard to believe there is a difference in operation. I would much prefer the Energi operation. With the hybrid there's a considerable braking effect when shifting to L - the engine rpm almost doubles.

 

Others in thie thread have validated the increase in engine speed when in L and lower FE in L than D. I wonder why the difference in the use of L between the models.

[ArizonaEnergi]

I suspect the high reving ICE in the Hybrid is due to the fact there's little or no regeneration to be done, so the excess revolutions must be borne by the ICE, rather than the electric motor/generator. In the Energi the battery can take the charging so the silent motor/generator does the spinning and regeneration.

 

How does that sound?

[viajero]

I suspect the high reving ICE in the Hybrid is due to the fact there's little or no regeneration to be done, so the excess revolutions must be borne by the ICE, rather than the electric motor/generator. In the Energi the battery can take the charging so the silent motor/generator does the spinning and regeneration.

 

How does that sound?

 

That sounds believable to me.  The hybrid and Energi have different kinds of batteries, and supposedly a different final drive ratio.  It seems like either of those could affect the computer's decision of when to use regen vs. engine braking.

 

http://www.sae.org/mags/aei/11705

 

Oh, well, it's late and it's a school night.  Maybe I'll ponder this more tomorrow.

[plus 3 golfer]

In normal Hybrid driving there's generally enough HVB available storage capacity for regeneration most of the time even when slowing from say 70 mph to zero. So, L_Energi operation would make sense.  But, if one was going down a long steeper grade (which is generally why one uses engine braking), then it would make little sense to use L_Energi operation in the Hybrid since one would quickly fill the battery and have to use brake regeneration.  Now in the Energi, it makes a lot of sense to use L_Energi operation before the brakes to simulate engine braking regeneration since there will likely be significant HVB available storage capacity in the Energi.  

 

Every time I've downshifted to L, engine rpm has always increased irrespective of the battery level although I don't recall the level being say below 25% or so.  It would not surprise me if the Hybrid is "fixed" to engine braking only.  While I'll bet the default for the Energi would likely be increased regeneration when shifting to L and perhaps if the HVB was near full, it would switch to engine braking.

 

viajero, you can switch to EV later mode with a full battery and see what happens when you shift to L.

Edited May 21, 2013 by Plus 3 Golfer

[fotomoto]

We need someone with a scan gauge to monitor fuel flow while in L going down a steep grade.  I know in the Prius it would shut off the injectors so the ICE becomes a simple air pump/brake.

 

As an aside, the volt does something similar but with its much larger battery also adds very aggressive regen in L till the battery is topped off.  A volt forum owner traveling down Pikes Peak said there is a stopping point coming down the mountain where park rangers measure front brake temps with a infrared gun to warn those who may be overheating.  The ranger said his volt had the lowest temp he'd ever recorded.  

Edited May 21, 2013 by fotomoto

[plus 3 golfer]

I can't think of a reason for Ford to fuel the engine if no additional engine torque is required when in L even though the engine is spinning.

 

I believe you can look at fuel data in Engineering Test Mode and see Trip A and B fuel consumption to 2 decimal points in liters. Also, there is other fuel data displayed in counts? that continually changes when driving.  So, one likely doesn't need a scan gauge to see fuel change.  

 

I'd test but there's no steep hill around that's long enough for me to make sure of the ETM readings.  I could also record data on my laptop such as fuel, battery charge level, rpm but again I'd like a longer steep hill to test.  The nearest suitable hill is about 15 miles away and I very rarely travel in that direction.

Edited May 21, 2013 by Plus 3 Golfer

[viajero]

viajero, you can switch to EV later mode with a full battery and see what happens when you shift to L.

 

I tried this and it did the same thing it does in L in EV Auto mode with a full charge.  The engine started, the car bucked and lurched, and then the engine revved like a kid showing off before a stoplight drag race.  I shifted back to D right away.

 

This happens not while decelerating, but while gradually rolling away from the charger in a parking garage.  I suppose the designers of this car just didn't think anyone would drive in L all the time and they never planned for or tested this case.  The control firmware doesn't handle it gracefully.

 

So, I'll stick with my habit of driving in D the first quarter mile and then shifting to L.  At least now I know not to tell anyone with a non-Energi to drive in L, since I would have assumed it behaved the same.