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Running in 1st gear full time


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15 replies to this topic

#1 OFFLINE   homestead

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Posted 31 October 2018 - 09:21 PM

Was talking with a friend today who recently bought a Chevy Spark EV car.  He told me what a volt owner was doing with his car.  He puts it in 1st gear and runs with it that way all the time.  When he wants to stop or slow he just lets up on the accelerator and the car automatically goes into regen and slows down quickly.  He says it charges the battery quicker that way.  So my friend tried it and says it works great and makes it easier to drive since he hardly ever needs to step on the brake anymore.  I'm not ready to try this just yet with my c-max but am wondering if anyone has tried this and what the results were.  Wondering if this would strain the transmission running full speed in 1st gear.

 

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#2 OFFLINE   stolenmoment

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Posted 01 November 2018 - 09:44 AM

There's only one gear, so there's no extra strain.  What the Cmax does in L is to turn up the regen when you lift off the accelerator pedal, a purely electronic action.  I drive this way pretty much all the time; I only apply the brake pedal when I want to actually stop.  If I have to use it to stop sooner, I have planned badly.

 

This way, you're certain to not use the physical brakes inadvertently, which wastes juice.

 

It's really gratifying to do this decelerating off the highway and watch the "brakes" shove a couple percent charge into the battery!


Edited by stolenmoment, 01 November 2018 - 09:45 AM.


#3 OFFLINE   jdbob

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Posted 01 November 2018 - 03:20 PM

Yeah, the Volt is a similar setup to the C-Max. The gears never change. On the C-Max Ford calls it "L", on the Volt Chevy calls it "B".



#4 OFFLINE   Plus 3 Golfer

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Posted 01 November 2018 - 05:29 PM

Yes, you do put more charge in the HVB by shifting to Low but you stop in a significantly shorter distance than you would with Normal Regen Coasting (which is simulating normal engine braking), or shifting into Neutral.  So, if one uses LOW, one needs to account for the energy required to cover the difference in distance from Normal Regen Coasting or coasting in Neutral.  For example, I just ran some tests and recorded data with ForScan.  To keep it simple I ran the test from 24 mph to 10 mph results in the following covered distances.  Distances were computed by integating speed over time with ForScan data.  Of course, if  one can apply brakes to get 100% brake score in shortest distance, then the data should move towards Low Coasting.

 

Low Coasting = 95 feet

Normal Regen Coasting = 554 feet

Coasting in Neutral = 1155 feet

 

The estimated net energy stored based on integrating current flow in/out of HVB is:

 

Low Coasting = 11.4 Wh

Normal Regen Coasting = 7.8 Wh

 

If one assumes 250 Wh per mile, the 11.4 Wh of energy stored from Low Coasting would be equivalent to about 241 feet of EV.  The 7.8 kWh would be equivalent to about 164 feet of EV.   So, Low Coasting comes up short by 382 feet total compared to Normal Regen Coasting (164+554) - (241+95) = 382 feet.  Extra energy is needed to cover the 382 feet.  At 250 Wh per miles, 382 feet requires about 18 Wh of energy. 

 

Bottom line: Regeneration is not as efficient as most think it is.  It's much better to coast in neutral or with normal regen and allow as much kinetic energy to move the car rather than be converted to electrical energy.  Use the kinetic energy of the moving vehicle to the fullest extent before applying the brakes to stop (more regen or friction braking).  The downside of such is one's time (the reason I don't coast in Neutral).  I do coast in Drive when timing lights.  I see no benefit to use Low to increase regen other than to shorten travel time. :)


Edited by Plus 3 Golfer, 01 November 2018 - 07:40 PM.


#5 OFFLINE   fbov

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Posted 01 November 2018 - 10:15 PM

Attached File  Energy Flow Diagram.jpg   88.71KB   0 downloads

This bears repeating... You can only lose energy. The trick is losing as little as you can.  

 

The ICE is the least efficient link, but a necessary one. Run at low RPM at high load to minimize losses. 

Regen braking suffers from dual losses; between the charging, storage, conversion and EV inefficiencies, you lose 20%. 

Climbing a hill has no energy losses, beyond those due to aero and rolling resistances that are present in all cases. 

Continuing to roll (as in Neutral) also has no losses, beyond aero/rolling. 

 

It seems to me that running in L eliminates that last option, which I find to be very efficient. It optimizes regen, but that uses the 20% loss path more often than necessary. I see the appeal of this "hydro-static" transmission mode, just not an advantage.  

 

Have fun,

Frank



#6 OFFLINE   cr08

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Posted 02 November 2018 - 06:16 AM

The problem is how often do you have the convenience of coasting to a stop for almost a full 1000ft? I imagine most people don't and will have to stop much sooner than that especially with other traffic following. And to reduce irritation to other drivers, keeping that stopping distance within reasonable limits. Additionally most who advocate for using 'L' or the equivalent mode in other EV's know to modulate the accelerator to essentially let it coast with no regen or acceleration so it isn't like it is totally out of the question.

 

Overall not arguing about efficiencies but what is doable in the real world. 'No-loss' coasting is not off the table when using 'L' but then it also allows for maximum energy recovery when coming to a full stop in a more reasonable amount of time. Win-win.

 

(FWIW I hardly ever use L and stick to the old school method with my Energi. I've gotten very good at constantly getting 99-100% braking score. Though I do fully see the appeal of using the L gear. I will usually use it if I am taking a highway offramp and need a quick decel.)


Edited by cr08, 02 November 2018 - 06:17 AM.


#7 OFFLINE   SnowStorm

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Posted 02 November 2018 - 08:18 AM

Does using 'L' ever cause the ICE to spin up for breaking purposes?  I hardly ever use it - I think it does but not sure.  Spinning the ICE is definitely an energy waster.  At times I don't use the down hill button because it will spin the ICE - better to just use the brakes.  (Of course there are times when that button works well.)  In normal driving I've often wished there was no regen when your foot is off the accelerator.  Most of the time your foot isn't off the accelerator because your stopping but for changing road and traffic conditions which can usually be predicted.  What would really be nice is steering wheel paddles that you squeeze to control regen.  Squeeze harder for more regen up to maximum without ever spinning the ICE or applying friction brakes.  It would be super easy to get 100% score every time!



#8 OFFLINE   cr08

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Posted 02 November 2018 - 08:44 AM

It will spin up the ICE if the HVB is full. However if the engine is already warmed up it is not going to be using any gas but simply acting as an air pump at that stage. If the engine hasn't warmed up, it is going to run its warmup cycle first before it can run fuel-less engine braking. However for you guys with hybrids the chance of being in that mode is considerably minimal. For us Energi owners this has come up once or twice especially those taking off with a fully charged battery and a cold engine straight away in L mode. In that case it is better to run in D for a little bit first to drain off a bit of the battery before going into L. Or if intending to use the ICE, make sure it gets warmed up first.



#9 OFFLINE   jdbob

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Posted 02 November 2018 - 12:21 PM

The engine running situation is something I actively have to deal with every time I go down from my house into town (about 600 foot drop in 4 miles). I prefer to drive in "L" down the winding hill but keep an eye on the battery percentage and if it gets to 100% I switch back into "D" for the rest of the downhill. Just one of those annoyances that Ford will never fix. 


Edited by jdbob, 02 November 2018 - 12:23 PM.


#10 OFFLINE   fbov

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Posted 02 November 2018 - 11:56 PM

The engine running situation is something I actively have to deal with every time I go down from my house into town (about 600 foot drop in 4 miles)....

Sounds like a job for "grade assist." Use the button on the side of the gear shift. 

Frank


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#11 OFFLINE   jdbob

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Posted 03 November 2018 - 01:15 PM

Sounds like a job for "grade assist." Use the button on the side of the gear shift. 

Frank

 

Grade assist works find on grades that are at a consistent angle. The trip down has steep sections interspersed with near level sections, it doesn't work too well. Using grade assist will also trigger the engine running if you fill the battery.



#12 OFFLINE   raadsel

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Posted 03 November 2018 - 01:30 PM

Grade assist works find on grades that are at a consistent angle. The trip down has steep sections interspersed with near level sections, it doesn't work too well. Using grade assist will also trigger the engine running if you fill the battery.

 

I don't see the issue with starting the battery if the battery fills -- the engine isn't using any gasoline, it is merely being used as a "brake." Grade assist works quite well, it seems to do a good job of holding your speed without needing to use the physical brakes (causing wear and tear) -- even if for your drive you'll need to turn it on and off a couple of times. The only issue that I can think of is if the area you are driving have noise restrictions and prohibit the use of engine braking.


Edited by raadsel, 03 November 2018 - 01:31 PM.


#13 OFFLINE   jdbob

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Posted 03 November 2018 - 02:56 PM

I don't see the issue with starting the battery if the battery fills -- the engine isn't using any gasoline, it is merely being used as a "brake." Grade assist works quite well, it seems to do a good job of holding your speed without needing to use the physical brakes (causing wear and tear) -- even if for your drive you'll need to turn it on and off a couple of times. The only issue that I can think of is if the area you are driving have noise restrictions and prohibit the use of engine braking.

 

That's not what actually happens. If the engine is cold (which mine always is, because this is the 1st trip of the day), then it does actually run the engine until it heats up. This might be related to the engine not having run for some period of days, I don't know. On mine I usually go for a couple of months without running the engine and then force it to run to stir up the fluids.



#14 OFFLINE   Plus 3 Golfer

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Posted 03 November 2018 - 04:06 PM

Does using 'L' ever cause the ICE to spin up for breaking purposes?  I hardly ever use it - I think it does but not sure.  Spinning the ICE is definitely an energy waster.  At times I don't use the down hill button because it will spin the ICE - better to just use the brakes.  (Of course there are times when that button works well.)  In normal driving I've often wished there was no regen when your foot is off the accelerator.  Most of the time your foot isn't off the accelerator because your stopping but for changing road and traffic conditions which can usually be predicted.  What would really be nice is steering wheel paddles that you squeeze to control regen.  Squeeze harder for more regen up to maximum without ever spinning the ICE or applying friction brakes.  It would be super easy to get 100% score every time!

Yes, when shifting to L whether the engine is hot or cold, ICE spins in the Hybrid.  My guess is the Energi is the same.  The quickest way to find out is to put the tach up in MY VIEW and watch what happens when one shifts to L.  Could someone with an Energi see what happens in all modes when shifting to L?  I'll put up a graph of ForScan data showing this in another post.

 

As far as the grade assist, the algorithm uses regen first (assuming HVB has room) then engine braking to control speed.  It doesn't take much of a steeper down hill to fill the Hybrid HVB.  As long as one is not going very fast down the steeper hill, engine braking usually will control speed extremely well.  I have gone down some steeper grades at 65 - 70 mph where engine braking wasn't sufficent to control speed and had to use friction brakes.  


Edited by Plus 3 Golfer, 03 November 2018 - 04:09 PM.


#15 OFFLINE   cr08

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Posted 03 November 2018 - 05:39 PM

So to clarify between the hybrid and Energi is the situation is the same. If the battery is full on either one in L it'll spin up the engine to brake the vehicle. Obviously with the Energi you have a lot more room in the battery to work with.

 

The other bit that jdbob somewhat alluded to is if the engine is cold and needs to enter the cold start warm up mode, it will do in L, burning gas in the process. Once it is warmed and can run normally it'll spin but burn no gas. Hybrids theoretically should never have this issue or run into it very little. Those of us with Energi's will have a higher chance of experiencing this with ICE runtime being much less depending on the scenario.



#16 OFFLINE   Plus 3 Golfer

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Posted 03 November 2018 - 06:58 PM

Here's a graph from recorded ForScan data on our short trip to dine out.  Note when in LOW, ICE is ON (spinning) when coasting until speed drops to about 12 mph (around 45 seconds) where it shuts OFF.and RPM drops down to zero.  Also, note that when I shifted to Neutral at 47 mph (around 65 seconds), ICE shut OFF and RPM droped to zero very quickly.  However, when speed was 50 mph (around 237 seconds) and I shifted to Neutral, ICE RPM dropped from about 2500 to 1500 rpm and then gradually declined to about 900 rpm and 9 mph before ICE shut OFF.

 

Attached File  Low.JPG   94.28KB   0 downloads


Edited by Plus 3 Golfer, 03 November 2018 - 09:39 PM.







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