Coasting in Neutral

[NorfolkOracle]

On downhills I notice that I generate more than I consume but in neutral the net should be zero or negative if you consider the energy required to get the car moving to a reasonable speed, A/C use, etc.. Coasting beyond the hill could be a different story.

The OP simply needs to learn how to drive the car which means unconventional practices such as using the accelerator even when going down hill.

But if you used no power, is that more beneficial than using some or getting some back with regen.

 

[NorfolkOracle]

If someone who uses the same route regularly could try and work out coasting points, or coasting as best you can, over a certain period and report back that would be great, it is surprising when you start doing it and figure out how much of your journey you don't need to use any power at all, maybe better in urban setting or with short legs between waypoints, but a road about half a mile long you only need power for about 25% of it and momentum and coasting does the rest, you will also find there are times with normal driving when you would still be accelerating that you could of stopped using power way before then.

 

[mswlogo]

Good thread. In the long run Tesla could optimize how the car runs over the terrain.

 

[derotam]

Yeah, TACC can do this now to a point but it isn't all that efficient...There are a few scenarios for coasting that have different "fixes".

1. Normal driving, on TACC - The software could be programmed to i'll call it "half rubber-band". When on TACC and car in front starts to slow down, Tesla could just start coasting in the gap a bit before applying regen/braking. Obviously some slop has to be added into the TACC distance setpoint but that could easily be done.

2. Going down a hill and then back up - Here, just like the "how much do you want to speed" setting, there could be a user setting for how much over the speed set point do you want to allow the car to go during regen caused by a hill. Then on the uphill part, the car should only add power to maintain the TACC speed set point.

I do #2 every day to and from work. Goign downhill I let the car coast up to a certain speed and then I let that extra speed bleed off on the uphill.

Now the fun one would be having the car bleed off as much speed as it can going up over the crest of a hill so that it can regain it back on the downhill. This unfortunately would require, 1- Making sure there is no traffic behind you that you would piss off. and 2-Having elevation knowledge for the route. They could make this part of a "hypermiling" mode!

 

[DopeGhoti]

It is true that freewheeling as much as possible is the most efficient. This is because of physics.

If you regen-brake, you are converting kinetic energy into heat and more charge in the battery. Some energy in this conversion will be lost as heat, because entropy.
If you actually-brake, you are converting kinetic energy into heat and, sometimes, sound. All of this energy is lost.

When you accelerate, you are converting battery charge into sound, heat, and kinetic energy.

Any time you convert energy from one medium to another, there are losses to heat. The most efficient means is to convert energy as infrequently as possible. The Neutral gear does this.

In hybrids, like a Prius, you can also freewheel without switching to Neutral by feathering the accelerator pedal so as to neither regen, nor accelerate. The same can be done with a Tesla; it's just harder to do so (if you're in standard regen mode) because the response curve on the pedal is so much steeper. That said, folks do this somewhat frequently (see the "rolling forward in Reverse!" threads).

 

[67King]

I don't have a tomtom, tomtom have used my concept that I have the patent for in the UK, France and Germany, we had to give up with the USA as the patent office kept saying my idea was similar to others, which when you looked at them were totally different, but arguing cost about $12,000.
Yes you may burn more fuel idling than in gear, but is that the same for any distance, 100 metres or less maybe in gear, half a mile, a mile in neutral and idling?
It is illegal to coast in neutral in some states, but isn't in most countries in Europe.

It doesn't matter, your engine is motoring from teh couple through the drivetrain, until you get to the point at which the torque conveter unlocks, which is basically going to be idle speed.

 

[Søren Jessen]

Modern cars utilize a technology called "Decel Fuel Shot-off," or DFSO for short. When you are in gear and coasting, the engine is motoring (via drivetrain to street), but no fuel is being burned. If you are in neutral, then fuel is being burned to keep the engine running since it is decoupled. So you will burn LESS fuel keeping it in gear than in neutral.

And you can't compare an ICE powered car to en electric when it comes to this. So if your tomtom is set up for that, then ignore it.

Speke is idea you’ve got.

However, although you will burn less fuel while coasting in gear you will also break the car faster and therefore have to accelerate earlier again to get to or keep the speed you want. Coasting in gear looses energy in the form of friction in the engine. In an electric car the regeneration only recovers roughly half of the energy harvested. An electric car would preserve more energy (=speed) by being in neutral.

Coasting in neutral or by pressing the clutch when such exists will preserve speed for long time. In a petrol car this will make the engine use only the fuel needed to run at idle. In an electric car, which has very low engine friction, the loss of energy during coasting in neutral would be really small = optimal for miling.

What electrical cars need is: 1: regenerative breaking only when you press the break, and 2: a “pseudo-neutral” function when you do not press the accelerator.

 

[G78M3]

Worse than you having no control, the bigger problem is that while in Neutral, the car does not have control. This means none of the active safety features that could save your life will be able to do anything when the unexpected happens.

It is dangerous to shift into neutral when cruising the highway. You have no contol over your throttle in case something happens.

 

[derotam]

Speke is idea you’ve got.

However, although you will burn less fuel while coasting in gear you will also break the car faster and therefore have to accelerate earlier again to get to or keep the speed you want. Coasting in gear looses energy in the form of friction in the engine. In an electric car the regeneration only recovers roughly half of the energy harvested. An electric car would preserve more energy (=speed) by being in neutral.

Coasting in neutral or by pressing the clutch when such exists will preserve speed for long time. In a petrol car this will make the engine use only the fuel needed to run at idle. In an electric car, which has very low engine friction, the loss of energy during coasting in neutral would be really small = optimal for miling.

What electrical cars need is: 1: regenerative breaking only when you press the break, and 2: a “pseudo-neutral” function when you do not press the accelerator.

Tesla's regeneration efficiency is a lot better than 50%, more like at least 85%. If you modulate the accelerator in a Tesla to where the power bar is not showing anything on the left or right of center then you are, for the most part, fully coasting just as if you were in Neutral. Doing this will also allow you to react to a dynamic driving environment faster than having to get back into gear first.

Coasting in Neutral is illegal in a lot of the U.S. for safety reasons.

 

[Søren Jessen]

Tesla's regeneration efficiency is a lot better than 50%, more like at least 85%. If you modulate the accelerator in a Tesla to where the power bar is not showing anything on the left or right of center then you are, for the most part, fully coasting just as if you were in Neutral. Doing this will also allow you to react to a dynamic driving environment faster than having to get back into gear first.

Coasting in Neutral is illegal in a lot of the U.S. for safety reasons.

I don’t mean to say that you should use the current neutral functionality. Rather I propose a new functionally should be developed.

I’m not so sure with the feathering approach of keeping the bars at zero: let’s assume a situation where the car would be able to run downhill at 60 mph by gravity pull which at that speed would be balanced exactly by drag and frictional forces, while the car’s cruise control was set to limit the speed to 50 mph. This would of course lead to regenerative breaking. Now, if one needs to push down the accelerator to balance the regeneration that would mean you use some electricity. This energy is used to spin around the axel of the engine to an rpm corresponding to a speed of at least 50 mph. In an ICE that energy is quite a lot bigger than the energy needed to run the engine at idle. Therefore pressing the clutch in an ICE car increases mileage a whole lot. How big is that energy in an electric engine?

Does the 85% include storage of the kinetic energy AND reuse efficiency back into the tires?

best regards
Soren

 

[DR61]

This would of course lead to regenerative breaking. Now, if one needs to push down the accelerator to balance the regeneration that would mean you use some electricity.

I don't think this is correct. Pushing down the accelerator to the neutral point on the energy bar would not use any more energy than going to neutral position with the shift lever. Moving the shift lever to neutral just turns off both regeneration and acceleration, but changes nothing mechanically.

 

[derotam]

I don’t mean to say that you should use the current neutral functionality. Rather I propose a new functionally should be developed.

I’m not so sure with the feathering approach of keeping the bars at zero: let’s assume a situation where the car would be able to run downhill at 60 mph by gravity pull which at that speed would be balanced exactly by drag and frictional forces, while the car’s cruise control was set to limit the speed to 50 mph. This would of course lead to regenerative breaking. Now, if one needs to push down the accelerator to balance the regeneration that would mean you use some electricity. This energy is used to spin around the axel of the engine to an rpm corresponding to a speed of at least 50 mph. In an ICE that energy is quite a lot bigger than the energy needed to run the engine at idle. Therefore pressing the clutch in an ICE car increases mileage a whole lot. How big is that energy in an electric engine?

Does the 85% include storage of the kinetic energy AND reuse efficiency back into the tires?

best regards
Soren

Yeah stop thinking about the way an ICE works.

So if you are regenerating and you push the accelerator, you are just causing less regeneration, you are not causing a fight against the up to ~70kW of potential regeneration.

Whatever the efficiency of regeneration is, is the efficiency of getting the kinetic energy into the battery. Getting it back to motion is efficiency of the motor.

 

[Bill Foster]

Modern cars utilize a technology called "Decel Fuel Shot-off," or DFSO for short. When you are in gear and coasting, the engine is motoring (via drivetrain to street), but no fuel is being burned. If you are in neutral, then fuel is being burned to keep the engine running since it is decoupled. So you will burn LESS fuel keeping it in gear than in neutral.

And you can't compare an ICE powered car to en electric when it comes to this. So if your tomtom is set up for that, then ignore it.

DFCO but yes you are correct

 

[67King]

DFCO but yes you are correct

It was DFSO when I was working on it as an engineer for Ford, but that was back in 2001 (on the 2004 Explorer). Ford usually used the SAE terms for things at that point, but people used acronyms as soon as they could figure out a way to, so it may have been internal. Who knows, I left the industry in 2007.

 

[Bill Foster]

It was DFSO when I was working on it as an engineer for Ford, but that was back in 2001 (on the 2004 Explorer). Ford usually used the SAE terms for things at that point, but people used acronyms as soon as they could figure out a way to, so it may have been internal. Who knows, I left the industry in 2007.

I get that term from tuning Chevy trucks. maybe different terms from different manufacturers

 

[Kevy Baby]

Would a satnav device that notifies you of all coasting opportunities be beneficial to use in electric cars? Why use any power if you don't need to and still get to your next waypoint.

There is no upside to coasting in an electric car. You are better off learning how to feather the accelerator. Even if your country doesn't have a law against it, putting your car in neutral is a safety hazard. In addition to the other reasons, as @G78M3 mentioned, it disables many (if not all) of the Tesla safety features.
__________________________________________________

One other thing that might be considered: set the regenerative braking to Low. It will still capture some energy, but not slow the car down as much. To do it, got to Controls > Driving > Regenerative Braking. See page 66 of the (North America) Owner's Manual for more info.

 

[Orwell]

I wish we had adjustable regen levels using paddle shifters; it would have a similar feeling to driving an ICE car with paddle shifters to change gears. Left paddle to downshift or increase Regen, right paddle to upshift or decrease Regen.

There would be 4 levels. Default would be sailing/coasting or freewheeling, 1 left paddle click would be low Regen, another click of the left paddle would be medium Regen, and 1 more left paddle click would be high Regen which would also allow for 1 pedal driving if you just keep it on this mode. Right paddle would decrease Regen up 1 level up till back to coasting.

And it would be nice to have an auto mode that automatically switches back to sailing/coasting/free wheeling after a few seconds.

Mercedes has a similar feature in the EQC. Hyundai has a similar feature in the Ioniq and Kona EV. VW had a similar feature using the gear lever in the eGolf. Audi has paddles in the etron.

The EQC has five different levels of regenerative braking. The most interesting is the default setting, called Auto. In this mode regenerative braking is constantly adjusting based on topography, traffic, stereo cameras, and radar data, to intelligently set the strength of regeneration. Mercedes believes most drivers will appreciate how well this mode works, and use it for the majority of their driving. For those who want stronger or weaker regeneration, there are paddles on the left and right side of the steering wheel, just like Hyundai has on the Kona Electric.

The left paddle strengthens the amount of regen, and the right one lessens it. One pull of the right paddle from the default Auto mode puts the car in "sailing" mode. We were told this is basically the same as freewheel coasting. The other extreme is One-Pedal mode which is activated by two pulls from the left paddle. In D mode the vehicle mimics a conventional ICE with an automatic transmission. Below is how Mercedes describes the 5 regenerative braking modes:

• D Auto (recuperation via ECO Assist to suit the situation)
• D + (coasting)
• D (low recuperation)
• D – (medium recuperation)
• D – – (high recuperation). This makes one-pedal driving possible, because in most situations the recuperative deceleration is enough not to require operation of the brake pedal.

 

[Knightshade]

I wish we had adjustable regen levels using paddle shifters; it would have a similar feeling to driving an ICE car with paddle shifters to change gears. Left paddle to downshift or increase Regen, right paddle to upshift or decrease Regen.

There would be 4 levels. Default would be sailing/coasting or freewheeling, 1 left paddle click would be low Regen, another click of the left paddle would be medium Regen, and 1 more left paddle click would be high Regen which would also allow for 1 pedal driving if you just keep it on this mode. Right paddle would decrease Regen up 1 level up till back to coasting.

And it would be nice to have an auto mode that automatically switches back to sailing/coasting/free wheeling after a few seconds.

Mercedes has a similar feature in the EQC. Hyundai has a similar feature in the Ioniq and Kona EV. VW had a similar feature using the gear lever in the eGolf. Audi has paddles in the etron.

Instead of adding a bunch of extra controls- if you want less regen, use the accelerator. more If you want more regen, use less accelerator.

 

[Kevy Baby]

Instead of adding a bunch of extra controls- if you want less regen, use the accelerator. more If you want more regen, use less accelerator.

Oh, fine: just be all logical and stuff

 

[Samovr]

I would prefer to have a quick shortcut button to simply disable regen until I hit the button again. Accelerator would still work but you could freely coast until you want to enable regen again.