Backing off or braking in Neutral doesn't cause any regenerative braking; the brake pedal response is really quite different in Neutral to Drive or Low. Which power meter were you using - the centre console flow one or the mini power distribution one in front of the driver?

 

In reality you don't want to regen at all.....I know that sounds strange but as its not 100% efficient you are far better not using the power in the first place......If you have to slow down rapidly then regen is better than friction breaks, but if you can anticipate the situation and slow down without regen then you will have saved more energy than slowing down later and regening...

 

If you are descending a slight slope e.g. some motorway stretches, it may be that taking foot off accelerator while in D may regen enough to slow you down ; but you want to maintain constant speed, so you have to feather the throttle as best you can. Chances are you will do a mix of slight accelerating followed by some regenning as you back off. Or, you can select neutral and coast; the car stays in gear, and presumably draws the minimum electricity to match motor speed to wheel speed. No acceleration power is used, and no regenning happens. So this is very slightly more efficient. I use this as a "better" form of coasting, but only when traffic is light and zero chance of needing to accelerate suddenly.

 

I thought that I had read in this forum that power does not flow back into the battery if you're in neutral and that therefore, to get best mileage, you should stay in gear. Is that correct?

Especially in the Ampera, do NOT flip it into neutral.

If you are in CS2 or CD2 then you will actually see your power consumption INCREASE if you push it into neutral. This is because to maintain road speed at the output shaft, the two motors are then forced to work against each other to sustain the road speed.

It's generally pointless in a single fixed speed BEV, you are just manually setting the switching to zero output, which you can do by just adjusting the pedal to the 'coast' position. I realise that can be difficult to 'feel' for, but plus or minus a few kW will make no difference.

In the Ampera it is fundamentally different. It's not designed like that when running CS/CD2, I recommend you don't even try. I am quite sure it will cope just fine, just don't do it. It'll be one of those 'abuse' tests that would have been done, but it has a non-intuitive outcome, which is to ensure the motor speeds remain consistent because the transaxle output speed is always the road speed, but the two inputs are not fixed in ratio.

 

I try to use cruise control as much as possible. Especially on roads around me where there are so many average speed cameras now. I find it switches between battery and regen more efficiently. With the battery use graphics up you can see it flick between the two as the car senses dips in the road where it can coast for regen.

 

Hasn't there been some (quite a lot actually!) discussion about coasting downhill in neutral to use the brakes manually to give the discs something to do every now and then? Is this still ok as your post is referring to maintaining road speed but the brake workout is clearly only downhill so it shouldn't affect the CS/CD2 @donald?

 

If the car is in CS/CD2 then the clutches cannot spontaneously change themselves quicker than you pick neutral. I doubt it will harm the car, once in a while, but you will see the energy go up because the motors are fighting each other to keep a neutral speed.

 

I do occasionally pop into Neutral to get some wear into the brake discs, but only when running in EV mode, not in Mountain/Hold mode... now...!

 

I find my own experimental numbers rather convincing - flipping my Gen1 Ampera to N when going downhill or approaching red traffic lights, instead of coasting down in D, increases my electric range by several km (note: rolling in neutral gear is not illegal where I live). Also when standing in traffic lights, N saves power because the motor is not straining against the brakes. The only concern I have is whether this traditionally "bad driving habit" of switching between D and N will wear down Ampera's powertrain components (which ones?) faster than keeping the gear in D. I'm not familiar with the inner workings of Ampera's transmission, expert opinions would be appreciated.

 

I find my own experimental numbers rather convincing - flipping my Gen1 Ampera to N when going downhill or approaching red traffic lights, instead of coasting down in D, increases my electric range by several km

I cannot understand how not using regen could result in better economy overall. I think what was said previously is that NOT USING power in the first place thus avoiding the need to use regen is more efficient. But not to use regen when slowing or downhill cannot possibly increase economy. There must be some quirk in the electronics that causes it to display a higher economy figure rather than an actual increase in economy.

 

Actually I get what you are saying and it does sound like you might be right! Thing is what would be the logic of the E-pedal in the new Leaf then - that forces regen as much as possible, from what your saying it would be more efficient to have no regen at all when lifting off the accelerator and only apply regen when braking? I'm not saying it can't be true - only that the manufacturers seem to think otherwise I guess!

 

I know next to nothing about the Leaf... but you have to keep in mind that rolling in N is illegal in some states/countries. Also, not all drivers are into hypermiling, and want to keep their driving experience as simple as possible. The one thing I do know, from the basic laws of physics, is that regen is always lossy - you only get back part of what you use.

 

When I had a Prius there was a long discussion about this on the Toyota Owners Club forum, the conclusion being that as you say regen is lossy and maximum economy is obtained by coasting when possible. Regen will capture some energy back but then more power is needed sooner than in N, and each time power goes either way through the inverter/motors etc. there is some loss.

Hypermilers using the 'pulse & glide' technique in a Prius would not actually go into N when gliding but keep the accelerator pedal pressed just enough so the power meter shows no power being used or regenned. With a low drag coefficient the Prius is able glide a long way before needing further power input.

 

There appears to be mode between D and L where the wheels are driven but there is no regen. a few people have hit this by accident and it wont normally stay there. I've only seen this in normal and its tricky to hit but this would be the mode for pulse and glide.
I wonder if it was intended or is an accident .

 

So, coasting to a stop (without using regen or the physical brakes) will use the least amount of energy and so give you the greatest range

.... only if your motoring consists solely of getting up to a speed and then coasting to a stop to arrive at your destination or a place where you must stop such as the car in front of you, a junction etc at exactly the right time even if that means slowing down to a speed that would cause serious hindrance to other road users. Without the need to ever slow down faster than the car will provide by friction with road and moving components whatever the steepness of the road, plus you must never speed up more than needed to allow you to stop naturally once foot is off accelerator.

I would like to see the "foot off" condition of the accelerator be a zero energy position where there is no regen and no power being used. That would be perfect... instead you have to find the zero power position manually by feathering the accelerator slightly and using the power meter. If you don't have a power meter then you just have to guess by the feel of the car.

Such a position would be infinitely variable and only work for a specific downward road inclination and also wetness of the road, state of tyres, wind speed, all of which are constantly changing, thus unless the goal is to slow down to a specific speed (including zero) or you are on a downward slope with the exact constant slope that combats friction, the "zero position" does not exist.

Such is the difference between theory and practice.

 

Such a position would be infinitely variable and only work for a specific downward road inclination and also wetness of the road, state of tyres, wind speed, all of which are constantly changing, thus unless the goal is to slow down to a specific speed (including zero) or you are on a downward slope with the exact constant slope that combats friction, the "zero position" does not exist.

Remember... these cars are basically computers on wheels. I can see no reason that it would have to be a fixed setting as you say. It would be dead easy to programme it in such a way as to constantly compare regen and power and to vary the power delivered to the motor or regen at that pedal position (up!) as conditions change. I would want a zero power condition with the pedal up... no power to the motor and no regen. Should be pretty easy to do IMO.

 

I cannot understand how not using regen could result in better economy overall.

As Paul says, it involves avoiding that inefficient period of energy conversion.

Of course, this means that your velocity profile would be flatter, i.e. you would begin to slow down earlier for a stop ahead. The thing is that if you know you are stopping, why would you carry on with powered driving up to the point where you need to regen to stop in time?

So it is not something for nothing, you do actually get to the stop point quicker if you regen, but why do you want to get to the back of that traffic queue or that red stop light sooner? That just wastes energy, and the fact that you used regen is, in a way, a manifestation that you've not used the 'natural' deceleration rate (i.e. tyres, aero, transmission drag) in an efficient way to benefit your economy.

TBH, it makes very little difference unless you are already at the ragged edge of absolutely maximum energy efficiency. So basically, if you are not achieving in the range of >5.5mi/kWh then you won't really notice an actual effect, and if you are then you will already be doing these things, like letting the car glide when you can.

 

Another example of not using regen is where you crest the brow of a hill. If you back off a little up the hill so that on the way down you can regain your road speed with minimal regen then this is going to be more efficeint than keeping the power on to the top and then using regen to recoup some of the energy on the way down. Again, your velocity profile will be flatter and slower, of course, but 'in the real world' (as people like to say) it really will add nothing to your journey time, despite what the hoodlum loony behind you might be thinking about your grandma mode.

 

Right I can see why I was misunderstanding, the point everyone was making was a mainly theoretical one in that if purely coasting to a stop it will use less overall power than using regen or brakes to stop. However coming from a very urban environment it didn't really enter my imagination that one could drive at such speed as to have frictional forces alone (without brakes) bring the car to a halt, it simply would not be possible as most of my driving is during rush hour. I THOUGHT (wrongly) people were referring to using the breaks in neutral as to avoid regen, but of course regen instead of breaks IS more efficient, hence the misunderstanding!

But having understood your point(s) I accept in theory it would indeed be more efficient, just simply impractical in 99% situations, at least where I live!

 

But having understood your point(s) I accept in theory it would indeed be more efficient, just simply impractical in 99% situations, at least where I live!

I think you are right... it is pretty theoretical. Or rather, the savings are real but the amount you might save isn't likely to extend your range by any useful amount over using regen to slow/stop

but I do admit making use of the no-penalty margin above the speed limit

In the UK there is no "no-penalty" margin as such. The limit is the limit... end of. But as all speedos in the UK over-read by as much as 6-10% (that is a requirement) if you stick to the indicated speed you are always safe. I think that you are driving slightly over the limit to allow for that error in the speedo. Well, I do that as well but I have tested my speedo against a GPS and so I know exactly how much it over reads by so I am always safe. If you are going to do that then I recommend that you check your speedo readings at various speeds against a GPS and see how much margin you might have.

For example... if you assume that your speedo over reads by 10% at 70mph but it actually over reads by 6% then you would potentially drive at an indicated 77mph thinking it was actually 70mph when it really was nearer 73mph. I know you are not likely to get stopped but it is over the limit and I have heard of people being flashed by a camera for being just 3mph over. Madness but the limit is the limit.

 

We're like two peas in a pod Donald - PhD in physics myself, 29 years of university research and lecturing in the field of energy under my belt. I assure you I'm not making my numbers up.

The 0kW approach makes perfect sense, and I'd be happy to adopt it if only GM had engineered it into a selectable automatic driving mode. Based on the numbers, the cruise control certainly doesn't seem to use it.

But as I said, I'm not a hypermiling fanatic - I have an OBD dongle, but I certainly won't divert any attention from traffic to an app on my phone screen to chase that 0kW sweet spot manually. The little extra mileage I get from rolling in N is usually enough to prevent the ICE from starting due to empty battery in my everyday winter driving.

 

Yes, most speedos over-read (e.g. my Ampera by about 5 km/h over a wide speed range). If the speed limit is 60 km/h, I can set my cruise control to 65 to drive exactly at the speed limit - but the police traffic cameras over here won't click until you're about 6 km/h (4 mph) over the limit, so the cruise control can be set to about 70 (=65 km/h true speed) without worries.

I didn't know about the strict speed limit policy in the UK (good to know ). The Norwegians have that too. I guess our no-penalty margin is a relic from old times when speedos were less accurate. On the open roads, we didn't even have speed limits before the late 60's... with luck I survived on the back seat of my dad's old Opel Rekord (like this one: https://upload.wikimedia.org/wikipedia/commons/b/bb/Opel_Rekord_A_front_20091211.jpg) with no seatbelts

 

I thought that I had read in this forum that power does not flow back into the battery if you're in neutral and that therefore, to get best mileage, you should stay in gear. Is that correct? Driving home this evening, I had the Power Flow meter on display and thought I would see what happens when you go into neutral. As far as I can see, the graphical display of power flowing back into the battery is the same when you're in gear and back off the accelerator as it is when you do the same in neutral, or when you brake in gear, or brake in neutral. That may just be a function of the limitations of the Power Flow display but perhaps the level of actual recharging varies in each of these circumstances?

I started this thread because I was surprised to see power flowing back into the battery when in N. I've since discovered that that is not always the case and sometimes you will see power still flowing out when in N. I cannot explain this but I tend to agree with Paul Moxhay (and others), that it's possible to get better range using N than via using regen (as that will have greater loss through friction generating heat).

However, what worries me is Donald describing using N as an abuse and saying that "Especially in the Ampera, do NOT flip it into neutral" Although I frequently don't understand Donald's technical explanations, (I've no idea what is meant by CS2 or CD2 for example), if that's his view, then I think that we have to very seriously consider if it is a bad thing to do and whether to forego the extra range for possible better longevity of the car's systems.

 

However, what worries me is Donald describing using N as an abuse and saying that "Especially in the Ampera, do NOT flip it into neutral" Although I frequently don't understand Donald's technical explanations, (I've no idea what is meant by CS2 or CD2 for example), if that's his view, then I think that we have to very seriously consider if it is a bad thing to do and whether to forego the extra range for possible better longevity of the car's systems.

I defer to Donald's better knowledge on this and if he says it isn't a good idea mechanically then I am happy to believe it but also remember that it is never good driving practice to ever run any car in N... on a test it would be a fail (S level probably) and from a practical point of view when in N you cannot be fully in control as you cannot accelerate... particularly important if the surface is slippery too. I would suggest to everyone not to run any car in neutral for whatever reason you chose to consider. Also, the software on these computer-driven cars (and that is all EVs) is not designed or expecting you to drive in N and so traction control, anti-lock and ESP systems may not work as you would want them too if they were needed

 

I did not design the system, nor have I worked on it, but my logic is pretty simple so I figure that means it is pretty sound;-

There is a good chance you are in CD2 or CS2 mode (ie power-split, with both motors engaged through the coupling epicyclic). because if you were slow enough to be in CD/CS1 then you'd probably not have time, or be bothered, to try to glide in N for the short distance that would mean.

If you are in power split and hit neutral, the 'system' will be trying to match the combined output by adjusting the speed of the motors. As there is no torque demand, the motors will adopt some odd relationship that, presumably, must be embedded in the software somewhere and you generally see that as a power draw.

I have tried it a couple of times on a few fast steep hills and it always drew additional power for being in neutral. I had no reason to believe it was doing anything other than 'glide' so I interpret that to mean the two motors are fighting for control to ensure zero net torque is delivered.

As they do this, and if you were slowing down, at some point it would try to shift to CD/CS1 which involves changing clutch settings. As the two motors are opposed to generate zero torque, this might mean the clutches have to undertake a torque transition, i.e. slip. They are not designed to slip, they are designed so the motors together, along with the positive torque demand of the moment, work to couple and uncouple the clutches with zero differential speed, ie no slip.

I would not hesitate to agree with you this is only my theoretical machinations, and may not be correct. However, on the basis that, personally, I have only ever seen a net draw of power for zero torque output, thus I can't see any reason to actually want to do this, then to merely hope it is OK when it is not needed anyway would seem misguided.

So, what the transmission actually does, we understand. Whether it actually does any long term harm, it would only be IMHO that it is not a particularly great idea but you probably won't notice a bit of extra clutch wear. If you are happy about that and feel the small power draw is the lesser inefficiency compared with trying to find 0kW on the pedal, then feel free.....