Battery Electric Vehicle News / Enjoying the Transportation Revolution

JKenH

Solarchaser said:

Martyn1981 said:

JKenH said:

Hypermiling makes use of the technique of gaining momentum on downhill sections and using that momentum to go up the next incline. You need the gauge to keep you in that sweet spot so you neither regen or use power going downhill, until your speed moves out of an acceptable range given the presence of other road users. It’s easy in a manual ICE car as you can just dip the clutch for more momentum but in an EV unless you put it in neutral you will always risk regen which wastes energy. Without the gauge I just don’t see how you can judge it perfectly.

Couple of problems with that. Firstly you seem to be applying ICE hypermiling rules, where all retardation is a waste, so braking on a downhill is wasteful. But for a BEV you need to compare the losses in the regen, perhaps 20%, to the increase in wind resistance losses as the vehicle speeds up rolling down a hill.
Secondly, dipping the clutch, rather than coasting in high gear will burn more petrol/diesel as the car can keep the engine turning via momentum, whereas dipping the clutch will start the fuel supply up to keep the engine spinning. I may be wrong about the technicalities, but I think this really became the case when we transitioned from carbs to fuel injection, about 30yrs ago.

Yep, you are right.
Its a thing of especially people of an older generation who remember carbs.

The amount of folk who say things like yeah I dipped the clutch on the downhill to save fuel.... err no, you cost yourself fuel there.

If only it were that simple. What you say sounds logical in so far as it goes but it doesn’t go far enough. Yes I would use fuel turning the engine over at idle when coasting but all the time I would be gaining kinetic energy as I descended the hill and picking up (say) 10mph as I did so. You meanwhile would be using the kinetic energy of your car to turn the engine over (engine braking) which produces heat which is dissipated through the car cooling system, i.e. energy is wasted. I believe the same amount of energy would be wasted in heat as I have gained increasing my speed by 10mph but don’t hold me to that. If I arrive at the bottom of the hill travelling ten mph faster I have a lot more kinetic energy than you. You would then have to fuel your engine to accelerate the car by 10 mph to reach my speed. So I have gained my 10mph by running the engine at idle downhill but for your car to achieve the same state of kinetic energy you actually have to use extra fuel to accelerate your car and accelerating will always use more fuel than idling. (Effectively you’re having to put back the energy you lost as heat by engine braking). 

I will, also, always be a little bit further down the road as my average speed has been higher while actually using less energy. 

Edit: please note that these comments relate back to my earlier post about dipping the clutch to gain momentum as a hypermiling technique when descending hills where the kinetic energy gained can be used to ascend the next hill or carry more speed on the flat. I agree that coasting up to lights in neutral is wasteful of energy for the reasons you outlined but that was not what I was suggesting. 

Edit 2. If you are going downhill so fast that you have to brake in an ICE car then, yes, it is better to be in gear than coasting (and better to be in a high state of regen than low in an EV). Using the brakes is wasteful in either type of car. 

JKenH

Tesla leads the EV charge, but others are getting the credit

https://www.teslarati.com/tesla-leads-ev-charge-others-getting-credit/

JKenH

Maybe a corvette conversion next? I love the idea of a manufacturer offering EV conversion kits for classic vehicles. Maybe MG next?😉

https://electrek.co/2020/10/29/gm-1977-k5-blazer-e-converted-electric-power-ecrate-conversion-kit/

Solarchaser

Erm no.
Firstly you are not generating heat, the engine becomes an air pump, since no fuel is being burned,  and so actually you cool everything down, including your coolant,  and because you are pumping air this cleans out the crankcase,  so that when you press the go pedal again, nice clean air goes into the engine, so you get a more efficient burn, and more energy per cycle.
Since you will be in a high gear, the biggest restriction to your speed will be friction of tyres on road and the air pressure building up in front of the car... faster car = more air resistance to overcome.

Talking about internal combustion engines here.

I mean, I like your theory and the thought you have put into it, but as someone who has spent a fair bit of time making my engine (and many others) as efficient at putting out two or three times their manufactured power as possible,  I assure you it doesn't work that way.

JKenH

Solarchaser said:

Erm no.
Firstly you are not generating heat, the engine becomes an air pump, since no fuel is being burned,  and so actually you cool everything down, including your coolant,  and because you are pumping air this cleans out the crankcase,  so that when you press the go pedal again, nice clean air goes into the engine, so you get a more efficient burn, and more energy per cycle.
Since you will be in a high gear, the biggest restriction to your speed will be friction of tyres on road and the air pressure building up in front of the car... faster car = more air resistance to overcome.

Talking about internal combustion engines here.

I mean, I like your theory and the thought you have put into it, but as someone who has spent a fair bit of time making my engine (and many others) as efficient at putting out two or three times their manufactured power as possible,  I assure you it doesn't work that way.

I realise this is taking the thread even further away from EV news but I do need to respond to that.

If, as you say, your engine is acting as an air pump, what is driving it? The kinetic energy of the car, of course, the turning of the wheels is turning the engine over. All that compressing of air inside the engine generates heat. It’s basic physics, compressing air requires an input of energy and produces heat. Just think of your bicycle pump, it gets hot as you use it. 

I realise we are not going to agree which is the most efficient approach but as it seems we can’t even agree on basic physics, perhaps we should leave it there.

Edit:

I found this on the internet about closed throttle running. Although the question was asked about a carburettor engine what is happening inside the engine is the same.

As long as the engine is spinning, it is pumping air. All the air that goes into the engine has to pass through the throttle, the runners in the intake manifold, and finally the intake valve(s) before it gets into the cylinder. When the throttle is closed, it creates a severe restriction on that airflow. The air needs a steep pressure gradient to get through that obstruction. Since the air upstream of the throttle is at (less or more) atmospheric pressure, the air on the downstream side has to be below atmospheric pressure. This is called manifold vacuum. A typical engine might pull 20 inches (Hg) of vacuum at idle. Google says that’s 9.82 psi.

After the air gets through the throttle, it still has to flow through the intake manifold and valves. Those aren’t designed to create restriction like the throttle, but the air still needs some pressure gradient to get through them. Let’s say the inside of the cylinder is at 10 psi vacuum. The bottom side of the piston, however, is at atmospheric pressure. Due to the heat inside the crankcase and the PCV valve, it might even be higher than the atmosphere, but we’ll assume it’s 0 psi. Take a typical Chevy 350. The bore on that engine is 4″. That means the total force on one piston is

𝐹=𝜋4∗(4")2∗10𝑝𝑠𝑖F=π4∗(4")2∗10psi

The crankshaft has to pull down on each piston with 125 pounds each time that piston is on the intake stroke. The stroke of a 350 is 3.48″. The energy exerted on one intake stroke is

𝐸=125.66𝑙𝑏𝑠∗(3.4812𝑓𝑡)E=125.66lbs∗(3.4812ft)

Every intake stroke robs the engine of 36 ft-lbs of energy. At 2000 RPM, there are 8000 intake strokes every minute (8 cylinders; each has one intake per two revolutions). The power required just to pump the air at that speed:

𝑃=36.44𝑓𝑡−𝑙𝑏∗8000𝑚𝑖𝑛∗1𝑚𝑖𝑛60𝑠∗1𝐻𝑃550𝑓𝑡−𝑙𝑏/𝑠P=36.44ft−lb∗8000min∗1min60s∗1HP550ft−lb/s

The power required to pump the air into the cylinder is almost 9 HP. If we assume for simplicity’s sake that the power required for exhaust is equal, that means that the engine needs 18 HP just to keep itself running, if it weren’t connected to the drivetrain. Since the engine is burning very little fuel, the power to pump the air is converted from the vehicle’s kinetic energy. 

Martyn1981

JKenH said:

Solarchaser said:

Erm no.
Firstly you are not generating heat, the engine becomes an air pump, since no fuel is being burned,  and so actually you cool everything down, including your coolant,  and because you are pumping air this cleans out the crankcase,  so that when you press the go pedal again, nice clean air goes into the engine, so you get a more efficient burn, and more energy per cycle.
Since you will be in a high gear, the biggest restriction to your speed will be friction of tyres on road and the air pressure building up in front of the car... faster car = more air resistance to overcome.

Talking about internal combustion engines here.

I mean, I like your theory and the thought you have put into it, but as someone who has spent a fair bit of time making my engine (and many others) as efficient at putting out two or three times their manufactured power as possible,  I assure you it doesn't work that way.

I realise this is taking the thread even further away from EV news but I do need to respond to that.

If, as you say, your engine is acting as an air pump, what is driving it? The kinetic energy of the car, of course, the turning of the wheels is turning the engine over. All that compressing of air inside the engine generates heat. It’s basic physics, compressing air requires an input of energy and produces heat. Just think of your bicycle pump, it gets hot as you use it. 

I realise we are not going to agree which is the most efficient approach but as it seems we can’t even agree on basic physics, perhaps we should leave it there.

It's not just the physics, it's also reality. Firstly all your claims are based on the ability to gain speed, so you have to be below the speed limit and the road conditions. But more importantly, have you driven a car the last 30yrs??? in an overgear (top gear) you don't get much engine braking, so I think you are applying extreme example theories to real life, and it simply ain't so.

Back to BEV's, yesterday I drove about 150 miles, almost all on motorways (for an animal rescue (semi-emergency)). I was very conscious given the recent discussions about the fact I was in high regen. This allowed me at even high speeds to drive one pedal almost the entire way, despite horrific rain conditions (the second worst I've ever driven in), heavy traffic at times with vehicles pulling into my 'safe space', and motorway speeds for most of the return journey fluctuating every 2 miles from 7 to 70mph. The only braking I needed to do were at a couple of roundabouts and traffic lights, all of which would have been avoided if I hadn't been in creep mode.
As I was driving it occurred to me, how low to no regen would not have been suitable at all. It also occurred to me how road conditions, wind, rise and fall etc meant my foot pressure was varying a lot, as of course it does naturally when driving in response to the input from the eyes and the bum - any chance to coast between power and regen would be minimal to negligible most of the time.
Have to say, whilst chatting about the theory is always interesting, I find it rather tiresome when some folk try to argue against real life with extreme edge cases, getting ever more silly.

EricMears

I'm certainly not (nor I think is anyone else) advocating never using regen !  In its place it's very useful.  However,  having it intrude into situations where it's not needed is just plain silly.

Martyn1981

EricMears said:

I'm certainly not (nor I think is anyone else) advocating never using regen !  In its place it's very useful.  However,  having it intrude into situations where it's not needed is just plain silly.

Absolutely Eric, that would be silly. Hence the need to focus on reality rather than theories.
So going back to the start, I believe Tesla's idea behind removing the option to select low regen (thus removing standard regen from the GO pedal) is to improve efficiency (something we all seem to be seeking) and perhaps also some benefit to battery life. So great news all round then.

JKenH

Martyn1981 said:

EricMears said:

I'm certainly not (nor I think is anyone else) advocating never using regen !  In its place it's very useful.  However,  having it intrude into situations where it's not needed is just plain silly.

Absolutely Eric, that would be silly. Hence the need to focus on reality rather than theories.
So going back to the start, I believe Tesla's idea behind removing the option to select low regen (thus removing standard regen from the GO pedal) is to improve efficiency (something we all seem to be seeking) and perhaps also some benefit to battery life. So great news all round then.

I think you may be right; Tesla have removed low regen to improve its efficiency rating in the EPA and other similar tests - not in the real world. 
As Tesla are the leaders which others follow will we now see all the other EV manufacturers do the same? 

JKenH

Well they haven’t removed the low regen option for safety reasons.