[Jeroen]

Originally Posted by electric_eel

Do I think cruise control can be designed better ? Absolutely. By making it less aggressive in maintaining the speed I think it can be better.

What is less aggressive?

I installed a very simple aftermarket cruise control on my Mercedes. Even at a small gradient it drops the speed by 5-7%. Waste of kinetic energy. There are some theories and even experiments that you should hold your throttle in the exact same position going up and down a hill. Which means you loose speed going up and gain speed going down. Not so sure about that either.

In the real world an import factor is also at which speed you drive up and down an incline/hill. You get very different effects at say 50km/h or 100km/h. Primarily due to drag. So loosing 5 km/h at 50 km/h compared to loosing 5km/h at 100 km/h makes for a very different outcome in terms of how much energy you need to add to regain your original speed.

Originally Posted by electric_eel

Also your assumption that drivers keep the speed constant as we climb is wrong.

If you read carefully, this is what I said:

One of the reason is that almost anybody will slow down going from a flat road up on a hill. Which means you loose kinetic energy

So people driving manually have very poor constant speed control, we can agree on that.

Originally Posted by electric_eel

I mostly drive with an aim of maximising passenger comfort and then keeping the speed constant as we climb/descent is as bad as acceleration --- steeper the climb worse it is. So I modulate the throttle (of course with limits). In that sense, it is different from cruise control.

Why is the keeping the speed constant during climb/descent bad? Passenger comfort is about maintaining constant speed! Modulating the throttle is always in efficient, be it ICE or EV. Because your right foot always over controls and thus you waste energy, be it petrol and or electrical charge.

Originally Posted by electric_eel

In addition to safety issues of using cruise control without ADAS, I find cruise control on undulating terrain seriously compromising passenger comfort and hence use it sparingly.

Not sure why, as it keeps the speed constant. Passengers notice small changes in speed as decelaration/acceleration and it is a contributing factor to car sickness.

I can’t validate your driving experiences, but I will say they are personal and should not be used as generic evidence of anything. If you’re happy with it that’s fine, but it might not apply to others.

I am just a simple (retired) engineer. So I look to understand the engineering principles behind things. Without the engineering principles understood and agreed, there is no debate, just personal opinions and experiences.

My experience using cruise control from yours appears to be different. That doesn’t make your or my experience better. I will say this though, I think I understand the mechanics and the engineering of why I am getting my experience.

Enjoy your EV, be careful with the right foot!

Jeroen

[srini1785]

Originally Posted by electric_eel

The point with regen 0 is that there is no current carrying coil inside the magnetic field:

A generator with no load connected has no current in the coil by definition. Hence the resistance is minimal (those in the bearings and due to some minimal eddy currents may be). When the load is connected --- for charging the battery in this case --- there is current in the coil (drawn by the charging system) and hence the back emf adds resistance to the rotation (which is what you were alluding to). This is what acts like braking.

Yes that's exactly what i am talking about. I had written about the back emf being the other name for regen braking in some other thread. Good to know that there is someone who understands electrical basics.

Consider the situation when the regen is 0 and we take the foot of the accelerator. The motor is now like a generator (the rotor is rotating) but without a load.

Yes It is totally possible to run a generator on no load (open circuit). What is problematic is when you throw the load switch. In this case the throwing of the switch involves putting your foot on the A pedal again after running it on no load. What would be the reaction of the motor?. Its akin to raising the rpm of an engine and engaging the clutch suddenly while in first gear. It would be a jerky start. So it makes some sense in keeping the rotor coil current to a minimum instead of bringing to total zero. While not impossible, it wouldn't be practical to just open circuit the regeneration.

[electric_eel]

Originally Posted by Jeroen

What is less aggressive?

I installed a very simple aftermarket cruise control on my Mercedes. Even at a small gradient it drops the speed by 5-7%. Waste of kinetic energy. There are some theories and even experiments that you should hold your throttle in the exact same position going up and down a hill. Which means you loose speed going up and gain speed going down. Not so sure about that either.

May I ask whether it is an EV or a ICE ? I have a feeling that CC, the way it is implemented on Nexon EV is overly aggressive due to the instant and continuous torque of the EV drive train. I have never driven an ICE vehicle with CC and a/any Merc is unfortunately beyond my reach.

My point is what you claim as lost kinetic energy is gained potential energy (due to the height) and for best efficiency the mechanical energy is to be kept constant and not the speed. It turns out that on flat surfaces this is same as maintaining a constant speed and I do agree that cruise control is the best on flat highways and no human probably can match that efficiency.

I also agree with the theory of constant throttle where the constant is choosen so as to counter the other forces (wind resistance predominantly) and not in changing the mechanical energy. In an ideal world where there is very less wind resistance (Mars perhaps ) then the constant should be zero.

In the real world an import factor is also at which speed you drive up and down an incline/hill. You get very different effects at say 50km/h or 100km/h. Primarily due to drag. So loosing 5 km/h at 50 km/h compared to loosing 5km/h at 100 km/h makes for a very different outcome in terms of how much energy you need to add to regain your original speed.

This is also correct and can be explained by taking the rate of change of mechanical energy. Even neglecting wind resistance the rate of change of kinetic energy is proportional to the speed v (derivative of v^2) and hence at higher speeds the loss of energy in the throttle-regen cycle is worse.

Why is the keeping the speed constant during climb/descent bad? Passenger comfort is about maintaining constant speed! Modulating the throttle is always in efficient, be it ICE or EV. Because your right foot always over controls and thus you waste energy, be it petrol and or electrical charge.

Not sure why, as it keeps the speed constant. Passengers notice small changes in speed as decelaration/acceleration and it is a contributing factor to car sickness.

I am completely with you if it is a flat terrain and you may be right in general but I am not so sure on undulating terrain. Climb involves a change in velocity and hence is acceleration (much like taking a curve at constant speed). I have felt it is best to slow down at the apex of the climb before taking the plunge (into the descent). With cruise control, there is a feeling of weightlessness that comes at this apex point which I find uncomfortable.

In summary I completely agree that cruise control is best on flat express ways and no human can match it. Even my original post says so (may be I was not clear about this point). But in many situations like the highways on which I drive regularly, this is not the case and the explanation for this was the fly overs that occur in regular intervals in this stretch.

[sidoxic]

The best tool for maximising range in an EV is anticipatory driving - and of course by extension, for minimising Rs/KM in ICE/Hybrid/EV

Regen merely recuperates a fraction of braking losses, but isn't it always better to prevent the loss in the first place? Not accelerating to a red signal or a toll queue, predicting that someone is going to cut you off in your lane, you won't have enough space to squeeze through 2 way traffic on a narrow street with pedestrians and so on. All of this does basically one thing - don't spend energy via the A pedal unnecessarily, which will be marginally recovered via the B pedal. Of course, safety over mileage/range extraction. The best part is anticipatory driving aides in safety in most cases.

Originally Posted by electric_eel

Drive such that you never supply/demand any energy from it. Needless to say be reasonable in applying this in strategy: safety trumps efficiency always.

Originally Posted by electric_eel

Acceleration-deceleration cycle is the killer of range.

I basically rephrased your statements
Thanks for sharing this in a physics backed manner!
Even though I understood a bit less than all of it, appreciate the thinking behind making this point!

7 years of driving a Figo TDCI taught me how to modulate the milage between 12kmpl (Andheri rickshaw mode) to 20kmpl (anticipatory mode). Now in an EV, the same applies fundamentals apply. A full tank is giving me a range of 160 to 300 km. The regen mode barely moves the needle compared to the heaviness of the foot. The tight efficiencies of an EV makes the outcome more pronounced and game changing on highways.

Originally Posted by electric_eel

In fact I have found that in NExon EV, anything beyond regen 1 is useless except for certain really steep descents.

I have the exact same experience in the XUV400. 'L' gear is for higher regen. It does only 2 things:
- acts as some sort of hill descent control while regenerating so adding range from Pune to Mumbai for example.
- single pedal driving for traffic. This is more for driving experience than increasing range.

[aashishnb]

I would think, from general common sense, can't the brake pedal itself have this sequence to slow down the vehicle, = regen --> more aggressive regen --> use brake disks (i.e. heat loss) to slow down the vehicle.

Or is it too challenging technically?

[electric_eel]

Originally Posted by aashishnb

I would think, from general common sense, can't the brake pedal itself have this sequence to slow down the vehicle, = regen --> more aggressive regen --> use brake disks (i.e. heat loss) to slow down the vehicle.

Or is it too challenging technically?

That is how most EVs set up their brake and that is the reason why I think paddle shifter for regen level change is not so relevant (although in the initial days I did think it was
a good feature to have).

However I am not sure of pure regen 0 level though. Needs to check this.

Originally Posted by sidoxic

The best tool for maximising range in an EV is anticipatory driving - and of course by extension, for minimising Rs/KM in ICE/Hybrid/EV

Completely agree. A drivers aim should be

1. Safety
2. Passenger Comfort
3. Efficiency

in that order. Thankfully, the laws of the universe have conspired in such a way that improvement on any one of these aspects most likely is rewarded with improvement on all of them. You can have the cake and eat it to; not just once but twice.

[Jeroen]

Originally Posted by electric_eel

May I ask whether it is an EV or a ICE ? I have a feeling that CC, the way it is implemented on Nexon EV is overly aggressive due to the instant and continuous torque of the EV drive train. I have never driven an ICE vehicle with CC and a/any Merc is unfortunately beyond my reach.

My Mercedes is very old and very cheap. It is a 40 year old petrol W123. I added an aftermarket cruisecontrol to it. In general I would not think the torque or the type of drive train makes a difference. It is all down to how the mechanical and electronic/software properties of the cruise control work together. When a CC drops the speed too much on an incline that is usually a sign of some limitation in its control cycle. Modern Cruise controls are so called PID controllers. Earlier CC were PI controllers and thus tended so suffer from various hysteresis effects.

Originally Posted by electric_eel

My point is what you claim as lost kinetic energy is gained potential energy (due to the height) and for best efficiency the mechanical energy is to be kept constant and not the speed.

You keep saying that and claiming you have proved it scientifically, but you have not. You have stated some formulas and opinions and personal (unverifiable) observations. That is not science.

Luckily, we can do the math based on the formulas you shared. Lets see what science really tells us.

Now, as I mentioned I am a very old engineer. I learned calculus with pen, paper and slide rule. So excuse me, but I just wrote it out on paper, with my pen and did the calculations on my slide rule. Because I have no clue how to deal with all these math symbols on my phone/ipad.

So here goes, lets have a look how the relation between kinetic and potential energy is. Obviously, in a no loss / 100% efficiency scenario.



I have calculate using your formulas how much potential energy a car has and how far it will go up (how high it could reach) when all of its potential energy is converted to height. (Example 1 and 2)

Example 3 is along the scenario what you are claiming;

My point is what you claim as lost kinetic energy is gained potential energy (due to the height

It shows a loss of speed from 90 to 72 km/h. That gets you an amount of energy equal to a height of 1,25m!!

I have said it before, kinetic energy is the big one compared to potential energy in these sort of driving conditions. As the speed is squared. So the effect increases exponentially with the increase of speed!

That is, as my calculations and your formulae show that maintaining a constant speed (i.e. maintaining kinetic energy) is way way way more important than gaining potential energy (i.e. height). Or conversely, that it does not makes sense to trade potential energy into kinetic energy. Keep that speed constant. The faster you go, the more important it is to keep the momentum!

That is what the math shows, at least that is what I think the numbers tell me. Do you see it differently?

Originally Posted by electric_eel

I am completely with you if it is a flat terrain and you may be right in general but I am not so sure on undulating terrain. Climb involves a change in velocity and hence is acceleration (much like taking a curve at constant speed). I have felt it is best to slow down at the apex of the climb before taking the plunge (into the descent). With cruise control, there is a feeling of weightlessness that comes at this apex point which I find uncomfortable.

Again, you are the one claiming your statements are science based. I say, lets do the math!! Here we go:



When a car drives from a horizontal surface onto an incline at a constant speed, it is very easy to calculate the horizontal and vertical speed component.

Here you see two examples, respectively an angle of 5o and 10o.

Comfort, or lack thereof in such a scenario is based on the acceleration/decelaration. So we need to calculate the change in both vertical and horizontal speeds first. Easy peasy using sinus and cosinus.

At a 10o angle the change in vertical speed is only 1km/h. The horizontal change in speed is 12,5 km/h. How many flyovers in India sport 10o slopes? In almost all cases there are much more shallow.

In order to calculate the acceleration/decelaration you need to define or assume how long it took (either by time or by distance). Since speed is constant, you have can calculate the distance over which the speed decays.

Acceleration/decelaration is change in velocity over the change in time.

You can do the math yourself, but at 72 km/h and a change road orientation from level to 10 degrees up, and say the speed decays over 40 meters, you will find that the deceleration is 3,47 / 2 = 1,7G

But if the distance was, say 80 meters it would be only 1,35G.

To put that number into some perspective. There has been a large number of studies done to what people find a comfortable level of acceleration/deceleration. You can google it, but 1,35G is way way low, not anywhere where people will start to notice let alone start feeling uncomfortable. And that 1,35G is based on a pretty maximum scenario.

To translate that into something more practical, you need to look at hills or flyovers and look at their angle and how much distance it takes to get that gradient. I can tell you the above is already pretty extreme! I have not even bothered to calculate the vertical acceleration/decelaration as you can see it will be completely minute!

So on normal road with some normal up and down type of gradient it really is not speed fluctuations (horizontal and vertical due to constant speed) that determine passenger comfort.

[ecenandu]

Originally Posted by electric_eel

Do I think cruise control can be designed better ? Absolutely. By making it less aggressive in maintaining the speed I think it can be better.

How much of speed variation is present from the set speed on cruise control in your Nexon EV?

I have used cruise control on BMW and Mercedes in Dubai and have observed a variation of +-1 kmph from the target speed.

[electric_eel]

Originally Posted by Jeroen

You keep saying that and claiming you have proved it scientifically, but you have not. You have stated some formulas and opinions and personal (unverifiable) observations. That is not science.

Luckily, we can do the math based on the formulas you shared. Lets see what science really tells us.


Attachment 2475591

Thanks for taking the pain in calculation. The way I see it is that your exact calculations justify my case even better in the range 70-90 speed (a speed suggested by folk wisdom for best efficiency) . It seems we agree on the math but not the interpretation.

Firstly there is a calculation mistake in yours but it only makes my case better. For a 90-72-90 cycle you have taken the height equivalent to be 1/2 (25-20)^2/g where as it should be 1/2 (25^2 - 20^2)/g. You get a very small height 1.25 m where as it is about 11 m. The smaller height justifies my claim even better (We can neglect the mass of the car
in each of this calculations as they cancel off)


The way I see it is that an acceleration-decelaration cycle of 72-90-72 on flat surface (to take your strategically chosen figures) is equivalent to a climb-descent of about 11 m at constant speed (the magnitude does not matter). In another words, I do a 11 m up-down at cruise control set to 72 (actually the speed does not matter here), I should treat it as an acceleration from 72 to 90 and back on flat highway as far as loss in accelerate-regen-brake is concerned.

This is the kind of speed range I use and is generally recommended for best efficiency. I try to maintain at 70-90 mostly close to 75-80. And 11.0 m looks like a good enough height for a typical flyover (3 floors = 10 m).

Let us do one more calculation: The 90-108-90 cycle would be equivalent to a 14.0 m climb. So a flyover at (constant speed) at 14 m will cost me equivalent to the 90-108-90
acceleration cycle. So even in the higher cruising speed (which I do not do) a 14m height difference has the same effect of 5 m/s difference in speeds. Seems to justify my claim
of disabling cruise control for undulating high ways.

I understand your point too: If one is cruising at (much) higher speeds then effect of undulations is not too much. i.e the acceleration-deceleration cycle due to the imperfections of human driving will be big enough that the equivalent undulations required is going to be too big. This is correct as you rightly pointed out. But such high speeds are anyway not good at giving good F.E for the following reasons

1. A small imperfection in the cruise control is also going to cost you so much in the accelerate-regen cycle (cost is proportional to difference in K.E which is proportional
to speed)

2. The elephant in the room that we were neglecting so far wind resistance.

Regarding passenger comfort I will have to think a bit. I did not put it in the original post mostly because I do not have a crisp argument for it.

[electric_eel]

Originally Posted by ecenandu

How much of speed variation is present from the set speed on cruise control in your Nexon EV?

I have used cruise control on BMW and Mercedes in Dubai and have observed a variation of +-1 kmph from the target speed.

Difficult to say exactly as the speedometer is analog but I think it should be similar. At least they allow finer adjustments by +-2 km/h so clearly it should not be worse than that.