Difference between Eco, normal and sport modes

[decrep]

yes of course, at 100% regen doesn't work at all.
But it doesn't stay there for long.

 

[Gibroom]

I think we can all agree that high regen breaking or OPD is the best in town. There is just no way you could comfortably slow an ICE car down in town by just throttle control. The main thing in an EV is getting to know how much to use your throttle/regen breaking without losing too much energy. Equally, don't worry about it either, most of us here probably have use of a slow charger at home or work. With that, costs are going to be way down compared to ICE cars even if driven like the STIG.

I stay in normal drive mode and have learned to adapt with it. I do not tear off when stopped at lights and generally drive economically but I like to have the power on hand when I need it.

 

[MG4JP]

(...) annoys the hell out of the cars behind me if I push it too far. A car doing 70kmh takes ages to roll to a stop, and friction brakes have to be used (...).
Rolling to a halt just isn't practical.

Indeed, you can't just drive like this all the time and in regular traffic. It's not realistic to assume so and that's why I mentioned "in theory" and "ideally".

Having said that, when going for the pedal brake (and if done gently) you will activate regenerative braking as well, so you can keep the feature at its lowest setting and still benefit from it when really needed.

 

[decrep]

True, but I dislike using the pedal brake when I don't have to. I have enough fine control to keep regen to 0 and just cruise up to the cars stopped in front of me.
My speed on the freeway hardly varies, only with changes in gradient, as I keep a steady pedal pressure.
I'm fairly sure any energy I waste being in OPD would fit inside a match box.

EDIT,
for over 20years I've been driving for economy.
The brake pedal was my worst enemy, (and my tires enemy as well because I'd corner fast).
So the instinct to avoid the brake pedal is built in.
Now I can slow down a bit more for corners, and be more friendly to the tires.

 

[Tangoed Man]

Well, I would very much like to see some measurements of the recovered energy from regenerative braking. Random thoughts and hand waving aside! I do know that kinetic energy is removed quite quickly in mode 3, either there is a lot of waste heat in the motor/generator or controller, or quite a bit of energy is flowing back into the battery. A SERIOUS question, has anyone done any REAL measurements. This information must be around somewhere. After all I spent 60 years as an electronic engineer, built 5 electric vehicles and was the technician who grew the very first Indium Antimonide single crystals (Hall effect) back in my youth in the early 1960's, so I have a genuine interest.
As to brakes, are people not aware that one of the big advantages of a hybrid/electric vehicle is brake life?

A good friend of mine is a world expert on EV's, (he designs and builds them, too), and in particular Lithium Ion battery technology. He once showed me a report highlighting that over a typical range of a fully charged EV you could expect a maximum of about 5% overall benefit from regenerative braking, often far less. Newton had it covered in his three laws of motion and so regen is only ever of benefit if you are FORCED to slow down, (junctions, traffic lights etc), but it is always more efficient just to keep the car rolling at the speed you are going. It is even a false economy to use regen going down a hill IF it stops you building up a little more speed to climb up the next hill that is inevitably ahead of you. Going up a hill and down the other side (using maximum regen) is always going to be far less efficent than driving the same distance on the flat, i.e. you will not recover anything like the extra energy used to climb the hill from the regen enjoyed on the downward stretch; for steeper hills it isn't even close.

 

[Rolfe]

5% as opposed to what, though? If it's 5% you wouldn't have otherwise, is that to be sneezed at?

 

[decrep]

That's 5% over the whole trip, when most of it isn't braking, likie a long motor way trip. It's very different for short urban driving with plenty of stop start driving. This is where the EV really comes into it's own, unlike an ICE vehicle that has better consumption figures on a long non stop drive, the EV has better figures in short stop start driving.

 

[wattmatters]

I'm sure Mr Google will give me the formula.

The equations will be near enough identical to those used for cycling as described by Martin et al, the main difference will be the nature of bearing drag (which relative to everything else is pretty small). Else the physics is the same. This from a page on an old website of mine where I outlined the equations:

Solving for power from speed is not difficult but solving for speed from power requires solving a cubic equation. Doing the algebra is a bit tricky.

For most scenarios (except for steep declines) there is usually a closed form solution using Cardano's method. I have it all set up in a spreadsheet. If Cardano's method is unable to be used then an iterative process via Newton's method does the trick.

For steady state (constant velocity / conditions) it's pretty straightforward.

Once you have changes in velocity then of course it's a dynamic calculation. I would use a forward integration method for that. All doable in a spreadsheet.

 

[decrep]

I was thinking more along the line, that kinetic energy is a function of velocity and mass.
Finding the efficiency of converting that energy into electricity, is just a matter of knowing how many watts go back into the battery.

 

[wattmatters]

I was thinking more along the line, that kinetic energy is a function of velocity and mass.
Finding the efficiency of converting that energy into electricity, is just a matter of knowing how many watts go back into the battery.

Hence my earlier comment:

The only way I can see to get the data are using an OBD reader with high frequency data logger capturing speed and power data while doing controlled decelerations. The deceleration data will tell you the total energy dissipated while the power data will record the amount of regen.

 

[decrep]

Thanks wattmatters, guess we just rely on guess work then.

so how far off do you think 80% could be, you know a +/- number.

 

[MG4JP]

It is even a false economy to use regen going down a hill IF it stops you building up a little more speed to climb up the next hill that is inevitably ahead of you.

It's not even necessary to have a hill ahead, but that's a good example.

I'll add another one.
Imagine a part of a road which is flat, then downhill for a bit, then flat again. Driving speed is 50mph.

Driver #1 has regen set to off/lowest setting and once he gets to the downhill part he removes his foot from the accelerator and lets the car roll freely. The descent makes the car hit, say, 55mph at the bottom of the hill. He keeps his foot off the accelerator for a while longer and gets back to it once the speeds matches the original 50mph and proceeds at this speed.

Driver #2 has regen set to the max setting. Once he reaches the downhill part he lifts his foot just enough to keep the car at the same speed throughout the whole descend (50mph), while regening in the process. Another way to put it is to set the ACC to 50mph and let the car do its thing.

If we measure the energy spend by each driver, between a point before the downhill and a few meters after, the conclusion will be that Driver #2 drove less efficiently than Driver #1 - even after spending the energy he regenerated.

If it's 5% you wouldn't have otherwise, is that to be sneezed at?

But did you benefit from gaining those 5% in the first place? That's the whole point, as explained above.



For the record, I want to make it clear that I'm not saying that regen is a bad thing or that one shouldn't use it; on the contrary. Because in real life and actual traffic we often are forced to brake/stop, it is a blessing to have regen and be able to reuse part of that energy.

I also agree that, because EVs are so much cheaper to run than ICEVs, we should actually be less worried about efficiency (especially in such small amounts as the ones involved in this regen discussion) and just enjoy the benefits of electric driving.

But I also think it is just as important for people to understand that the whole idea of using regen "as much as possible" is not necessarily a good thing (from an efficiency point of view).

 

[decrep]

>>the conclusion will be that Driver #2 drove less efficiently than Driver #1 - even after spending the energy he regenerated. >>>

Agreed, because regen isn't 100% efficient, but if my assumption of 80% is close to the mark, the difference will be minimal.

But if driver #2 does the same as driver#1 and keeps regen to 0 with subtle foot control, then the results will be the same.

So the difference is down to driving style, not regen level set.

One of the reasons I don't use cruise control, it's much more efficient slowing down going up hill and speeding up going down.

 

[Seajays]

So as said there are a lot of factors that effect regeneration performance. One of the major ones is speed at which you start braking - lower speeds regenerate much less (and indeed very slow speeds aren't very efficient at all - they do slow the car down well, but they don't recover much energy!)

For example, this study looked at efficiency of regeneration over three different routes, with different profiles/traffic etc. This table showing the results of one route shows the minimum regeneration, maximum and the "average". As you can see the average efficiency over the journey was about 37% - this was replicated in the other routes, with some variation, but not by huge amounts.

Certainly the maximum regeneration possible in perfect braking condition from a high speed was coming out at just below 80%, but for the most part, it averages just below 40% for the whole journey...

 

[M44LCY]

This is a professional 'economy' / consumption tester.

His test drive of the MG5 FL (no test of MG4 yet) is here:

 

[decrep]

So as said there are a lot of factors that effect regeneration performance. One of the major ones is speed at which you start braking - lower speeds regenerate much less (and indeed very slow speeds aren't very efficient at all - they do slow the car down well, but they don't recover much energy!)

For example, this study looked at efficiency of regeneration over three different routes, with different profiles/traffic etc. This table showing the results of one route shows the minimum regeneration, maximum and the "average". As you can see the average efficiency over the journey was about 37% - this was replicated in the other routes, with some variation, but not by huge amounts.

View attachment 29595

Certainly the maximum regeneration possible in perfect braking condition from a high speed was coming out at just below 80%, but for the most part, it averages just below 40% for the whole journey...

View attachment 29596

I've had a read of that article, and it doesn't make a lot of sense to me.
It doesn't explain, what the "energy losses " are how they come about and vary from route to route. I'm far from being an expert, but I get the feeling they are missing something?

 

[MG4JP]

This is a professional 'economy' / consumption tester.

Even more to the point, he makes reference to a specific video in which he compares OPD (One-Pedal Driving) vs Coasting.

This is the video:


These are the results:

Spoiler: *drum roll*

 

[Seajays]

I've had a read of that article, and it doesn't make a lot of sense to me.
It doesn't explain, what the "energy losses " are how they come about and vary from route to route. I'm far from being an expert, but I get the feeling they are missing something?

They measured the energy recovered by calculating what was put back into the battery, vs the kinetic energy "lost" due to braking of the vehicle:

They were interested in the efficiency, and not specifically in all the ways that the efficiency can be reduced... but there are other papers on that. There are lots of reasons to "slow down" the charge rate from regeneration, current SoC, maximum safe recharge rate of the battery, current battery temperature, mechanical/electromagnetic losses, speed of the motor (slower motor less efficient - even to the point that a very slow motor can actually use energy - though this would be offset by the braking system using friction brakes), braking system decisions on how much "mix" of friction braking might be required etc.

 

[Rolfe]

There are moments when I think this is about as relevant as asking whether your tea will cool down faster if you don't put the milk in until you're ready to drink it.

 

[Seajays]

There are moments when I think this is about as relevant as asking whether your tea will cool down faster if you don't put the milk in until you're ready to drink it.

I think the main takeaway is there's not a single figure such as "regenerative braking recovers 90% of the energy", or anything like that, as there are a myriad of factors at work.

Suffice to say the answer is, "it's complicated", and enjoy the drive. ?