Why regenerative braking belongs on the brake pedal

[insaneoctane]

Yes they are expensive, as they hardly used in the industry, for now.
Buy the best ultracapacitors and supercapacitors online

It appears voltage might be a slight problem as supercaps are around 2.8V each.
Regular EV would therefore need 140 of them in series. It looks like on chain is
more than enough.

That's like $8K?

 

[EVDRVN]

I am amazed that we have 23 pages discussing regen should be on the brake pedal. For all of you that want regen on the brake pedal, buy a hybrid. It is doubtful that anyone agreeing with this probably does not own a Tesla. If you own one, please sell it and buy a hybrid so you can get regen where you want it.

I will stop watching this thread since it is never going to happen. Tesla has the regen where it needs to be.

Agree. I drove the first Tesla drive prototype ever build with 0-100% regen and IMO there needs to be an option for even more regen off pedal on the accelerator. I find that most people that advocate strongly for brake regen are hyper miler types or those that will not accept something new. If I want to coast in my EV I can do it now.

 

[apsen]

That's actually a very good point for what one advantage of regen on brake is. Appropriately engineered, it can handle the necessity for reduced regen transparently. A minor quibble, but valid.

Tesla could have still used regen to brake - just dump excess electricity that it cannot use into a resistor. In cold weather that could even be used to warm up the battery.

EDIT: Oh, yea, you could also use that electricity to run AC to cool it too. Although that would be trickier.

 

[RossBrindleyAU]

I am 64 and have been racing since my 20's. I have experienced every example used by OP and am totally familiar with controlling all of the issues raised. My racing has mainly been tarmac rally with lots of club sprints and a few circuit races. My experience includes rallies such as Targa Tasmania and Targa New Zealand. Being an old school, seat of the pants, driver I have NEVER used pace notes as I prefer to read the road and react to what I come across as it is happening. I have placed 3rd & 10th outright in Targa Tasmania and 4th outright in Targa New Zealand. I am not boasting here, I simply want people to understand that I DO have expertise in very high performance driving.

I took my P85D (FIRST TESLA) for a seriously hard run through the mountains soon after I purchased it and well before I became totally familiar with the regen on accelerator. Not once did the car do ANYTHING unexpected. It was a revelation to me that the car was so neutral under braking, acceleration and cornering. My car has air suspension and of course 4 wheel drive (D) so my experience may vary with RWD models, but I highly doubt it.

I adore the regen on accelerator and get great pleasure during normal driving from picking the point I need to fully back-off so as to be almost completely stopped where I need to be, without using the brakes until the last couple of metres/yards..

 

[JBT66]

I absolutely love regen on the accelerator. That is all.

 

[apsen]

I have had Autopilot scare me by maintaining speed into a traffic jam too far before hitting the regen.

Adjust the following distance of the autopilot to comfortable one so that it will start braking before you'd want to use the brakes yourself.

I have been in situation where autopilot's late braking caused me to tense up at first but I have been happy since I've adjusted that setting.

 

[drj3]

Forgive me if this has been brought up somewhere between page 5 and 24 (I skipped to the end), but every decision made in the design of a car has trade offs. The OP's article mentions a risk of oversteer from on throttle regen, but fails to note a safety advantage from throttle regen. In panic braking, the car will start significant deceleration during the fraction of a second as the foot is moved from the throttle to the brake. (I experienced this myself when someone unexpectedly pulled out in front of me.) From a safety standpoint, panic braking is far more common than someone getting loose from coming off the throttle in a corner. So the added safety benefit of quicker a quicker panic stop (a more common experience) would outweigh the disadvantage of potential oversteer (much less common). Where the OP does have a point when it comes to safety is the change in handling when regen is limited due to cold or full battery. Tesla does mitigate this risk by displaying a warning when regen is limited, and applying the brakes is a natural instinct when the car does not slow as expected. So I don't see this as a major issue.

Having driven cars with both implementations (Fusion Energi and Model 3), I prefer regen on the throttle.

 

[SDRick]

I love the current set up and one pedal driving.

Unfortunately, within 20 years or so, most of us will have no pedal driving as the only option.

 

[jgs]

Tesla could have still used regen to brake - just dump excess electricity that it cannot use into a resistor. In cold weather that could even be used to warm up the battery.

EDIT: Oh, yea, you could also use that electricity to run AC to cool it too. Although that would be trickier.

The idea of dumping excess to a resistor comes up now and then and it used to sound pretty compelling to me. It doesn't any more for a couple reasons --

First, a resistor is just a heater of course, and for anything more than a trivial amount of braking would need to be cooled itself to prevent it burning out. So now we have a radiator and fan and whatnot to cool our resistor. But wait, we still also have friction brakes, we can't get rid of those because for one thing they work even if the car electronics are completely dead. So now we have two systems that both take kinetic energy and throw it away as heat. One of the systems we had to have no matter what. The other represents excess weight, cost and complexity.

Second, although it seems attractive to have the car handle the same in all conditions, I care about the energy efficiency of my driving. So for me, there is some benefit to having only as much regen as the car can productively use, because it means I can adjust my driving behavior to suit the conditions. If I want more deceleration, I can always use the brake pedal.

 

[Electroman]

Here is an idea.. have a 0.5 kWh (or maybe even less) battery just to store the excess regen power, and that
will be drained in the next few minutes for either heating the battery or cooling the battery depending on the ambient temperature.

So you will have this battery always empty ready to take the excess power, but not used for propulsion. This battery will degrade and is to be treated as a wear&tear item to be replaced every year. How much does a 0.5kWh battery cost? less than $100?

[I will take my Nobel prize money in cashiers check please]

 

[Lon12]

Here is an idea.. have a 0.5 kWh (or maybe even less) battery just to store the excess regen power, and that
will be drained in the next few minutes for either heating the battery or cooling the battery depending on the ambient temperature.

So you will have this battery always empty ready to take the excess power, but not used for propulsion. This battery will degrade and is to be treated as a wear&tear item to be replaced every year. How much does a 0.5kWh battery cost? less than $100?

[I will take my Nobel prize money in cashiers check please]

So you're saying to put in a battery heater as well?

 

[apsen]

The idea of dumping excess to a resistor comes up now and then and it used to sound pretty compelling to me. It doesn't any more for a couple reasons --

First, a resistor is just a heater of course, and for anything more than a trivial amount of braking would need to be cooled itself to prevent it burning out. So now we have a radiator and fan and whatnot to cool our resistor. But wait, we still also have friction brakes, we can't get rid of those because for one thing they work even if the car electronics are completely dead. So now we have two systems that both take kinetic energy and throw it away as heat. One of the systems we had to have no matter what. The other represents excess weight, cost and complexity.

Second, although it seems attractive to have the car handle the same in all conditions, I care about the energy efficiency of my driving. So for me, there is some benefit to having only as much regen as the car can productively use, because it means I can adjust my driving behavior to suit the conditions. If I want more deceleration, I can always use the brake pedal.

You only need to deal with cooling that resistor if the regeneration is limited. If you do not want to add much in terms of complexity just take care of cold end of the range. This way you do not need to add much - just use the battery heater. This is already present in S/X so at least on those it should be possible to do via a firmware. This is of course is more of an issue for 3 as it doesn't have a heater and you cannot precondition the battery and BTW that decision is puzzling for me...

I did not own Tesla long enough to experience the limited regeneration due to heat so I'm not sure how severe it gets but on cold side you may not have any regen at all. If this is quite problematic on the hot side you could use existing battery cooling system. So if you are already running an AC to cool the battery use portion of the produced electricity to help run AC and dump the rest of the heat into the cooling loop of it. Depending on the severity of the problem you may still need to limit the regeneration later on or you could opt for bigger AC. This side of equation does add complexity but I do not think it is a huge one on the physical side of things and most of it would be in the form of software managing it. But if I am mistaken and it is indeed something that would add significant in cost or complexity just fix it on the cold side - that would be an improvement already.

 

[stonelance]

This is an old thread and i haven't read the whole thing, but I have a couple reasons i wish the regen was not on the accelerator, but it doesn't come down to safety or efficiency. For me it is about comfort.

I have an injury on my right foot, and have found in the several months since I bought my Model 3 it is now extremely difficult to make my 30 minute commute without my foot being in significant discomfort by the end. I think the accelerator regen, combined with the fairly strong force needed on the pedal, and the low clearance between the accelerator and the center console area makes it so I need to keep constant fairly strong pressure on the right side of my foot which is the worst for me. I never had issues when i drove a manual. I find it hard to even adjust my foot on the pedal since I can't even take my foot off for a second without the car significantly slowing down. I am basically forced into using EAP to try to avoid having to keep my foot on the pedal, but my route which has a lot of entering and leaving traffic, and traffic lights makes EAP pretty annoying to use. I'm seriously considering switching to low regen, but it makes me sad to lose out on that efficiency. I wish there was an option to move at least some of the regen to the brake pedal instead, so I still have the option to coast without pressure on my foot.

 

[apsen]

Excellent post! I agree. I had many problems with the Tesla Model S regeneration on accelerator:

• My foot would get tired when I wanted to let the car coast but I had to keep my foot on the pedal to do so, nursing its speed in a herky jerky way to do so, further exacerbating my pains. My factory computer chip controlled Mercedes never ever did that to me, and was sublimely wonderful.

You seem to be arguing for and have no problem paying extra for complex expensive systems so why wouldn't you buy enhanced autopilot?

 

[apsen]

But actually, Tesla's battery can regen at much higher rates, of at least 100-120kW. It's just software that limits it. And the limit is there as there is no blending on Tesla's. Tesla couldn't allow 120kW regen with all pedals released. Like I said, no adjustability and no blending.

I do not think that is inability of battery to accept that rate but the degradation from huge number of short high current bursts. If you will charge extensively at superchargers your charging rate will eventually be limited to protect battery life. This kind of regenerative usage will degrade battery much faster than superchargers.

 

[StealthP3D]

Here is an idea.. have a 0.5 kWh (or maybe even less) battery just to store the excess regen power, and that
will be drained in the next few minutes for either heating the battery or cooling the battery depending on the ambient temperature.

That is an unrealistic/unworkable solution. A battery that small cannot take the charge rate of the regen energy from even one stop from 60 mph. You need more batteries to absorb that much energy, that quickly.

But to stick to the topic at hand, I'm glad Tesla couples regen to the accelerator and that's coming from an experienced motorcyclist who is accustomed to having independent control of the front/rear brake bias by using the front brake hand lever and the rear brake foot lever. I've driven my P3D in a sporting manner on curvy snowy mountain roads and regen on accel is awesome. I've driven quite a few FWD cars in the snow so I am accustomed to using light throttle application to maintain my line through slippery corners and this works well with regen coupled to the accelerator also. It gives me more instantaneous control and I don't have to use both feet (aka left foot braking). It does require a small amount of retraining to use at it's highest potential but that is true of most things in life.

 

[jgs]

You only need to deal with cooling that resistor if the regeneration is limited. If you do not want to add much in terms of complexity just take care of cold end of the range. This way you do not need to add much - just use the battery heater.

The pack heater is 6 kW. Max regen is 60 kW. Even if the power electronics are laid out such that it’s physically possible to dump the power directly into the pack heater without being routed through the battery, you’re not going to get full regen braking feel out of it. Still true if you add in the cabin heater (which has its own problems besides). I mean, an extra 6 kW of braking isn’t nothing, I wouldn’t mind it, but it’s no game-changer.

I imagine driving the AC compressor off of regen is a non-starter. It’s a mechanical system, bursty power would probably not be kind to it.

 

[apsen]

The pack heater is 6 kW. Max regen is 60 kW. Even if the power electronics are laid out such that it’s physically possible to dump the power directly into the pack heater without being routed through the battery, you’re not going to get full regen braking feel out of it. Still true if you add in the cabin heater (which has its own problems besides). I mean, an extra 6 kW of braking isn’t nothing, I wouldn’t mind it, but it’s no game-changer.

I imagine driving the AC compressor off of regen is a non-starter. It’s a mechanical system, bursty power would probably not be kind to it.

For the AC the power would definitely would need to be smoothed and heating/cooling is also not instantaneous so that does some buffering too. The question is whether you could devise some software control to be able to handle that. But even at 6 vs 60 KW ratio that should kill it too not to mention the AC being more efficient so the ratio would be even more.

Though on the other end often you do not need to dump the full 60 kW into heater but it is indeed most useful when you do... Come to think about it if the heater could only consume 10% of full regen the car may already be doing it - it is just not really noticeable... We need bigger heater

 

[StealthP3D]

Come to think about it if the heater could only consume 10% of full regen the car may already be doing it - it is just not really noticeable...

This is a good point and I think turning the cabin heater on full heat does allow a small amount of additional regen when regen is limited by the battery's temperature or state of charge.

I base this on the fact that the power/regen bar graph reflects climate control consumption. To see how this works, coast down a hill in neutral and turn the heater on high. You will see consumption indicated. Previously, I was under the impression the bar graph only reflected MOTOR regen or consumption. I now realize it is BATTERY regen or consumption.

 

[Ulmo]

You seem to be arguing for and have no problem paying extra for complex expensive systems so why wouldn't you buy enhanced autopilot?

When it drops in price, I'll gladly own it. All three of my Mercedes were used and cheap.