Why regenerative braking belongs on the brake pedal

[insaneoctane]

I'm guessing the expense & complexity are a deterrent. Let us assume that you want a capacitor to store a few stops before it rids it's charge to either the motor or the battery. If you want to take 150kW regenerative charge for 10 seconds just once, you would need a 25 farad capacitor. If you wanted to store that, say, 5 times, you are up to 125 farads. That sounds like some expensive caps to me ... But, I'm a mechanical guy, so here is my math:

150,000W*(1hr/60min)*(1min/60sec)*(10sec)=416.7Wh
416.7Wh*(3600J/1Wh)=1.5MJ
1.5E6J*2/(350V^2)=24.5 Farads

 

[arnis]

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.

 

[S100D]

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.

 

[Johann Koeber]

Thanks for the informative post.

After reading it and thinking about it: NO - I like it as it is.

If need be: make it an option in the settings.

 

[nvx1977]

Bjorn did a video that showed how much energy he could save by going into neutral for hills as opposed to doing the regen-re-accelerate mess. It was a lot, and saved a lot of wear and tear, adding miles he could travel.

Can you or anyone else post a link to the vid? Sounds interesting to me. Wasn't able to find it.

 

[mongo]

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.

Ultra caps have a resistance limitation
Are you refering to these?
SCA3200 3200 F 2.85 V 0.09 mOhm
140 of those in a string would be a
399 V ,22.8 F, 12.6 ohm string
Max current you could put in with a 400V BEMF from motor would be (400-0)/12.6= 31.75 amps, or 12.7 kW.

You also have the issue of motor control. Either you add a second multi-kW power converter or you size the capacitor bank to keep its voltage inline with the lithium pack (cap bank woukd have low enough ESR to prevent pack overcharge rate). If that route is chosen, you only get the energy storage in the small delta voltage you move within.

 

[arnis]

Ultra caps have a resistance limitation

Resistance is the one thing supercaps DON'T have

0,09mOhm*140=12,6mOhm=0,0126Ohm

 

[mongo]

Resistance is the one thing supercaps DON'T have

0,09mOhm*140=12,6mOhm=0,0126Ohm

Doh, double unit-ed myself. You're right by 3 orders of magnitude.

 

[Jim R]

Forgive me for not reading through 23 pages of comments if my comment is a repeat of someone else. And I have zero experience driving cars with regen.

The main argument the OP makes is about understeer. Surely modern cars are equipped with anti-skid systems that react to a loss of traction on any wheel and seek to straighten the car through opposite wheel braking. Wouldn't this negate the problem?

 

[mongo]

Forgive me for not reading through 23 pages of comments if my comment is a repeat of someone else. And I have zero experience driving cars with regen.

The main argument the OP makes is about understeer. Surely modern cars are equipped with anti-skid systems that react to a loss of traction on any wheel and seek to straighten the car through opposite wheel braking. Wouldn't this negate the problem?

Understeer occurs without locking up any of the wheel/ loss of rotational traction. Rather, the rear wheels push the front ones forward fighting the front ones trying to push the nose sideways.To a pure ABS, the front wheels might look to be spinning slower than rear due to effective angle, but its only recourse at that point is to brake less.

A stability control system can compare yaw rate with steering angle and use braking on the inside rear wheel to assist.

The Roadster 2020 has dual rear motors with torque vectoring which will be able to manage under/over steer.

 

[nvx1977]

Forgive me for not reading through 23 pages of comments if my comment is a repeat of someone else. And I have zero experience driving cars with regen.

The main argument the OP makes is about understeer. Surely modern cars are equipped with anti-skid systems that react to a loss of traction on any wheel and seek to straighten the car through opposite wheel braking. Wouldn't this negate the problem?

I think you meant oversteer (rear of the car slips sideways). Instinctively for inexperienced drivers, in both understeer (car skids forward despite hard turn of the wheel) and oversteer conditions, the reaction is to slow down. That is the correct reaction for understeer but not for oversteer. Letting go of the accelerator is an act of slowing down (countering the human factors argument the OP tried to make regarding pedal function), so putting regen on the accelerator makes slowing down even more pronounced, and thereby making the oversteer condition worse for inexperienced drivers.

The OP's post that he linked to was enlightening for me because in my RWD Model S, the only deficiency I felt in handling/traction control was preventing oversteer. Going up a hill, no problem because I'm applying throttle. It's crazy how well EV RWD handles snowy uphills compared to ICE RWD. But going downhill on a snowy hill, it's very easy for the car to start oversteering (fishtailing) due to deceleration. And that's a tough place to be. To recover you have to apply some throttle, and doing so on a decline means you pick up more speed, which you really don't want in snowy or slick conditions. You do need to be careful how much regen you let the car provide in those situations. That's where winter tires really help.

After reading the OP's linked post, I went out and deliberately created some oversteer conditions while there was tons of snow and slush on the road. Indeed, applying a bit of throttle the instant you feel the slippage in the rear causes the rear to instantly snap back in place. For that aspect of his post, I'm grateful. I think we ought to be improving our driving skills constantly and not always be reliant on traction systems. But I wasn't very convinced by the OP's arguments for putting regen on the brakes otherwise.

 

[AZ Desert Driver]

I've been driving my AWD MS for about 1.5 years. I am a long way shy of being an expert one-pedal driver. I find I often default to slowing toward a traffic light by touching the brake pedal. I have had Autopilot scare me by maintaining speed into a traffic jam too far before hitting the regen.
Can someone offer a good training method to get to be a better one-pedal driver?

 

[Mickie]

I haven't read through 23 pages, or even past the title. But you'll pull my 1-pedal driving from my cold, dead hands.

 

[Johann Koeber]

Upon more thought, I would even consider a one footed driving. Apply the brakes when the pedal is not pressed at all.
This would be similar to a joystick. Save one pedal. Drive and brake with one foot.

Sure needs getting used to, but is simpler than two pedal setups. Remember the clutch pedal - we got rid of that one long ago.

 

[SDRick]

Can someone offer a good training method to get to be a better one-pedal driver?

Look farther down the road while driving. There is really no need to use the brake in normal driving. Looking a little bit farther down the road you'll find it becomes easier to anticipate when and how much you need to slow down.

To me, the Tesla system is so intuitive I was comfortable with one pedal driving after one or two days.

 

[Stretch2727]

One pedal driving is a huge hidden advantage to EV's. I really miss it when I have to drive an ICE.

With most automatic ICE cars today they really freewheel with almost no engine braking. I believe this is to improve gas mileage. The disadvantage you are constantly on the brakes in around town driving.

 

[malcolm]

But you'll pull my 1-pedal driving from my cold, dead hands.

Foot.

Plus IIRC Tesla offers two levels of regen, selectable from the menu.

Is the lighter option better when driving downhill in heavy snow? Or is it not light enough?

 

[mongo]

Upon more thought, I would even consider a one footed driving. Apply the brakes when the pedal is not pressed at all.
This would be similar to a joystick. Save one pedal. Drive and brake with one foot.

Sure needs getting used to, but is simpler than two pedal setups. Remember the clutch pedal - we got rid of that one long ago.

Youch, full braking on no accelerator?

I liked my clutch pedal, press it and instant zero motor torque. Also handy getting unstuck, harder to rock an automatic.

 

[Icer]

Why not some way to switch it?

 

[Mickie]

Foot.

Plus IIRC Tesla offers two levels of regen, selectable from the menu.

Is the lighter option better when driving downhill in heavy snow? Or is it not light enough?

Foot. Well played! Zero experience with inclement downhill driving. Live in the flattest State of the union...

There are two levels though, Low and Standard. I’d definitely think you’d want it in Low for your scenario, especially after reading someone having a rear end collision due to regen causing a slide. Or until EM discovers how to cheat physics.