Question about regenerative coasting

[Rothgarr]

As I understand it, the M3 doesn't have regenerative braking, is that correct?

I borrowed a Chevy Bolt for four days and it had both regenerative braking and regenerative coasting. It had a "one pedal mode" where the car would come all the way to a stop without having to use the brakes. (You could set normal and aggressive single-pedal driving)

Does the M3 have settings for how aggressive the regenerative coasting slowdown is? Will it eventually come all the way to a stop? (one pedal driving)

Thanks!

 

[dhrivnak]

Yes the M3 has regenerative braking and you can select low or normal.

 

[mongo]

As I understand it, the M3 doesn't have regenerative braking, is that correct?

I borrowed a Chevy Bolt for four days and it had both regenerative braking and regenerative coasting. It had a "one pedal mode" where the car would come all the way to a stop without having to use the brakes. (You could set normal and aggressive single-pedal driving)

Does the M3 have settings for how aggressive the regenerative coasting slowdown is? Will it eventually come all the way to a stop? (one pedal driving)

Thanks!

All Tesla have regenerative braking controlled by the accelerator pedal. The regen is user configurable between two levels. The regen will not stop the car entirely.

Edit: However, TACC will stop the car if the car in front stops.

 

[JulienW]

Just made a post about it yesterday Here:

Blended regen brakes???

It appears that Tesla doesn't "blend" regen and braking. The way it works is regen is independent of braking. When you let off the accelerator you get full regen. If you push the brake the regen keeps the same amount and you ADD friction braking.

 

[Eno Deb]

It appears that Tesla doesn't "blend" regen and braking. The way it works is regen is independent of braking. When you let off the accelerator you get full regen. If you push the brake the regen keeps the same amount and you ADD friction braking.

Yes, but note that this can be less efficient if you brake hard. Essentially, if you use the friction brake it converts some part of the kinetic energy into heat. If the energy left is smaller than the maximum energy that the motor and battery can absorb via regen braking, you lose energy. A well designed blended brake can be slightly more efficient by never applying the friction brake more than necessary to achieve the braking power intended by the driver.

 

[Darmie]

I have learned to hate coasting in my ICE car. I would love to own 2 Tesla's but if there is one car that I need to drive in and out of construction site, it will be the $6,000 ford fiesta. Talk about no power, but hate when I have to coast coast and use the brakes.

 

[Saghost]

As I understand it, the M3 doesn't have regenerative braking, is that correct?

I borrowed a Chevy Bolt for four days and it had both regenerative braking and regenerative coasting. It had a "one pedal mode" where the car would come all the way to a stop without having to use the brakes. (You could set normal and aggressive single-pedal driving)

Does the M3 have settings for how aggressive the regenerative coasting slowdown is? Will it eventually come all the way to a stop? (one pedal driving)

Thanks!

Tesla gives you two strength options, Normal and Low. You can of course vary the car's deceleration rate by controlling the pedal.

Because of the motor designs Tesla chose, they cannot regen to a complete stop, and unlike some others they won't use the friction brakes to simulate it. You do have to switch to the brake pedal for the last couple mph.

 

[JulienW]

I have learned to hate coasting in my ICE car....

Pre Tesla but had an ELR. Needed to borrow my bosses SUV to move something (ELR terrible space/hauling/trunk opening). Almost freaked the first time I lifted off the accelerator. Thought it was speeding up.

 

[mongo]

Tesla gives you two strength options, Normal and Low. You can of course vary the car's deceleration rate by controlling the pedal.

Because of the motor designs Tesla chose, they cannot regen to a complete stop, and unlike some others they won't use the friction brakes to simulate it. You do have to switch to the brake pedal for the last couple mph.

Do the other cars really harvest energy at the low speeds, or just run the motor in negative (braking) torque mode?
Tesla can stop the car using the existing motors like other cars (at least with the 3 rear motor, the AC induction would be trickier), it just isn't energy efficient.

 

[JulienW]

Do the other cars really harvest energy at the low speeds, or just run the motor in negative (braking) torque mode?
Tesla can stop the car using the existing motors like other cars (at least with the 3 rear motor, the AC induction would be trickier), it just isn't energy efficient.

Any electric motor running in "reverse" by FORCE is a generator. So what would you not harvest this "free" energy.

EDIT: Just to add I had an ELR and it regened up until the point "creep" kicked in.

 

[Saghost]

Do the other cars really harvest energy at the low speeds, or just run the motor in negative (braking) torque mode?
Tesla can stop the car using the existing motors like other cars (at least with the 3 rear motor, the AC induction would be trickier), it just isn't energy efficient.

PMSR isn't much like the PMAC motors used by most of the rest; it's actually switched reluctance with a few permanent magnets added to the stator as additional poles to smooth things out.

I'm not sure if they actually harvest energy at the bottom end, but the energy remaining in the car is insignificant.

I'd have to look for it, but I remember reading that one of the early cars to come to a complete stop under regen was actually using the friction brakes at the end, even without you pushing the pedal. Tesla could certainly do that if it seemed like a good idea.

 

[mongo]

Any electric motor running in "reverse" by FORCE is a generator. So what would you not harvest this "free" energy.

Back-EMF is proportional to speed. That is why you can short a brushed DC motor and spin it at slow speeds fairly easily, but at higher RPM, it is harder to turn. Available kinetic energy is proportional to the square of the vehicle velocity. Combining these two things makes low speed regen less of a net gain scenario, and more of just the motor as a brake. You need large currents to work with the low back-EMF and there is not much to be recaptured.

PMSR isn't much like the PMAC motors used by most of the rest; it's actually switched reluctance with a few permanent magnets added to the stator as additional poles to smooth things out.

Right, the big factor I was thinking of is that the PMSR has an absolute phase encoder versus just rotational so it can detect direction of motion and know when the car is stopped (versus overshooting stopped and going into reverse, like on a hill)

I'm not sure if they actually harvest energy at the bottom end, but the energy remaining in the car is insignificant.

Agreed.

I'd have to look for it, but I remember reading that one of the early cars to come to a complete stop under regen was actually using the friction brakes at the end, even without you pushing the pedal. Tesla could certainly do that if it seemed like a good idea.

I'm not a fan of that level of one pedal, but they can. One maker just had a recall due to the software not handling the blending properly.

 

[Saghost]

Back-EMF is proportional to speed. That is why you can short a brushed DC motor and spin it at slow speeds fairly easily, but at higher RPM, it is harder to turn. Available kinetic energy is proportional to the square of the vehicle velocity. Combining these two things makes low speed regen less of a net gain scenario, and more of just the motor as a brake. You need large currents to work with the low back-EMF and there is not much to be recaptured.



Right, the big factor I was thinking of is that the PMSR has an absolute phase encoder versus just rotational so it can detect direction of motion and know when the car is stopped (versus overshooting stopped and going into reverse, like on a hill)


Agreed.


I'm not a fan of that level of one pedal, but they can. One maker just had a recall due to the software not handling the blending properly.

A valid point. If I'm not going to be able to get useful energy out anyway, I'd rather have it just use the friction brakes and transition to vehicle hold at the end.

I'm of mixed minds about that as a feature. Vehicle hold I love, and having the car drop right into it is convenient and prevents mistakes.

As it stands, I often regen a little early and use the free float at the end to get to the stop line before hitting the brakes, but I imagine I'd get used to feathering off the regen a bit to get to the line as it hits the brakes.

 

[azred]

While regenerative braking is much like any other car that has it, you cannot totally stop without lightly applying the brakes at the very end of braking. (When on traffic assisted cruise or autopilot the braking seems somewhat late and aggressive, so I suspect more than regenerative braking is involved.)

 

[Bill Price]

While regenerative braking is much like any other car that has it, you cannot totally stop without lightly applying the brakes at the very end of braking. (When on traffic assisted cruise or autopilot the braking seems somewhat late and aggressive, so I suspect more than regenerative braking is involved.)

I owned two Lexus hybrids before taking delivery of my Tesla. They BOTH had regenerative braking and regenerative coasting. The regen on coasting was much like the low setting on the Tesla. EVERY time you put your foot on the brake you were enabling regenerative charging except when you REALLY had to step on the brake which would then go past the regen and apply standard brakes. At the very end of braking during a normal drive with the Lexus hybrid system, you were still regenerating. Lexus techs told me that at the point where regen stops and braking actually begins, you almost have to be in an emergency brake situation. So normal braking with that system is always providing regen. Brake pad replacement or rotor turning with hybrids was like finding a unicorn according to the Lexus techs. Wish Tesla was designed that way.

 

[Saghost]

I owned two Lexus hybrids before taking delivery of my Tesla. They BOTH had regenerative braking and regenerative coasting. The regen on coasting was much like the low setting on the Tesla. EVERY time you put your foot on the brake you were enabling regenerative charging except when you REALLY had to step on the brake which would then go past the regen and apply standard brakes. At the very end of braking during a normal drive with the Lexus hybrid system, you were still regenerating. Lexus techs told me that at the point where regen stops and braking actually begins, you almost have to be in an emergency brake situation. So normal braking with that system is always providing regen. Brake pad replacement or rotor turning with hybrids was like finding a unicorn according to the Lexus techs. Wish Tesla was designed that way.

Lexus tech told you wrong. HSD cars are limited to about half the regen a Tesla generates. Anything more than that is using the friction brakes.

I've driven quite a few cars with blended brakes, and I've never had one feel completely natural. I've also never had one where you could easily tell when you started using the pads.

I like Tesla's approach better. The brakes are tight and natural, and I can easily choose whether to use friction brakes on any given deceleration.