Mountains and steep downhills

[MikeK]

No one on the planet has been able to make regen on the brake pedal work properly. There is always a jerk when the car transitions from regen to friction brakes.

I'm going to disagree with you there. My 2002 Toyota RAV4-EV has blended regen on the brake pedal, and it is utterly seamless. If you hook up the "RAV4 Info" Palm Pilot app to the OBD-II port, you can display two indicators showing the hydraulic pressure to the brakes and the regenerative current, and watch the hydraulic pressure ramp up smoothly as the available regen torque ramps down.

It has been a long time since I had my EV-1, but my recollection is that it was also well blended.

 

[jerry33]

I'm going to disagree with you there. My 2002 Toyota RAV4-EV has blended regen on the brake pedal, and it is utterly seamless. If you hook up the "RAV4 Info" Palm Pilot app to the OBD-II port, you can display two indicators showing the hydraulic pressure to the brakes and the regenerative current, and watch the hydraulic pressure ramp up smoothly as the available regen torque ramps down.

It has been a long time since I had my EV-1, but my recollection is that it was also well blended.

There is nothing wrong with the blending on my 2004 Prius either.

 

[smorgasbord]

There is nothing wrong with the blending on my 2004 Prius either.

Hmm. Goggle for "Prius brake feel" and you come up with a lot of complaints.

 

[Cottonwood]

Hmm. Goggle for "Prius brake feel" and you come up with a lot of complaints.

Me included, owning a 2001, 2002, and 2005 Prius, there was always a small, but annoying transition from regen to friction. I only owned Gen II and III Prii, but it does exist in those.

I far prefer the Tesla approach than trying to pretend the car is something that it is not.

 

[jerry33]

Hmm. Goggle for "Prius brake feel" and you come up with a lot of complaints.

You'll find almost all of those are with brand new cars. After the car has a few miles on it, it becomes very hard to feel and most of the time (like 99%) I can't feel it at all. At least that's what I found. I suppose there are individual differences between cars.

 

[SteveH]

I agree with Jerry33. It may by that I'm just not sensitive to it, but I've been reading those reviews for years and trying to feel it with my 2006 Prius. Sometime I can and sometimes I can't, but only if I'm really paying attention. During normal driving I don't notice the transition at all.

 

[richkae]

Me included, owning a 2001, 2002, and 2005 Prius, there was always a small, but annoying transition from regen to friction. I only owned Gen II and III Prii, but it does exist in those.

I far prefer the Tesla approach than trying to pretend the car is something that it is not.

I have always hated that there is no easy way to tell the difference between regen and friction in the Prius.
So glad I don't drive it anymore.

 

[Accentcreate]

The brake pedal activates friction brakes only. Regen is entirely connected to the accelerator. Most seem to like this setup.

You can easily exceed the maximum allowable regen on a downhill slope (even one that's not steep), so increasing regen to maintain speed would be impossible. (Well, not impossible but inadvisable). The amount of regen is limited by the rate at which the battery can be recharged without damage. This limits the amount of regen braking force that can be achieved.

So. does having the dual-motor option increase the available regen braking? I've been a manual driver for 50 years, so hitting the brake pedal is not in my DNA.

 

[mblakele]

So. does having the dual-motor option increase the available regen braking? I've been a manual driver for 50 years, so hitting the brake pedal is not in my DNA.

Wow, a thread from 2012, brought back from the dead and walking among us

Tesla doesn't seem to publish regen specs. Reportedly max regen is around 60-70 kW. Maybe you can turn than into braking force and decide if it's enough. To me, Model S 90D regen feels much like engine braking, and I've rarely touched the brakes when driving mountain roads around here. That includes some pretty steep grades in the Sierra Nevadas.

New skills to learn: there are no gears, so you have to learn to manage the accelerator when you want less than full regen.

 

[Accentcreate]

Wow, a thread from 2012, brought back from the dead and walking among us

Tesla doesn't seem to publish regen specs. Reportedly max regen is around 60-70 kW. Maybe you can turn than into braking force and decide if it's enough. To me, Model S 90D regen feels much like engine braking, and I've rarely touched the brakes when driving mountain roads around here. That includes some pretty steep grades in the Sierra Nevadas.

New skills to learn: there are no gears, so you have to learn to manage the accelerator when you want less than full regen.

Sounds like fun! I'll be waiting a while for my M3, so plenty of time to decide whether single or dual motors. Glad to revive the thread. I was just googling info on regen.

 

[whttiger25]

The main issue here could be that a motor-generator system is capable of handling a much higher electric INPUT than it can OUTPUT as long as the motor is powering something that is producing resistance to the rotation when it is receiving energy and this resistance is greater than the maximum electromagnetic the resistance the motor can produce as a generator. This is because the RPM on the output (power input) is limited by the torque the engine is applying to the system, i.e. propelling the car up a hill, while when the motor is generating power, the only torque available to generate power against is created by the electromagnetic fields of the magnets, presumably a much smaller than the weight of the car etc.

If you applied the max power that the motor can handle without a torque to resist the rotation, the motors would exceed their maximum rotation speed and fail. Not accounting for lots of variables, this is the speed you would need to achieve to generate the same power. To generate the maximum power that the batteries could absorb while warm, say 120kw, the motors would have to be spinning much faster than they currently are. The gear ratios are optimized for acceleration and energy efficiency, and since they are fixed, they cannot be adjusted to increase the generation RPM of the motors and thus generate more energy when regen braking.

I have never tried regen braking from 150mph, in theory you would be able to achieve much higher power, but I assume that Tesla has placed limitations on actual regen power to keep the system stable or within safe bounds for the components involved, which are likely separate from supercharger components that can handle higher currents. Clearly they have an algorithm that limits regen at high speeds for reasons unknown to me, but I suspect that at normal highway speeds, regen is maximized.

This is why the max output power is 250+kw, but the max regen is about 50-70kw. It's either a limitation of the components that handle regen current, or a limit on the actual regenerative capacity of the motors at RPMs highway speeds can provide, or a combination of both. My experience is that I can achieve max regen probably around 40mph, indicating that regen at speeds higher than this are limited by the battery and current limitations on regen components. It's also possible Tesla wants to closely control the regen experience, they don't want it to be too strong. That could pose safety or ride quality issues.

Who knows, lots of possibilities!

 

[GatorGuy]

So. does having the dual-motor option increase the available regen braking? I've been a manual driver for 50 years, so hitting the brake pedal is not in my DNA.

Regen can slow the car by itself, without brakes to about 5 mph. You need brakes to bring it to a complete stop. Very similar to downshifting but smooth.

 

[lymex2018]

I believe X and S behave the same as far as regen and downhill are concerned.

There are two (may be more) factors for limiting the max regen power, which are extreme low/hi temperature and near full charge state of the battery. Apart from these. The max regen power of my car is 100kW according to Scan my Tesla.

1. The regen power when letting the acceleration pedal up varies according to the speed. Normally the faster the more regen.
2. The regen power when letting the acceleration pedal up depends also the setting: "Regenerative braking" in "Driving" control.
3. Regen power is usually below the max regen power limit especially the speed is not fast when let the acceleration pedal up. In this case, touch the brake pedal slightly won't invoke the friction brake but increase the regen power. Therefore, touching of the brake pedal on the Tesla S DOES increase the regenerative charging if the max regen power is not reached.
4. If the aim is not to waste the potential energy on the friction brake, then keep the speed low so that the regen power is reasonably smaller than the max regen power.
5. If the aim is to charge the battery as much as possible, then there is a trade off of speed between the air fiction and the regen power: the total regen energy became large while the speed increase because of more efficiency of the motor (now generator), but the air drag also increase much faster/larger with the speed.

There is a Bjorn's video describing a downhill contest of EV's where the lease consumption/most gain wins. In the end, he won it with a large margin. And one of his strategy is "not touch the brake" (at 00:02:43). What I regard this is not let the friction brake kicks in.

 

[Rocky_H]

Regen power is usually below the max regen power limit especially the speed is not fast when let the acceleration pedal up. In this case, touch the brake pedal slightly won't invoke the friction brake but increase the regen power. Therefore, touching of the brake pedal on the Tesla S DOES increase the regenerative charging if the max regen power is not reached.

That has never been the case, and I'm pretty sure it's still not the case. That is what all of the hybrid cars do, which is kind of annoying. Tesla has never put any portion of regen activated by the brake pedal. It's all in how far you pull your foot back off the accelerator.

 

[Snowstorm]

Therefore, touching of the brake pedal on the Tesla S DOES increase the regenerative charging if the max regen power is not reached.

That is not true.
Tesla completely separates friction and regen brake. Touching the brake paddle only activates the friction brake, and does nothing for regen