How was increased regenerative braking achieved with 8.0?

[David99]

Don't mix { cruise control, stability / traction control, standing water }. On my RWD P85, the experience (I-90 east towards Ellensburg) is ... unsettling.

cruise control and standing water is a very dangerous combination. The standing water causes the car to slow down and cruise control tries to compensate for it with lots of throttle. Of course having the front wheels slow down the car strongly (standing water) and the rear wheels push hard is a very dangerous combo. Has nothing to do with regen, though.

 

[brianman]

cruise control and standing water is a very dangerous combination. The standing water causes the car to slow down and cruise control tries to compensate for it with lots of throttle. Of course having the front wheels slow down the car strongly (standing water) and the rear wheels push hard is a very dangerous combo. Has nothing to do with regen, though.

I disagree. I've never experienced this problem in another vehicle and, as such, expect that if there was a way to disable regen completely (i.e. "Off" rather than "Low") the experience would be more comfortable for the driver.

 

[isaax]

In my few days driving with 8.0, I notice a difference in my RWD 70 between it and 7.1 when coming to a stop in city driving. I remember 7.1 would slow me down to about 5-6 mph then continue at that speed (requiring me to always hit the brake pedal), but it seems like 8.0 slows me down a tiny bit faster then, instead of keeping at 5-6 mph, it more slowly takes me to 1 mph. Not sure if others are seeing this, too.

I had the exact same observations from my RWD 70 as well. I love it.

 

[rfmurphy81]

I had the exact same observations from my RWD 70 as well. I love it.

Honestly, though, I'd prefer it if the regenerative braking were able to bring the car to 0 mph consistently so one could truly do one pedal braking. The fact that it slows down to 5-6 mph then keeps going a bit more before slowing to 0 (or close to 0) just means more movement between accelerator and brake pedals.

 

[RogerHScott]

People complain all the time about releases reducing regen, and people always say it's all in their head, I suspect that's because each change is so little that it's hard to see enough difference to quantify it, so people assume it's not real.

How about the fact that in several instances @Ingineer said there was no change to any of the relevant modules? That seems like
fairly convincing evidence of placebo effect.

 

[RogerHScott]

Honestly, though, I'd prefer it if the regenerative braking were able to bring the car to 0 mph consistently so one could truly do one pedal braking. The fact that it slows down to 5-6 mph then keeps going a bit more before slowing to 0 (or close to 0) just means more movement between accelerator and brake pedals.

Or, to flail upon a deceased equine, the act of "braking" itself could invoke regen. Doesn't solve the 1-pedal/2-pedal issue but
it would provide a smooth, regenerative path from full speed to stopped. Of course, in a Tesla, everything should be options
and nothing should be unnecessarily decided for the driver.

 

[brucet999]

How much regen is applied is just a software setting. It is not limited by the hardware.

You might want to reconsider this assertion. In fact, regen must be limited by hardware because it comes from electromotive force caused by the motor acting as generator. A certain sized motor rotated at a certain rpm can only generate a certain maximum EMF and no more. Conversely, that same motor is limited by its design to a certain maximum power output .

Software can limit regen to some level below its physical design limits but cannot increase regen beyond its physical limits.

 

[brucet999]

Honestly, though, I'd prefer it if the regenerative braking were able to bring the car to 0 mph consistently so one could truly do one pedal braking.

Unfortunately, physics is against you there. Regen is the electromotive force resisting the motor's turning while it is functioning as a generator when it is being driven by the momentum of the car. As speed decreases, so does EMF until a point is reached where there is not enough rpm to produce significant force, at which point the car will coast until the brakes are applied or friction brings it to a stop.

A hypothetical perfectly efficient motor/battery system could produce regen without energy losses and so might be able to bring the car to a complete stop. Unfortunately, those perfect motors and batteries are all being used by the perpetual motion machine industry and so aren't available to Tesla.

 

[RogerHScott]

Unfortunately, physics is against you there. Regen is the electromotive force resisting the motor's turning while it is functioning as a generator when it is being driven by the momentum of the car. As speed decreases, so does EMF until a point is reached where there is not enough rpm to produce significant force, at which point the car will coast until the brakes are applied or friction brings it to a stop.

While this may be true in general, there's a discontinuity in the velocity-deceleration curve for the MS that suggests that they're
purposefully decreasing (my guess is: ceasing) regen at around 5mph. So while it may not be possible to regen all the way to a
dead stop it probably would be be possible to slow more than what the current system does.

 

[Cosmacelf]

There is no reason Tesla cannot come to a complete stop without brakes, they just choose not to. The BMW i3, for example easily comes to a full stop just by releasing the accelerator. Now, the car can't stop exclusively by using regen. At some point, the coils cannot overcome inherent energy losses in the system. This means that to come to a complete stop, the car would have to apply brakes for you. Which is very doable in cars with the iBoost brakes (last couple of years of the Model S, and all Model X). Why Tesla doesn't do this, while BMW and others do, is a mystery.

 

[techmaven]

There is no reason Tesla cannot come to a complete stop without brakes, they just choose not to. The BMW i3, for example easily comes to a full stop just by releasing the accelerator. Now, the car can't stop exclusively by using regen. At some point, the coils cannot overcome inherent energy losses in the system. This means that to come to a complete stop, the car would have to apply brakes for you. Which is very doable in cars with the iBoost brakes (last couple of years of the Model S, and all Model X). Why Tesla doesn't do this, while BMW and others do, is a mystery.

My understanding is that the i3 has a permanent magnet motor while Tesla uses AC induction motors and that's the difference. On an AC induction motor, at too low of an rpm and the induction effect is effectively zero.

 

[David99]

My understanding is that the i3 has a permanent magnet motor while Tesla uses AC induction motors and that's the difference. On an AC induction motor, at too low of an rpm and the induction effect is effectively zero.

Again, it's just software. The motor can be brought to a standstill and stopping the car. Of course it's not technically regen down to zero. The inverter would apply negative torque and adjust to based on speed to make the car come to a stop, then apply the parking brakes. It's totally doable and the fact that traffic aware cruise control can do exactly that shows that Tesla has already implemented it in the software. It is plain and simple a choice on Tesla's side to have regen fade out at 5 mph and let it coast. Why is up to speculation, but there is no technical reason.

You might want to reconsider this assertion. In fact, regen must be limited by hardware because it comes from electromotive force caused by the motor acting as generator.

Of course there is a hardware limit to the maximum amount, but it's way way higher than what we get with regen at the moment. Currently the regen limit is around 60 kW. That is nowhere near the what the motor/inverter could deliver. The amount of regen Tesla decides to give the driver is currently not limited by hardware. It's just a software setting and a choice on Tesla's side.

 

[rfmurphy81]

Unfortunately, physics is against you there. Regen is the electromotive force resisting the motor's turning while it is functioning as a generator when it is being driven by the momentum of the car. As speed decreases, so does EMF until a point is reached where there is not enough rpm to produce significant force, at which point the car will coast until the brakes are applied or friction brings it to a stop.

A hypothetical perfectly efficient motor/battery system could produce regen without energy losses and so might be able to bring the car to a complete stop. Unfortunately, those perfect motors and batteries are all being used by the perpetual motion machine industry and so aren't available to Tesla.

 

[contaygious]

So did I get increased regen in my rwd? I dont know who to believe!

 

[rfmurphy81]

So did I get increased regen in my rwd? I dont know who to believe!

There's definitely a difference but perhaps not as much as AWD vehicles.

 

[Plug Life]

I noticed it immediately. But I am also curious, how did they do it with software update alone?

 newRegen=oldRegen*1.3

That's it.

 

[Jurnimon]

How much regen is applied is just a software setting. It is not limited by the hardware. Various software updates changed the regen amount and how it's applied at what speed, level of charge, battery temperature or how it fades in and out. It's all software.

I have a RWD and never had the car slip or become unstable when regen in any weather condition except once when I was driving in pure black ice and cars were sliding in the ditch left and right. The conditions were so slippery that driving at all was too dangerous.

Glad you made it through that!

I agree it is a software setting and I expect there are limits to how much force and duration the regen is applied on a single motor MS vs AWD MS is the point/hypothesis I am suggesting.

 

[ORB]

Makes sense that the AWD cars could have more aggressive regen at highway speeds, as the 2nd motor would allow more energy generation. The regen in my Dec 2012 S is "pinned" until the speed drops below 40 MPH or so.

However I believe that there is more regen available to be used earlier in the speed taper from 40 to 5 MPH even with older cars, but is not being offered either due to Tesla's perception of what the average driver would be comfortable with, or possibly due to concern over mechanically stressing the motor/drivetrain over time (I hope I'm wrong about the latter). I have fond memories of the aggressive regen in this taper curve I had in the early days (sigh), we need a Sport regen mode! Haven't noticed any dramatic change with the 8.0 update.

 

[ThortsMD]

Point of clarification: Are you saying you have 8.x on your RWD and can feel the difference?

I think there is a slight increase in regen on my 2013 RWD model.

 

[chillaban]

Again, it's just software. The motor can be brought to a standstill and stopping the car. Of course it's not technically regen down to zero. The inverter would apply negative torque and adjust to based on speed to make the car come to a stop, then apply the parking brakes. It's totally doable and the fact that traffic aware cruise control can do exactly that shows that Tesla has already implemented it in the software. It is plain and simple a choice on Tesla's side to have regen fade out at 5 mph and let it coast. Why is up to speculation, but there is no technical reason.

Actually (having done a few years of high power AC servomotor control for a defense contractor), it isn't just software. AC induction motors, even with resolvers for rotor position, are a pain to control as a servomotor and at extremely low speeds (e.g. commanding a fixed position, slowing down to a stop). Once the speed gets down to a certain level, you have a lot more torque pulsing effects that might lead to low speed shudder especially if something else happens (e.g. hitting a small bump in the pavement, wind blowing, etc). And the net effect would be a loss in energy as opposed to regen.


WITH THAT SAID, nothing prevents Tesla from just hitting the mechanical brakes to simulate regenning down to zero and just have the brakes apply below 10mph and smoothly slow you to a stop. That aspect is just software. But inherently, a PMSM makes sense for true regen down to zero. An ACIM does not.