P85D - Electric Mechanical Braking System

[EarlyAdopter]

Why are people pushing for regen to be moved to the brakes? Keeping regen on the accelerator pedal is, IMHO, one of the best "driving feeling" decisions Tesla's made. Not just because it avoids the complexity of trying to keep natural braking feel, but because it lets you control the car in most driving situations without moving your foot very much.

Not moved to the brakes entirely - keep the current 60kW regen on lifting off the accelerator, same as today, like driving a manual with engine braking. After that, for any additional regen available beyond 60kW due to a second motor or untapped regen available today which would induce _considerable_ deceleration and be too much for "engine braking", tie it to the first stage of braking.

 

[jerry33]

Why are people pushing for regen to be moved to the brakes? Keeping regen on the accelerator pedal is, IMHO, one of the best "driving feeling" decisions Tesla's made. Not just because it avoids the complexity of trying to keep natural braking feel, but because it lets you control the car in most driving situations without moving your foot very much.

I have no clue as to why. Doesn't make any sense whatsoever.

 

[Cosmacelf]

It isn't regen beyond 60kw that is the issue. When you lift your foot off the accelerator, it only does 60 kW regen for a period of time. As the car slows down, the amount of regen also slows down. So, when you are 30 mph, the regen might only be 30 kW. If at that point, you press on the brake, it would be nice if the car acted like a hybrid, and used the iBoost capability of increasing regen back up 60 kW if needed and only then go to friction brakes if more stopping power is needed.

This would result in no perceptible driving feel change, yet would result in less energy usage, and even less brake wear.

 

[jerry33]

It isn't regen beyond 60kw that is the issue. When you lift your foot off the accelerator, it only does 60 kW regen for a period of time. As the car slows down, the amount of regen also slows down. So, when you are 30 mph, the regen might only be 30 kW. If at that point, you press on the brake, it would be nice if the car acted like a hybrid, and used the iBoost capability of increasing regen back up 60 kW if needed and only then go to friction brakes if more stopping power is needed.

This would result in no perceptible driving feel change, yet would result in less energy usage, and even less brake wear.

The current system brakes on regen down to 3-5 mph at about the same speed I would brake in any car, so the only time it would get "more regen" would be when I'm surprised and have to stop more rapidly. I don't see a lot of energy savings to be had.

 

[bhzmark]

Why can't people understand that no one is advocating to move the existing accelerator pedal regeneration power to the brake pedal. The point is a different one. Let any additional regeneration power be triggered by application of the brake pedal. How hard is that to understand?

 

[Todd Burch]

Why can't people understand that no one is advocating to move the existing accelerator pedal regeneration power to the brake pedal. The point is a different one. Let any additional regeneration power be triggered by application of the brake pedal. How hard is that to understand?

It's not hard to understand the "what" of the request...but the "why". If you keep any additional regen tied to the accelerator, you have to move your foot to the brake even less when driving, and the system remains dramatically simpler mechanically.

 

[WarpedOne]

"Why" is simple.
It is not a problem when max regen power is 60kW and even in this case the onset is gradual to give you some time to react.
It is a problem and even a safety hazard if max regen power is 120kW.

You do not want your car to decelerate that strongly (far stronger than any ICE 'resistance') without you actively demanding it. Lifting a foot from accelerator cannot and should not end in 120kW braking.

 

[Todd Burch]

"Why" is simple.
It is not a problem when max regen power is 60kW and even in this case the onset is gradual to give you some time to react.
It is a problem and even a safety hazard if max regen power is 120kW.

You do not want your car to decelerate that strongly (far stronger than any ICE 'resistance') without you actively demanding it. Lifting a foot from accelerator cannot and should not end in 120kW braking.

I don't think regen power on the D is going to be significantly larger than 60 kW. It certainly could be, but for the very reason you mentioned Tesla chose 60 kW as the limit. Sure, some additional energy could be recovered at higher regen power, but the total amount of energy lost due to "panic stops" relative to normal regen may be insignificant enough that the additional mechanical/software complexity to do this wouldn't be worth it. It will be interesting to see which way Tesla goes.

 

[vgrinshpun]

It's not hard to understand the "what" of the request...but the "why". If you keep any additional regen tied to the accelerator, you have to move your foot to the brake even less when driving, and the system remains dramatically simpler mechanically.

I totally agree. It is really puzzling why there is so much insistence on having some regen on brake pedal. After 16 months of ownership and more than 26K miles driven I am certain that keeping ALL regen on accelerator pedal is not only mechanically simpler, but most importantly leads to much less fatique on a long trip, especially in heavy traffic. Moving your foot back and forth between acceleartor and brake requires more concentration and focus than using just one pedal, resulting in more fatique. I would be very disappointed if additional regen is added to the brake pedal instead of the accelerator.

- - - Updated - - -

"Why" is simple.
It is not a problem when max regen power is 60kW and even in this case the onset is gradual to give you some time to react.
It is a problem and even a safety hazard if max regen power is 120kW.

You do not want your car to decelerate that strongly (far stronger than any ICE 'resistance') without you actively demanding it. Lifting a foot from accelerator cannot and should not end in 120kW braking.

You are describing an artificial scenario. The application of regen is modulated by accelerator pedal, which allows to modulate regen anywhere between 0 and 120kW (if it is the max available in D). When discussing the brake pedal, you wouldn't treat it as having two positions only: not depressed and fully depressed would you? So why are you treating the accelerator pedal that way?

 

[WarpedOne]

Artificial scenario you say? Three are people out there who already tried many things themselves, metricmind is such a guy:

- Off-throttle regen, where you'd set middle of throttle pedal position as "neutral" (coasting) and from that position fully depressed is 100% acceleration demand and fully released - 100% regen demand (so one pedal operation) almost got me into big trouble. IT may be OK for someone just learning to drive, but such setup is very different from conventional, and if your hands and feet in emergency operate vehicle quicker than brain thinking about it, you won't like such change. It is relearning to drive. Once I drove on a freeway evaluating such set up. First, I noticed I have to freeze my foot in strictly one position as I drive, no stretches, no movements. I had to take something from behind my seat while cruising on a freeway, and to reach that far corner I had to stretch and take my foot off the accelerator pedal for 2-3 seconds - action I never think about as it would not be noticeable for "normal" setup. Well, it was equivalent to slamming brakes 100% while in the middle of freeway and no one in front of me, so no one behind would expect such a stunt. And, I wasn't consciously braking, the effect was as if some one slams on the brakes for you without any warning. The rear of the car breaks loose, I'm thrown toward wind shield and intuitively as in any emergency situation, before my brain assess the situation, my right foot goes from already 100% braking accelerator to real brake pedal, compounding effect. Now the car really grips the road, scarring me out of my pants! Mind you, I had about 450kg (1,000 lb.) of lead in the car at that time (I think around 2002). It would take thinking twice to realize that to rectify situation I had to slam on "gas". Anyway, I'm coming to a complete sketching stop in the middle lane of I84 freeway. I was LUCKY - no one was following me on my lane, and I noticed couple of by passers looked at me as if I was total moron (and I probably was!). This was first and last time I tried off-throttle regen. You may like it, but it would take a lot of money to make me do it again...

Say what you wish, the reality and truth are not affected by dis/agreements.

10kW off-pedal regen is not the same as 60kW and 120kW is once again completely diffrent thing.
Claiming that there is not much to be gained from additional regen while breaking is utter foolishness in a car that owners obsess about 1 lost mile of range.

 

[vgrinshpun]

Artificial scenario you say? Three are people out there who already tried many things themselves, metricmind is such a guy:


Say what you wish, the reality and truth are not affected by dis/agreements.

10kW off-pedal regen is not the same as 60kW and 120kW is once again completely diffrent thing.
Claiming that there is not much to be gained from additional regen while breaking is utter foolishness in a car that owners obsess about 1 lost mile of range.

The description you quoted is obviously from somebody who did NOT drive Model S. Why is it relevant here? So I stand by my original remark - for some reason you are focused on artificial scenarios.

Engineering a car is optimization proces. TM did excellent optimization with the accelerator pedal and its sensitivity. Based on my experience driving this car for 26K miles, having ALL regen on accelerator pedal is safer, less fatiquing, and great for performance driving. I would not want it any other way!

 

[WarpedOne]

Why is it relevant here?

Yeah, it's pretty obvious you just don't get it.
So be it.

 

[EarlyAdopter]

Based on my experience driving this car for 26K miles, having ALL regen on accelerator pedal is safer, less fatiquing, and great for performance driving. I would not want it any other way!

Up to 60kW I think we all agree. Beyond that we don't know, but some of us are suggesting that 120kW of regen on the accelerator pedal may not be safer. Inducing wheel lockup, rotation of the car, and firing of the ABS and stability control systems are not behaviors I would expect from lifting on the accelerator. 120kW of regen is a LOT of deceleration.

 

[Todd Burch]

OK, thinking about this some more, this applies to more than just panic stops. If you're going 60 mph and a light turns red at the "worst" possible time such that you have to stop, the extra 60 kW can be fed into the battery in that situation too. This scenario is much more common than a panic stop and often occurs at higher speeds.

If you have to stop in 4 seconds (and just for the sake of argument assuming a constant additional 60 kW of regen), this gains you an extra 60 kW * (4 /3600) hr = 0.067 kWh per stop. Assuming such stops occur 10 times per full charge (probably an optimistic estimate), you net an additional 0.67 kWh of charge. At 300 Wh/mi, that's an additional 2 1/4 miles of range per full charge. This is an optimistic estimate, so the real value will be less than this...probably somewhere between 1-2 miles of range per full charge.

There is also the benefit of reduced wear on the brakes.

Given this, it's arguable whether the additional complexity is worthwhile, but factoring the additional reduced wear on the brakes, perhaps it is worthwhile. Considering also that the new EM braking system actually facilitates this without significant additional complexity, it probably IS worthwhile.

So if Tesla goes this route, there's no reason they couldn't also add some regen on braking to RWD models too. The only drawback would be increased tire wear. It's hard to say what impact that would have--it could be a setting.

 

[jerry33]

OK, thinking about this some more, this applies to more than just panic stops. If you're going 60 mph and a light turns red at the "worst" possible time such that you have to stop, the extra 60 kW can be fed into the battery in that situation too. This scenario is much more common than a panic stop and often occurs at higher speeds.

If you have to stop in 4 seconds (and just for the sake of argument assuming a constant additional 60 kW of regen), this gains you an extra 60 kW * (4 /3600) hr = 0.067 kWh per stop. Assuming such stops occur 10 times per full charge (probably an optimistic estimate), you net an additional 0.67 kWh of charge. At 300 Wh/mi, that's an additional 2 1/4 miles of range per full charge. This is an optimistic estimate, so the real value will be less than this...probably somewhere between 1-2 miles of range per full charge.

There is also the benefit of reduced wear on the brakes.

Given this, it's arguable whether the additional complexity is worthwhile, but factoring the additional reduced wear on the brakes, perhaps it is worthwhile. Considering also that the new EM braking system actually facilitates this without significant additional complexity, it probably IS worthwhile.

So if Tesla goes this route, there's no reason they couldn't also add some regen on braking to RWD models too. The only drawback would be increased tire wear. It's hard to say what impact that would have--it could be a setting.

One other thing to consider is that for a given vehicle gross weight (vehicle plus passengers and luggage) there is only a certain amount of kinetic energy available, so regen from both motors isn't likely to help and may hurt due to the additional friction of the drive train (the reduction gears will still move and create friction).

As far as the unexpected stops from high speeds go, I have that happen every day and although I always think "I'm going to have to use the brakes", the current regen almost always slows me down to the correct amount. I stand by my statement that there would be little gain by additional regen on the brakes. Regen on the front wheels rather than the rear could be more efficient, not enough information to tell at this time.

 

[bhzmark]

I'll try one more time.

Everybody who likes accell regen as it is now, and the limited braking effect as it is now. Terrific. Keep that EXACTLY AS IT IS. !! no changes to the accell regen at all.!!!!

The only change is:

During that rare occasion when you do have to press the brake pedal (because you need to stop faster than the current braking effect from accel lift off) imagine you get the exact same additional braking effect. But the only difference is: instead of making brake dust, you are making electricity. Can we all agree that making electricity is better than making brake dust?

 

[vgrinshpun]

Up to 60kW I think we all agree. Beyond that we don't know, but some of us are suggesting that 120kW of regen on the accelerator pedal may not be safer. Inducing wheel lockup, rotation of the car, and firing of the ABS and stability control systems are not behaviors I would expect from lifting on the accelerator. 120kW of regen is a LOT of deceleration.

I just do not understand why we should assume that additional 60kW of regen would induce wheel lockup? I am applying brakes on top of the 60kW regen routinely when a traffic light turns red on the divided roadway with 55mph speed limit. I never locked up my wheels in these situations. Why would my wheels over a sudden lock up if instead of applying conventional brakes on top of 60kW of regen, I would apply more regen?

I also do not understand why you are assuming max 120 kW regen for the purpose of this discussion. The point is that regen can be infinitely varied by the accelerator pedal. One can always obtain just enough braking force via regen, as required - 60, 90, 120kW or any point in between.

 

[EarlyAdopter]

I just do not understand why we should assume that additional 60kW of regen would induce wheel lockup? I am applying brakes on top of the 60kW regen routinely when a traffic light turns red on the divided roadway with 55mph speed limit. I never locked up my wheels in these situations. Why would my wheels over a sudden lock up if instead of applying conventional brakes on top of 60kW of regen, I would apply more regen?

I also do not understand why you are assuming max 120 kW regen for the purpose of this discussion. The point is that regen can be infinitely varied by the accelerator pedal. One can always obtain just enough braking force via regen, as required - 60, 90, 120kW or any point in between.

I don't know what it's like where you live, but it's cold, rainy, and hilly where I live and yes even at 60kW of regen I have induced lockup lifting on the accelerator on a steep decline. The traction control system handles it well, but at 120kW in these conditions it would be very unexpected.

 

[breser]

Just wondering why you guys think 120kW of regen? In the case of the P85D the front motor is not as big as the back motor. In the case of an 60D/85D the front and back motors are smaller than the RWD equivalents. Maybe I'm missing something but shouldn't these smaller motors be capable of less regen?

 

[gpetti]

I'll try one more time.

Everybody who likes accell regen as it is now, and the limited braking effect as it is now. Terrific. Keep that EXACTLY AS IT IS. !! no changes to the accell regen at all.!!!!

The only change is:

During that rare occasion when you do have to press the brake pedal (because you need to stop faster than the current braking effect from accel lift off) imagine you get the exact same additional braking effect. But the only difference is: instead of making brake dust, you are making electricity. Can we all agree that making electricity is better than making brake dust?

This makes total sense to me.