Regenerative braking

[mt2]

Alternatively, you could choose to select the Constant Speed Cruise for all gradients if you prefer not to travel more slowly uphill.

Oh, sorry, didn't read closely enough. You're just suggesting different regen profiles. Okay, I can buy that. Although I'm not sure I would like the Constant Power Cruise.

Instead, I think I just see it as modifying the bounds the firmware operates in. An economy mode tells the firmware that it's all right to slip a mile or two below the desired speed. Whereas regular mode tries to keep the car within a half a mile an hour of the desired speed. Or something like that - my numbers are purely hypothetical.

 

[TEG]

(some recap)

Regen braking serves two purposes:

#1: Increase overall efficiency by recapture of kinetic energy. (thus increasing vehicle range)
#2: Increase friction brake pad life.

If the Roadster doesn't tie the regen into the brake pedal, and the software doesn't invoke regen aggressively "off throttle" than you don't take full advantage of these benefits.

There is a bit of a conflict as to how much regen to activate when the
accelerator pedal is backed off. Too much and people are bothered by the need to carefully modulate the pedal if they wish to coast. Too little and people use the friction brake pedal instead of using regen.

There has been discussion about cabin adjustable regen levels (which some other vehicles have done), and perhaps different driving profiles. As far as I know Tesla only has 2 regen profiles based on the setting of the gear selector (1st or 2nd). 1st gear is probably appropriate in hills and stoplight to stoplight city driving. 2nd gear (with more coasting) is probably best for freeway cruising.

----

mt2 wrote:
"There's friction brakes at that end of the decelerator."

Note - this posting is in the Roadster technical forum. Are you talking about Whitestar there? As far as I know the "decelerator" (brake pedal) is nothing but friction brakes on the roadster. Sure, if you have lifted off the accelerator pedal there may be some regen happening in parallel but NOT maximized before the friction brakes take over.

Keep in mind that Tesla has hired up some of the best "talent" in the industry now. I imagine that they are going to do everything they can to do the best possible regen implementation with Whitestar. I understand that the Roadster was engineeried with driving dynamics and simplicity first, with efficiency as a secondary consideration, so it probably isn't an example of where Tesla plans to go with regen on their future vehicles.

 

[mt2]

Note - this posting is in the Roadster technical forum.

Oooo.... never mind.

 

[tonybelding]

Regen braking serves two purposes:

#1: Increase overall efficiency by recapture of kinetic energy. (thus increasing vehicle range)
#2: Increase friction brake pad life.

I would say that #1 is the purpose of regen, and #2 is the side benefit. A welcome bonus, if you will.

If the Roadster doesn't tie the regen into the brake pedal, and the software doesn't invoke regen aggressively "off throttle" than you don't take full advantage of these benefits.

There is a bit of a conflict as to how much regen to activate when the
accelerator pedal is backed off. Too much and people are bothered by the need to carefully modulate the pedal if they wish to coast. Too little and people use the friction brake pedal instead of using regen.

My intuition is that regen should be fairly strong, at least in low gear. If you really want to coast, then you can engage the cruise control, or you can put it into neutral. This is what you would do if you were driving a gasoline-powered car with a stick -- or else you'd hold down the clutch, which is something we don't have.

There has been discussion about cabin adjustable regen levels (which some other vehicles have done), and perhaps different driving profiles. As far as I know Tesla only has 2 regen profiles based on the setting of the gear selector (1st or 2nd). 1st gear is probably appropriate in hills and stoplight to stoplight city driving. 2nd gear (with more coasting) is probably best for freeway cruising.

I think they've got the right idea. I am against adjustable regen levels. That's something Tesla's engineers are much better qualified to figure out than the customers are. If it's adjustable, most people will leave it on the factory default settings anyhow. Some other people will fiddle with it and just mess it up.

I'm not speaking from experience on this. I'm sure I'll have more firm opinions on this subject after I've gotten my car and driven around a bit.

 

[TEG]

If you really want to coast, then you can engage the cruise control, or you can put it into neutral.

Would people really turn the cruise control on and off like that?
My impression is that people only use cruise control when they are on a long freeway/highway for extended periods of time. Maybe in rural Texas you have lots of opportunity to do that, but in the SF bay area I almost never have enough consistent speed to feel like cruise control is worth activating.

Regarding "neutral"... Do you know if the Roadster even has it? Could it be that you are in either 1st, 2nd, or reverse with no neutral?
I see that the shift lever can sit in the middle between R, 1 & 2, but it isn't labeled as a Neutral.

By the way - on my wife's Highlander Hybrid, the dealer advises against leaving the vehicle in neutral because it disengages the ICE from the generator so it can't recharge the batteries. They say if you want to disengage to put it in Park instead (which wouldn't work for coasting) so it can run the gas engine to recharge the batteries as needed (if for instance you have the A/C running). In my Lexus I often shift to Neutral when I come to a stoplight so the gas motor doesn't have to fight against the torque converter while waiting. Out of habbit I did this while driving my wife's hybrid until she told me it wasn't considered good practice.

 

[tonybelding]

Regarding "neutral"... Do you know if the Roadster even has it? Could it be that you are in either 1st, 2nd, or reverse with no neutral?
I see that the shift lever can sit in the middle between R, 1 & 2, but it isn't labeled as a Neutral.

They don't label it on an conventional stick-shift either. I can't think of any reason why they wouldn't want the neutral position to work the same on a Tesla as it does on other cars.

Or put it this way. . . If you've moved the stick to neutral position, what else would you expect the car to do? Keep running in the same gear it was in before you moved the stick? That would be very counter-intuitive, I think.

 

[WarpedOne]

In the last post on Tesla blog Darryl comments:

Editor’s note: the brake feel has already been improved on other Tesla prototypes with the use of a faster gear ratio for the brake pedal.

What do you guys make of this? Does Roadster automagically shift into first gear under hard braking to increase the regen effect?

 

[tonybelding]

What do you guys make of this? Does Roadster automagically shift into first gear under hard braking to increase the regen effect?

No, I don't think it means anything like that.

Previously several people had commented that the brakes felt "mushy" or that they had to depress the pedal more than expected to make them work. I'm sure he just means they've changed the brake linkage so that less pedal movement will be required to make it engage. It has nothing to do with regen or the transmission.

 

[TEG]

Here is a picture of the Elise brake pedal mechanism:

I am not sure how "gear ratio" would come into play as I don't see any gears between pedal and the cylinder which pushes fluid to the calipers.

They could modify the the distance of the yolk attachment point from the rotation point of the pedal to change the ratio of pedal travel to yolk travel. That way they could make it require less pedal travel (but more effort) to cause the braking effect.

 

[vfx]

"They could modify the the distance of the yolk attachment point from the rotation point of the pedal to change the ratio of pedal travel to yolk travel. That way they could make it require less pedal travel (but more effort) to cause the braking effect. "

This is what I thought. Changing the pick point of the pedal fulcrum. Of course he could have meant an electronic "Gear Ratio".

 

[TEG]

I don't think any electronics are involved.
As far as I know the braking system is all mechanical.

Regen is apparently based on speed, accelerator pedal position and gear selection.

(The above info is based on educated guessing... Someone tell me if you know otherwise)

 

[W8MM]

I don't think any electronics are involved.
As far as I know the braking system is all mechanical.

That is exacty what I was told last March when I visited Tesla and they answered my bazzillion questions.

 

[vfx]

So it sounds like the Elise brake "gearing" was not quite enough to handle the extra weight of the ESS.

Like towing a trailer, the extra weight makes it seem like the brake pedal travel has a longer thow to a complete stop.