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Why regenerative braking belongs on the brake pedal
- Thread starter JeffC
- Start date
The Bosch ibooster solved the brake feel problem and it's already Incorporated in the Tesla. It's simply a matter of matter of software to allocate how the driver user interface takes in braking/decel input. Right now all regen capacity is triggered from accel pedal because having a certain amount gives a good one pedal driving experience. If they could get a lot more regen, they may reach a point where there is simply too much on the accel pedal and the car would come screeching to a halt on an accel pedal lift off. Then it would make sense to map some regen to the brake pedal. The ibooster would make that easy.. but some people are scared of that.
more info on ibooster which has been in Tesla since October 2014. Horrors! It solved the brake feel problem with ability to trigger regen from brake pedal input! Tesla software just doesn't use it (I think) because the accel pedal lift off maxes out the current battery capacity for regen.
http://life.bosch.com.cn/ebrochures2015/automated/cc/cc_at/ibooster/ibooster_292000p12j_en_low.pdf
"When the driver presses the brake pedal, the pedal travel sensor measures the driver‘s braking request. ESP® hev requests a braking torque from the generator consistent with pedal travel and decelerates the vehicle. The hydraulic volume shifted into the braking system by the driver‘s foot is stored temporarily in the low-pressure accumulator chamber of the ESP® hev, meaning that no braking torque is produced at the wheel brakes. If the generator is not able to cover the braking request by means of recuperation, for example shortly before the vehicle comes to a stop, the volume available in the low-pressure accumulator chamber is shifted into the wheel brakes and the vehicle decelerates through conventional braking. The iBooster adjusts the pedal feel independently of the level of deceleration, and delivers a consistent pedal feel across the whole braking range. (on the last page)
Also:
"Adaptive pedal characteristics thanks to programmable pedal characteristic curves
"Virtually 100 percent recuperation thanks to high blending capability in combination with ESP® hev
"Regenerative braking and the associated efficiency are key when it comes to hybrid and electric vehicles. The regenerative braking torque produced by the generator should be fully utilized wherever possible, within the limits of vehicle stability.
"Conventional vacuum brake boosters allow the hydraulic volume to be shifted only within a limited range — the „jump-in area“ — in order to conceal the brake torque. Furthermore, the volume cannot be concealed without repercussions for the pedal feel. Therefore, braking actions can only recuperate below 0.2 g.
"The iBooster enables virtually full recuperation with deceleration values of up to 0.3 g when combined with ESP® hev. This is due to the iBooster’s ability to adjust the supporting force at any time in line with the hydraulic conditions by means of software controls. This covers all common braking maneuvers when driving on roads. This level of recuperation enables electric vehicles to increase their range by up to 20 percent."
http://life.bosch.com.cn/ebrochures2015/automated/cc/cc_at/ibooster/ibooster_292000p12j_en_low.pdf
"When the driver presses the brake pedal, the pedal travel sensor measures the driver‘s braking request. ESP® hev requests a braking torque from the generator consistent with pedal travel and decelerates the vehicle. The hydraulic volume shifted into the braking system by the driver‘s foot is stored temporarily in the low-pressure accumulator chamber of the ESP® hev, meaning that no braking torque is produced at the wheel brakes. If the generator is not able to cover the braking request by means of recuperation, for example shortly before the vehicle comes to a stop, the volume available in the low-pressure accumulator chamber is shifted into the wheel brakes and the vehicle decelerates through conventional braking. The iBooster adjusts the pedal feel independently of the level of deceleration, and delivers a consistent pedal feel across the whole braking range. (on the last page)
Also:
"Adaptive pedal characteristics thanks to programmable pedal characteristic curves
"Virtually 100 percent recuperation thanks to high blending capability in combination with ESP® hev
"Regenerative braking and the associated efficiency are key when it comes to hybrid and electric vehicles. The regenerative braking torque produced by the generator should be fully utilized wherever possible, within the limits of vehicle stability.
"Conventional vacuum brake boosters allow the hydraulic volume to be shifted only within a limited range — the „jump-in area“ — in order to conceal the brake torque. Furthermore, the volume cannot be concealed without repercussions for the pedal feel. Therefore, braking actions can only recuperate below 0.2 g.
"The iBooster enables virtually full recuperation with deceleration values of up to 0.3 g when combined with ESP® hev. This is due to the iBooster’s ability to adjust the supporting force at any time in line with the hydraulic conditions by means of software controls. This covers all common braking maneuvers when driving on roads. This level of recuperation enables electric vehicles to increase their range by up to 20 percent."
Last edited:
jgs
Active Member
You've mentioned this several times. When you say "it solved" do you mean "this product is marketed as solving the blended brake problem" or "I have tried a vehicle that uses iBooster blended brakes and I can't tell it from the real thing"? (Or some variant on one of those.) Naturally I and I'm sure others reading this thread am well aware of how Bosch markets the iBooster, and it would be great if it performs as described. OTOH, I also remember those "close as a blade or your money back" ads, which actually meant "in no sense as close as a blade, but we think you'll find the performance adequate and the convenience sufficient that you won't ask for your money back once you've tried it, and we are willing to write off the returns as a marketing expense."
It's nice that Bosch claims that iBooster is the best thing since sliced bread, but until some third party confirms it, I for one am giving their press releases as much weight as I do other manufacturer press releases.
I don't think any other car currently uses ibooster -- so hard to test that part of it.
But it is brake by wire.
"The pedal feel can be adjusted through the definition of the braking characteristic curves and adapted to suit vehicle manufacturer and brand-specific requirements."
The brake pedal is a controllable UI input device controlled and tweaked by software. Our primary brake pedal inputs since Oct 2014 builds have been electrical by wire rather than mechanical. That true brake pedal feel that everyone is petrified to lose has been lost to all those with an AP car. And they never knew it was gone.
Since the pedal itself is brake-by-wire, so there is no feedback to get through the pedal. There is still the potential that the transition from regen to brake dust could still be a bad transition even if it isn't passed through to the brake pedal -- it would just be noticed in the braking effect in the car as a whole: perhaps an abrupt g force feeling one way or the other upon the transition from regen to brake dust. But TACC does this all the time -- applying decel through regen and then to brake dust and I've never noticed any change in the feeling.
From those two facts I infer that ibooster, and Tesla's implementation of it, solved the problem (actually not a problem, but just a subtle sensation that was noticeable in some hybrids)
People afraid of technology and change will remain attached to the idea of only ever making brake dust through the brake pedal, but generally those aren't the sort of people that would buy a tesla in the first place.
But it is brake by wire.
"The pedal feel can be adjusted through the definition of the braking characteristic curves and adapted to suit vehicle manufacturer and brand-specific requirements."
The brake pedal is a controllable UI input device controlled and tweaked by software. Our primary brake pedal inputs since Oct 2014 builds have been electrical by wire rather than mechanical. That true brake pedal feel that everyone is petrified to lose has been lost to all those with an AP car. And they never knew it was gone.
Since the pedal itself is brake-by-wire, so there is no feedback to get through the pedal. There is still the potential that the transition from regen to brake dust could still be a bad transition even if it isn't passed through to the brake pedal -- it would just be noticed in the braking effect in the car as a whole: perhaps an abrupt g force feeling one way or the other upon the transition from regen to brake dust. But TACC does this all the time -- applying decel through regen and then to brake dust and I've never noticed any change in the feeling.
From those two facts I infer that ibooster, and Tesla's implementation of it, solved the problem (actually not a problem, but just a subtle sensation that was noticeable in some hybrids)
People afraid of technology and change will remain attached to the idea of only ever making brake dust through the brake pedal, but generally those aren't the sort of people that would buy a tesla in the first place.
MartinAustin
Active Member
I read the first 6 pages out of 17... not seeing anything substantially different before I make my "measured" response. Congratulations on originating a thread that has seen so much interest. You're obviously an EV nut 
I respect the right that the owners of the forum have given you to come on here and post ideas... and you must respect the right others have to place responses. Looks like there hasn't been a flame war so far! But IMO a flame war was never warranted.
The fact of the matter is, I imagine Tesla will keep their design fundamentally the way it is. So this entire subject, including your website article, is simply "pissing in the wind" with a lot of typing effort from a great many people (including me) that will result in nothing. Nevertheless, in I go...
To me this is an open and shut case. I couldn't disagree more with your idea. To move braking over to the left pedal would be sheer lunacy and remove one of the coolest features of the Tesla... and one of the many that differentiates it from conventional cars (a group I define by those that rely on the left pedal for braking).
The conventional system is thus: For accelerating or maintaining speed under load e.g. uphill, use the right pedal. For slowing down and stopping, use the left pedal.
The Tesla system is thus: For all regular driving, use the right pedal. For unanticipated slow-downs and emergency/low speed stops, use the left pedal.
Having up to 60kW of regen on the right pedal gives you almost all the braking force you need in most driving, meaning, you get to control the car without moving your foot back and forth. This single benefit helps enormously to elevate the smoothness of the riding experience for driver+passengers. I have given demo rides to countless people and they all comment on how the car glides so smoothly. This is in part due to having no gears, the lack of engine sound which would enable them to anticipate movement, and the overall lack of vibration. But a key part IMO is that I don't move my foot back and forth. This assumes a driving style that allows it - if you're constantly driving super-close to the cars in front... you will need more than 60kW of braking force from time to time. (and stress out your passengers) If you keep enough distance, you can do all the braking you need with 60kW or less.
I recently passed the 62,500 service interval in my P85 and took it in for the inspection. They reported that it has 7mm of brake pads left. New brake pads have 9mm, so it is tracking to need new pads at 281,250 miles. (not sure about the discs) I believe that moving the braking of the car over to the left pedal would shorten this distance and require more brake servicing work.
I believe regen is critical for the range of Tesla's cars - which by the way is longer than anyone else's (including a lot of competitors' cars that haven't been released yet!) If regen was moved to the left pedal, the range of the car would be reduced, because some small fraction of your driving time would be employed "coasting" the car without pressing either pedal. Also the time taken to move your foot from right pedal to left pedal would result in lost opportunity for regen. With the current situation, you get regen almost immediately. Like I said, all of these tiny moments add up to a few extra miles of range. If they are gone... you get less range.
Finally, the "lag" whose absence Teslas are well-known for, is exacerbated by a requirement for two-pedal driving. If you realise you want to slow down, in a convention car you can't do it until you have moved your foot from the right pedal to the left one and set your foot pressure correctly. This could be what, a 0.25-second delay? Then once you have realised your need to slow the car down is over, and you need to accelerate, in the conventional car you need to move your foot back to the accelerator and get it to the correct pressure to make a difference to the car's momentum. Another 0.25-second delay? I would hate all that extra lag. In the Tesla, there is no lag of any kind because (for most driving) your foot is already on the correct pedal, and already at the tipping point of the pressure you need it to be at. Ultimately no drivers care if there is a throttle and brake. What they want is "speed control." With Tesla's one-pedal system (along with all that lovely torque) you get better control over your car's speed than the two-pedal system could ever hope to achieve.
The one place Tesla drivers need to be careful about the one-pedal driving technique is on very slippery surfaces like ice. Regen needs to be set to "low" on those surfaces in order to reduce the risk of skidding on the ice when you take your foot off the accelerator. Read Bjorn Nyland's posts on this elsewhere on the web.
I respect the right that the owners of the forum have given you to come on here and post ideas... and you must respect the right others have to place responses. Looks like there hasn't been a flame war so far! But IMO a flame war was never warranted.
The fact of the matter is, I imagine Tesla will keep their design fundamentally the way it is. So this entire subject, including your website article, is simply "pissing in the wind" with a lot of typing effort from a great many people (including me) that will result in nothing. Nevertheless, in I go...
To me this is an open and shut case. I couldn't disagree more with your idea. To move braking over to the left pedal would be sheer lunacy and remove one of the coolest features of the Tesla... and one of the many that differentiates it from conventional cars (a group I define by those that rely on the left pedal for braking).
The conventional system is thus: For accelerating or maintaining speed under load e.g. uphill, use the right pedal. For slowing down and stopping, use the left pedal.
The Tesla system is thus: For all regular driving, use the right pedal. For unanticipated slow-downs and emergency/low speed stops, use the left pedal.
Having up to 60kW of regen on the right pedal gives you almost all the braking force you need in most driving, meaning, you get to control the car without moving your foot back and forth. This single benefit helps enormously to elevate the smoothness of the riding experience for driver+passengers. I have given demo rides to countless people and they all comment on how the car glides so smoothly. This is in part due to having no gears, the lack of engine sound which would enable them to anticipate movement, and the overall lack of vibration. But a key part IMO is that I don't move my foot back and forth. This assumes a driving style that allows it - if you're constantly driving super-close to the cars in front... you will need more than 60kW of braking force from time to time. (and stress out your passengers) If you keep enough distance, you can do all the braking you need with 60kW or less.
I recently passed the 62,500 service interval in my P85 and took it in for the inspection. They reported that it has 7mm of brake pads left. New brake pads have 9mm, so it is tracking to need new pads at 281,250 miles. (not sure about the discs) I believe that moving the braking of the car over to the left pedal would shorten this distance and require more brake servicing work.
I believe regen is critical for the range of Tesla's cars - which by the way is longer than anyone else's (including a lot of competitors' cars that haven't been released yet!) If regen was moved to the left pedal, the range of the car would be reduced, because some small fraction of your driving time would be employed "coasting" the car without pressing either pedal. Also the time taken to move your foot from right pedal to left pedal would result in lost opportunity for regen. With the current situation, you get regen almost immediately. Like I said, all of these tiny moments add up to a few extra miles of range. If they are gone... you get less range.
Finally, the "lag" whose absence Teslas are well-known for, is exacerbated by a requirement for two-pedal driving. If you realise you want to slow down, in a convention car you can't do it until you have moved your foot from the right pedal to the left one and set your foot pressure correctly. This could be what, a 0.25-second delay? Then once you have realised your need to slow the car down is over, and you need to accelerate, in the conventional car you need to move your foot back to the accelerator and get it to the correct pressure to make a difference to the car's momentum. Another 0.25-second delay? I would hate all that extra lag. In the Tesla, there is no lag of any kind because (for most driving) your foot is already on the correct pedal, and already at the tipping point of the pressure you need it to be at. Ultimately no drivers care if there is a throttle and brake. What they want is "speed control." With Tesla's one-pedal system (along with all that lovely torque) you get better control over your car's speed than the two-pedal system could ever hope to achieve.
The one place Tesla drivers need to be careful about the one-pedal driving technique is on very slippery surfaces like ice. Regen needs to be set to "low" on those surfaces in order to reduce the risk of skidding on the ice when you take your foot off the accelerator. Read Bjorn Nyland's posts on this elsewhere on the web.
jgs
Active Member
I find TACC transition from regen to brakes pretty noticeable, at least at low speeds.
... and from my own experience, I infer the opposite, or at least that the "I'm from Missouri, show me" maxim applies.
Indeed. And as I've said elsewhere, I wouldn't be freaked out if Tesla experimented with this, unless it were at the expense of a fairly long list of other things that need improvement more urgently.
jgs
Active Member
I wonder if this is still true, in AWD models but also in general. It certainly seems like something the control systems could monitor and compensate for.
Ciaopec
Active Member
Yes, I understand that software controls the amount. But let's say that if there were no software, the direct gearing of the Tesla, would begin slowing the car upon throttle lift and dissipate that energy as heat. So making regen upon braking one would have to add software to allow that. Seems unnecessarily complicated. I prefer it the way it is (and the way my Lexus is).
Darryl
ModelXTracker.com Co-Adm
I agree with @MartinAustin, the Model X current regenerative breaking is ideal and you rarely have to to use the break pedal. I don't see any improvement is needed. Any further discussion is a waste of time. 17 pages of responses is enough and any further discussion is just a waste of people's time.
mspohr
Well-Known Member
On computer forums, everybody is always making car analogies so I guess it's appropriate to have a computer analogy on a car forum... or how about a music analogy... more regen = more cowbell!
(BTW, cough, cough... I use the terminal in OSX daily)
Red Sage
The Cybernetic Samurai
JPWhite
Member
My opinion is regenerative braking belongs where the driver wants it.
If the driver wants it on the brake pedal, fine, there's an option for that (or at least there should be).
If the driver wants regen on release or relaxation of accelerator, there's an option for that too.
Around town single pedal driving is what I'd want with as strong as regen as you can get.
On the interstate I'd want more gentle regen.
It's not about what's right, its about right sizing and making a vehicle be flexible. Something Tesla is typically good at.
If the driver wants it on the brake pedal, fine, there's an option for that (or at least there should be).
If the driver wants regen on release or relaxation of accelerator, there's an option for that too.
Around town single pedal driving is what I'd want with as strong as regen as you can get.
On the interstate I'd want more gentle regen.
It's not about what's right, its about right sizing and making a vehicle be flexible. Something Tesla is typically good at.
That's what I've found after driving a C-Max Energi for a few years. I keep it in (D)rive when heading down the highway and then shift it to (L)ow? which increases the regen when I get into a congested area or stop and go traffic on the highway. While not the same level of regen as cars with bigger batteries, it still allows one pedal driving in many cases.
jgs
Active Member
jackbowers
Jack Bowers
Tesla's decision to put regen on the accelerator was made for the Roadster back around 2004, and like their decision to use a liquid-cooled battery pack it ran counter to established norms for EVs at the time. While riskier than putting regen on the brakes (the driver can be surprised by a lack of regen if the pack is cold or charged nearly full), the decision allowed for a significant increase in range, both in EPA test cycles and in real world driving. For the average driver it also means that your brakes and rotors will probably never need replacement. I was skeptical at first, but after a week of driving the Roadster I quickly adapted and came to favor this "single-pedal driving" approach. 200k Tesla miles later, I wouldn't have it any other way. It's very easy to know when you are wasting energy: any time you step on the brake.
I don't think that's necessarily true. Having lots of regen on the go pedal makes it more convenient to use braking and it may well encourage people to use more regen and less coasting than if the braking behavior was on the brake pedal.
This is almost true for the Prius which has mild regen on the go pedal and blended regen and friction on the brake pedal. It's common for Prius owners to go for over 100,000 miles in the car between brake jobs.
Typical owners may also never need a brake job in the Volt if it's driven with moderate regen plus additional blended regen on the brake.
I'm not saying Tesla's choices when designing the Roadster were wrong. I think they made very sensible choices that continue to work well for them today.
I agree.
I use the mild regen setting ('D') when cruising on the highway but "shift" to stronger regen ('L') when driving in slower stop & go situations on city streets and congested highways.
With mild regen settings I find it easier to make small and gradual speed adjustments in relatively uncongested highway traffic. It also makes it easier to switch in and out of cruise control smoothly at highway speeds as the situation warrants.
The level of maximum regen is not based solely on battery capacity. The S/X 90 kWh cars have the same max regen as the 18 kWh Spark EV. Yes, obviously there is a limit derived by the battery capacity, SOC and temperature; but I have no doubt Tesla could increase the max regen beyond the current 60 kW if they desired. This may require a hardware change, and may not be possible via software alone.
My point is that the Tesla engineers have tuned the regen with clear forethought and intent, balancing a variety of factors including inadvertent accelerator lift, stability control authority and dynamic response, battery and motor limits, not to mention what drivers prefer or can readily adapt to. Tesla could have made regen more powerful but they have purposefully designed the system to react like it does.
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