P85D - Electric Mechanical Braking System

[Kipernicus]

Brake Feel

So what would new electromechanical brakes feel like if they were set up for optimal efficacy rather than engineered to feel like conventional brakes?

Is Brake Feel something like Creep that is actually a by-product of old technology that we need to train ourselves to not miss?

 

[Saghost]

My understanding (and it could be wrong) is that the ones that come closest use more friction braking in the mix, which reduces the amount of energy captured.

With their electro-mechanical system's instant wheel by wheel response, Tesla could do the initial bite on friction pads and then gradually replace it with motor torque if that's what it took to get the right feel. It wouldn't cost much energy and would give a consistent feel that's identical to what the electromechanical cars do today. It might not be necessary, though.
Walter

 

[Arb1ter]

Because there is a transition from regen to friction brakes that can't be hidden if there is regeneration on the brakes--this would be true even without a direct connection between the foot and the braking system. Also with this kind of system there is always some braking done by the friction brakes. With the accelerator pedal only system the transition is hidden because you move your foot so the brake pedal feel is always constant.

I still don't understand. Unless I'm mistaken, the "friction brake feel" is provided by the feedback of the vacuum servo/brake booster that the brake pedal is physically connected to.

Almost every car on the road has a brake booster, but the new Model S brake-by-wire system will not. According to http://www.roadandtrack.com/go/first-looks/first-look-tesla-model-s-p85d-dual-motor, the pedal feel of Tesla's new braking system will be provided by a spring and an electric motor (software controlled).

This would be the same for regen braking and friction braking, so they should feel the same if the pedal's software makes it so.

 

[Saghost]

This would be the same for both regen braking and friction braking, so they should feel the same unless the software makes them feel different.

All of the hybrids and most EVs have force feedback systems for the brake pedal as well. The problem isn't in the pedal itself - it's in the way the car responds.

Most of the regen systems seem to have a delay in the start of braking effect of a fraction of a second, which produces a mushy feel to the pedal - at first you push the pedal and nothing seems to happen, then the car suddenly bucks as it catches up with how far you've pushed the pedal. Substantial regen on the gas pedal is one way to avoid/mask this response - and half the reason I drive my Volt in L almost all the time.

I'm not sure if Tesla can avoid the delay in regen starting, but they could mask it with the electromechanical brakes if they choose to. (Assuming they put more regen into the brake pedal in the first place, which seems like a no brainer to me but hasn't been announced anywhere.)
Walter

 

[jdbob]

All of the hybrids and most EVs have force feedback systems for the brake pedal as well.

Apparently not all. From the Energi service manual: "The brake pedal uses a pedal feel simulator that acts against a curved bracket to give the driver a simulated pedal resistance as the brake pedal is applied." which sounds like a fancy spring, I've never found any sort of force feedback system in the wiring diagram.

Pushing the pedal varies the voltage to the an input on the ABS computer. If it can it uses regenerative braking and if that isn't available or isn't enough it: "the ABS module activates a mechanical relay which supplies power to a solid state relay that activates a vacuum pump. At the same time, the ABS module sends aPWM voltage to a solenoid mounted on the brake booster. The solenoid allows vacuum from the vacuum pump to enter the brake booster which moves the booster push rod andapplies the conventional brakes."

The only time you actually feel any kind of brake feedback is when: "During certain braking events, the friction brakes can be applied directly by the driver. The brake booster push rod is equipped with an adjustable stop, once the brake pedal travels farenough to engage the stop, the brake booster push rod is forced into the master cylinder and the conventional friction brakes are applied."

 

[CHG-ON]

Awesome comments on regen guys and gals. I know little about the science. But my experience so far has been that the regen off the go pedal works very well. To me, it feels like I am at 5K in an ICE in gear 2 or 3 and I release the pedal: good compression braking. I really like the slowing and find it to be quite predictable. Great for lining up the next curve. I do find the brakes to be a bit touchy, but not too much so. Just today I had to hit the brakes hard after initiating regen (the guy in front of me hit them hard after a slow decent) and I found the combination of the two (regen for the go pedal and hitting the brakes hard) to be quite seamless and predictable. I have not driven one of the other electric only cars, but everything I have read says that brake-based regen needs lots of work. I don't feel that way about the Model S.

 

[mdevp]

I probably missed this on the new EM brakes but are they coming to all models or just the DMs in Feb.?

 

[Saghost]

I probably missed this on the new EM brakes but are they coming to all models or just the DMs in Feb.?

From the available information, we believe that EM brakes are installed on all Model S cars built since three weeks ago.
Walter

 

[tezco]

My Leaf requires pressure on the brake pedal to give you that last notch of regen. I much prefer the Tesla method of keeping it all on the accelerator pedal. I'm not a fan of having to move my foot every time I want high regen. With the Tesla method it is also quite clear when you have failed to absorb all of your forward momentum, and are now wasting it on friction.

 

[Todd Burch]

Hi all,

I now have about 250 miles on a car that finished production about 12 days ago (and 32,000 miles on an early car). My new car has the new braking system, and I notice some differences in the new system that are fairly noticeable:

First, when starting the car and first pressing the brake on non-autopilot-equipped systems, you can hear the vacuum booster powering up (commonly mistaken for the air suspension). In the new systems, this sound is not there (no vacuum booster, as I understand).

Second, the new braking system feels more firm than the old system. By this I mean that there's less pedal travel requred to get firm braking. Along with this, the brakes are now slightly more sensitive, but not annoyingly so. I would classify them as "inspiring confidence".

I'd say the new system feels a little better, but honestly they both felt great to me.

 

[EarlyAdopter]

Thanks for the update, Todd! Has me even more excited to get my D.

The sound of the brake booster vacuum pump has always mildly annoyed me, and I've found the brakes on the Model S, while strong in their stopping ability, lacked the quick grabbiness I had been accustomed to from BMW and Audi's. It was my one piece of negative feedback to Tesla after my first Get Amped drive back in July 2012, and I posted the same on here.

This is great news indeed!

 

[Cosmacelf]

On the older model S, when you come to a complete stop, it is very hard to feather the brake so that you don't get a slight jerk at the very end ... All disc brakes seem to do this. Is it any different with the new brakes?

 

[CHG-ON]

Because there is a transition from regen to friction brakes that can't be hidden if there is regeneration on the brakes--this would be true even without a direct connection between the foot and the braking system. Also with this kind of system there is always some braking done by the friction brakes. With the accelerator pedal only system the transition is hidden because you move your foot so the brake pedal feel is always constant.

- - - Updated - - -


I suspect that the amount you don't have is quite small. And you don't jam the brakes every time you come to a stop (I hope) so it's even less.


So basically, you're saying it's not going to be used anyway.


So long as you don't care about consistent brake pedal feel.



Having driven extensively on such a system, it's not an improvement.

My few observations are that I would not want complete full regen deceleration as I would think that would be hard to control and not the best driving experience. I have found that when I am under 60kW regen and I hit the brakes moderately but firmly, as when not slowing as much as I would like, that the gauge still shows 60 kW. So I surmise that that the battery is getting the most regen, based on the settings, even under braking, unless I really plant them in a sudden stop. I really like the regen profile. But I am updating my SW tonight and based on other threads, I am a bit nervous that this might change. 42 min to go on the update!

 

[Todd Burch]

On the older model S, when you come to a complete stop, it is very hard to feather the brake so that you don't get a slight jerk at the very end ... All disc brakes seem to do this. Is it any different with the new brakes?

I haven't found it difficult to feather the old or new brakes.

 

[mdevp]

Give us any follow up on the new brakes todd. I think you are the only one posting real life feedback on the new braking system which I'm sure a lot of people are interested in.

 

[Todd Burch]

Give us any follow up on the new brakes todd. I think you are the only one posting real life feedback on the new braking system which I'm sure a lot of people are interested in.

Sure. I'm up to 350 miles on them, about 50% stop-n-go driving .

They are firm. Very nice. It certainly is a little bit more difficult to feather the brakes--if you apply too much pedal travel early on, you'll find the car braking harder than you expect. Having said that though, it doesn't take much to get used to it and you can certainly feather these brakes nicely. Very linear braking control. As usual, this car has awesome stopping power.

It's nice because when you apply the brakes, you don't hear the noise of a master cylinder pushing hydraulic fluid like I did on my VIN1653....and no vacuum booster noise at startup either. But you do need to recognize that a little bit of pedal travel goes a long way.

I have no idea how these brakes work yet. Maybe they DO have some sort of master cylinder...I still need to find out. But I don't hear that telltale master cylinder hydraulic sound when applying pressure to the pedal.

 

[EarlyAdopter]

It's nice because when you apply the brakes, you don't hear the noise of a master cylinder pushing hydraulic fluid like I did on my VIN1653....and no vacuum booster noise at startup either. But you do need to recognize that a little bit of pedal travel goes a long way.

Me likey.

Cannot wait for my D.

With this, I can't think of anything else I'd like changed or added. I'll likely be keeping my D for a long time.

 

[Todd Burch]

Me likey.

Cannot wait for my D.

With this, I can't think of anything else I'd like changed or added. I'll likely be keeping my D for a long time.

Until Tesla comes out with the Double D. Everybody likes some DDs.

 

[EarlyAdopter]

Well, OK. Maybe if they came out with a Q, with one motor driving each wheel independently...

 

[CHG-ON]

I just got 6.xx on Thursday, so I am still figuring it out. But my initial impression after 200 mi is that it seems to initiate more smoothly, but the gauge still shows the same amount of regen. I am not yet seeing a change in my energy usage. That will take some time. When I first drove her after the update I felt as if I were pressing the brakes harder to stop. But by the end of the day I did not find myself doing that and it seemed quite similar to prior to the update. I do have the general impression that the car is easier to modulate on my mountain roads: a bit more predictable, but not much.