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I thought we had antilock brakes
- Thread starter Nikola M3
- Start date
insaneoctane
Well-Known Member
How can ABS detect lock-up and slightly release pressure if there is no lock-up? I think the wheel has to lock-up (and leave rubber) for the slightest amount of time before the ABS can release the brake pressure and rinse and repeat. That said, I don't know how much rubber you typically see with an ABS stop.
Daniel in SD
(supervised)
I think it detects that the wheel speed is changing too fast as the tire begins to lock up. It doesn't fully lock up but it is moving more slowly than the ground for a split second. It's also looking at the speed of all the other wheels.
Knightshade
Well-Known Member
This is stolen from James Walker Jrs article on the interaction of ABS and big brake kits (and why they can cause problems together), but it gives a simplified overview of basic ABS functionality-
ABS Control In Super-Slow-Mo
In order to best explain how the ABS "depends" on the base braking system, let's have a look at a typical ABS event at the micro level – from the processing algorithm's perspective.
Say you are driving down the highway at 75 MPH (the posted speed limit, of course) when all of a sudden the truck in front of you spills its load of natural spring water across all three lanes of traffic. Now, this alone would not be so bad, except the water is still sealed in 55-gallon drums – one of which would certainly make a mess of your car’s front fascia. Time to take evasive action.
Being the trained high-speed individual that you are, you immediately lift off the gas, push in the clutch (you are driving a manual transmission, right?), and simultaneously nail the brake pedal...but in the heat of the moment you hit it a little too hard.
Meanwhile, the ABS is hanging back watching the world go by, seeing a constant stream of 75 MPH signals from its four wheel speed sensors. Let’s call this "observation mode." Upon your application of the brake, however, the ABS snaps to attention, its antenna up, ready for action. You have just hit the brake pedal after all, and who know what’s coming next.
After 50 milliseconds (it’s actually much faster than that – 7 to 10 milliseconds is typical – but it makes the math easier) the ABS takes another snapshot of the wheel speed information in an attempt to figure out what's going on. This time the wheel speed sensors are all reporting a speed of 74 MPH. Doing a quick calculation, the ABS determines that in order to have slowed 1 MPH in a 50ms period the wheels must be decelerating at a rate of 0.91g’s. Because you are driving a sports car, the engineer who calibrated the system ‘taught’ the ABS that your car is capable of decelerating at this rate, so the ABS continues to hang back and watch the event from the spectator’s booth. No problem so far.
The next 50ms, however, are a little more interesting. This time around, the wheels are reporting 72.5 MPH. Now, it may not seem like a big jump, but to slow 1.5 MPH in a 50ms window equates to a deceleration of 1.36g’s. Not alarming, but the ABS ‘knows’ that based on this deceleration level, the wheels are probably beginning to slip a little more than they should – after all, your car is probably not decelerating at quite 1.36g’s..and any error between the two indicates slip.
ABS is now in "ready mode." It’s probably too soon to jump in, as the wheels might spin back up on their own in the next 50ms loop, but things are definitely looking bad!
As the first barrels of spring water bounce left and right, missing your car by inches, you stay on the brake pedal but push even harder. This time around, the left front wheel speed sensor is registering 68 MPH – a 4.5 MPH drop in the last 50ms, or a deceleration level of 4.1g’s. Doing the math faster than you can (after all, you are busy dodging barrels of spring water), the ABS quickly comes to the conclusion that, unlike the left front wheel at this moment, the car cannot possibly be decelerating at 4.1g’s. Best case is that the car was decelerating at 1.0g (or thereabouts) over the last 50ms, so the ‘real’ vehicle speed is still somewhere around 71.5 MPH, even though the left front wheel speed is reading 68 MPH – a 3.5 MPH error.
So, based on a wheel deceleration of 4.1g’s, a slip level of 5% (3.5 MPH¸ 71.5 MPH), and a couple other factors not listed here, the ABS jumps in and enters "isolation mode." (Note that the wheels are nowhere even near "wheel lock" – the 100% slip point.) The first thing the ABS does is shut off the hydraulic line from the master cylinder to the left front caliper, isolating the driver from applying more pressure – after all, it was the driver that got us into this mess in the first place.
Next, the ABS starts work in "decrease mode," releasing the excess pressure from the left front caliper in order to allow the left front wheel to reaccelerate back up to the vehicle’s actual speed – 71.5 MPH in this case. Since the ABS knows how quickly the wheel is decelerating (4.1g), how fast the car is actually going (71.5 MPH), and the pressure-torque characteristics of the left front caliper/pad/rotor assembly (we’ll come back to this one in just a second), it can precisely calculate how long to open its release valve to vent that extra pressure, leaving just enough pressure in the caliper to maintain 1.0g of deceleration (or thereabouts).
Let’s say that calculated time turned out to be 10 milliseconds (this again makes the math easier later on). Bang! Valve opens, pressure is released, and 10ms later it closes, leaving just the right amount of pressure in the caliper so that the wheel spins back up to exactly 71.5 MPH, but continues to decelerate at 1.0g. Everything is going as planned.
Time to close the loop and enter "increase mode." Once the ABS sees that the left front wheel has returned to near the ‘real’ vehicle speed, it slowly reapplies pressure from the master cylinder to make sure that maximum sustainable brake force is being utilized. To this end, the ABS calculates precisely how long to pulse open the isolation valve, slowly building pressure at the left front caliper until once again the left front wheel begins to slip. It performs this calculation based on – you guessed it – how quickly the wheel is re-accelerating, how fast the car is actually going, and the pressure-torque characteristics of the caliper/pad/rotor assembly.
In our hypothetical little world, the ABS calculated that four pulses of 5ms each were necessary to build the wheel pressure back up to the point that the wheel began to slip again, returning to "isolation mode."
The cycle is repeated on all four wheels simultaneously until either the driver gets out of the brake pedal, or until the car has come to a stop. Hopefully, this did not include punting a spring water barrel or two along the way as the ABS kept all four wheels slips in the 5%-10% range, allowing you to turn and swerve to your heart’s content as the drums bounced out of your path. Happy car, happy driver.
ABS Control In Super-Slow-Mo
In order to best explain how the ABS "depends" on the base braking system, let's have a look at a typical ABS event at the micro level – from the processing algorithm's perspective.
Say you are driving down the highway at 75 MPH (the posted speed limit, of course) when all of a sudden the truck in front of you spills its load of natural spring water across all three lanes of traffic. Now, this alone would not be so bad, except the water is still sealed in 55-gallon drums – one of which would certainly make a mess of your car’s front fascia. Time to take evasive action.
Being the trained high-speed individual that you are, you immediately lift off the gas, push in the clutch (you are driving a manual transmission, right?), and simultaneously nail the brake pedal...but in the heat of the moment you hit it a little too hard.
Meanwhile, the ABS is hanging back watching the world go by, seeing a constant stream of 75 MPH signals from its four wheel speed sensors. Let’s call this "observation mode." Upon your application of the brake, however, the ABS snaps to attention, its antenna up, ready for action. You have just hit the brake pedal after all, and who know what’s coming next.
After 50 milliseconds (it’s actually much faster than that – 7 to 10 milliseconds is typical – but it makes the math easier) the ABS takes another snapshot of the wheel speed information in an attempt to figure out what's going on. This time the wheel speed sensors are all reporting a speed of 74 MPH. Doing a quick calculation, the ABS determines that in order to have slowed 1 MPH in a 50ms period the wheels must be decelerating at a rate of 0.91g’s. Because you are driving a sports car, the engineer who calibrated the system ‘taught’ the ABS that your car is capable of decelerating at this rate, so the ABS continues to hang back and watch the event from the spectator’s booth. No problem so far.
The next 50ms, however, are a little more interesting. This time around, the wheels are reporting 72.5 MPH. Now, it may not seem like a big jump, but to slow 1.5 MPH in a 50ms window equates to a deceleration of 1.36g’s. Not alarming, but the ABS ‘knows’ that based on this deceleration level, the wheels are probably beginning to slip a little more than they should – after all, your car is probably not decelerating at quite 1.36g’s..and any error between the two indicates slip.
ABS is now in "ready mode." It’s probably too soon to jump in, as the wheels might spin back up on their own in the next 50ms loop, but things are definitely looking bad!
As the first barrels of spring water bounce left and right, missing your car by inches, you stay on the brake pedal but push even harder. This time around, the left front wheel speed sensor is registering 68 MPH – a 4.5 MPH drop in the last 50ms, or a deceleration level of 4.1g’s. Doing the math faster than you can (after all, you are busy dodging barrels of spring water), the ABS quickly comes to the conclusion that, unlike the left front wheel at this moment, the car cannot possibly be decelerating at 4.1g’s. Best case is that the car was decelerating at 1.0g (or thereabouts) over the last 50ms, so the ‘real’ vehicle speed is still somewhere around 71.5 MPH, even though the left front wheel speed is reading 68 MPH – a 3.5 MPH error.
So, based on a wheel deceleration of 4.1g’s, a slip level of 5% (3.5 MPH¸ 71.5 MPH), and a couple other factors not listed here, the ABS jumps in and enters "isolation mode." (Note that the wheels are nowhere even near "wheel lock" – the 100% slip point.) The first thing the ABS does is shut off the hydraulic line from the master cylinder to the left front caliper, isolating the driver from applying more pressure – after all, it was the driver that got us into this mess in the first place.
Next, the ABS starts work in "decrease mode," releasing the excess pressure from the left front caliper in order to allow the left front wheel to reaccelerate back up to the vehicle’s actual speed – 71.5 MPH in this case. Since the ABS knows how quickly the wheel is decelerating (4.1g), how fast the car is actually going (71.5 MPH), and the pressure-torque characteristics of the left front caliper/pad/rotor assembly (we’ll come back to this one in just a second), it can precisely calculate how long to open its release valve to vent that extra pressure, leaving just enough pressure in the caliper to maintain 1.0g of deceleration (or thereabouts).
Let’s say that calculated time turned out to be 10 milliseconds (this again makes the math easier later on). Bang! Valve opens, pressure is released, and 10ms later it closes, leaving just the right amount of pressure in the caliper so that the wheel spins back up to exactly 71.5 MPH, but continues to decelerate at 1.0g. Everything is going as planned.
Time to close the loop and enter "increase mode." Once the ABS sees that the left front wheel has returned to near the ‘real’ vehicle speed, it slowly reapplies pressure from the master cylinder to make sure that maximum sustainable brake force is being utilized. To this end, the ABS calculates precisely how long to pulse open the isolation valve, slowly building pressure at the left front caliper until once again the left front wheel begins to slip. It performs this calculation based on – you guessed it – how quickly the wheel is re-accelerating, how fast the car is actually going, and the pressure-torque characteristics of the caliper/pad/rotor assembly.
In our hypothetical little world, the ABS calculated that four pulses of 5ms each were necessary to build the wheel pressure back up to the point that the wheel began to slip again, returning to "isolation mode."
The cycle is repeated on all four wheels simultaneously until either the driver gets out of the brake pedal, or until the car has come to a stop. Hopefully, this did not include punting a spring water barrel or two along the way as the ABS kept all four wheels slips in the 5%-10% range, allowing you to turn and swerve to your heart’s content as the drums bounced out of your path. Happy car, happy driver.
If they admit something was wrong with the ABS or the brake system, ask them to replace the tires as well.
I thought about this but wonder if it is that much tire loss. for sure it is on one side so that may be significant.
I did talk to the service center and they are escalating the problem. They said that they would be reading the logs since I did a bug report and have an exact time. It will probably be Thursday before I hear anything back.
Correct me if I am wrong, but I believe the OP was just called a liar.
In a most polite manner.
I look forward to further info. (I have been skeptical of the electronic brake fix.)
I read Consumer Reports article on the brakes. I think it was after multiple, quickly repeated stops; please correct me if I'm wrong. That is not a "real world" situation. Although you might experience it on a very long down hill situation without the ability to shift to a lower gear, normally that is only experienced on a race track, and this ain't a race car.
Every auto magazine has tested the Model 3, and I doubt that they only tested the brakes via "one and done"; I only double-checked one mag, but it listed the stopping distance right in line with the other cars tested, and I don't remember any complaints before CR came out with theirs. IMHO, Elon thought he had to make an immediate response to that article, and he did. The fix certainly worked as far as the bad publicity, but does it actually benefit the 'normal' use of the car??
I read Consumer Reports article on the brakes. I think it was after multiple, quickly repeated stops; please correct me if I'm wrong. That is not a "real world" situation. Although you might experience it on a very long down hill situation without the ability to shift to a lower gear, normally that is only experienced on a race track, and this ain't a race car.
Every auto magazine has tested the Model 3, and I doubt that they only tested the brakes via "one and done"; I only double-checked one mag, but it listed the stopping distance right in line with the other cars tested, and I don't remember any complaints before CR came out with theirs. IMHO, Elon thought he had to make an immediate response to that article, and he did. The fix certainly worked as far as the bad publicity, but does it actually benefit the 'normal' use of the car??
Daniel in SD
(supervised)
Go reread that whole saga. They tested it the next day and it still had increased stopping distance. Also at least one other publication had similar issues. Anyway I don't think that's necessarily related to OPs issue. They didn't observe wheel lockup in any their tests.
sperkin
Active Member
Your picture of the skid marks showed that ABS was working otherwise the marks would be straight. SInce you turned the wheels the tires turned and you still had control. If you didn't have ABS, the turned wheel will slide straight leaving straight skid marks.
LargeHamCollider
Battery cells != scalable
Max braking occurs at around 7% slippage, you should be seeing a bit of a mark. Not sure what the issue is.
Also why were you driving on the wrong side of the road? If those are marks from braking the near end of them is where you came to a stop.
But really this image looks exactly like a burnout made by a car going in the correct direction and not much like a panic stop made by a car driving in the left lane (it certainly *wasn't* made by a panic stop in the right lane).
Also why were you driving on the wrong side of the road? If those are marks from braking the near end of them is where you came to a stop.
But really this image looks exactly like a burnout made by a car going in the correct direction and not much like a panic stop made by a car driving in the left lane (it certainly *wasn't* made by a panic stop in the right lane).
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erthquake
Active Member
Calling out FUD here. Locked wheel skid marks don't fade with distance like the OP's do. These are burnout marks. They also don't look far apart enough to be from the Model 3. I'll bet if we measure pixels, the measurements won't be consistent with those of the Model 3.
tire skid mark analysis - Google Search
tire skid mark analysis - Google Search
All I met the OP and his wife last week in San Diego ..looks like this event happened afternoon he drove back ..for those that are calling this FUD or say he’s a troll I call BS ...he is a genuinely enthusiastic Tesla owner and let’s see what Cathedral City SC has to say
LargeHamCollider
Battery cells != scalable
I suspect he took a picture of the wrong tire marks in that case.
