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      03-26-2012, 01:48 PM   #23
Dackelone
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Neil, I wonder if the ABS cutting in... could be due to brake pad dust buildup on the ABS wheel sensors. How many sets of pads have you been thru? Perhaps using some compressed air or even removing each wheel speed sensor - and cleaning them - might be a good idea.
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      03-26-2012, 01:54 PM   #24
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Quote:
Originally Posted by Dackelone View Post
Neil, I wonder if the ABS cutting in... could be due to brake pad dust buildup on the ABS wheel sensors. How many sets of pads have you been thru? Perhaps using some compressed air or even removing each wheel speed sensor - and cleaning them - might be a good idea.
Yes, it's the ABS cutting in, but it's by design! This is BMW's description of Cornering Brake Control:


Cornering Brake Control (CBC).


For greater safety when braking on curves - Cornering Brake Control stabilises your BMW by applying braking pressure asymmetrically despite physically difficult conditions (e.g. the car swerving towards the inside of the bend when the wheel load changes).

Cornering Brake Control (CBC) reduces the danger of vehicle instability that can arise when the brakes are applied while taking a bend at speed. Without CBC, the load shift caused by braking can reduce traction on the wheels on the side towards the inside of the bend, thereby applying excessive load to the other side. This load imbalance may result in a loss of directional control, causing the vehicle to skid out of the curve.
CBC counteracts this tendency by asymmetrically distributing brake pressure to the left- and right-side brakes or by reducing pressure (to the rear axle), even if the driver brakes outside the normal range of ABS. The result: a significant improvement in stability and safety when applying light brake pressure, even on bends.


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      03-26-2012, 08:10 PM   #25
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New (and Hopeful) Info on Corner Brake Control

OK, I have delved into this further and learned more about the CBC (corner brake control) system and it suggests that it might be possible to disable it without disabling the ABS.

First, a far more detailed description of how CBC operates out of BMW literature -- not specific to the 1M -- on Dynamic Stability Control (DSC).

"CBC can occur if the vehicle is cornering and ABS regulation is not taking place.

If the [DSC] control unit detects transverse acceleration in excess of 0.6g and the brakes are applied, CBC prevents a build up in brake pressure to the inside rear wheel. This prevents the vehicle from entering into an unstable situation that can lead to Oversteer.

The DSC [control unit] accomplishes this by closing the Inlet Valve, thus not allowing brake pressure to increase at the rear caliper.

The difference in braking force between the two rear wheels creates a yaw force that opposes the oversteer and allows the vehicle to handle neutrally."

I also learned that there is a small "transverse acceleration sensor" -- likely underneath the carpet below the drivers seat -- that is connected to the DSC control module that "produces a linear voltage signal for the lateral acceleration (G-force) that ranges from 0.5 to 4.5 volts. The DSC control module uses this input to determine the side forces acting on the vehicle for DSC regulation."

I'm no engineer, but this suggests to me that it may be possible to disable the CBC either by pulling certain of the fuses for the DSC control module or by "tricking" the transverse acceleration sensor so it never sees voltage that would indicate 0.6g.

Any thoughts about this would be greatly appreciated!

Neil

Last edited by MDORPHN; 03-26-2012 at 10:07 PM.
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      03-26-2012, 10:05 PM   #26
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Do you think this sensor info is the same as what shows up in the CAN bus which I can see in my display of the performance steering wheel? If it is, I wouldn't be surprised if the traction control and perhaps side impact devises would be effected if this was disabled. It would be nice if we could just pull the fuse on the traction control module (valves) which probably executes this feature; at least when the car is being used at the track.
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      03-26-2012, 10:14 PM   #27
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Quote:
Originally Posted by scotth944 View Post
Do you think this sensor info is the same as what shows up in the CAN bus which I can see in my display of the performance steering wheel? If it is, I wouldn't be surprised if the traction control and perhaps side impact devises would be effected if this was disabled. It would be nice if we could just pull the fuse on the traction control module (valves) which probably executes this feature; at least when the car is being used at the track.
Don't know whether or not this sensor info would be displayed.

And I suspect you're right that attempting to disable CBC by pulling fuses for the DSC module might also disable ABS. For this reason, tricking the transverse acceleration sensor may be the better solution.

I'd prefer keeping the ABS, even for use on the track, since I don't have a large enough tire budget to replace flatspotted tires...

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      03-26-2012, 10:26 PM   #28
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If it's just an analog voltage that drives the system, this would not be dificult to generate. If you can get to the sensor it wouldn't be that dificult to measure so a devise can be made to replace it. I'm hoping the sensor already has power being sent to it which a substitute signal could be derived from without alot of rewiring.
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      03-26-2012, 11:16 PM   #29
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I read this as CBC works even if the driver Brakes outside the normal Range of ABS. Meaning the driver Breaks hard enough to activate the ABS.

"CBC counteracts this tendency by asymmetrically distributing brake pressure to the left- and right-side brakes or by reducing pressure (to the rear axle), even if the driver brakes outside the normal range of ABS. The result: a significant improvement in stability and safety when applying light brake pressure, even on bends."

However the preferred method is listed below.

Results of CBC is "a significant improvement in stability and safety when applying light brake pressure, even on bends"

You may want to consider adjusting your driving style before disconnecting the ABS safety net.
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      03-27-2012, 07:48 AM   #30
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Quote:
Originally Posted by Redadair View Post
You may want to consider adjusting your driving style before disconnecting the ABS safety net.
Just to reiterate some earlier points, I'm not talking about street driving, but driving aggressively on road courses with fellow instructors and time trialers where it is a normal technique to use the brakes to rotate the car.

I've already adjusted by driving style to accomodate the CBC (and now have over 30 days on track with my 1M), but it's hurting my lap times and I don't like it!

It's also worth noting that when you turn the DSC off on the E9x M3, the CBC is disabled. Sure wish it was that way on the 1M.

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      03-27-2012, 08:02 AM   #31
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Quote:
Originally Posted by scotth944 View Post
If it's just an analog voltage that drives the system, this would not be dificult to generate. If you can get to the sensor it wouldn't be that dificult to measure so a devise can be made to replace it. I'm hoping the sensor already has power being sent to it which a substitute signal could be derived from without alot of rewiring.
The hard part would be doing this without triggering a lateral acceleration sensor plausibility code (or some such).

It is also possible that the DSC control's triggering of the CBC is based not only on input from the lateral acceleration sensor, but also on steering input and the left and right front wheel speed sensors to verify the turning rate in the corner.

Damn this is complicated!

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      03-27-2012, 01:26 PM   #32
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Yeah it really interferes especially when braking into a hairpin and dropping into first.

With my 300zx I can use that gear drop and trail braking to kind of hop the car into a slight over-steer, keeping small amount of power on and pointing through the gate perfectly for the best acceleration out.

In my 1M, it kicks me back and I have to wait for the front end to come around before I can get my shot. Basically it makes me go wider. I can compensate by entering even slower, but you lose time that way.
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      03-27-2012, 02:25 PM   #33
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Quote:
Originally Posted by Redadair View Post
It sounds like you are too hard on the brakes on trailbraking, there is no reason for the ABS to even be activated unless the wheels are breaking loose from over breaking.

I'll agree with Mdorphin... the car gets a good wiggle sometimes under hard braking when this happens. it;s not a matter of adjusting driving style. I have not found it horrible.. but it is a bit distracting.. Like Mdorphin, I have several track days on my car. I have done a fair amount of driving on track with the traction control in MDM mode.. possibly a factor. In addition, I think my rear pads may actually be wearing faster than the fronts because of CBC
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      03-28-2012, 09:40 AM   #34
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Another quick update.

The DSC control unit in the 1M is a Continental Teves MK60E5.

I believe that it gets input from three different sensors for the Corner Brake Control (CBC) function: a combined rotation rate/lateral acceleration sensor, a steering angle sensor, and the left and right front wheel speed sensors.

Neil
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      07-21-2012, 02:42 PM   #35
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... In addition, I think my rear pads may actually be wearing faster than the fronts because of CBC
if it basically limits the inside rear wheel pressure, in what way does it end up increasing wear?
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      07-21-2012, 05:38 PM   #36
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I wonder if this contributed to why Randy Pobst did not like our car on the track so much.

I think you could have this feature "coded" out of the car if you could find someone to help identify where that specific item exists. It may be worthwhile to ask on the BMW Coding website. You'd probably want to learn how to code if you want to turn it on/off. (if you do not already know how) I tried, have the cable but could not figure it out well enough to do myself. I did have a guy who is local come by though and do some things.
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      07-23-2012, 02:55 PM   #37
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Quote:
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if it basically limits the inside rear wheel pressure, in what way does it end up increasing wear?
by using the brakes to control wheelspin.. The traction control and CBC utilize the brakes to slow one wheel or another to help with traction.
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      07-23-2012, 04:19 PM   #38
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on my 130i cup car we removed the complete control unit which sits under de Drivers seat.

We only had a continue cell burning on the dash and DSC is always off. But ABS worked fine.

Don t know if this will work on the 1M.
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      07-23-2012, 08:49 PM   #39
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Quote:
Originally Posted by Advevo View Post
on my 130i cup car we removed the complete control unit which sits under de Drivers seat.

We only had a continue cell burning on the dash and DSC is always off. But ABS worked fine.

Don t know if this will work on the 1M.
The CBC didn't seem to bother you too much at the track!
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      07-24-2012, 11:19 AM   #40
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no it doesn t.

Just try to brake mostly in a straight line. Trail braking into corners can be done just be very easy on the brake.
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      08-28-2012, 08:42 AM   #41
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Retrofitting E9x M3 ABS Pump controller?

Having just spent 3 days at VIR, I'm once again obsessing about how to eliminate the dreadful Corner Braking Control (CBC) function.

Anyone have insight into feasability of replacing the existing ABS Pump controller with one from an E9x M3?

Since the programming is in the controller, this might allow the CBC to be turned off as it is on the E9x M3.

Of course, as must be done whenever this device is replaced, there would need to be some coding to the ecu and, possibly, valve and sensor calibration.

Thoughts/opinions appreciated!

Neil
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      08-28-2012, 11:56 AM   #42
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Quick question.... How does the car know its in a corner? Do the mechanical levers that are connected to the front suspension arms have anything to do with it? If not, what do they do exactly? I was wondering if disconnecting them would do anything.
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      08-28-2012, 11:59 AM   #43
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Quote:
Originally Posted by tkbr0wn View Post
Quick question.... How does the car know its in a corner? Do the mechanical levers that are connected to the front suspension arms have anything to do with it? If not, what do they do exactly? I was wondering if disconnecting them would do anything.
The levers (really linkages) that I suspect you're referring to are part of the adaptive headlight system.

The car knows it's in a corner through lateral g sensors, a steering angle sensor and computation based on the different rates of rotation of the front wheels.

Neil

Last edited by MDORPHN; 08-28-2012 at 03:56 PM.
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      08-28-2012, 12:24 PM   #44
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I have not yet been to the track, but have done some autocrossing with rather quick setups (65-30ish mph braking in 2 places) and have been working on trail braking more aggressively. I have not felt anything like what you describe. I am on stock pads. Could it have to do with the amount of forward g's you are getting, not only the lateral g's?
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