Brake Pressure Sensor Considerations Re:ABS
07-19-2018, 03:17 PM
#1
Brake Pressure Sensor Considerations Re:ABS
Hi,
Currently planning the install of an AIM brake pressure sensor in a 987-1 SPC. Wondering about the implications of being upstream or downstream of the ABS module. Does it matter, if all other things, like line diameter, are equal? I do understand that I will only get one wheel instead of two. One consideration is comparing brake traces following any ice-pedal incidents to determine cause and/or mitigation techniques and if the sensor location matters beyond monitoring at least one front brake.
Thanks, Tim
Currently planning the install of an AIM brake pressure sensor in a 987-1 SPC. Wondering about the implications of being upstream or downstream of the ABS module. Does it matter, if all other things, like line diameter, are equal? I do understand that I will only get one wheel instead of two. One consideration is comparing brake traces following any ice-pedal incidents to determine cause and/or mitigation techniques and if the sensor location matters beyond monitoring at least one front brake.
Thanks, Tim
07-19-2018, 04:16 PM
#2
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Hi,
Currently planning the install of an AIM brake pressure sensor in a 987-1 SPC. Wondering about the implications of being upstream or downstream of the ABS module. Does it matter, if all other things, like line diameter, are equal? I do understand that I will only get one wheel instead of two. One consideration is comparing brake traces following any ice-pedal incidents to determine cause and/or mitigation techniques and if the sensor location matters beyond monitoring at least one front brake.
Thanks, Tim
Currently planning the install of an AIM brake pressure sensor in a 987-1 SPC. Wondering about the implications of being upstream or downstream of the ABS module. Does it matter, if all other things, like line diameter, are equal? I do understand that I will only get one wheel instead of two. One consideration is comparing brake traces following any ice-pedal incidents to determine cause and/or mitigation techniques and if the sensor location matters beyond monitoring at least one front brake.
Thanks, Tim
As to Ice Mode, if you tune up with the right people, it's pretty well understood what causes it and how to mitigate it. The cause is the performance of the car exceeds the design limits of the system. That is why companies like Pagid have brake pad formulations specific to ABS cars and spend lots of time setting bias, bite, and heat profiles to match the systems.
07-20-2018, 09:40 AM
#3
Three Wheelin'
Having 1 sensor at the wheel to monitor ABS events won't get you much. You really have to have all 4 corners tapped to get a glimpse at what it is doing. Otherwise all you're going to see is if ABS is active or not. There are many potential triggers that would get you low output from the ABS system, so to actually see why it is triggering you need to be analyzing all 4 corners.
07-20-2018, 10:13 AM
#4
Thanks for the insight, Matt.
Driver first, in terms of study. I certainly have a ways to go. Upstream would make the most sense and the first choice.
We, as a race class, (Spec Cayman (987-1)) continue to look at ways to minimize frequent ABS issues across the class participants, including pad formulations, front to rear bite ratios, PCCB PIWIS programming for steel rotors, brake application technique etc. As you say, the cause is well understood. No silver bullet yet, even with some smart tuners involved. Perhaps, none is possible with this car.
It would be helpful to get ABS activations data from the CAN bus instead of looking at sensors. I believe the car supports it but, like brake pressure, its not in the AIM ECU protocol for this car. Let me know if there is an option regarding this.
Driver first, in terms of study. I certainly have a ways to go. Upstream would make the most sense and the first choice.
We, as a race class, (Spec Cayman (987-1)) continue to look at ways to minimize frequent ABS issues across the class participants, including pad formulations, front to rear bite ratios, PCCB PIWIS programming for steel rotors, brake application technique etc. As you say, the cause is well understood. No silver bullet yet, even with some smart tuners involved. Perhaps, none is possible with this car.
It would be helpful to get ABS activations data from the CAN bus instead of looking at sensors. I believe the car supports it but, like brake pressure, its not in the AIM ECU protocol for this car. Let me know if there is an option regarding this.
07-20-2018, 10:26 AM
#5
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Matt’s given great advice. All of the SPC setups I’ve sold are equipped with brake pressure at the exit of the master cylinder.
To diagnose ABS issues, wheel speeds are the key performance indicator required, as any anomaly in those will trigger ABS “events.”
However, an ABS MIL or status channel log can validate and often help diagnose improper codings, bad wspd sensors, poor and intermittent connections and control unit malfunctions.
There have been instances of folks using portions of 987.2 AiM protocol to get more information (specifically brake pressure!?!) out of a 987.1, so clearly there is a lot more there.
With the advent of the latest generation of equipment that allows custom protocols to be built, it’s now possible to combine and make a pretty complete template. I’m certainly working in this direction for the many customers I have who could benefit from it.
I spoke to Joe Hullett after he had just spent three days working on building a MoTeC template for the 981 and all it takes is experience, time and money!
Of course, the more variables you throw at it (pad material, rotor material, cooling, tires), the more you can benefit from monitoring temps, temp rise and temp balance front to back. But SPC is a “spec class,” right?
To diagnose ABS issues, wheel speeds are the key performance indicator required, as any anomaly in those will trigger ABS “events.”
However, an ABS MIL or status channel log can validate and often help diagnose improper codings, bad wspd sensors, poor and intermittent connections and control unit malfunctions.
There have been instances of folks using portions of 987.2 AiM protocol to get more information (specifically brake pressure!?!) out of a 987.1, so clearly there is a lot more there.
With the advent of the latest generation of equipment that allows custom protocols to be built, it’s now possible to combine and make a pretty complete template. I’m certainly working in this direction for the many customers I have who could benefit from it.
I spoke to Joe Hullett after he had just spent three days working on building a MoTeC template for the 981 and all it takes is experience, time and money!
Of course, the more variables you throw at it (pad material, rotor material, cooling, tires), the more you can benefit from monitoring temps, temp rise and temp balance front to back. But SPC is a “spec class,” right?
07-20-2018, 11:48 AM
#6
I will see how I get on with a brake pressure sensor, tire temp sensors, wheel speed and related math channels in the next few weeks and perhaps return to the ABS status issue later in the season. Especially, since it is a custom effort.
Thank you for the input.
Thank you for the input.
07-25-2018, 04:42 PM
#7
Three Wheelin'
I would suggest the following math channels to help you down this path.
Wheel slip percentage. Calculated as the percentage difference between vehicle speed (GPS speed preferred) and the wheel speed. You'll learn more with this signal than with wheel speed alone. You can measure tire slip and produce a simple mu/slip table to figure out where the tire peaks. Using that you can evaluate the wheel slips and long accel channels to better understand how the ABS system is moving pressure around.
Wheel slip percentage. Calculated as the percentage difference between vehicle speed (GPS speed preferred) and the wheel speed. You'll learn more with this signal than with wheel speed alone. You can measure tire slip and produce a simple mu/slip table to figure out where the tire peaks. Using that you can evaluate the wheel slips and long accel channels to better understand how the ABS system is moving pressure around.
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07-31-2018, 07:06 PM
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07-31-2018, 07:10 PM
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I would suggest the following math channels to help you down this path.
Wheel slip percentage. Calculated as the percentage difference between vehicle speed (GPS speed preferred) and the wheel speed. You'll learn more with this signal than with wheel speed alone. You can measure tire slip and produce a simple mu/slip table to figure out where the tire peaks. Using that you can evaluate the wheel slips and long accel channels to better understand how the ABS system is moving pressure around.
Wheel slip percentage. Calculated as the percentage difference between vehicle speed (GPS speed preferred) and the wheel speed. You'll learn more with this signal than with wheel speed alone. You can measure tire slip and produce a simple mu/slip table to figure out where the tire peaks. Using that you can evaluate the wheel slips and long accel channels to better understand how the ABS system is moving pressure around.
Thats why going off each axle (drive versus a ground speed channel) is often more valuable.
Good idea, for sure. Your suggestion will certainly be good for relative comparison with changes.
Just need to be aware of the limitations.
08-01-2018, 08:53 AM
#11
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You'll also need to be sure to log wheel speeds at a high frequency... 5ms loop time minimum (we do it on 1ms, but you probably don't need to try for that just to see what it's up to, roughly).
Oh, and yes, caliper pressure at the same rate...
Of course, you probably only REALLY need to see the front brake pressures, since those would be the ones that'd kill your decel. But you'd need to track all 4 wheel speeds, yes.
Oh, and yes, caliper pressure at the same rate...
Of course, you probably only REALLY need to see the front brake pressures, since those would be the ones that'd kill your decel. But you'd need to track all 4 wheel speeds, yes.
