Vehicle Applications: USDM MK7 GTI / Golf R
10/30/2017
Use of this system requires some knowledge of how a PID system works. The current system is using only the P and I components at this time. Proportional control is a direct acting parameter based on the immediate offset of the value from the target value. Integral is a reaction to the difference between the target value and the current value which adds or subtracts against itself over time.
Traction Control Enable will need to be set to 1 for the system to apply power reductions based on slip. If the system is disabled, calculations will still be available to monitor, but no ignition reductions will be applied. Traction Control can be enabled or disabled in realtime with Accesstuner software.
The values used in Torque Reduction from Spark will have an effect on the values that you use for P and I, since P and I values calculate the Trac Torque Reduction Percent value which is referenced in the Torque Reduction from Spark table. If you lower the values for ignition timing you will find that you need a higher P and I to produce same ignition reduction result. The opposite would be true if you raised the values.
The base table values for the Traction Control system are generic and may need further adjustment for each vehicle. You may or may not be able to take the calibration settings from one application and transfer them to others, even for the exact same mechanical setup! Take the time to adjust each component for the specific use case scenarios applicable to your customers.
In order to tune the system quickly using real time tables you have the option of setting Slip Target Multiplier (Mode Selector) to 9. This will allow you to change the values of any table whose label starts with Mode 9 in real time. Using modes 1-8 will result in various 1D and 2D table lookups to be used from ROM values (normal per-gear and base table mode), and using mode 9 will allow you to tune and run the real time tables. Keep in mind that tables with the BR icon can also be adjusted in realtime regardless of the mode!
iState Maximum can be used like a hysteresis for the system becoming active due to wheel slip.
iState Minimum is the maximum correction the integral and proportional component will be able to apply and will also limit the maximum Trac Torque Reduction Percent which can be calculated. You can use the parameter to limit the maximum amount of timing you would like to see removed.
The COBB traction control system has a special designation for a shift event for more accurate torque control during shift events. While traction is still being controlled heavily, especially in lower gears, the system is very useful.
For vehicles equipped with DSG Transmissions:
In order to tell the system that a shift is occurring we look to see if Current Gear is equal to Current Gear Predicted. When these are not equal we set Trac Shift Occurring which starts a timer Trac Gear Change Recognition Delay which references the table Gear Change Recognition Delay to offset the time before the shift is accounted for by the traction system. The reason for this offset is the length of time from when the gear shift is started electronically and then actually physically achieved, and we'd like to freeze the traction control calculations at the very last moment for the greatest amount of accuracy. This parameter is configurable in real time. When Trac Shift Occurring is active, traction calculations are frozen at their last known value. This allows for any major changes in wheel speed as a result of a shift to be ignored by the system so that it does not over compensate and reduce torque further than necessary. For a car with a standard DSG transmission the value should be 0. This feature is meant for cars which have aftermarket clutch packs installed which map alter the normal operation of the transmission.
For vehicles with Manual Transmissions:
In order to tell the system that a shift is occurring we look for the top clutch switch and then set Trac Shift Occurring which starts a timer Trac Gear Change Recognition Delay which references the table Manual Gear Change Delay. Trac Shift Occurring will be active after the clutch has been pressed until Trac Gear Change Recognition Delay exceeds the value of Manual Gear Change Delay. During this time traction calculations are frozen at their last known value. This allows for any major changes in wheel speed as a result of a shift to be ignored by the system so that it does not over compensate and reduce torque further than necessary. This value should be set based on the average shift speed of the intended driver for the car. If the value is set too high, you will have a torque reduction (if the system was reducing torque before the clutch was pressed) in the next gear which will be removing power unnecessarily.
The COBB traction control system includes compensation to account for mismatched front/rear tires. This feature was designed originally for drag-racers who run "slicks and skinnies". The system works ONLY for the Traction Control feature, and will not correct any other wheel speed measurements for the OEM systems. The reason for this compensation is to ensure appropriate slip can be calculated when there are rotational speed differences between axles. This system is not for individual wheels, but paired axles. This means both FL/FR, or RL/RR wheels will need to match for the compensation to be useful. This compensation is configurable in real time, and default values may not be sufficient for most users. Once the system is activated, simply adjust the Front Tire Circumference and Rear Tire Circumference tables as needed.
The COBB traction control system includes compensation to account for changes in steering angle. The input is measured using Steering Angle and feeds directly into the Steering Wheel Angle Slip Modification table. The value in the table is applied to Trac Slip Percent Filtered. The reason for this compensation is to ensure appropriate slip is accounted for as the wheels begin to turn at different speeds when turning. This table is not configurable in real time, but default values may be sufficient for most users. If this system is going to be used outside of straight line acceleration, it will be important to adjust this compensation along with the Slip Target: table for the application.
Current Gear: This is the current transmission engaged gear.
Current Gear Predicted: This is the next requested gear from the transmission (DSG Only).
Steering Angle: Steering wheel angle from center.
Trac Gear Change Recognition Delay: This is a timer which starts when Trac Shift Occurring is active.
Trac SWA Comp: Steering Wheel Angle compensation multiplier based on current Steering Wheel Angle.
Trac Shift Occurring: This is active when Current Gear and Current Gear Predicted are not equal, or if the clutch pedal has been depressed. See 'Traction Control During Gear Changes' description for further details.
Trac Slip Percent: Wheel slip calculated before filtering and compensations.
Trac Slip Percent Filtered: Filtered and compensated (Trac SWA Comp), this is what is used as the final slip calculation for torque reduction.
Trac Slip Target: Current target wheel slip from the Slip Target table.
Trac Slip Target Mult Selected: User selected multiplier for target slip (from Slip Target Multiplier Table).
Trac Slip iState: Total of P and I correction.
Trac Spark Reduction: Total spark timing reduction applied to reduce torque based on Trac Slip Target and Trac Torque Reduction Percent.
Trac Torque Red. Integral Comp.: I-Term singled out from traction system for fine tuning.
Trac Torque Red. Proportional Comp.: P-Term singled out from traction system for fine tuning.
*** To quickly calculate the circumference of a tire use the following criteria and formulas:
Example Tire Size - 275/45/17 | |
---|---|
Tire Width | 275 mm |
Aspect Ratio | 0.45 |
1. Calculate: Tire Width * Aspect Ratio:
2. Double result from step1!
3. Convert rim size to metric units (inches to mm):
4. Add result from step2 to step3 to find the diameter
5. Change units to meters 679.3 / 1000 = .6793m