Volkswagen Traction Control

Vehicle Applications: USDM MK7 GTI / Golf R

10/30/2017

Traction Control System

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.
  

Traction Calculation During Gear Changes

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.  

Stagger (Tire Circumference) Compensation (GTI Only)

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.

Steering Wheel Angle Compensation

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.

Traction Monitors

• 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.

• Trac Torque Reduction Percent: Calculated torque reduction percent used in Torque Reduction from Spark.

Traction Table Descriptions

• Folder: PID Adjustments (Traction)
  
  • (Mode 9) Integral Component: This is the value used when mode 9 is selected using the Slip Target Multiplier (Mode Selector). This is a real-time variable to help tune traction control. When in use, this value will override the per-gear settings from the base table.
  • (Mode 9) Proportional Component: This is the value used when mode 9 is selected using the Slip Target Multiplier (Mode Selector). This is a real-time variable to help tune traction control. When in use, this value will override the per-gear settings from the base table.
  • Per-Gear Integral Component: Integral term, per gear, used to calculate Trac Torque Reduction Percent.
  • Per-Gear Proportional Component: Proportional term, per gear, used to calculate Trac Torque Reduction Percent.
  • iState Maximum: Maximum integral value allowed. 
  • iState Minimum: Minimum integral value allowed. This will affect maximum Trac Torque Reduction Percent allowed.
• Folder: Tire Stagger Compensation
  • Activate Traction Stagger Calcs: This switch enables user adjustable circumference values for the individual drive axles to correct wheel speed. These values will be run through calculations against the OEM setting to determine the appropriate compensation amount. This calculation ONLY applies to wheel speed values used in the Traction Control feature, and applicable COBB Custom Features.
  • Front Tire Circumference: The circumference of the front tires. This value will be run through calculations against the OEM setting to determine the appropriate compensation amount. This calculation ONLY applies to wheel speed values used in the Traction Control feature, and applicable COBB Custom Features.***
  • Rear Tire Circumference: The circumference of the rear tires. This value will be run through calculations against the OEM setting to determine the appropriate compensation amount. This calculation ONLY applies to wheel speed values used in the Traction Control feature, and applicable COBB Custom Features.***
• Folder: COBB Traction Control
  • Default User Traction Slot: This is the default traction control slot for Slip Target Multiplier. The map will be changed to this slot at each key cycle.
  • Gear Change Recognition Delay: This value is the offset from the initial shift request from the transmission to the actual time when the transmission will complete the shift. This value is used to delay the traction control strategy at the optimal time to maintain traction and forward momentum. The value will need to be adjusted for transmissions with more clutch plates than stock. (DSG Only)
  • Manual Gear Change Delay: This value is the total time for Trac Shift Occurring to be active, which is how long the traction control calculations will be frozen. See 'Traction Control During Gear Changes' description for further details. 
  • Minimum Vehicle Speed for Trac System Active: Minimum wheel speed before traction control system will be active. This is measured at the undriven wheels.
  • Mode 9 Slip Target Multiplier: This is the value used when mode 9 is selected using the Slip Target Multiplier (Mode Selector). This is used by the end user to adjust the slip target for different conditions by multiplying target slip by this value. Please note that this variable is ONLY used when in mode 9. When using mode 1-8, the Slip Target Multiplier values will be used but not reflected here. 
  • Slip Calculation Offset: This value offsets the slip calculation to help create a zero point. In some vehicles, there may be a margin of error between the front and rear wheels which will result in a slightly inaccurate measure of slip. Use this table to ensure accuracy in slip detection. This value is added from the active slip calculation.
  • Slip Target Multiplier: Multiply target slip value by this value. This is used by the end user to adjust the slip target for different conditions.
  • Slip Target Multiplier (Mode Selector): This is the user selected mode for the Trac Slip Target Mult Selected, as well as the means to switch to real-time adjustment. Set this between 1-8 for gear based P and I gains and also as the axis in the Slip Target Multiplier table. Set to 9 in order to use the real-time adjustable 1d values.
  • Steering Wheel Angle Slip Modification: This compensation allows for correction of the measured slip occurring from changes in steering wheel angle. The steering wheel angle axis is normalized to represent both left and right turn angles equally. Manipulate this table as needed to ensure accurate slip is being reported while turning.
  • Target Slip: Target wheel slip, Vehicle speed vs pedal position. 
  • Torque Reduction from Spark: This table represents the amount of timing which will be subtracted from current timing to aid in the reduction of wheel slip. The x-axis is Trac Torque Reduction Percent.
  • Traction Control Enable: Set to 1 to enable traction control system, set to 0 to disable.
    
    

*** To quickly calculate the circumference of a tire use the following criteria and formulas:

1. Calculate: Tire Width * Aspect Ratio:

• 275mm * 0.45 = 123.75mm

2. Double result from step1!

• 123.75mm * 2 = 247.5mm

3. Convert rim size to metric units (inches to mm):

• 17" * 25.4mm = 431.8mm

4. Add result from step2 to step3 to find the diameter

• 247.5mm + 431.8mm = 679.3mm

5. Change units to meters 679.3 / 1000 = .6793m