Ford Traction Control

Vehicle Applications: Fiesta ST, Focus ST, Focus RS, Mustang EcoBoost 

7/6/2016

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.

 
Enable Switch (Traction Control) 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 Slip Reduction (Spark) will have an effect on the values that you use for P and I, since P and I values calculate the (TRAC) Slip Reduction value which is referenced in the Slip Reduction (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 a 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 (TRAC) Slip Target Multiplier (Mode) 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!
 
I-Term Limit (High) can be used like a hysteresis for the system becoming active due to wheel slip. 
I-Term Limit (Low) is the maximum correction the integral and proportional component will be able to apply and will also limit the maximum (TRAC) Slip Reduction 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. In order to tell the system that a shift is occurring we use Slip Reduction Delay Limit (Shifting) to offset Gear Commanded 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. This parameter is configurable in real time. You will want to monitor the parameter (TRAC) Shift Delay Count, and the start of the actual shift event where you will see the rpm monitor start to decrease. Taking that value where rpm is about to or has just started to decrease for the delay count will let the system know when to freeze torque reduction calculation. (TRAC) Slip Reduction calculation will hold a constant value until Gear Current matches Gear Commanded, signaling that the shift has been completed, and (TRAC) Slip Reduction calculations can resume.

Stagger (Tire Circumference) Compensation

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. 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 Tire Circumference (Front) and Tire Circumference (Rear) tables as needed.

Steering Wheel Angle Compensation (except Fiesta ST)

The COBB traction control system includes compensation to account for changes in steering angle. The input is measured using (TRAC) Steering Wheel Angle and feeds directly into the Slip Compensation (SWA) table. 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.

YAW Compensation (except Fiesta ST)

The COBB traction control system includes compensation to account for changes in YAW. The input is measured using (TRAC) YAW Rate and feeds directly into the Slip Compensation (YAW) table. The reason for this compensation is to ensure appropriate slip is accounted for as the wheels begin to turn at different speeds when the vehicle begins to rotate. 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

• Gear Current: This is the current transmission engaged gear.
• (TRNS) Gear Commanded: This is the next requested gear from the transmission (AT Only).
• (TRAC) Enable Flag (Main): Status of the Traction Control system, 1 is enabled, 0 is disabled.
• (TRAC) Enable Flag (Stagger): Status of the Traction Control tire circumference compensation system, 1 is enabled, 0 is disabled.
• (TRAC) Front Circumference: User entered value for the front tire circumference compensation system, only used when (TRAC) Enable Flag (Stagger). ***
• (TRAC) I-Gain: Integral gain for the Traction Control PI system.
• (TRAC) I-Portion: I-Term singled out from traction system for fine tuning
• (TRAC) P-Gain: Proportional gain for the Traction Control PI system.
• (TRAC) P-Portion: P-Term singled out from traction system for fine tuning
• (TRAC) Rear Circumference: User entered value for the rear tire circumference compensation system, only used when (TRAC) Enable Flag (Stagger). ***
• (TRAC) SWA Compensation: Steering Wheel Angle compensation multiplier based on current (TRAC) Steering Wheel Angle.
• (TRAC) Shift Delay Count: Starts to count from the time Gear Commanded initiates, used for determining the necessary Slip Reduction Delay Limit (Shifting). (AT Only)
• (TRAC) Shift Delay Target: Target value from the Slip Reduction Delay Limit (Shifting). (AT Only)
• (TRAC) Slip Actual: Calculated wheel slip, filtered data, used for torque reduction calculations.
• (TRAC) Slip Desired: Current target wheel slip from the Slip Target table.
• (TRAC) Slip Reduction: Calculated value from PI control system parameters used as the x-axis in the Slip Reduction (Spark) table.
• (TRAC) Slip Target Multiplier: The current multiplier applied to the (TRAC) Slip Desired amount based on the current (TRAC)Slip Target Multiplier (Mode).
• (TRAC) Slip Target Multiplier (Mode): This is the user selected mode for the (TRAC) Slip Target Multiplier, and other associated tables.
• (TRAC) Spark Retard: Total spark timing reduction applied to reduce torque based on (TRAC) Slip Actual and (TRAC) Slip Reduction.
• (TRAC) Steering Wheel Angle: Steering Wheel Angle measured in absolute degrees.
• (TRAC) YAW Compensation: YAW Velocity compensation multiplier based on current (TRAC) YAW Rate.
• (TRAC) YAW Rate: YAW Velocity used to aid in compensation for the (TRAC) Slip Actual accuracy.

**Also see other Engine & Transmission Monitor List for Ford Vehicles 

Traction Table Descriptions

• Folder: PID (Traction)
  
  • (Mode 9) Gain (Integral): 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) Gain (Proportional): 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.
  • Gain (Integral): Integral term, per gear, used to calculate (TRAC) Slip Reduction.
  • Gain (Proportional): Proportional term, per gear, used to calculate (TRAC) Slip Reduction.
  • I-Term Limit (High): Maximum integral value allowed.
  • I-Term Limit (Low): Minimum integral value allowed. This will affect maximum (TRAC) Slip Reduction allowed.
• Folder: Stagger Compensation
  • Enable Switch (Stagger Compensation): 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.
  • Tire Circumference (Front): 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.***
  • Tire Circumference (Rear): 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: Traction Control
  • (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. They will be reflected in the (TRAC) Slip Target.
  • Enable Speed: Minimum wheel speed before traction control system will be active. This is measured at the undriven wheels.
  • Enable Switch (Traction Control): Set to 1 to enable traction control system, set to 0 to disable.
  • 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 Compensation (SWA): 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.
  • Slip Compensation (YAW): This compensation allows for correction of the measured slip occurring from changes in yaw rate. The yaw rate axis is normalized to represent both left and right rate changes equally. Manipulate this table as needed to ensure accurate slip is being reported during applicable yaw rate change events.
  • Slip Reduction (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) Slip Reduction percent.
  • Slip Reduction Delay Limit (Shifting): 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. (AT Only)
  • Slip Target: Target wheel slip, Vehicle speed vs pedal position. 
  • 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 Multiplier, as well as the means to switch to real-time adjustment. Set this between 1-8 for gear based gains using the ROM set values in the Slip Target Multiplier table. Set to 9 in order to use the real-time adjustable 1d value.
    
    

*** 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. Now calculate the tire circumference 

• Tire circumference: Circumference = Diameter * PI
• Where Diameter was calculated from step4
• Where PI = 3.141592
• 679.3mm * 3.141592 = 2134.08mm

6. Input the calculated Circumference value calculated in step5 for the current axle.