Cobb Custom Features: GT-R Traction Control


GT-R Traction Control

Vehicle Application: WM 08-12 GT-R (USDM 09-13) 


4/25/2016




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 work.
 
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 tables are different for CBA and DBA cars in the Torque Reduction from Spark table due to the way that the system works with each timing strategy. You will not be able to take the exact spark and P and I settings and transfer them from CBA to DBA or vice versa, even for the exact same mechanical setup! Transferring between CBA only or DBA only will work fine. 
 
In order to tune the system quickly using real time tables you have the option of setting Traction Map Selection to 8. This will allow you to change the values of any table whose label starts with Mode 8 in real time. At this time there is only Mode 0 (normal per-gear and base table mode), and Mode 8, which all allows you to tune and run the real time tables. 
 
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 (and throttle) 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 Delay Count for Recognizing Gear Request to offset Gear Requested 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 using the Mode 8 version of the variable. You will want to monitor the parameter Trac Gear Requested 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. Torque Reduction calculation will hold a constant value until Gear Current matches Gear Requested, signaling that the shift has been completed, and traction control torque reduction calculation can resume.




Traction Monitors:

  • Gear Current: This is the current transmission engaged gear
  • Gear Requested: This is the next requested gear from the transmission
  • Trac Accel Pedal Reduction: Accel pedal reduction for slip control
  • Trac Gear Requested Delay Count: Starts to count from the time Gear Request initiates, used for determining the necessary Delay Count for Recognizing Gear Request
  • Trac Slip Percent: Calculated wheel slip, raw data
  • Trac Slip Percent Filter: Calculated wheel slip, filtered data, used for torque reduction calculations
  • Trac Slip Target: Current target wheel slip
  • Trac Slip dstate: not used currently
  • Trac Slip iState: Current integral correction used to calculate Trac Slip Reduction Percent
  • Trac Spark Reduc: Total spark timing reduction
  • Trac Torque Red. Integral Component: I-term singled out from traction system for fine tuning
  • Trac Torque Red. Proportional Component: P-term singled out from traction system for fine tuning
  • Trac Torque Reduction Percent: Calcuated value from P&I parameters used as the x-axis in the ignition torque reduction tables




Traction Table Descriptions:

  • (Mode 8) Delay Count for Recognizing Gear Request: 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. - Mode 8 real time table only available when Traction Map Selection = 8
  • Minimum Vehicle Speed for Trac System active: Minimum wheel speed before traction will be active
  • Mode 8 Integral Component: Value used only when in mode 8 of Traction Map Selection. Live variable to help tune traction control. Overrides Per-Gear Integral Component - (axis by gear) table
  • Mode 8 Proportional Component: Value used only when in mode 8 of Traction Map Selection. Live variable to help tune traction control. Overrides Per-Gear Proportional Component - (axis by gear) table
  • Per-Gear Integral Component - (axis by gear): Integral term, per gear, used to calculate Trac Slip Reduction Percent
  • Per-Gear Proportional Component - (axis by gear): Proportional term, per gear, used to calculate Trac Slip Reduction Percent
  • Slip Control Weight Filter 1: Do not modify
  • Slip Control Weight Filter 2: Do not modify
  • Slip Control Weight Filter 3: Do not modify
  • Slip Target Multiplier: Multiplies the current slip target from Target Slip
  • Target Slip: Target wheel slip, Vehicle speed vs pedal position 
  • Target Slip User Multiplier: Multiply target slip value by this value. Allows user to have different "traction slots"
  • Torque Reduction from Accel Pedal: X-axis is Trac Slip Reduction Percent. Table values are accelerator pedal position
  • Torque Reduction from Fuel Cut Severity: Not used currently
  • Torque Reduction from Spark: X-axis is Trac Slip Reduction Percent. Table values represent amount of ignition timing which will be subtracted
  • Traction Control Enable: Set to 1 to enable traction control system, Set to 0 to disable
  • Traction Map Selection: Set to 0 for gear based control, set to 8 in order to use the Mode 8 Integral Component, and Mode 8 Proportional Component 
  • (Mode8) iState Maximum: Maximum integral value allowed - Mode 8 real time table only available when Traction Map Selection = 8
  • (Mode 8) iState Minimum: Minimum integral value allowed - will effect minimum Trac Slip Reduction Percent allowed - Mode 8 real time table only available when Traction Map Selection = 8