GM > Engine > Torque Management > Engine Torque

Engine Torque Model
The PCM uses a airflow, fuel and thermal efficiency and heat based model of torque.

• Inertia Factor: This is an engine inertia factor that is used to estimate torque required to accelerate/decelerate the engine.
• Fuel Qc Factor: This is the constant used to represent the Heat Of Combustion (Qc) in the torque model.
• MBT Torque Filter: This is the filter coefficient used to filter the calculated Mean Best Torque (MBT).
• Transfer Case Ratio: Transfer case ratio used in 4WD applications to calculate torque values when in 4WD low range.
• Accessory Torque: This is the model of accessory torque load on the engine (excluding AC compressor when engaged).
• Friction Torque: This is the model of friction torque loss within the engine.
• Friction Torque Multiplier: This is a multiplier on the friction torque value at various oil temperatures.

AC Compressor Torque
The AC compressor places a large and variable load on the engine when engaged. The PCM has a complex model of AC Torque load including inertia effects and ramp in/out when the AC clutch first engages. The AC torque calculation is also used to calculate the Idle AC Airflow compensation for IAC/ETC control during idle.

• Torque vs. AC Pressure: This is the torque loss of the AC compressor versus AC Pressure.
• Torque vs. IAT: This is the increase in AC torque loss due to inlet air temperature.
• Inertia Torque: This is the model of inertia torque load for the AC clutch when it engages.
• On Hold Time: Time to hold Inertia Torque before ramp out begins when AC clutch first engages.
• Inertia Torque Airflow Ramp: This controls the ramp out rate of AC inertia torque once the On Hold Time expires.
• Off Hold Time: Time to hold AC torque before decaying to zero when AC clutch is disengaged.
• Torque Reduction: Maximum amount of torque reduction that the AC can request.

AC Bump Torque
This is the transient model of AC torque load when the AC clutch engages and disengages.

• Delay: Time delay between commanding the AC on and the compressor loading up the engine.
• Ramp In: Ramp in rate for AC Compressor torque.
• Ramp Out: Ramp out rate for AC Compressor torque.
• Duration Max: Maximum duration for transient torque model ramp out. After this time AC torque will be set to zero when AC disengages.
• Reset Limit: If AC torque loss delta is less than this the adaptive idle cells will be reset to zero.
• ETC% Max: Maximum amount of extra ETC throttle position the AC airflow can command.
• On Delay: Delay before retarding spark when the AC engages.
• Off Delay: Delay before retarding spark when the AC disengages.
• max Spark Retard: Maximum spark retard the AC transient can request.
• Spark Off Delay: Delay before ramping spark out when the AC disengages. After Off Hold Time expires.

Delivered Torque PWM
The delivered torque PWM is used in various applications. eg. for some Holden vehicles it is used to control the fuel pump voltage.

• Stall: commanded PWM % when stall protect is activated.
• Shift In Progress: commanded PWM % when a shift is in progress.
• Normal Minimum: Minimum allowed PWM %
• Minimum Factor: Factor used to calculate PWM minimum PWM %.
• Fail Condition: PWM % applied to when torque management failure conditions are detected.

Stall Protect

• Enable RPM: If RPM drops below this them Stall Protect PWM % will be commanded.
• Delta Gain: Used for calculating RPM derivative factor to determine if engine stall is likely.
• Disable Factor - Hi: If RPM derivative factor is above this multiplied by current Desired Idle RPM then stall protect will disable (if enabled).
• Disable Factor - Lo: If RPM derivative factor is below this multiplied by current Desired Idle RPM then stall protect will disable (if enabled).