From BeamNG

The Torque Converter (device name "torqueConverter") is a model of a typical 3-element fluid torque converter. The advantage of a torque converter over a fluid coupling or friction clutch is that it provides torque multiplication at low speeds, as well as a smooth launching ability without any active clutching method. Our model is based on the "Capacity Factor" or "K-factor" model with an added relationship for torque converter sizing, as well as some modifications to work in all speed ratios. It also contains a clutch for "lockup" ability. In a Powertrain, it should be connected to a combustionEngine or an electricMotor, and an automaticGearbox should connect to it.

Jbeam Properties

Name Type Optional Default Value Description
converterDiameter number Ok 0.3 This value is the outer diameter (m) of the torque converter, and is used to scale the capacity of the torque converter. A higher number creates a lower stall speed and stronger coupling between the engine and powertrain. This diameter can often be found in sales or engineering data for torque converters and applied directly to our model. A tiny change in diameter can have a strong effect on stall rpm because the relationship is to the 5th power.
converterStiffness number Ok 10 This value controls the shape of the capacity factor curve. A higher value creates a stiffer feeling torque converter. 5 to 15 is a reasonable range.
converterTorque number Ok Auto calculated The limit for input torque, used for stability reasons. This value is calculated by finding the torque required to stop the engine from redline in 1 second with full power. Not recommended to change.
stallTorqueRatio number Ok 2 This value is the initial torque multiplication ratio when stalled (output speed is 0). Reasonable values are 1.5 to 2.5. This value can be found from typical torque converter literature.
couplingAVRatio number Ok 0.9 This value determines the speed ratio where the torque multiplication reduces to 1 and the torque converter acts as a fluid coupling. Torque converters with higher stallTorqueRatio tend to couple at a lower AV ratio. Reasonable values are 0.8 to 0.95. This value can be found from typical torque converter literature.
fluidDensity number Ok 844 The density of the fluid in the torqueConverter (kg/m^3). Different values will change the effect of diameter. The default is for typical automatic transmission fluid.
lockupClutchTorque number Ok 100 The maximum torque of the lockup clutch. Once torque exceeds this value, the clutch will slip.
lockupClutchSpring number Ok Auto calculated The spring stiffness of the lockup clutch.
kFactorSmoothing number Ok 75 Controls a smoother that reduces torque spikes and increases numerical stability. Too much can cause the torque converter to become laggy and unresponsive. Too little could cause unstable behavior with large diameter converters on small vehicles.
additionalEngineInertia number Ok 0 Sets the inertia of the torque converter in Kg*m^2. This will be automatically added to the engine inertia.


Here is an example of the required powertrain section, along with the additional section for the properties.

    "powertrain": [
        ["type", "name", "inputName", "inputIndex"],
        ["torqueConverter", "torqueConverter", "mainEngine", 1],
    "torqueConverter": {
        "converterDiameter": 0.252,