Documentation/Engine/Units/accessory engine data

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The accessory_engine_data unit class is used to define the engine characteristics for the player's vehicle, as well as some upshift and downshift characteristics for automatic transmission gameplay. Units of this type are usually defined in /def/vehicle/truck/<brand.model>/engine/*.sii


Many common attributes are inherited from accessory_data.

Name Type Default Value Description
info array<string> This member is attribute of accessory data, however three info members are usually defined for accessory_engine_data.
info[]: "197 @@hp@@ (147@@kw@@)"     // The first is the rated power
info[]: "550 @@lb_ft@@ (782 @@nm@@)" // The second is the peak torque
info[]: "1@@dg@@200 @@rpm@@"         // The third is the peak torque speed

Note: The info attribute has no effect on the engine simulation. Rather, it is used for UI display and for attaching to World of Trucks profile truck uploads.

TIP: The strings surrounded by @ are for localization — @@hp@@ displays the localized shorthand for horsepower, @@dg@@ displays the localized thousands separator, etc.

torque float 0 This defines the maximum torque output of the engine in N·m.
torque_curve array<float2> See description This defines the torque output of the engine at various engine speeds, relative to the maximum torque defined in torque. If unset, the default curve is used:
  torque_curve[]: (300, 0)
  torque_curve[]: (440, 0.5)
  torque_curve[]: (1000, 1)
  torque_curve[]: (1300, 1)
  torque_curve[]: (1900, 0.77)
  torque_curve[]: (2400, 0.4)
  torque_curve[]: (2600, 0)

The torque output is linearly interpolated between data points. For engine speeds outside the domain of the data points, the output is clamped to the values at the highest/lowest rpm points. The valid range for torque output is 0-1.

resistance_torque float -1 This is the resistive torque in N·m at 2000rpm, used for passive engine braking and consumption. (New as of ETS 1.27/ATS 1.6)

Note: When unset, or when set to any negative value, resistance_torque is calculated as (volume × 20.0).

rpm_idle float 550 This is the engine speed the virtual engine controller will attempt to maintain with no throttle input.
rpm_limit float 2500 This is the maximum engine speed the virtual engine controller will allow except if the engine is being driven by the wheels (e.g. if the vehicle is running away downhill or the player makes an ill-advised downshift).
rpm_limit_neutral float 2500 This is the maximum engine speed the virtual engine controller will allow if the transmission is in neutral – unless rpm_limit is lower, in which case it is clamped.
rpm_range_low_gear float2 (700, 1500) Defines the downshift and upshift engine speeds in low-range gears. (Automatic transmission)
rpm_range_high_gear float2 (1000, 1500) Defines the downshift and upshift engine speeds in high-range gears. (Automatic transmission)
rpm_range_engine_brake float2 (1500, 2500) Defines the downshift and upshift engine speeds while the engine brake is operating.
rpm_range_power_boost float2 (550, 450) Defines the change to rpm_range_low_gear and rpm_range_high_gear at full throttle when adaptive automatic transmission is enabled.

TIP: Be careful that the resulting values when rpm_range_power_boost is added to rpm_range_*_gear don't exceed rpm_limit. Otherwise, the transmission may fail to shift correctly in adaptive automatic mode.

engine_brake float 1.0 Engine braking torque relative to a typical exhaust brake on an engine of the same volume.
engine_brake_downshift bool true When true, automatic transmissions will downshift upon beginning engine brake behavior, within rpm_range_engine_brake.
engine_brake_positions uint 3 Defines the number of strength levels for the engine brake. The braking torque at each position is based linearly on the number of positions. So for engine_brake_positions: 3 the first position will have 13 of the maximum strength, the second position will have 23 of the maximum strength, and the highest position will have the maximum strength.
volume float 0.0 The (four-stroke) volumetric displacement of the engine in liters. It is used in fuel consumption calculations.

Note: For two-stroke diesel engines, this should be roughly twice the swept volume.

consumption_coef float 1.0 This is used to scale the fuel consumption of the engine relative to the game's calculated value.
adblue_consumption float 0.05 This is how many liters of AdBlue (Diesel Exhaust Fluid) are consumed per liter of fuel.

TIP: For older engines which do not use AdBlue, this attribute should be set to 0.

no_adblue_power_limit float 1.0 When the AdBlue tank is empty, the engine's power is scaled by this factor.

Relevant Unit Conversions and Formulas

Cubic Inches to Liters

1 cu·in = 0.0164 L

Pound-Feet to Newton-Meters

1 lbf·ft = 1.3558 N·m

Horsepower to Kilowatts

1 hp = 0.7457 kW

Torque from Power and Speed (Metric Units)

T [N·m] = ( P [kW] × 9549 ) ÷ N [RPM]

Torque from Power and Speed (English Units)

T [lbf·ft] = ( P [hp] × 5252 ) ÷ N [RPM]