- #1

Chimaera987

- 8

- 1

- TL;DR Summary
- Hi, I’m making a vehicle simulator and I'm unsure how to calculate the inertia of the drivetrain.

Hi, I’m making a vehicle simulator and I’m not entirely sure if my inertia calculations are right or are completely wrong. What I currently have now is something like this:

1. Engine:

if 4WD:

5. Differential:

7. Wheel:

1. Engine:

- engine_Out_Inertia = engine_Inertia;
*this should contain the inertia of the engine and all of it’s auxiliaries, the flywheel and the clutch parts connected to it*

- clutch_In_Inertia = engine_Out_Inertia

- clutch_Out_Inertia = clutch_Inertia;
*the clutch plate rotates with the gearbox, I guess it also could be included in transmission_Inertia, then this would be 0*

- clutch_Out_Inertia = clutch_In_Inertia + clutch_Inertia

- clutch_Out_Inertia = clutch_In_Inertia * clucthLocking +clutch_Inertia;
*where clucthLocking is a 0-1 value where 0 is clutch is disengaged and 1 is locked? Or should I transfer all of the engine_Inertia once the clutch is engaged??*

- tranmsmission_In_Inertia = clucth_Out_Inertia
- transmission_Out_Inertia = (tranmsmission_In_Inertia + transmission_Inertia) * gearRatio^2

- transfercase_In_Inertia = transmission_Out_Inertia

- transfercase_Out_Inertia_FrontAxle = transfercaseFront_Inertia
*; front axle is disconnected, so only the inertia of the front driveshaft has to be taken into account?* - transfercase_Out_Inertia_ RearAxle = (transfercase_In_Inertia +transfercaseRear_Inertia) * gearRatio^2

if 4WD:

- transfercase_Out_Inertia_FrontAxle = (transfercase_In_Inertia +transfercaseFront_Inertia) * gearRatio^2
- transfercase_Out_Inertia_ RearAxle = (transfercase_In_Inertia +transfercaseRear_Inertia) * gearRatio^2

*Should I divide the transfercase input inertia into two, given that the transfercase splits the torque 50/50?In the case of rear axle inertia should I also add the inertia of the front axle components, given that the whole drivetrain is locked together? Something like this?*- transfercase_Out_Inertia_RearAxle = (transfercase_In_Inertia + transfercaseRear_Inertia + FrontRight_Wheel_Inertia + FrontLeft_Wheel_Inertia) * gearRatio^2

*If this is the case, then full time 4WD cars that have a center differential should also behave like this? or only when the center differential is locked?*5. Differential:

*Like in the case of the tranfercase, do I split the input inertia based on the left/right torque distribution in the differential? Do I include the left wheel side inertia in the right wheel side inertia calculation?*- Rear_Differential_In_Inertia = transfercase_Out_Inertia_RearAxle
- Rear_Differential_Out_Inertia_Left = (Rear_Differential_In_Inertia +differential_inertia) * finalDrive^2
- Rear_Differential_Out_Inertia_Right = (Rear_Differential_In_Inertia +differential_inertia) * finalDrive^2

- Rear_Axle_Out_Inertia_LeftWheel = (Rear_Differential_Out_Inertia_Left + halfshaftLeft_Inertia)
- Rear_Axle_Out_Inertia_RightWheel = (Rear_Differential_Out_Inertia_Right + halfshaftRight_Inertia)

*Sometimes you have unequal length halfshafts, part of the reason why cars torque steer?*7. Wheel:

- Right_Wheel_Inertia = Rear_Axle_Out_Inertia_RightWheel +wheelAssembly_Inertia + brakeDisc_Inertia