Modelling automatic semi truck transmission using transmission block

I'm trying to achieve a somewhat realistic semi truck driveline for my autonomous semi truck diploma work. I've already achieved a generic engine block with somewhat realistic torque curves. Now i'm stuck on implementing a transmission. The problem i face is im kind of lost on setting the transmission block up. Before the first gearshift i get a somewhat realistic torque curve, but after the shift, it just turns into a constant torque. Also after the initial shift lag, the torque is immediately back straight vertical line, which is not what i would expect. Any ideas how i could implement this in a more sensible way?

Any kind of help is much appreciated, and thank you all in advance.

Answer 1

[Satyam]

Hi Adam,

The sudden constant torque and sharp vertical rise after shifts are typically due to transmission and clutch configuration. You can follow these troubleshooting steps to fix your issue:

Shift model:

• Use Finite shift time (e.g., 300–500 ms) instead of Instantaneous to avoid abrupt torque jumps.

Clutch actuation:

• Replace step-like clutch engagement with a smooth ramp (pressure or torque command).
• Ensure realistic static/kinetic friction torques.

Torque converter:

• Verify Drive/Coast capacity factors and disable lock-up initially. Incorrect vectors can cause constant torque output.

Inertia and damping:

• Add realistic inertias and shaft stiffness/damping to avoid instantaneous speed equalization.
• Modeling Driveline Dynamics

Signal logging:

• Plot torque and speed at engine, turbine, and output shafts to confirm where torque becomes constant.
• Use Simscape Results Explorer for clarity.