Understanding Speed / Torque Shift Strategies

Like most OEM transmission controllers, the COMPUSHIFT also has the ability to have different shift strategies based on the torque output of the engine. This dual strategy only applies to clutch-to-clutch shifts, and even then not to all of them.

During a gear change, there are two transitions that need to take place to complete the shift. Torque and Speed.

Torque transition is referring to the transfer of torque from one clutch to another.

Speed transition is referring to the change in speed from one ratio to another.

The primary difference between the two strategies is which transition happens first.

The two types of strategies are therefor defined as:

• Torque-Speed (TS) - Torque transitions first, then the speed change happens.
• Speed-Torque (ST) - Speed change happens first, then the torque transitions.

Each upshift and downshift generally will have both an TS and a ST shift depending on drivers demand torque, vehicle speed, current gear, etc. To know which type of shift is happening, helps with being able to tune the COMPUSHIFT to ensure the shift is doing exactly what it should.

Upshifting - Torque/Speed

In most cases, upshifting while on-throttle is going to be a TS shift. Engaging the next gear will start applying the Torque to the next clutch which will result in bringing the expected slip to 0 (Speed Change), and now you are in the next gear. Torque Transitions first, then Speed Changes.

Upshifting - Speed/Torque

If you were travelling downhill with little or no throttle application, eventually you will get fast enough for the transmission to upshift. This is where the speed change needs to happen first before we can transition the torque. While you technically could do a TS shift, it would usually create an uncomfortable thump.

Downshifting - Torque/Speed

This is referred to as an engine braking downshift as we are using the engine to slow down the vehicle. By applying transitioning to torque to the next clutch, this forces the engine to change speed.

Downshifting - Speed/Torque

This strategy is commonly seen while executing an overtaking procedure. While stepping down on the throttle, you cause the engine speed to rise, causing the speed change to happen. Then engaging the clutch allows the torque transition to happen.