Only having limited knowlage of bike engines I can only hazard a guess that a torque limiter spring puts preasure on the clutch at the limit of power for each gear and disengages it slightly to stop over reving through the gears a bit like a waste gate or dump valve to stop the engine blowing up. Please do not quote me on this as I am guessing myself. If you find out for sure please let me know as I do not have a manual.