Sorry.....Errr.."clutch"....
My understanding, both before and after that great graphic, is that the spring-loaded plunger is released by the solenoid (when the DISC switch is held), and positions itself in the rotating wormdrive of the IDG input shaft.
That rotation then forces the wormdrive to displace the input shaft of the IDG such that the spline is fully withdrawn and all IDG rotation ceases, with (manual) reset only available on the ground with the engine shut down.
If the engine is operating at less than idle RPM, the spline drive may not fully withdraw, and although the IDG will still cease to rotate, the two will not be 100% disconnected, like just enough to damage the spline entry surfaces.
Understand, this is quite a violent mechanical action when actuated, the pin drops in and WHAM, the drive is forced out at great speed, enough to fully separate the two drive ends.
That's about as basic as I can explain it!
Cheers..FD..
