You are correct of course its prime function is within the operation and control of the IDG/CSD variable swash plate and being pumped by the pistons a la automatique....to ensure a constand output speed to the generator - whence the heat generation is built up then for the oil to do its next function of cooling while all the time lubricating the moving bits....
The charge oil is then used:
- as a motive flow in the hydraulic and control system,
- for cooling and lubrication of the hydraulic parts.
Remember not to overfill the oil system as this will also cause overheating of the IDG/CSD as the frothed up oil struggles to move round the cooling system.
For once too mush oil is not good.....