The Integrated Drive Generator system, or IDG, is a key power system found on aircraft that controls all of the engine hydraulic systems. An IDG consists of a Constant Speed Drive (CSD) and AC generator mounted side by side in a single housing assembly. The CSD uses controlled differential action to maintain the constant output speed necessary to power the generator. Because the IDG has such an important role in powering key components of the aircraft, its reliability is paramount. This blog will explain Integrated Drive Generator systems, how they work, and how to service them properly.
Hydraulic fluids such as oil are critical components of the IDG. Oil is not only used for cooling and lubrication, but also plays a pivotal role within the CSD where it is used to mechanically control the rotational speed of the generator. The IDG is driven by an external engine accessory gearbox, accessible in the engine nacelle. A huge factor in the reliability and effectiveness of the Integrated Drive Generator is the quality, cleanliness, and quantity of oil being used.
The oil level is monitored by the sight glass, which is a tube-shaped level sensor and indicator. The sight glass is transparent, allowing the operator to observe the oil level. The measures an operator should take to ensure the oil’s cleanliness can differ from system to system, so the specific aircraft’s maintenance manual is a valuable source. Contamination of the oil can cause the filter to fail prematurely, leading to excessive wear, eventually causing the IDG to overheat. Oil cans and tools should also be kept in a clean, dry environment, and it is recommended to use a new can of oil each time the IDG is serviced.
The IDG oil system consists of three basic parts: the IDG itself, the external cooling unit, and the IDG oil cooler. While in use, oil is pumping away from the IDG to be sent to the cooler. It is pumped through the pressure fill port, then the filter, before exiting into the external cooling circuit. The oil flows from the external circuit and into the cooler. Here, the oil is cooled and sent back through the same path to the IDG. Like any other part of an aircraft, the IDG must be serviced at regular intervals. Reasons for servicing the IDG include: refilling the IDG with oil, filling a newly-installed IDG, adjusting the oil level, replacing the filter element, and replacing the cooling system.
However, before servicing an IDG, there are a few important things to note. First, be careful when working on engine components shortly after the engine is shut down. Engine components, including the IDG, can remain hot for up to an hour after use. Not only are the metal pieces extremely hot, the oil will be scalding. Wear goggles, insulated gloves, and other protective clothing. Oil of such high temperatures can burn eyes or skin, requiring serious and immediate medical attention.
There are a few more safety tips to know about operating the IDG. First, the IDG should not be operated if there is too much or too little oil present. Either of these scenarios can cause serious damage to the machine. Also, when filling or topping off the IDG, operators should only use new oil whenever possible. Contaminants can easily enter open oil cans, leading to quick degradation of the IDG.