Cosmitron

So vital of a part that Ironhide can't even recall the name.

A cosmotron is a piece of Cybertronian technology of unspecified function. What is known is that Optimus Prime's cosmotron was severely damaged during a battle with the Decepticons, and the Autobot leader surely would have perished if his cosmotron had not been replaced, suggesting that whatever purpose it serves is a vital one.

From Teletraan I: The Transformers Wiki, a Wikia wiki.