The Kronosphere was a device of Decepticon design which is actually a time machine, though a funny looking one.
It had an automatic recall mechanism allowing it to bring back anything it sent through time.
The Transformers cartoon
The time machine was created by Shockwave under the orders of Megatron who planned to use it to travel into Cybertron's past where he would steal Energon from earlier periods in Cybertronian history before the outbreak of th Great War when the planet had plenty of energy for everyone.
After the Aerialbots were making a nuisance of themselves to Decepticon operations on Earth, Megatron decided to dispose of them by sending them so far back in time that nothing existed, not even the galaxy itself. Starscream managed to lead the dumb bots into the machine where they were supposed to be hopelessly lost in time.
Sadly, in our last chance to get rid of Slingshot, the Autobots attacked Megatron's base where Optimus Prime destroyed the Kronosphere controls thus dumping the Aerialbots in Cybertron's Golden Age which was 9 million years ago. Why Prime, why?!
Once that was done, the Autobots attempted to repair the device in order to get the Aerialbot back to the present. While attempting to fix the machine, the Decpticons attempted to get it back as Megatron believed that it would be disastrous if the Autobots made use of the Kronosphere. which they were successful in doing. Good timing to as the Autobots needed Superion to fight a repaired Guardian robot that the Decepticons fixed and set loose on the Autobots.
The Kronosphere was subsequently destroyed.
In the year 2005, the time-tossed Decepticon Ravage scavenged the shattered remnains of the Kronosphere and rebuilt it, seeking to use its power to alter the flow of history. In the midst of the decisive battle between Optimus Prime and Megatron's forces, Ravage struck, using the Kronosphere to transport Megatron and many of the Decepticons outside of space and time. In doing so, Ravage altered the timeline, leaving the victorious Autobots to face the looming threat of Unicron alone, after which Ravage would bring Megatron and his army back, allowing them to easily crush the weakened Autobots.
The original timeline was later restored thanks to the efforts of a mysterious entity from the far future, but the "Binal-Time" continuity created by Ravage's tampering was also preserved as an alternate timeline.