Keane said: "Andy brings added quality to our side in an area that I feel needed to be strengthened. It's always healthy to have competition for places in the squad. I'm sure he'll do well for the club."
He told safc.com: "It's a massive club and it's a great opportunity for me to play in the Premier League.
"The manager played a part in me coming here, but I think he would be a big factor in anyone signing for the club.
"Apart from the manager, I know some of the lads which obviously helps. I've played with a few of them and hopefully that will let me settle in quicker.
"Sunderland is a big club and that's one of the main reasons why I've come here.
"It wasn't a case that I was unhappy at Charlton, it was a case of an opportunity presenting itself, it was too good to turn down."