Public sector unions in Rhode Island have made good on a threat to challenge sweeping changes to the state’s public pension system. Four lawsuits challenging the landmark pension overhaul were filed Friday in Superior Court. The law suspends pension increases, raises retirement ages, and merges future pensions with 401(k) accounts. Judge Sarah Taft-Carter met with lawyers from both sides Friday and denied the union’s request to block the changes from taking effect July 1. The overhaul was crafted by Governor Lincoln Chafee and Treasurer Gina Raimondo and was passed by lawmakers last fall.