Lock-up clutch of fluid transmission device

A lock-up clutch of a fluid transmission device mounted between a pump impeller and a turbine impeller and capable of connecting said impellers directly to each other, comprising

• an annular clutch outer mounted in a side cover connected to the pump impeller to cover a back of a turbine impeller, a clutch inner disposed radially inside said clutch outer and connected to said turbine impeller, a driving friction plate axially movably connected to said clutch outer, first and second follower friction plates connected to said clutch inner for movement toward and away from each other with said driving friction plate interposed therebetween, an inner chamber defined between said first and second follower friction plates, and an outer chamber defined in said side cover and faced by outer sides of said first and second follower friction plates wherein the inside of said inner chamber is put at a pressure higher than that in said outer chamber to bring said lock-up clutch into a disengaged state in which said follower friction plates are spaced apart from said driving friction plate, and the inside of said outer chamber is put at a pressure higher than that in said inner chamber to bring said lock-up clutch into an engaged state in which said follower friction plates are in pressure contact with said driving friction plate, wherein said clutch outer comprises a pair of sidewalls axially opposed to each other, and a peripheral wall integrally connecting said sidewalls to each other on the side of an outer periphery, said clutch outer having a plurality of narrower portions and a plurality of wider portions, which are formed alternately thereon, said narrower portions having a smaller distance between said sidewalls, and said wider portions having a larger distance between said sidewalls, and transmitting claws projectingly provided on an outer periphery of said driving friction plate are axially movably disposed within said narrower portions, and damper springs are accommodated within said wider portions with their opposite ends resiliently engaged with end faces of said narrower portions and said transmitting claws.