US Patent 9425448 Sealed battery and safety valve

A sealed battery includes a return type safety valve. An annular projection that projects toward a valve body from a valve port is formed on a valve seat for the safety valve. The projection includes a first projection region and a second projection region that are defined by a shape of a tip of the projection and arranged in parallel in a circumferential direction of the valve port. The first projection region and second projection region have different curvature radii in a cross-section of the projection taken along an axial direction of the valve body. The pressure per unit area applied to the second projection region by the valve body is higher than the pressure per unit area applied to the first projection region by the valve body.