Abstract: A support member 10 having a tubular portion 11 is joined at an end portion of a muffler pipe 1. The support member 10 forms a flange 12 as a valve seat and a support bracket 14. The support bracket 14 has a valve disk 20 supported rotatably via a hinge axis 15. The valve disk 20 has an outer peripheral portion 12 as a contact surface with the valve seat, and a weight 30 is welded to a bead portion 23 with an inner portion thereof projecting to the back face. A spring is wound around the hinge axis, with one end 18 engaging a back face of the valve wall 21 for the valve disk, the other end engaging a support bracket. The resonance frequency is decreased by the weight, thereby preventing the beat sound from arising in a normal range of the engine speed. The weight is welded to the bead portion, thereby not causing the outer peripheral portion 23 as the contact surface to be distorted.

Abstract: A support member 10 having a tubular portion 11 is joined at an end portion of a muffler pipe 1. The support member 10 forms a flange 12 as a valve seat and a support bracket 14. The support bracket 14 has a valve disk 20 supported rotatably via a hinge axis 15. The valve disk 20 has an outer peripheral portion 12 as a contact surface with the valve seat, and a weight 30 is welded to a bead portion 23 with an inner portion thereof projecting to the back face. A spring is wound around the hinge axis, with one end 18 engaging a back face of the valve wall 21 for the valve disk, the other end engaging a support bracket. The resonance frequency is decreased by the weight, thereby preventing the beat sound from arising in a normal range of the engine speed. The weight is welded to the bead portion, thereby not causing the outer peripheral portion 23 as the contact surface to be distorted.