Shift operation device of automatic transmission

A shift operation device of an automatic transmission, the shift operation device comprising:

• a shift operation member including:
• a shaft portion supported in a casing of the transmission so as to make a relative displacement in a select direction;
• and
• an arm portion protruding in a radial direction with respect to a center axis of the shaft portion, and moving in the select direction while being retained in a set-back position in which the arm portion is movable in the select direction, thereafter being rotated around the center axis to perform shift operation of a gear;
• and
• a plurality of shift rail members, each of which includes:
• a rail portion supported in the casing so as to make a relative displacement;
• a shift fork portion protruding from the rail portion and performing shift operation of a gear;
• and
• a shift lug portion protruding from the rail portion and capable of being engaged with the arm portion;
• wherein an engagement portion of the shift lug portion which is engaged with the arm portion includes a pair of columnar projections arranged at positions mutually different in the shift direction and in the select direction,
• one of the columnar projections includes a one-side pressure receiving surface for receiving a one-direction pressing force in one direction of the shift direction from the arm portion,
• the other of the columnar projections includes an other-side pressure receiving surface for receiving an opposite-direction pressing force in a direction opposite to the one-direction pressing force from the arm portion,
• when the shift lug portion is retained in a neutral position, the one-side pressure receiving surface and the other-side pressure receiving surface are approximately positioned on a reference orthogonal surface which is superimposed on the center axis of the shaft portion and which is orthogonal to the rail portion, and
• the arm portion is rotated around the center axis from the set-back position to apply the one-direction processing force to the one-side pressure receiving surface, thereby shift-actuating the shift fork portion in one direction and the arm portion is rotated reversely around the center axis from the set-back position to apply the other-direction pressing force to the other-side pressure receiving surface, thereby shift-actuating the shift fork portion in the other direction.