Automatic transmission

An automatic transmission comprising:

• an input member that is disposed in a housing and that receives power of a driving source via a torque converter;
• a planetary gear mechanism including a plurality of elements that are rotatable in the housing;
• a plurality of engagement mechanisms that are switchable to a connection state in which the elements are connected to each other or to a fixed state in which the elements are fixed to the housing;
• an output member;
• a shift position detecting unit that detects a shift position;
• an input rotational speed detecting unit that detects a rotational speed of the input member;
• and
• a controller that receives information regarding the detected rotational speed from the input rotational speed detecting unit and information regarding the shift position from the shift position detecting unit, and that controls the engagement mechanisms,
• wherein the rotational speed of the input member is changed into a plurality of gear speeds and rotation of the input member being freely output from the output member;
• and
• the automatic transmission further comprises
• a switching mechanism that is switchable between a reverse-rotation prevention state and a fixed state, the reverse-rotation prevention state being a state in which forward rotation of one of the plurality of elements is allowed and reverse rotation of the one of the plurality of elements is prevented, the forward rotation being in a rotation direction when a vehicle moves forward, the reverse rotation being in a rotation direction when the vehicle moves backward, the fixed state being a state in which the one of the plurality of elements is fixed to the housing,
• wherein the controller sets the switching mechanism in the reverse-rotation prevention state when the shift position is set in a forward movement range and sets the switching mechanism in the fixed state when the shift position is set in a backward movement range, and
• wherein, when the vehicle is moving backward and the shift position is switched from the backward movement range to the forward movement range, if a vehicle speed is greater than or equal to a first predetermined speed, the controller controls the engagement mechanisms so that the input member is capable of rotating freely and rotation of the output member is prevented.