Automatic transmission

1. An automatic transmission, comprising:

an input member disposed inside a casing and configured to rotate by receiving a driving force from a driving source;

a planetary gear mechanism having a plurality of elements rotatable inside the casing;

a plurality of engagement mechanisms which are switchable to a connected state in which the plurality of elements are connected to each other or are switchable to a fixed state in which the plurality of elements are fixed to the casing;

an output member configured to output rotation; and

a control part configured to control the engagement mechanisms,

wherein the automatic transmission is mounted in a vehicle, the vehicle transfers a rotation of the input member into a plurality of gear shift stages by the planetary gear mechanism and the engagement mechanism and outputs from the output member,

the automatic transmission further comprising:

a lubricating fluid supply mechanism configured to supply a lubricating fluid to one of the plurality of elements;

an output member rotation speed detector configured to detect an rotation speed of the output member; and

a driving source output detector configured to detect an output of the driving source,

wherein each of the plurality of engagement mechanisms comprises:

a switching mechanism corresponding to a predetermined element among the plurality of elements and capable of switching between a reverse rotation prevention state configured to allow normal rotation of the predetermined element and to prevent reverse rotation of the predetermined element, and the fixed state, and

a frictional engagement mechanism capable of switching between the connected state or the fixed state and an open state for releasing the connected state or the fixed state is released,

the switching mechanism comprises a first member fixed to the casing, a second member connected to the predetermined element corresponding to the switching mechanism and configured to perform normal rotation or reverse rotation with respect to the first member, and a switching member installed on the first member and engageable with the second member,

the switching member prevents normal rotation of the second member at a time of engaging with the second member and causes the predetermined element corresponding to the switching mechanism to be in the fixed state and allows normal rotation of the second member at a time of not engaging with the second member and causes the predetermined element corresponding to the switching mechanism to be in the reverse rotation prevention state,

an input torque varying on a basis of the output of the driving source and a friction torque generated in a direction opposite to the input torque are input to the second member, wherein the friction torque is generated by the lubricating fluid present inside the frictional engagement mechanism and varying on a basis of the rotation speed of the output member, and

the control part recognizes the input torque and the friction torque when an instruction to switch the switching mechanism from the fixed state to the reverse rotation prevention state is received while the frictional engagement mechanism is in the open state, and switches the switching mechanism from the fixed state to the reverse rotation prevention state while the input torque is equal to or greater than the friction torque.

2. The automatic transmission according to claim 1 , further comprising a temperature detector configured to detect a temperature of the lubricating fluid,

wherein the control part recognizes the friction torque applied to the switching mechanism due to the lubricating fluid present inside the frictional engagement mechanism on a basis of the rotation speed of the output member and the temperature.