US Patent 7954394 Range switching device

A parking switching valve includes a spool that is movable to a first position and to a second position. The parking switching valve also has an oil chamber that generates a biasing force from a difference in the pressure receiving area between the land portions of the spool. The oil chamber has a second input port to which a line pressure is input while the spool is in the second position. Because the line pressure is input to the second input port, a biasing force is generated so that the spool is held in the second position against a spring. As a result, a parking device is held in a parking release state.