Friction roller type reduction gear

A friction roller type reduction gear comprising:

• an input shaft configured to receive at least power;
• a first sun roller, mounted on the input shaft, configured to move in an axial direction of the input shaft;
• a plurality of first cam grooves opened in such surface of the first sun roller as is perpendicular to the axial direction and arranged in a periphery of the input shaft, while a depth of the first cam grooves in the axial direction becomes largest in an extending-direction central portions;
• a second sun roller mounted on the input shaft such that the second sun roller is opposed to the surface of the first sun roller on an opposite side of the first cam grooves;
• a plurality of intermediate rollers contacted with outer peripheral portions of the first and second sun rollers;
• an annular roller having an inner peripheral surface that is configured to contact with the intermediate rollers;
• a cam plate mounted on the input shaft such that the cam plate is opposed to the surface of the first sun roller on the first cam groove side;
• a plurality of second cam grooves opened in such surface of the cam plate as is opposed to the first cam grooves and arranged in the periphery of the input shaft, while the depth in the axial direction is largest in the central portions;
• rolling elements interposed between the first and second cam grooves;
• and
• a cage configured to contact with the rolling elements and configured to hold the rolling elements rollably, with a pitch circle diameter of a position for holding the rolling elements different from pitch circle diameter of the first and second cam grooves.