Fixed-type, constant-velocity universal joint

A fixed type constant velocity universal joint, comprising:

• an outer joint member having an inner surface in which a plurality of guide grooves are formed;
• an inner joint member having an outer surface in which a plurality of guide grooves are formed;
• a plurality of balls interposed between the plurality of guide grooves of the outer joint member and the plurality of guide grooves of the inner joint member, for transmitting torque;
• and
• a retainer for retaining the plurality of balls, the fixed type constant velocity universal joint being of a track offset type in which a center of each of the plurality of guide grooves of the outer joint member and a center of each of the plurality of guide grooves of the inner joint member are offset to opposite sides in an axial direction by equal distances, respectively, with respect to a spherical surface center of the inner surface and a spherical surface center of the outer surface,
• wherein R1 representing F/PCR falls within a range of 0.045≦R1≦0.065 on a premise that
• a track offset amount is F, and that
• a length of a segment connecting the center of each of the plurality of guide grooves of the outer joint member or the center of each of the plurality of guide grooves of the inner joint member and a center of each of the plurality of balls to each other is PCR, and
• wherein as representing αt/α falls within a range of 0.045≦As≦0.065 on a premise that
• an angle formed between the following is αt:
• a segment connecting a center of an outer surface of the retainer or a center of an inner surface of the retainer and the center of each of the plurality of balls to each other;
• and
• the segment connecting the center of each of the plurality of guide grooves of the outer joint member or the center of each of the plurality of guide grooves of the inner joint member and the center of each of the plurality of balls to each other, that
• an angle formed between the following is αc:
• the segment connecting the center of the outer surface of the retainer or the center of the inner surface of the retainer and the center of each of the plurality of balls to each other;
• and
• a line connecting a joint center and the center of each of the plurality of balls to each other, and that
• a total of the angles is α.