Oil pump having plurality of outer rotor pieces

An oil pump comprising:

• a rotatable inner rotor including a vane-housing unit that houses a plurality of vanes such that the plurality of vanes is slidable in a radial direction;
• a rotatable annular outer rotor including a plurality of vane-connecting parts connected with tip ends of the plurality of vanes located radially outward;
• a first volume-changing part, which is provided between the rotatable inner rotor and the rotatable annular outer rotor, a first volume of which is changed in response to eccentricity of the rotatable inner rotor with respect to the rotatable annular outer rotor, thereby providing a pumping function;
• and
• a second volume-changing part, which is provided in the rotatable annular outer rotor, a second volume of which is changed by a change in a distance between the plurality of vane-connecting parts adjacent to each other in a circumferential direction in response to the eccentricity of the rotatable inner rotor with respect to the rotatable annular outer rotor, thereby providing a pumping function, wherein
• the rotatable annular outer rotor includes a plurality of outer rotor pieces annularly connected to each other,
• each of the plurality of outer rotor pieces includes a first engaging part provided in a first end surface of each of the plurality of outer rotor pieces in an axial direction and a second engaging part provided in a second end surface of each of the plurality of outer rotor pieces in the axial direction and being engageable with the first engaging part of an adjacent one of the plurality of outer rotor pieces,
• the plurality of outer rotor pieces is circumferentially arranged in a state where the first engaging part and the second engaging part of the plurality of outer rotor pieces being adjacent to each other engage with each other such that a distance therebetween in the circumferential direction is variable,
• the first engaging part is provided in the first end surface of each of the plurality of outer rotor pieces in the axial direction to extend in an arcuate manner,
• the second engaging part is provided in the second end surface of each of the plurality of outer rotor pieces in the axial direction to extend in the arcuate manner,
• the first engaging part and the second engaging part engage with each other such that the same are slidable in the circumferential direction with respect to each other in an engaging state,
• the first engaging part is formed by one of a convex part and a concave part provided in the first end surface of each of the plurality of outer rotor pieces in the axial direction to extend in the arcuate manner, and
• the second engaging part is formed by the other of the convex part and the concave part provided in the second end surface of each of the plurality of outer rotor pieces in the axial direction to extend in the arcuate manner and being engageable with the first engaging part of the adjacent one of the plurality of outer rotor pieces.