Oil pump

An oil pump comprising:

• a pump housing having a shaft bearing bore, a pumping chamber, an inlet port and a discharge port, all provided in the pump housing;
• a drive shaft rotatably supported on the shaft bearing bore and connected with meshed pump rotors, for discharging working fluid, which is pressurized within the pumping chamber by way of rotary motion of the drive shaft, through the discharge port, the pump housing and the drive shaft cooperating with each other for defining therebetween first and second journal portions, the first journal portion being located at a first end of two opposing ends of the pump housing for rotatably supporting one axial end of the drive shaft, the second journal portion being located at the second end of the pump housing for rotatably supporting the other axial end of the drive shaft facing the pumping chamber, and the first and second journal portions being positioned at one side of the pump rotors, an inner peripheral surface of the pump housing and an outer peripheral surface of the drive shaft cooperating with each other for defining an annular space between the first and second journal portions in an axial direction of the drive shaft;
• a communication passage portion located in the second journal portion for intercommunicating the annular space and the discharge port on a side of the second journal portion, the pump housing being provided with a cylindrical portion that is integrally formed with the pump housing, and the shaft bearing bore penetrating the pump housing and being formed at the cylindrical portion;
• and
• a plurality of ribs whose one end is connected to the pumping chamber side of the pump housing and whose other end extends up to an end side of the cylindrical portion being integrally provided on an outer peripheral surface of the cylindrical portion,
• wherein the drive shaft is provided with a chain-driven sprocket to which a turning torque is transmitted through an endless chain,
• wherein the ribs longitudinally extend in an overlapping manner with a longitudinal axis of the annular space, and
• wherein oil is provided and stored in the annular space and oil is provided to each journal portion from an entire circumference direction of the annular space.