Oil pump with air vent structure

1. An oil pump for an automatic transmission, the automatic transmission comprising:

an oil an filled with a volume of oil to a predetermined oil level and coupled to a transmission case and a pump cover of the oil pump;

where the oil pump comprises a suction port connected to a first suction passage, wherein the first suction passage is arranged in parallel with a second suction passage connected to an auxiliary pump, and the first and second suction passages branch from an upstream suction passage leading to an oil strainer submerged in the volume of oil;

a discharge outlet connected to a first discharge passage;

the pump cover formed with a discharge port, the discharge port connected to the discharge outlet;

an air vent hole formed in the oil pump cover disposed downstream of the suction port and upstream of the discharge outlet;

where the transmission case is coupled to a control valve body; and a communication passage connected to the air vent hole and comprising the control valve body which projects toward a bottom of the oil pan and a lower portion of the control valve body is located below the predetermined oil level in the oil pan so as to communicate the air vent hole with the volume of oil inside the oil pan, where the communication passage is formed to extend through an inside of the transmission case and the control valve body.

2. The oil pump as claimed in claim 1 , wherein:

the first discharge passage is arranged in parallel with a second discharge passage connected to the auxiliary pump;

the first and second discharge passages join at a junction into a downstream discharge passage;

the first discharge passage is provided with a first unidirectional valve configured to open and close the first discharge passage, wherein the first unidirectional valve is arranged upstream of the junction; and

the second discharge passage is provided with a second unidirectional valve configured to open and close the second discharge passage, wherein the second unidirectional valve is arranged upstream of the junction.

3. The oil pump as claimed in claim 2 , wherein:

the first unidirectional valve is arranged to close in response to receipt of oil pressure from the second discharge passage, and to open so as to communicate an upstream side of the first unidirectional valve with a downstream side of the first unidirectional valve in response to a condition that the upstream side is higher in pressure than the downstream side by a predetermined amount; and

the second unidirectional valve is arranged to close in response to receipt of oil pressure from the first discharge passage, and to open so as to communicate an upstream side of the second unidirectional valve with a downstream side of the second unidirectional valve in response to a condition that the upstream side of the second unidirectional valve is higher in pressure than the downstream side of the second unidirectional valve by a predetermined amount.

4. The oil pump as claimed in claim 1 , comprising a hollow projection constitutes the control valve body.

5. The oil pump as claimed in claim 1 , comprising:

a pump housing layered on the oil pump cover so as to define a pump chamber therebetween, wherein:

the air vent hole is constituted by a groove formed in the oil pump cover; and

the groove extends from the discharge port along a surface of the oil pump cover in contact with the pump housing.

6. The oil pump as claimed in claim 1 , comprising:

a pump housing layered on the oil pump cover so as to define a pump chamber therebetween, wherein:

the air vent hole extends from the discharge port in an axial direction of the oil pump cover.