Gear pump

A gear pump, comprising:

• a drive shaft;
• a rotary shaft arranged in parallel to the drive shaft;
• a first pump constructed from a first drive gear, a first driven gear rotatably arranged coaxially with the rotary shaft and a first pump chamber for receiving the first drive gear and the first driven gear, the first drive gear being rotated by driving of the drive shaft, the first driven gear engaging the first drive gear, the first pump chamber having a first suction port via which oil is suctioned in accordance with rotation of the first drive gear and rotation of the first driven gear and a first discharge port from which the oil is discharged;
• and
• a second pump constructed from a second drive gear rotatably provided coaxially with the rotary shaft, a second driven gear rotatably provided coaxially with the drive shaft and a second pump chamber for receiving the second drive gear and the second driven gear, the second driven gear engaging with the second drive gear, the second pump chamber having a second suction port via which oil is suctioned in accordance with rotation of the second drive gear and rotation of the second driven gear and a second discharge port from which the oil is discharged,
• wherein the rotary shaft is configured such that the first driven gear and the second drive gear engage directly with and disengage from the rotary shaft in a rotation direction by being moved in an axial direction, and
• wherein the gear pump is configured to selectively operate in a first state or second state,
• wherein in the first state, the first driven gear and the second drive gear are configured to rotate relatively and the rotation of the first driven gear is not transmitted to the second drive gear, thereby operating only the first pump, and
• wherein in the second state, the first driven gear and the second drive gear are not configured to rotate relatively and the rotation of the first driven gear is transmitted to the second drive gear, thereby operating both of the first pump and the second pump.