Electric pump for hydrogen circulation

An electric pump for supplying a hydrogen gas to a fuel cell, comprising:

• a housing defining therein a pump chamber;
• an electric motor disposed in the housing, the motor includes a cylindrical stator that is stationary relative to the housing, a cylindrical motor rotor disposed inside the stator and rotatable relative to the stator, and a cylindrical guide member disposed inside the motor rotor so as to be rotatable with the motor rotor, wherein the cylindrical motor rotor has a first axial end and a second axial end;
• a rotary shaft rotatably supported in the housing, the rotary shaft being rotated by the motor rotor, the rotary shaft being inserted through the guide member so as to be rotatable relative to the stator;
• a rotor disposed in the pump chamber and rotated as the rotary shaft is rotated;
• a transmitting member being a key provided in a key seat extending along the axial direction of the rotary shaft on one of an outer peripheral surface of the rotary shaft between the first end and the second end of the motor rotor and an inner peripheral surface of the guide member which faces the outer peripheral surface of the rotary shaft so that the transmitting member is rotatable therewith;
• and
• a groove formed in the other of the outer peripheral surface of the rotary shaft between the first end and the second end of the motor rotor and the inner peripheral surface of the guide member for the transmitting member to be inserted therein, the groove having an inner surface extending along the axial direction of the rotary shaft, the groove transmitting a rotary torque of the motor rotor to the rotary shaft by a parallel surface contact between the inner surface of the groove and a side surface of the transmitting member such that when contacting, the groove's inner surface is parallel to the transmitting member's side surface, the groove having an opening width along a rotary direction of the rotary shaft, the opening width of the groove being set so that the motor rotor is rotatable for a rotation angle of 2 degrees or more relative to the rotary shaft until the transmitting member is brought into the parallel surface contact with the inner surface of the groove from a state where the transmitting member and the inner surface of the groove are out of contact, the groove and the transmitting member producing an impact torque when the electric pump is started that is transmitted to the rotor disposed in the pump chamber, wherein the transmitting member and the inner surface of the groove are lubricated by a lubricating oil, a plurality of seal members being provided between the electric motor and the rotary shaft for preventing the lubricating oil from leaking out of the electric motor, each seal member is a lip seal, and the groove is positioned between two of the seal members.