Contra-rotating propeller marine propulsion device

1. A contra-rotating propeller marine propulsion device that makes a front propeller and a rear propeller rotate in directions opposite to each other by a rotational driving power source, wherein the contra-rotating propeller marine propulsion device comprises:

(a) a hollow outer shaft having the front propeller attached to a rear end thereof and the hollow outer shaft is rotatably supported by a ship body;

(b) an inner shaft having the rear propeller attached to a rear end thereof and the inner shaft is rotatably supported in the outer shaft;

(c) a contra-rotating front bearing and a contra-rotating rear bearing provided at a distance in an axial direction between the hollow outer shaft and the inner shaft in order to rotatably support the inner shaft with respect to the hollow outer shaft;

(d) a contra-rotating front seal unit and a contra-rotating rear seal unit respectively provided in front of the contra-rotating front bearing and behind the contra-rotating rear bearing in order to prevent leakage of first lubricant oil supplied to the contra-rotating front bearing and to the contra-rotating rear bearing, and wherein the hollow outer shaft includes a hollow outer intermediate shaft surrounding the contra-rotating front seal unit, and the hollow intermediate shaft is rotated by a driving unit that is the rotational driving power source;

(e) lubricant oil supply means is disposed to supply second lubricant oil into the hollow outer intermediate shaft, and wherein the second lubricant oil is supplied to the contra-rotating front seal unit as the second lubricant oil is accumulated in the hollow outer intermediate shaft; and

(f) an oil amount adjusting unit that has a circular opening and functions as a dam, wherein the oil amount adjusting unit is provided on a front side of the hollow outer intermediate shaft, wherein the oil amount adjusting unit is located at a position that exists on a front side of the contra-rotating front seal unit and that is separated from the contra-rotating front seal unit in an axial direction of the hollow outer intermediate shaft, wherein the second lubricant oil from the oil supply means is supplied into the hollow outer intermediate shaft through the circular opening from the front side of the hollow outer intermediate shaft, and wherein a diameter of the circular opening is set so that the second lubricant oil accumulates in the hollow outer intermediate shaft in an amount that enables the second lubricant oil to be supplied to the contra-rotating front seal unit.

2. The contra-rotating propeller marine propulsion device according to claim 1 , wherein the oil amount adjusting unit adjusts the amount of the second lubricant oil accumulated in the hollow outer intermediate shaft, and wherein the second lubricant oil in the hollow outer intermediate shaft rotates along with the hollow outer intermediate shaft, and sticks to an inner peripheral surface of the hollow outer intermediate shaft due to centrifugal force during the rotation, thereby forming a hollow cylindrical shape, and wherein the second lubricant oil of an amount exceeding a storage capacity of the hollow outer intermediate shaft is discharged from the circular opening.

3. The contra-rotating propeller marine propulsion device according to claim 2 , wherein the contra-rotating propeller marine propulsion device further comprises:

(g) the driving unit that provides rotational driving power; and

(h) a power transmission unit that outputs the rotational driving power of the driving unit from an outer output shaft and an inner output shaft that are concentrically and rotatably arranged, wherein the outer output shaft and the hollow outer intermediate shaft are connected together via a gear coupling, and wherein the second lubricant oil is supplied into the hollow outer intermediate shaft through an engagement portion of the gear coupling, and wherein the second lubricant oil of an amount exceeding the storage capacity of the hollow outer intermediate shaft is a discharged from a lower engagement portion of the gear coupling through the circular opening.

4. The contra-rotating propeller marine propulsion device according to claim 3 , wherein the power transmission unit is a gear drive mechanism, and the power transmission unit has a housing that houses the outer output shaft and the inner output shaft, wherein a hood that covers the gear coupling and that communicates with an inside of the housing is disposed on a rear side of the housing, and wherein the second lubricant oil is supplied to the gear coupling from a housing side of the power transmission unit.