Drive device for construction machine

1. A drive device for a construction machine, the drive device driving a driven portion in the construction machine, the drive device comprising:

a motor serving as a drive source, and having a motor shaft for outputting a rotational force at a given rotational speed; and

a speed reduction unit for reducing the rotational speed of the rotational force output from said motor, and transmitting the rotational force at a reduced rotational speed to said driven portion, wherein said speed reduction unit has

a casing having an inner wall surface defining an inner space for containing an amount of lubricant oil,

a gear mechanism disposed in the inner space of the casing for reducing the rotational speed of the rotational force output from said motor, the gear mechanism being submersed in the lubricant oil contained in the inner space of the casing,

a speed reduction output shaft connected with the gear mechanism for outputting the rotational force at the reduced rotational speed to said driven portion, the speed reduction output shaft axially aligning with the motor shaft in a vertical direction, the speed reduction output shaft being disposed below the motor shaft so that a driven member attached to the speed reduction output shaft and constituting the gear mechanism lies deeper in the lubricant oil contained in the inner space than a driver member attached to the motor shaft and constituting the gear mechanism,

a hollow cylindrical body arranged in the inner space and above said gear mechanism and having an inner diameter larger than an outer diameter of the motor shaft to thereby define a gap between the entire inner surface of the hollow cylindrical body and the outer surface of the motor shaft to keep the hollow cylindrical body from imparting a mechanical force to the motor shaft,

an oil receiver arranged in the inner space and above said gear mechanism, and mounted on the outer surface of said cylindrical body, said oil receiver having a main storage portion extending in a radially outward direction of the motor shaft, and formed with an oil drain opening for discharging a given amount of lubricant oil from the main storage portion to said gear mechanism, the main storage portion having an outer end radially spaced away from the inner wall surface of the casing, whereby said oil receiver can receive, store and discharge a given amount of lubricant oil,

a support member arranged above said oil receiver and mounted on the outer surface of the cylindrical body and said casing to support said cylindrical body, and

an oil passage formed between the inner wall surface of the casing and the outer end of the oil receiver for guiding a given amount of lubricant oil rising through said oil passage to the main storage portion.

2. The drive device for a construction machine according to claim 1 , wherein said main storage portion has a center hole passing the motor shaft.

3. The drive device for a construction machine according to claim 1 , wherein said oil passage lies along the entire periphery of the oil receiver.

4. The drive device for a construction machine according to claim 3 , wherein

said oil passage has a specified height and a specified radial width, the radial width of a bottom of said oil passage being larger than the radial width of a top of said oil passage.

5. The drive device for a construction machine according to claim 1 , wherein

said main storage portion has a bottom wall arranged above said gear mechanism, and

said oil drain opening is a hole formed in said bottom wall to discharge a specific amount of lubricant oil per unit time, the specific amount being smaller than an amount of lubricant oil fed into said main storage portion per unit time.

6. The drive device for a construction machine according to claim 1 , wherein

said oil drain opening is arranged at such a position that the lubricant oil discharged through said oil drain opening drops toward said gear mechanism.

7. The drive device for a construction machine according to claim 1 , wherein

said support member has an auxiliary storage portion for receiving and storing an amount of lubricant oil rising beyond said oil receiver, and

said support member is provided with an oil inlet port for feeding lubricant oil into said auxiliary storage portion, and an oil outlet port for discharging a given amount of lubricant oil from said auxiliary storage portion.

8. The drive device for a construction machine according to claim 7 , wherein

said oil outlet port is arranged at such a position that the lubricant oil discharged from said auxiliary storage portion through the oil outlet port flows and falls toward said oil receiver.

9. The drive device for a construction machine according to claim 1 , wherein

said support member has an auxiliary storage portion for receiving and storing an amount of lubricant oil rising beyond said oil receiver, and

said support member is provided with an oil outlet and inlet port functioning as both an oil inlet port for feeding lubricant oil into said auxiliary storage portion, and an oil outlet port for discharging a given amount of lubricant oil from said auxiliary storage portion.

10. The drive device for a construction machine according to claim 9 , wherein

said oil outlet and inlet port is arranged at such a position that the lubricant oil discharged from said auxiliary storage portion through the oil outlet and inlet port flows and falls toward said oil receiver.

11. The drive device for a construction machine according to claim 1 , wherein

said casing has an upper end portion on which an outer circumference portion of said support member is mounted, and

the inner wall surface of said casing is smooth from a lower end to an upper end.

12. The drive device for a construction machine according to claim 1 , wherein

the gear mechanism has a plurality of meshing gears and connected with the motor shaft, and

the main storage portion of the oil receiver has a bottom wall extending in a radially outward direction of the motor shaft at a vertical level above the plurality of meshing gears.