Transmission mechanism for electric drill and electric drill including the same

1. An electric drill, comprising a motor, a transmission mechanism, and a drill rod assembled on an output shaft of the transmission mechanism, the transmission mechanism comprising:

a primary planet carrier having a plurality of primary planetary gear shafts arranged at one end thereof and a sun gear arranged at the other end thereof;

a primary gear assembly comprising a primary gear ring and a primary gear set located in the primary gear ring;

a secondary planet carrier comprising a plurality of secondary planetary gear shafts arranged at one end thereof and an output shaft of the secondary planet carrier arranged at the other end thereof; and

a secondary gear assembly comprising a secondary gear ring and a secondary planetary gear set located in the secondary gear ring;

wherein, the primary gear set comprises at least two primary planetary gear sets; the at least two primary planetary gear sets are pivotably mounted on the primary planetary gear shafts, an outer side of the primary planetary gear set engages with the primary gear ring, and an inner side of the primary planetary gear set engages with a central gear arranged on a motor output shaft;

wherein, the secondary planetary gear set is pivotably mounted on the secondary planetary gear shafts, an outer side of the secondary planetary gear set engages with the secondary gear ring, and an inner side of the secondary planetary gear set engages with the sun gear.

2. The electric drill of claim 1 , wherein the at least two primary planetary gear sets are overlapped in an axial direction of the primary gear ring.

3. The electric drill of claim 2 , wherein each primary planetary gear set has four planetary gears, which are evenly distributed on a periphery of the primary ring gear along the axial direction.

4. The electric drill of claim 1 , wherein the transmission mechanism further comprises a gear box receiving the primary gear assembly and the secondary gear assembly; wherein positioning ribs are arranged on a side wall of the gear box facing the primary gear assembly c; and wherein a side wall of the primary gear ring or the secondary gear ring facing the positioning ribs comprises a flat wall engaged with the positioning ribs.

5. The electric drill of claim 4 , wherein the number of the positioning ribs is four, and the positioning ribs are evenly distributed on the side wall of the gear box; and wherein the flat wall comprises four flat walls, and the four flat walls are evenly distributed on the side wall of the first primary gear ring or the secondary gear ring.

6. The electric drill of claim 1 , wherein the transmission mechanism further comprises a gear box receiving the primary gear assembly and the secondary gear assembly; wherein the gear box comprises assembling holes; wherein a fixing portion is arranged on side walls of the primary gear ring and the secondary gear ring respectively and extends axially throughout the thickness of the primary gear ring and the secondary gear ring respectively; and wherein the assembling holes and the fixing portion cause the primary gear assembly and the secondary gear assembly to be secured in the gear box through fasteners.

7. The electric drill of claim 6 , wherein the fixing portion comprises a slot on a side facing the side wall of the gear box, and the fixing portion is configured to be a semi-circular slot.

8. The electric drill of claim 6 , wherein a fixing plate is arranged on an end of the primary gear assembly away from the secondary gear assembly so as to limit the primary planetary gear set in the primary gear ring.

9. The electric drill of claim 8 , wherein the fixing plate comprises a main body and an elastic resisting portion extending from the main body, and wherein the elastic resisting portion elastically abuts against the side wall of the gear box.