Lawn mower

1. A lawn mower comprising:

a housing including an opened bottom;

a rotation shaft extending in a vertical direction of the housing and including a lower end positioned within the housing;

a cutter blade provided for the rotation shaft and accommodated in the housing, the cutter blade extending along a horizontal line which is perpendicular to the rotation shaft;

a flap provided for at least part of the cutter blade, the flap having a flap angle changeable along the horizontal line;

an actuator configured to provide an output to control the flap angle of the flap; and

a transmission mechanism configured to transmit the output of the actuator to the flap,

wherein the rotation shaft comprises a hollow shaft; and

the transmission mechanism is accommodated inside the hollow shaft.

2. The lawn mower according to claim 1 , wherein the transmission mechanism comprises:

a control shaft fitted in the hollow shaft in a manner that the control shaft is slidable in an axial direction; and

a conversion mechanism accommodated inside the hollow shaft, the conversion mechanism capable of converting sliding movement of the control shaft into movement to change the flap angle of the flap,

wherein a lower end of the control shaft is coupled to the flap through the conversion mechanism; and

an output shaft of the actuator is combined with an upper end of the control shaft in a manner that the control shaft is driven to move in a sliding manner.

3. The lawn mower according to claim 2 , wherein the conversion mechanism comprises:

a pin extending radially outward from the lower end of the control shaft; and

a cam including a cam surface which can contract the pin,

wherein the cam is rotatably supported by the hollow shaft about a swing center of the flap, and provided for the flap; and

the cam surface comprises a cam groove capable of converting sliding movement of the pin which is displaced vertically together with the control shaft in a sliding manner into rotation movement of the cam.

4. The lawn mower according to claim 3 , wherein the cam groove is formed around the swing center of the flap, and has a V-shape oriented substantially in a lateral direction.

5. The lawn mower according to claim 2 , wherein the actuator comprises a linear actuator including the output shaft slidable in the axial direction of the control shaft; and

a roller bearing is interposed between the output shaft and the control shaft.

6. The lawn mower according to claim 1 , further comprising a lower cutter blade positioned below the cutter blade, wherein the lower cutter blade comprises a fixed blade fixed to the hollow shaft.