Draft control device for tractor and tractor including same

1. A draft control device of a tractor, which automatically lifts a three-point hitch to decrease a traction load when a work machine, which is connected to the three-point hitch at a rear side of the tractor, plows so deep that the traction load becomes excessive, the draft control device comprising:

a top link fixing bracket ( 40 ) fixed at the rear side of the tractor;

a top link swing bracket ( 42 ) hinge-coupled to the top link fixing bracket ( 40 ) through a connection pin ( 41 ), and carrying out a rotational motion with respect to an axial center of the connection pin ( 41 ) according to a change of a compressive force of a top link which is caused by a change of a traction resistance of the work machine;

a leaf spring ( 44 ) provided between the top link fixing bracket ( 40 ) and the top link swing bracket ( 42 ) to supply a restoring force for the rotational motion of the top link swing bracket ( 42 ) with respect to the top link fixing bracket ( 40 ); and

a sensitivity adjustment unit ( 46 ) provided between the top link swing bracket ( 42 ) and the leaf spring ( 44 ), and changing an acting point, at which the top link swing bracket ( 42 ) pushes the leaf spring ( 44 ), to adjust a traction load sensitivity of the work machine.

2. The draft control device according to claim 1 , wherein:

the top link swing bracket ( 42 ) has top link mounting holes ( 425 ) formed at opposite upper ends in a diagonal direction relative to a hinge point, at which the top link swing bracket ( 42 ) is hinge-connected to the top link fixing bracket ( 40 ) by the connection pin ( 41 ), and

one end portion of the top link, connected to the work machine is bendably connected to the top link mounting holes ( 425 ).

3. The draft control device according to claim 1 , wherein the leaf spring ( 44 ) is fixed to a fixing member ( 400 ) of the top link fixing bracket ( 40 ) through a spring fixing member ( 43 ) at a lower end portion of the leaf spring ( 44 ) so as to be spaced apart from and parallel to the fixing member ( 400 ).

4. The draft control device according to claim 1 , wherein the sensitivity adjustment unit ( 46 ) includes:

a height adjustment rotation bolt ( 460 ) rotationally provided to the top link swing bracket ( 42 ); and

a push ( 462 ) whose vertical position, at which the push ( 462 ) comes into contact with the leaf spring ( 44 ), varies according to a rotational operation of the height adjustment rotation bolt ( 460 ).

5. The draft control device according to claim 4 , wherein the push ( 462 ) is screw-coupled to the height adjustment rotation bolt ( 460 ), and slidingly comes into contact with a surface of the top link swing bracket ( 42 ), which faces the leaf spring ( 44 ), and the leaf spring ( 44 ), respectively, at one side and an opposite side of a portion of the push ( 462 ), which is screw-coupled with the height adjustment rotation bolt ( 460 ).

6. The draft control device according to claim 4 , wherein:

the push ( 462 ) has a rectangular shape in a plan view:, and

a side surface portion of the push ( 462 ), which comes into contact with the leaf spring ( 44 ), has a convexly curved shape.

7. The draft control device according to claim 1 , further comprising:

a feedback link ( 48 ) provided to operatively connect the top link swing bracket ( 42 ) to a lifting control valve, which controls the lifting of the three-point hitch, so that the top link swing bracket ( 42 ) and the lifting control valve operate in association with each other.

8. A tractor comprising:

the draft control device according to claim 1 ; and

a lifting control valve ( 50 ) compensating an oil pressure of a three-point hitch lifting cylinder in proportion to a displacement of the draft control device, which is displaced according to a change of the traction load of the work machine.

9. A tractor comprising:

the draft control device according to claim 2 ; and

a lifting control valve ( 50 ) compensating an oil pressure of a three-point hitch lifting cylinder in proportion to a displacement of the draft control device, which is displaced according to a change of the traction load of the work machine.

10. A tractor comprising:

the draft control device according to claim 3 ; and

a lifting control valve ( 50 ) compensating an oil pressure of a three-point hitch lifting cylinder in proportion to a displacement of the draft control device, which is displaced according to a change of the traction load of the work machine.

11. A tractor comprising:

the draft control device according to claim 4 ; and

a lifting control valve ( 50 ) compensating an oil pressure of a three-point hitch lifting cylinder in proportion to a displacement of the draft control device, which is displaced according to a change of the traction load of the work machine.

12. A tractor comprising:

the draft control device according to claim 5 ; and

a lifting control valve ( 50 ) compensating an oil pressure of a three-point hitch lifting cylinder in proportion to a displacement of the draft control device, which is displaced according to a change of the traction load of the work machine.

13. A tractor comprising:

the draft control device according to claim 6 ; and

a lifting control valve ( 50 ) compensating an oil pressure of a three-point hitch lifting cylinder in proportion to a displacement of the draft control device, which is displaced according to a change of the traction load of the work machine.

14. A tractor comprising:

the draft, control device according to claim 7 ; and

a lifting control valve ( 50 ) compensating an oil pressure of a three-point hitch lifting cylinder in proportion to a displacement of the draft control device, which is displaced according to a change of the traction load of the work machine.