Electric actuator

1. An electric actuator, comprising:

a differential device comprising:

a driving rotary body rotatable about a rotation axis;

a planetary rotary body capable of rotating on its axis and revolving about the rotation axis;

a driven rotary body rotatable about the rotation axis,

the planetary rotary body meshing with the driving rotary body and the driven rotary body;

a first speed reducer formed between the planetary rotary body and the driving rotary body; and

a second speed reducer formed between the planetary rotary body and the driven rotary body,

the first speed reducer and the second speed reducer having different speed reduction ratios;

an electric motor comprising a rotor configured to drive the planetary rotary body;

a first bearing configured to support the planetary rotary body on an inner side of the rotor; and

a second bearing configured to support the planetary rotary body at a position shifted in an axial direction so as to be prevented from overlapping the rotor,

wherein the second bearing is a deep-groove ball bearing,

wherein the first bearing comprises rolling elements that roll in contact with the planetary rotary body,

wherein the planetary rotary body has an outer peripheral surface on which the rolling elements roll in contact with the outer peripheral surface, and

wherein the outer peripheral surface of the planetary rotary body contacts the rolling elements on the inner side of the rotor.

2. The electric actuator according to claim 1 , wherein the second bearing is configured to support both of the first speed reducer and the second speed reducer.

3. The electric actuator according to claim 2 ,

wherein the differential device further comprises an eccentric member configured to rotate integrally with the rotor and change a rotation phase difference of the driven rotary body with respect to the driving rotary body, and

wherein the second bearing comprises:

an outer ring fixed to an inner periphery of the eccentric member; and

an inner ring fixed to an outer periphery of the planetary rotary body.

4. The electric actuator according to claim 3 , wherein the first bearing is a needle roller bearing.

5. The electric actuator according to claim 4 , further comprising:

a sprocket provided to the driving rotary body; and

a cam shaft provided to the driven rotary body,

wherein the electric actuator is applied to a variable valve timing device configured to change an opening/closing timing of a valve by changing a rotation phase difference between the sprocket and the cam shaft.

6. The electric actuator according to claim 3 , further comprising:

a sprocket provided to the driving rotary body; and

a cam shaft provided to the driven rotary body,

wherein the electric actuator is applied to a variable valve timing device configured to change an opening/closing timing of a valve by changing a rotation phase difference between the sprocket and the cam shaft.

7. The electric actuator according to claim 2 , wherein the first bearing is a needle roller bearing.

8. The electric actuator according to claim 7 , further comprising:

a sprocket provided to the driving rotary body; and

a cam shaft provided to the driven rotary body,

wherein the electric actuator is applied to a variable valve timing device configured to change an opening/closing timing of a valve by changing a rotation phase difference between the sprocket and the cam shaft.

9. The electric actuator according to claim 2 , further comprising:

a sprocket provided to the driving rotary body; and

a cam shaft provided to the driven rotary body,

wherein the electric actuator is applied to a variable valve timing device configured to change an opening/closing timing of a valve by changing a rotation phase difference between the sprocket and the cam shaft.

10. The electric actuator according to claim 2 ,

wherein the first speed reducer comprises first inner tooth portions and first outer tooth portions meshing with each other,

wherein the second speed reducer comprises second inner tooth portions and second outer tooth portions meshing with each other,

wherein at least one of tooth surfaces of the first inner tooth portions and tooth surfaces of the first outer tooth portions have a plurality of dimples, and

wherein at least one of tooth surfaces of the second inner tooth portions and tooth surfaces of the second outer tooth portions have a plurality of dimples.

11. The electric actuator according to claim 1 , wherein the first bearing is a needle roller bearing.

12. The electric actuator according to claim 11 ,

wherein the outer peripheral surface of the planetary rotary body has a plurality of dimples.

13. The electric actuator according to claim 11 , further comprising:

a sprocket provided to the driving rotary body; and

a cam shaft provided to the driven rotary body,

wherein the electric actuator is applied to a variable valve timing device configured to change an opening/closing timing of a valve by changing a rotation phase difference between the sprocket and the cam shaft.

14. The electric actuator according to claim 1 , further comprising:

a sprocket provided to the driving rotary body; and

a cam shaft provided to the driven rotary body,

wherein the electric actuator is applied to a variable valve timing device configured to change an opening/closing timing of a valve by changing a rotation phase difference between the sprocket and the cam shaft.

15. The electric actuator according to claim 1 ,

wherein the first speed reducer comprises first inner tooth portions and first outer tooth portions meshing with each other,

wherein the second speed reducer comprises second inner tooth portions and second outer tooth portions meshing with each other,

wherein at least one of tooth surfaces of the first inner tooth portions and tooth surfaces of the first outer tooth portions have a plurality of dimples, and

wherein at least one of tooth surfaces of the second inner tooth portions and tooth surfaces of the second outer tooth portions have a plurality of dimples.

16. The electric actuator according to claim 15 , further comprising:

a cam shaft provided to the driven rotary body,

wherein the driving rotary body comprises a sprocket, and

wherein the electric actuator is applied to a variable valve timing device configured to change an opening/closing timing of a valve by changing a rotation phase difference of the cam shaft with respect to the sprocket.

17. An electric actuator, comprising:

a differential device comprising:

a driving rotary body rotatable about a rotation axis;

a planetary rotary body capable of rotating on its axis and revolving about the rotation axis;

a driven rotary body rotatable about the rotation axis,

the planetary rotary body meshing with the driving rotary body and the driven rotary body;

a first speed reducer formed between the planetary rotary body and the driving rotary body; and

a second speed reducer formed between the planetary rotary body and the driven rotary body,

the first speed reducer and the second speed reducer having different speed reduction ratios;

an electric motor comprising a rotor configured to drive the planetary rotary body;

a first bearing configured to support the planetary rotary body on an inner side of the rotor; and

a second bearing configured to support the planetary rotary body at a position shifted in an axial direction so as to be prevented from overlapping the rotor,

wherein the differential device further comprises an eccentric member configured to rotate integrally with the rotor and change a rotation phase difference of the driven rotary body with respect to the driving rotary body,

wherein the second bearing is a deep-groove ball bearing, and

wherein the second bearing comprises:

an outer ring fixed to an inner periphery of the eccentric member; and

an inner ring fixed to an outer periphery of the planetary rotary body.

18. The electric actuator according to claim 17 , wherein the first bearing is a needle roller bearing.

19. The electric actuator according to claim 18 , further comprising:

a sprocket provided to the driving rotary body; and

a cam shaft provided to the driven rotary body,

wherein the electric actuator is applied to a variable valve timing device configured to change an opening/closing timing of a valve by changing a rotation phase difference between the sprocket and the cam shaft.

20. The electric actuator according to claim 17 , further comprising:

a sprocket provided to the driving rotary body; and

a cam shaft provided to the driven rotary body,

wherein the electric actuator is applied to a variable valve timing device configured to change an opening/closing timing of a valve by changing a rotation phase difference between the sprocket and the cam shaft.