Electric actuator

Abstract

An electric actuator such that a nut threadedly engaged with a sliding screw shaft is displaced along an axial direction under the operation of a motor, the sliding screw shaft being made of a light metal or light metal alloy. A diamond-like carbon film is formed on at least either a portion of screw threads of the nut that is located at least within three threads from a starting end in the axial direction, or screw threads of the sliding screw shaft.

The invention claimed is: 
     
       1. i. An electric actuator comprising a sliding screw shaft, and a nut screw-engaged with the sliding screw shaft, the sliding screw shaft being configured to rotate under operation of a motor to thereby cause the nut to be displaced in an axial direction of the sliding screw shaft,
 ii. Wherein the sliding screw shaft is made of light metal or light metal alloy; and 
 iii. a diamond-like carbon film is formed on a region of a threaded part of the nut, the region being located within a range from a starting end of the threaded part of the nut in an axial direction thereof to at least a third thread of the threaded part of the nut; and 
 iv. a thickness of the diamond-like carbon film on a first starting end portion of the threaded part of the nut that is located at a first thread from the starting end is larger than a thickness of the diamond-like carbon film on a second starting end portion of the threaded part of the nut that is located at a second thread from the starting end. 
 
     
     
       2. The electric actuator according to  claim 1 , wherein the diamond-like carbon film is formed on a region of the threaded part of the nut that is located within the range from a terminating end of the threaded part of the nut in the axial direction to at least a third thread of the threaded part of the nut. 
     
     
       3. The electric actuator according to  claim 1 , wherein a thickness of the diamond-like carbon film on a first terminating end portion of the threaded part of the nut that is located at a first thread from the terminating end is larger than a thickness of the diamond-like carbon film on a second terminating end portion of the threaded part of the nut that is located at a second thread from the terminating end. 
     
     
       4. The electric actuator according to  claim 1 , wherein the diamond-like carbon film is formed on a region of the threaded part of the nut that is located within a range from the starting end to the terminating end. 
     
     
       5. The electric actuator according to  claim 4 , wherein a thickness of the diamond-like carbon film on the region of the threaded part of the nut that is located within the range from the starting end to the third thread and on the region thereof that is located within the range from the terminating end to the third thread is equal to or larger than a thickness of the diamond-like carbon film on an intermediate region of the threaded part of the nut, the intermediate region being located within a range from a fourth thread from the starting end to a fourth thread from the terminating end. 
     
     
       6. An electric actuator comprising a sliding screw shaft, and a nut screw-engaged with the sliding screw shaft, the sliding screw shaft being configured to rotate under operation of a motor to thereby cause the nut to be displaced in an axial direction of the sliding screw shaft,
 wherein the sliding screw shaft is made of light metal or light metal alloy; and 
 a diamond-like carbon film is formed on a threaded part of the nut, the region being located within a range from a starting end of the threaded part of the nut in an axial direction thereof to at least a third thread of the threaded part of the nut, 
 wherein the diamond-like carbon film is not formed on at least part of an intermediate region of the threaded part of the nut that is located within a range from a fourth thread from the starting end to a fourth thread from the terminating end. 
 
     
     
       7. The electric actuator according to  claim 1 , wherein the diamond-like carbon film is formed on the threaded part of the sliding screw shaft. 
     
     
       8. The electric actuator according to  claim 1 , wherein the sliding screw shaft is made of aluminum or aluminum alloy;
 an alumite film is formed on the threaded part of the sliding screw shaft. 
 
     
     
       9. The electric actuator according to  claim 7 , wherein the nut is made of light metal or light metal alloy. 
     
     
       10. The electric actuator according to  claim 1 , wherein the diamond-like carbon film is formed on the threaded part of the sliding screw shaft;
 the nut is made of aluminum or aluminum alloy. 
 
     
     
       11. The electric actuator according to  claim 1 , wherein a thickness of the diamond-like carbon film is 0.1 μm or more and 6.0 μm or less. 
     
     
       12. The electric actuator according to  claim 1 , wherein the sliding screw shaft includes clearance space, and crests of the threaded part of the nut are placed in the clearance space in a state where the crests and the sliding screw shaft do not contact each other. 
     
     
       13. The electric actuator according to  claim 12 , wherein the clearance space is configured to store lubricant. 
     
     
       14. The electric actuator according to  claim 1 , wherein the diamond-like carbon film is formed on a region of the threaded part of the nut that is located within a range from the starting end to the terminating end. 
     
     
       15. The electric actuator according to  claim 6 , wherein the diamond-like carbon film is formed on a region of the threaded part of the nut that is located within a range from the starting end to the terminating end. 
     
     
       16. The electric actuator according to  claim 8 , wherein the nut is made of light metal or light metal alloy. 
     
     
       17. The electric actuator according to  claim 6 , wherein the diamond-like carbon film is formed on the threaded part of the sliding screw shaft. 
     
     
       18. The electric actuator according to  claim 6 , wherein the sliding screw shaft is made of aluminum or aluminum alloy;
 an alumite film is formed on the threaded part of the sliding screw shaft. 
 
     
     
       19. The electric actuator according to  claim 17 , wherein the nut is made of light metal or light metal alloy. 
     
     
       20. The electric actuator according to  claim 6 , wherein the diamond-like carbon film is formed on the threaded part of the sliding screw shaft; and
 the nut is made of aluminum or aluminum alloy.