Gap expanding method of ball screw and fine motion control rod drive mechanism incorporating gap expanded ball screw

Patent metadata

Field	Value
Publication number	US-9695918-B2
Application number	US-201414172224-A
Country	US
Kind code	B2
Filing date	Feb 4, 2014
Priority date	Feb 20, 2013
Publication date	Jul 4, 2017
Grant date	Jul 4, 2017

Abstract

It is an object of the present invention to provide a gap expanding method of a ball screw for preventing an increase in torque relative to an electric motor due to a protruding bulge caused by generation of a scar on the traveling side of the screw shaft of the ball screw, and to provide a control rod drive mechanism incorporating the gap expanded ball screw. In a ball screw disposed in a control rod drive mechanism, the ball screw has a screw shaft and a ball nut engaged with the screw shaft via travelling balls, and the balls are each configured to have a diameter smaller than that of the existing ball, thereby expanding a gap between a ball traveling side of the screw shaft and the ball and a gap between the ball and a ball traveling side of the ball nut.

First claim

What is claimed is:

1. A method for gap expanding in a ball screw, the method comprising:
disposing the ball screw in a control rod drive mechanism, the ball screw converting via a driving shaft rotational motion of an electric motor to vertical motion to thereby move a hollow piston up or down, wherein
the ball screw has a screw shaft and a ball nut engaged with the screw shaft via traveling balls,
the gap coefficient (A) is given by: A=((2×R−L)−D)÷(2×R−L)), in which R is a distance between a curved surface forming a ball traveling side and a curvature center point thereof, R being determined for two different curved surfaces, each of the two different curved surfaces having a different curvature center point, L is a distance between the two curvature center points, and D is a diameter of the traveling balls,
the gap coefficient is more than 0.03 and less than 0.17, and
determining the diameter of the traveling balls to satisfy the expression given by A, in which A has the value of more than 0.03 and less than 0.17, thereby expanding a gap between the ball traveling side of the screw shaft and the traveling balls and a gap between the traveling balls and a ball traveling side of the ball nut.

2. The Method of claim 1 , wherein
the screw shaft and the ball nut are each configured to have a ball traveling side whose groove shape is made larger.

Assignees

• Hitachi Ge Nuclear Energy Ltd

Inventors

• Matsushita Yuuichi
• Kodama Toshihiro
• Harada Kiyoshi
• Akatsuka Hirokazu
• Tsuchiya Takahiro

Classifications

• Y02E30/30

  Nuclear fission reactors · CPC title

• Y10T74/18576

  including screw and nut · CPC title

• F16H25/2214 Primary

  with elements for guiding the circulating balls · CPC title

• F16H25/2204

  with balls · CPC title

• G21C7/14 Primary

  Mechanical drive arrangements · CPC title