JP2017211043A - Ball screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw in which the seizure of the ball screw caused by oil shortage between a spiral groove of a ball screw nut and a spiral groove of a screw shaft does not occur.SOLUTION: A ball screw comprises: a screw shaft 1 in which a spiral groove 11 is formed at an external peripheral face; a ball screw nut 2 in which a spiral groove 21 is formed at an internal peripheral face; a plurality of balls 3 which are arranged between trajectories formed of the spiral groove 11 of the screw shaft 1 and the spiral groove 21 of the ball screw nut 2; and a ball return passage 5 for returning the balls 3 to starting points from terminal points of the trajectories. The spiral groove 21 of the ball screw nut 2 comprises a diameter-contracted part 22 whose both end parts are formed so as not to reach both ends of the ball screw nut 2 in an axial direction, and holds a lubricant in the ball screw nut 2.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ball screw.

The ball screw has a ball screw nut having a spiral groove formed on the inner peripheral surface, a screw shaft having a spiral groove formed on the outer peripheral surface, and a track formed by the spiral groove of the ball screw nut and the spiral groove of the screw shaft. A plurality of balls arranged between them and a ball return path for returning these balls from the end point of the track to the start point, and the nut is screwed by rolling the balls in the track (load path). It is a device that moves relative to the shaft. Such a ball screw has one or a plurality of ball circulation circuits composed of the track and the ball return path.
With the electrification of injection molding machines, forging devices, press machines, and jacks that were conventionally driven by hydraulic pressure, the ball screw is placed vertically (with the axial direction aligned vertically) in the load path. There are an increasing number of cases where high loads are applied to these balls. In such a case, it is necessary to hold a lubricant between the spiral groove of the ball screw nut, the spiral groove of the screw shaft, and the ball.

  Patent Document 1 describes a ball screw seal capable of holding a lubricant inside a ball screw nut. The ball screw seal is mounted in seal member mounting holes formed at both ends of a ball screw nut screwed onto the ball screw shaft via a ball.

JP 2002-364726 A

  However, in the ball screw described in Patent Document 1, the shape of both ends of the spiral groove of the ball screw nut is cut through. Therefore, the lubricant is easily discharged out of the ball screw and cannot be held inside the ball screw nut, causing oil shortage between the spiral groove of the ball screw nut and the spiral groove of the screw shaft and the ball. May cause seizure.

  The present invention has been made in view of the above-described problems, and its purpose is to provide a ball screw that does not cause seizure of the ball screw due to oil shortage between the spiral groove of the ball screw nut, the spiral groove of the screw shaft, and the ball. To provide a screw.

In order to solve the above problems, a ball screw of the present invention includes a screw shaft having a spiral groove formed on an outer peripheral surface, a ball screw nut having a spiral groove formed on an inner peripheral surface, and a spiral groove of the screw shaft. A plurality of balls disposed between the tracks formed by the spiral groove of the ball screw nut, and a ball return path for returning the ball from the end point of the track to the start point, the spiral groove of the ball screw nut, The both ends are provided with reduced diameter portions formed so as not to reach both ends of the ball screw nut in the axial direction, and a lubricant is held inside the ball screw nut.
In the present invention, an inner diameter of the reduced diameter portion is smaller than an inner diameter of a land portion formed between spiral grooves of the ball screw nut.

  According to the ball screw of the present invention, by providing a cut-up at both ends of the spiral groove of the ball screw nut, an oil reservoir structure in which the lubricant easily collects inside the ball screw nut is obtained, and the lubricant can be held. For this reason, the ball screw does not seize without causing oil shortage between the spiral groove of the ball screw nut, the spiral groove of the screw shaft, and the ball.

It is a fragmentary sectional view of the ball screw of an embodiment. FIG. 2 is a detailed view of a portion in FIG. 1. It is a fragmentary sectional view of the ball screw nut and seal of an embodiment.

Hereinafter, an example of an embodiment of the present invention will be described.
As shown in FIG. 1, the ball screw of this embodiment includes a screw shaft 1 having a spiral groove 11 formed on the outer peripheral surface, a ball screw nut 2 having a spiral groove 21 formed on the inner peripheral surface, and a screw shaft. A plurality of balls 3 arranged in a freely rolling manner between tracks formed by the spiral groove 11 and the spiral groove 21 of the ball screw nut 2, and a tube for returning the balls 3 from the end point of the track to the start point (ball return path) 5, a tube presser 6 that fixes the tube (ball return path) 5, and a seal 7 that prevents entry of foreign matter such as dust from the outside.

  The screw shaft 1 is for moving and guiding the ball screw nut 2 along the axial direction of the screw shaft 1. A spiral groove 11 having a semicircular cross section having substantially the same radius of curvature as the radius of the ball 3 is formed over the entire length of the outer peripheral surface.

The ball screw nut 2 moves along the axial direction of the screw shaft 1, and a spiral groove 21 having the same shape facing the spiral groove 11 is formed on the inner peripheral surface thereof.
In addition, a flange 22 is formed at one end of the ball screw nut 2 in the axial direction, and the raceway of the ball 3 is formed by the spiral grooves 11 and 21. Then, the ball 3 rolls in this track in a loaded state, and the ball screw nut 2 moves linearly relative to the screw shaft 1. A plurality of balls 3 are slidably loaded on a spiral track formed by the spiral groove 11 of the screw shaft and the spiral groove 21 of the ball screw nut 2. A synthetic resin spacer 4 is disposed between adjacent balls 3.

  The tube 5 (ball return path) is formed in a substantially portal shape, and both ends thereof are inserted into through holes 24 provided in a cylinder forming the ball screw nut 2 (see FIG. 3), and the starting point and the ending point of the track. Are arranged diagonally across the screw shaft 1. Therefore, the ball 3 that has reached the end point of the track passes through the tube 5 (ball return path) and is returned to the start point of the track. The tube 5 (ball return path) is fixed by a tube presser 6.

  As described above, when the screw shaft 1 rotates, the ball screw nut 2 screwed through the plurality of balls 3 moves linearly in the axial direction of the screw shaft 1, and the balls 3 roll to move into the spiral groove 21. , The ball 3 that has reached the one end side of the spiral groove 21 rolls in the tube 5 and is supplied to the other end side of the spiral groove 21 to circulate again.

  Synthetic resin seals 7 are disposed at both ends of the ball screw nut 2 to prevent foreign matter from entering the ball screw nut 2 from the outside.

  As shown in FIG. 3, the spiral groove 21 formed in the ball screw nut 2 is formed with a reduced diameter portion 22 so that both ends thereof do not reach both ends of the ball screw nut 2 in the axial direction. In this way, by so-called rounding up only the two axial ends of the ball screw nut, since there is no notch shape by the spiral groove 21 on the entire circumference of the inner diameter, a structure in which the lubricant is more easily collected in the spiral groove 21 is obtained. The agent can be retained. The reduced diameter portion 22 is formed at the stage of processing the thread groove of the ball screw nut.

  In detail, as shown in FIG. 2, the inner diameter of the reduced diameter portion 22 is smaller by Δd than the inner diameter of the land portion 23 formed between the spiral grooves 21 (between adjacent ball screw grooves). In the conventional ball screw, a lubricant is held by a sealing member (seal). However, in the present invention, the reduced diameter portion 22 is formed to be smaller than the inner diameter of the land portion 23 by Δd, thereby providing lubrication. Even if the agent is about to flow out of the ball screw nut 2, it is stopped by the reduced diameter portion 22, and an oil sump is created inside the ball screw nut 2 to prevent oil shortage and improve the lubrication performance.

  The reduced diameter portion 22 only needs to have a configuration that can prevent the lubricant from flowing out from the oil reservoir inside the ball screw nut 2, and the degree of the reduced diameter is not limited to this embodiment. Absent.

  Therefore, in the present invention, when it is desired to improve the lubricity without changing the dimensions of the ball screw nut 2 or the addition of other parts, etc., when it is desired to reduce the supply amount of the lubricating oil but to improve the lubricity, This is effective when you want to improve lubricity although there are restrictions.

DESCRIPTION OF SYMBOLS 1 Screw shaft 11 Spiral groove of screw shaft 2 Ball screw nut 21 Spiral groove of ball screw nut 22 Reduced diameter part 23 Land part 24 Through hole 3 Ball 4 Spacer 5 Tube (ball return path)
6 Tube retainer 7 Seal

Claims (2)

A screw shaft having a spiral groove formed on the outer peripheral surface;
A ball screw nut having a spiral groove formed on the inner peripheral surface;
A plurality of balls disposed between tracks formed by the spiral groove of the screw shaft and the spiral groove of the ball screw nut;
A ball return path for returning the ball from the end point of the trajectory to the start point,
The spiral groove of the ball screw nut includes a reduced diameter portion formed so that both end portions thereof do not reach both ends in the axial direction of the ball screw nut, and holds a lubricant inside the ball screw nut. And ball screw.   The ball screw according to claim 1, wherein an inner diameter of the reduced diameter portion is smaller than an inner diameter of a land portion formed between spiral grooves of the ball screw nut.

Images