Ball screw

• US 7,536,928 B2
• Filed: 06/16/2006
• Issued: 05/26/2009
• Est. Priority Date: 06/16/2005
• Status: Active Grant

• Current Assignee: NTN Corporation
• Original Assignee: NTN Corporation
• Inventors: Kazuno, Keisuke
• Primary Examiner(s): FENSTERMACHER, DAVID MORGAN
• Application Number:
  US11/455,296
• Publication Number:
  US 20070000342A1
• Time in Patent Office: 1,075 Days
• Field of Search: 74/892.3, 74/894.2, 744/247.1, 744/247.5, 744/248.6, 744/248.7, 384/516
• US Class Current: 74/424.75
• CPC Class Codes: F16H 2025/2242 Thread profile of the screw or nut showing a pointed "gothic" arch in cross-section
• CPC Class Codes: F16H 25/2204 with balls
• CPC Class Codes: F16H 25/2223 Cross over deflectors between adjacent thread turns, e.g. S-form deflectors connecting neighbouring threads
• CPC Class Codes: Y10T 74/18728 Backlash
• CPC Class Codes: Y10T 74/19721 Thread geometry
• CPC Class Codes: Y10T 74/19753 Plural independent recirculating element paths
• CPC Class Codes: Y10T 74/19767 Return path geometry

Abstract

A ball screw, which improves its durability under circumstances where a radial load and a moment load are applied to it, has a screw shaft (2) formed with a helical screw groove (2a) on its outer circumferential surface. A nut (3) is adapted to mate with the screw shaft (2). The nut (3) is formed with a helical screw groove (3a) on its inner circumferential surface. The nut helical screw groove (3a) corresponds to the screw shaft screw groove (2a). A number of balls (4) are rollably contained within a ball rolling passage formed by the oppositely arranged screw grooves (2a, 3a). Bridge members (5), each formed with a connecting groove (5a) on its inner circumferential surface, connect the screw grooves (3a) of the nut (3). A contact angle (α) between each ball (4) and one or both the screw grooves (2a, 3a) is set within a range of about 20˜40°.

Claims

1. A ball screw comprising:

a screw shaft formed with a helical screw groove on its outer circumferential surface;

a nut adapted to mate with the screw shaft, said nut formed with a helical screw groove on its inner circumferential surface, said nut helical screw groove corresponding to the screw shaft screw groove;

a number of balls rollably contained within a ball rolling passage formed by oppositely arranged screw grooves; and

bridge members, each formed with a connecting groove on its inner circumferential surface, for connecting the nut screw grooves; and

a contact angle between the ball and the screw groove is set within a range of about 20˜

40°

.

2. The ball screw of claim 1 wherein the outer diameter of each ball is set within 75˜

110% of the lead of the ball screw.

3. The ball screw of claim 1 wherein the groove depth of the screw groove is set at 35% or less than the outer diameter of the ball.

4. The ball screw of claim 1 wherein it is used for a driving portion of an actuator for an automobile.