US-12624749-B2 - Linear actuator with translating screw and torque tube

US12624749B2US 12624749 B2US12624749 B2US 12624749B2US-12624749-B2

Abstract

A compact linear actuator having a long stroke is provided. An actuator housing houses a motor having a tubular shaft and a ball nut, both of which are rotatable about an axis. The motor shaft and ball nut are axially spaced and a torque transfer assembly transfers torque from the motor shaft to the ball nut. The assembly includes a torque transfer tube having a first axial end coupled to the motor shaft and a second axial end coupled to a coupling between the tube and ball nut. A ball screw extends through at least a portion of the motor shaft, the tube and the ball nut and outward from the housing and moves along the axis responsive to rotation of the ball nut. The coupling is axially spaced from, and configured for movement along the axis relative to, the tube to prevent transfer of axial loads to the tube.

Inventors

Michael Frank Matczak

Assignees

THOMSON INDUSTRIES, INC.

Dates

Publication Date: 20260512
Application Date: 20240829

Claims (20)

1 . A linear actuator, comprising: a housing; a motor disposed within the housing and having a tubular motor shaft configured for rotation about an axis; a ball nut disposed within the housing and configured for rotation about the axis, the ball nut axially spaced from the motor shaft; a torque transfer assembly configured to transfer torque from the motor shaft to the ball nut, the torque transfer assembly including a torque transfer tube configured for rotation about the axis and having first and second axial ends, the first axial end coupled to the motor shaft for rotation therewith; and, a first coupling positioned axially between the second axial end of the torque transfer tube and the ball nut, the first coupling configured for rotation with the ball nut and the torque transfer tube; and, a ball screw extending through at least a portion of the motor shaft and through the torque transfer tube and the ball nut and outward from the housing, the ball screw configured for movement along the axis in response to rotation of the ball nut wherein the first coupling is configured for movement along the axis relative to the torque transfer tube in response to a load applied to the ball screw in the direction of the axis.
2 . The linear actuator of claim 1 , further comprising an angular contact bearing disposed between the housing and the first coupling, the angular contact bearing and first coupling disposed in a radial plane extending perpendicular to the axis.
3 . The linear actuator of claim 1 wherein the ball screw extends through an entire length of the motor shaft.
4 . The linear actuator of claim 1 , further comprising a bushing disposed within the motor shaft and supporting a first axial end of the ball screw.
5 . The linear actuator of claim 1 , further comprising a brake disposed within the housing and configured to apply a braking torque to the motor shaft.
6 . The linear actuator of claim 5 wherein the motor shaft includes first and second axial ends, the first axial end of the motor shaft coupled to the first axial end of the torque transfer tube and the brake disposed about the second axial end of the motor shaft.
7 . The linear actuator of claim 1 , further comprising a bellows having a first end coupled to the housing and a second end coupled to the ball screw.
8 . The linear actuator of claim 7 wherein the first end of the bellows and the ball nut are disposed in a radial plane extending perpendicular to the axis.
9 . The linear actuator of claim 1 , further comprising a second coupling between the first axial end of the torque transfer tube and the motor shaft, the second coupling configured for rotation with the motor shaft and the torque transfer tube.
10 . A linear actuator, comprising: a housing; a motor disposed within the housing and having a tubular motor shaft configured for rotation about an axis; a ball nut disposed within the housing and configured for rotation about the axis, the ball nut axially spaced from the motor shaft; a torque transfer assembly configured to transfer torque from the motor shaft to the ball nut, the torque transfer assembly including a torque transfer tube configured for rotation about the axis and having first and second axial ends, the first axial end coupled to the motor shaft for rotation therewith; and, a first coupling between the second axial end of the torque transfer tube and the ball nut, the first coupling configured for rotation with the ball nut and the torque transfer tube; and, a ball screw extending through at least a portion of the motor shaft, the torque transfer tube and the ball nut and outward from the housing, the ball screw configured for movement along the axis in response to rotation of the ball nut wherein the first coupling is configured for movement along the axis relative to the torque transfer tube in the presence of a load applied to the ball screw in the direction of the axis and further comprising a brake disposed within the housing and configured to apply a braking torque to the motor shaft wherein the ball screw extends through at least a portion of the brake.
11 . A linear actuator, comprising: a housing; a motor disposed within the housing and having a tubular motor shaft configured for rotation about an axis; a ball nut disposed within the housing and configured for rotation about the axis, the ball nut axially spaced from the motor shaft; a torque transfer assembly configured to transfer torque from the motor shaft to the ball nut, the torque transfer assembly including a torque transfer tube configured for rotation about the axis and having first and second axial ends, the first axial end coupled to the motor shaft for rotation therewith; and, a first coupling between the second axial end of the torque transfer tube and the ball nut, the first coupling configured for rotation with the ball nut and the torque transfer tube; and, a ball screw extending through at least a portion of the motor shaft and through the torque transfer tube and the ball nut and outward from the housing, the ball screw configured for movement along the axis in response to rotation of the ball nut wherein a first radially extending surface formed in an axial end of one of torque transfer tube and the first coupling faces a second radially extending surface of the other of the torque transfer tube and the first coupling and the first and second radially extending surfaces are axially spaced from one another by an air gap.
12 . The linear actuator of claim 11 , further comprising and an angular contact bearing disposed between the housing and the first coupling, the angular contact bearing and first coupling disposed in a radial plane extending perpendicular to the axis.
13 . The linear actuator of claim 11 wherein the ball screw extends through an entire length of the motor shaft.
14 . The linear actuator of claim 11 , further comprising a bushing disposed within the motor shaft and supporting a first axial end of the ball screw.
15 . The linear actuator of claim 11 , further comprising a brake disposed within the housing and configured to apply a braking torque to the motor shaft.
16 . The linear actuator of claim 15 wherein the motor shaft includes first and second axial ends, the first axial end of the motor shaft coupled to the first axial end of the torque transfer tube and the brake disposed about the second axial end of the motor shaft.
17 . The linear actuator of claim 15 wherein the ball screw extends through at least a portion of the brake.
18 . The linear actuator of claim 11 , further comprising a bellows having a first end coupled to the housing and a second end coupled to the ball screw.
19 . The linear actuator of claim 18 wherein the first end of the bellows and the ball nut are disposed in a radial plane extending perpendicular to the axis.
20 . The linear actuator of claim 11 , further comprising a second coupling between the first axial end of the torque transfer tube and the motor shaft, the second coupling configured for rotation with the motor shaft and the torque transfer tube.

Description

BACKGROUND OF THE INVENTION a. Field of the Invention This disclosure relates to a linear actuator. In particular, the disclosure relates to a linear actuator that has a relatively long stroke, but is also relatively compact. b. Background Art Linear actuators convert rotary motion into linear motion to move an object back and forth along a line. Linear actuators are used in a wide variety of applications and the form of the linear actuator will vary depending on the requirements of the application. One of the primary variables that is considered when designing or selecting a linear actuator for a particular application is the stroke length of the actuator (i.e., the distance that the rod of the actuator will travel when moved from a fully retracted position to a fully extended position and from the fully extended position to the fully retracted position). The length of the rod, and therefore, the linear actuator, will be at least as long as the stroke length. The length of the linear actuator, however, is often much greater than the stroke length. In particular, the motor of the linear actuator and power transmission devices that are used to transfer power from the motor to the rod will add to the length of the actuator—particularly in an inline arrangement in which the motor output shaft is coaxial with the rod. In some linear actuators, the length of the actuator is reduced using a parallel arrangement in which the motor output shaft is parallel to the rod. This arrangement, however, significantly expands the width of the linear actuator. Certain applications require a relatively long stroke length, but also require that the actuator have a relatively small size (i.e., a relatively small length and width). For example, forklifts used to move objects from one location to another include a mast at a forward end. The mast includes a pair of outer rails and a pair of inner rails that may be moved relative to the outer rails. The inner rails support a carriage on which a load backrest and forks are mounted to support objects that are being moved. The inner rails, carriage, load backrest, forks and objects are typically raised and lowered using hydraulic cylinders. Replacing the hydraulic cylinders with an electric linear actuator would eliminate significant maintenance issues associated with the use of hydraulic cylinders. For certain types of forklifts, however, the potential height of the mast is limited and, therefore, the potential size of the linear actuator is also limited. For example, for forklifts that are used to load and unload trailers of tractor-trailers, the potential height of the mast is limited by the height of the trailer interior. As a result, the available space in the mast for a linear actuator is also limited. When the forklift is used to move objects outside of the trailer (e.g., to place or remove objects from storage locations in a building), however, a relatively long stroke length may still be needed to move objects to and from an appropriate location. The inventors herein have recognized a need for a linear actuator that will minimize and/or eliminate one or more of the above-identified deficiencies. BRIEF SUMMARY OF THE INVENTION This disclosure relates to a linear actuator. In particular, the disclosure relates to a linear actuator that has a relatively long stroke, but is also relatively compact. A linear actuator in accordance with one embodiment includes a housing, a motor disposed within the housing and having a tubular motor shaft configured for rotation about an axis and a ball nut disposed within the housing and configured for rotation about the axis. The ball nut is axially spaced from the motor shaft. The linear actuator further includes a torque transfer assembly configured to transfer torque from the motor shaft to the ball nut. The torque transfer assembly includes a torque transfer tube configured for rotation about the axis and having first and second axial ends. The first axial end is coupled to the motor shaft for rotation therewith. The torque transfer assembly further includes a coupling between the second axial end of the torque transfer tube and the ball nut. The coupling is configured for rotation with the ball nut and the torque transfer tube. The linear actuator further includes a ball screw extending through at least a portion of the motor shaft, the torque transfer tube and the ball nut and outward from the housing. The ball screw is configured for movement along the axis in response to rotation of the ball nut. The coupling is configured for movement along the axis relative to the torque transfer tube in the presence of a load applied to the ball screw in the direction of the axis. A linear actuator in accordance with another embodiment includes a housing, a motor disposed within the housing and having a tubular motor shaft configured for rotation about an axis and a ball nut disposed within the housing and configured for rotation about the axis. The bal