Linear Electromechanical Actuator For A Steering System Of A Motor Vehicle

• US 20070278031A1
• Filed: 03/09/2005
• Published: 12/06/2007
• Est. Priority Date: 03/15/2004
• Status: Active Grant

• Current Assignee: ABet SKF
• Original Assignee: ABet SKF
• Inventors: Andersson, Per-Erik
• Granted Patent: US 7,686,125 B2
• Time in Patent Office: Days
• US Class Current: 180/444
• CPC Class Codes: B62D 5/0427 the axes being coaxial
• CPC Class Codes: B62D 5/0448 Ball nuts
• CPC Class Codes: Y10T 74/19795 Parallel to shaft

Abstract

A linear electromechanical actuator, for a steering system of the ‘center take-off’ type in a motor vehicle comprises: two electric motors each having a stator, and a rotor, a screw mechanism having an axially stationary innerscrew coupled to the rotors of the motor for rotating about an axis, and an outer nut rotationally fixed and axially translatable along the axis, a connection block, axially translatable with the nut, for connecting the nut to two tie rods of the steering system.

Claims

1. A linear electromechanical actuator for a centered take-off type steering system in a motor vehicle, comprising:

at least one electric motor with a stator and a rotor,

a screw mechanism with

an axially stationary inner screw coupled to the rotor of the electric motor for rotating about an axis, and

an outer nut rotationally fixed and axially translatable along said axis,

connection means, axially translatable with the nut for connecting the nut to two tie rods of the steering system.

2. The actuator of claim 1, wherein the screw mechanism further comprises a casing forming an axially extended inner cylindrical wall for slidably accommodating the translatable nut.

3. The actuator of claim 2, wherein said connection means projects radially outwardly of a rectilinear axial slit formed by the inner cylindrical wall of the casing.

4. The actuator of claim 3, wherein the connection means is engaged along the rectilinear slit for preventing rotation of the nut about the translation axis.

5. The actuator of claim 1, wherein the screw mechanism is a ballscrew mechanism.

6. The actuator of claim 2, wherein the nut is an elongated tubular member with opposite end portions each provided with an element of a low friction material slidingly contacting the inner cylindrical wall of the casing.

7. The actuator of claim 6, wherein the low friction elements are annular cylindrical elements.

8. The actuator of claim 1, comprising two electric motors fixed at opposite axial end portions of the screw mechanism, wherein the rotors of the electric motors are keyed on two respective opposite axial end portions of the screw.

9. The actuator of claim 1, wherein the two electric motors are fixed symmetrically to the opposite axial end portions of the screw mechanism.

10. The actuator of claim 1, further comprising at least one rotation sensor operatively associated with the screw.

11. The actuator of claim 10, wherein the rotation sensor is fitted near a bearing for rotatably supporting the screw about the axis.

12. The actuator of claim 10, wherein the rotation sensor is integrated in a bearing for rotatably supporting the screw about the axis.

13. The actuator of claim 1, wherein the screw is rotatably supported by two axially spaced rolling bearings, wherein one of said bearings is an angular contact bearing with a dual set of balls having an outer race and an inner race axially locked with respect to a casing and the screw, respectively.

14. The actuator of claim 1, further comprising an absolute linear sensor device for detecting the axial position of the nut along the axis.

15. The actuator of claim 14, wherein the linear sensor device includes a fixed linear element carried by the casing and extending parallel to the translation axis.

16. The actuator of claim 15, wherein the linear sensor device includes a mobile sensor element mounted on said connection means and operatively facing the fixed linear sensor element.

17. The actuator of claim 14, wherein the linear sensor device is of the contactless type.