Cantilever worm gear assembly with a limiter bushing

Abstract

A power steering assembly includes an electric motor having an output shaft extending from the electric motor. The assembly also includes a housing having a worm gear operatively coupled to a steering shaft, the worm gear being rotatable about a worm gear axis. The assembly further includes an electric motor and a worm, the worm being arranged to mesh with the worm gear, the worm extending as a single and integrally formed shaft from the output shaft of the electric motor, the single and integrally formed shaft extending axially from a first end to a second end and being cantilevered to allow deflection of the second end. The assembly further includes a bushing surrounding a portion of the shaft near the second end of the shaft, the bushing and the portion of the shaft defining a clearance between the bushing and the portion of the shaft.

Description

Background Art

[0001] Vehicles may employ a power steering mechanism that provides torque assistance to the vehicle's steering shaft and / or road feedback to the handwheel through a worm / worm gear reduction assembly. Various arrangements of the cantilevered worm may be over-constrained or, on the other hand, allowed to be bent to the breaking point. Summary of the Invention

[0002] According to one aspect of the present disclosure, there is provided a power steering assembly including an electric motor having an output shaft extending from the electric motor. The assembly further includes a housing having a worm gear operatively coupled to the steering shaft, the worm gear being rotatable about a worm gear axis. The assembly further includes an electric motor and a worm, the worm being arranged to mesh with the worm gear, the worm extending as a single and integrally formed shaft from the output shaft of the electric motor, the single and integrally formed shaft extending axially from a first end to a second end and being cantilevered to allow deflection of the second end. The assembly further includes a bushing surrounding a portion of the shaft near the second end of the shaft, the bushing and the portion of the shaft defining a gap therebetween.

[0003] According to another aspect of the present disclosure, there is provided a power steering assembly including an electric motor having an output shaft extending from the electric motor. The assembly further includes a housing having a worm gear operatively coupled to the steering shaft, the worm gear being rotatable about a worm gear axis. The assembly further includes an electric motor and a worm, the worm being arranged to mesh with the worm gear, the worm extending as a single and integrally formed shaft from the output shaft of the electric motor, the single and integrally formed shaft extending axially from a first end to a second end and being cantilevered to allow deflection of the second end. The assembly further includes a portion of the housing surrounding a portion of the shaft near the second end of the shaft, the portion of the housing and the portion of the shaft defining a gap therebetween.

[0004] According to another aspect of the present disclosure, there is provided a method of assembling a power steering assembly. The method includes linearly adjusting at least one component of the power steering assembly to set backdrive caused by contact between the threads of the worm and the teeth of the worm gear. The method further includes supporting the worm in a cantilever manner to allow deflection of one end of the worm. The method further includes restricting deflection of the end of the worm.

[0005] These and other advantages and features will become apparent from the following description in conjunction with the drawings. Brief Description of the Drawings

[0006] The claims in the conclusion of this specification particularly point out and distinctly claim as the subject matter of the present invention. The above and other features and advantages of the present invention will become apparent in the following detailed description taken in conjunction with the accompanying drawings, in which:

[0007] Figure 1 A perspective view of a part of a power steering assembly; and

[0008] Figure 2 A front view of a worm gear assembly of a power steering assembly. Detailed Description

[0009] Now referring to the accompanying drawings, the present invention will be described with reference to specific embodiments, but is not limited thereto. It should be understood that the embodiments of the present disclosure are only illustrative of the present disclosure, and the present disclosure can be implemented in various forms and alternative forms. Various elements of the embodiments of the present disclosure can be combined or omitted to form other embodiments of the present disclosure. The drawings are not necessarily to scale, as some features may be enlarged or reduced to show details of specific components. Therefore, the details of the specific structures and functional aspects disclosed herein should not be construed as restrictive, but only as a representative basis of the present invention to guide those skilled in the art to apply the present disclosure in various ways.

[0010] Reference Figure 1 , a part of the steering column assembly is shown and generally designated by reference numeral 10. The steering column assembly 10 includes a steering shaft 12 that is operatively connected at one end to a steering input device (such as a steering wheel) and is connected to one or more intermediate components that transmit the rotation of the steering shaft to the vehicle wheels. The wheel connection of the steering shaft 12 can be electrical, such as in a steer-by-wire application. The steering shaft 12 is at least partially surrounded by an upper sheath 14 that extends within a lower sheath 16.

[0011] Now referring to Figure 2 and continuing to refer to Figure 1 , a power steering assembly 20 is provided to assist a vehicle driver with steering maneuvers performed through the steering column assembly 10. The power steering assembly 20 includes a worm gear 22 that is at least partially disposed within a first housing 24 ( Figure 1)。In the illustrated embodiment, a portion of the lower housing 16 is the first housing 24 because they are integrally formed components. The power steering assembly 20 also includes a worm 26 that is at least partially disposed within a second housing 28 that also houses an electric actuator, such as a motor 30. Although the worm 26 and the worm gear 22 described above and shown in the figures are located in different housings, it should be understood that in some embodiments a single housing is employed to at least partially house both the worm 26 and the worm gear 22.

[0012] The motor 30 includes a motor shaft that rotates during operation of the motor 30. The motor shaft is integrated with the worm 26 as a single and integral component (i.e., the shaft) and extends as a rotatable output member of the motor 30. Thus, the worm 26 and the motor shaft may also be referred to herein as the shaft and are denoted by the reference numeral 26. The threads of the worm 26 are configured to engage the worm gear 22 such that rotation of the worm 26 causes rotation of the worm gear 22. The worm gear 22 is operatively coupled to the steering shaft 12 to provide torque to the steering shaft 12 to assist the driver during turning maneuvers (i.e., EPS) or to provide a resistance for road feedback to the driver (i.e., steer-by-wire).

[0013] The shaft 26 extends in the axial direction from a first end 34 to a second end 36. The motor shaft portion of the shaft 26 is closer to the first end 34 than the second end 36. The worm portion of the shaft 26 is closer to the second end 36 of the shaft 26. A first bearing 38 is located near the motor shaft portion of the shaft 26 to support the shaft 26. In other words, the first bearing 38 is closer to the first end of the shaft than the second end 36. The second bearing 40 is axially spaced from the first bearing 38 and is located further from the first end of the shaft compared to the distance between the position of the first bearing 38 and the first end 34. The second bearing 40 cantilevers the worm section of the shaft 26 (i.e., the threaded portion of the shaft 26).

[0014] Due to the cantilever nature of the assembly, the second end 36 of the shaft 26 is allowed to deflect as the power steering assembly 20 is loaded. A limiter bushing 50 surrounds that portion of the shaft 26 near the second end 36. There is a gap between the limiter bushing 50 and the shaft 26 to avoid overconstraining the assembly. However, while the gap is adjusted to avoid contact between the limiter bushing 50 and the shaft 26 under normal operating conditions, contact is allowed under extreme operating conditions to ensure that the worm shaft 26 does not break during significant deflection.

[0015] Although the limiter bushing 50 contributes to the controlled gap of the shaft 26 described above, it should be understood that alternative embodiments do not include a limiter bushing and rely only on the structure of the surrounding housing.

[0016] The embodiments described herein can be combined with the linear sliding ability of the steering assist assembly 20. As described in U.S. Patent No. 16 / 598827, filed October 10, 2019 (which is incorporated herein by reference in its entirety), linear sliding sets the frictional force of the steering assist assembly 20 in the direction marked by reference numeral 60. However, it should be understood that other methods of setting the frictional force are also contemplated.

[0017] Although the invention has been described in detail with reference to only a limited number of embodiments, it should be understood that the invention is not limited to these disclosed embodiments. On the contrary, the invention can be modified to include any number of variations, alterations, substitutions or equivalents heretofore not described, all of which are within the spirit and scope of the invention. Moreover, although various embodiments of the invention have been described, it should be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention should not be regarded as being limited by the foregoing description.

Claims

1. A power steering assembly, comprising: a motor having an output shaft extending therefrom; a housing accommodating a worm gear operatively connected to a steering shaft, the worm gear being rotatable about a worm gear axis; a worm provided to mesh with the worm gear, the worm extending as a single and integrally formed shaft from the output shaft of the motor, the single and integrally formed shaft extending axially from a first end to a second end and being cantilevered to allow deflection of the second end; and a bushing surrounding a portion of the shaft near the second end of the shaft, the bushing and the portion of the shaft defining a gap therebetween, wherein the bushing is an adjacent member relative to the second end of the shaft.

2. The power steering assembly according to claim 1, wherein the first end of the shaft is supported by a first bearing, and an intermediate portion of the shaft is cantilevered by a second bearing.

3. The power steering assembly according to claim 1, wherein the gap between the bushing and the portion of the shaft allows the second end of the shaft to deflect a predetermined amount before the bushing and the portion of the shaft come into contact.

4. The power steering assembly according to claim 1, wherein the housing is linearly movable to set the friction level of the power steering assembly.

5. The power steering assembly according to claim 1, wherein the assembly is part of a steer-by-wire system.

6. A power steering assembly, comprising: a motor having an output shaft extending therefrom; a housing having a worm gear operatively connected to a steering shaft, the worm gear being rotatable about a worm gear axis; a worm provided to mesh with the worm gear, the worm extending as a single and integrally formed shaft from the output shaft of the motor, the single and integrally formed shaft extending axially from a first end to a second end and being cantilevered to allow deflection of the second end; and a portion of the housing surrounding a portion of the shaft near the second end, the portion of the housing and the portion of the shaft defining a gap therebetween, wherein the portion of the housing is an adjacent member relative to the second end of the shaft.

7. The power steering assembly according to claim 6, wherein the first end of the shaft is supported by a first bearing, and an intermediate portion of the shaft is cantilevered by a second bearing.

8. The power steering assembly according to claim 6, wherein the gap between the portion of the housing and the portion of the shaft allows the second end of the shaft to deflect a predetermined amount before the portion of the housing and the portion of the shaft come into contact.

9. The power steering assembly according to claim 6, wherein the housing is linearly movable to set the backdrive of the power steering assembly.

10. The power steering assembly according to claim 6, wherein the assembly is part of a steer-by-wire system.

11. A method of assembling a power steering assembly, comprising: linearly adjusting at least one component of the power steering assembly to set the backdrive caused by contact between the threads of the worm and the teeth of the worm gear; Support the worm in a cantilever manner to allow one end of the worm to deflect; and Use an adjacent component relative to this end of the worm to limit the deflection of this end of the worm, wherein a gap is defined between the adjacent component relative to this end of the worm and this end of the worm.

12. The method according to claim 11, wherein, The deflection of this end of the worm is limited by a bushing, and the bushing surrounds a part of the worm near this end of the worm.

13. The method according to claim 11, wherein, The deflection of this end of the worm is limited by a part of the housing, and this part of the housing surrounds a part of the worm near this end of the worm.

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