CN113492904A

CN113492904A - Radially preloaded rack bearing

Info

Publication number: CN113492904A
Application number: CN202110274771.XA
Authority: CN
Inventors: K·P·道格拉斯; R·D·哈里斯; F·N·戈尔达; J·R·科茨
Original assignee: Steering Solutions IP Holding Corp
Current assignee: Steering Solutions IP Holding Corp
Priority date: 2020-03-18
Filing date: 2021-03-15
Publication date: 2021-10-12
Also published as: DE102021103930A1

Abstract

The rack and pinion steering system includes a housing, a rack, a pinion, and a radially preloaded rack bearing. A rack is supported by the housing, and a pinion is engaged with the rack. A radially preloaded rack bearing is supported and preloaded to the housing and to the rack.

Description

Radially preloaded rack bearing

RELATED APPLICATIONS

This patent application is a continuation-in-part application of U.S. patent application serial No. 15/594,909 filed on 15/5/2017 (which claims priority to U.S. provisional patent application serial No. 62/339,670 filed on 20/5/2016), the disclosure of which is incorporated herein by reference in its entirety.

Background

Rack and pinion (rack and neutral) steering systems are a common type of system that is often used in the automotive industry. Typical rack and pinion steering systems are used to convert rotational motion to linear motion and may include elongated steering racks (i.e., racks), tie rods (tie rods), steering shafts, and pinions. Tie rods, typically connected with respective front tires, are attached to the steering rack at opposite ends thereof. The pinion is attached to one end of the steering shaft, and the steering wheel is attached to the other end of the steering shaft. The pinion gear is operatively engaged with the teeth of the steering rack. Rotation of the steering wheel rotates the pinion, which in turn moves the rack in a linear manner.

Many system components typically assist in the operable engagement of the pinion gear with the rack gear and may include a rack bearing (i.e., a rack yoke or shoe), a housing, and other components. Known designs and configurations to support the mating connection may be prone to undesirable noise, provide undesirable feel (feel) performance, increase maintenance complexity, and other problems.

Accordingly, it is desirable to improve the operably engaged connections and/or associated components to, for example, minimize system noise, improve system feel, and optimize robustness.

Disclosure of Invention

In one exemplary and non-limiting embodiment of the present disclosure, a rack and pinion steering system includes a housing, a rack, a pinion, and a radially preloaded rack bearing. A rack is supported by the housing, and a pinion is engaged with the rack. A radially preloaded rack bearing is supported and preloaded to the housing, and to the rack.

In another exemplary embodiment, a rack bearing for a rack and pinion steering system includes a first semi-cylindrical section and a second semi-cylindrical section. The second semi-cylindrical section is operably coupled to the first semi-cylindrical section to radially expand and contract.

These and other advantages and features will become more apparent from the following description taken in conjunction with the accompanying drawings.

Drawings

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a partial cross-sectional view of a rack and pinion steering system according to an exemplary embodiment of the present disclosure;

FIG. 2 is a cross-sectional view of a rack and pinion steering system similar to FIG. 1, but with some components removed to show detail;

FIG. 3 is a cross-sectional view of the rack and pinion steering system as viewed in the direction of arrows 3-3 in FIG. 2;

FIG. 4 is a perspective view of a rack bearing of the rack and pinion steering system showing a first end face;

FIG. 5 is another perspective view of the rack bearing showing an opposing second end face;

FIG. 6 is a perspective view of a second embodiment of a rack bearing;

FIG. 7 is a perspective view of a semi-cylindrical section of the rack bearing;

FIG. 8 is a cross-sectional view of a third embodiment of a rack and pinion steering system;

FIG. 9 is a cross-sectional view of a rack bearing of the rack and pinion steering system as viewed in the direction of arrows 9-9 in FIG. 8;

fig. 10 is a perspective view of a rack bearing according to another aspect of the present disclosure; and

fig. 11 shows the rack bearing of fig. 10.

Detailed Description

Referring now to the drawings, wherein the present invention will be described with reference to specific embodiments without limiting the same, a rack and pinion steering system 20, which may be used in an automobile, assists in converting rotational motion to linear motion. Referring to fig. 1, a rack and pinion steering system 20 may include an elongated steering rack 22 (i.e., a rack bar), two tie rods (not shown), a steering shaft 24, a pinion gear 26, a housing 28, a rack bearing 30, and a resilient flexible member 32 adapted to exert a biasing force in an axial direction relative to a centerline C2. In one example, the member 32 may be a coil spring. Each tie bar may span between and be operatively connected to a respective end of the rack 22 and a respective tire (e.g., front tire), not shown. A pinion 26 may be attached to one end of the steering shaft 24 for rotation about the axis a, and a steering wheel (not shown) may be attached to the opposite end. The pinion gear 26 is constructed and arranged to operatively engage the teeth 34 of the steering rack 22. Rotation of the steering wheel rotates the pinion 26, which in turn moves the rack 22 along the centerline C1 in a substantially linear manner.

Referring to fig. 1-3, the rack bearing 30 is adapted to support the rack 22 and preload the meshing engagement between the pinion 26 and the rack 22. The rack bearing 30 may generally (generally) and slidably fit within a substantially cylindrical bore having a boundary defined by a substantially cylindrical inner surface 38 of the housing 28. Bore 36 and surface 38 may be substantially centered about a centerline C2, which centerline C2 may be orthogonal to centerline C1 and/or may intersect centerline C1. Because the rack bearing 30 slides axially within the bore 36 of the housing 28, the rack bearing 30 is able to transfer the axial preload (see arrow 40 in fig. 2) of the adjuster spring 32 (see fig. 1) to the meshing engagement. The amount of sliding movement can be limited by adjustment of an adjuster plug 42, which may be threadably engaged to the housing 28, relative to the rack bearing 30.

Referring to fig. 2 to 5, the rack bearing 30 may include: an axial base end face 44, which may be annular in shape; and an opposing rack contacting end face 46, which may be concave in shape, to make sliding contact with the rack 22. The rack bearing 30 may include a bore 48, which may be a blind bore, having a boundary defined by a generally cylindrical inner surface 50 of the rack bearing 30 and a spring seat 52. The adjustment spring 32 may apply the axial preload 40 directly between the spring seat 52 and the adjustment plug 42. The generally cylindrical outer surface 54 of the rack bearing 30 may span axially between the

end surfaces

44 and 46 relative to the centerline C2 and radially opposite the inner surface 38 of the housing 28.

The rack bearing 30 may also include a slot 56 that may be coplanar with the centerline C2 (i.e., located in a common imaginary plane), may communicate with the blind bore 48, and may communicate through the outer surface 54, the inner surface 50, the

end surfaces

44 and 46, and the spring seat 52. More specifically, the slot 56 may communicate through two diametrically opposed locations of the inner surface 50 and one circumferential location of the outer surface 54. Since the slot does not communicate through two diametrically opposed locations of the outer surface 54, the rack bearing 30 may generally be a unitary and homogeneous component having two

semi-cylindrical sections

58, 60 attached by an integral hinge portion 62 of the rack bearing 30. That is, the slot 56 segments a majority of the rack bearing 30, leaving a small portion of flexible material for the hinge portion 62.

The hinge portion 62 may be generally elongate extending axially relative to the centerline C2. The end faces 44, 46 and a relatively small portion of the outer surface 54 may be carried by the integral hinge portion 62. In one example, the rack bearing 30 may be made of injection molded polymer.

Referring to fig. 2 and 3, the outer diameter of the rack bearing 30 (see arrow 64) may be sized to achieve an initial, circumferentially low gap (see arrow 66) measured between the inner surface 38 of the housing 28 and the outer surface 54 of the rack bearing 30. Radial compression of the rack bearing 30 via flexing of the hinge portion 62 may generally increase the gap 66, and radial expansion of the bearing may generally decrease the gap 66 until the gap is no longer circumferentially continuous and the inner surface 38 and the outer surface 54 are in direct sliding contact with each other at the lobes 80. It is contemplated and understood that the hinge portion 62 may be adjusted to exert a biasing force on the

semi-cylindrical sections

58, 60 to move the sections radially outward.

Referring to fig. 3 and 5, the boundaries of the slot 56 may be defined by

opposing sides

68, 70 of the respective

semi-cylindrical sections

58, 60. The rack and pinion system 20 may also include at least one resilient member 72 extending between the

sides

68 and 70 and in biased contact with each

segment

58, 60 to apply a force (see arrow 74 in fig. 2 and 3) that biases the

segments

58, 60 radially outward. Generally, the resilient member 72 may be proximate the outer surface 54 and diametrically opposed to the hinge portion 62. The elastic member 72 may be made of rubber or a rubber-like material. Another example of the member 72 may be an elastic spring.

During assembly of the rack bearing 30 into the housing 28, the rack bearing 30 may radially contract against (against) the biasing force 74 of the resilient member 72, thereby further compressing the member between the

sides

68, 70 of the respective

semi-cylindrical sections

58, 60. With the resilient member 72 properly compressed, a gap 66 is typically formed between the inner surface 38 of the housing 28 and the outer surface 54 of the rack bearing 30 to enable axial insertion of the rack bearing 30 into the bore 36 of the housing 28. Once inserted, the release of the rack bearing 30 may expand the resilient member 72, thereby radially expanding the rack bearing 30 until the outer surface 54 of the rack bearing 30 contacts the inner surface 38 of the housing 28.

The size of the gap 66, the compressibility (i.e., the compression coefficient) of the resilient member 72, and other factors may be appropriately designed and determined to compensate for any coefficient of thermal expansion between the components (e.g., the rack bearing 30 and the housing 28). The interaction of thermal expansion between the components depends at least in part on the type of material. For example, the rack bearing 30 may be made of a polymer, while the housing 28 may be made of metal. One example of a metal may be aluminum. These material choices may be desirable for weight reduction, and the novel configuration of the components may prevent or reduce any possibility of the rack bearing 30 jamming (sizing) the housing 28.

The radially preloaded rack bearing 30 may provide a line-to-line fit between the rack bearing 30 and the housing 28 during temperature changes. As the temperature increases, the rack bearing 30 may compress slightly if it grows (expands) more than the housing 28. When the temperature decreases and the rack bearing 30 contracts more than the housing 28, the resilient member 72 may expand the rack bearing 30 against the housing 28.

Because the radially preloaded rack bearing 30 can compensate for the dimensional difference between the rack bearing outer diameter and the housing inner surface diameter, the housing inner surface tolerance can be increased. This will reduce the number of machining operations and cycle time. Further, when the rack bearing 30 is made of polymer, the rack bearing 30 may not require any secondary machining or other secondary sizing operation (sizing operation) after the injection molding process.

During normal operation and in order to limit system rattle (rattle and stick) and optimize system "feel" performance, the rack bearing 30 may remain in line-to-line engagement with the housing inner surface 38 under all temperatures and operating conditions. Also during operation, the adjustment spring 32 may be supported (bear upon) along the centerline C2 on the spring seat 52 of the rack bearing 30. Further, the contact end surface 46 of the rack bearing 30 is supported on the rack 22. The profile of the contact end face 46 may substantially match the profile of the rack 22 and/or may include a general contact point 76, 78 (see fig. 2) such that the rack 22 and the rack bearing 30 contact each other at a point that is offset from one or both centerlines C1, C2 by approximately forty-five (45) degrees. Generally, the contact points 76, 78 may be formed by having the radius of curvature of the end face 46 of the rack bearing 30 be greater than the radius of curvature of the opposing outer cylindrical surface of the steering rack 22.

The arrangement or orientation of the contact points 76, 78 may help the rack bearing 30 expand radially outward and may force the rack bearing 30 into contact with the inner surface 38 of the housing 28. In one embodiment, a plurality of bosses 80 (i.e., four as shown) may be circumferentially spaced about the centerline C2 and carried between the outer surface 54 of the rack bearing 30 and the inner surface 38 of the housing 28. In one embodiment, the rack bearing 30 may carry the boss 80, and the inner surface 38 of the housing 28 may be cylindrical and/or may be more cylindrical than the outer surface 54 of the rack bearing 30. Although not shown, it is contemplated and understood that each semi-cylindrical section 58, 60 (i.e., substantially cylindrical) may include only one lobe 80, thus a total of two lobes are circumferentially spaced about one hundred and eighty degrees (180 degrees) from each other.

The boss 80 may promote stability without maintaining a high consistency between the circular rack bearing outer diameter and the housing bore 36. It is contemplated and understood that in some embodiments, the use of the protrusion 80 and/or the use of the contact points 76, 78 may have some design flexibility so as to deviate slightly from the generally cylindrical shape of the surface 54 and/or the end face 46 of the rack bearing 30.

In one embodiment, the resilient member 72 may not be required due to the operating characteristics. For example, in operation, as the rack force increases due to steering or input from the vehicle chassis, the preload force 74 between the rack bearing 30 and the housing 28 may increase proportionally. The more the rack bearing 30 is loaded, the greater the backlash force (delashing force) is applied. The resilient member 72 may not be required where the radial preload is sufficient to prevent rattle while maintaining smooth operation.

Referring to fig. 6 and 7, a second embodiment of a rack bearing is shown, wherein like elements to the first embodiment have like reference numerals (except for the suffix with an upper prime). The rack bearing 30 ' may include two separate semi-cylindrical sections 58 ', 60 ' having sides 68 ', 70 ' opposite each other. To simplify manufacturing and reduce cost, each section 58 ', 60' may be identical. A first key 72 ' may project from each side portion 68 ', 70 ' to be received in a recess 82 defined by the opposite side portion 70 ', 68 '. The keys 72 ' are generally adjusted to orient and maintain orientation between the sections 58 ', 60 ' as the sections 58 ', 60 ' radially expand and contract. In one example, the key 72 ' may be an integral and homogeneous component to the respective sections 58 ', 60 '. In another example, the key 72' may be an elastic member. Examples of the elastic member may include an elastomeric material (e.g., rubber), a spring, and the like.

Referring to fig. 8 and 9, a third embodiment of a rack bearing is shown, wherein like elements to the first and second embodiments have like reference numerals (except for the double primed suffix). Similar to the second embodiment, the rack bearing 30 "may include two separate semi-cylindrical sections 58", 60 ". These sections may include respective sides 68 ", 70" opposite one another. To simplify manufacturing and reduce cost, each section 58 ", 60" may be identical. A plurality of resilient members 72 "(i.e., six are shown) may extend between and be in biasing contact with each of the side portions 68", 70 ".

The resilient member 72 "may be oriented to ensure the desired radial expansion. For example, the opposing side portions 68 ", 70" may remain substantially parallel to one another during radial expansion and contraction. In one example, a first set of three resilient members 72 "may be axially spaced from one another, circumferentially aligned with one another, and proximate to the substantially cylindrical surface 54". A second set of three resilient members 72 "may be axially spaced from one another, circumferentially aligned with one another, and proximate the substantially cylindrical surface 54". The first set of resilient members 72 "may be circumferentially spaced about one hundred and eighty degrees (180 degrees) from the second set of resilient members 72". As shown, the resilient member 72 "is a coil spring; however, these members may be made of any material that can be elastically expanded and compressed.

Fig. 10 and 11 illustrate another embodiment of a rack bearing and the rack bearing is generally designated by the reference numeral 130. Unless specifically described otherwise, the components described above in connection with the embodiment of fig. 1-9 are the same as in the embodiment of fig. 10 and 11.

The rack bearing 130 includes first and second sections 158, 160 that are similar to the semi-cylindrical sections described above, but in fig. 10 and 11, the sections 158, 160 need not be semi-cylindrical and may be referred to as primary sections, such as first and second primary sections 158, 160. Unlike other embodiments described herein, the sections 158, 160 are not structurally bonded to each other. Instead, the first and second sections 158, 160 are identical and fit together within the housing to form a scissor-like bearing.

The rack contact force will cause the two sections 158, 160 to tilt in the housing bore in a scissor motion (tip). To ensure that the scissors bearing does not yield (yield) during extreme load strokes (extreme load extensions), a significant axial clearance is provided between the two halves. This gap region is indicated by reference numeral 170 in fig. 11. To prevent bearing sections 158, 160 from yielding, these sections are designed to fit together with axial gap 170. Under an extreme load stroke, the gap will close and the axial load will be transferred from one bearing section through the other into the adjuster plug. If the clearance is too large, bearing section yielding will occur before the load is transferred to the other bearing half. However, if the gap is too small, scissor movement may be prevented and radial preload may be reduced. To improve the stability of the housing bore, the scissors rack bearing has a hex lobe design as shown in FIG. 11.

Advantages and benefits of the present disclosure include a design that compensates for tolerance stack-up (tolerance stack) and allows for greater casing diameter tolerances, thereby reducing manufacturing costs and time. The present design facilitates the use of polymer rack bearing assemblies by compensating for differences in thermal expansion between the aluminum housing and the plastic rack bearing assembly components. Other advantages include the frictional force between the rack bearing 30 and the housing 28, which provides damping in the rack and pinion disengagement direction and eliminates the need for any more conventional radial O-rings.

While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description.

Claims

1. A rack and pinion steering system comprising:

a housing;

a rack supported by the housing;

a pinion gear engaged with the rack; and

a radially preloaded rack bearing supported and preloaded to the housing and preloaded to the rack, the rack bearing formed from a first segment and a second segment, the first segment and the second segment being structurally unconnected to each other.

2. The rack and pinion steering system according to claim 1 wherein said rack bearing is axially preloaded against said rack and radially preloaded against said housing.

3. The rack and pinion steering system according to claim 2 wherein said rack bearing is in direct contact with said housing.

4. The rack and pinion steering system according to claim 1 wherein the first and second sections of the rack bearing have the same geometry.

5. A rack bearing for a rack and pinion steering system, comprising:

a first section; and

a second section operably coupled to the first section to radially expand and contract.

6. The rack bearing according to claim 5, wherein the first section and the second section are formed in the same geometric shape.

7. The rack bearing according to claim 5, wherein the first and second segments are structurally unconnected to each other.

8. The rack bearing according to claim 5, wherein the rack bearing is made of a polymer.