Expansion shaft

This application claims the benefit under 35 U.S.C. § 119 of Japanese Patent Application Nos. 11-343700 and 2000-350738, the abstract of disclosure of which is incorporated herein by reference.

The present invention relates to an expansion shaft. More particularly, the invention is directed to an improved structure of the expansion shaft for preventing vibrations resulting from play in fit portions of a pair of shaft sections.

The expansion shaft is used as, for example, a steering shaft of an automobile.

The expansion shaft is also used as an intermediate shaft interconnecting the automotive steering shaft and a steering mechanism such as a rack and pinion type mechanism. In this case, the extending function is used for adjustment of the intermediate shaft length for accommodating a relative displacement between a steering gear and a steering column while a vehicle is driven, or used for adjustment of the length of the intermediate shaft at the time of being assembled.

A spline or serration is generally employed as a structure for establishing fitting engagement between the pair of shaft sections of the expansion shaft.

For instance, the two shaft sections may be integrally rotatably joined together by inserting an end of a second shaft section into a fit hole formed at an end of a first shaft section. The fit hole includes a female serration (also called an internal serration) while the end of the second shaft section includes a male serration (also called an external serration).

In this case, the second shaft section cannot be inserted into the fit hole if there is no clearance between the male serration and the female serration. Unfortunately, the clearance has the adverse effect of permitting the shaft sections to be radially or circumferentially displaced relative to each other, thus causing rattle which is annoying to a driver.

For this reason, the second shaft section is configured such that a part of the male serration is cut away to produce a cutaway portion or to define a D-shape in section. With a flat plate spring of a bent form placed on the cutaway portion, the second shaft section is fitted in the fit hole of the first shaft section thereby preventing the occurrence of rattle.

However, the configuration suffers a poor assemblability because of a fear that the plate spring on the cutaway portion of the second shaft section may move out of place when the second shaft section is inserted in the fit hole of the first shaft section. In some cases, the second shaft section may be assembled with the plate spring displaced out of place. This leads to the variations of an anti-rattle effect.

As an approach to overcome this problem, an anti-rattle member as shown in FIG. 8 has heretofor been proposed (Unexamined Japanese Utility Model No.7(1995)-40360). The anti-rattle member is arranged such that one shaft section 51 is formed with a thick shaft portion 52 at an end thereof, which is formed with a male serration 53 , while a female serration 54 for fittingly receiving the male serration 53 is formed at an inner circumferential surface of a fit hole 56 of the other shaft section 55 . The male serration 53 includes a first portion 53 a and a second portion 53 b which are axially separated from each other. A thin shaft portion 57 is defined between the first and second portions 53 a, 53 b and is adapted to be brought into fitting engagement with an anti-rattle member 58 .

Referring to FIGS. 8 and 9 A- 9 B, the anti-rattle member 58 includes two legs 59 substantially of an annular shape (C-shape) having a smaller inside diameter than an outside diameter of the thin shaft portion, and a body 60 interconnecting these legs 59 at their mid portions.

When the one shaft section 51 is inserted in the fit hole 56 of the other shaft section 55 , the anti-rattle member 58 is stably retained on the one shaft section 51 by way of the legs 59 resiliently clamping the thin shaft portion 57 . This eliminates a fear of disengagement of the anti-rattle member 58 during assembly.

The body 60 is of a bent shape raised at its intermediate portion. The body is designed to prevent the occurrence of rattle by way of its top portion resiliently pressing against the female serration 54 .

However, the thin shaft portion 57 is increased in the axial length because of the anti-rattle member 58 having the pair of legs 59 , 59 axially spaced from each other by a distance D. As a result, the male serration 53 is increased in the overall axial length. Hence, a fit length between the pair of shaft sections 51 , 55 is increased so that the overall weight and costs of the expansion shaft increase.

In view of the foregoing, it is an object of the invention to provide an expansion shaft capable of achieving the reduction of size and weight.

In accordance with a preferred aspect of the invention for achieving the above object, an expansion shaft comprises a first and a second shaft section aligned on the same axis, the expansion shaft further comprising a fit hole formed at the first shaft section for receiving the second shaft section; a thin shaft portion defined on the second shaft section; a pair of thick shaft portions formed on the second shaft section as axially sandwiching the thin shaft portion therebetween; a groove and a ridge respectively formed in an inner circumferential surface of the fit hole and on the thick shaft portions for coming into fitting engagement thereby integrally rotatably interconnecting the first and second shaft sections as allowing the shaft sections to axially move relative to each other; and a resilient member interposed between the inner circumferential surface of the fit hole of the first shaft section and an opposite outer peripheral surface of the second shaft section for preventing the shaft sections from radially moving relative to each other. The resilient member includes a single C-shaped snap ring resiliently clamping the thin shaft portion, and an arm extended from the snap ring in at least one axial direction of the second shaft section and serving to press against the inner circumferential surface of the fit hole of the first shaft section.

According to the embodiment, the single C-shaped snap ring is used for retaining the resilient member on the thin shaft portion of the second shaft section so that the thin shaft portion can be reduced in the axial length. This contributes to the reduction of the fit length between the first and second shaft sections, thus enabling the realization of a compact, lightweight expansion shaft. In addition, the arm resiliently presses against the inner circumferential surface of the fit hole of the first shaft section thereby positively preventing the vibrations due to a loose fit between the first and second shaft sections as well as the occurrence of noise associated with the vibrations.

FIG. 1 is an exploded perspective view showing an expansion shaft according to one embodiment of the invention;

FIG. 2 is a perspective view showing an anti-rattle member;

FIGS. 3A and 3B are a plan view and a side view showing the anti-rattle member attached to a second shaft section;

FIG. 4 is a sectional view showing the expansion shaft in which two shaft sections are assembled with an arm of the anti-rattle member pressing against a female serration;

FIG. 5 is a perspective view showing an anti-rattle member according to another embodiment of the invention;

FIG. 6 is a sectional view showing an expansion shaft according to still another embodiment of the invention;

FIGS. 7A and 7B are sectional views showing an expansion shaft according to yet another embodiment of the invention;

FIG. 8 is an exploded perspective view showing a conventional expansion shaft; and

FIGS. 9A and 9B are a perspective view and a plan view showing an anti-rattle member employed by the expansion shaft of FIG. 8 .

Now, preferred embodiments of the invention will be described with reference to the accompanying drawings. Referring to FIGS. 1-4, an expansion shaft according to one embodiment of the invention will be described.

As seen in FIG. 1, the expansion shaft is constructed such that a fit hole 4 with a female serration 3 is formed at an end 2 of a first shaft section 1 while an end 7 of a second shaft section 6 is inserted in the fit hole 4 , the end 7 of the second shaft section 6 having a male serration 5 to engage with the female serration 3 .

The end 7 of the second shaft section 6 includes a thin shaft portion 8 having a smaller diameter and a predetermined width, and a pair of thick shaft portions 16 , 17 of a greater diameter axially sandwiching the thin shaft portion 8 therebetween. The thick shaft portions 16 , 17 are respectively formed with a male serration 5 a, 5 b at their outer peripheries. That is, the male serration 5 is divided into the two male serrations 5 a, 5 b disposed on axially opposite sides of the thin shaft portion 8 . FIG. 1 schematically shows the male serrations 5 a, 5 b and the female serration 3 . An anti-rattle member 9 formed of a resilient member is mounted on the thin shaft portion 8 . The anti-rattle member 9 is constructed from a sheet metal by press forming.

Referring to FIGS. 2, 3 A and 3 B, the anti-rattle member 9 includes a leg portion 10 serving as a single snap ring substantially of an annular form (C-shaped arcuate form) extending along a circumference of the thin shaft portion 8 , and a pair of arms 11 , 12 extended from an intermediate portion (a midportion, for example) of the leg portion 10 in axially opposite directions of the thin shaft portion 8 .

The leg portion 10 extends substantially along the overall circumference of the thin shaft portion 8 , resiliently clamping the thin shaft portion 8 . Each of the arms 11 , 12 is of a bent form, raised at its intermediate portion 13 such that the intermediate portion 13 may resiliently contact the female serration 3 , as shown in FIG. 4, when the two shaft sections 1 , 6 are assembled. As shown in FIGS. 1, 3 A and 3 B, the male serrations 5 a, 5 b are respectively formed with teeth-free areas 14 , 15 for accommodating the corresponding arms 11 , 12 .

Referring to FIG. 4, each serration tooth 18 defines a ridge, the serration tooth extending axially of the male serration 5 a and having a triangular shape in section. Each serration tooth 18 as the ridge of the male serration 5 a is fitted in a groove 20 defined between adjoining serration teeth 19 of the female serration 3 .

In the present embodiment, an axial length L 1 of the thin shaft portion 8 (see FIG. 3B) can be reduced because a single leg portion 10 serves to retain the anti-rattle member 9 on the thin shaft portion 8 of the second shaft section 6 . This contributes to a reduced fit length L 2 between the serrations 3 , 5 (see FIG. 3B) and hence, to the realization of a compact, lightweight expansion shaft. In addition, a sufficient anti-rattle effect can be attained by virtue of the pair of arms 11 , 12 pressing against the female serration 3 , the arms extended axially of the thin shaft portion 8 in a bent fashion.

During the assembly of the expansion shaft, in particular, the arms 11 , 12 are accommodated in the corresponding teeth-free areas 14 , 15 of the male serrations 5 a, 5 b so that the arms 11 , 12 may not interfere with the assembly of the shaft sections. Thus, the assembly of the expansion shaft is facilitated.

It is to be noted that the present invention should not be limited to the foregoing embodiment. As shown in FIG. 5, for instance, an anti-rattle member 9 A may include either one of the arms 11 , 12 . Such a design requires only one teeth-free area, further reducing the production costs.

As shown in FIG. 6, a second shaft section 6 A may comprise a spline shaft. In this case, each spline tooth 22 defines the ridge, the spline tooth extending on a male spline 21 of the second shaft section 6 A and having a trapezoidal or groove-like shape in section. On the other hand, a groove 25 is defined between adjoining spline teeth 24 of a female spline 23 of a first shaft section 1 A.

Further, as shown in FIG. 7A, the male serration 5 may be coated with a synthetic resin of low friction coefficient such as fluoroplastics to provide a coating film 26 .

In this case, the synthetic-resin coating film 26 serves to reduce sliding resistance between the serrations 3 , 5 . Particularly, quite a great anti-rattle effect can be attained at low costs because the synthetic-resin coating film 26 not only serves to reduce the clearance between the serrations 3 , 5 but also cooperates with the anti-rattle member 9 to prevent the occurrence of rattle. The reasons for this are the following.

If the prevention of rattle depends only on the synthetic-resin coating film adjusting the clearance between the serrations 3 , 5 , a highly severe control of the thickness of the synthetic-resin coating film is required. Considering the variations of the dimensional tolerances of individual serrations 3 , 5 , an operation is required for selectively combining individual serrations 3 , 5 that can achieve a desired clearance. This approach is not practicable given the number of steps required for this operation and the associated cost increase. In contrast, the embodiment of FIG. 7A negates the need for the severe control of the thickness of the synthetic-resin coating film 26 , contributing the low-cost production. Thus, the reduction of sliding resistance and the prevention of rattle can be attained at low costs.

It is noted that the synthetic-resin coating film 26 may be laid over the female serration 3 , as shown in FIG. 7 B. Other various changes and modifications may be made to the invention without departing from the spirit and scope thereof.