Abstract:
Disclosed is a slip joint including a shaft having a plurality of shaft grooves formed on an outer peripheral surface in the longitudinal direction; a pipe having pipe grooves formed on an inner peripheral surface, the pipe grooves facing the shaft grooves so as to define cylindrical spaces, an end of the shaft being inserted into the pipe; a pin inserted into one of the cylindrical spaces; a first spring pin inserted into a different one of the cylindrical spaces, the first spring pin being made of a cylindrical elastic body having a longitudinal seam; a second spring pin inserted into the first spring pin, the second spring pin being made of an elastic body; and a connector for integrally connecting the first spring pin to the pin so as to constitute a slipper.

Description:
RELATED APPLICATION  
       [0001]     This application claims convention priority to Korean patent application No. 2005-0094998 filed on Oct. 10, 2005, the content of which is incorporated by reference.  
         [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a slip joint for a steering system. More particularly, the present invention relates to a slip joint for a steering system, which can reduce noise and vibration, improve steering precision, and guarantee easy fabrication by modifying the characteristics of a spring pin for reducing the clearance between a pipe and a shaft, which constitute the slip joint in a universal joint.  
         [0004]     2. Description of the Prior Art  
         [0005]     As generally known in the art, an automobile is provided with various devices in order to improve the safety and aid convenient driving. For example, a steering system is used to alter the direction of the automobile as desired by rotating a steering wheel. Particularly, the steering system changes the center of rotation of front wheels so that the automobile moves in a desired direction.  
         [0006]     When the driver rotates the steering wheel in a desired direction, the steering system rotates a steering shaft, which is connected to the steering wheel. Then, the steering shaft transmits rotational force to a gearbox, which is composed of a rack and a pinion, via a universal joint.  
         [0007]     The universal joint is positioned on the steering shaft, which is connected to the center of rotation of the steering wheel. The universal join generally includes two yoke joints and a slip joint. The yoke joints are commonly used as connection means when two shafts intersect with each other at an angle. The yoke joints are designed so as to accommodate any change in angle of intersection of both shafts during driving. Particularly, the steering shaft is allowed to deflect within an angle of about 30°. The slip joint transmits rotational force from the steering shaft while allowing the shaft to extend/contract so that force acting in the direction of the shaft is absorbed.  
         [0008]      FIG. 1  is a top view partially showing a conventional slip joint on a universal joint. The slip joint includes a driving shaft  100 , yokes  110 , spiders  115 , a shaft  120 , a pipe  130 , and a following shaft  135 .  
         [0009]     The universal joint  140  has yoke joints  105  positioned on both ends thereof, respectively. Each yoke joint  105  has two yokes  110  positioned therein so as to engage with each other and a cross-shaped spider  115  positioned between the yokes  110  so that rotational force can be transmitted even when the steering shaft is deflected at an angle.  
         [0010]     The yoke joints  105  on both ends of the slip joint  125  are connected to the shaft  120  and the pipe  130 , respectively, so that rotational force is transmitted between the yoke joints  105  while allowing slip in the axial direction.  
         [0011]     The pipe  130  is hollow so that the shaft  120 , which has the shape of a rod, is inserted into the pipe  130  and connected thereto. As the shaft  120  is moved into/out of the pipe  130 , force acting in the longitudinal direction of the driving and following shafts  100  and  135  is absorbed.  
         [0012]      FIG. 2  is a sectional view showing a conventional slip joint, which includes a shaft  120 , a pipe  130 , first spring pins  200 , shaft grooves  210 , pipe grooves  205 , and pins  215 .  
         [0013]     As shown, the shaft  120  has shaft grooves  210  formed on its outer peripheral surface, and the pipe  130  has pipe grooves  205  formed on its inner peripheral surface. The pipe grooves  205  and the shaft grooves  210  extend in the longitudinal direction of the slip joint. Respective shaft grooves  210  are coupled to corresponding pipe grooves  205  while facing each other so that cylindrical spaces are defined between them.  
         [0014]     The pins  215  have the shape of rods and guarantee tranmission of rotational force from the pipe  130  to the shaft  120 , or vice versa. The first spring pins  200  are inserted into cylindrical spaces positioned opposite the pins  215 . The first spring pins  200  have a seam extending in the longitudinal direction so that, due to elastic restoration force, they can enlarge, i.e. their outer diameter can increase. As such, the first spring pins  200  act as a type of elastic bodies.  
         [0015]     The tendency of the first spring pins  200  towards enlargement reduces the clearance between the first spring pins  200  and the pipe grooves  205  and between the first spring pins  200  and the shaft grooves  210 , as well as the clearance between the pins  215  (which are positioned opposite the first spring pins  200 ) and the shaft grooves  210  and between the pins  215  and the pipe grooves  205 .  
         [0016]      FIG. 3  is a perspective view showing a first spring pin of a conventional slip joint.  
         [0017]     As shown, the first spring pin  200  is obtained by rolling a metal plate and has a continuous seam. The gap  220  at the seam enables the first spring pin  200  to enlarge towards the outer peripheral surface (i.e. the inner diameter increases) or contract towards the inner peripheral surface (i.e. the inner diameter decreases).  
         [0018]     When the first spring pins  200  are to be inserted into a cylindrical space, the inner diameter of the first spring pin  200  is reduced. After insertion, the elastic force of the first spring pin  200  removes the clearance between the shaft groove  210  and the spring pin  215  and between the pipe groove  205  and the spring pin  215 . The spring pin  215  is made of a metallic material.  
         [0019]     According to the prior art, the first spring pins  200 , the shaft  120 , and the pipe  130  are made of a metallic material. This means that, when rotational force is transmitted from the shaft  120  to the pipe  130 , noise and vibration are also transmitted from the shaft  120  to the pipe  130  via the first spring pins  200 . As a result, vibration and noise are transmitted from the steering system to the driver, who operates the steering wheel, and discomfort him.  
       SUMMARY OF THE INVENTION  
       [0020]     Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a slip joint for a steering system, which can reduce noise and vibration, improve steering precision, and guarantee easy fabrication by modifying the characteristics of a spring pin for reducing the clearance between a pipe and a shaft, which constitute the slip joint in a universal joint.  
         [0021]     In order to accomplish this object there is provided a slip joint for a steering system having a steering shaft and a gear unit for converting rotational movement of the steering shaft into linear movement, the steering shaft having a slip joint adapted to extend or contract in a longitudinal direction, the slip joint including a shaft having a plurality of shaft grooves formed on an outer peripheral surface in the longitudinal direction; a pipe having pipe grooves formed on an inner peripheral surface, the pipe grooves facing the shaft grooves so as to define cylindrical spaces, an end of the shaft being inserted into the pipe; a pin inserted into one of the cylindrical spaces; a first spring pin inserted into a different one of the cylindrical spaces, the first spring pin being made of a cylindrical elastic body having a longitudinal seam; a second spring pin inserted into the first spring pin, the second spring pin being made of an elastic body; and a connector for integrally connecting the first spring pin to the pin so as to constitute a slipper. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0023]      FIG. 1  is a top view partially showing a conventional slip joint on a universal joint;  
         [0024]      FIG. 2  is a sectional view showing a conventional slip joint;  
         [0025]      FIG. 3  is a perspective view showing a first spring pin of a conventional slip joint;  
         [0026]      FIG. 4  is a sectional view showing a slip joint according to a first embodiment of the present invention;  
         [0027]      FIG. 5  is a sectional view showing a slip joint according to a second embodiment of the present invention;  
         [0028]      FIG. 6  is a sectional view showing a slip joint according to a third embodiment of the present invention;  
         [0029]      FIG. 7  is a perspective view partially showing a slip joint according to the third embodiment of the present invention;  
         [0030]      FIG. 8  is a perspective view partially showing a slip joint according to a fourth embodiment of the present invention;  
         [0031]      FIG. 9  is a perspective view partially showing a slip joint according to a fifth embodiment of the present invention;  
         [0032]      FIG. 10  is a perspective view partially showing a slip joint according to the fourth and fifth embodiments of the present invention; and  
         [0033]      FIG. 11  is a sectional view partially showing a slip joint according to the fourth and fifth embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0034]     Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description and drawings, the same reference numerals are used to designate the same or similar components, and so repetition of the description on the same or similar components will be omitted.  
         [0035]      FIG. 4  is a sectional view showing a slip joint according to a first embodiment of the present invention. The slip joint includes a shaft  120 , a pipe  130 , shaft grooves  210 , pipe grooves  205 , pins  215 , and second spring pins  400 .  
         [0036]     As shown, the shaft  120  has shaft grooves  210  formed on its outer peripheral surface, and the pipe  130  has pipe grooves  205  formed on its inner peripheral surface. The pipe grooves  205  and the shaft grooves  210  extend in the longitudinal direction of the slip joint. Respective shaft grooves  210  are coupled to corresponding pipe grooves  205  while facing each other so that cylindrical spaces are defined between them.  
         [0037]     According to the present embodiment, six cylindrical spaces are positioned at an angular interval of 60°. As shown, a pin  215  is inserted into one of a pair of cylindrical spaces, which face each other, and a second spring pin  400  is inserted into the other.  
         [0038]     The pins  215  have the shape of rods and guarantee transmission of rotational force from the pipe  130  to the shaft  120 , or vice versa. The pins  215  have smaller diameters than those of the cylindrical spaces. The second spring pins  400  have larger diameters than those of the cylindrical spaces and are inserted into the cylindrical spaces positioned opposite the pins  215 . The diameters of the second spring pins  400  shrink as the second spring pins  400  are inserted into the cylindrical spaces so that the second spring pins  400  tend to enlarge, due to their elastic restoration force, in such direction that their diameters increase.  
         [0039]     The tendency of the second spring pins  400  towards enlargement reduces the clearance between the second spring pins  400  and the pipe grooves  205  and between the second spring pins  200  and the shaft grooves  210 , as well as the clearance between the pins  215  (which are positioned opposite the second spring pins  400 ) and the shaft grooves  210  and between the pins  215  and the pipe grooves  205 . Characteristically, the second spring pins  400  are made of a plastic material.  
         [0040]     The second spring pins  400  have a continuous seam. The gap  220  at the seam enables the second spring pins  400  to enlarge towards the outer peripheral surface (i.e. the inner diameter increases) or contract towards the inner peripheral surface (i.e. the inner diameter decreases).  
         [0041]     When the second spring pins  400  are to be inserted between the outer peripheral surface of the shaft  120  and the inner peripheral surface of the pipe  130 , the inner diameter of the second spring pins  400  is reduced. After insertion, the elastic force of the second spring pins  400  removes the clearance between the shaft grooves  210  and the spring pins  215  and between the pipe grooves  205  and the second spring pins  400 .  
         [0042]     According to the prior art, the first spring pins  200 , the shaft  120 , and the pipe  130  are made of a metallic material. This means that, when rotational force is transmitted from the shaft  120  to the pipe  130 , noise and vibration are also transmitted from the shaft  120  to the pipe  130  via the first spring pins  200 . As a result, vibration and noise are transmitted from the steering system to the driver, who operates the steering wheel, and discomfort him. In contrast the second spring pins  400  according to an embodiment of the present invention are made of a plastic material, not a metallic material, and reduce the amount of vibration and noise transmitted from the pipe  130  to the shaft  120 , or vice versa.  
         [0043]      FIG. 5  is a sectional view showing a slip joint according to a second embodiment of the present invention. The slip joint includes a shaft  120 , a pipe  130 , pipe grooves  205 , shaft grooves  210 , pins  215 , second spring pins  400 , and third spring pins  500 .  
         [0044]     The second spring pins  400  are made of a plastic material, which has weaker elastic restoration force than metal. Therefore, metallic third spring pins  500  are positioned on the inner peripheral surface of the second spring pins  400 , respectively. The third spring pins  500  have a continuous seam and can enlarge towards the outer peripheral surface (i.e. the inner diameter increases) or contract towards the inner peripheral surface (i.e. the inner diameter decreases).  
         [0045]     When the third spring pins  500  are to be positioned on the inner peripheral surface of the second spring pins  400 , the inner diameter of the third spring pins  500  is reduced. After positioning, the elastic force of the third spring pins  500  enlarges the second spring pins  400  and removes the clearance between the shaft grooves  210  and the spring pins  215  and between the pipe grooves  205  and the spring pins  215 .  
         [0046]      FIG. 6  is a sectional view showing a slip joint according to a third embodiment of the present invention. The slip joint includes a shaft  120 , a pipe  130 , pipe grooves  205 , shaft grooves  210 , pins  215 , second spring pins  400 , third spring pins  500 , and a connector  600 .  
         [0047]     The connector  600  connects the pins  215  to the second spring pins  400 . According to the present embodiment, three pairs of pins  215  and three pairs of third spring pins  500  (i.e. a total of six separate components) are configured as an integral unit, which is hereinafter referred to as a slipper  700 . This simplifies the assembly process.  
         [0048]      FIG. 7  is a perspective view partially showing a slip joint according to the third embodiment of the present invention. The slip joint includes pins  215 , second spring pins  400 , third spring pins  500 , and a connector  600 .  
         [0049]     As shown, the connector  600  connects one side of the second spring pins  400  to one side of the pins  215  and extends along the outer peripheral surface of the shaft  120  or along the inner peripheral surface of the pipe  130 . Although the connector  600  continuously extends along the pins  215  and the second spring pins  400  in the present embodiment, the connector  600  may partially connect them in an alternative embodiment.  
         [0050]      FIG. 8  is a perspective view partially showing a slip joint according to a fourth embodiment of the present invention. The slip joint includes pins  215 , second spring pins  400 , a connector  600 , and latching portions  800 .  
         [0051]     As shown, the slipper  700  is provided with latching portions  800 , which fix the slipper  700  to the shaft grooves  210 . The pins  215  and the second spring pins  400  are configured as an integral unit by the connector  600 .  
         [0052]     In order to fix the slipper  700  to the shaft  120 , the latching portions  800  extend from the outer peripheral surface of an end of the slipper  700  towards the center of the shaft  120 .  
         [0053]      FIG. 9  is a perspective view partially showing a slip joint according to a fifth embodiment of the present invention. The slip joint includes a shaft  120 , shaft grooves  210 , and a latching portion groove  900 .  
         [0054]     The latching portion groove  900  is formed by depressing the outer peripheral surface of an end of the shaft  120  so that the latching portions  800 , which are formed on the slipper  700  shown in  FIG. 8 , are seated on the shaft  120 .  
         [0055]      FIG. 10  is a perspective view partially showing a slip joint according to the fourth and fifth embodiments of the present invention. The slip joint includes a shaft  120 , shaft grooves  210 , pins  215 , second spring pins  400 , third spring pins  500 , a connector  600 , latching portions  800 , and a latching portion groove  900 .  
         [0056]     When the shaft  120  is placed inside the slipper  700 , the pins  215  and the second spring pins  400  are seated on the shaft grooves  210 . When the slipper  700  is fully placed inside the slipper  700 , the latching portions  800  on the slipper  700  are seated on the latching portion groove  900  and fix the slipper  700  to the shaft  120 . Furthermore, third spring pins  500 , which are made of a metallic material, are positioned on the inner peripheral surface of the second spring pins  400 . When the shaft  120  is placed into the pipe  130  with the slipper  700  mounted thereon, assembly of the slip joint  125  is completed.  
         [0057]     According to the prior art, the pins  215  and the first spring pins  200  are separately positioned on the pipe  130  or the shaft  120 . This requires a long assembly time and costs a large amount of money. However, the present invention has solved these problems.  
         [0058]      FIG. 11  is a sectional view partially showing a slip joint according to the fourth and fifth embodiments of the present invention. The slip joint includes a pipe  130 , a shaft  120 , a slipper  700 , a latching portion  800 , a latching portion groove  900 , and a step  1105 . In the drawing, reference numeral  1115  refers to the inner diameter of the latching portion  800 , and  1110  refers to the outer diameter of the step  1105 .  
         [0059]      FIG. 11  shows in detail the slipper  700  (shown in  FIG. 11 ) when fixed to the shaft  120 . The latching portion  800  protrudes from an end of the slipper  700  towards the center of the shaft  120 , which is provided with a latching portion groove  900  so that the latching portion  800  is seated thereon.  
         [0060]     The step  1105  is positioned on the shaft  120  to the right of the latching portion groove  900 . The distance between the upper end of the step  1105  and the center of the shaft  120  is defined as the outer diameter  1105  of the step  1105 , and the distance between the lower end of the latching portion  800  and the center of the shaft  120  is defined as the inner diameter  1115  of the latching portion  800 . The outer diameter  1110  of the step  1105  is larger than the inner diameter  1115  of the latching portion  300 .  
         [0061]     The slipper  700  cannot detach from the shaft  120  unless it moves over the step  1105 . However, due to the fact that the outer diameter  1110  of the step  1105  is larger than the inner diameter  1115  of the latching portion  300 , the slipper  700  cannot easily detach from the shaft  120 . When the slipper  700  is to be assembled to the shaft  120 , it must be press-fitted to it.  
         [0062]     As mentioned above, the slip joint for a steering system according to the present invention is advantageous in that, since it has a clearance compensation structure, it can reduce noise and vibration and improve steering precision by positioning a slipper between a pipe and a shaft, which constitute the slip joint in a universal joint, so that the clearance is compensated for.  
         [0063]     Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.