Abstract:
A steering shaft boot of a molded elastic material comprises an inner boot portion including a first cylindrical portion that is adapted to cover a steering shaft, a first flange portion that extend radially outward from one axial end of the first cylindrical portion and is adapted to be secured to a panel member and a first upper wall portion that extends radially inward from the other axial end of the first cylindrical portion and is adapted to be put on an outer surface of the steering shaft; and an outer boot portion including a second cylindrical portion that covers the first cylindrical portion while keeping a certain clearance therebetween, a second flange portion that extends radially outward from one axis end of the second cylindrical portion and is adapted to be secured to the panel member and a second upper wall that extends radially inward from the other axial end of the second cylindrical portion to the other axial end of the first cylindrical portion. The first and second flange portions are separate members but engageable when in use.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to automotive steering shaft boots or covers, and more particularly to the steering shaft boots of a type that elastically holds a steering shaft to a dash panel of the vehicle in a manner to seal a steering shaft bore of the dash panel through which the steering shaft passes. 
   2. Description of the Related Art 
   Japanese Laid-open Patent Application (Tokkaihei) 8-198122 shows a steering shaft boot of the above-mentioned type. That is, the steering shaft boot of this published Application generally comprises a flange that is secured to a peripheral portion of the steering shaft bore of the dash panel, a holder that holds the steering shaft through a ball bearing, an inner rubber boot that extends from the flange to the holder and an outer rubber boot that also extends from the flange to the holder while covering the inner rubber boot. Due to provision of a so-called double layer boot unit constituted by the inner and outer rubber boots, the sealing of the steering shaft bore is assured. 
   SUMMARY OF THE INVENTION 
   However, in the above-mentioned steering shaft boot, the inner and outer rubber boots that constitute the double layer boot unit are separate parts, and thus, assembling the steering shaft boot and setting the same to a right position need a troublesome and time-consumed assembling and setting work. Furthermore, due to separate production of the inner and outer rubber boots, cost of the steering shaft boot is inevitably increased. Furthermore, due to the separate construction of the inner and outer rubber boots, the double layer boot unit has a higher possibility of having air permeable clearance between mutually mated portions of the inner and outer rubber boots particularly after long use. If such clearance appears, the sealing of the steering shaft bore is lowered. 
   It is therefore an object of the present invention to provide a steering shaft boot which is free of the above-mentioned drawbacks. 
   According to the preset invention, there is provided a steering shaft boot of molded resin that comprises inner and outer boot portions that are arranged to constitute a double layer boot unit, wherein respective parts of the inner and outer boot portions are integrally connected. 
   According to the present invention, there is further provided an arrangement that comprises a dash panel having an opening, a steering shaft passing through the opening and a steering shaft boot wherein the steering shaft boot is hermetically secured to dash panel while covering the steering shaft. 
   In accordance with a first aspect of the present invention, there is provided a steering shaft boot of a molded elastic material for use with a steering shaft that passes through an opening formed in a panel member. The steering shaft boot comprises an inner boot portion including a first cylindrical portion that is adapted to cover the steering shaft, a first flange portion that extend radially outward from one axial end of the first cylindrical portion and is adapted to be secured to the panel member and a first upper wall portion that extends radially inward from the other axial end of the first cylindrical portion and is adapted to be put on an outer surface of the steering shaft; and an outer boot portion including a second cylindrical portion that covers the first cylindrical portion while keeping a certain clearance therebetween, a second flange portion that extends radially outward from one axis end of the second cylindrical portion and is adapted to be secured to the panel member and a second upper wall that extends radially inward from the other axial end of the second cylindrical portion to the other axial end of the first cylindrical portion, wherein the first and second flange portions are separate members. 
   In accordance with a second aspect of the present invention, there is provided an arrangement which comprises a panel member having an opening; a steering shaft that passes through the opening of the panel member; a steering shaft boot of an elastic material, the steering shaft boot comprising an inner boot portion including a first cylindrical portion that covers the steering shaft, a first flange portion that extend radially outward from one axial end of the first cylindrical portion and is secured to the panel member and a first upper wall portion that extends radially inward from the other axial end of the first cylindrical portion and is put on an outer surface of the steering shaft, and an outer boot portion including a second cylindrical portion that covers the first cylindrical portion while keeping a certain clearance therebetween, a second flange portion that extends radially outward from one axis end of the second cylindrical portion and is secured to the panel member and a second upper wall that extends radially inward from the other axial end of the second cylindrical portion to the other axial end of the first cylindrical portion, the first and second flange portions being separate members; and a bracket secured to the panel member to define therebetween a pocket into which mutually contacting parts of the first and second flange portions are tightly received. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a sectional view of a steering shaft boot which is a first embodiment of the present invention; 
       FIG. 1A  is an enlarged view of the part enclosed by circle indicated by arrow “A” of  FIG. 1 ; 
       FIG. 2  is a perspective view of the steering shaft boot of the first embodiment of the present invention; 
       FIG. 3  is an enlarged sectional view taken along the line III-III of  FIG. 2 ; 
       FIG. 4  is a view similar to  FIG. 1 , but showing a steering shaft boot of a second embodiment of the present invention; 
       FIG. 5  is a sectional view of an essential portion of a steering shaft boot which is a third embodiment of the present invention; and 
       FIG. 6  is a sectional view of a split mold unit in a set condition by which the steering shaft boot of the present invention is molded. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   In the following, embodiments  100 ,  200  and  300  of the present invention will be described in detail with reference to the accompanying drawings. 
   For ease of understanding, various directional terms, such as, right, left, upper, lower, rightward and the like are used in the following description. However, such terms are to be understood with respect to only a drawing or drawings in which a corresponding part or portion is shown. Throughout the specification, substantially same parts or portions are denoted by the same numerals. 
   Referring to  FIGS. 1 to 3  of the drawings, particularly  FIGS. 1 and 2 , there is shown a steering shaft boot or cover  100  which is the first embodiment of the present invention. 
   As is best understood from  FIG. 1 , the steering shaft boot  100  is arranged aslant to support a steering shaft  2  while sealing a clearance defined between the steering shaft  2  and a dash panel  3  through which the steering shaft  2  passes. 
   The dash panel  3  is a partition panel installed between an engine room  4  and a passenger cabin  5 , and has a steering shaft bore  6  through which the steering shaft  2  passes. As shown, the steering shaft bore  6  is defined by an annular ridge  7  bent back from a major part of the dash panel  3  toward the passenger cabin  5 . 
   It is to be noted that the steering shaft boot  100  is a molded one-body member made of an elastic material and generally comprises an inner boot  8  that covers the steering shaft  2  and an outer boot portion  9  that covers the inner boot portion  8  leaving a cylindrical clearance  19  defined therebetween. That is, the steering shaft boot  100  has a so-called double layer construction. Due to this double layer construction, the steering shaft boot  100  can exhibit a satisfied noise blocking performance against a noise that would be inevitably transmitted from the engine room  4  to the passenger cabin  5  as will become apparent as the description proceeds. 
   The steering shaft boot  100  is constructed of a soft thermoplastic resin or the like, such as a thermoplastic resin having a specific gravity ranging from about 1.4 to about 1.7. 
   For example, a polypropylene (PP) added with barium sulfate or an ethylene propylene dien monomer (EPDM) added with calcium carbonate may be used as the material. 
   As shown in  FIG. 1 , the inner boot portion  8  comprises generally a first cylindrical portion  10  that covers the steering shaft  2 , a first flange portion  11  that extends radially outward from a lower end of the first cylindrical portion  10  and a first upper wall portion  13  that extends radially inward from an upper end of the first cylindrical portion  10  and has an annular opening  12  intimately put on the steering shaft  2 . 
   The first cylindrical portion  10  has an inner diameter sufficiently larger than an outer diameter of the steering shaft  2 . Thus, upon assembly, there is defined a cylindrical clearance between the inner surface of the first cylindrical portion  10  and the outer surface of the steering shaft  2 . The first flange portion  11  is intimately put on a peripheral portion of the steering shaft bore  6  of the dash panel  3 . A lower surface  11   a  of the first flange portion  11  is formed with two annular seal lips  14  and  14  that are pressed against the surface of the dash panel  3 . 
   Furthermore, the lower surface  11   a  of the first flange portion  11  is formed with an annular groove  15  for receiving therein the above-mentioned bent back annular ridge  7  of the dash panel  3 . 
   The first upper wall portion  13  is thinner than the first cylindrical portion  10  and has at radially opposed portions a generally S-shaped cross section. Due to this construction, the first upper wall portion  13  is constantly pressed against the outer surface of the steering shaft  2  to keep an intimate and hermetical contact therebetween. 
   The outer boot portion  9  covers the first cylindrical portion  10  of the inner boot portion  8  keeping a cylindrical clearance  19  therebetween. 
   As shown, the outer boot portion  9  is integral with the inner boot portion  8 . More specifically, as will be described in detail in the following, the outer boot portion  9  extends from the upper end of the first cylindrical portion  10  of the inner boot portion  8  toward the first flange portion  11 . 
   The outer boot portion  9  comprises generally a second cylindrical portion  16  that has a diameter larger than the first cylindrical portion  10  of the inner boot portion  8 , a second flange portion  17  that extends radially outward from a lower end of the second cylindrical portion  16  and a second upper wall portion  18  that extends from an upper end of the second cylindrical portion  16  to the upper end of the first cylindrical portion  10  of the inner boot portion  8 . 
   The second cylindrical portion  16  surrounds the first cylindrical portion  10  of the inner boot portion  8  defining the cylindrical clearance  19  therebetween. The second flange portion  17  has a lower surface  17   a  intimately put on an upper surface  11   b  of the first flange portion  11  of the inner boot portion  8 . The second upper wall portion  18  of the outer boot portion  9  is thinner than the second cylindrical portion  16  and has a generally S-shaped cross section. Due to this construction, the second upper wall portion  18  has an elastically flexible structure. 
   As shown in  FIG. 1 , a bracket  20  is secured to the dash panel  3  for tightly connecting the steering shaft boot  100  to the dash panel  3 . That is, the bracket  20  is secured to the dash panel  3  to define therebetween a pocket (no numeral) into which radially outer parts of the mutually contacting first and second flange portions  11  and  17  are tightly received. 
   As is seen from  FIGS. 2 and 3 , particularly  FIG. 3 , bolts  21  (three in the illustrated embodiment) are used for assuring the tight connection of the first and second flange portions  11  and  17  to the dash panel  3 . 
   As shown in  FIG. 3 , each bolt  21  passes through a bolt opening  22  defined by four aligned openings (no numerals) formed in the bracket  20 , the second flange portion  17 , the first flange portion  11  and the dash panel  3 . Although not shown, a nut is operatively engaged with the bolt  21 . As shown in this drawing, the first flange portion  11  of the inner boot portion  8  is formed with a sub seal lip  23  that is shaped to surround the bolt opening  22  with the aid of a part of the inner annular seal lip  14 . With this sub seal lip  23 , undesired seal leakage which may occur due to presence of the bolt opening  22  is suppressed. 
   As is shown by a phantom line in  FIG. 1 , in a dismantled condition of the steering shaft boot  100  wherein substantially no stress is applied to the same, the second flange portion  17  of the outer boot portion  9  and the first flange portion  11  of the inner boot portion  8  are kept separated. That is, for this separate construction of the two boots  8  and  9 , a core removing technique is used for molding the steering shaft boot  100 . This will be well understood from the following description. 
     FIG. 6  shows an essential portion of a split mold unit in a set condition by which the steering shaft boot  100  is produced or molded. The split mold unit generally comprises four outer dies A, B, C and D and one core  26 . As shown, before molding, the four outer dies A, B, C and D are assembled in the illustrated manner and the core  26  is installed in a space defined by the four outer dies A, B, C and D. As shown, due to presence of the core  26 , the space is divided into four major shaped spaces  10 ′,  11 ′,  16 ′ and  17 ′ which are connected in the illustrated manner. Upon molding, a pressurized fluid material of the above-mentioned thermoplastic resin is led into the four shaped spaces  10 ′,  11 ′,  16 ′ and  17 ′, and after certain curing or hardening of the material, the four outer dies A, B, C and D are dismantled. With this, the material in the four shaped spaces  10 ′,  11 ′,  16 ′ and  17 ′ forms the first cylindrical portion  10 , the first flange portion  11 , the second cylindrical portion  16  and the second flange portion  17  of the molded steering shaft boot  100  having the core  26  unstably left in the product, that is, the molded steering shaft boot  100 . 
   Then, the core  26  is removed from the product  100 . Due to the separate connection between the two shaped spaces  11 ′ and  17 ′ as is seen from  FIG. 6 , the first and second flange portions  11  and  17  thus produced are separately molded and thus easily flexed from each other, which allows the easy removal of the core  26  from the molded product  100 . It is to be noted that the space in which the core  26  has been left forms the cylindrical clearance  19  of the product  100 . As is described hereinabove, when it is intended to connect the steering shaft boot  100  to the dash panel  3 , the first and second flange portions  11  and  17  are put on each other and press-fitted into the bracket  20 . During this, the second upper wall portion  18  serves as a hinge means because of its elastic deformation. 
   As is described hereinabove, upon mounting to the dash panel  3  in the above-mentioned manner, the steering shaft boot  100  constitutes a so-called double layer construction that has an isolated cylindrical clearance  19  defined therein. It is to be noted that even though it has the isolated cylindrical clearance  19 , the steering shaft boot  100  is of a one-body construction. Thus, production and assembly of the boot  100  are easily and economically carried out unlike the case of the above-mentioned conventional steering shaft boot. 
   As is seen from  FIG. 1 , for mounting the steering shaft boot  100  to the dash panel  3 , the first and second flange portions  11  and  17  are press-fitted in the pocket of the bracket  20 . Thus, the seal lips  14  and  14  of the first flange portion  11  are pressed against the dash panel  3  thereby assuring a sealing of the first flange portion  11  to the dash panel  3 , that is, an acoustical separation between the engine room  4  and the passenger cabin  5 . Furthermore, due to the double layer construction of the boot  100 , a satisfied noise blocking against a noise transmittance from the engine room  4  to the passenger cabin  5  is much assured. Furthermore, usage of the thermoplastic resin of the specific gravity from 1.4 to 1.7 as the material of the boot  100  promotes the noise blocking performance of the boot  100 . 
   Furthermore, due to provision of the bent back annular ridge  7  of the dash panel  3  and the annular groove  15  of the first flange portion  11 , the positioning of the boot  100  relative to the dash panel  3  is easily achieved. 
   Referring to  FIG. 4 , there is shown a steering shaft boot  200  which is the second embodiment of the present invention. 
   Since the boot  200  of this embodiment is similar to the above-mentioned boot  100  of the first embodiment, only parts or portions that are substantially different from those of the first embodiment  100  will be described in the following. The substantially same parts and portions as those of the first embodiment  100  are denoted by the same numerals and detailed explanation of such same parts and portions are omitted from the following description for simplification of the same. 
   As is seen from  FIG. 4 , in this second embodiment  200 , a second upper wall portion  18 A, a first flange portion  11 A and a second flange portion  17 A are different from the second upper wall portion  18 , the first flange portion  11  and the second flange portion  17  of the first embodiment  100 . 
   That is, as shown, the second upper wall portion  18 A is shaped like a bellows. With this, the flexibility of the wall portion  18 A is much higher than the wall portion  18  of the first embodiment  100 . This means much easy mating of the first and second flange portions  11 A and  17 A. 
   Furthermore, in this second embodiment  200 , the mating between the first and second flange portions  11 A and  17 A is made through mutually engaged stepped surfaces  32  and  33 . That is, the first flange portion  11 A has a single stepped surface  32  and the second flange portion  17 A has a double stepped surface  33 , and upon mating of the first and second flange portions  11 A and  17 A in the pocket of the bracket  20 , these stepped surfaces  32  and  33  are intimately engaged with each other in a so-called dove-tail connection manner, and respective front surfaces  11   a  and  17   a  of the first and second flange portions  11 A and  17 A are pressed against the dash panel  3  and a rear surface  17   b  of the second flange potion  17 A is pressed against a rear wall of the pocket. The front surface  17 A of the second flange portion  17 A has the seal lips  14  pressed against the dash panel  3 . As shown, in such condition, a rear surface  11   b  of the first flange portion  11 A defines a front wall of the cylindrical clearance  19 . 
   Due to employment of the stepped surfaces  32  and  33  for the mating of the first and second flange portions  11 A and  17 A, the sealing between these flanges portions  11 A and  17 A is assured, and due to the dove-tail connection between the two stepped surfaces  32  and  33 , the mutual positioning therebetween is much assured. 
   Referring to  FIG. 5 , there is partially shown a steering shaft boot  300  which is the third embodiment of the present invention. It is to be noted that the part shown by this drawing is a portion that corresponds to the portion indicated by arrow “V” of  FIG. 4 . 
   Since the boot  300  of this embodiment is similar to the boot  200  of the second embodiment, only parts or portions that are substantially different from those of the second embodiment  200  will be described in the following. 
   As is seen from  FIG. 5 , in this third embodiment  300 , first and second flange portions  11 B and  17 B are different from the first and second flange portions  11 A and  17 A of the second embodiment  200 . 
   That is, as shown, the first flange portion  11 B has a single stepped surface  42  and the second flange portion  17 B has also a single stepped surface  43 , and upon mating of the first and second flange portions  11 B and  17 B, these stepped surfaces  42  and  43  are intimately engaged with each other. Furthermore, in this third embodiment  300 , the second flange portion  17 B is formed with a larger annular seal lip  44  that extends along an outer periphery of the second flange portion  17 B. With this lip  44 , the hermetical sealing between the dash panel  3  and the boot  300  is much improved. 
   The entire contents of Japanese Patent Application 2005-59932 filed Mar. 4, 2005 are incorporated herein by reference. 
   Although the invention has been described above with reference to the embodiments of the invention, the invention is not limited to such embodiments as described above. Various modifications and variations of such embodiments may be carried out by those skilled in the art, in light of the above description.