Abstract:
Positioning projections for engaging recesses in an outer peripheral surface of a mating member project from an inner peripheral surface of a grommet, and the position of a minimum inside diameter portion of each positioning projection after being fitted to the mating member is offset from interference of a jointing member. In a case where the positioning projections are formed in front of a sealing projection, a larger cylindrical portion is absent around their outer peripheries. Therefore, the enlargement of the diameter of the grommet during fitting to the mating member is not restricted, resistance during fitting is alleviated, and the positioning projections are engaged in the recesses with large elastic reaction force. Hence, a click feel is excellent.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a boot for covering a constant velocity joint which is indispensable as a joint for a drive shaft of a front-wheel-drive vehicle. 
   2. Description of the Related Art 
   Conventionally, a joint portion of a constant velocity joint is covered with a bellows-shaped boot with grease sealed therein, to maintain large-angle and smooth rotation by preventing the entry of water and dust. This constant velocity joint boot is comprised of a larger cylindrical portion having a large diameter and retained by a joint outer race or the like, a smaller cylindrical portion having a smaller diameter than the larger cylindrical portion and retained by a shaft, and a conical bellows portion for integrally connecting the smaller cylindrical portion and the larger cylindrical portion. During use, the bellows portion undergoes deformation in correspondence with a change in an angle (joint angle) formed by the shaft and the joint outer race or the like. Therefore, even if the angle becomes large, the joint portion can be reliably sealed by the boot. 
   This constant velocity joint boot was formerly formed of rubber in many cases. However, since there is a limit to durability in the case of rubber, a thermoplastic elastomer excelling weather resistance and fatigue resistance has come to be used in recent years. Meanwhile, in the case of the constant velocity joint boot, there is a need to impart a sealing function for reliably preventing the entry of water and dust into the joint. However, if the thermoplastic elastomer is used as the material, since there are many cases where the larger cylindrical portion is fitted in the form of different-shape fitting or non-circle fitting, and since the resiliency of the thermoplastic elastomer is high and its follow-up characteristic is not as good as rubber, there has been a problem in that it is difficult to ensure sealability. In addition, blow molding is convenient as a method of molding the constant velocity joint boot. Nevertheless, the surface of a mating member is generally noncircular, so that the boot needs to be provided with a shape corresponding thereto. However, in the case where such a boot is manufactured, with blow molding, it is difficult to form the shape of the inner peripheral surface of the larger cylindrical portion such that its sealability with respect to the mating member becomes high. In this aspect as well, it is difficult to ensure sealability. 
   Accordingly, JP-UM-A-02-087131 discloses a constant velocity joint boot in which the boot body is formed of a polyester-based thermoplastic elastomer, and a soft rubber-made annular grommet is inserted in its larger cylindrical portion. According to this constant velocity joint boot, even a grommet which has thick-walled portions and thin-walled portions and whose inner peripheral surface is noncircular can be manufactured with high accuracy by injection molding or the like. Therefore, the boot body may not necessarily have very high geometrical accuracy and can be manufactured by blow molding. Further, a tightening force based on a clamp is transmitted to the grommet through the larger cylindrical portion, and the grommet undergoes elastic deformation, thereby exhibiting the sealing function. Namely, the boot body is capable of ensuring durability, while the grommet is capable of ensuring sealability with respect to the mating member. In addition, since the boot body having a large shape as compared to the grommet can be manufactured by blow molding, man-hour can be reduced and the cost can be lowered. 
   The constant velocity joint boot thus made up of the boot body and the grommet is fitted to the mating member in a state in which the grommet is inserted in the larger cylindrical portion, and is subsequently tightened by a clamp from the outer peripheral side of the larger cylindrical portion. Accordingly, during the fitting to the mating member, the positioning of insertion becomes necessary. For this reason, conventionally, a recess is formed in an outer peripheral surface of the mating member, while a positioning projection is formed on an inner peripheral surface of the grommet, and positioning is effected by causing the positioning projection to engage the recess. 
   However, there has been a problem in that although the grommet is soft, since the hard larger cylindrical portion is present on its outer periphery, when the positioning projection is brought into sliding contact with the outer peripheral surface of the mating member during fitting to the mating member, the deformation in the diameter enlarging direction of the grommet is restricted, which constitutes resistance in fitting, so that the operational efficiency in fitting is poor. In addition, there are cases where an axial offset occurs between the larger cylindrical portion and the grommet. Further, there has been a drawback in that even if the positioning projection is engaged with the recess of the mating member during fitting, since the amount of deformation of the grommet is small, it is impossible to obtain a click feel of fitting, and it is impossible to confirm whether or not the positioning has been effected. 
   In addition, an annular sealing projection is formed on the inner periphery of the grommet, and its position in axial direction is located in the range of interference of the clamp. In addition, there are many cases where a sealing projection is also formed at a distal end of the positioning projection. However, during fitting to the mating member, since the sealing projections come into sliding contact with the mating member, wear and damage can occur in the sealing projections, in which case trouble occurs in sealability. 
   Accordingly, JP-UM-A-02-071122 discloses a constant velocity joint boot in which a slit extending in the axial direction from an end face of the larger cylindrical portion is formed, and a positioning protrusion is formed by avoiding that slit. If such an arrangement is provided, the enlargement of the diameter of the larger cylindrical portion is facilitated by the slit, and resistance during fitting can be reduced, but it is difficult to obtain a click feel at the time the positioning projection engages the recess. In the constant velocity joint boot made up of the boot body and the grommet, if consideration is given to the adoption of this structure, the formation of the slit in the grommet or the larger cylindrical portion is not recommendable from the viewpoint of sealability in addition to the problem of the click feel, and there is also the problem of increased man-hour. 
   SUMMARY OF THE INVENTION 
   The present invention has been devised in view of the above-described circumstances, and its object is to provide a constant velocity joint boot which is capable of maintaining sealability to a high degree, of reducing resistance during fitting to the mating member, and of obtaining a click feel upon completion of fitting. 
   The constant velocity joint boot of the invention for overcoming the above-described problems is characterized by comprising: a boot body including a smaller cylindrical portion retained by a shaft, a larger cylindrical portion disposed coaxially with the smaller cylindrical portion in spaced-apart relation thereto and having a larger diameter than the smaller cylindrical portion; and a conical bellows portion for integrally connecting the smaller cylindrical portion and the larger cylindrical portion; and an annular grommet which is formed of a softer material than the larger cylindrical portion and whose inner peripheral cross section is noncircular, the annular grommet having a sealing projection on an inner peripheral surface thereof and being fitted to a mating member after being inserted into the larger cylindrical portion, the larger cylindrical portion and the grommet being tightened on the mating member as a jointing member by reducing diameters from an outer peripheral surface of the larger cylindrical portion, wherein a positioning projection engageable in a recess in an outer peripheral surface of the mating member projects from the inner peripheral surface of the grommet, and a position of a minimum inside diameter portion of the positioning projection after the mating member is fitted to the grommet inserted in the larger cylindrical portion is offset in axial direction from interference of the jointing member. 
   The larger cylindrical portion is preferably absent around an outer periphery of the positioning projection. In addition, a protrusion against which an end face of the larger cylindrical portion abuts is preferably provided on an outer peripheral surface of the grommet. 
   According to the constant velocity joint boot of the invention, since the axial position of a minimum inside diameter portion of the positioning projection is offset from the interference of the jointing member, the positioning projection does not affect sealability. In addition, in a case where the positioning projection is formed in front of the sealing projection (on the opening side of the larger cylindrical portion), it is possible to provide an arrangement in which the larger cylindrical portion is absent around its outer periphery. Therefore, the enlargement of the diameter of the grommet during fitting to the mating member is not restricted, and resistance during fitting is alleviated. Furthermore, when the positioning projection reaches the position of the recess of the mating member, the portion subjected to enlargement in diameter is restored to its original shape by a large elastic reaction force. Therefore, it is possible to obtain a favorable click feel and effect positioning reliably. 
   Meanwhile, in a case where the positioning projection is formed in the rear of the sealing projection (on the bellows portion side), since the amount of movement of the positioning projection during fitting is small, the resistance during fitting is alleviated. Further, if the recess of the mating member is formed in the shape of a notch which is open in a distal end of the mating member, even if the grommet is not diametrically enlarged to a large degree, fitting can be effected. Moreover, since the positioning projection abuts against an end of the notch, the resistance increases sharply, so that the positioning of fitting can be effected reliably. 
   In addition, a protrusion against which the end face of the larger cylindrical portion abuts is provided on the outer peripheral surface of the grommet, it is possible to prevent an offset between the larger cylindrical portion and the grommet during fitting. Additionally, it is possible to obtain a more click feel as the load for pushing back the protrusion by the end face is released by the fitting of the positioning projection into the mating groove. 
   The boot body is made up of a smaller cylindrical portion retained by a shaft, a larger cylindrical portion disposed coaxially with the smaller cylindrical portion in spaced-apart relation thereto and having a larger diameter than the smaller cylindrical portion, and a conical bellows portion for integrally connecting the smaller cylindrical portion and the larger cylindrical portion. The boot body is basically similar to a conventional one. At least, a construction is preferably provided such that a clamp groove for engagement with a jointing member such as a clamp is formed in the outer peripheral surface of the larger cylindrical portion, and a protrusion is formed on its inner peripheral surface, such that as the protrusion is engaged with the outer peripheral surface of the grommet, sealability between the boot body and the grommet is ensured. 
   This boot is preferably formed of a thermoplastic elastomer such as a polyester-based or polyolefin-based one. It is thereby possible to provide a high-durability boot. In addition, although the molding method is not particularly limited, the boot body is preferably formed by blow molding in view of the cost. In the boot body formed by blow molding, it is difficult to control the shape of the inner peripheral surface of the larger cylindrical portion, and the dimensional accuracy of the wall thickness is low, but these do not constitute problems in the constant velocity joint boot using a grommet. 
   The grommet is an annular one whose inner peripheral cross section is noncircular, which has a sealing projection on an inner peripheral surface thereof, and which has thick-walled portions and thin-walled portions corresponding to the shape of the outer peripheral surface of the mating member to be fitted to. A positioning projection engageable in a recess in an outer peripheral surface of the mating member projects from the inner peripheral surface of the grommet. The position of the positioning projection suffices if the position of a minimum inside diameter portion of the positioning projection after being fitted to the mating member is offset in axial direction from the interference of the jointing member. The number of the positioning projections may be one or more. The sealing projection is formed on that portion of the inner peripheral surface of the jointing member which corresponds to its interference. As this sealing projection, one sealing projection may be used, but it is preferable to use two or more. In addition, a protrusion against which the end face of the larger cylindrical portion abuts is preferably provided on the outer peripheral surface of the grommet. By so doing, it is possible to prevent an axial offset between the larger cylindrical portion and the grommet during fitting to the mating member. 
   The positioning protrusion may be formed around the entire inner periphery of the grommet, or may be formed only on the thick-walled portions or the thin-walled portions. Since there are many cases where sealability is ensured by the thick-walled portions having sufficient elasticity, it is preferable to form the positioning projections on the thin-walled portions so as to distribute the functions between the thin-walled portions and the thick-walled portions. If the positioning projections are formed on the thin-walled portions, the processing of the recesses of the mating member is facilitated. In addition, a sealing projection may also be formed at a distal end of the positioning projection. The positioning projection is preferably provided with a cross-sectional shape having an inclined surface which is smoothly inclined on its surface oriented in the fitting direction. Resistance during fitting can thereby be reduced. In addition, if the surface of the positioning projection away from the inclined surface is formed as a surface which rises up rather acutely from the inner peripheral surface of the grommet, it is possible to reliably prevent the grommet from coming off the mating member. 
   As the material of the grommet, it suffices if it is softer than the boot body, and it is possible to use an expensive polyolefin-based thermoplastic elastomer (TPO) or such as rubber. In addition, the molding method is not particularly limited; the grommet may be formed by compression molding, injection molding, or the like. The positioning projections and the sealing projections are formed integrally with the grommet. 
   As the mating member, the joint outer race is typically used, and corresponding recesses are formed at positions on its outer peripheral surface where the positioning projections are engaged. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded perspective view illustrating a constant velocity joint boot in accordance with an embodiment of the invention together with a mating member; 
       FIG. 2  is an enlarged cross-sectional view of essential portions illustrating the constant velocity joint boot in accordance with the embodiment of the invention in a state of being fitted to the mating member; 
       FIG. 3  is an enlarged cross-sectional view of the essential portions illustrating the constant velocity joint boot in accordance with the embodiment of the invention in the midst of being fitted to the mating member; 
       FIG. 4  is an enlarged cross-sectional view of essential portions illustrating the constant velocity joint boot in accordance with a second embodiment of the invention in the state of being fitted to the mating member; and 
       FIG. 5  is an enlarged cross-sectional view of essential portions illustrating the constant velocity joint boot in accordance with a third embodiment of the invention in the state of being fitted to the mating member. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereafter, a detailed description will be given of the embodiments of the invention with reference to the accompanying drawings. 
   First Embodiment 
     FIG. 1  shows an exploded perspective view of a constant velocity joint boot in accordance with a first embodiment of the invention.  FIG. 2  shows an enlarged cross-sectional view of essential portions in a state in which the constant velocity joint boot is fitted to a mating member. This constant velocity joint boot is comprised of a boot body  1  and an annular grommet  2  inserted in a larger cylindrical portion  11  of the boot body  1 . The boot body  1  is formed of a relatively hard thermoplastic elastomer by blow molding, and the grommet  2  is formed of rubber or a relatively soft thermoplastic elastomer by injection molding. 
   The boot body  1  is made up of a smaller cylindrical portion  10 , a larger cylindrical portion  11  having a larger diameter than the smaller cylindrical portion  10 , and a conical bellows portion  12  for integrally connecting the smaller cylindrical portion  10  and the larger cylindrical portion  11 . An annular protrusion  13  is circumferentially formed on an inner peripheral surface of the larger cylindrical portion  11 . The surface of the protrusion  13  is formed with a circular arc-shaped cross section. A wide and substantially flat clamp groove  14  having a width (W) is formed on an outer peripheral surface of the larger cylindrical portion  11 , and an annular U-groove  15  is formed on the surface of the clamp groove  14  at a position corresponding to a reverse side of the protrusion  13 . By virtue of the presence of this U-groove  15 , the formation of the protrusion  13  by blow molding is made possible. The bellows portion  12  continues to an end of the clamp groove  14  of the larger cylindrical portion  11 , and an end of the bellows portion  12  forms an end of the one end of the clamp groove  14 . 
   The grommet  2  is inserted in the larger cylindrical portion  11  and is, in that state, fitted over a joint outer race  3  which is a mating member. This grommet  2  has a completely round outer periphery, but its inner peripheral surface is formed in the shape of a non-circle corresponding to an outer peripheral surface of the joint outer race  3 , thick-walled portions  20  and thin-walled portions  21  being formed alternately in the circumferential portion. 
   Two annular sealing projections  22   a , which are brought into resilient contact with the joint outer race  3 , are formed on the inner peripheral surface of the grommet  2  over the entire circumference in parallel with each other. In addition, three positioning projections  23  extending in the circumferential direction are formed in the vicinities of one end faces of the thin-walled portions  21  in such a manner as to be spaced apart from each other. Two annular sealing projections  22   b , which are brought into resilient contact with the larger cylindrical portion  11 , are formed on the outer peripheral surface of the grommet  2  over the entire circumference in parallel with each other. An annular groove  24 , with which the protrusion  13  is engaged, is formed on the outer peripheral surface of the grommet  2  between the sealing projections  22   b . An annular protrusion  25  is formed on the outer peripheral surface of the grommet  2  in the vicinity of its end face where the positioning projections  23  are located. 
   On the joint outer race  3 , large-diameter portions  30  having a large diameter and small-diameter portions  31  having a small diameter are formed alternately in the circumferential direction, and a circumferentially extending recess  32  is formed on the surface of each large-diameter portion  30 . 
   In the constant velocity joint boot of this embodiment constructed as described above, the grommet  2  is inserted into the larger cylindrical portion  11  from its end portion on the side away from the end portion where the positioning projections  23  are formed, and the positioning of the insertion is effected as a distal end face of the larger cylindrical portion  11  abuts against the protrusion  25 . At this time, the protrusion  13  is engaged with the annular groove  24 , the two sealing projections  22   a  are both located within the width of the clamp groove  14 , and the positioning projections  23  are located outwardly of the end face of the larger cylindrical portion  11 . 
   In this state, the joint outer race  3  is fitted into the grommet  2 . Since a minimum inside diameter of the positioning projections  23  is smaller than a maximum outside diameter of the joint outer race  3 , a diametrically enlarging force acts on the grommet  2 . Since the positioning projections  23  are located outwardly of the end face of the larger cylindrical portion  11 , the end portion of the grommet  2  at this time is easily elastically deformed, as shown in  FIG. 3 , thereby alleviating fitting resistance by the positioning projections  23 . 
   When the fitting further progresses and the positioning projections  23  come to be located at the positions of the recesses  32 , the positioning projections  23  suddenly enter the recesses  32  owing to their built-up elastic reaction force. At that instant, the fitting resistance suddenly declines. Accordingly, it is possible to perceive the completion of the positioning with a click feel, making it possible to prevent faulty fitting. In addition, as the distal end face of the larger cylindrical portion  11  abuts against the protrusion  25 , an axial offset between the larger cylindrical portion  11  and the grommet  2  is prevented. 
   In addition, in the fitted state, the positioning projections  23  are located away from the clamp groove  14 , so that a tightening force based on a clamp (not shown) is transmitted only to the two annular sealing projections  22   a , thereby demonstrating high sealability. 
   Further, a sealing between the larger cylindrical portion  11  and the grommet  2  is provided by the sealing projections  22   b . Between the large cylindrical portion  11  and the grommet  2 , the tightening force based on the clamp is transmitted to the pair of annular sealing projections  22   b  and the protrusion  13 , so that high sealability is obtained between the larger cylindrical portion  11  and the grommet  2 . 
   Second Embodiment 
     FIG. 4  shows a state in which the constant velocity joint boot in accordance with a second embodiment is fitted to the joint outer race  3 . This embodiment has a construction similar to that of the first embodiment except that the positioning projections  23  are formed in the vicinity of an opposite end of the grommet  2 , and that the recesses  32  are formed in the vicinity of a distal end of the joint outer race  3 . 
   In the case where the constant velocity joint boot of this embodiment is fitted to the joint outer race  3 , the positioning projections  23  do not abut against the joint outer race  3  in an initial period of fitting, and abut against it for the first time in a final period of fitting. Accordingly, the period during which the resistance due to the positioning projections  23  appears during fitting is short, so that fitting can be effected relatively easily. 
   In the fitted state, the positioning projections  23  are located away from the clamp groove  14 , so that the tightening force based on the clamp is transmitted only to the two annular sealing projections  22   a , thereby demonstrating high sealability. 
   Third Embodiment 
     FIG. 5  shows a state in which the constant velocity joint boot in accordance with a second embodiment is fitted to the joint outer race  3 . This embodiment has a construction similar to that of the first embodiment except that positioning projections  26  are formed at the end of the grommet  2  on the side of the bellows portion  12 , and that notched recesses  33  are formed at the distal end of the joint outer race  3 . 
   In the case where the constant velocity joint boot of this embodiment is fitted to the joint outer race  3 , the positioning projections  26  are only guided into the notched recesses  33  during a final period of fitting, and the resistance due to the positioning projections  26  does not appear from the initial period of fitting until the completion of fitting, so that fitting can be effected quite easily. In addition, as the positioning projections  26  abut against ends of the recesses  33 , the insertion is made difficult further than that, so that positioning can be effected reliably. 
   In the fitted state, the positioning projections  26  are located away from the clamp groove  14 , so that the tightening force based on the clamp is transmitted only to the two annular sealing projections  22   a , thereby demonstrating high sealability.