Patent Publication Number: US-2020300349-A1

Title: Camshaft assembly support structure

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Applications No. 2019-049714 filed on Mar. 18, 2019 and No. 2019-200595 filed on Nov. 5, 2019. The entire contents of the priority application are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a camshaft assembly support structure. 
     BACKGROUND 
     A known camshaft assembly support structure (hereinafter, a support structure) includes a camshaft assembly and a support member supporting the camshaft assembly. In the support structure of this type, the support member includes multiple bearings (journal bearings) that support the journals of the camshaft assembly. The camshaft assembly is supported by the multiple bearings arranged in the axial direction. For example, Japanese Unexamined Patent Application Publication No. 2008-157062 describes a support member of this type. The support member is a solid (single) member in which each of the bearing holes, which receive a journal, has a seamless inner surface over the entire circumference. In the solid support member, the shaft center is less likely to be displaced and a lubricant oil is more likely to be uniformly distributed over the inner surface of the bearing than in a support member including a bearing constituted of separate upper and lower portions. The support structure is eventually fixed to a cylinder head of an internal combustion engine, for example, by bolting. 
     SUMMARY 
     In the support member of the known technology, bearings are connected to each other by a frame located around the bearings and are arranged in lines. When a camshaft assembly is attached to the support member, multiple cam pieces need to be fixed to the shaft at the same time, for example, by shrink-fitting, with the shaft of the camshaft assembly being received by the bearing of the support member. Thus, it is difficult to attach the camshaft to the known support member. Furthermore, the frame of the support member may limit the space for the attachment operation of the cam pieces to the shaft. For example, when the cam pieces are fixed to the shaft by shrink-fitting, it may be difficult to position a jig for holding the cam piece near the bearing. 
     An object of the technology described herein is to provide a camshaft assembly support structure including a camshaft assembly and a support member that are readily assembled. 
     A camshaft assembly support structure includes two camshaft assemblies, support members, and positioning members. The camshaft assemblies include two shafts parallel to each other and multiple cam pieces fitted on outer surfaces of the shafts. The support members are independent from each other. The support members include bearings having bearing surfaces. Each of the support members includes two of the bearings receiving the shafts, respectively. Each of the bearing surfaces is seamless over an entire inner circumference of each of the bearings. The positioning members include through holes in which the shafts are fitted and tightly hold the shafts. The positioning members are disposed on both sides of each of the support members to position the support members in an axial direction of the shafts with the shafts being received in the bearings. 
     The technology described herein provides a camshaft assembly support structure including a camshaft assembly and a support member that are readily assembled. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view illustrating a portion of a camshaft assembly support structure according to a first embodiment. 
         FIG. 2  is a perspective view illustrating a cam piece. 
         FIG. 3  is a perspective view illustrating a support member. 
         FIG. 4  is a perspective view illustrating a positioning member. 
         FIG. 5  is an explanatory view illustrating a step of assembling a camshaft assembly support structure. 
         FIG. 6  is an explanatory view illustrating a step of assembling the camshaft assembly support structure. 
         FIG. 7  is an explanatory view illustrating a step of assembling the camshaft assembly support structure. 
         FIG. 8  is an explanatory view illustrating a step of assembling the camshaft assembly support structure. 
         FIG. 9  is an explanatory view illustrating a step of attaching the camshaft assembly support structure onto a cylinder head by using a bolt. 
         FIG. 10  is a plan view illustrating a portion of a camshaft assembly support structure according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     A first embodiment of the invention is described with reference to  FIGS. 1 to 8 .  FIG. 1  is a plan view illustrating a portion of a camshaft assembly support structure  1  according to the first embodiment. A camshaft assembly support structure  1  (hereinafter, may be simply referred to as a “support structure  1 ”) mainly includes two camshaft assemblies  2 , multiple support members  3 , and multiple positioning members  4 . 
     In this specification, in some cases, one of the camshaft assemblies  2  that is on the upper side in  FIG. 1  is referred to as a “camshaft assembly  2 A” (intake camshaft assembly) and the other on the lower side in  FIG. 1  is referred to an “camshaft assembly  2 B” (exhaust camshaft assembly). 
     The camshaft assembly  2  includes a shaft  21  and multiple cam pieces (cam lobes)  22  fitted on an outer surface of the shaft  21 . The support structure  1  of this embodiment, which includes the two camshaft assemblies  2 , includes two shafts  21  and the cam pieces (cam lobs)  22  fitted on the outer surface of each of the shafts  21 . In this specification, in some cases, the shaft  21  of the camshaft assembly  2 A on the upper side in  FIG. 1  is referred to as a “first shaft  21 A”, and the shaft  21  of the other camshaft assembly  2 B on the lower side in  FIG. 1  is referred to as a “second shaft  21 B”. 
     The shaft  21  is formed by processing a metal material into a rod-like overall shape. The two shafts  21  supported by the support members  3  are arranged parallel to each other. As illustrated in  FIG. 1 , the cam pieces  22  on each of the shafts  21  are arranged in a direction along the axis L of the shaft  21  (axial direction). In this specification, the axis L of the first shaft  21 A is referred to as an “axis L 1 ”, and the axis L of the second shaft  21 B is referred to as an “axis L 2 ” in some cases. A portion of each of the shafts  21  supported by a bearing  32  of the support member  3  is referred to as a “journal” in some cases. 
       FIG. 2  is a perspective view of the cam piece  22 . The cam piece  22  has a substantially oval overall shape and has a through hole  22   a  that receives the shaft  21 . The inner diameter of the through hole  22   a  is substantially the same as the outer diameter of the shaft  21 . The cam piece  22  has a cam base  22   b  having an arc-like shape concentric with the through hole  22   a  and a cam nose  22   c  in which a distance from the center of the through hole  22   a  to the outer edge of the cam piece  22  is longer than that in the cam base  22   b . The cam piece  22  is formed by processing a metal material into a predetermined shape. The cam piece  22  is fixed to the shaft  21  by shrink-fitting with the shaft  21  being received in the through hole  22   a.    
       FIG. 3  is a perspective view of the support member  3 . The support member  3  is designed to support the two camshaft assemblies  2  and eventually fix the support structure  1  onto a cylinder head of an internal combustion engine. The support structure  1  includes multiple independent support members  3 . The support members  3  are arranged in the axis L direction with a space therebetween and are each attached to the two camshaft assemblies  2 . The support member  3  includes a body  31  having a flat cuboidal overall outer shape and two bearings  32  supporting the shafts  21  inserted therein, respectively. The bearings  32  include holes  32   a  that receive the shaft  21 , respectively. The holes  32   a  have inner surfaces  32   b . The support member  3  is obtained by processing a metal material, such as an aluminum alloy, and is a single (solid) member. The support members  3  are not connected to each other and are independent from each other. 
     As illustrated in  FIG. 1 , the body  31  supports both the two shafts  21  (camshaft assemblies  2 ) parallel to each other. The body  31  includes two bearings  32  arranged in a direction perpendicular to the axis L direction. Furthermore, the body  31  has bolt through holes  31   a  extending through the body  31  in the vertical direction. In this embodiment, the number of bolt through holes  31   a  is three. One of the bolt through holes  31   a  is located in the middle of the body  31  and the other two of the bolt through holes  31   a  are located at the ends of the body  31  in the direction perpendicular to the axis L direction. 
     The bearing  32  is a journal bearing and rotatably supports the shaft  21  (journal) with the shaft  21  (journal) being received in the hole  32   a . The inner surface  32   b  of the hole  32   a  is seamless over the entire circumference. 
       FIG. 4  is a perspective view of the positioning member  4 . The positioning members  4  position the support member  3  in the axial direction (axis L direction) of the shafts  21  with the shafts  21  being received by the bearings  32 . Each of the positioning members  4  has a ring-like overall shape with a hole  4   a  that receives the corresponding shaft  21 . The inner diameter of the hole  4   a  is substantially the same as the outer diameter of the shaft  21 . The shafts  21  are fitted in the holes  4   a  in the positioning members  4 , and the positioning members  4  are fixed to the shafts  21  by shrink-fitting. The shafts  21  are tightly held in the holes  4   a  in the positioning members  4 . 
     The support structure  1  includes multiple positioning members  4 . As illustrated in  FIG. 1 , four positioning members  4  are used for one support member  3  to position the shafts  21  in the axial direction. For example, for the support member  3  on the left in  FIG. 1 , two positioning members  4  are disposed on the first shaft  21 A and two positioning members  4  are disposed on the second shaft  21 B. 
     To position the support member  3  on the left in  FIG. 1  relative to the first shaft  21 A, two positioning members  4  are fixed to the first shaft  21 A while being arranged in a line in the axis L 1  direction with the support member  3  therebetween. The positioning members  4  on the first shaft  21 A are arranged on the both sides of the support member  3  with the support member  3  therebetween. Furthermore, to position the support member  3  on the left in  FIG. 1  relative to the second shaft  21 B, two positioning members  4  are fixed to the second shaft  21 B while being arranged in a line in the axis L 2  direction with the support member  3  therebetween. The positioning members  4  on the second shaft  21 B are arranged on both sides of the support member  3  with the support member  3  therebetween. 
     In other words, two positioning members  4  are disposed adjacent to one side surface (left side in  FIG. 1 ) of the support member  3  and two positioning members  4  are disposed adjacent to the other side surface (right side in  FIG. 1 ) of the support member  3 . 
     The positioning members  4  do not need to be in close contact with the support member  3 . A space may be left between the support member  3  and the positioning member  4  as long as the movement of the support member  3  on the shafts  21  in the axial direction is limited to some extent. The space between the support member  3  and the positioning member  4  absorbs a dimension error when the support structure  1  is attached to a predetermined portion of a cylinder head. 
     Next, with reference to  FIGS. 5 to 8 , a method of assembling the support structure  1  (production method) is described. As illustrated in  FIG. 5 , in the method of assembling the support structure  1 , first, one positioning member  4  is fixed to each of two shafts  21  by shrink-fitting. Specifically described, the positioning member  4  to be fixed to the first shaft  21 A and the positioning member  4  to be fixed to the second shaft  21 B are arranged in the direction perpendicular to the axis L direction as illustrated in  FIG. 5  while each being held by a jig having a heat generator. Then, the positioning members  4  held by the jigs are each heated to increase the inner diameter of the hole  4   a , and the shafts  21  at room temperature are inserted into the respective enlarged holes  4   a  in the positioning members  4 . The positioning members  4  are positioned at predetermined portions of the shafts  21 . After the insertion of the shafts  21 , the positioning members  4  are brought back to room temperature. The inner diameter of the hole  4   a  decreases as the temperature of the positioning member  4  decreases to room temperature, and thus the inner surface of the hole  4   a  is closely fitted to the outer surface of the shaft  21 . Thus, the positioning member  4  is fixed to a predetermined position of the shaft  21 . The positions of the positioning members  4  on the shaft  21  are suitably determined depending on the position of the support member  3 , which is positioned by the positioning members  4 . 
     Next, as illustrated in  FIG. 6 , the two shafts  21  having the positioning members  4  are inserted into the two bearings  32  of the support member  3 , and thus the support member  3  is attached to the two shafts  21 . Then, one positioning member  4  is fixed to each of the two shafts  21  by shrink-fitting. In this way, the support member  3  is positioned between the two positioning members  4  on the first shaft  21 A and positioned between the two positioning members  4  on the second shaft  21 B, and thus the support member  3  is positioned in the axial direction (axis L direction) of the shafts  21 . 
     Then, as illustrated in  FIG. 7 , the cam pieces  22  are fixed to the shafts  21  by shrink-fitting at predetermined positions. Specifically described, two cam pieces  22  to be attached to the first shaft  21 A are arranged in the axis L direction and two cam pieces  22  to be attached to the second shaft  21 B are arranged in the axis L direction while each being held by a jig having a heat generator. The cam pieces  22  are each held by a jig such that the cam nose  22   c  faces in a predetermined direction. Then, the cam pieces  22  held by the jigs are each heated to increase the inner diameter of the through holes  22   a , and the shafts  21  at room temperature are inserted into the respective enlarged through holes  22   a  in the cam pieces  22 . The cam pieces  22  are positioned at predetermined portions of the shafts  21 . After the insertion of the shafts  21 , the cam pieces  22  are brought back to room temperature. The inner diameter of the through hole  22   a  decreases as the temperature of the cam piece  22  decreases to room temperature, and thus the inner circumferential surface of the through hole  22   a  is closely fitted to the outer circumferential surface of the shaft  21 . Thus, the cam piece  22  is fixed to a predetermined portion of the shaft  21 . 
     After the cam pieces  22  are attached to the shafts  21 , as illustrated in  FIG. 8 , one positioning member  4  is attached to each of the shafts  21  by shrink-fitting. Then, another support member  3  is attached to the two shafts  21  in the same way as the above-described support member  3 . Then, as illustrated in  FIG. 1 , one positioning member  4  is attached to each of the shafts  21 . 
     As described above, the support structure  1  of this embodiment is produced by sequentially attaching the positioning members  4 , the support member  3 , the positioning members  4 , the cam pieces  22 , and the other components to the two shafts  21  from one end to the other end. In the support structure  1  having such a configuration, the camshaft assemblies  2  and the support members  3  are readily assembled. The support members  3  are each positioned in the axial direction of the camshaft assembly  2  (shaft  21 ) by the positioning members  4  positioned on the both sides of the support member  3 . The support structure  1  having such a configuration is easy to transport and is also easy to eventually attach to a cylinder head. 
     Furthermore, in the support structure  1  of the embodiment, the support members  3  are independent from each other and not connected to each other. Thus, a space for jigs, which hold the positioning members  4  or the cam pieces  22 , is readily provided around the shafts  21 . 
     Although not illustrated in the drawings, the end portion of the shaft  21  (camshaft assembly  2 ) has a sprocket on which a timing belt, which transmits rotary motion of the crankshaft, is to be wound. 
     The support structure  1  of this embodiment is eventually fixed to a cylinder head by bolting.  FIG. 9  is an explanatory view illustrating a process of attaching the camshaft assembly support structure  1  to a cylinder head  200  with bolts  100 . Specifically described, the bolts  100  are inserted through the bolt through holes  31   a  in the support member  3 , respectively. The bolts  100  include projecting ends  100   a  that project from the bolt through holes  31   a  are screwed into screw holes  201  in the cylinder head  200 , respectively. With the bolts  100 , the support structure  1  is attached to the cylinder head  200 . 
     The diameter R 1  of the bolt through hole  31   a  (dimension in the axis L direction in  FIG. 1 ) may be defined in view of the followings. Here, a position error (variability) of the screw hole in the cylinder head in the axis L direction is indicated by “Xa”. Furthermore, a position error (variability) of the bolt through hole  31   a  in the support member  3  in the axis L direction is indicated by “Xb”. Furthermore, the space (clearance) between the support member  3  and each of the positioning members  4  on the both sides of the support member  3  in the axis L direction is indicated by “Xc”. The space (clearance) between the bolt having the diameter R 2  and the bolt through hole  31   a  in the axis L direction is indicated by “Xd”. The relationship of “Xd&gt;Xa+Xb+Xc” is preferably satisfied to achieve easy attachment of the support structure  1  to a cylinder head. 
     Other Embodiments 
     The technology disclosed herein is not limited to the embodiment described above and with reference to the drawings. The following embodiments may be included in the technical scope of the present technology. 
     (1) In the above-described embodiment, the positioning members  4  have a ring-like shape, but the present technology is not limited to this. The positioning members  4  may have any shape that has a hole to receive the shaft and can position the support member. 
     (2) In the above-described embodiment, the positioning member  4  and the cam piece  22  are different members independent from each other. However, the present technology is not limited to this configuration. In some embodiments, for example, as illustrated in  FIG. 10 , a cam piece  22 X and a positioning member  4 X adjacent to the cam piece  22 X may be portions of a single solid component (a solid member  5 X). The cam piece  22 X may be attached to the same shaft  2  ( 2 A or  2 B). This configuration in which the cam piece  22 X and the positioning member  4 X are the portions of the single solid component reduces the number of parts. This may make the attachment of the cam pieces  22 X and the other components to the shaft  2  ( 2 A,  2 B) easier.  FIG. 10  is a plan view illustrating a portion of the camshaft assembly support structure  1 X according to another embodiment. In  FIG. 10 , components identical to those in the first embodiment are assigned the same reference numerals as those in the first embodiment without duplicated explanation. 
     (3) In the above-described embodiment, the positioning members  4  are used to position the support member  3  relative to the shafts  21 . However, in some embodiments, after the attachment position accuracy of the positioning members  4  on the both sides of the support member  3  in the axial direction is improved, the positioning members  4  may be used to position (cam thrust) the camshaft assembly  2  in the axial direction (axis L direction) relative to the cylinder head.