Patent Publication Number: US-8522738-B2

Title: Vehicle engine

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2010-001987 filed Jan. 7, 2010. The entire content of this priority application is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to vehicle engines. 
     BACKGROUND 
     Conventionally, a vehicle engine includes: a cylinder head; a cam housing fixed to a top of a cylinder head; a cam cap fixed to a top of the cam housing; a camshaft rotatably supported between the cam housing and the cam cap; a cam provided around the camshaft; a rocker arm configured to be pushed by the cam; and a lash adjuster that supports one end of the rocker arm from below. One of such vehicle engines includes a cam housing having a mounting recess, wherein the lash adjuster is mounted. 
     In such a vehicle engine, when the cam pushes the rocker arm, the pressure of the cam is exerted sequentially on the rocker arm, the lash adjuster, and the cam housing. 
     Therefore, the cam housing of the conventional vehicle engine needs to have a higher rigidity so as not to deform under the pressure of the cam. 
     In order to provide the higher rigidity of the cam housing, thickening the cam housing is necessary. However, thickening the cam housing can result in upsizing and weight increase of the cam housing. Accordingly, the space on the top of the cylinder head for fixing such a cam housing can be insufficient. 
     Thus, there is a need for a vehicle engine that exerts less pressure of the cam on the cam housing so as to permit downsizing of the cam housing. 
     SUMMARY 
     An aspect of the present invention is a vehicle engine including: a cylinder head; a cam housing fixed to a top of the cylinder head; a cam cap fixed to a top of the cam housing; a camshaft that is rotatably supported between the cam housing and the cam cap; a cam provided around the camshaft; a rocker arm that is pushed by the cam; a supporting member that supports one end of the rocker arm from below; a cylindrical bore portion for mounting the supporting member; and a base portion for supporting a bottom surface of the supporting member. The bore portion is provided integrally with the cam housing. The base portion is provided integrally with the cylinder head. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a state in which a cam housing, a cam cap, and camshafts are assembled together; 
         FIG. 2  is a perspective view illustrating a state before the cam housing, the cam cap, and the camshafts are assembled together; 
         FIG. 3  is a perspective view of the cam housing; 
         FIG. 4  is a sectional view of a vehicle engine; and 
         FIG. 5  is an enlarged sectional view of a cylinder head and a lash adjuster. 
     
    
    
     DETAILED DESCRIPTION 
     &lt;Embodiment&gt; 
     An embodiment in accordance with the present invention will hereinafter be described with reference to drawings. 
     As illustrated in  FIG. 4 , a vehicle engine  10  of this embodiment includes a cylinder head  50 , a cam housing  12 , a cam cap  14 , camshafts  16 , cams  18 , rocker arms  20 , and valves  22 . The cam housing  12  is fixed to a top of the cylinder head  50 . The cam cap  14  is fixed to a top of the cam housing  12 . The camshafts  16  are rotatably supported between the cam housing  12  and the cam cap  14 . The cams  18  are provided around the camshafts  16 . The cams  18  can push the rocker arms  20 . The rocker arms  20  can push the valves  22  so that the valves  22  operate. The vehicle engine  10  is a so-called DOHC engine, including the left and right camshafts  16  for operating the intake and exhaust valves  22 , respectively. 
     As illustrated in  FIG. 4 , the cam housing  12  and the cam cap  14  are bolted on the top of the cylinder head  50  with bolts  52 . 
     One end of each rocker arm  20  is supported from below by a corresponding lash adjuster  24 . The other end contacts a stem  22   a  of the corresponding valve  22  from above. The lash adjuster  24  corresponds to a “supporting member”. 
     As a crankshaft (not illustrated in the drawings) rotates, the camshafts  16  rotate so that the cams  18  push down rollers  20   a  of the rocker arms  20 . Then, the rocker arms  20  swing up and down about top ends of the lash adjusters  24  while reciprocating the valves  22  up and down against the elastic forces of valve springs  26 . Thus, the camshafts  16 , the cams  18 , the rocker arms  20 , the lash adjusters  24 , and the valve springs  26  configure a valve train for operating the valves  22 . 
     The cam housing  12  and the cam cap  14  are made by finishing (e.g. cutting) metal cast (e. g. aluminium alloy cast). The cam housing  12  and the cam cap  14  can be manufactured by, for example, die casting. 
     As illustrated in  FIG. 3 , the cam housing  12  includes a rectangular outer frame  12   a  and partitions  12   b . The outer frame  12   a  defines a space, while the partitions  12   b  partition the space into a plurality of subspaces. Each of the subspaces defined by the partitions  12   b  accommodates the valve train components for operating the cylinder valves  22 . 
     As illustrated in  FIG. 2 , each camshaft  16  is a round bar made with metallic material such as JIS STKM (Carbon Steel Tubes for Machine Structural Purposes). The cams  18  are integrally provided on the circumference of the camshaft  16 . The cams  18  are arranged in the axial direction of the camshaft  16 . 
     Each camshaft  16  is rotatably supported between the cam housing  12  and the cam cap  14 . Specifically, the camshaft  16  is rotatably supported between bearing recesses  28  and bearing recesses  30 . Each of the bearing recesses  28 ,  30  is generally semicircular in cross section. The bearing recesses  28  are formed in the top face of the cam housing  12 . The bearing recesses  30  are formed in the bottom face of the cam cap  14 . 
     Two oil pipes  32  are provided integrally with the cam housing  12 . Through the oil pipes  32 , lubricant oil (hereinafter referred to simply as “oil”) is supplied to the lash adjusters  24 . Because the oil pipes  32  are integral with the cam housing  12 , the oil pipes  32  can be formed at the same time when, for example, the cam housing  12  is formed. 
     The oil pipes  32  extend substantially parallel to the axes of the camshafts  16  and through the thicknesses of the partitions  12   b . Each oil pipe  32  has a center hole  34  running through the axis thereof. The center hole  34  is an oil path. An oil pump pumps up oil from an oil pan. The oil is then forced through the center hole  34  to the lash adjusters  24 . Each oil pipe  32  corresponds to an “oil flow path”. 
     As illustrated in  FIG. 3 , bore portions  36  for mounting the lash adjusters  24  are provided integrally with the cam housing  12 . In other words, the oil pipes  32  are provided integrally with the cam housing  12 , and the bore portions  36  are provided integrally with outer circumferential surfaces of the oil pipes  32 . 
     Each bore portion  36  is substantially cylindrical, and a mounting bore  38  is formed in the inside of the bore portion  36  (see  FIG. 5 ). The top and bottom ends of the mounting bore  38  are open. The lash adjuster  24  is fitted in the mounting bore  38  in close contact with the inner surface of the mounting bore  38 . 
     On the other hand, as illustrated in  FIGS. 4 and 5 , substantially columnar cylindrical base portions  40  are provided integrally with the cylinder head  50  at the top surface of the cylinder head  50  so as to protrude upward. Each base portion  40  supports a bottom surface of the corresponding lash adjuster  24  from below. 
     Furthermore, as illustrated in  FIG. 5 , there is a clearance  42  having a predetermined size between the bottom end of the bore portion  36  and the top surface of the base portion  40 . 
     Operational functions achieved by the vehicle engine  10  will now be described. 
     In the vehicle engine  10  of this embodiment, the base portion  40  for supporting the bottom surface of the lash adjuster  24  is provided integrally with the cylinder head  50 . Therefore, the base portion  40  can receive the pressure of the cam  18  exerted on the lash adjuster  24 , while the cam housing  12  does not have to receive the pressure of the cams  18  exerted on the lash adjusters  24 . As a result of this, the cam housing  12  does not have to have a higher rigidity, and the thickness of the cam housing  12  can be less. This makes it possible to downsize and reduce the weight of the cam housing  12 . 
     In the vehicle engine  10  of this embodiment, the clearance  42  is provided between the bottom end of the bore portion  36  and the top surface of the base portion  40 . Accordingly, when mounting the lash adjusters  24  in the bore portion  36 , air in the bore portion  36  can be bled from the clearance  42 . As a result of this, unlike conventional vehicle engines, providing air-bleed holes in the cylinder head  50  or in the cam housing  12  by cutting etc. for bleeding air when mounting the lash adjusters  24  is unnecessary. This makes it possible to reduce the processing cost and the material cost of the vehicle engine  10 . 
     In the vehicle engine  10  of this embodiment, the oil pipe  32  for supplying oil to the lash adjuster  24  is provided integrally with the cam housing  12 . Accordingly, unlike conventional vehicle engines, providing an oil supply path in the cylinder head  50  by cutting etc. for supplying oil to the lash adjuster  24  is unnecessary. Furthermore, by partially coarse-material molding the oil pipe  32 , which is molded integrally with the cam housing  12 , with casting etc., the processing cost and the material cost of the vehicle engine  10  can be reduced. 
     In the vehicle engine  10  of this embodiment, the clearance  42  is provided between the bottom end of the bore portion  36  and the top surface of the base portion  40  as illustrated in  FIG. 5 . Accordingly, because the bottom end of the bore portion  36  does not contact and interfere the top surface of the base portion  40 , the difference in level between a bottom surface S 2  of the bore portion  36  and a tightening surface S 1  to the cylinder head  50  of the cam housing  12  can be within a wider tolerance. In other words, precision machining the cam housing  12  to create a predetermined difference in level between the tightening surface S 1  and the bottom surface S 2  of the bore portion  36  is unnecessary. Because precision machining the cylinder head  50  is thus unnecessary, the processing cost of the cylinder head  50  can be reduced. 
     &lt;Other Embodiments&gt; 
     The present invention is not limited to the embodiment described above with the drawings. For example, following embodiments are also included within the scope of the present invention. Further various variations other than the following embodiments are also possible within the scope and spirit of the invention. 
     (1) In the above embodiment, the supporting member that supports the one end of the rocker arm  20  from below is illustratively the lash adjuster  24 . The present invention is not limited to this. For example, the supporting member may be a solid pivot. 
     (2) In the above embodiment, the shape of the base portion  40  is illustratively columnar. The present invention is not limited to this. The shape of the base portion  40  may be, for example, substantially rectangular parallelepiped.