Patent Publication Number: US-7594488-B2

Title: Cylinder head cover and method for mounting cylinder head cover to cylinder head

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a cylinder head cover fixed to a cylinder head of an internal combustion engine. The present invention further relates to a method for mounting a cylinder head cover to a cylinder head. 
   Conventionally, internal combustion engines are known in which an oil control valve for controlling supply and drainage of hydraulic oil to and from a variable valve actuation mechanism is attached to a cylinder head cover (for example, refer to Japanese Patent No. 3525709). 
   Typically, such a cylinder cover is formed to have relatively thin walls to reduce the weight. This reduces the rigidity of the cylinder head cover compared to that of the cylinder head. Therefore, when such a cylinder head cover is fixed to a cylinder head, the cover could be deformed. Such deformation can deform a portion of the cover to which an oil control valve is attached. As a result, supply and drainage control performed by the valve is likely to be adversely affected. 
   Accordingly, in the configuration disclosed in the document, the cylinder head cover includes a main body fixed to a cylinder head and a valve case that is formed separately from the main body and receives an oil control valve. In this configuration, deformation of the cover is hardly transmitted to the portion of the valve case to which the valve is attached. Thus, the attaching portion is hardly deformed. 
   In the configuration disclosed in the above patent, a flange is formed on a surface (contacting surface) of the valve case that contacts the cylinder head cover. The valve case is placed on the cylinder head cover main body with the flange contacting an upper surface (outer surface) of the cylinder head cover main body. The valve case is then fixed to the cylinder head cover main body with bolts. Further, in the above-described configuration, a variable valve actuation mechanism is provided in the cylinder head. An oil passage for supplying and draining hydraulic oil to and from the variable valve actuation mechanism extends through both of the cylinder head and the oil control valve. The passage thus has a separated structure, that is, the passage has a section formed in the valve case and a section formed in the cylinder head. In other words, the oil passage having separate sections has a joint. 
   When securing the cylinder head cover main body to attach the valve case to the cylinder head, an upper surface of the cylinder head in which an opening of the oil passage is formed is pressed downward by a lower surface of the valve case. This guarantees the sealing performance at the joint in the oil passage and facilitates the assembly. 
   However, when the valve case is attached so that the pressing occurs, the reaction force applied to the valve case from the cylinder head acts as external force (separating force) that pushes the valve case away from the upper surface of the cylinder head cover. The separating force acts to degrade the attachment of the valve case to the cylinder head cover. Further, such separating force is likely to a produce local reaction force in the valve case and the cylinder head cover main body, which can deform the valve case and the cylinder head cover main body. As a result, the portion of the valve case to which the oil control valve is attached is likely to be deformed. 
   Since the rigidity of the cylinder head cover main body is likely to be reduced as described above, vibrations transmitted from the engine to the cylinder head cover main body can further degrade the state of attachment. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an objective of the present invention to provide a cylinder head cover that maintains a firm attachment of a valve case to a cylinder head. Another objective of the present invention is to provide an improved method for mounting a cylinder head cover to a cylinder head. 
   To achieve the above-mentioned objective, the present invention provides a cylinder head cover for covering a cylinder head of an internal combustion engine. The engine has a variable valve actuation mechanism and a control valve for controlling supply and drainage of hydraulic oil to and from the variable valve actuation mechanism. The cylinder head cover includes a cover main body fixed to the cylinder head; and a valve case to which the control valve is attached. The valve case is caused to contact a side of the cover main body that corresponds to the cylinder head. 
   Further, the present invention provides a method for mounting a cylinder head cover to a cylinder head. The cylinder head cover covers the cylinder head of an internal combustion engine having a variable valve actuation mechanism. The cylinder head cover has a cover main body having a through hole and a valve case. The valve case has a valve attaching portion and a held portion. The method includes inserting the valve attaching portion into the through hole; fixing the cover main body to the cylinder head such that the held portion is held between the cover main body and the cylinder head; and attaching a control valve to the valve attaching portion. The control valve controls supply and drainage of hydraulic oil to and from the variable valve actuation mechanism. 
   Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
       FIG. 1  is a cross-sectional view illustrating a part of a cylinder head cover according to one embodiment of the present invention and its surroundings; 
       FIG. 2  is a cross-sectional view illustrating an OCV before installation, a part of the cylinder head cover according to the embodiment of  FIG. 1 , and its surroundings; 
       FIG. 3A  is a top plan view illustrating a valve case according to the embodiment of  FIG. 1 ; 
       FIG. 3B  is a front view illustrating the valve case of  FIG. 3A ; 
       FIG. 3C  is a bottom view illustrating the valve case of  FIG. 3A ; 
       FIG. 3D  is a perspective view illustrating the valve case of  FIG. 3A ; 
       FIG. 3E  is a left side view illustrating the valve case of  FIG. 3A ; 
       FIG. 3F  is a right side view illustrating the valve case of  FIG. 3A ; 
       FIG. 4A  is a perspective view illustrating a sleeve according to the embodiment of  FIG. 1 ; 
       FIG. 4B  is a front view illustrating the sleeve of  FIG. 4A ; 
       FIG. 4C  is a left side view illustrating the sleeve of  FIG. 4A ; 
       FIG. 4D  is a right side view illustrating the sleeve of  FIG. 4A ; and 
       FIG. 4E  is a bottom view illustrating the sleeve of  FIG. 4A . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is a cross-sectional view illustrating a part of a cylinder head cover  2  according to a preferred embodiment of the present invention. Specifically,  FIG. 1  illustrates a state where a valve case  4  is fitted and fixed to a resin main body  3  of the cylinder head cover  2 .  FIG. 2  is a cross-sectional view illustrating the cylinder head cover  2  in a state where an oil control valve (hereinafter, referred to as OCV)  6  is about to be attached to the cylinder head cover  2 . In the following, a direction toward the top side of each of  FIGS. 1 and 2  is defined as upward direction, and a direction toward the bottom side is defined as downward direction. 
   The valve case  4  is integrally molded with resin into a shape as shown in  FIGS. 3A to 8F .  FIG. 3A  is a plan view,  FIG. 3B  is a front view,  FIG. 3C  is a bottom view,  FIG. 3D  is a perspective view,  FIG. 3E  is a left side view, and  FIG. 3F  is a right side view. 
   The valve case  4  includes a contacting portion  10  that functions as a flange. An attaching portion  12  formed into a substantially cylindrical shape with resin is located on the upper surface of the contacting portion  10 . A sleeve (reinforcing member)  14  is embedded in the resin that forms the attaching portion  12  with an OCV insertion end  14   a  open to the outside. Specifically, when integrally molding the valve case  4  with resin, the sleeve  14  is embedded in the valve case  4  by insert molding. 
   The sleeve  14  is cylindrical as shown in  FIGS. 4A to 4E  and is formed of material that has a rigidity higher than that of the resin of the valve case  4  and has the same coefficient of thermal expansion as a spool housing  7  of the OCV  6  shown in  FIGS. 1 and 2 . More specifically, the sleeve  14  is formed of aluminum base alloy. The sleeve  14  may also be formed of metal material that is exactly the same as that of the spool housing  7  of the OCV  6 . 
   The sleeve  14  includes oil holes  18 ,  20 ,  22 ,  24 ,  26 , which are formed at positions corresponding to five ports  7   a,    7   b,    7   c,    7   d,    7   e  formed on the spool housing  7  of the OCV  6 . The oil holes  18 ,  20 ,  22 ,  24 ,  26  extend from an mounting bore  16  formed inside the sleeve  14  to the outer circumferential surface of the sleeve  14 . A tapered surface  28  is formed at the OCV insertion end  14   a  of the sleeve  14  to facilitate insertion of the OCV  6 . In  FIGS. 1 and 2 , the oil holes  18 ,  20 ,  22  are shown by broken lines on the sleeve  14  since the oil holes  18 ,  20 ,  22  are located in a part that has been cut away as viewed in the drawings. 
   Primer is applied to an outer circumferential surface  14   b  of the sleeve  14  before insert molding. Thus, when covered with resin during insert molding, the primer is strongly bonded to the resin due to its adhesivity. Therefore, the sleeve  14  is strongly bonded with the resin of the attaching portion  12  of the valve case  4  formed by insert molding. During the insert molding, slide pins are arranged in the mold to be continuous with the oil holes  18  to  26  formed in the sleeve  14 . In this manner, oil passages that are connected to the oil holes  18  to  26  are also formed in the valve case  4 . 
   As the above mentioned oil passages, three oil passage portions  38 ,  40 ,  42  having oil passages  38   a,    40   a,    42   a  are formed on the outer circumferential portion of the attaching portion  12 . The oil passages  38   a,    40   a,    42   a  are connected to the three oil holes  18 ,  20 ,  22  of the sleeve  14 . The middle oil passage portion  40 , which is a supplying oil passage portion, has the oil passage  40   a,  which is a supplying oil passage, is connected to a hydraulic oil supplying path of a cylinder head  44  through a pipe and other oil passages. Thus, hydraulic oil is supplied to the OCV  6  inside the sleeve  14 . The oil passage portions  38 ,  42 , which are draining oil passage portions located on both sides of the middle oil passage portion  40 , include the oil passages  38   a,    42   a,  which are draining oil passages. Hydraulic oil is thus directly drained from the OCV  6  to the interior of the resin cylinder head cover  2 . 
   Furthermore, among the above mentioned oil passages of the valve case  4 , intermediate passages  46 ,  48  are connected to the oil holes  24 ,  26  of the sleeve  14 . The intermediate passages  46 ,  48  are formed in an oil passage coupling portion  50 . The intermediate passages  46 ,  48  permit hydraulic oil to be supplied and drained to and from the OCV  6  and a variable valve actuation mechanism  30  (see  FIGS. 1 and 2 ). An O-ring  52  is located below a lower surface  50   a  of the oil passage coupling portion  50  about openings  46   a,    48   a  of the intermediate passages  46 ,  48 . The O-ring  52  functions as a sealing member when the oil passage coupling portion  50  abuts against an upper surface  54   e  of one of cam caps  54 . In this embodiment, an opening  3   a,  which is a through hole formed on the cylinder head cover main body  3 , is directly above the cam caps  54  that is closest to the variable valve actuation mechanism  30 . 
   A bolt screw-in hole  12   b  is formed in an OCV insertion end  12   a  of the attaching portion  12 . As shown in  FIG. 1 , when the spool housing  7  of the OCV  6  is accommodated in the mounting bore  16  of the sleeve  14 , a bolt hole  6   c  of a bracket  6   b  provided on the OCV  6  is located in front of the bolt screw-in hole  12   b.  Thus, the OCV  6  is fastened to the valve case  4  by fastening a bolt through the bolt hole  6   c.    
   The valve case  4  configured as described above is formed by first arranging the sleeve  14  in a mold for injection molding and then integrally molding the contacting portion  10 , the attaching portion  12 , and the oil passage coupling portion  50  with resin. 
   The valve case  4  formed in this manner is fixed to the cylinder head cover  2  by inserting the attaching portion  12  into the opening  3   a  of the cylinder head cover main body  3  from below, and welding the contacting portion  10  to a lower surface  3   b  of the resin main body  3  about the opening  3   a  (see  FIGS. 1 and 2 ). As a result, the opening  3   a  of the resin cylinder head cover main body  3  is completely closed. 
   A broken line in  FIG. 3C  represents the arrangement of the opening  3   a  of the resin cylinder head cover main body  3  with respect to the contacting portion  10  of the valve case  4  when the contacting portion  10  is welded to the resin cylinder head cover main body  3 . The contacting portion  10  is welded at the entire circumference of the opening  3   a  in an area  10   a  of the contacting portion  10  where the resin cylinder head cover main body  3  and the contacting portion  10  overlap each other. Therefore, the draining oil passages  38   a,    42   a  drain hydraulic oil to the inside of the cylinder head cover  2 . The supplying oil passage  40   a  in the middle oil passage portion  40  is connected to another supplying passage (not shown), thereby permitting hydraulic oil to be supplied to the OCV  6 . 
   The opening  3   a  of the resin cylinder head cover main body  3  is directly above one of the cam caps  54  that is closest to the variable valve actuation mechanism  30 , when the cylinder head cover  2  is attached to the cylinder head  44 . Thus, when the cylinder head cover  2  is located on the cylinder head  44  as shown in  FIG. 2  and fastened to the cylinder head  44  with a bolt, the intermediate passages  46 ,  48  of the oil passage coupling portion  50  are connected to cam cap passages  54   a,    54   b  of the cam cap  54 , respectively. With the valve case  4  inserted into the opening  3   a,  the contacting portion  10  and the passage coupling portion  50  are held between the cylinder head  44  and the cover main body  3 . 
   Pressing force produced by fastening the bolt at the lower surface  50   a  of the passage coupling portion  50  and the upper surface  54   e  of the cam cap  54  increases the sealing between the surfaces  50   a,    54   e.  Also, upward reaction force acting on the valve case  4  due to the pressing acts in a direction increasing the adherence of the contacting portion  10  to the lower surface  3   b  of the resin cylinder head cover main body  3 . 
   The spool housing  7  of the OCV  6  is inserted in the cylinder head cover  2  configured as described above from the OCV insertion end  14   a  of the sleeve  14  to the inside of the mounting bore  16  as shown in  FIG. 2 . The mounting bore  16  of the sleeve  14  is formed with high precision such that the clearance between the spool housing  7  and the sleeve  14  is constant. Since the sleeve  14  is formed of metal material that has rigidity sufficiently higher than the resin that forms the attaching portion  12 , the dimensional accuracy of the mounting bore  16  is sufficiently maintained despite of deformation of the resin after the insert molding, deformation of the resin caused by fastening the cylinder head cover  2  to the cylinder head  44  by bolts, and subsequent thermal deformation. 
   Therefore, the spool housing  7  is easily inserted into a predetermined position in the mounting bore  16 , and the OCV  6  is attached to the attaching portion  12  in a suitable manner as shown in  FIG. 1 . An O-ring  7   f  is arranged at the proximal portion of the spool housing  7  to prevent hydraulic oil that slightly leaks from the clearance between the spool housing  7  and the sleeve  14  from being drained to the outside of the cylinder head cover  2 . The bracket  6   b  is then fastened with a bolt and the attachment of the OCV  6  is completed. 
   The OCV  6  is mounted as described above and an electronic control unit (ECU)  58  controls exciting current to an electromagnetic solenoid section  6   a  of the OCV  6  in accordance with the operating state of the engine. Accordingly, the hydraulic oil supplied to the port  7   b  of the spool housing  7  from the supplying oil passage  40   a  is supplied to one of the oil holes  24 ,  26  and drained from the other one of the oil holes  24 ,  26 . In this manner, the hydraulic oil is supplied to and drained from the variable valve actuation mechanism  30  using the intermediate passages  46 ,  48 , the cam cap passages  54   a,    54   b,  and two oil passages  60   a,    60   b  located in a camshaft  60 . For example, the-variable valve actuation mechanism  30  is actuated to retard the valve timing when the hydraulic oil is supplied to the variable valve actuation mechanism  30  through one of the paths, that is, through the intermediate passage  48 , the cam cap passage  54   b,  and the oil passage  60   b,  and the hydraulic oil is drained via the other path, that is, the intermediate passage  46 , the cam cap passage  54   a,  and the oil passage  60   a.  Thus, the rotational phase of the camshaft  60  with respect to a timing sprocket  62  is retarded, thereby retarding the valve timing. 
   Contrastingly, the variable valve actuation mechanism  30  is actuated to advance the timing when the hydraulic oil is supplied to the variable valve actuation mechanism  30  through the intermediate passage  46 , the cam cap passage  54   a,  and the oil passage  60   a,  and is drained through the intermediate passage  48 , the cam cap passage  54   b,  and the oil passage  60   b.  Thus, the rotational phase of the camshaft  60  with respect to the timing sprocket  62  is advanced, thereby advancing the valve timing. 
   The present invention has the following advantages. 
   (1) According to the present embodiment, the contacting portion  10  of the valve case  4  contacts the lower surface  3   b  of the resin cylinder head cover main body  3 . That is, the valve case  4  is caused to contact lower surface  3   b,  i.e., a side of the cover main body  3  that corresponds to the cylinder head  44 . Thus, even if upward reaction force acts on the valve case  4  from the cam cap  54  when installing the cylinder head  44 , the reaction force acts to press the contacting portion  10  against the resin cylinder head cover main body  3 . That is, for example, unlike the configuration in which the contacting portion  10  is fixed to the upper surface of the resin cylinder head cover main body  3 , the reaction force does not act in the direction separating the contacting portion  10  from the main body  3 , but in the direction pressing the contacting portion  10  against the main body  3 . Since stress produced in the valve case  4  and the main body  3  due to the reaction force is dispersed over the entire valve case  4  and the main body  3 , the valve case  4  and the main body  3  are prevented from being deformed by the reaction force. 
   Therefore, the valve case  4  is pressed against and reliably supported by the resin cylinder head cover main body  3  with reduced deformation. This improves the reliability of the installation. Thus, the valve case  4  is reliably installed to the cylinder head cover  2 . 
   (2) The reaction force is produced when the lower surface  50   a  of the oil passage coupling portion  50 , in which the openings  46   a,    48   a  of the intermediate passages  46 ,  48  are formed, is pressed against the upper surface  54   e  of the cam cap  54 , in which an opening  54   c  of the cam cap passage  54   a  and an opening  54   d  of the cam cap passage  54   b  are formed. Therefore, by securing the cylinder head cover main body  3 , to which the valve case  4  is attached, to the cylinder head  44 , the passage openings  46   a,    48   a  of the valve case  4  are connected to the passage openings  54   c,    54   d  of the cam cap  54 . Further, since the lower surface  50   a  of the valve case  4  and the upper surface  54   e  of the cam cap  54  are pressed against each other, the sealing at the joint of the passages is improved. The contacting portion  10  and the oil passage coupling portion  50  function as a held portion that is held between the cylinder head  44  and the cylinder head cover main body  3 . 
   (3) Since the contacting portion  10  is formed by the flange provided at the outer circumference of the calve case  4 , the contacting area of the valve case  4  and the resin cylinder head cover main body  3  at the contacting portion  10  is increased without significantly increasing the weight of the valve case  4 , and the increased contacting area facilitates the assembly that involves contacting of components. 
   (4) Since the cylinder head cover main body  3  and the valve case  4  are made of resin, the cylinder head cover  2  is relatively light, easy to mold, and capable of reducing noise caused by vibration. 
   Further, since resin is used, the resin cylinder head cover main body  3  and the valve case  4  are secured to each other by an easy process such as welding. Since the cylinder head cover main body  3  and the valve case  4  are secured to each other in advance, the assembled cover main body  3  and the valve case  4  are easily assembled with the cylinder head  44 . 
   (5) According to the present embodiment, the contacting portion  10  of the valve case  4  contacts and is secured to the lower surface  3   b  of the resin cylinder head cover main body  3 . Such welded portions hardly receive pulling force (separating force) that acts to separate these portions. As a result, unlike a conventional configuration in which the contacting portion  10  is, for example, secured to the upper surface of the resin cylinder head cover main body  3 , the welded portions are prevented from separating without any auxiliary components for securing such as bolts. Even if the welding (securing) is performed in a part of the contacting portions of the valve case  4  and the resin cylinder head cover main body  3 , the stress produced by the fact that these components are pressed against each other is dispersed not only to the welded portions but also to the entire contacting portions. Therefore, the valve case  4  and the cover main body  3  are prevented from being deformed. 
   (6) The sleeve  14  is formed in the valve case  4 . In other words, a reinforcing member made of a material (aluminum alloy) having a rigidity higher than the resin forming the case  4  is provided about the mounting bore  16 . Therefore, even if deformation in the part of the resin main body  3  is slightly transmitted to the valve case  4 , the shape of the mounting bore  16  is hardly affected since it is surrounded by the rigid reinforcing member. 
   (7) The sleeve  14  is secured to the resin surface of the interior of the valve case  4  through the insert molding. The valve case  4  is fixed to the cylinder head cover main body  3  after the sleeve  14  is adhered to the resin surface with the primer. Thus, for example, compared to the configuration in which the valve case  4  is attached to the resin cylinder head cover main body  3  before fixing the sleeve  14  to the inner resin surface of the valve case  4 , the components are easily handled when securing the sleeve  14 , and the sleeve  14  is reliably secured by adhesion. 
   (8) Further, in the present embodiment, the valve case  4  is attached to the head cover main body  3  at a position directly above the one of the cam caps  54  that is closest to the variable valve actuation mechanism  30 . Such arrangement of the valve case  4  permits the OCV  6  to supply and drain oil to and from the variable valve actuation mechanism  30  through extremely short oil passages. This improves the control response of the variable valve actuation mechanism  30 . 
   It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the invention may be embodied in the following forms. 
   In the above embodiment, the passage openings  46   a,    48   a,    54   c,    54   d  are formed in the lower surface  50   a  of the valve case  4  and the upper surface  54   e  of the cam cap  54  contacting the lower surface  50   a.  However, the openings  46   a,    48   a,    54   c,    54   d  may be omitted. That is, the present invention may be applied to a configuration in which no passage openings are formed in the contacting portions of a member of the cylinder head  44  and the valve case  4 . 
   In the above embodiment, the valve case  4  is located substantially directly above one of the cam caps  54  that is closest to the variable valve actuation mechanism  30 . However, the valve case  4  may be located substantially directly above another cam cap  54 . Alternatively, the valve case  4  may be located in a position that is not substantially directly above any of the cam caps  54 . The member of the cylinder head  44  that contacts the valve case  4  does not need to be the cam cap  54 . 
   In the above embodiment, the valve case  4  is fixed to the resin cylinder head cover main body  3  by welding. However, the valve case  4  may be fixed to the cover main body  3  by adhesive. Alternative, the valve case  4  may be fixed to the main body  3  by rivets or screws. When using screws to fix the valve case  4  to the main body  3 , internal threads may be formed in one of the valve case  4  and the main body  3 , and sheet metal screws may be used. Alternatively, screws and nuts may be used. In a case where the resin cylinder head cover main body  3  and the valve case  4  are formed of metal, these components may be fixed to each other by swaging. 
   In the above embodiment, the valve case  4  is fixed to the cylinder head cover main body  3  by welding, adhering, or threading. However, the valve case  4  does not need to be fixed to the main body  3  in these manners. For example, the valve case  4  may be held between a member of the cylinder head  44  such as the cam cap  54  and the resin cylinder head cover main body  3 . In this case, it is preferable that projections are formed in one of the head cover main body  3  and the valve case  4 , and engaging recesses corresponding to the projections are formed in the other one of the head cover main body  3  and the valve case  4 , so that the valve case  4  is not laterally displaced (for example, a direction along the upper surface  54   e ) with respect to the cylinder head  44 . 
   In the valve case  4 , the contacting portion  10  that contacts the cylinder head cover main body  3  does not need to be formed on the entire circumference of the valve case  4 . Also, the contacting portion  10  does not need to be formed like a flange. 
   In the above embodiment, the sleeve  14  is provided on the inner resin surface of the valve case  4 . However, the valve case  4  may be, for example, embedded in the resin. 
   The sleeve  14  may be fixed to the resin portion of the valve case  4  by a method other than insert molding. For example, after the resin portion is formed, the sleeve  14  may be fixed to the resin portion with adhesive. Alternatively, the sleeve  14  may be press fitted to the attaching portion  12  of the valve case  4  without using adhesive. Further, an external thread may be formed on the outer circumferential surface of the sleeve  14 , and the sleeve  14  may be screwed to the attaching portion  12  of the valve case  4 . 
   In the above embodiment, the valve case  4 , to which the sleeve  14  is fixed, is attached to the resin cylinder head cover main body  3 . However, for example, the valve case  4  may be attached (for example, fixed) to the cylinder head cover main body  3  before the sleeve  14  is fixed to the valve case  4 , and the sleeve  14  may then be fixed to the valve case  4 . 
   In the above embodiment, the sleeve  14  serving as a reinforcing member is provided in the valve case  4 . However, if the valve case  4  has a sufficient strength, no reinforcing member is required. 
   The cylinder head cover main body and the valve case  4  do not need to be formed of resin, but may be other materials such as aluminum, an aluminum alloy, and iron.