Patent Publication Number: US-2017361541-A1

Title: Synthetic resin joined body and method of manufacturing the same

Description:
TECHNICAL FIELD 
     The present invention relates to a synthetic resin joined body formed by welding synthetic resin parts to each other and a method of manufacturing the same. 
     BACKGROUND ART 
     Conventionally, there is a known technique of a synthetic resin joined body formed by welding synthetic resin parts to each other. An example of the technique is disclosed in Patent Literature 1. 
     In Patent Literature 1, a synthetic resin joined body (laser-welded structure) including a baffle plate which is disposed in a cylinder head cover of an engine and which is in a rectangular flat plate shape and a flow passage forming member which is brought in contact with (laid over) the baffle plate from below to form an oil passage is disclosed. The baffle plate and the flow passage forming member are welded to each other at a welding portion (a contact face of the fluid passage forming member) adjacent to the oil passage. 
     In the synthetic resin joined body formed in this manner, the welding portion performs two functions, i.e., securing sealing performance of the oil passage and securing joint strength between the baffle plate and the flow passage forming member. 
     However, in the synthetic resin joined body described in Patent Literature 1, a certain or larger welding area of the welding portion is necessary to secure the joint strength by the welding portion. Therefore, it takes time to melt the welding portion, which results in a longer welding time. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Application Laid-open No. 2007-127014 
     SUMMARY OF INVENTION 
     Technical Problem 
     The present invention has been made with the above circumstances in view and it is an object of the invention to provide a synthetic resin joined body and a method of manufacturing the same, in which it is possible to secure both sealing performance of a flow passage and joint strength between synthetic resin parts even if an area of a portion to be welded is reduced. 
     Solution to Problem 
     The problem to be solved by the present invention is as described above and solutions to the problem will be described next. 
     In other words, a synthetic resin joined body according to an aspect of the invention includes: a first synthetic resin part; a second synthetic resin part which comes in contact with the first synthetic resin part; a flow passage which is formed between the first synthetic resin part and the second synthetic resin part and through which fluid flows; a sealing portion which is formed by welding the first synthetic resin part and the second synthetic resin part to each other on an outer side of the flow passage to seal a periphery of the flow passage; and a joint portion for joining the first synthetic resin part and the second synthetic resin part to each other. 
     The sealing portion is disposed so as to be positioned between the flow passage and the joint portion. 
     The joint portion is disposed along the flow passage. 
     The joint portion is disposed along an outer periphery of the sealing portion. 
     The first synthetic resin part is a baffle plate which is disposed on a cylinder head cover, the second synthetic resin part is an oil passage forming member including a recessed portion recessed to an opposite side from the baffle plate, the flow passage is an oil passage through which lubricant flows, and the oil passage is formed by the recessed portion and the baffle plate by joining the oil passage forming member to one face of the baffle plate. 
     A method of manufacturing a synthetic resin joined body according to another aspect of the invention includes: a transmission-side synthetic resin part preparing step of preparing a laser light transmissive transmission-side synthetic resin part including a first flow passage forming portion for forming one part of a flow passage through which fluid flows; an absorption-side synthetic resin part preparing step of preparing a laser light absorbing absorption-side synthetic resin part including a second flow passage forming portion for forming the other part of the flow passage and a welding portion which is formed into a protruding shape at a periphery of the second flow passage forming portion; a disposing step of disposing the transmission-side synthetic resin part and the absorption-side synthetic resin part so that the first flow passage forming portion and the second flow passage forming portion are laid over each other to form the flow passage and that the welding portion comes in contact with the transmission-side synthetic resin part; a sealing step of radiating laser light to the welding portion from a side of the transmission-side synthetic resin part to melt the welding portion to thereby weld the welding portion and the transmission-side synthetic resin part to each other to seal a periphery of the flow passage; and a joining step of joining the transmission-side synthetic resin part and the absorption-side synthetic resin part to each other. 
     In the method of manufacturing the synthetic resin joined body according to the other aspect of the invention, the transmission-side synthetic resin part on which one of a protruding portion and a through hole is formed is prepared in the transmission-side synthetic resin part preparing step, the absorption-side synthetic resin part on which the other of protruding portion and the through hole is formed is prepared in the absorption-side synthetic resin part preparing step, the transmission-side synthetic resin part and the absorption-side synthetic resin part are disposed so that the protruding portion is inserted through the through hole in the disposing step, and the transmission-side synthetic resin part and the absorption-side synthetic resin part are joined to each other by staking the protruding portion in the joining step. 
     In the method of manufacturing the synthetic resin joined body according to the other aspect of the invention, an outer portion of the welding portion of the absorption-side synthetic resin part and the transmission-side synthetic resin part are joined to each other in the joining step. 
     The flow passage is an oil passage through which the lubricant flows, the transmission-side synthetic resin part is a baffle plate which is disposed on a cylinder head cover, the absorption-side synthetic resin part is an oil passage forming member for forming the oil passage between the baffle plate and the oil passage forming member, and the second flow passage forming portion of the oil passage forming member is recessed in an opposite direction to a protruding direction of the welding portion. 
     Advantageous Effects of Invention 
     As effects of the aspects of the present invention, the following effects are exerted. 
     In the synthetic resin joined body according to the one aspect of the invention, even if an area of the portion to be welded is reduced, it is possible to secure both of sealing performance of the flow passage and joint strength between the synthetic resin parts (the first synthetic resin part and the second synthetic resin part). 
     In the synthetic resin joined body according to the one aspect of the invention, it is possible to prevent the fluid from reaching the joint portion. 
     In the synthetic resin joined body according to the one aspect of the invention, it is possible to secure the joint strength between the first synthetic resin part and the second synthetic resin part along the flow passage. 
     In the synthetic resin joined body according to the one aspect of the invention, it is possible to secure the joint strength between the first synthetic resin part and the second synthetic resin part along the outer periphery of the sealing portion. 
     In the synthetic resin joined body according to the one aspect of the invention, even if the area of the portion to be laser-welded is reduced, it is possible to secure both of the sealing performance of the oil passage and the joint strength between the baffle plate and the oil passage forming member. 
     In the method of manufacturing the synthetic resin joined body according to the other aspect of the invention, even if the area of the portion to be laser-welded is reduced, it is possible to secure both of the sealing performance of the fluid passage and the joint strength between the synthetic resin parts (the transmission-side synthetic resin part and the absorption-side synthetic resin part). 
     In the method of manufacturing the synthetic resin joined body according to the other aspect of the invention, the transmission-side synthetic resin part and the absorption-side synthetic resin part can be joined to each other and the transmission-side synthetic resin part and the absorption-side synthetic resin part can be positioned with respect to each other. 
     In the method of manufacturing the synthetic resin joined body according to the other aspect of the invention, it is possible to prevent the fluid from reaching the portion joined in the joining step. 
     In the method of manufacturing the synthetic resin joined body according to the other aspect of the invention, even if the area of the portion to be laser-welded is reduced, it is possible to secure both of the sealing performance of the oil passage and the joint strength between the baffle plate and the oil passage forming member. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of an inside of a cylinder head cover of an engine and shows a state of use of a baffle plate and an oil passage forming member according to an embodiment of the present invention. 
         FIG. 2( a )  is a bottom view of the baffle plate and  FIG. 2( b )  is a front view of the baffle plate. 
         FIG. 3  is a plan view of the oil passage forming member. 
         FIG. 4  is a plan view of a joined body formed by the baffle plate and the oil passage forming member. 
         FIG. 5  is a cross-sectional view taken along line A-A in  FIG. 4 . 
         FIG. 6  is a flowchart of a method of manufacturing the joined body formed by the baffle plate and the oil passage forming member according to the embodiment of the invention. 
         FIG. 7  is a partial cross-sectional view showing the baffle plate and the oil passage forming member in a disposing step. 
         FIG. 8  is a partial cross-sectional view showing the baffle plate and the oil passage forming member in a sealing step. 
         FIG. 9  is a partial cross-sectional view showing the baffle plate and the oil passage forming member in a joining step. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     Directions shown by arrows U, D, F, B, L, and R in the diagrams are respectively defined as an upward direction, a downward direction, a forward direction, a backward direction, a leftward direction, and a rightward direction and a description will be given below. 
     First, by using  FIG. 1 , a structure of an engine  1  including a baffle plate  110  and an oil passage forming member  120  according to an embodiment of the present invention will be described. 
     The engine  1  according to the embodiment includes valve gears  30 , which will be described later, on both of an intake side and an exhaust side. Because structures of the valve gears  30  on the intake side and the exhaust side are substantially the same, the structure on the exhaust side (the structure on a left side in  FIG. 1 ) will be mainly described and the structure on the intake side (the structure on a right side in  FIG. 1 ) will be omitted appropriately for convenience of description. 
     The engine  1  mainly includes a cylinder head  10 , a cylinder head cover  20 , the valve gear  30 , a cam cap  40 , the baffle plate  110 , and the oil passage forming member  120 . 
     The cylinder head  10  along with a cylinder block (not shown) forms a main structural body of the engine  1 . The cylinder head  10  is fixed to an upper portion of the cylinder block. The cylinder head  10  mainly includes cylinder head-side bearing portions  11  and oil galleries  12 . 
     The cylinder head-side bearing portion  11  supports an exhaust-side camshaft  32 A (described later) from below so that the exhaust-side camshaft  32 A can rotate. The cylinder head-side bearing portion  11  is formed in a left portion of the cylinder head  10  to form a semicircular recess with an upper side open in front view. 
     The oil gallery  12  is an oil passage for feeding lubricant to respective portions of the engine  1 . The oil gallery  12  is formed to pass through a left wall of the cylinder head  10  in a front-back direction. 
     The cylinder head cover  20  covers an upper portion of the cylinder head  10 . The cylinder head cover  20  is formed in a shape of a bowl with a lower side open. The cylinder head cover  20  is placed on the upper portion of the cylinder head  10  and suitably fixed with bolts or the like. The baffle plate  110  (described later) is mounted to an inner side of the cylinder head cover  20  to form an oil separator chamber  21 . The oil separator chamber  21  can store blow-by gas and cause the gas to flow back to an intake system after carrying out oil dropping. 
     The valve gear  30  is for opening and closing exhaust ports (not shown) of the engine  1  at predetermined times. The valve gear  30  mainly includes exhaust valves  31 A and the exhaust-side camshaft  32 A. 
     The exhaust valves  31 A are for opening and closing the exhaust ports (not shown) of the engine  1 . Each of the exhaust valves  31 A is disposed with its longitudinal direction oriented substantially in a vertical direction. A lower end of the exhaust valve  31 A extends to the exhaust port. A middle portion of the exhaust valve  31 A in the vertical direction is inserted through the cylinder head  10  to be able to slide. 
     The exhaust-side camshaft  32 A is for driving the valve gear  30  for opening and closing. The exhaust-side camshaft  32 A is placed on the cylinder head-side bearing portion  11  of the cylinder head  10  with its longitudinal direction oriented substantially in the front-back direction. The exhaust-side camshaft  32 A includes cams  33 . 
     Each of the cams  33  is a portion formed in a plate shape having an irregular distance from a center of rotation (center of the exhaust-side camshaft  32 A) to an outer periphery. The cam  33  is disposed in a position corresponding to each of cylinders in the front-back direction. The cam  33  is disposed above the exhaust valve  31 A. The cam  33  rotates about an axial center of the exhaust-side camshaft  32 A to thereby cause the exhaust valve  31 A to slide in the vertical direction with respect to the cylinder head  10 . 
     The cam cap  40  is fixed to the upper portion of the cylinder head  10  to retain the exhaust-side camshaft  32 A between the cylinder head  10  and the cam cap  40 . The cam cap  40  is formed in a substantially rectangular parallelepiped shape with its longitudinal direction oriented in the left-right direction. The cam cap  40  mainly includes a cam cap-side bearing portion  41 . 
     The cam cap-side bearing portion  41  supports the exhaust-side camshaft  32 A from above so that the exhaust-side camshaft  32 A can rotate. The cam cap-side bearing portion  41  is formed in a left portion of the cam cap  40  to form a semicircular recess with a lower side open in front view. The cam cap-side bearing portion  41  is formed in a position facing the cylinder head-side bearing portion  11  in the cylinder head  10  and cooperates with the cylinder head-side bearing portion  11  to rotatably support the exhaust-side camshaft  32 A. 
     Although it is not described concretely, the engine  1  having the above-described structure includes, as an intake-side structure (structure on a right side in  FIG. 1 ), the (intake-side) valve gear  30  for opening and closing intake ports (not shown) of the engine  1  at predetermined times. The intake-side valve gear  30  includes intake valves  31 B for opening and closing the intake ports (not shown) of the engine  1  and an intake-side camshaft  32 B for driving the intake-side valve gear  30  for opening and closing as shown in  FIG. 1 . 
     By using  FIGS. 1 to 5 , structures of the baffle plate  110  and the oil passage forming member  120  will be described below in detail. 
     The baffle plate  110  shown in  FIGS. 1, 2, 4, and 5  is a member for defining the oil separator chamber  21 . The baffle plate  110  is formed in a rectangular plate shape. The baffle plate  110  is mounted to the inner side of the cylinder head cover  20 . The baffle plate  110  is disposed with its longitudinal direction oriented in the front-back direction and its plate faces facing in the vertical direction. The baffle plate  110  has protruding portions  111  and an oil passage forming face  112 . 
     The protruding portions  111  shown in  FIGS. 2( a ), 2( b ) , and  5  are for joining the baffle plate  110  and the oil passage forming member  120  (described later). The protruding portions  111  are formed in circular columnar shapes. The protruding portions  111  are formed to extend downward from a bottom face (the oil passage forming face  112  described later) of the baffle plate  110 . The plurality of protruding portions  111  are formed respectively in positions overlapping through holes  125  (described later) in the oil passage forming member  120 . 
     The oil passage forming face  112  shown in  FIGS. 2( a ), 2( b ) , and  5  is a face forming a part of an oil passage  130  described later. The oil passage forming face  112  is a lower face (bottom face) of the baffle plate  110 . The oil passage forming face  112  is formed in a planar shape. The protruding portions  111  are formed on the oil passage forming face  112 . 
     The oil passage forming member  120  shown in  FIGS. 1 and 3 to 5  is a member for forming a lubricant feed path for feeding the lubricant to predetermined lubrication portions. The oil passage forming member  120  has such an outside shape in plan view as to surround a periphery of the lubricant feed path. The oil passage forming member  120  is formed in a plate shape with its central portion (portion corresponding to the lubricant feed path) protruding downward (see  FIG. 5 ). The oil passage forming member  120  is fixed to a bottom face of the baffle plate  110 . The oil passage forming member  120  includes a recessed portion  121 , an introduction port  122 , discharge ports  123 , a welding portion  124 , and a through hole  125 . 
     The recessed portion  121  shown in  FIGS. 3 and 5  forms a part of the oil passage  130  described later. The recessed portion  121  is formed with its portion corresponding to the lubricant feed path recessed downward (in an opposite direction to a protruding direction of the welding portion  124  described later). The recessed portion  121  is branched so as to form end portions in positions corresponding to the predetermined lubrication portions. With the oil passage forming member  120  fixed to the oil passage forming face  112  of the baffle plate  110 , the recessed portion  121  forms the oil passage  130  (see  FIG. 5 ) between the baffle plate  110  and the oil passage forming member  120 . In other words, the oil passage forming face  112  forms an upper wall of the oil passage  130  and the recessed portion  121  forms side walls and a bottom wall of the oil passage  130 . The oil passage  130  is formed in a hatched area in  FIG. 4  so as to feed the lubricant from the oil gallery  12  fed through a predetermined oil passage to the predetermined lubrication portions (e.g., the cams  33 ). 
     The introduction port  122  shown in  FIG. 3  is a portion for introducing the lubricant into the oil passage  130 . The introduction port  122  is formed to extend downward from a bottom face of the recessed portion  121  to pass through the oil passage forming member  120  in the vertical direction. The introduction port  122  is formed near a front left end portion of the oil passage forming member  120 . The introduction port  122  communicates with the oil gallery  12  through the predetermined oil passage. 
     The discharge ports  123  shown in  FIGS. 3 and 5  are portions for discharging the lubricant flowing through the oil passage  130  to the predetermined lubrication portions. The discharge ports  123  are formed to extend downward from the bottom face of the recessed portion  121  to pass through the oil passage forming member  120  in the vertical direction. The discharge ports  123  are respectively formed at the respective end portions (positions corresponding to the predetermined lubrication portions) of the recessed portion  121  (oil passage  130 ). To put it concretely, the discharge ports  123  are formed above the cams  33 . 
     The welding portion  124  shown in  FIGS. 3 and 5  is a portion to be welded to the baffle plate  110 . Before the oil passage forming member  120  is welded to the baffle plate  110 , the welding portion  124  is formed in a protruding shape on an upper face of the oil passage forming member  120  (face facing the baffle plate  110 ). The welding portion  124  is formed in a hatched area in  FIG. 3  to extend from a position near a front end to a position near a back end of the oil passage forming member  120  in plan view. To put it concretely, the welding portion  124  is formed to lay a closed trail on an outer side of the recessed portion  121  along the recessed portion  121  in plan view. 
     The through holes  125  shown in  FIGS. 3 and 5  are for joining the baffle plate  110  and the oil passage forming member  120 . The through holes  125  are formed to pass through the oil passage forming member  120  in the vertical direction. The through holes  125  are formed on an outer side of the welding portion  124 . To put it concretely, the through holes  125  are formed on the outer side of an area surrounded with the welding portion  124  in plan view. In other words, the through holes  125  are disposed so that the welding portion  124  is positioned between the recessed portion  121  and the through holes  125 . The through holes  125  are disposed along an outer periphery of the welding portion  124 . The plurality of through holes  125  are formed at intervals in a direction along the outer periphery of the welding portion  124 . Through the through holes  125 , the protruding portions  111  are to be inserted. Each of the through holes  125  is formed so as to have a larger diameter than each of the protruding portions  111  and leave as small a clearance as possible between an inner wall of the through hole  125  and an outer wall of the protruding portion  111 . 
     By laying the baffle plate  110  and the oil passage forming member  120  over each other in the vertical direction and welding and joining by staking them to each other, the joined body (synthetic resin joined body) is formed. A sealing portion  140  and joint portions  150  are formed at the joined body. 
     The sealing portion  140  shown in  FIG. 5  seals a periphery of the oil passage  130 . The sealing portion  140  is formed by laser-welding the baffle plate  110  and the oil passage forming member  120  on an outer side of the oil passage  130 . The sealing portion  140  is formed by laser-welding (the oil passage forming face  112  of) the baffle plate  110  and the welding portion  124  of the oil passage forming member  120  to each other. The sealing portion  140  is formed to lay a closed trail along an outer periphery of the oil passage  130  (surround an entire periphery of the oil passage  130 ). 
     The joint portions  150  shown in  FIG. 5  join the baffle plate  110  and the oil passage forming member  120  to each other. Each of the joint portions  150  is formed by each of the protruding portions  111  on the baffle plate  110  and each of the through holes  125  in the oil passage forming member  120 . To put it concretely, the joint portion  150  is formed by inserting the protruding portion  111  through the through hole  125  and staking the protruding portion  111 . The joint portions  150  are formed in positions corresponding to the protruding portions  111  and the through holes  125  (see  FIG. 3 ). To put it concretely, the joint portions  150  are formed on an outer side of the sealing portion  140  (outside an area surrounded with the sealing portion  140  in plan view). In other words, the joint portions  150  are disposed so that the sealing portion  140  is positioned between the oil passage  130  and the joint portions  150  (see  FIG. 5 ). The plurality of joint portions  150  are formed at intervals along an outer periphery of the sealing portion  140 . 
     By using  FIGS. 6 to 9 , the method of manufacturing the joined body formed by the baffle plate  110  and the oil passage forming member  120  will be described below in detail. In a manufacturing process of the manufacturing method according to the embodiment, the baffle plate  110  is disposed on a lower side and the oil passage forming member  120  is disposed on an upper side. 
     The method of manufacturing the joined body formed by the baffle plate  110  and the oil passage forming member  120  according to the embodiment of the invention includes a baffle plate preparing step, an oil passage forming member preparing step, a disposing step, a sealing step, and a joining step. 
     In the baffle plate preparing step, the baffle plate  110  is prepared (step S 101 ). The baffle plate  110  is made of laser light transmissive synthetic resin. It is essential only that the baffle plate  110  have transmittance of the laser light to be used (laser light of a predetermined wavelength) and the baffle plate  110  having the laser light transmittance not lower than 25% may be used, for example. To put it concretely, as material of the baffle plate  110 , polyester resin such as polybutylene terephthalate (PBT) and polyethylene terephthalate (PET), polyolefin resin such as polyethylene and polypropylene, polyamide resin, vinyl chloride resin, fluorine resin, and the like can be used. 
     In the oil passage forming member preparing step, the oil passage forming member  120  is prepared (step S 102 ). The oil passage forming member  120  is made of laser light absorbing synthetic resin. It is essential only that the oil passage forming member  120  have absorbance of the laser light to be used and the oil passage forming member  120  having the transmittance of the laser light not higher than 5% can be used, for example. To put it concretely, as material of the oil passage forming member  120 , the same synthetic resin as that used for the above-described baffle plate  110  into which an absorbent such as carbon black for increasing the absorbance is mixed can be used. 
     In the disposing step shown in  FIG. 7 , the baffle plate  110  and the oil passage forming member  120  are disposed (step S 103 ). The baffle plate  110  is disposed with the oil passage forming face  112  facing upward. The oil passage forming member  120  is disposed with its face having the welding portion  124  facing downward. The baffle plate  110  and the oil passage forming member  120  are disposed so that a bottom face of the welding portion  124  comes in contact with the oil passage forming face  112 . At this time, the oil passage forming face  112  and the recessed portion  121  are laid over each other to form the oil passage  130 . 
     The baffle plate  110  and the oil passage forming member  120  are disposed so that the plurality of protruding portions  111  are respectively inserted through the plurality of through holes  125 . In this way, it is possible to position the oil passage forming member  120  with respect to the baffle plate  110  in a horizontal direction. 
     In the sealing step shown in  FIG. 8 , the periphery of the oil passage  130  is sealed (step S 104 ). By radiating laser light toward the welding portion  124  from below the baffle plate  110 , (the bottom face of) the welding portion  124  and (the oil passage forming face  112  of) the baffle plate  110  are laser-welded to each other. A light source of the laser light is not especially restricted and a semiconductor laser, a YAG laser, or the like may be used. 
     Because the baffle plate  110  is made of the laser light transmissive synthetic resin, most of the laser light radiated from below the baffle plate  110  is not absorbed by the baffle plate  110  and passes through the baffle plate  110 . Then the laser light is absorbed by the oil passage forming member  120  made of the laser light absorbing synthetic resin. To put it concretely, the laser light is absorbed by the welding portion  124  near the bottom face of the welding portion  124 . 
     Energy of the laser light absorbed by the welding portion  124  is converted into heat. In this way, the bottom face of the welding portion  124  is heated. When a temperature of the bottom face of the welding portion  124  increases, an area near the oil passage forming face  112  of the baffle plate  110  in contact with the bottom face of the welding portion  124  is also heated due to heat transfer. As a result, a melted layer is formed at a contact portion between the oil passage forming member  120  and the baffle plate  110  (between the bottom face of the welding portion  124  and the oil passage forming face  112  of the baffle plate  110 ). The melted layer cools down and sets and, as a result, the baffle plate  110  and the oil passage forming member  120  become welded to each other. 
     In this manner, the sealing portion  140  is formed. The sealing portion  140  is formed at the periphery of the oil passage  130  so as to surround the entire periphery of the oil passage  130 . In this way, it is possible to prevent lubricant flowing through the oil passage  130  from leaking outside the sealing portion  140 . 
     In the joining step shown in  FIG. 9 , the baffle plate  110  and the oil passage forming member  120  are joined to each other (step S 105 ). This joining is carried out by staking the protruding portions  111  inserted through the through holes  125 . As a method of staking, heat staking can be employed. To put it concretely, by pressing a heated die against each of the protruding portions  111  from above, an upper end portion of the protruding portion  111  is heated and pressurized simultaneously. As a result, the upper end portion of the protruding portion  111  is thermally deformed (plastically deformed) so as to spread in the horizontal direction. In this way, the baffle plate  110  and the oil passage forming member  120  are joined to each other by staking. 
     In this manner, the joint portions  150  are formed. With the joint portions  150 , joint strength between the baffle plate  110  and the oil passage forming member  120  is secured. With the joint portions  150 , pressure resistance to oil pressure of the lubricant flowing through the oil passage  130  can be secured as well. In other words, it is possible to prevent detachment of the baffle plate  110  and the oil passage forming member  120  from each other due to the oil pressure of the lubricant. 
     The joined body according to the embodiment has the joint portions  150  formed by the heat staking in addition to the sealing portion  140  formed by the laser welding. The sealing portion  140  seals the periphery of the oil passage  130  to perform a function of preventing the lubricant from leaking outside the sealing portion  140 . As a result, the sealing portion  140  joins the baffle plate  110  and the oil passage forming member  120  to each other. 
     The joint portions  150  join the baffle plate  110  and the oil passage forming member  120  to each other independently of the joining by the sealing portion  140 . Therefore, even if the joint strength (pressure resistance to the oil pressure of the lubricant) obtained by the sealing portion  140  is not sufficient, it is possible to secure the sufficient joint strength between the baffle plate  110  and the oil passage forming member  120  with the joint portions  150 . 
     Therefore, it is essential only that the sealing portion  140  be formed to secure sealing performance and the sealing portion  140  need not provide high joint strength. Consequently, the joined body according to the embodiment does not require a large area of the portion to be laser-welded (i.e., area of the bottom face of the welding portion  124 ). Therefore, it is possible to reduce the area of the portion to be laser-welded to thereby shorten a time required for the laser welding. Moreover, it is unnecessary to increase a laser output. 
     In the joined body according to the embodiment, the joint portions  150  are formed along the outer periphery of the sealing portion  140 . The oil pressure of the lubricant flowing through the oil passage  130  applies a force for rupturing the sealing portion  140  to the sealing portion  140 . However, because the joint portions  150  are formed along the outer periphery of the sealing portion  140 , a force for resisting the oil pressure of the lubricant is applied to the sealing portion  140 . Therefore, it is possible to prevent the sealing portion  140  from being ruptured by the oil pressure of the lubricant. 
     The joint portions  150  are formed on the outer side of the sealing portion  140 . Because the lubricant does not go outside the sealing portion  140 , the lubricant does not reach the joint portions  150 . Therefore, it is possible to prevent the lubricant from leaking from the joint portions  150  (from the clearance between the outer wall of each of the protruding portions  111  and the inner wall of each of the through holes  125 ). 
     As described above, the joined body (synthetic resin joined body) according to the embodiment includes the baffle plate  110  (first synthetic resin part), the oil passage forming member  120  (second synthetic resin part) which comes in contact with the baffle plate  110 , the oil passage  130  (flow passage) which is formed between the baffle plate  110  and the oil passage forming member  120  and through which the lubricant (fluid) flows, the sealing portion  140  which is formed by welding the baffle plate  110  and the oil passage forming member  120  to each other on the outer side of the oil passage  130  to seal the periphery of the oil passage  130 , and the joint portions  150  for joining the baffle plate  110  and the oil passage forming member  120  to each other. 
     With this structure, even if the area of the portion to be welded is reduced, it is possible to secure both of the sealing performance of the oil passage  130  and the joint strength between the synthetic resin parts (the baffle plate  110  and the oil passage forming member  120 ). 
     Moreover, the sealing portion  140  is disposed so as to be positioned between the oil passage  130  and the joint portions  150 . 
     With this structure, it is possible to prevent the lubricant from reaching the joint portions  150 . 
     The joint portions  150  are disposed along the oil passage  130 . 
     With this structure, it is possible to secure the joint strength between the baffle plate  110  and the oil passage forming member  120  along the oil passage  130 . 
     The joint portions  150  are disposed along the outer periphery of the sealing portion  140 . 
     With this structure, it is possible to secure the joint strength between the baffle plate  110  and the oil passage forming member  120  along the outer periphery of the sealing portion  140 . 
     The baffle plate  110  is disposed on the cylinder head cover  20 , the oil passage forming member  120  includes the recessed portion  121  recessed to the opposite side from the baffle plate  110  and the oil passage  130  through which the lubricant flows is formed by the recessed portion  121  and the baffle plate  110  by joining the oil passage forming member  120  to one face of the baffle plate  110 . 
     With this structure, even if the area of the portion to be laser-welded is reduced, it is possible to secure both of the sealing performance of the oil passage  130  and the joint strength between the baffle plate  110  and the oil passage forming member  120 . 
     The method of manufacturing the joined body (synthetic resin joined body) according to the embodiment includes the baffle plate preparing step (transmission-side synthetic resin part preparing step) of preparing the laser light transmissive baffle plate  110  (transmission-side synthetic resin part) including the oil passage forming face  112  (first flow passage forming portion) for forming one part of the oil passage  130  (flow passage) through which the lubricant (fluid) flows, the oil passage forming member preparing step (absorption-side synthetic resin part preparing step) of preparing the laser light absorbing oil passage forming member  120  (absorption-side synthetic resin part) including the recessed portion  121  (second flow passage forming portion) for forming the other part of the oil passage  130  and the welding portion  124  which is formed into the protruding shape at a periphery of the recessed portion  121 , the disposing step of disposing the baffle plate  110  and the oil passage forming member  120  so that the oil passage forming face  112  and the recessed portion  121  are laid over each other to form the oil passage  130  and that the welding portion  124  comes in contact with the baffle plate  110 , the sealing step of radiating the laser light to the welding portion  124  from the side of the baffle plate  110  to melt the welding portion  124  to thereby weld the welding portion  124  and the baffle plate  110  to each other to seal the periphery of the oil passage  130 , and the joining step of joining the baffle plate  110  and the oil passage forming member  120  to each other. 
     With this structure, even if the area of the portion to be laser-welded is reduced, it is possible to secure both of the sealing performance of the oil passage  130  and the joint strength between the synthetic resin parts (the baffle plate  110  and the oil passage forming member  120 ). 
     The baffle plate  110  on which the protruding portions  111  are formed is prepared in the baffle plate preparing step, the oil passage forming member  120  in which the through holes  125  are formed is prepared in the oil passage forming member preparing step, the baffle plate  110  and the oil passage forming member  120  are disposed so that the protruding portions  111  are inserted through the through holes  125  in the disposing step, and the baffle plate  110  and the oil passage forming member  120  are joined to each other by staking the protruding portions  111  in the joining step. 
     With this structure, the baffle plate  110  and the oil passage forming member  120  can be joined to each other and the baffle plate  110  and the oil passage forming member  120  can be positioned with respect to each other. 
     In the joining step, an outer portion of the welding portion  124  of the oil passage forming member  120  and the baffle plate  110  are joined to each other. 
     With this structure, it is possible to prevent the lubricant from reaching the joint portions  150  (portions joined in the joining step). 
     The oil passage  130  is a passage through which the lubricant flows, the baffle plate  110  is disposed on the cylinder head cover  20 , the oil passage forming member  120  forms the oil passage  130  between the baffle plate  110  and itself, and the recessed portion  121  in the oil passage forming member  120  is recessed in the opposite direction to the protruding direction of the welding portion  124 . 
     With this structure, even if the area of the portion to be laser-welded is reduced, it is possible to secure both of the sealing performance of the oil passage  130  and the joint strength between the baffle plate  110  and the oil passage forming member  120 . 
     Although the embodiment of the invention has been described above, the invention is not restricted to the above-described structure and can be changed in various ways without departing from the scope of the invention described in the claims. 
     For example, though the joined body is formed by joining the baffle plate  110  and the oil passage forming member  120  to each other to form the oil passage  130  through which the lubricant flows between them in the embodiment, the invention is not restricted to it. The joined body may be formed by joining synthetic resin parts other than the baffle plate  110  and the oil passage forming member  120  and a flow passage through which fluid other than the lubricant flows may be formed between the synthetic resin parts. 
     Although the sealing portion  140  is formed by laser-welding the baffle plate  110  and the welding portion  124  of the oil passage forming member  120  to each other, the invention is not restricted to it. As the welding method of forming the sealing portion  140 , it is possible to employ ultrasonic welding, vibration welding, hot plate welding, or the like, besides the laser welding. 
     Although the joint portions  150  are formed by heat staking of the protruding portions  111  of the baffle plate  110  to the oil passage forming member  120 , the invention is not restricted to it. As the method of forming the joint portions  150 , it is possible to employ any method by which the baffle plate  110  and the oil passage forming member  120  can be joined to each other. For example, the protruding portions  111  may be snaps (structures each of which can be inserted through a through hole  125  by being elastically deformed and can be staked to an oil passage forming member  120  by being restored to its original shape). As the method of forming the joint portions  150 , it is possible to employ other staking methods such as rivet staking. 
     Although the protruding portions  111  are formed on the baffle plate  110  and the through holes  125  are formed in the oil passage forming member  120  in the joint portions  150 , the invention is not restricted to it. For example, protruding portions may be formed on an oil passage forming member  120  and through holes may be formed in a baffle plate  110  in joint portions  150 . 
     Although the recessed portion  121  is formed in the oil passage forming member  120  and the recessed portion  121  and the oil passage forming face  112  of the baffle plate  110  are laid over each other to form the oil passage  130 , the invention is not restricted to it. For example, a recessed portion may be formed in a baffle plate  110  and the recessed portion and one face of an oil passage forming member  120  may be laid over each other to form an oil passage  130 . Alternatively, recessed portions may be formed in both of a baffle plate  110  and an oil passage forming member  120 . 
     The invention can be applied to the synthetic resin joined body formed by welding the synthetic resin parts to each other and the method of manufacturing the same. 
     REFERENCE SIGNS LIST 
       20 : Cylinder head cover 
       110 : Baffle plate (First synthetic resin part) (Transmission-side synthetic resin part) 
       111 : Protruding portion 
       112 : Oil passage forming face (First flow passage forming portion) 
       120 : Oil passage forming member (Second synthetic resin part) (Absorption-side synthetic resin part) 
       121 : Recessed portion (Second flow passage forming portion) 
       124 : Welding portion 
       125 : Through hole 
       130 : Oil passage 
       140 : Sealing portion 
       150 : Joint portion