JP5806583B2 - Overhead cam engine - Google Patents

Description

  The present invention relates to an overhead cam engine (internal combustion engine), and more particularly, to a mounting structure for a cylinder head cover in an overhead cam engine.

  An overhead cam (OHC) engine has a valve mechanism including a cam shaft at the upper part of a cylinder head, and has a structure in which the valve mechanism is covered by a cylinder head cover attached to the cylinder head. The cylinder head cover is generally attached to the cylinder head by a plurality of bolts with an elastic seal member interposed between the head cover mounting flange surface formed along the outer periphery of the cylinder head.

  In addition, as a cylinder head cover mounting structure, a bolt fastening boss portion having a screw hole is formed on the upper portion of the cam cap for rotatably mounting the cam shaft to the cylinder head, and the bolt penetrating the cylinder head cover is a bolt fastening boss portion. It is known that a bolt fastening portion of a cylinder head cover for a cylinder head is set immediately above a cam shaft by being screwed into a screw hole (for example, Patent Document 1).

Japanese Utility Model Publication No. 2-87951

  Since the cylinder head cover has a bat shape that is inverted upside down, the ceiling wall tends to cause membrane vibration. This becomes conspicuous when the cylinder head cover is made thinner or made of synthetic resin, and causes the NVH characteristics to deteriorate.

  A cylinder head cover bolt fastening portion set directly on the camshaft with respect to the cylinder head has an effect of suppressing membrane vibration of the upper wall portion of the cylinder head cover. The suppression of the membrane vibration by the bolt fastening portion is most effective when the membrane vibration amplitude (primary vibration amplitude) is maximized, but the cylinder head cover membrane vibration amplitude is directly above the cam shaft. It is not always the maximum. In particular, in a double overhead cam (DOHC) engine in which the camshaft is separately arranged in two rows for the intake valve and the exhaust valve, the portion where the amplitude of the primary vibration of the cylinder head cover is maximum is the portion directly above the camshaft. And in the central region of the head cover width direction between the intake valve cam shaft and the exhaust valve cam shaft (a direction orthogonal to the cylinder arrangement direction in plan view), the cylinder head cover with respect to the cylinder head is directly above the cam shaft. In the case where the bolt fastening portion is set, the membrane vibration of the cylinder head cover cannot be effectively reduced.

  In addition, in a three-cylinder or two-cylinder small engine, the problem of vibration is particularly great. The sealing performance of the cylinder head itself, the insertion portion of the ignition plug or fuel injection valve that passes through the cylinder head cover and is installed inside the engine The sealing performance of is strict.

  The problem to be solved by the present invention is that even in an engine where the amplitude of the membrane vibration of the cylinder head cover is not directly above the camshaft, the membrane vibration of the cylinder head cover can be reduced by appropriately setting the bolt fastening portion of the cylinder head cover with respect to the cylinder head. It is to reduce effectively.

  In the overhead cam engine according to the present invention, the cam shafts (36, 42) of the valve operating mechanism are halved and the bearings (10H, 10J) are formed on the cylinder head (10), and the cylinder head (10) is bolted. The head cover mounting flange surface (10L) formed along the outline of the cylinder head (10) is rotatably supported by the half-shaped cam cap (32, 38, 90) fixed by the seal member (70). The cylinder head cover (68) is attached to the cam cap (90) with a cylinder head cover (68) sandwiched between the cam cap (90) and an arm portion (92) extending laterally from the cam cap (90). A screw hole (92B) is formed at the tip of the arm portion (92), and the cylinder head cover -(68) has a bolt through hole (68D) formed at a position corresponding to the screw hole (92B), and a headed bolt passed through the bolt through hole (68D) from the outside of the cylinder head cover (68). (94) is screw-engaged with the screw hole (92B) of the arm portion (92).

  According to this configuration, the fixing position of the cylinder head cover (68) by the headed bolt (94) is the arrangement position of the screw hole (92B) at the tip of the arm portion (92), that is, the extension of the arm portion (92). The position of the cylinder head cover (68) is fixed to the position of the cylinder head cover (68) without interfering with the members arranged in the valve operating chamber (86) such as the valve operating mechanism. It can be provided at a site where the amplitude of the membrane vibration increases.

  In an overhead cam engine according to the present invention, as one embodiment, the cam shafts (36, 42) are individually arranged in two rows for an intake valve and an exhaust valve, and the arm portion (92) is an intake valve. It is formed integrally with the cam cap (90) of at least one of the cam shafts (36, 42) for the valve and the exhaust valve and extends toward the other cam shaft.

  According to this configuration, the fixing position of the cylinder head cover (68) by the headed bolt (94) is set at an intermediate portion between the cam shafts for the intake valve and the exhaust valve, and the fixing position is set to the cylinder head cover (68). It can be provided at a site where the amplitude of the membrane vibration (the amplitude of the primary vibration) increases.

  According to an overhead cam engine of the present invention, as an embodiment, the camshafts (36, 42) are individually arranged in two rows for an intake valve and an exhaust valve, and for the intake valve and the exhaust valve. A valve opening / closing timing variable setting device (60) for variably setting the valve opening / closing timing with respect to the crank angle is connected to only one of the camshafts, and the arm portion (92) is connected to the valve opening / closing timing variable setting device (60). It is integrally formed with the cam cap (90) of the cam shaft that is not connected.

  According to this configuration, vibration due to the operation of the variable valve opening / closing timing setting device (60) is not transmitted to the cylinder head cover (68) via the fixing portion of the cylinder head cover (68) by the headed bolt (94).

  In the overhead cam engine according to the present invention, the cylinder head (10) is integrally formed with a cylindrical portion (30) defining an insertion hole (28) for a spark plug or a fuel injection valve, and the arm portion (92). ) Extends toward the vicinity of the tubular portion (30).

  According to this configuration, the fixing portion of the cylinder head cover (68) by the bolt (94) using the arm portion (92) does not hinder the layout of the spark plug or the fuel injection valve.

  In the overhead cam engine according to the present invention, preferably, the arm portion (92) is in a valve operating chamber (86) defined by the cylinder head (10) and the cylinder head cover (68), and the cylinder head ( 10) No contact with the wall surface.

  According to this configuration, direct vibration transmission is not performed between the arm portion (92) and the cylinder head (10), and the cylinder head cover (68) by the bolt (94) using the arm portion (92). ) Does not interfere with a member disposed in the valve operating chamber (86) such as a valve operating mechanism.

  In the overhead cam engine according to the present invention, preferably, the cam cap (90) is placed on both sides of a half-shaped portion (90A) supporting the cam shaft (42), and the cam cap (90) is placed on the cylinder head (10). And a bolt fastening boss portion (90B) formed with a bolt through hole (90C) into which a bolt (40) for fixing to the bolt is inserted, and the arm portion (92) is provided on one side of the bolt fastening boss. It extends in the horizontal direction from the part (90B).

  According to this configuration, the length of the arm portion (92) can be set to the shortest, and the fastening force of the cylinder head cover (68) is sufficient even if the arm portion (92) is not formed thick in order to increase rigidity. It becomes possible to catch it.

  The overhead cam engine according to the present invention is preferably a tubular distance member in which the head bolt (94) is inserted between the head of the head bolt (94) and the arm portion (92). (98) is provided.

  According to this configuration, the maximum screw-in amount of the headed bolt (94) is defined by the distance member (98), and it is possible to avoid a dent in the cylinder head cover (68) due to excessive tightening.

  According to the overhead cam engine of the present invention, the fixing position of the cylinder head cover by the headed bolt is determined with a high degree of freedom by the extending direction and length of the arm portion, and is disposed in the valve operating chamber such as the valve operating mechanism. Without interfering with the member, the fixing position of the cylinder head cover can be provided at a portion where the amplitude of the membrane vibration of the cylinder head cover is increased.

1 is a plan view of a cylinder head of one embodiment of an overhead cam engine according to the present invention. Longitudinal sectional view of the overhead cam engine according to the present embodiment (cross sectional view taken along line II-II in FIG. 1) The expansion perspective view of the special cam cap used for the overhead cam engine by this embodiment.

  Hereinafter, an embodiment of an overhead cam engine according to the present invention will be described with reference to FIGS. The overhead cam engine according to this embodiment is a spark ignition engine (gasoline engine), which is a three-cylinder double overhead cam engine. In the following description, horizontal and vertical (up and down) are directions for convenience in the case of an engine arrangement in which the cylinder axis X of the engine is vertical as shown in FIG. The cylinder arrangement direction may be referred to as the front-rear direction, and the direction orthogonal to the cylinder arrangement direction may be referred to as the width direction or the left-right direction.

  The cylinder head 10 is made of a light alloy and is attached to a cylinder block (not shown) so as to close a top dead center side of a combustion chamber (not shown), and has a combustion chamber ceiling wall portion 10A on the lower side. The cylinder head 10 has an intake passage 12 that communicates with an intake port (not shown) on one side (left side in FIG. 1) when viewed from a plane orthogonal to the cylinder arrangement direction. On the right side), exhaust passages 14 communicating with exhaust ports (not shown) are provided for each of the number of cylinders.

  An intake valve 16 that opens and closes an intake port (not shown) and an exhaust valve 18 that opens and closes an exhaust port (not shown) are attached to the cylinder head 10, two for each cylinder. The intake valve 16 is a compression coil attached between a spring retainer 20 attached to the tip of the valve stem of the intake valve 16 and an upper wall portion 10B formed above the combustion chamber ceiling wall portion 10A of the cylinder head 10. The spring 22 is biased in the valve closing direction. The exhaust valve 18 is urged in the valve closing direction by a compression coil spring 26 attached between a spring retainer 24 attached to the tip of the valve stem of the exhaust valve 18 and the upper wall portion 10B of the cylinder head 10. .

  A cylindrical portion that protrudes upward in the form of penetrating the upper wall portion 10B from the combustion chamber ceiling wall portion 10A of the cylinder head 10 and defines a spark plug insertion hole 28 on the inner side at the center portion in the width direction of the cylinder head 10. 30 are integrally formed at a predetermined interval in the cylinder arrangement direction by the number of cylinders.

  Between the left outer wall portion of the cylindrical portion 30 of each cylinder and the left wall 10C of the cylinder head 10, an intake side standing wall 10D that connects them is integrally formed perpendicular to the upper wall portion 10B. Further, an exhaust side standing wall 10F that connects the right outer wall portion of the cylindrical portion 30 of each cylinder and the right wall 10E of the cylinder head 10 is integrally formed perpendicular to the upper wall portion 10B. The intake side standing wall 10D and the exhaust side standing wall 10F are in each cylinder and are in a straight line in the left-right direction with the cylindrical portion 30 interposed therebetween. The intake side standing wall 10D and the exhaust side standing wall 10F are formed with an oil circulation opening 10G penetrating in the cylinder arrangement direction for returning the oil accumulated in the cylinder head 10 to the oil pan.

  The upper end portion of the front wall 10K of the cylinder head 10 and the upper end portion of the intake side standing wall 10D are formed by a half-shaped bearing portion 10H, that is, a semicircular recess opened on the upper surfaces of the front wall 10K and the intake side standing wall 10D. A bearing portion 10H is formed. A halved cam cap 32 is fixed to the upper surface of the front wall 10K and the upper surface of the intake side standing wall 10D by a bolt 34 with a hexagon head. The cam cap 32 has a bearing portion 32 </ b> A formed by a semicircular recess opened on the lower bottom surface, and supports the intake valve cam shaft 36 in a rotatable manner in cooperation with the bearing portion 10 </ b> H of the cylinder head 10.

  The upper end portion of the front wall 10K of the cylinder head 10 and the upper end portion of the exhaust side standing wall 10F are formed by a half-shaped bearing portion 10J, that is, a semicircular recess opened on the top surfaces of the front wall 10K and the exhaust side standing wall 10F. A bearing portion 10J is formed. A half-shaped light alloy cam cap 38 is fixed to the upper surface of the front wall 10K and the upper surface of the exhaust side standing wall 10F by a bolt 40 with a hexagon head. The cam cap 38 has a bearing portion 38 </ b> A that is a semicircular recess opened on the lower bottom surface, and supports the exhaust valve cam shaft 42 in cooperation with the bearing portion 10 </ b> J of the cylinder head 10.

  One of the plurality of cam caps (38) that support the exhaust valve cam shaft 42 is a special cam cap, which will be described later, indicated by reference numeral 90. The other cam caps 32 and 38 are the same parts made of a light alloy, and each has an arch-shaped portion that forms a bearing portion 32A and 38A by a semi-circular concave portion upside down. Bolt fastening boss portions 32B and 38B formed integrally through bolt through holes (not shown) into which the bolts 34 and 40 are inserted are provided on both sides.

  The intake valve cam shaft 36 and the exhaust valve cam shaft 42 are arranged in two rows at the same height and parallel to each other along the cylinder arrangement direction. The intake valve cam shaft 36 has a cam-shaped portion 36 </ b> A for opening and closing the intake valve 16 for each intake valve 16. The exhaust valve cam shaft 42 has a cam-shaped portion 42 </ b> A for opening and closing the exhaust valve 18 for each exhaust valve 18.

  On the intake valve cam shaft 36 side of the cylinder head 10, an intake side swing arm 46 having one end abutting against a fulcrum member 44 fixed to the cylinder head 10 and the other end abutting against the stem tip of the intake valve 16 is provided for each intake. Each valve 16 is arranged. The intake side swing arm 46 rotatably supports a cam follower roller 50 by a shaft 48 at an intermediate portion. The cam follower roller 50 is in contact with the outer peripheral surface of the corresponding cam-shaped portion 36 </ b> A of the intake valve cam shaft 36.

  On the exhaust valve cam shaft 42 side of the cylinder head 10, there are exhaust side swing arms 54 with one end abutting against a fulcrum member 52 fixed to the cylinder head 10 and the other end abutting against the stem tip of the exhaust valve 18. Each exhaust valve 18 is arranged. The exhaust-side swing arm 54 rotatably supports a cam follower roller 58 by a shaft 56 at an intermediate portion. The cam follower roller 58 is in contact with the outer peripheral surface of the corresponding cam-shaped portion 42 </ b> A of the exhaust valve cam shaft 42.

  In this way, a swing arm type DOHC valve operating mechanism is configured, and the intake valve 16 of each cylinder is opened and closed by the rotation of the intake valve cam shaft 36, and the exhaust valve 18 of each cylinder is rotated by the rotation of the exhaust valve cam shaft 42. Opens and closes.

  The front end portion of the intake valve cam shaft 36 is connected to a cam drive sprocket (not shown) via a valve opening / closing timing variable setting device (VTC) 60 in a torque transmission relationship. A cam drive sprocket (not shown) is fixed to the front end of the exhaust valve cam shaft 42. A cam drive sprocket (not shown) of the intake valve camshaft 36, a cam drive sprocket (not shown) of the exhaust valve camshaft 42, and a crankshaft sprocket (not shown) fixed to the crankshaft (not shown). One endless chain 62 is stretched over. As a result, the cam drive sprockets of the intake valve camshaft 36 and the exhaust valve camshaft 42 are simultaneously driven by the crankshaft.

  The VTC 60 may be a known hydraulic type, and quantitatively sets the valve opening / closing timing (advance angle / retard angle) with respect to the crank angle. Of the cam caps 32 of the intake valve cam shaft 36, the cam cap 32 that is closest to the VTC 60, that is, the cam cap 32 at the foremost end when viewed in the axial direction of the intake valve cam shaft 36 is relative to the VTC 60. An oil passage (not shown) for supplying and discharging hydraulic pressure is formed on the inner side and has a wide width.

  A chain case mounting portion 64 is integrally formed at the front portion of the cylinder head 10. A chain case 66 made of synthetic resin is shown on the front part of the chain case mounting part 64 with a liquid seal (not shown) interposed therebetween so as to cover the front side, the bottom part, and the left and right sides of the arrangement part of the VTC 60 and the endless chain 62. It is attached by flange surface joining with a plurality of bolts (not shown).

  A head cover mounting flange surface 10 </ b> L is formed on the cylinder head 10 along the outline of the cylinder head 10. In this embodiment, the left side wall 10C, the right side wall 10E, the rear wall 10M, and the upper surface of the chain case mounting portion 64 of the cylinder head 10 are at the same height, and the upper surface of the chain case 66 that is open upward is the chain case mounting portion 64. The bearing portions 10H and 10J of the cam shafts 36 and 42 are formed on the front wall 10K, and the cam caps 32 and 38 are attached to the upper surface of the chain case mounting portion 64. Therefore, the left side wall 10C, the right side wall 10E, the rear wall 10M, the chain case mounting portion 64, and the upper surface of the chain case 66 form a continuous loop-shaped (substantially rectangular frame-shaped) head cover mounting flange surface 10L.

  A cylinder head cover 68 made of synthetic resin is airtightly attached to the head cover attachment flange surface 10L with an elastic seal member 70 made of a rubber-like elastic body interposed therebetween. The cylinder head cover 68 has a shallow pad shape that is inverted upside down. The cylinder head cover 68 is continuously present on the upper part of the cylinder head 10 and the upper part of the chain case 66, and includes a valve mechanism including cam shafts 36 and 42, a VTC 60, and an endless type. The chain 62 covers the upper side of the arrangement portion in a lump. Although not shown, the cylinder head cover 68 is integrally formed with a cylindrical portion that defines an access hole that communicates with each spark plug insertion hole 28 and is suspended from the ceiling wall portion 68A. The lower end surface of the cylindrical portion faces the upper end surface of the cylindrical portion 30, and an elastic seal member 72 (see FIG. 2) made of a rubber-like elastic body is sandwiched between both end surfaces.

  Note that the sealing surfaces of the cylinder head 10 and the chain case 66 and the cylinder head cover 68 by the elastic seal members 70 and 72 are shaded in FIG.

  Next, a structure for attaching the cylinder head cover 68 to the cylinder head 10 will be described.

  A plurality of screw bosses 74 are integrally formed on the left side wall 10C, the right side wall 10E, and the rear wall 10M of the cylinder head 10. A plurality of screwing boss portions 76 are also integrally formed on the upper portion of the front wall portion 66 </ b> A of the chain case 66. Screw holes 78 and 80 are formed in the screwing boss portions 74 and 76 so as to penetrate them vertically.

  A bolt fastening boss portion 82 is integrally formed at a position corresponding to the top and bottom of each of the screwing boss portions 74 and 76 at the lower portion of the outer peripheral portion of the cylinder head cover 68. Bolt through holes (not shown) are vertically formed through the bolt fastening boss portion 82.

  The cylinder head cover 68 is configured such that a hexagon headed bolt 84 passed through a bolt through hole (not shown) of the bolt fastening boss portion 82 is screw-engaged with the screw holes 78 and 80 of the screwing boss portions 74 and 76. A valve operating chamber 86 is defined which is detachably fixed to the cylinder head 10 and the upper part of the chain case 66 and accommodates the valve operating mechanism described above in cooperation with the cylinder head 10.

  As shown in FIG. 3, the special cam cap 90 for supporting the exhaust valve camshaft 42 is the same part made of light alloy, and is a bearing with a semicircular recess that is inverted upside down. An arch-shaped portion that forms the portion 90A and a bolt fastening boss portion 90B that is formed through the bolt through-hole 90C into which the bolt 40 is inserted on both sides of the bearing portion 90A are integrally provided. As with the other cam caps 38, the cam cap 90 is fixed to the upper surface of the exhaust side standing wall 10F by a bolt 40 passed through the bolt through hole 90C and cooperates with the bearing portion 10J of the cylinder head 10 for the exhaust valve. The cam shaft 42 is rotatably supported.

  Further, the cam cap 90 is integrally formed with an arm portion 92 extending laterally from the side outer wall of the one bolt fastening boss portion 90B. The arm portion 92 is a cantilever whose base end is connected to one bolt fastening boss portion 90B, and extends from one bolt fastening boss portion 90B in a direction away from the other bolt fastening boss portion 90B. The arm portion 92 integrally has a pot-shaped screwing boss portion 92A at the tip. A screw hole 92B opened on the upper surface of the screwing boss 92A is formed in the screwing boss 92A.

  In a state in which the cam cap 90 is fixed to the cylinder head 10, the arm portion 92 is connected to the intake valve cam shaft from the bolt fastening boss portion 90B on the intake valve cam shaft 36 side (left side in FIGS. 1 and 2). Toward the center of the cylinder head 10, that is, horizontally extending obliquely forward toward the center side in the width direction of the cylinder head 10, and is in the valve operating chamber 86 and is not in contact with the inner wall surfaces of the cylinder head 10 and the cylinder head cover 68. Therefore, it exists as if it floated in the valve operating chamber 86.

  The cam cap 90 is applied to a cam cap attached in the center of the cylinder arrangement direction, in the case of a three-cylinder engine, in the vicinity of the second cylinder, and the arm 92 is a spark plug insertion hole 28 for the second cylinder. It extends toward the vicinity of the outer wall of the cylindrical portion 30.

  A cylindrical bolt fastening boss portion 68C is integrally formed in a form that hangs down from the ceiling wall portion 68A at a portion where the ceiling wall portion 68A of the cylinder head cover 68 is located immediately above the screwing boss portion 92A of the arm portion 92. Yes. The bolt fastening boss portion 68C is formed with a bolt through hole 68D that penetrates the bolt fastening boss portion 68C in the axial direction (vertical direction). A bolt 94 with a hexagon head is passed through the bolt through hole 68D from the outside (external) of the cylinder head cover 68, and the bolt 94 is screwed into a screw hole 92B at the tip of the arm portion 92.

  An elastic seal member 96 made of a rubber-like elastic body is sandwiched between the lower end surface of the bolt fastening boss portion 68C and the upper surface of the screwing boss portion 92A. Between the bottom surface of the head of the bolt 94 and the top surface of the screwing boss portion 92A, a cylindrical distance member 98 inserted into the bolt through hole 68D and passed through the bolt 94 is provided. The distance member 98 defines the maximum screwing amount of the bolt 94 into the screw hole 92B, and prevents excessive dents in the bolt fastening boss portion 68C portion of the ceiling wall portion 68A and excessive initial deformation of the elastic seal member 96.

  Due to the mounting structure described above, the cylinder head cover 68 is fixed to the cylinder head 10 and the chain case 66 at a plurality of locations on the outer peripheral edge by a plurality of bolts 84, and in addition to the front, rear, left and right of the ceiling wall 68A by the bolts 94. A substantially central portion is fixed to the cylinder head 10. Thereby, the mounting strength and rigidity of the cylinder head cover 68, particularly the ceiling wall portion 68A, with respect to the cylinder head 10 are increased, and the ceiling wall portion 68A is difficult to be deformed and vibrated.

  Thus, the cylinder head cover 68 is less likely to vibrate, so that the sealing performance between the cylinder head 10 and the cylinder head cover 68 by the elastic seal member 70 is good even in a three-cylinder or two-cylinder small engine that easily generates vibration. This improves the reliability of the sealing performance.

  The fixing position of the cylinder head cover 68 by the bolt 94 is determined with a high degree of freedom by the arrangement position (position of the screw hole 92B) of the screwing boss portion 92A of the arm portion 92, that is, the extending direction and length of the arm portion 92, With these optimum settings, the fixed position of the cylinder head cover 68 is fixed to the ceiling within a range that does not interfere with the members arranged in the valve operating chamber 86 such as the valve operating mechanism and does not contact the inner wall surfaces of the cylinder head 10 and the cylinder head cover 68. The wall 68A can be provided at a portion where the amplitude of the membrane vibration (the amplitude of the primary vibration) is increased.

  Thereby, even in an engine in which the portion where the amplitude of the membrane vibration of the cylinder head cover 68 increases is not directly above the cam shaft, the membrane vibration (resonance) of the cylinder head cover 68 is effectively reduced without complicating the configuration of the cylinder head 10. be able to. Note that the fixing portion of the cylinder head cover 68 by the bolt 94 using the arm portion 92 is set at a portion that avoids both the primary vibration and the secondary vibration of the cylinder head cover 68, and both the primary vibration and the secondary vibration are set. Can also be reduced.

  Further, the fixing portion of the cylinder head cover 68 by the bolt 94 using the arm portion 92 is not set by the bolt mounting seat portion protruding from the upper wall portion 10B of the cylinder head 10, so that only the weight of the arm portion 92 is increased. It is possible to effectively prevent the resonance of the cylinder head cover 68 without minimizing the increase in weight, making it lightweight and compact, and without impeding the layout of the members arranged in the valve operating chamber 86, such as the valve operating mechanism. it can. Since the arm portion 92 is in the valve operating chamber 86 and is not in contact with the wall surface of the cylinder head 10, direct vibration transmission is not performed between the arm portion 92 and the cylinder head 10, so The fixing portion of the cylinder head cover 68 by the bolt 94 using the above does not interfere with a member disposed in the valve operating chamber 86 such as a valve operating mechanism.

  The upper surface of the screwing boss portion 92A is preferably positioned below the uppermost surface of the cam cap 90 when viewed in the cylinder axial direction (up and down direction), and this setting does not affect the engine height in the cylinder axial direction. In addition, fastening with the bolt 94 can be performed at a position close to the mounting surface of the cylinder head cover 68 with respect to the cylinder head 10, and vibration prevention becomes more effective. Further, since the arm portion 92 extends from the bolt fastening boss portion 90B of the cam cap 90, the arm length can be set to the shortest, and the fastening force of the cylinder head cover 68 can be set without increasing the thickness to increase rigidity. Can be received sufficiently.

  Further, since the fixing portion of the cylinder head cover 68 by the bolt 94 using the arm portion 92 is in the vicinity of the outer wall of the cylindrical portion 30, the layout of the spark plug is not hindered, and the upper end of the cylindrical portion 30 is not disturbed. An effect of appropriately setting the seal pressure (compression amount) applied to the elastic seal member 72 is also obtained. Thereby, even in a small engine having a large problem of vibration, the sealing performance of the spark plug insertion hole 28 can be improved with a simple structure, and the reliability of the sealing performance can be improved.

  Further, the cam cap 90 with the arm portion 92 has a cam shaft on the side where the VTC 60 is not attached, the main shaft so that vibration due to the operation of the VTC 60 is not transmitted to the cylinder head cover 68 via the fixing portion of the cylinder head cover 68 by the bolt 94. In the embodiment, it is applied to the cam cap of the exhaust valve cam shaft 42. In an engine without a VTC 60, the valve opening (valve lift amount) is basically smaller on the exhaust side than on the intake side. Therefore, avoiding interference with valve system parts, use the arm portion 92 at a lower position. The cam cap 90 with the arm portion 92 is preferably applied to the cam cap of the exhaust valve cam shaft 42 in forming the fixing portion of the cylinder head cover 68 by the bolt 94.

  Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to such embodiments so that those skilled in the art can easily understand, and departs from the spirit of the present invention. It is possible to change appropriately within the range not to be.

  For example, the present invention can be applied to a single overhead cam engine that uses a common camshaft for the intake valve 16 and the exhaust valve 18, and the number of cylinders may be limited to three or a spark ignition type gasoline engine. If it is an overhead cam type, it can also be applied to a diesel engine. In the case of a diesel engine, the spark plug insertion hole 28 formed by the cylindrical portion 30 is an insertion hole for a fuel injection valve for direct injection.

  The valve operating mechanism is not limited to a swing arm type, but may be a rocker arm type or a direct drive type. The cylinder head cover 68 is not limited to the one made of synthetic resin, but may be one made of light alloy die cast. Further, the number of cam caps 90 having the arm portions 92 is not limited to one, and a plurality of cam caps 90 may be provided according to the number of cylinders and the like.

  In addition, all the components shown in the above embodiment are not necessarily essential, and can be appropriately selected without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 10 Cylinder head 10H Bearing part 10J Bearing part 10L Head cover mounting flange surface 16 Intake valve 18 Exhaust valve 28 Spark plug insertion hole 30 Cylindrical part 32 Cam cap 34 Bolt 36 Intake valve cam shaft 38 Cam cap 40 Bolt 42 Exhaust valve cam Shaft 46 Intake side swing arm 54 Exhaust side swing arm 56 Shaft 58 Cam follower roller 60 Valve open / close timing variable setting device (VTC)
66 Chain case 68 Cylinder head cover 68D Bolt through hole 70 Elastic seal member 86 Valve valve chamber 90 Cam cap 90A Bearing portion 90B Bolt fastening boss portion 90C Bolt through hole 92 Arm member 92 Arm portion 92A Boss portion 92B Screw hole 94 Bolt 98 Distance member

Claims (5)

The camshafts of the valve mechanism are individually arranged in two rows for the intake valve and the exhaust valve, and the valve opening / closing timing relative to the crank angle is variably set only on one of the intake and exhaust valve camshafts A variable valve opening / closing timing setting device is connected,
A head cover mounting flange which is rotatably supported by a half-shaped bearing portion formed on the cylinder head and a half-shaped cam cap fixed to the cylinder head by bolt fastening, and formed along the outer periphery of the cylinder head An overhead cam engine in which a cylinder head cover is attached by bolt fastening with a seal member sandwiched between surfaces,
The cam cap of the cam shaft not connected to the valve opening / closing timing variable setting device is inserted with bolts for fixing the cam cap to the cylinder head on both sides of the half-shaped portion supporting the cam shaft. A bolt fastening boss part formed with a bolt through hole to be integrated, and the cam cap of the cam shaft not connected to the valve opening / closing timing variable setting device has a base end of the half-shaped part. An arm part , which is a cantilever beam connected to one of the bolt fastening boss parts on both sides and extends in a direction away from the other bolt fastening boss part on the both sides, is integrally formed, A screw hole is formed in a tip portion of the portion, and a bolt through hole is formed in the cylinder head cover at a position corresponding to the screw hole. Overhead cam engine of the outside from the bolt through headed bolt passed through the hole is threaded engaged into the threaded hole of the arm portion. Before SL arm portion according to claim 1 which extends toward the side of the camshaft other it is integrally formed on at least one of the cam cap of the cam shaft for exhaust valves and intake valves overhead cam engine of. The tubular portion defining an insertion hole of the spark plug or the fuel injection valve in the cylinder head are integrally formed, the arm portion according to claim 1 or 2 extends toward the vicinity of the tubular portion The overhead cam engine. The overhead cam engine according to any one of claims 1 to 3 , wherein the arm portion is in a valve operating chamber defined by the cylinder head and the cylinder head cover and is not in contact with a wall surface of the cylinder head. The overhead cam engine according to any one of claims 1 to 4 , wherein a cylindrical distance member into which the headed fastening bolt is inserted is provided between a head of the headed bolt and the arm portion. .

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