JP2007107431A - Valve gear for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a valve gear for an internal combustion engine, suppressing control dispersion between cylinders of a variable valve train. <P>SOLUTION: In this valve gear, a relationship between widths A1, A2 of a journal portion 20 of a cam shaft 12 and a journal hole portion 21 rotatably holding the journal portion 20 is established so that at least the width of the journal hole portion 21 at its side of receiving load from the journal portion 20 is longer than that of the journal portion 20. Thus, even when the cam shaft 12 is shifted to the axial direction with the operating force of the variable valve train 45, the journal portion 20 is simply displaced in the journal hole portion 21 and a supporting distance between the journal portion 20 supported in the journal hole portion 21 and the cam 17 remains unchanged. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a valve operating apparatus for an internal combustion engine that continuously controls the characteristics of a valve by varying the contact position with a cam.

  In a reciprocating engine (internal combustion engine) valve gear mounted on an automobile, the intake valve (or exhaust valve) characteristics are continuously controlled in order to reduce fuel consumption by measures against engine exhaust gas and improving pumping loss. A variable valve mechanism is incorporated.

Many of such variable valve mechanisms continuously change, for example, the opening / closing timing of the intake valve, the valve opening period, and the valve lift amount as the characteristics of the intake valve from the change of the contact position of the camshaft with the intake cam. (See Patent Document 1).
Japanese Patent Laid-Open No. 5-231116

  By the way, in order to hold the camshaft, a structure in which a journal portion is formed in the camshaft, a journal hole portion is formed in the cylinder head, and the journal portion is rotatably held by the journal hole portion is used. In general, a holding structure is used in which the width dimension (axial length) of the journal hole is longer than the width dimension (axial length) of the journal section (see Patent Document 1).

  On the other hand, the variable valve mechanism is a precision device that continuously controls the valve characteristics in response to cam displacement of the camshaft, so even if the cam position (axial position) of the camshaft changes, the valve characteristics change. There are features. Moreover, due to the movement and tolerance of each part of the variable valve mechanism, the reaction force (load) in the direction of moving the camshaft in the axial direction from the part in contact with the cam during operation (during variable control of valve characteristics) ) May be transmitted.

  Normally, the camshaft is movable in the axial direction in order to allow an assembly error of engine parts. For this reason, in the valve operating apparatus in which the camshaft and the variable valve mechanism are combined, when the reaction force is transmitted to the camshaft from the contact portion of the variable valve mechanism that contacts the cam, the camshaft and the variable valve mechanism move in the axial direction of the camshaft. It tends to appear as a gap.

  However, in the camshaft holding structure, as shown in FIG. 14A, the width A1 of the journal part b is shorter than the journal hole part A2 of the journal holding part f. The deviation appears as a change in the support state of the journal part b as it is. Specifically, the support distance L from the journal part b supported in the journal hole part d shown in FIG. 14 (a) to the cam e formed on the camshaft a is L1 shown in FIG. 14 (b). And L2 (L2 <L <L1).

  When the support distance L changes in this way, the deflection (generated by the load applied at the time of valve lift) at the point where the cam e is uniform changes for each cylinder, Since the clearance between the journal holes changes, the axial center position of the cam e, which is uniform for each cylinder, changes. For this reason, the variable valve mechanism tends to operate while causing control variations between cylinders, which has a problem of affecting engine performance. In addition, in a variable valve mechanism that can reduce the valve lift amount, when the amount of air taken into the engine is controlled by setting the valve lift amount small or shortening the valve open period, If the amount of air varies between cylinders, the air-fuel ratio varies, a difference appears in the combustion state, and it is easily affected by deterioration of exhaust gas, vibration, and the like.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a valve operating apparatus for an internal combustion engine that can suppress control variation among cylinders of a variable valve operating mechanism.

  In order to achieve the above object, according to the first aspect of the present invention, the relationship between the width dimension of the journal portion formed on the camshaft and the journal hole portion that rotatably holds the journal portion is at least the journal hole. The width dimension of the part receiving the load from the journal part was set to be longer than the width dimension of the journal part.

  With this configuration, even if the camshaft is displaced in the axial direction due to a reaction force (load) caused by the operation of the variable valve mechanism, the journal portion is simply displaced within the journal hole portion. Since the support distance from the supported journal portion to the cam is not changed, the control variation is eliminated.

    The invention according to claim 2 uses a configuration in which the journal portion is included in the journal hole portion so that the performance of keeping the support distance constant is sufficiently exhibited.

  In the invention according to claim 3, the camshaft has an intake cam arranged in the center between the journal portions, and an exhaust cam is provided on both sides of the intake cam so that the effect is exhibited in the SOHC type valve gear. The cam has a symmetrical arrangement, the valve has an intake valve driven by an intake cam and an exhaust valve driven by an exhaust cam, and the variable valve mechanism has an intake cam In response, the intake valve characteristics are continuously controlled.

  The invention according to claim 4 further provides an exhaust cam on both sides sandwiching the intake cam so that the behavior when the exhaust valve is driven in the SOHC type valve gear does not affect the intake cam that is continuously variable controlled. Used the same cam profile at least near the valve closure.

  According to a fifth aspect of the present invention, the variable valve mechanism is provided in the internal combustion engine so as to be swingable. The swing valve drives the intake valve or the exhaust valve. The variable valve mechanism receives the cam and swings so that the displacement of the cam can be changed. The structure provided with the transmission member which transmits to a moving cam was employ | adopted.

    According to the first and second aspects of the present invention, the support distance from the journal portion supported in the journal hole portion to the cam is not affected by the axial displacement of the camshaft caused by the variable valve mechanism. Can be kept constant.

  Therefore, it is possible to suppress variation among the cylinders of the variable valve mechanism due to the axial displacement of the camshaft by the variable valve mechanism. As a result, engine performance can be enhanced. In particular, when the journal part is included in the journal hole part, it is possible to sufficiently exhibit the performance of keeping the support distance constant.

According to the third aspect of the present invention, in the SOHC type internal combustion engine, it is possible to obtain the performance of keeping the support distance from the journal portion to the intake cam constant. Moreover, not only the load applied when lifting the intake valve is evenly applied between the journal portions, but also the load applied when lifting the exhaust valve is equally applied. Control variation can be suppressed.

  According to the fourth aspect of the present invention, it is possible to suppress variations among the cylinders due to the movement and deflection of the camshaft due to the load received by the exhaust cam, and to suppress variations in the intake air amount.

  According to the fifth aspect of the present invention, the variation in the cam position of the camshaft is suppressed, so that the variation between the cylinders of the variable valve mechanism of the intake valve or the exhaust valve can be suppressed, and the engine performance is improved. be able to.

[First Embodiment]
The present invention will be described below based on the first embodiment shown in FIGS.

  1 is a partial plan view (only two cylinders are shown) of a cylinder head 1 of a multi-cylinder internal combustion engine, for example, an in-line four-cylinder reciprocating gasoline engine, and FIG. 2 is taken along line II-II in FIG. 3 is a sectional view taken along the line III-III in FIG. 1, FIG. 4 is an exploded view of the variable valve mechanism 45, and FIG. 5 is a sectional view taken along the line IV--in FIG. (Only two cylinders are shown), and FIGS. 6 to 9 show the operating states of the variable valve mechanism 45, respectively.

  The cylinder head 1 will be described with reference to FIGS. 1 to 3. On the lower surface of the cylinder head 1, four parallel cylinders 3 formed in the cylinder block 2 (only two cylinders in FIG. 2 are shown by a two-dot chain line). Combustion chambers 4 (shown only in FIG. 2) are formed respectively. Each of these combustion chambers 4 is formed with, for example, two (a pair) intake ports 5 and exhaust ports 6 (shown only in FIGS. 2 and 3). An intake valve 7 that opens and closes the intake port 5 and an exhaust valve 8 that opens and closes the exhaust port 6 are assembled to the top of the cylinder head 1. Both the intake valve 7 and the exhaust valve 8 are normally closed reciprocating valves that are urged in the closing direction by a valve spring 9. A piston 10 is housed in the cylinder 3 so as to be able to reciprocate (only two-dot chain lines in FIG. 2).

  In FIG. 1 to FIG. 5, reference numeral 11 denotes, for example, a SOHC type valve operating system mounted on the upper part of the cylinder head 1 (the one driving the intake valve 7 and the exhaust valve 8 with one camshaft 12: the valve operating apparatus of the present application). Equivalent). The valve train 11 will be described. Reference numeral 12 denotes a camshaft that is rotatably disposed along the longitudinal direction of the cylinder head 1 above the combustion chamber 2, and reference numeral 14 denotes an intake port 5 side (one side) sandwiching the camshaft 12. ) Is pivotably disposed on the intake side rocker shaft (also serves as a control shaft), 15 is an exhaust side rocker shaft disposed on the opposite exhaust port 6 side, and 16 is a rocker shaft 14 and rocker shaft 15. The support shaft arrange | positioned in the upper point (near rocker shaft 15) in between is shown. The rocker shafts 14 and 15 and the support shaft 16 are all arranged in parallel (in parallel) with the camshaft 12.

  The camshaft 12 is a component that is rotationally driven along an arrow direction in FIG. 2 by an output from an engine crankshaft (not shown). As shown in FIGS. 1, 4, and 5, the camshaft 12 includes an intake cam 15 (one corresponding to the intake valve driving cam of the present application) for each combustion chamber 4 (for each cylinder 3). Exhaust cams 18 (two: corresponding to the exhaust valve driving cam of the present application) are formed. One intake cam 17 is arranged in the center of the top of the combustion chamber 4, and the exhaust cams 18, 18 are symmetrically arranged at adjacent points on both sides of the intake cam 17, and the cams have the same overall cam profile. Is used. More specifically, when exhaust cams 18 and 18 having different cam profiles are used, the cam profile around the timing at which the exhaust valve 8 overlaps with the timing at which the intake valve of the intake cam 17 is opened is made the same. A cam is used. That is, the timing at which the intake valve 7 is opened may coincide with the timing at which the exhaust valve 8 is closed, and at this time, the cylinder due to the movement or deflection of the camshaft 12 due to the load applied to the exhaust cam 18 sandwiching the intake cam 17. In order to suppress the variation between the three and the influence on the intake cam 17, a cam having at least the same cam profile in the vicinity of the valve closing is used. The end portions of the cam shaft 12 and the shaft portions disposed between the cylinders (between the combustion chambers) are wall-shaped cams that protrude integrally from the upper surface 1a of the cylinder head 1 as shown in FIGS. The shaft holder 19 is rotatably held. For example, a cam-in head structure is used for the holding structure. For example, as shown in FIG. 4, the holding structure includes the other end of the camshaft 12 and an inter-cylinder portion of the camshaft 12, that is, a cam group (one intake cam 17 and two exhaust cams on both sides thereof. A disc-shaped journal portion 20 having an outer diameter larger than that of the intake cam 17 and the exhaust cam 18 is formed on the shaft portion between the portions 18 and 18), and the remaining one end portion has a journal portion. The journal portion 21a having an outer diameter smaller than 20 is formed, and the circular journal hole portions 21a and 21 for rotatably accommodating the journal portions 20a and 20 are formed in the respective camshaft holding portions 19 so that the camshaft 12 is The camshaft 12 is rotatably held on the cylinder head 1 by the operation of being inserted into the journal holes 21a and 21 from one end. The camshaft 12 is provided with an intake cam 17 (one) in the center between the journal portions 20a, 20 and the journal portions 20, 20, and exhaust cams 18, 18 (two) symmetrically on both sides of the intake cam 17. With the same layout, the load applied during the valve lift is uniformly supported by the camshaft holding portion 19 through the journal portions 20a, 20 and the journal portions 20, 20 on both sides. In order to hold the camshaft 12 at this time, the journal portions 20a and 20 are formed of an iron-based member such as cast iron or cast steel, and the camshaft holding portion 19 is different from the journal portion 20a such as an aluminum member or an aluminum alloy member. , 20 is formed of an aluminum-based member having a thermal expansion coefficient larger than that of the journal portion 20a, 20 and the journal hole portions 21a, 21 to ensure a clearance for bearings. However, although not shown, between the journal portions 20a, 20 and the journal hole portions 21a, 21 is lubricated with lubricating oil. And the cam sprocket 22 is assembled | attached with the bolt member 23 at the camshaft end protruded from the last (insertion direction) camshaft holding | maintenance part 19, for example. The cam sprocket 22 is connected to a crankshaft end via an endless timing member such as a timing belt or a timing chain (not shown), and the camshaft 12 is driven by a crank output transmitted from the timing member. It is like that.

  Among the holding portions 13a to 13c formed by the journal portions 20a and 20 and the journal hole portions 21a and 21, for example, the holding portions 13b and 13c formed by the journal portion 20 and the journal hole portion 21 are devised. . As shown in FIGS. 4 and 5, the device is such that the width dimension (axial length) of the journal portion 20 is “A1”, and the width dimension (axial length) of the journal hole portion 21 is “A2”. In this case, the width dimension A1 of the journal part 20 is shorter than the width dimension A2 of the journal hole part 21 (A1 <A2). Thus, at least the width dimension of the journal hole portion 21 on the side receiving the load from the journal portion 20 is made longer than that of the journal portion 20. This relationship is set by the dimension values of the width dimensions A1 and A2 that allow the axial deviation generated in the camshaft 12 to be allowed. In particular, the journal part 20 is included in the center part of the width dimension A2 of the journal hole part 21, and even if the camshaft 12 is displaced in the axial direction (one direction or the other direction) by the force (load) acting from the outside. The journal 20 is only moved in the journal hole 21. Of course, the same structure may be applied to the holding portion 13a formed by the journal portion 20a and the journal portion 21a.

  The remaining intake-side rocker shaft 14, exhaust-side rocker shaft 15 and support shaft 16 are respectively placed on the upper portion of each camshaft holding portion 19 by, for example, two kinds of holding members 24 and 25 as shown in FIGS. It is supported. The holding member 24 is a part suitable for holding the shaft end, for example, and the holding member 25 is a part suitable for holding the shaft in the middle, for example. Among these, as shown in FIG. 4, the holding member 24 is a component having cap portions 26 and 27 arranged in parallel on the lower side and a columnar receiving portion 28 on the upper side. The ends of the rocker shafts 14 and 15 are fitted to the cap portions 26 and 27 so as to be rotatable. An end of the support shaft 16 is fixed to the receiving portion 28 with a bolt member 30. And the holding member 24 is being fixed to the upper part of the camshaft holding | maintenance part 19 arrange | positioned at the camshaft end using several bolt member 32a, 32b.

  As shown in FIG. 4, the holding member 25 has cylindrical fitting insertion portions 34 and 35 arranged in parallel on the lower side, has a columnar receiving portion 36 on the upper side, and further exhausts the cylinder head 1 on the lower side. A component having an extending portion 37 extending to the port 6 side is used. An intermediate shaft portion between the rocker shafts 14 and 15 is rotatably inserted into the fitting insertion portions 34 and 35. An intermediate shaft portion of the support shaft 16 is fixed to the receiving portion 26 with a bolt member 39. The holding member 25 is fixed to the upper portion of the camshaft holding portion 19 that supports each intermediate portion of the camshaft 12 by using a bolt member 40. The extending portion 37 is fixed to the upper surface portion near the side edge portion of the cylinder head 1 with a bolt member 41, avoiding the periphery of the rocker shaft 14 where it is difficult to secure a fixing space as shown in FIG. It is.

  As shown in FIGS. 1, 3, and 4, an exhaust cam 18 (for each exhaust valve 8) and an exhaust valve rocker arm 43 are rotatably supported on the rocker shaft 15 on the exhaust side. . The intake side rocker shaft 14 incorporates a variable valve mechanism 45 for each intake cam 17 (for each pair of intake valves 7).

  Of these, the rocker arm 43 has a cam contact, for example, a roller member 47 at one end as shown in FIGS. 3 and 4, and a portion for driving the exhaust valve 8 at the other end, for example, an adjust task screw portion. 48. The roller member 47 of the rocker arm 43 is brought into rolling contact with the exhaust cam 18, and the adjuster screw portion 48 faces the upper ends (valve stem ends) of the exhaust valves 8 and 8, respectively. Thus, when the exhaust cam 18 rotates, the rocker arm 43 swings with the rocker shaft 15 as a fulcrum, and the exhaust valves 8 and 8 are driven.

  As shown in FIGS. 2 and 4, the variable valve mechanism 45 includes an intake valve rocker arm 50 that is swingably supported by the rocker shaft 14, and a swing cam 60 (swing cam) that is combined with the rocker arm 50. The center rocker arm 70 (transmission arm) that receives the displacement of the intake cam 17 and transmits the displacement of the cam 17 to the swing cam 60, and the contact position of the center rocker arm 70 with the intake cam 17 can be varied. And a support mechanism 80 for supporting the structure.

  Of these, the rocker arm 50 has a bifurcated structure as shown in FIGS. 1 and 4, for example. Specifically, the rocker arm 50 has a pair of parallel rocker arm pieces in which a cylindrical rocker shaft support boss 51 is formed at the center, and a portion for driving the intake valve 7, for example, an adjusting screw portion 52 is assembled on one end side. 53 and a rotatable roller member 54 (which forms a cam contact) sandwiched between the other end portions of these rocker arm pieces 53. Reference numeral 55 denotes a short shaft for pivotally supporting the roller member 54 between the rocker arm pieces 53. The rocker shaft support bosses 51 and 51 are fitted into the rocker shaft 14 so as to be swingable, and the roller member 54 is disposed on the support shaft 16 side (the center side of the cylinder head 1). The remaining adjustment screw portions 52 are arranged at the upper ends (valve stem ends) of the intake valves 7 and 7, respectively. That is, when the rocker arm 50 swings around the rocker shaft 14 as a fulcrum, the intake valves 7 and 7 are driven.

  As shown in FIGS. 2 and 4, the swing cam 60 has a cylindrical boss portion 61 that is rotatably inserted into the support shaft 16, and from the boss portion 61 toward the roller member 57 (the rocker arm 50). The arm portion 62 is formed to have an extending arm portion 62 and a receiving portion 63 formed below the arm portion 62. Of these, a cam surface that transmits displacement to the rocker arm 50, for example, a cam surface 64 that extends in the vertical direction is formed on the distal end surface of the arm portion 62. The cam surface 64 is in rolling contact with the outer peripheral surface of the roller member 47. For example, as shown in FIG. 4, in the receiving portion 63, a recessed portion 65 is formed in a lower portion of the lower portion of the arm portion 62 that is directly above the camshaft 12, and the camshaft 12 is formed in the recessed portion 65. And a structure in which the short shaft 66 is rotatably supported in the same direction as in FIG. Reference numeral 67 denotes a concave portion having a flat bottom surface formed on the outer peripheral portion of the short shaft 66 portion exposed from the concave portion 65.

  For example, as shown in FIGS. 2 and 4, the center rocker arm 70 includes a rolling contact that rolls in contact with the cam surface of the intake cam 17, for example, a cam follower 71, and a frame-shaped holder that rotatably supports the cam follower 71. An approximately L-shaped member having a portion 72 is used. Specifically, the center rocker arm 70 is centered on the cam follower 71 and passes through the upper rocker shafts 14 and 15 from the upper portion of the holder portion 72 to the support shaft 16 and the holder portion 72. And a fulcrum arm portion 74 extending downward from the shaft portion 14c (shown in FIGS. 6 to 9) of the rocker shaft 14 exposed between the pair of rocker arm pieces 53, and formed in an L shape. It is. The fulcrum arm 74 is divided into, for example, a bifurcated shape. Further, an inclined surface 75 is formed at the tip (upper end surface) of the relay arm 73 as a drive surface so that the rocker shaft 14 side is low and the support shaft 16 side is high. The leading end of the relay arm 73 extends into the recessed portion 65 of the swing cam 60. With this structure, the center rocker arm 70 is interposed between the intake cam 17 and the swing cam 60. The inclined surface 75 of the arm portion 73 is slidably abutted against a receiving surface 67a formed on the bottom surface of the recess 67, and when the intake cam 17 rotates, the cam displacement of the intake cam 17 is relayed. The arm 73 is transmitted to the swing cam 60 with a slip.

  For example, as shown in FIG. 2 and FIG. 4, the support mechanism 80 is configured to be capable of swinging the center rocker arm 70 using a control arm 81 and to adjust the position of the center rocker arm 70. A structure in which the adjustment unit 90 is combined is used. Of these, the support portion 82 will be described. A through hole 83 is formed in the center of the shaft portion 14c in the vertical direction perpendicular to (intersects with) the axis of the shaft portion 11c. The control arm 81 includes a shaft portion 84 having a circular cross section, a disk-like pin coupling piece 85 formed at one end of the coaxial portion 84, and a support hole 85a formed in the pin coupling piece 85 (see FIG. 4 only). (Shown). An end portion of the shaft portion 84 is inserted into the through hole 83 from below the shaft portion 14c. Note that the inserted shaft portion 84 is movable in the axial direction and the circumferential direction. The end of the shaft portion 84 abuts against a component of the adjusting portion 90 described later. The pin coupling piece 85 is inserted into the fulcrum arm portion 74 divided into two forks. A pin 86 is inserted into the arm portion 74 and the support hole 85a, and the fulcrum arm portion 74 is connected to the end portion of the control arm 81 so as to be rotatable in the undulation direction of the intake cam 17. . With this connection, when the intake cam 17 rotates, the center rocker arm 70 is swung (up and down) with the pin 86 as a fulcrum. In conjunction with the movement of the center rocker arm 70, the swing cam 60 has the support shaft 16 as a fulcrum, the short shaft 66 as an action point (a point where a load from the center rocker arm 70 acts), and the cam surface 64 as a force point (rocker arm). The point 50 is driven) so that it is periodically swung. Reference numeral 87 denotes a pusher that compensates the pressing force when the spring force of the valve spring 9 is not acting.

  For example, an output portion (not shown) of a control motor 100 (shown by a two-dot chain line only in FIG. 4) is connected to the end of the rocker shaft 14 as an actuator. By this connection, the rocker shaft 14 is driven (rotated) around the axis. The rotation of the rocker shaft 14 allows the control arm 81 to change from a substantially vertical posture shown in, for example, FIGS. 6 and 7 to a greatly inclined posture shown in, for example, FIGS. 8 and 9. . From the change in the posture of the control arm 81, the center rocker arm 70 can be moved (displaced) in a direction crossing the axial direction of the shaft portion 14c. That is, the cam follower 71 is configured such that the rolling contact position with respect to the intake cam 17 can be changed in the advance direction or the retard direction. By changing the rolling contact position, the posture of the cam surface 64 of the swing cam 60 is changed to control the characteristics of the intake valve 7. Specifically, the opening / closing timing, valve opening period, and valve lift amount of the intake valve 7 are continuously varied at the same time. This variable will be described. For the cam surface 64, for example, a curved surface whose distance from the center of the support shaft 16 changes is used. For example, as shown in FIG. 2, the upper side of the cam surface 64 is formed by a base circle section α that is an arc surface centered on the axis of the support shaft 13. The lower side is formed by a lift section β composed of a plurality of arc surfaces that are continuous with the arc of the base section. That is, the lift section β is a section formed by an arc surface similar to the cam shape of the lift area of the intake cam 18. Thus, when the cam follower 71 is displaced in the advance angle direction or the retard angle direction of the intake cam 17, the swing range of the swing cam 60 is changed so that the region of the cam surface 64 with which the roller member 54 contacts is changed. is there. In other words, the ratio of the base circle section α and the lift section β where the roller member 54 passes is changed while the phase of the intake cam 17 is shifted in the advance direction or the retard direction. The valve opening period and the valve lift amount are continuously varied.

  For example, as shown in FIGS. 2 and 4, the adjusting unit 90 has a structure that supports the inserted control arm end with a screw member 91. For example, a female screw (not shown) is formed on the inner surface of the hole portion (upper portion) opposite to the control arm end of the through hole 83 to form a screw hole, and the screw member 91 advances and retreats into the screw hole from above. It is screwed as possible. Thereby, the end of the control arm 81 abuts with the insertion end of the screw member 91 in the middle of the through hole 83. The control arm 81 is supported by this butting. When the screw member 91 is rotated by this support, the distance between the shaft center of the shaft portion 14c and the tip of the control arm 72, that is, the protrusion amount of the shaft portion 84 protruding from the shaft member 14c is varied, and the intake air amount by the protrusion amount is changed. The opening timing and closing timing of the intake valve 7 are adjusted from the change of the rolling contact position of the cam 17. However, 92 is, for example, a cross-shaped groove formed on the upper end surface of the screw member 91 for rotating the screw member 91, 93 is a lock nut screwed into the end of the screw member 91, and 94 is the same The notch which forms the bearing surface of the lock nut 93 is shown.

  In FIG. 2, reference numeral 95 denotes an ignition plug for igniting the air-fuel mixture in the combustion chamber 4.

  Next, the operation of the valve train 11 will be described with reference to FIGS.

  Now, it is assumed that the camshaft 11 is driven (rotated) by the shaft output of the engine transmitted from the cam sprocket 22 as shown by the arrow direction in FIG.

  At this time, the cam follower 71 of the center rocker arm 70 receives the intake cam 17 and is driven in accordance with the cam profile of the cam 17. As a result, the center rocker arm 70 swings in the vertical direction with the pin 86 as a fulcrum.

  The receiving surface 67 a of the swing cam 60 receives the swinging displacement of the center rocker arm 70 from the inclined surface 75. Here, since the receiving surface 67a and the inclined surface 75 are slidable, the swing cam 60 repeats the swinging motion of being pushed up and lowered by the inclined surface 75 while sliding on the inclined surface 75. As the swing cam 60 swings, the cam surface 64 of the swing cam 60 reciprocates in the vertical direction.

  At this time, since the cam surface 64 is in rolling contact with the roller member 54 of the rocker arm 50, the cam surface 64 periodically presses the roller member 54. In response to this pressing, the rocker arm 50 is driven (swinged) with the rocker shaft 14 as a fulcrum, and opens and closes the intake valve 7 (a pair).

  On the other hand, each rocker arm 43 on the exhaust side receives the exhaust cam 18 and is driven according to the cam profile of the cam 18. Accordingly, each rocker arm 43 swings in the vertical direction with the rocker shaft 15 as a fulcrum, and opens and closes the exhaust valves 8 and 8, respectively.

  Due to the opening / closing operation of the intake valve 7 and the exhaust valves 8 and 8 and the movement (reciprocation) of the piston 10 at this time, the combustion cycle (for example, the intake stroke, the compression stroke, the explosion stroke, the exhaust stroke) in each cylinder 3. 4 cycles).

  Here, it is assumed that the engine is operated at a high speed by stepping on an accelerator pedal (not shown). Then, the motor 100 (actuator) receives the accelerator signal, rotates the rocker shaft 14, and moves the control arm 81 at a point where a high valve lift is secured, for example, as shown in FIGS. 6 and 7. Move (rotate) to the point where the posture is reached. By this high valve lift control, the center rocker arm 70 receives the rotational displacement of the control arm 81 and is displaced along the rotational direction on the intake cam 14. Thus, as shown in FIGS. 6 and 7, the cam surface 64 of the swing cam 60 is positioned in a posture having an angle close to vertical.

  Depending on the posture of the cam surface 64, the region (ratio) where the roller member 54 of the cam surface 64 crosses is determined as a region that causes a high valve lift. For example, the ratio is set such that the shortest base circle section α is the longest lift section β. As a result, for example, the intake valve 7 is driven so as to ensure the maximum valve lift amount, for example, as shown in the diagram of A1 in FIG.

  Further, when the accelerator pedal (not shown) is returned and, for example, the engine is operated at a low speed, the rocker shaft 14 is rotated by the drive of the control motor 100, and the control arm 81 as shown in FIGS. Is displaced in a direction approaching the intake cam 14. Then, the center rocker arm 70 receives the rotation of the control arm 81 and moves on the intake cam 17 forward in the rotational direction. As a result, as shown in FIGS. 8 and 9, the rolling contact position (contact position) between the center rocker arm 70 and the intake cam 17 is shifted in the direction of advance on the intake cam 17. By changing the rolling position, the TOP position of the valve lift curve moves in the advance direction. The inclined surface 75 also slides on the receiving surface 67a in the advance direction in response to the movement of the center rocker arm 70.

  By the movement of the center rocker arm 70, the swing cam 60 changes to a posture in which the cam surface 64 is inclined downward as shown in FIGS. As the inclination increases, the region of the cam surface 64 where the roller members 54 come and go changes to a ratio in which the base circle section α is gradually longer and the lift section β is gradually shortened. As the cam profile of the variable cam surface 64 is transmitted to the roller member 54, the intake valve 7 is driven so that the lift amount is lowered while the entire cam profile is advanced.

  As a result, the opening / closing timing and the valve lift amount of the intake valve 5 are changed from the high rotation operation of the engine to the low rotation according to the movement of the fulcrum position of the center rocker arm 70 as shown in the diagrams A1 to A6 in FIG. Until operation, the valve opening timing is maintained from about the same time as the maximum valve lift, and continuously variable control is performed while the valve closing timing is greatly changed.

  During such continuous variable control, a reaction force F (load) for directing the camshaft 12 in the axial direction is transmitted from each variable valve mechanism 45 to the camshaft 12 (for example, each part of the variable valve mechanism 45). Due to movement and tolerances).

  Since the camshaft 12 is movable in the axial direction, when the force is transmitted, the camshaft 12 is changed from the initial state shown in FIG. 11A, for example, as shown in FIG. Shift to one side in the axial direction (displacement). In the figure, δ indicates the amount of deviation at that time.

  At this time, the width dimension A1 of the journal part 20 is narrower than the width dimension A2 of the journal hole part 21 holding the journal part 20 (at least the width dimension of the journal hole part 21 on the side receiving the load from the journal part 20). Is longer than the journal part 20). For this reason, as shown in FIG. 11B, even if the camshaft 12 is displaced in the axial direction, the journal supported by the journal hole 21 only by the journal 20 being displaced in the journal hole 21. The support distance L from the portion 20 to the intake cam 17 does not change (constant).

  As a result, the clearance between the journal portion 20 and the journal hole portion 21 is maintained uniformly in any of the holding portions 13b and 13c, so that the change in the axial center position of the intake cam 17 is suppressed.

  Therefore, the control variation of the variable valve mechanism 45 between the cylinders caused by the change in the support distance L can be eliminated. As a result, the engine driving performance can be improved, and various performances such as engine output, fuel consumption, and exhaust gas can be improved. In addition, when the journal portion 20 is included in the journal hole portion 21, the effective performance can be sufficiently exhibited.

  In particular, in the case of an SOHC engine, if the intake cam 17 is arranged in the center between the journal portions 20a and 20 and between the journal portions 20 and 20, and the exhaust cams 18 are arranged symmetrically on both sides thereof, the intake valve 17 is lifted. Since the load applied when the exhaust valves 8 and 8 are lifted is not only equally applied between the journal portions 20a and 20 and between the journal portions 20 and 20, but also when the exhaust valves 8 and 8 are lifted, the variable valve mechanism 45 Can be expected to sufficiently suppress the control variation. In addition, for example, as shown by a two-dot chain line X in FIG. 10, the exhaust cams 18, 18 on both sides have at least a cam profile in the vicinity of the valve closing (= portion overlapping with the vicinity of the valve opening of the intake cam 17). If the cams with the same cam are used, even if the exhaust cams 18 and 18 having different cam profiles are used, the load is applied evenly in the vicinity of the valve opening of the important intake cam 17, so that the control variation between the cylinders is reduced. Can be suppressed. In particular, when the exhaust cams 18 and 18 have the same cam profile as in the present embodiment, control variations can be minimized.

[Second Embodiment]
FIG. 12 shows a second embodiment of the present invention.

  In the first embodiment, the cam-in head structure has been described in which the cam shaft 12 is rotatably held by the cam shaft holding portion 19. However, the present invention is not limited thereto, and a cam cap structure as shown in FIG. The present invention may be applied to a structure in which the camshaft 12 is rotatably held.

  That is, the cam cap structure has a semicircular shape formed in the journal camshaft holding portion 113 that forms the journal hole portion 21 around the journal portion 20 formed on the camshaft 12 and having a diameter smaller than the outer diameter of the cam. And a semicircular recess 116 formed in a cam cap 115 attached to the end of the camshaft holding portion 113 and held rotatably. Reference numeral 117 denotes a bolt member that fixes the cam cap 115 to the camshaft holding portion 113.

  Even if a technique for making the width dimension of the journal portion 20 shorter than the width dimension of the journal hole portion 21 is applied to such a cam cap structure as in the first embodiment, the same effect as the first embodiment is achieved. Play.

  However, in FIG. 12, the same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

Note that the present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the present invention is applied to the intake valve. However, the present invention is not limited to this, and the present invention may be applied to an exhaust valve. In the embodiment, an example using a variable valve mechanism including a swing cam and a center rocker arm has been described. However, the present invention is not limited to this, and a variable valve mechanism having another structure may be used. In the above-described embodiment, an SOHC engine is used as an example. However, the present invention may be applied to a DOHC engine using camshafts that are separately provided on the intake side and the exhaust side.

  Further, in the above-described embodiment, the width of the journal portion 20 is longer than the entire width of the journal hole portion 21, but the load applied to the camshaft 12 is unidirectional as in the third embodiment shown in FIG. In this case, the surface 21a in the direction in which the load is applied may be lengthened. That is, the surface 21a on the opposite side (the load receiving side) where the cam abuts against the rocker arm or the like is lengthened, and the side abutting on the rocker arm or the like (side not receiving the load) may be the same as in the prior art (A3 ≦ A1 < A2). In this case, the wall of the camshaft holding portion 113 can be made thin, and the cam cap 115 can be made small, which is effective for weight reduction or compactness.

The top view of the cylinder head carrying the valve gear which concerns on the 1st Embodiment of this invention. Sectional drawing of the variable valve mechanism and cylinder head which follow the II-II line | wire in FIG. FIG. 3 is a cross-sectional view of a cylinder head including an exhaust-side rocker arm along line III to III in FIG. 1. The disassembled perspective view which shows each part of a valve operating apparatus. Sectional drawing which shows the holding structure of the camshaft which follows the IV-line in FIG. Sectional drawing which shows a state when a center rocker arm is contacting the base circle area of the cam surface at the time of the high valve lift control of the valve gear. Sectional drawing which shows a state when the rocker arm is contacting the lift area of a cam surface similarly. Sectional drawing which shows a state when the rocker arm is contacting the base circle area of the cam surface at the time of the low valve lift control of the valve gear. Sectional drawing which shows a state when the rocker arm is contacting the lift area of a cam surface similarly. The diagram which shows the performance of the valve operating apparatus. Sectional drawing for demonstrating a behavior when the camshaft of the valve operating apparatus has shifted in the axial direction. The perspective view which shows the structure used as the principal part of the 2nd Embodiment of this invention. Sectional drawing explaining the principal part of the 3rd Embodiment of this invention. Sectional drawing for demonstrating a behavior when the camshaft shifts | deviates to the axial center direction in the conventional valve gear.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Cylinder head (internal combustion engine), 7 ... Intake valve, 8 ... Exhaust valve, 11 ... Valve-operating system (valve-operated device), 12 ... Cam shaft, 17, 18 ... Intake cam, Exhaust cam (cam), DESCRIPTION OF SYMBOLS 20 ... Journal part, 21 ... Journal hole part, 45 ... Variable valve mechanism, 60 ... Swing cam, 70 ... Center rocker arm, A1 ... Journal part width dimension, A2 ... Journal hole part width dimension.

Claims (5)

A camshaft having a cam and a plurality of journal portions;
A journal hole provided in an internal combustion engine and rotatably holding the journal part;
A valve driven by the cam;
A variable valve mechanism that receives the cam and continuously controls the characteristics of the valve;
A valve operating apparatus for an internal combustion engine, characterized in that at least a width dimension of the journal hole that receives a load from the journal section is set to be longer than a width dimension of the journal section.   The valve operating apparatus for an internal combustion engine according to claim 1, wherein the journal portion is included in the journal hole portion. The camshaft is configured such that an intake cam is disposed in the center between the journal portions, and exhaust air cams are disposed symmetrically on both sides of the intake cam,
The valve has an intake valve driven by the intake cam and an exhaust valve driven by the exhaust cam,
3. The valve operating apparatus for an internal combustion engine according to claim 1, wherein the variable valve mechanism receives the intake cam and continuously controls the characteristics of the intake valve. 4.   4. The valve operating apparatus for an internal combustion engine according to claim 3, wherein the exhaust cams on both sides have the same cam profile at least in the vicinity of the valve closing.   The variable valve mechanism is provided in an internal combustion engine so as to be swingable. The swing valve drives the intake valve or the exhaust valve. The variable valve mechanism receives the cam and changes the displacement of the cam to the swing cam. The valve operating apparatus for an internal combustion engine according to any one of claims 1 to 4, further comprising a transmission member.

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