Valve train

Abstract

To provide a valve train capable of avoiding increase in inertial mass of a lash adjuster and maintaining a tappet clearance at "0".SOLUTION: A valve mechanism comprises: a push rod (31) that reciprocates when pushed by a rotating cam (33); a rocker arm (21) that tilts when pushed by the push rod (31); a valve (41) that is pushed and operated by the tilt of the rocker arm (21); holding members (61, 61a) that hold a tilting center axis of the rocker arm (21) so that it can be displaced; and a lash adjuster (5) that is in contact with the holding members (61, 61a), and generates a biasing force that displaces the rocker arm (21) so that the push rod (31) is displaced toward the cam (33).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a valve train, for example, to a valve train applied to an internal combustion engine. [Background technology]

[0002] In this type of valve train, for example, a force transmission path is configured from a tappet that contacts a cam that rotates in response to the rotation of the crankshaft, through a push rod that contacts the tappet and a rocker arm that tilts (rotates) around a rotation axis, to a valve that opens and closes the combustion chamber. More specifically, when the valve is opened, the rocker arm rotates due to the tappet being pressed by the cam, and the rotated rocker arm presses the valve, opening the combustion chamber and connecting it to the intake path or the exhaust path. On the other hand, when the valve is closed (i.e., when the cam stops pressing the tappet), the valve moves due to the biasing force of the valve spring, closing the combustion chamber, and the rocker arm is pressed by the valve, causing it to rotate in the opposite direction.

[0003] In other words, the tappet and the push rod repeatedly reciprocate during operation of the internal combustion engine. At this time, a lash adjuster may be used to prevent the tappet from moving away from the cam (i.e., to maintain the tappet clearance at "0"). For example, Patent Document 1 discloses a lash adjuster attached to a push rod. With this lash adjuster, when the tappet is pressed by the cam (i.e., when a force (contraction force) that contracts the lash adjuster in the longitudinal direction is acting on the lash adjuster), the contraction is restricted and the lash adjuster becomes rigid. On the other hand, when no contraction force is acting on the lash adjuster, the lash adjuster generates a biasing force in the direction of extension. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-17881 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, the above-mentioned lash adjuster repeatedly reciprocates together with the push rod during operation of the internal combustion engine, and so it is necessary to increase its strength to a level that can withstand this reciprocating movement. This may result in the weight (inertial mass) of the lash adjuster becoming relatively large. If the inertial mass of the lash adjuster becomes large, it will become necessary to increase the spring constant of the valve spring and increase the strength of the push rod, so it is desirable for the inertial mass of the lash adjuster to be as small as possible.

[0006] The present invention has been devised in view of the above-mentioned circumstances, and has an object to provide a valve train that can avoid an increase in the inertial mass of the lash adjuster and maintain the tappet clearance at "0". [Means for solving the problem]

[0007] In order to solve the above problems, the valve mechanism of the present invention comprises a push rod that moves back and forth when pushed by a rotating cam, a rocker arm that tilts when pushed by the push rod, a valve that is pushed and operated by the tilting of the rocker arm, a retaining member that holds the tilting central axis of the rocker arm so that it can be displaced, and a lash adjuster that abuts against the retaining member and generates a biasing force that displaces the rocker arm so that the push rod is displaced toward the cam.

[0008] In this valve train, for example, one end (tip) of the lash adjuster abuts against the retaining member, while the other end of the lash adjuster is fixed to the cylinder head of the internal combustion engine. That is, the rocker arm (and therefore the push rod) is displaced toward the cam by the biasing force of the lash adjuster, so that the tappet clearance is maintained as close to "0" as possible, while the lash adjuster does not reciprocate with the push rod. Therefore, with this valve train, it is not necessary to increase the strength of the lash adjuster more than necessary in consideration of the reciprocating movement, and it is possible to prevent the inertial mass of the lash adjuster and other members in the valve train from becoming excessive.

[0009] In one aspect of the valve mechanism, the retaining member is rotatably held and has a contact surface that abuts against the lash adjuster, and the rotation central axis of the retaining member is spaced from the tilt central axis and is approximately parallel to the tilt central axis.

[0010] In this case, the retaining member rotates due to the biasing force of the lash adjuster, which causes the rocker arm (and thus the push rod) to displace toward the cam. Therefore, according to this aspect, the valve mechanism can be easily constructed.

[0011] In the above aspect of the valve mechanism, the holding member may be provided with a holding member pressing portion that protrudes in the direction of the central axis of rotation, and the abutment surface may be provided on the holding member pressing portion.

[0012] In this case, an oil passage for supplying hydraulic oil to the lash adjuster can be formed in the retaining member pressing portion, thereby preventing the structure of the valve mechanism from becoming excessively complicated.

[0013] Alternatively, in the above aspect of the valve mechanism, the retaining member may have a generally cylindrical shape with a cutout portion, and the abutment surface may be provided in the cutout portion.

[0014] In this case, instead of forming a holding member pressing portion, a contact surface is provided in the notch of the holding member, which can facilitate molding (manufacturing) the holding member.

[0015] Furthermore, in the above-described aspect of the valve mechanism, a convex spherical shape may be formed at one end of the push rod opposite the cam that abuts against the rocker arm, and the rocker arm may be formed with a valve pressing portion having a convex spherical shape and pressing the valve, and the tilting central axis may be located in the vicinity of a straight line connecting a center of the convex spherical shape of the push rod and a center of the convex spherical shape of the valve pressing portion.

[0016] In this case, when the tilt central axis of the rocker arm displaces in response to the extension and retraction of the lash adjuster, the abutment point of the rocker arm with the push rod (push rod abutment point) and the abutment point of the rocker arm with the valve (valve abutment point) displace generally together with the tilt central axis. Therefore, even when the lash adjuster extends or retracts, the positions of the push rod abutment point and the valve abutment point relative to the tilt central axis are prevented from changing significantly. [Brief description of the drawings]

[0017] [Figure 1] 1 is a configuration diagram of a main portion of an internal combustion engine including a valve train according to an embodiment; [Diagram 2] 2 is a cross-sectional view (broken line) of the valve mechanism shown in FIG. 1 along the line II-II of the arrows. [Diagram 3] FIG. 11 is a configuration diagram of a main portion of an internal combustion engine including a valve train according to a modified example of the embodiment. [Figure 4] 4 is a cross-sectional view of the valve mechanism shown in FIG. 3 taken along the line IV-IV of the arrows. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] An embodiment of the present invention will be described with reference to Figures 1 and 2. The same symbols (reference numbers) in the description refer to the same elements having the same functions without duplicate explanation. In the following description, terms that indicate either up, down, left, or right directions and rotation directions (specifically, clockwise and counterclockwise) are used. These terms are used for the convenience of the description with reference to the figures, and do not specify (limit) the structure of the embodiment.

[0019] The valve train according to the present invention is applied to an internal combustion engine 1. The internal combustion engine 1 is an overhead valve (OHV) type engine. Fig. 1 shows a cross section of a portion of a cylinder head 11 of the internal combustion engine 1. Engine oil of the internal combustion engine 1 is supplied as lubricating oil to each of the locations where the members constituting the valve train slide against other members. However, illustrations and descriptions of an oil pump, oil gallery, and the like for supplying engine oil to each location are omitted.

[0020] The valve train includes a rocker arm 21, a push rod 31, a tappet 32, a cam 33, a valve 41, a valve spring 42, a lash adjuster 5, and an adjustment shaft 61. The rocker arm 21 is fixed to a rocker shaft 22. As described later, the rocker shaft 22 is rotatably held by an adjustment shaft 61 (also referred to as a "holding member" for convenience). That is, the rocker arm 21 rotates about the rocker shaft 22. Point P1 in FIG. 1 and dashed dotted line L1 in FIG. 2 indicate the rotation center (tilt central axis) of the rocker arm 21 and the rocker shaft 22. As described later, during operation of the internal combustion engine 1, the rocker arm 21 repeats reciprocating rotational displacement. That is, the rocker arm 21 tilts (swings).

[0021] An adjust screw 23 is fixed to one end of the rocker arm 21 (specifically, the right side in FIG. 1). A male thread is formed on the upper part of the adjust screw 23 (not shown). The upper part of the adjust screw 23 passes through a through hole formed on one end of the rocker arm 21 and is screwed into a lock nut 24. The amount by which the adjust screw 23 protrudes downward is adjusted according to the amount by which the adjust screw 23 is screwed into the lock nut 24.

[0022] The lower end of the adjust screw 23 abuts against the upper end of the push rod 31, which has a substantially cylindrical shape. More specifically, the lower end of the adjust screw 23 is formed with a semispherical shape that opens downward. The upper end of the push rod 31 is formed with a convex spherical shape. Point P2 indicates the center of the convex spherical surface at the upper end of the push rod 31. The radius of curvature of the semispherical shape at the lower end of the adjust screw 23 is slightly larger than the radius of curvature of the convex spherical shape at the upper end of the push rod 31 (radius r1 shown in FIG. 1).

[0023] The lower end of the push rod 31 abuts against the upper end of the tappet 32. More specifically, the lower end of the push rod 31 is formed with a convex spherical shape. Meanwhile, the upper end of the tappet 32 ​​is formed with a semi-spherical shape that opens upward. The radius of curvature of the semi-spherical shape at the upper end of the tappet 32 ​​is slightly larger than the radius of curvature of the convex spherical shape at the lower end of the push rod 31. As described later, the push rod 31 and the tappet 32 ​​are interposed between the cam 33 and the rocker arm 21 and move back and forth (reciprocating displacement) in accordance with the rotation of the cam 33, and are collectively referred to as "longitudinal members" for convenience.

[0024] The lower surface of the tappet 32 ​​abuts against the cam 33. The cam 33 is fixed to the camshaft 34 and rotates together with the camshaft 34. Torque is transmitted to the camshaft 34 from the crankshaft (not shown) of the internal combustion engine 1. That is, the camshaft 34 rotates in response to the rotation of the crankshaft (more specifically, at half the rotational speed of the crankshaft). The cam 33 has a nose portion 33a (cam lobe) protruding from the camshaft 34.

[0025] A valve pressing portion 21a is formed at the other end of the rocker arm 21 (i.e., the left side in FIG. 1). The valve pressing portion 21a has a convex spherical shape that protrudes downward from the rocker arm 21. Point P3 indicates the center of the convex spherical surface of the valve pressing portion 21a. The radius of curvature of the convex spherical shape of the valve pressing portion 21a is radius r2 shown in FIG. 1.

[0026] The valve pressing portion 21a abuts against the upper end of the valve 41. The valve 41 is a member including a valve stem and an umbrella portion, which opens and closes the intake port 12 formed in the cylinder head 11. When the valve 41 is pressed by the valve pressing portion 21a, the intake port 12 opens and communicates with a combustion chamber (not shown) of the internal combustion engine 1. A valve spring 42 is disposed coaxially with the valve stem of the valve 41. The valve spring 42 is held (sandwiched) by the upper surface of the cylinder head 11 and a stopper 42a. The valve spring 42 biases the valve 41 so that the valve 41 closes the intake port 12 (i.e., so that the upper end of the valve 41 presses the valve pressing portion 21a).

[0027] Therefore, the valve mechanism according to this embodiment operates as follows: When the portion of the cam 33 that abuts against the underside of the tappet 32 ​​approaches the nose portion 33a, the longitudinal member is pushed and the rocker arm 21 rotates about the tilt central axis of the rocker shaft 22, and accordingly the valve pressing portion 21a pushes the valve 41 to open the intake port 12. That is, when the valve 41 opens, the rocker arm 21 rotates counterclockwise in FIG. 1 about the tilt central axis.

[0028] 1 about its central axis, closing the intake port 12. That is, the upper end of the valve 41 presses the valve pressing portion 21a due to the biasing force of the valve spring 42, causing the rocker arm 21 to rotate in the opposite direction to when the valve is opened, and the valve 41 to close.

[0029] In other words, the reciprocating displacement (reciprocating movement) of the longitudinal member is transmitted to the rocker arm 21, causing a reciprocating rotational displacement (tilting) of the rocker arm 21. In addition, the reciprocating rotational displacement of the rocker arm 21 causes a reciprocating displacement of the valve 41.

[0030] In order to prevent the tappet 32 ​​from separating from the cam 33 when the longitudinal member is reciprocatingly displaced, the lash adjuster 5 and the adjustment shaft 61 are provided. The lash adjuster 5 is a well-known hydraulic lash adjuster. The lash adjuster 5 is supplied with engine oil from the internal combustion engine 1 as hydraulic oil.

[0031] The lash adjuster 5 includes a body portion 51 and a plunger 52. The body portion 51 is a cylindrical member with a bottom. The body portion 51 is fixed to the protruding portion 13 that protrudes upward from the cylinder head 11. Fastening members such as bolts and nuts used to fasten the body portion 51 to the protruding portion 13, and fastening points to which the fastening members are applied, are omitted from the drawings.

[0032] The plunger 52 is a cylindrical hollow member. The plunger 52 is inserted into the body portion 51 so as to be movable up and down. A low pressure chamber 53 in which hydraulic oil is stored is formed inside the plunger 52. A convex spherical shape is formed at the upper end of the plunger 52. In addition, a top hole 52a through which hydraulic oil flows in and out is formed at the upper end of the plunger 52. A high pressure chamber 54 is formed inside the body portion 51, which is partitioned by the inner wall of the body portion 51 and the bottom surface of the plunger 52. A valve hole 52b is formed at the bottom surface of the plunger 52, which communicates between the low pressure chamber 53 and the high pressure chamber 54.

[0033] The high pressure chamber 54 accommodates a valve body 55, a retainer 56, a first spring 57, and a second spring 58. The valve body 55 is a spherical member (check ball). The retainer 56 has a cage shape and accommodates the valve body 55 in a recess. When the valve body 55 moves upward within the retainer 56 and comes into contact with the valve hole 52b, it closes the valve hole 52b.

[0034] The first spring 57 biases the retainer 56 upward relative to the bottom surface of the body portion 51 (i.e., so that the lash adjuster 5 extends). The second spring 58 is housed in a recess in the retainer 56. The second spring 58 biases the valve body 55 upward relative to the bottom surface of the retainer 56 (i.e., in a direction to close the valve hole 52b). Although not shown, a plurality of through holes are formed in the bottom surface of the retainer 56, and these through holes allow the movement of hydraulic oil between the upper and lower sides of the retainer 56 within the high pressure chamber 54 to be smooth.

[0035] The upper end of lash adjuster 5 (i.e., the upper end of plunger 52, and the tip of lash adjuster 5) abuts against an adjuster pressing portion 62 (specifically, abutment surface 63, described later) provided on adjust shaft 61. Adjuster pressing portion 62 (for convenience, also referred to as the "retaining member pressing portion") protrudes from the side surface of adjust shaft 61 to the right in Fig. 2 (i.e., the front side of the paper in Fig. 1, the opposite side of adjust shaft 61 to rocker arm 21).

[0036] The lower surface of adjuster pressing portion 62 is provided with abutment surface 63, which is a curved surface that is a substantially semicylindrical cutout portion that opens downward and against which the tip of lash adjuster 5 abuts (see FIG. 2). That is, the tip of lash adjuster 5 abuts against adjust shaft 61 via adjuster pressing portion 62 (specifically, abutment surface 63). The radius of curvature of abutment surface 63 (i.e., the radius of the cylinder in the substantially semicylindrical cutout portion) is substantially equal to the radius of curvature of the convex spherical shape at the upper end of plunger 52. The extension direction of abutment surface 63, which is a curved surface (i.e., the extension direction of the cylinder), is substantially perpendicular to both the longitudinal direction and the tilting central axis of plunger 52.

[0037] An oil passage 64 is formed in the adjuster pressing portion 62 to supply hydraulic oil to the top hole 52a of the plunger 52. Note that an engine oil guide path leading to the oil passage 64 is omitted in Figures 1 and 2. Hydraulic oil flows into the low pressure chamber 53 via the oil passage 64 and the top hole 52a, and when the pressure (hydraulic pressure) in the low pressure chamber 53 rises, the hydraulic oil is discharged from the top hole 52a.

[0038] The adjust shaft 61 has a substantially cylindrical shape. The adjust shaft 61 is rotatably held by the bearing portion 14 fixed to the protruding portion 13. Note that the bearing portion 14 is not shown in FIG. 1. Point P4 in FIG. 1 and dashed line L2 in FIG. 2 indicate the rotation center axis of the adjust shaft 61. The rotation center axis of the adjust shaft 61 is spaced apart from the tilt center axis of the rocker arm 21 (see point P1 in FIG. 1 and dashed line L1 in FIG. 2) and extends substantially parallel to the tilt center axis. Also, as can be seen from FIG. 1, the contact portion of the adjuster pressing portion 62 with the lash adjuster 5 (i.e., the contact surface 63 shown in FIG. 2) is spaced apart from the rotation center axis of the adjust shaft 61 (i.e., point P4) to the left in FIG. 1.

[0039] The bearing portion 14 is provided with annular guide portions 15-16 that protrude toward the rotation axis (i.e., dashed line L2) and have a rectangular cross section (see FIG. 2). The guide portions 15-16 restrict the adjustment shaft 61 from being displaced in the rotation axis direction relative to the bearing portion 14.

[0040] The adjust shaft 61 has a cylindrical through hole through which the rocker shaft 22 passes, and rotatably holds the rocker shaft 22 as described above. The rocker shaft 22 is provided with guide plates 25-26. The guide plates 25-26 are annular members having a rectangular cross section. The guide plates 25-26 restrict the rocker shaft 22 from being displaced in the tilt central axis direction relative to the adjust shaft 61.

[0041] When the valve 41 is opened (i.e., when the rocker arm 21 is pushed by the elongated member and rotates counterclockwise in FIG. 1 around the tilt central axis), the rocker shaft 22 tries to rotate the adjust shaft 61 counterclockwise in FIG. 1 around the rotation central axis. At this time, the abutment surface 63 presses the upper end of the plunger 52 downward.

[0042] In this case, valve element 55 closes valve hole 52b, preventing the flow of hydraulic oil from high pressure chamber 54 to low pressure chamber 53. This restricts the descent of plunger 52 relative to body portion 51 (i.e., contraction of lash adjuster 5 in the longitudinal direction), and lash adjuster 5 becomes rigid. Therefore, the counterclockwise rotation of adjust shaft 61 in FIG. 1 is restricted by lash adjuster 5.

[0043] On the other hand, when the valve 41 is closed (i.e., when the rocker arm 21 is pushed by the valve 41 and rotates clockwise in Fig. 1 around the tilt central axis), the rocker shaft 22 descends and tries to rotate the adjust shaft 61 clockwise in Fig. 1 around the rotation central axis. At this time, the pressure applied to the plunger 52 by the abutment surface 63 is released, so the valve body 55 moves away from the valve hole 52b, allowing the flow of hydraulic oil from the low pressure chamber 53 to the high pressure chamber 54.

[0044] Therefore, in this case, the urging force of the first spring 57 causes the lash adjuster 5 to extend, and the plunger 52 presses the abutment surface 63. That is, the lash adjuster 5 generates an urging force that rotates the adjust shaft 61 clockwise in FIG. 1 about the central axis of rotation. When the adjust shaft 61 rotates clockwise, the rocker shaft 22 (and therefore the push rod 31) moves downward in FIGS. 1 and 2. That is, the urging force of the first spring 57 that attempts to extend the lash adjuster 5 prevents the tappet 32 ​​from moving away from the cam 33 as much as possible.

[0045] In other words, the lash adjuster 5 generates a biasing force that displaces the rocker arm 21 (more specifically, the tilt central axis of the rocker arm 21) so that the push rod 31 (i.e., the longitudinal member) is displaced toward the cam 33. This causes the distance between the tappet 32 ​​and the cam 33 (i.e., the tappet clearance) to be maintained as close to "0" as possible when the valve 41 is open and when it is not.

[0046] Incidentally, when the adjust shaft 61 rotates, the upper end of the plunger 52 slides against the abutment surface 63. That is, the abutment position of the upper end of the plunger 52 on the abutment surface 63 moves. More specifically, for example, when the lash adjuster 5 extends, the adjust shaft 61 rotates clockwise in FIG. 1, and the abutment position of the upper end of the plunger 52 on the abutment surface 63 moves away from the rotation central axis (see point P4 in FIG. 1).

[0047] In other words, the abutment surface 63 has a semicylindrical shape (rather than a hemispherical shape) to allow the upper end of the plunger 52 to slide against the abutment surface 63. In addition, as described above, the radius of curvature of the abutment surface 63 is approximately equal to the radius of curvature of the convex spherical shape of the upper end of the plunger 52, so that the contact area between the abutment surface 63 and the plunger 52 is prevented from becoming too small.

[0048] 1, point P1 (i.e., the tilt central axis of the rocker arm 21) is located near the dashed line L3 (straight line) that passes through points P2 and P3. Specifically, when the adjust shaft 61 is rotationally displaced in association with the extension and contraction of the lash adjuster 5, the tilt central axis intersects with the dashed line L3 or is located near the dashed line L3. Therefore, even if the rocker arm 21 is displaced in association with the extension and contraction of the lash adjuster 5 (i.e., the rotation of the adjust shaft 61), the positional relationships among the push rod 31, the rocker arm 21, and the valve 41 are prevented from changing significantly.

[0049] More specifically, when the tilt central axis of rocker arm 21 is displaced in response to the extension and contraction of lash adjuster 5, the abutment point of rocker arm 21 with push rod 31 (push rod abutment point) and the abutment point of rocker arm 21 with valve 41 (valve abutment point) are displaced roughly together with the tilt central axis. This prevents the distance from the tilt central axis to the push rod abutment point and the distance from the tilt central axis to the valve abutment point from changing significantly due to the displacement of rocker arm 21. As a result, it prevents the ratio of the vertical displacement of valve 41 to the vertical displacement of push rod 31 from changing significantly due to the displacement of rocker arm 21.

[0050] (Modification) A modified example of the valve mechanism will be described with reference to Figures 3 and 4. The above-described adjust shaft 61 includes an adjuster pressing portion 62 protruding from the side, and adjuster pressing portion 62 is provided with an abutment surface 63 against which the tip of lash adjuster 5 abuts. On the other hand, adjust shaft 61a according to the modified example has a notch, and is provided with an abutment surface 63a against which the tip of lash adjuster 5 abuts. The following description will focus on this difference.

[0051] The valve train according to this modification is applied to an internal combustion engine 1a. In this modification, a lash adjuster 5 is fixed to a protruding portion 13a that protrudes upward from a cylinder head (not shown in Figs. 3 and 4) of the internal combustion engine 1a. An adjustment shaft 61a is rotatably held by a bearing portion 14a that is fixed to the protruding portion 13a. Note that the bearing portion 14a is not shown in Fig. 3.

[0052] The contact surface 63a is a curved surface that opens downward, similar to the outer circumferential surface of a cylinder, like the contact surface 63. An oil passage 64a that leads to the contact surface 63a is formed in the adjustment shaft 61a. In addition, an oil passage 64b through which engine oil of the internal combustion engine 1a is introduced is formed at a position that is higher than the adjustment shaft 61a in the bearing portion 14a and corresponds to the oil passage 64a. That is, the hydraulic oil is supplied to the top hole 52a of the plunger 52 through the oil passages 64a to 64b.

[0053] When the valve body 55 is not closing the valve hole 52b, the lash adjuster 5 presses the abutment surface 63a by the biasing force of the first spring 57. That is, the lash adjuster 5 generates a biasing force that rotates the adjustment shaft 61a clockwise in FIG. 3 about the rotation center axis (see point P4 in FIG. 3 and dashed line L2 in FIG. 4). When the adjustment shaft 61a rotates clockwise by the biasing force of the lash adjuster 5 (that is, when the lash adjuster 5 extends), the rocker shaft 22 (and therefore the push rod 31) moves downward in FIGS. 3 and 4. That is, when the lash adjuster 5 extends, the tappet 32 ​​approaches the cam 33 (not shown in FIGS. 3 and 4) as in the above-described embodiment, and the tappet 32 ​​is prevented from moving away from the cam 33 as much as possible.

[0054] Incidentally, in this modified example as well, as the lash adjuster 5 expands and contracts, the adjust shaft 61a rotates and the upper end of the plunger 52 slides against the abutment surface 63. Even when the adjust shaft 61a rotates, the tilting central axis of the rocker arm 21 (i.e., point P1 in FIG. 3) is located in the vicinity of the dashed dotted line L3 that passes through points P2 and P3, so that a large change in the positional relationship between the push rod 31, the rocker arm 21, and the valve 41 is avoided.

[0055] As described above, in the valve mechanism according to this embodiment, the lash adjuster 5 generates a biasing force to rotate the adjust shafts 61, 61a, and when the adjust shafts 61, 61a are rotated by this biasing force, the rocker arm 21 and the elongated member are displaced toward the cam 33. Therefore, the biasing force of the lash adjuster 5 prevents the tappet 32 ​​from moving away from the cam 33 as much as possible. In other words, the tappet clearance is maintained at "0" as much as possible when the valve 41 is open and closed.

[0056] If the above-mentioned valve train does not include the lash adjuster 5, it is necessary to make the radius of curvature of the portion (section) of the cam 33 where the tappet 32 ​​abuts against the tappet 32 ​​relatively large in order to prevent the tappet 32 ​​from moving away from the cam 33 when the valve 41 is opened. That is, it is difficult to increase the displacement amount of the longitudinal member per unit time when the valve 41 is opened (i.e., the moving speed of the longitudinal member). In other words, if the valve train does not include the lash adjuster 5, there is a high possibility that the degree of freedom in designing the cam 33 (specifically, in determining the shape) is reduced. On the other hand, according to the above-mentioned valve train including the lash adjuster 5, the shape of the cam 33 can be determined according to the required opening speed of the valve 41 (i.e., the target value of the moving speed of the longitudinal member when the valve 41 is opened), so that smooth intake of air into the combustion chamber of the internal combustion engine 1, 1a is not hindered.

[0057] On the other hand, the lash adjuster 5 is not included in the force transmission path from the cam 33 through the rocker arm 21 to the valve 41. In other words, while the internal combustion engine 1, 1a is in operation, the push rod 31 moves back and forth relative to the internal combustion engine 1, 1a, while one end (the lower end) of the lash adjuster 5 is fixed to the protruding portion 13, 13a and does not displace. Therefore, the lash adjuster 5 does not need strength sufficient for reciprocating movement. Therefore, compared to the case where the lash adjuster 5 moves back and forth together with the push rod 31, it is possible to make the inertial mass of the lash adjuster 5 etc. (i.e., the lash adjuster 5 and other members constituting the valve mechanism) relatively small.

[0058] If the inertial mass of the lash adjuster 5 and the like becomes large, the valve 41 is moved (closed) following the shape of the cam 33 when the valve 41 is closed, so that the spring constant of the valve spring 42 needs to be increased. In this case, the force with which the tappet 32 ​​presses the cam 33 (i.e., the contact surface pressure) also increases, so that it may become necessary to increase the radius of curvature of the cam 33 (particularly the nose portion 33a and its vicinity) so that the contact surface pressure does not exceed a predetermined upper limit value (i.e., the strength upper limit value). In other words, the degree of freedom in designing the cam 33 is likely to be reduced. On the other hand, according to the above-mentioned valve mechanism, the inertial mass of the lash adjuster 5 and the like is prevented from becoming excessively large, and therefore there is no need to increase the spring constant of the valve spring 42, so the degree of freedom in designing the cam 33 is not reduced. In other words, smooth intake of air into the combustion chamber of the internal combustion engine 1, 1a is not hindered.

[0059] Furthermore, as described above, since the tilting central axis of the rocker arm 21 is located in the vicinity of the dashed line L3, it is possible to prevent the positional relationship (relative position) between the rocker arm 21, the push rod 31, and the valve 41 from changing significantly as the adjustment shafts 61, 61a rotate.

[0060] Although the embodiment of the present invention has been described above with reference to the above structure, many alternatives, improvements, and modifications are possible without departing from the scope of the present invention. Therefore, the present invention includes all alternatives, improvements, and modifications that do not depart from the spirit and scope of the appended claims. The present invention is not limited to the specific structure described above, and may be modified, for example, as follows.

[0061] In the lash adjuster 5, hydraulic oil flows in and out through the top hole 52a. Alternatively, the lash adjuster 5 may be configured such that a through hole (side through hole) that passes through both the body portion 51 and the plunger 52 is formed in the side surface of the lash adjuster 5, and the hydraulic oil flows in from one of the top hole 52a and the side through hole, and flows out from the other.

[0062] Alternatively, the inlet and outlet for the hydraulic oil may be provided on the side surface and bottom portion, respectively, of the lash adjuster 5. In this case, the top hole 52a and the oil passages 64, 64a, 64b may be omitted.

[0063] The lower end of lash adjuster 5 was fixed to protrusions 13, 13a. In other words, lash adjuster 5 was fixed so as not to be able to swing. Alternatively, lash adjuster 5 may be held swingably at its lower part. In this case, the position of the swing center at the lower part of lash adjuster 5 and the shape of abutment surfaces 63, 63a, etc. may be adapted so that the swing angle of lash adjuster 5 changes as lash adjuster 5 expands and contracts, while the upper end (tip) of lash adjuster 5 does not slide against abutment surfaces 63, 63a.

[0064] The valve 41 of the valve train described above opens and closes the intake port 12 of the internal combustion engine 1, 1a. Instead of this, the valve 41 may be configured to open and close the exhaust port of the internal combustion engine 1, 1a. Even in this case, the freedom in designing the cam 33 is not lost as described above, so that smooth exhaust from the combustion chamber of the internal combustion engine 1, 1a can be achieved.

[0065] 1 and 3, the tilt central axis of the rocker arm 21 (i.e., point P1) is to the right of the rotation central axis of the adjust shafts 61, 61a (i.e., point P4), and the abutment surfaces 63, 63a are to the left of the rotation central axis of the adjust shafts 61, 61a. Alternatively, the tilt central axis may be to the left of the rotation central axis, and the abutment surfaces 63, 63a may be disposed to the right of the rotation central axis. In other words, it is sufficient that the adjust shafts 61, 61a are configured so that the rocker arm 21 and push rod 31 are displaced toward the cam 33 when the lash adjuster 5 extends.

[0066] The adjust shafts 61, 61a (i.e., the retaining members) are rotatably held by the bearings 14, 14a, and rotate in response to the expansion and contraction of the lash adjuster 5. However, the retaining members need not necessarily be rotatably held as long as they are configured so that the rocker shaft 22 (and thus the longitudinal member) is displaced toward the cam 33 by the biasing force of the lash adjuster 5 (i.e., the extension of the lash adjuster 5). For example, the valve mechanism may be configured so that the retaining member that rotatably holds the rocker shaft 22 is held so as to be displaceable in the vertical direction in Figure 1, and the extension of the lash adjuster 5 causes the retaining member to be displaced downward (i.e., toward the cam 33) together with the rocker shaft 22.

[0067] The retaining member that is held so as to be displaceable in the vertical direction together with the rocker shaft 22 is realized, for example, by a retaining member having a substantially rectangular cross section, with both ends of the retaining member being inserted into elongated holes extending in the vertical direction (i.e., bearings fixed to the cylinder head of the internal combustion engine 1, 1a). In this case, the upper end of the lash adjuster 5 is fixed to the cylinder head of the internal combustion engine 1, 1a, while the tip (lower end) of the lash adjuster 5 abuts against a contact surface provided on the retaining member, and the lash adjuster 5 may generate a biasing force to displace the retaining member downward. [Explanation of symbols]

[0068] 1, 1a…Internal combustion engine 11: cylinder head; 12: intake port; 13: protrusion 14, 14a... bearing portion, 15-16... guide portion, 21... rocker arm 21a... valve pressing portion, 22... rocker shaft, 23... adjust screw 24...Lock nut, 25~26...Guide plate 31...push rod, 32...tappet, 33...cam, 33a...nose portion 34…Camshaft 41...valve, 42...valve spring, 42a...stopper 5...Lash adjuster 51: body portion, 52: plunger, 52a: top hole, 52b: valve hole 53...low pressure chamber, 54...high pressure chamber, 55...valve body, 56...retainer 57...first spring, 58...second spring 61, 61a...Adjustment shaft (holding member) 62...Adjuster pressing portion (holding member pressing portion) 63, 63a…Contact surface 64, 64a, 64b...Oil road

Claims

1. A valve train, A push rod that moves back and forth by being pushed by a rotating cam, A rocker arm that is pushed by the push rod to tilt; a valve that is pushed and actuated by the tilting of the rocker arm; a holding member that holds the tilting central axis of the rocker arm so as to be displaceable; a lash adjuster that abuts against the retaining member and generates a biasing force that displaces the rocker arm so that the push rod is displaced toward the cam.

2. The valve mechanism according to claim 1 , the retaining member is rotatably held and has a contact surface that contacts the lash adjuster, A valve mechanism, wherein a rotation center axis of the holding member is spaced apart from and substantially parallel to the tilt center axis.

3. The valve mechanism according to claim 2, The holding member is provided with a holding member pressing portion protruding in a direction of the rotation central axis, The abutment surface is provided on the holding member pressing portion. A valve mechanism.

4. The valve mechanism according to claim 2, The holding member has a generally cylindrical shape with a notch, The contact surface is provided in the cutout portion.

5. The valve mechanism according to any one of claims 2 to 4, The push rod has an end, opposite to the cam, that abuts against the rocker arm and has a convex spherical shape formed thereon, The rocker arm is formed with a valve pressing portion having a convex spherical shape and pressing the valve, the tilt central axis is located near a straight line connecting a center of the convex spherical shape of the push rod and a center of the convex spherical shape of the valve pressing portion.

Images