JP2017078376A - Variable valve train - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable valve train capable of reducing the outer diameter size of a cam shaft while securing good mountability of the cam shaft.SOLUTION: A spacer 16 is assembled to an outer periphery of a journal part 12b of an intake cam shaft 12 by spline engagement. A position of the spacer 16 in a direction along the axial line of the intake cam shaft 12 is fixed by receiving energization force toward the radial direction outside from a coil spring 17b interposed between the spacer 16 and the journal part 12b. The coil spring 17b is arranged at a position where the energization force acts on a direction opposite to the projecting direction of a cam nose in a cam. This reduces the outer diameter size of the intake cam shaft 12 while securing good mountability of the intake cam shaft 12. Further, when an intake valve 10 is lifted, a bearing pressure on a spline-engagement portion between the journal part 12b and the spacer 16 can be reduced.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a variable valve mechanism used in, for example, an engine, and more particularly to an improvement in a camshaft bearing structure.

  Conventionally, as disclosed in Patent Document 1, a variable valve mechanism that can change lift characteristics of an intake valve and an exhaust valve of an engine is known. This variable valve mechanism changes the maximum lift amount of the valve according to the operating state of the engine.

  The variable valve mechanism disclosed in Patent Document 1 extrapolates a cam unit (cam carrier) provided with a plurality of cams to a cam shaft, and slides the cam unit in the axial direction (cam shaft direction). Thus, the cam switching system is configured to switch the cam used for opening and closing the valve.

Japanese translation of PCT publication 2010-520395

  The requirements for the variable valve mechanism include securing the lost motion amount and securing the cam lift amount. As a means for obtaining a large amount of lost motion, it is possible to increase the roller diameter of the roller rocker arm. Further, as means for obtaining a large cam lift amount (obtaining a variable range of the cam lift amount), it is possible to reduce the cam base circle diameter. In order to satisfy these requirements, it is necessary to reduce the outer diameter of the camshaft.

  However, in the camshaft, since the journal portions arranged at a plurality of positions in the longitudinal direction are rotatably supported by bearing means (the journal support portion of the cam housing and the cam cap), the camshaft sufficiently satisfies the above requirements. In the conventional bearing structure, the outer diameter dimension (shaft outer diameter) of the journal section must be smaller than the inner diameter dimension (journal inner diameter) of the bearing means, and in this case, the mounting performance of the camshaft is deteriorated. Will be invited. In general, the camshaft is provided with a cam (for example, a cam for a fuel pump) and a joint for operating other devices, and it is necessary to ensure bearing strength at this portion. Therefore, there is a limit to reducing the inner diameter dimension of the bearing means (reducing the inner diameter dimension of the bearing means to a dimension that matches the outer diameter dimension of the camshaft, which has been reduced to such a degree as to sufficiently satisfy the above requirement). . That is, in the prior art, it is difficult to reduce the outer diameter of the camshaft while ensuring the bearing strength of the camshaft.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a variable valve that can reduce the outer diameter of the camshaft while ensuring good mountability of the camshaft. To provide a mechanism.

  In order to achieve the above-mentioned object, the solution means of the present invention includes a camshaft provided with a journal portion which is a part rotatably supported by bearing means, a cam provided integrally with the camshaft, It is assumed that the variable valve mechanism includes a variable lift unit that varies a lift amount during valve lift by the cam accompanying rotation of the camshaft. With respect to this variable valve mechanism, a spacer is assembled integrally with the outer periphery of the journal portion by spline engagement. Further, the spacer receives a biasing force directed radially outward from a biasing means interposed between the spacer and the journal portion so that the position in the direction along the axis of the camshaft is fixed. To do. The urging means is disposed at a position where the urging force directed outward in the radial direction acts in a direction opposite to the direction in which the cam nose projects in the cam.

  By this specific matter, the camshaft can be rotatably supported by using the spacer assembled on the outer periphery of the journal portion of the camshaft. In other words, while the outer diameter of the camshaft itself is reduced, the camshaft is supported by the bearing means (for example, the journal support portion of the cam housing and the cam cap) at the position where the spacer is assembled (position where the diameter is large). It can be rotatably supported. For this reason, the outer diameter dimension (outer diameter dimension of the spacer) of the portion supported by the bearing means can be increased to such an extent that the bearing strength of the camshaft at the bearing means is sufficiently obtained. Therefore, it is possible to reduce the outer diameter of the camshaft while ensuring good mountability of the camshaft.

  Further, when the valve is lifted, the reaction force received from the valve acts on the camshaft via the cam, and this reaction force may increase the surface pressure at the spline engagement portion between the journal portion and the spacer. However, since the urging force in the direction opposite to the reaction force is applied to the journal portion of the camshaft by the urging means, the surface pressure can be reduced.

  In the present invention, a spacer is assembled to the outer periphery of the journal portion of the camshaft by spline engagement, and a biasing force in a direction opposite to the cam nose protruding direction of the cam is applied to the spacer. For this reason, by using a spacer to support the camshaft in a freely rotatable manner, the outer diameter of the camshaft can be reduced while ensuring good mountability of the camshaft. Further, when the valve is lifted, the urging force acts on the journal portion, so that the surface pressure of the spline engagement portion between the journal portion and the spacer can be reduced.

It is a schematic block diagram of the valve operating system of the engine equipped with the variable valve operating mechanism which concerns on embodiment of this invention. It is a perspective view which expands and shows the valve system by the side of intake in a predetermined cylinder. It is sectional drawing which shows a shift lock mechanism and its periphery. It is the figure which expanded the formation part of the guide groove in a cam unit, Comprising: It is a figure for demonstrating operation | movement in the case of sliding a cam unit to a high lift position. It is the figure which expanded the formation part of the guide groove in a cam unit, Comprising: It is a figure for demonstrating operation | movement in the case of sliding a cam unit to a low lift position. It is sectional drawing which shows the journal part and its peripheral part of an intake camshaft. It is sectional drawing of the intake camshaft and a spacer in the position corresponding to the VII-VII line of FIG. It is a figure for demonstrating the relationship between the direction of the urging | biasing force of a locking member, and the protrusion direction of a cam nose. It is a figure for demonstrating the load which acts on an intake camshaft.

  Embodiments in which the present invention is applied to a valve train of an engine will be described below with reference to the drawings. The engine 1 of this embodiment is an in-line four-cylinder gasoline engine 1 as an example, and as shown schematically in FIG. 1, the first to fourth four cylinders 3 (# 1 to # 4) are provided. They are arranged in the longitudinal direction of a cylinder block (not shown), that is, in the front-rear direction of the engine 1 (left-right direction in FIG. 1 indicated by arrows).

-Outline of valve system-
As shown in FIG. 1, a cam housing 2 is disposed in an upper portion (cylinder head) of the engine 1, and a valve operating system of an intake valve 10 and an exhaust valve 11 is accommodated therein. That is, as shown by broken lines in FIG. 1, two intake valves 10 and two exhaust valves 11 are provided in each of the four cylinders 3 arranged in a line in the longitudinal direction of the engine 1, Are driven by an intake camshaft 12 and an exhaust camshaft 13, respectively.

  Each of the intake camshaft 12 and the exhaust camshaft 13 is provided with a VVT (Variable Valve Timing) mechanism 14 that can continuously change the valve timing at the front end (left end in FIG. 1). Further, the intake camshaft 12 switches cams 41 and 42 (see FIG. 2) for driving the intake valve 10 for each cylinder 3 and changes its lift characteristics (cam unit 4 and actuator described later). 51, 52) is provided.

  As an example, as shown in the enlarged view of FIG. 2 for the second cylinder 3 (# 2), two cams 41 and 42 having different profiles are provided corresponding to the two intake valves 10 for each cylinder 3, respectively. Any one of them drives the intake valve 10 via the rocker arm 15. The two cams 41 and 42 are provided adjacent to the direction of the axis X (cam shaft direction) of the intake camshaft 12, and the left side (one side) cam 41 in FIG. The low lift cam 41 has a small protruding dimension, and the right (other side) cam 42 has a relatively large cam lobe (the cam nose has a large protruding dimension).

  The base circles of the low lift cam 41 and the high lift cam 42 have the same diameter and are formed as arc surfaces that are continuous with each other. In FIG. 2, the state is switched to the low lift cam 41, and the roller 15 a of the rocker arm 15 comes into contact with the base circle section and is pressed by the reaction force of the valve spring 10 a of the intake valve 10. In this manner, when the roller 15a of the rocker arm 15 is in contact with the base circle section, the intake valve 10 is not lifted.

  Then, when the intake camshaft 12 rotates in the direction of the arrow R, although not shown, the cam lobe of the low lift cam 41 presses the roller 15a and pushes down the rocker arm 15. As a result, the rocker arm 15 drives the intake valve 10 according to the profile of the cam lobe, and the intake valve 10 is lifted against the reaction force of the valve spring 10a as indicated by the phantom line in FIG.

-Configuration of cam switching mechanism-
In the present embodiment, the cam that lifts the intake valve 10 via the rocker arm 15 as described above is switched to either the low lift cam 41 or the high lift cam 42. That is, as shown in FIG. 3 in addition to FIG. 2, the two cams 41, 42 are integrally formed in a ring shape and are fitted to the end of the cylindrical sleeve 43 in the axis X direction. Unit 4 is configured. The cam unit 4 is slidably inserted on the intake camshaft 12.

  Spline inner teeth are formed on the inner periphery of the sleeve 43 of the cam unit 4, and meshed with spline outer teeth formed on the outer periphery of the intake camshaft 12. That is, the cam unit 4 (sleeve 43) is splined to the intake camshaft 12, and rotates together with the intake camshaft 12 and slides in the direction of the axis X. As a result of this sliding, the cam unit 4 has a low lift position (a position where the low lift cam 41 contacts the roller 15a of the rocker arm 15; a position shown in the upper part of FIG. ) And a high lift position where the high lift cam 42 is selected as the cam used to open and close the intake valve 10 (position where the high lift cam 42 contacts the roller 15a of the rocker arm 15; position shown in the lower part of FIG. 3). Can be switched.

  In order to slide the cam unit 4 in this way, the shift pins 53 and 54 that advance from the actuators 51 and 52 are provided on the outer periphery of the sleeve 43 (the outer periphery of the cam unit 4) in the intermediate portion in the axis X direction as described below. A guide groove 7 to be engaged is formed. The sleeve 43 in which the guide groove 7 is formed and the actuators 51 and 52 constitute a lift variable unit referred to in the present invention.

-Guide groove-
Hereinafter, the guide groove 7 will be described.

  FIG. 4 is a developed view of a portion where the guide groove 7 is formed in the cam unit 4. As shown in FIG. 4, the guide groove 7 includes a first groove 71 and a second groove 72 formed at predetermined intervals in the direction along the axis X (the vertical direction in FIG. 4), and the first groove 71. And a joining groove 73 formed by joining the groove 71 and the second groove 72.

  The first groove 71 and the second groove 72 are respectively continuous with the introduction portions 71a and 72a extending along the circumferential direction of the cam unit 4 (left and right direction in FIG. 4), and the introduction portions 71a and 72a. Inclined portions 71b and 72b that incline by a predetermined angle with respect to the direction in which 71a and 72a extend and extend toward the joining groove 73 are provided. Further, the joining groove 73 extends along the circumferential direction of the cam unit 4 (left and right direction in FIG. 4).

  Further, the distance (La in the drawing) between the center line L1 of the introduction part 71a of the first groove 71 and the center line L3 of the merge groove 73, and the center line L2 of the introduction part 72a of the second groove 72 The distance (Lb in the figure) between the merging groove 73 and the center line L3 coincides with each other. Thereby, the inclination angles (inclination angles inclined toward the center side of the cam unit 4) of the inclined portions 71b and 72b of the first groove 71 and the second groove 72 also coincide with each other.

  Further, each of the introduction portions 71a and 72a of the first groove 71 and the second groove 72 has a groove depth that gradually decreases toward one end side (right side in FIG. 4), and the outer peripheral surface (groove is formed) of the sleeve 43. Is not continuous to the outer peripheral surface). Similarly, the merging groove 73 also has a groove depth that gradually decreases toward one end side (left side in FIG. 4), and is continuous with the outer peripheral surface of the sleeve 43 (the outer peripheral surface where no groove is formed).

  Further, as shown in FIG. 2, first and second actuators 51 and 52 are disposed above the intake camshaft 12 for each cylinder 3. The first actuator 51 is disposed at a position facing the first groove 71 and includes a first shift pin 53 that moves forward and backward toward the first groove 71. The second actuator 52 includes a second shift pin 54 that is disposed at a position facing the second groove 72 and moves forward and backward toward the second groove 72.

  These actuators 51 and 52 are supported on the cam housing 2 by a stay (not shown), for example. The actuators 51 and 52 are for driving the shift pins 53 and 54 by electromagnetic solenoids. Therefore, when the first actuator 51 is turned on, the first shift pin 53 advances and engages with the first groove 71. On the other hand, when the second actuator 52 is turned on, the second shift pin 54 advances and engages with the second groove 72.

  When the first shift pin 53 advances and engages with the first groove 71, the first shift pin 53 is inclined from the introduction portion 71 a of the first groove 71 by the rotation of the cam unit 4 accompanying the rotation of the intake camshaft 12. It moves relative to the merging groove 73 via the portion 71b (see the movement locus of the first shift pin 53 in FIG. 4). When the first shift pin 53 moves on the inclined portion 71b of the first groove 71, the cam unit 4 is positioned on one side in the axis X direction so that the engagement between the first groove 71 and the first shift pin 53 is maintained. Slide (upper side in FIG. 4, left side in FIG. 2). As a result, the cam unit 4 is in the high lift position, and the high lift cam 42 comes into contact with the roller 15 a of the rocker arm 15. That is, the intake valve 10 is changed to a lift characteristic using the high lift cam 42.

  Conversely, when the second shift pin 54 advances and engages with the second groove 72, the second shift pin 54 is moved from the introduction portion 72 a of the second groove 72 by the rotation of the cam unit 4 accompanying the rotation of the intake camshaft 12. It moves relative to the merging groove 73 via the inclined portion 72b (see the movement locus of the second shift pin 54 in FIG. 5). When the second shift pin 54 moves on the inclined portion 72b of the second groove 72, the cam unit 4 is placed on the other side in the axis X direction so that the engagement between the second groove 72 and the second shift pin 54 is maintained. Slide down (lower side in FIG. 5, right side in FIG. 2). As a result, the cam unit 4 is in the low lift position, and the low lift cam 41 comes into contact with the roller 15 a of the rocker arm 15. That is, the intake valve 10 is changed to a lift characteristic using the low lift cam 41.

-Shift lock mechanism-
In the present embodiment, as described above, the position of the cam unit 4 (low lift position, high lift position) is maintained when the cam used to open and close the intake valve 10 is switched to the low lift cam 41 or the high lift cam 42. A shift lock mechanism 6 is provided. That is, as shown in FIG. 3, two annular grooves 43c and 43d are formed side by side on the inner peripheral surface of the sleeve 43 of the cam unit 4 in the vicinity of the center in the axis X direction (left and right direction in FIG. 3). The annular protrusion 43e formed so as to remain in between is positioned substantially at the center in the axis X direction.

  When the cam unit 4 is in the low lift position or the high lift position, the intake camshaft 12 has a locking member that can be projected and retracted on the outer periphery thereof so as to be engaged with one of the annular grooves 43c and 43d. 61 is disposed. For example, the lock member 61 is a lock ball, is accommodated in a hole 12 a having a circular cross section that opens on the outer peripheral surface of the intake camshaft 12, and is pressed outward by a coil spring 62. That is, the lock member 61 is pressed from the hole 12a of the intake camshaft 12 toward the inner peripheral surface of the sleeve 43 that faces radially outward.

  Thereby, as shown in the upper stage of FIG. 3, when the cam unit 4 is in the low lift position on the other side in the axis X direction (the right side in FIG. 3), the lock member 61 is engaged with the annular groove 43c. Holds the position. When the cam unit 4 is at a high lift position on one side in the axis X direction (left side in FIG. 3) as shown in the lower part of FIG. 3, the lock member 61 engages with the annular groove 43d and the position of the cam unit 4 is reached. Will come to hold.

-Bearing structure of intake camshaft-
The feature of this embodiment is the bearing structure of the intake camshaft 12. Hereinafter, this bearing structure will be described.

  6 is a cross-sectional view (a cross-sectional view in the direction along the axis X) showing the journal portion 12b of the intake camshaft 12 and its peripheral portion. FIG. 7 is a cross-sectional view of the intake camshaft 12 and a later-described spacer 16 at a position corresponding to the line VII-VII in FIG.

  As shown in these drawings, a journal portion 12b is provided between the positions where the cam units 4 and 4 are disposed on the intake camshaft 12 formed of a hollow pipe. A spacer 16 is assembled on the outer periphery of the journal portion 12b.

  The spacer 16 has a cylindrical shape, and an inner diameter thereof substantially coincides with an outer diameter of the journal portion 12 b of the intake camshaft 12. Further, spline inner teeth 16 a are formed on the inner peripheral surface of the spacer 16. On the other hand, spline external teeth 12 c are formed on the outer peripheral surface of the journal portion 12 b of the intake camshaft 12. Then, the teeth 16a and 12c of these splines are engaged with each other, whereby the spacer 16 is assembled to the outer periphery of the journal portion 12b. Thereby, the spacer 16 is integrally rotated with the intake camshaft 12.

  The intake camshaft 12 is supported such that the journal portion 12 b is rotatable via a spacer 16. Specifically, as shown in FIG. 6, the spacer 16 is placed on the journal support portion 21 of the cam housing 2, and a cam cap 22 is attached to the upper side of the journal support portion 21, thereby lowering the spacer 16. The half rotates on the inner surface (semi-circular arc-shaped inner surface) of the journal support portion 21 and the upper half of the spacer 16 rotates in a slidable contact with the inner side surface (semi-arc-shaped inner surface) of the cam cap 22. It is supported freely. These journal support portion 21 and cam cap 22 constitute a bearing means in the present invention. As described above, the portion of the intake camshaft 12 that is rotatably supported has a double structure of the journal portion 12b and the spacer 16, and the outer peripheral surface of this portion (the outer peripheral surface of the spacer 16) is the journal support. The portion 21 and the cam cap 22 are rotatably supported.

  Thus, since the journal portion 12b of the intake camshaft 12 is rotatably supported via the spacer 16, the position where the spacer 16 is assembled while reducing the outer diameter of the intake camshaft 12 itself. The intake camshaft 12 can be rotatably supported at the (large-diameter position). For this reason, the outer diameter of the supported portion (in practice, the outer diameter of the spacer 16 is reduced to the extent that the bearing strength of the intake camshaft 12 at the journal support portion 21 and the cam cap 22 of the cam housing 2 is sufficiently obtained. (Diameter dimension) can be increased. Accordingly, it is possible to reduce the outer diameter of the intake camshaft 12 while ensuring good mountability of the intake camshaft 12.

  The spacer 16 is fixed at a position in the axis X direction by a spacer lock mechanism 17. That is, as shown in FIG. 6, one annular groove 16b is formed on the inner peripheral surface of the spacer 16 in the vicinity of the center in the direction of the axis X (the left-right direction in FIG. 6). Further, the journal member 12b of the intake camshaft 12 is provided with a lock member 17a that can be projected and retracted on the outer periphery thereof. For example, the lock member 17 a is a lock ball that is housed in a hole 12 d having a circular cross section that opens to the outer peripheral surface of the intake camshaft 12 and is pressed outward by a coil spring 17 b disposed inside the intake camshaft 12. Has been. That is, the lock member 17a is pressed from the hole 12d of the intake camshaft 12 toward the inner peripheral surface of the spacer 16 that faces radially outward, and is fitted into the annular groove 16b. The lock member 17a and the coil spring 17b constitute an urging means in the present invention. Thereby, the position of the spacer 16 in the direction of the axis X is fixed by the spacer lock mechanism 17.

  Further, the arrangement positions of the lock member 17a and the coil spring 17b are such that the urging force (the urging force toward the radially outer side) that the lock member 17a urges toward the inner peripheral surface of the spacer 16 is the cam 41, 42, the cam noses 41a and 42a are disposed at positions that act in a direction opposite to the protruding direction of the cam noses 41a and 42a.

  FIG. 8 is a view for explaining the relationship between the direction of the urging force of the lock member 17a and the protruding direction of the cam nose 42a of the high lift cam 42. As shown in FIG. In FIG. 8, the spacer 16 assembled to the journal portion 12b between the cam unit 4 corresponding to the first cylinder 3 (# 1) and the cam unit 4 corresponding to the second cylinder 3 (# 2) is fixed. The spacer lock mechanism 17 is shown. Further, the cam shape (virtual line) shown in FIG. 8 represents the shape of the high lift cam 42 of the cam unit 4 located on both sides of the spacer 16 (both sides in the direction of the axis X). That is, the shape of the high lift cam 42a-1 of the cam unit 4 corresponding to the first cylinder 3 (# 1) and the high lift cam 42-2 of the cam unit 4 corresponding to the second cylinder 3 (# 2) are shown. Yes. The protruding direction of the cam nose 42a-1 in the high lift cam 42-1 of the cam unit 4 corresponding to the first cylinder 3 (# 1), and the high lift cam 42-2 of the cam unit 4 corresponding to the second cylinder 3 (# 2). There is a phase difference of 90 ° from the protruding direction of the cam nose 42a-2. In FIG. 8, the protruding direction of the cam nose 42a-1 in the high lift cam 42-1 of the cam unit 4 corresponding to the first cylinder 3 (# 1) is downward, and the second cylinder 3 (# 2) The protruding direction of the cam nose 42a-2 in the high lift cam 42-2 of the corresponding cam unit 4 is the right direction. Therefore, when the intake valve 10 of the first cylinder 3 (# 1) is lifted, a load (lift load) is applied to the high lift cam 42a-1 of the cam unit 4 corresponding to the first cylinder 3 (# 1). Will act (see arrow FA in FIG. 8). On the other hand, when the intake valve 10 of the second cylinder 3 (# 2) is lifted, a load acts on the high lift cam 42a-2 of the cam unit 4 corresponding to the second cylinder 3 (# 2). (See arrow FB in FIG. 8).

  The arrangement positions of the lock member 17a and the coil spring 17b are intermediate directions of the protruding directions of the cam noses 42a-1 and 42a-2 (the direction indicated by the broken arrow in FIG. 8; The urging force of the coil spring 17b is applied to the inner peripheral surface of the spacer 16 via the lock member 17a in a direction opposite to the direction (direction indicated by a solid arrow in FIG. 8; upper left direction in the figure). It has become so. That is, the lock member 17a and the coil spring 17b give a biasing force that moves the spacer 16 in this direction (upper left direction in the drawing) to the intake camshaft 12. In other words, the lock member 17a and the coil spring 17b are attached to move the intake camshaft 12 with respect to the spacer 16 in a direction opposite to this direction (the direction indicated by the broken arrow described above; the lower right direction in the figure). Giving power. That is, this urging force (the urging force in the direction indicated by the broken-line arrow) can act in the direction toward the protruding direction of the cam noses 42a-1 and 42a-2.

-Operation of cam switching mechanism-
The operation of the cam switching mechanism described above will be described together with the movement of the shift pins 53 and 54 in the guide groove 7.

  First, when the low lift cam 41 is selected during the operation of the engine 1 as described above with reference to FIG. 2, the lift amount and the working angle of the intake valve 10 driven by the rocker arm 15 are thereby relative to each other. It is small in size. In the shift lock mechanism 6, as shown in the upper part of FIG. 3, the lock member 61 is engaged with the annular groove 43c to hold the position of the cam unit 4 (low lift position).

  In this state, when the first actuator 51 is turned on to switch to the high lift cam 42, the first shift pin 53 advances and is inserted into the introduction portion 71a of the first groove 71 (the first shift pin indicated by I in FIG. 4). See position 53).

  When the cam unit 4 rotates, the first shift pin 53 relatively moves from the introduction portion 71a of the first groove 71 toward the inclined portion 71b. At this time, the first shift pin 53 presses the inner surface 71c of the inclined portion 71b (see the position of the first shift pin 53 marked II in FIG. 4), and the cam unit 4 is the upper side in FIG. 4 (FIG. 2). And slide to the left in FIG. That is, the cam unit 4 slides toward the high lift position.

  When the cam unit 4 slides in this way, the lock member 61 of the shift lock mechanism 6 gets over the annular protrusion 43e, and the lock member 61 fits into the annular groove 43d. Further, the first shift pin 53 moves to the joining groove 73 (see the position of the first shift pin 53 marked with IV in FIG. 4).

  When the cam unit 4 slides to the high lift position in this manner, the rocker arm 15 is pushed down by the high lift cam 42 pressed against the roller 15a, and the intake valve 10 operates with a large lift amount and working angle.

  At the time of cam lift using this high lift cam 42, as shown by arrows F1 (corresponding to the load FA or FB in FIG. 8) and F2 in FIG. 9, the reaction force (lift load) received from the intake valve 10 is the cam unit 4 (high It acts on the intake camshaft 12 via the lift cam 42), and this reaction force may increase the surface pressure at the spline engagement portion between the journal portion 12b and the spacer 16, but the locking member 17a Since the urging force (F3 in FIG. 9; the urging force in the direction indicated by the dashed arrow in FIG. 6) acts on the journal portion 12b of the intake camshaft 12 in a direction against this reaction force, The pressure can be reduced.

  On the other hand, when switching from the state where the high lift cam 42 is selected as described above to the state where the low lift cam 41 is selected, the second actuator 52 is turned on. As a result, the second shift pin 54 advances and is inserted into the introduction portion 72a of the second groove 72 (see the position of the second shift pin 54 marked I in FIG. 5).

  When the cam unit 4 rotates, the second shift pin 54 relatively moves from the introduction portion 72a of the second groove 72 toward the inclined portion 72b. At this time, the second shift pin 54 presses the inner side surface 72c of the inclined portion 72b (refer to the position of the second shift pin 54 marked II in FIG. 5), and the cam unit 4 is lower in FIG. 2 and the right side in FIG. That is, the cam unit 4 slides toward the low lift position.

  When the cam unit 4 slides in this way, the lock member 61 of the shift lock mechanism 6 gets over the annular protrusion 43e, and the lock member 61 is fitted into the annular groove 43c. Further, the second shift pin 54 moves to the joining groove 73 (see the position of the second shift pin 54 marked IV in FIG. 5).

  When the cam unit 4 slides to the low lift position in this way, the rocker arm 15 is pushed down by the low lift cam 41 pressed against the roller 15a, and the intake valve 10 operates with a small lift amount and working angle.

  Even during the cam lift using the low lift cam 41, the reaction force received from the intake valve 10 acts on the intake camshaft 12 via the cam unit 4 (low lift cam 41), and this reaction force causes the journal portion 12b and the spacer to move. There is a possibility that the surface pressure at the spline engaging portion with 16 will increase, but the urging force from the lock member 17a acts on the journal portion 12b of the intake camshaft 12 in a direction against this reaction force. Therefore, the surface pressure can be reduced.

  As described above, according to the variable valve mechanism (the intake camshaft 12, the cams 41 and 42, the lift variable unit (the lift variable unit including the sleeve 43 and the actuators 51 and 52)) according to the present embodiment as described above. The intake camshaft 12 can be rotatably supported using the spacer 16 assembled around the outer periphery of the journal portion 12b of the intake camshaft 12. That is, while reducing the outer diameter of the intake camshaft 12 itself, the intake camshaft 12 is connected to the journal support portion 21 of the cam housing 2 and the cam at the position where the spacer 16 is assembled (position where the diameter is large). The cap 22 can be rotatably supported. For this reason, the outer diameter dimension of the portion supported by the journal support portion 21 and the cam cap 22 to the extent that the bearing strength of the intake camshaft 12 at the journal support portion 21 and the cam cap 22 of the cam housing 2 is sufficiently obtained. The (outer diameter dimension of the spacer 16) can be increased. Accordingly, it is possible to reduce the outer diameter of the intake camshaft 12 while ensuring good mountability of the intake camshaft 12. As a result, it is possible to secure the lost motion amount and the cam lift amount.

  Further, when the intake valve 10 is lifted, a reaction force received from the intake valve 10 acts on the intake camshaft 12 via the cam unit 4, and this reaction force causes a spline between the journal portion 12 b of the intake camshaft 12 and the spacer 16. There is a possibility that the surface pressure at the engaging portion is increased, but since the urging force in the direction opposite to this reaction force acts on the journal portion 12b of the intake camshaft 12 by the coil spring 17b, the surface pressure is increased. Can be reduced. As a result, wear of each member at the spline engagement portion can be suppressed.

-Other embodiments-
The present invention is not limited to the configuration described in the above embodiment. The above embodiments are merely examples, and the configuration of the present invention is of course not limited to applications.

  In the above embodiment, the cam switching mechanism for switching the lift characteristic of the intake valve 10 in the DOHC type valve system of the engine 1 has been described. However, the present invention is not limited to this, and the lift characteristic of the exhaust valve 11 is not limited thereto. The present invention can also be applied to a cam switching mechanism for switching between. Further, the present invention is not limited to a DOHC type valve system, and the present invention can be applied to, for example, an SOHC type valve system.

  The present invention is applicable to a variable valve mechanism for an automobile engine.

4 Cam unit 7 Guide groove 12 Intake cam shaft 12b Journal portion 12c Spline outer teeth 16 Spacer 16a Spline inner teeth 17a Lock member (biasing means)
17b Coil spring (biasing means)
21 Journal support (bearing means)
22 Cam cap (bearing means)
41 Low lift cam 42 High lift cam 42a Cam nose 51 First actuator 52 Second actuator

Claims (1)

A camshaft provided with a journal portion which is a part rotatably supported by bearing means, a cam provided integrally with the camshaft, and a lift amount at the time of valve lift by the cam accompanying the rotation of the camshaft In a variable valve mechanism equipped with a variable lift unit that makes the variable
A spacer is rotatably assembled integrally with the outer periphery of the journal portion by spline engagement, and this spacer is directed radially outward from the urging means interposed between the spacer and the journal portion. The position in the direction along the axis of the camshaft is fixed by receiving an urging force,
The urging means is disposed at a position where the urging force directed outward in the radial direction acts in a direction opposite to a direction in which the cam nose projects in the cam.

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