JP2007278255A - Cam profile of variable valve mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the load on a control shaft in a high valve lift while enhancing a lift control accuracy in a high valve lift in a variable valve mechanism which changes the valve lift of an engine valve with the control shaft provided with a cam. <P>SOLUTION: The profile of a cam 57 provided to the control shaft 56 of the variable valve mechanism which controls the valve lift of a suction valve in an internal combustion engine includes two involute curve portions P1 and P2, and the radii R2 to R4 of base circles C2 to C4 defining the involute curve portion P2 at a low valve lift side are set shorter than the radius R1 of a base circle C1 defining the involute curve portion P1 at a high valve lift side. Thereby, the bending load getting in the control shaft in a high valve lift can be kept low while restraining the distortion of the control shaft 56 in a low valve lift to precisely control the valve lift. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a profile of a cam provided on a control shaft of a variable valve mechanism that controls a valve lift of an engine valve.

  A cam profile provided on a control shaft for changing the valve opening angle and valve lift of an engine valve of an internal combustion engine is composed of an involute curve portion and an arc portion, and is known from Patent Document 1 below.

In this cam profile, the involute curve part acts in the region from the lowest valve lift to the highest valve lift, and the valve lift gradually increases, and the arc part acts in the region of the highest valve lift to keep the valve lift constant. It has become. From the viewpoint of supply / exhaust efficiency, it is desirable to fix the valve opening angle and valve lift of the engine valve at the maximum position when the internal combustion engine is stopped, but by operating the arc portion of the cam profile at that position, the engine The reaction force of the valve spring of the valve prevents the control shaft from rotating and the valve opening angle and valve lift from changing in the decreasing direction.
JP 2004-339951 A

  By the way, in the region where the valve lift of the intake valve of the internal combustion engine is small, the intake air amount changes greatly and the output of the internal combustion engine also changes greatly only by a slight change of the valve lift, so precise control of the valve lift is necessary. become. However, since the reaction force of the valve spring is transmitted to the cam of the control shaft via the cam follower, there is a possibility that precise control of the valve lift may be hindered by twisting the control shaft and changing the phase of the cam. If the control shaft is thickened to prevent this, there is a problem that the weight increases.

  In addition, since the reaction force of the valve spring increases in the region where the valve lift is large, a large reaction force acts on the cam from the cam follower due to the reaction force, and a large bending load acts on the control shaft, causing bending, There is a problem that a large load acts on the bearing.

  The present invention has been made in view of the above circumstances, and in a variable valve mechanism that changes the valve lift of an engine valve with a control shaft provided with a cam, while increasing the lift control accuracy at the time of low valve lift, the high valve lift The goal is to reduce the load that the control shaft sometimes receives.

  To achieve the above object, the invention described in claim 1 is a profile of a cam provided on a control shaft of a variable valve mechanism for controlling a valve lift of an engine valve, wherein the profile includes at least two profiles. A variable motion characterized in that the radius of the base circle that includes the involute curve portion and that defines the involute curve portion on the side where the valve lift is small is smaller than the radius of the base circle that defines the involute curve portion on the side where the valve lift is large A cam profile of the valve mechanism is proposed.

  According to the invention described in claim 2, in addition to the configuration of claim 1, the profile is formed by an involute curve portion in which the radius of the basic circle gradually decreases as the valve lift moves from the large side to the small side. A cam profile of a variable valve mechanism characterized by being formed continuously is proposed.

  The intake valve 16 of the embodiment corresponds to the engine valve of the present invention.

  According to the configuration of the first aspect, the reaction force received by the cam from the cam follower is directed in the tangential direction of the basic circle at the portion where the profile of the cam provided on the control shaft of the variable valve mechanism is an involute curve portion. Therefore, when the valve lift is low, the reaction force is directed closer to the center of the control shaft, and when the valve lift is large, the reaction force is far from the center of the control shaft. Will be oriented.

  When the valve lift is low, it is required to control the valve lift of the engine valve with high accuracy. However, the torsional moment applied to the control shaft is reduced by directing the reaction force closer to the center of the control shaft. Thus, twisting deformation is suppressed, and the control accuracy of the valve lift of the engine valve is improved. At this time, since the reaction force is directed to a position close to the center of the control shaft, the bending load of the control shaft due to the reaction force increases. However, there is no problem because the reaction force itself is small during low valve lift.

  On the other hand, when the valve lift is high, the reaction force itself increases. However, the bending force applied to the control shaft can be kept small by directing the reaction force away from the center of the control shaft. At this time, the torsional moment applied to the control shaft increases because the reaction force is directed away from the center of the control shaft, but there is no problem because the required accuracy of valve lift control is low during high valve lift. .

  According to the second aspect of the present invention, the cam profile is continuously formed by the involute curve portion in which the radius of the base circle gradually decreases from the larger valve lift side to the smaller valve lift side. The torsional moment applied to the control shaft when changing between the low valve lift and the high valve lift can be prevented from changing suddenly.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  1 to 6 show a first embodiment of the present invention, FIG. 1 is a longitudinal sectional side view of an essential part of an internal combustion engine, FIG. 2 is a sectional view taken along line 2-2 of FIG. 1, and FIG. FIG. 4 is a sectional view taken along line 4-4 of FIG. 2 in a high valve lift state, FIG. 5 is a sectional view corresponding to FIG. 4 in a low valve lift state, and FIG. It is a figure which shows the profile of the cam of a shaft.

  First, in FIG. 1 to FIG. 4, a cylinder head 15 constituting a part of the engine body 14 is provided with intake valves 16, 16 that are a pair of engine valves for one cylinder so as to be opened and closed. The variable valve mechanism 17 that opens and closes both intake valves 16, 16 includes a camshaft 19 provided with valve cams 18, 18 individually corresponding to both intake valves 16, 16, and the valve cams 18, 18. A sub-cam 21 that is swingably supported by a movable support shaft 20 that is displaceable in a plane orthogonal to the rotation axis, that is, the axis of the camshaft 19, and that swings by the valve cams 18, 18, and the intake valve 16. , 16 and a pair of rocker arms 22, 22 that are individually linked and connected to the sub cam 21 and a movable support shaft 20 and the valve cams 18, 18, A control arm 23 that enables rotation about an axis parallel to the axis of the shaft 19 and holds the movable support shaft 20 at a position offset from the rotation axis, and driving means for rotating the control arm 23 24. By displacing the movable support shaft 20, the operation characteristics including the valve lift of the intake valves 16, 16 can be changed.

  Stems 16a and 16a of the intake valves 16 and 16 are slidably fitted into guide cylinders 25 and 25 disposed on the cylinder head 15, and retainers 26 and 26 provided at upper ends of the stems 16a and 16a, respectively. The intake valves 16, 16 are urged in the valve closing direction by the valve springs 28, 28 interposed between the retainers 27, 27 abutted on the cylinder head 15.

  The cylinder head 15 is provided with cam holders 29 and 29 so as to be arranged on both sides of the pair of intake valves 16 and 16, and in cooperation with these cam holders 29 and 29, the camshaft 19 is rotatably supported. Caps 30 and 30 are fastened to the upper surfaces of the cam holders 29 and 29.

  One end portions of the rocker arms 22 and 22 are swingably supported by the control arm 23 via hydraulic tappets 31 and 31. Further, the other end portions of the rocker arms 22 and 22 are provided with valve contact portions 22a and 22a that are in contact with the upper ends of the stems 16a and 16a of the intake valves 16 and 16, respectively. Further, first rollers 33 and 33 are pivotally supported at intermediate portions of the rocker arms 22 and 22 via needle bearings 32 and 32, and these first rollers 33 and 33 are in rolling contact with the sub cam 21.

  The control arm 23 is configured such that the axis parallel to the camshaft 19 and the side wall portions 23a, 23a disposed on both sides of the intake valves 16, 16 at intervals along the rotation axis is the rotation axis C. The shaft portions 23b, 23b that are connected to the outer surfaces of the side wall portions 23a, 23a at right angles, the first connecting wall portion 23c that connects one end portions of the side wall portions 23a, 23a, and the side wall portions 23a, 23a. And a second connecting wall portion 23d connecting the other ends of the first and second shafts 23b and 23b so that the shaft portions 23b and 23b can rotate in support holes 34 and 34 provided in the cam holders 29 and 29, respectively. Mated. That is, the control arm 23 is rotatably supported by the cam holders 29 and 29.

  The rotation axis C of the control arm 23, that is, the axis of the shaft portions 23b and 23b is arranged above the stems 16a and 16a of the intake valves 16 and 16, and is provided at the other end of the rocker arms 22 and 22. The valve contact portions 22a and 22a are formed so as to follow an arc centered on the rotation axis C of the control arm 23 when the intake valves 16 and 16 are in the closed seating state.

  The movable support shaft 20 having an axis parallel to the camshaft 19 includes a sub cam 21 disposed inside the both side walls 23a, 23a of the control arm 23, and a cylindrical spacer interposed between the intermediate portions of the sub cam 21. 35, both ends of the movable support shaft 20 are in contact with the inner side surfaces of the both side wall portions 23a, 23a, and bolts 36, 36 respectively inserted into the both side wall portions 23a, 23a are movable support members. Screwed into both ends of the shaft 20, needle bearings 37 and 37 are interposed between the movable support shaft 20 and the sub cam 21.

  That is, the sub cam 21 is rotatably supported by the movable support shaft 20 that is detachably attached to both side walls 23a, 23a of the control arm 23, and is a spacer that is separate from the movable support shaft 20. 35 is fitted on the outer periphery of the movable support shaft 20 so as to be interposed in the intermediate portion of the sub cam 21.

  In addition, in the sub cam 21, a portion corresponding to the portion between the shaft portions 23 b and 23 b of the control arm 23 and the movable support shaft 20 is formed in a substantially U shape opened to the camshaft 19 side and extends below the camshaft 19. The support arms 21a, 21a are integrally connected to each other, and a second roller 40 is pivotally supported via a needle bearing 39 on a support shaft 38 fixed between the tips of both the support arms 21a, 21a. The second roller 40 is in rolling contact with the valve cam 18 of the camshaft 19. That is, the sub cam 21 is rotated around the axis of the movable support shaft 20 when the second roller 40 contacts the valve cam 18 of the cam shaft 19.

  Further, a pressure receiving arm portion 21b is integrally provided on the sub cam 21 on the opposite side of the support shaft 38 from the cam shaft 19, and the second roller 40 is connected to the valve cam 18 on the pressure receiving arm portion 21b. The spring force that urges the sub cam 21 acts on the side to be brought into contact with rolling. That is, the tip of the pressing rod 44 urged by the lost motion spring 43 supported by the spring receiving hole 23e provided in the control arm 23 is elastically contacted.

  By the way, the lower surface of the sub cam 21 is provided with contact surfaces 46 and 46 for bringing the first rollers 33 and 33 of the rocker arms 22 and 22 into rolling contact with each other, and each contact surface 46 rotationally drives the rocker arm 22. And a base circular portion 46b having an equal distance from the axis of the movable support shaft 20 in order to keep the rocker arm 22 in a stationary state, and the lift portion 46a has a valve cam. The distance between the contact point of the lift portion 46a with the first roller 33 of the rocker arm 22 and the axis of the movable support shaft 20 is gradually increased when the sub cam 21 is rotated with the rotation of 18. It is formed so as to extend linearly.

  In the first connecting wall portion 23c of the control arm 23, the portions corresponding to the rocker arms 22 and 22 have end walls 47a and 47a at the end opposite to the movable support shaft 20, and the movable support shaft. The bottomed cylindrical tappet mounting cylinders 47 and 47 extending on the opposite side of the cylinder 20 are integrally provided, and the hydraulic tappets 31 and 31 are mounted on the tappet mounting cylinders 47 and 47.

  The hydraulic tappet 31 has a closed-end cylindrical body 48 fitted and mounted in the tappet mounting cylindrical portion 47 with the closed end abutting against the end wall 47a, and a plunger slidably mounted on the body 48. 49, and a high pressure chamber 50 formed between the closed end of the body 48 and one end of the plunger 49, and an oil chamber 51 formed in the plunger 49, and provided at one end of the plunger 49 A valve 52; and a return spring 53 provided between the body 48 and the plunger 49 to exert a spring force for urging the plunger 49 on the side of increasing the volume of the high-pressure chamber 50. One end portion of the rocker arm 22 is supported by a spherical head portion 49a formed in a swingable manner.

  Thus, the control arm 23 is provided with a hydraulic path 54 for guiding the hydraulic pressure to the hydraulic tappets 31, 31 up to the shaft portions 23b, 23b, and the cylinder head 15 through the shaft portions 23b, 23b. Hydraulic pressure is supplied to the hydraulic path 54.

  The drive unit 24 has a control shaft 56 that has an axis parallel to the movable support shaft 20 and is rotatably supported between the cam holders 29 and 29 and the caps 30 and 30, and a cam 57 provided on the control shaft 56. An electric motor 58 that rotationally drives the control shaft 56 and a cam follower 59 that is provided on the control arm 23 and abuts against the cam 57 are provided. The drive means 24 causes the control arm 23 to have shaft portions 23c, 23c. Is rotated around the axis of rotation, that is, the rotation axis C.

  When the control arm 23 is arranged at the position shown in FIG. 4 by the driving means 24, that is, when the highest lift portion of the cam 57 of the driving means 24 comes into contact with the cam follower 59, it rotates around the axis of the movable support shaft 20. The upper ends of the stems 16a and 16a in the intake valves 16 and 16 through the rocker arm 22 at the ends of the lift portions 46a and 46a of the contact surfaces 46 and 46 of the sub cam 21 opposite to the base circular portions 46b and 46b. Is driven in the valve opening direction, and in this state, the valve lift h of the intake valves 16, 16 is maximized.

  When the control arm 23 is rotated upward as shown in FIG. 5 by the driving means 24, that is, when the lowest lift portion of the cam 57 of the driving means 24 comes into contact with the cam follower 59, for example, the contact surface 46 of the sub cam 21. , 46 abuts against the first roller 33 of the rocker arm 22, and in this state, the valve lift h of the intake valves 16, 16 is minimum (= 0).

  In other words, when the control arm 23 is rotationally driven by the driving means 24, the valve lift of the intake valves 16 and 16 is changed. However, the valve cams 18 and 18 are moved by the second arm 40 by the rotational driving of the control arm 23. , 40 also changes the timing at which the intake valves 16, 16 are opened and closed.

  Next, the profile of the cam 57 provided on the control shaft 56 will be described with reference to FIG.

  The cam profile of the first embodiment includes a first involute curve portion P1 on the high valve lift side and a second involute curve portion P2 on the low valve lift side. The basic circle C1 of the first involute curve portion P1 has a constant radius R1. That is, when the yarn wound around the basic circle C1 having a certain radius R1 is rewound, the first involute curve portion P1 is formed by a curve drawn by one point on the yarn. In the second involute curve portion P2, the radius of the base circles C1, C2, and C3 continuously decreases from R1 → R2 → R3 from the high valve lift side to the low valve lift side. The end portion on the low valve lift side of the first involute curve portion P1 and the end portion on the high valve lift side of the second involute curve portion P2 are smoothly connected, and the low valve lift side of the second involute curve portion P2 And the base circle P3 are smoothly connected.

  The direction of the reaction force that an arbitrary point a on the first involute curve portion P1 receives from the cam follower 59 is the direction of the normal N that is perpendicular to the tangent T at the point a, and the direction of the normal N is the base circle. This is the direction in which the yarn wound around C1 extends. Accordingly, the direction of the reaction force acting on the point a from the cam follower 59 is the direction of the tangent to the base circle C1, and the length of the moment arm of the torsion moment acting to twist the control shaft 56 by the reaction force is It coincides with the radius R1 of the basic circle C1. This is also true for any point on the second involute curve portion P2.

  In a region where the valve lift of the intake valve 16 is small, the intake air amount changes greatly and the output of the internal combustion engine also changes greatly only by a slight change of the valve lift, so that the valve lift of the intake valve 16 can be precisely controlled. For this purpose, it is necessary to reduce the torsional moment acting on the control shaft 56 to minimize the twisting of the control shaft 56. In the present embodiment, as the valve lift of the intake valve 16 is smaller, the radius of the base circle of the involute curve of the cam profile is smaller. Therefore, the torsional moment generated by the reaction force that the cam 57 receives from the cam follower 59 is It becomes smaller by the smaller radius (moment arm) of the base circle.

  Thereby, the twist of the control shaft 56 can be minimized and the control accuracy of the valve lift at the time of low valve lift can be increased. In particular, at the time of a low valve lift in which a portion close to the base circle portion P3 of the second involute curve portion P2 acts, the reaction force is small because the compression amount of the valve spring 28 is small, and the torsional moment is also correspondingly small. Thus, the accuracy control is further improved. In this way, twisting deformation can be suppressed without particularly increasing the diameter of the control shaft 56, so there is no possibility that the weight of the control shaft 56 increases. Further, when the torsional moment applied to the control shaft 56 is reduced, the load of the electric motor 58 that rotationally drives it is also reduced, so that the power consumption of the electric motor 58 can be reduced.

  Further, by setting the radius R3 of the base circle C3 of the second involute curve portion P2 when the valve lift becomes the lowest valve lift to zero, the screw acting on the control shaft 56 when the valve lift becomes the lowest valve lift. The twisting moment can be reduced to zero and the valve lift control accuracy can be further improved. In addition, since the radii R1, R2, and R3 of the base circles C1, C2, and C3 of the second involute curve P2 continuously change, the control shaft 56 is changed when the valve lift is changed between the low valve lift and the high valve lift. It is possible to prevent the torsional moment acting on the abrupt change.

  Further, in the region where the valve lift is large, the amount of compression of the valve spring 28 increases and the reaction force also increases, so that a large reaction force acts on the cam 57 from the cam follower 59 and a large bending load acts on the control shaft 56. Therefore, there is a problem that bending occurs or a large load acts on the bearing of the control shaft 56. However, in the present embodiment, since the radius R1 of the base circle C1 is large during the high valve lift in which the first involute curve portion P1 acts, the reaction force acting on the cam 57 from the cam follower 59 is far from the center of the control shaft 56. Pass away. As a result, the bending load applied to the control shaft 56 and the load applied to the bearing of the control shaft 56 are reduced, and the weight can be reduced by reducing the diameter of the control shaft 56 and reducing the size of the bearing.

  In this case, the torsional moment acting on the control shaft 56 increases as the moment arm increases. However, even if the valve lift slightly increases or decreases during high valve lift, the effect on the intake air amount is small. There is no problem with twisting.

  FIG. 7 shows a second embodiment of the cam profile.

  The cam profile of the second embodiment is obtained by connecting the first involute curve portion P1 and the second involute curve portion P2 of the cam profile of the first embodiment with an arbitrary curve portion P4. is there. The arbitrary curve portion P4 may be anything as long as it smoothly connects the first and second involute curve portions P1 and P2.

  FIG. 8 shows a third embodiment of the cam profile.

  The cam profile of the third embodiment is obtained by connecting an arbitrary curve portion P4 on the higher valve lift side than the first involute curve portion P1 of the cam profile of the first embodiment. The arbitrary curve portion P4 may be anything as long as it is smoothly connected to the first involute curve portion P1.

  FIG. 9 shows a fourth embodiment of the cam profile.

  The cam profile of the fourth embodiment is obtained by connecting an arbitrary curve portion P4 on the lower valve lift side than the second involute curve portion P2 of the cam profile of the first embodiment. The arbitrary curve portion P4 may be anything as long as it is smoothly connected to the second involute curve portion P2 and the base circle portion P3.

  Also according to these second to fourth embodiments, the same functions and effects as those of the first embodiment can be exhibited.

  The embodiments of the present invention have been described above, but various design changes can be made without departing from the scope of the present invention.

  For example, in the embodiment, the intake valves 16 and 16 are exemplified as the engine valve, but the engine valve of the present invention may be an exhaust valve.

  In the embodiment, the cam follower 59 of the control arm 23 with which the cam 57 abuts is configured by a slipper. However, it may be configured by a roller.

  Further, in the profile of the cam 57 shown in FIGS. 6 to 9, the minimum lift portion is set at a position in contact with the base circle portion P4. However, as shown in FIG. The position where the cam 57 comes into contact with the cam follower 59 in FIG.

Longitudinal sectional side view of the internal combustion engine 2-2 sectional view of FIG. Exploded perspective view of essential parts of variable valve mechanism Sectional view taken along line 4-4 of FIG. 2 in a high valve lift state Sectional view corresponding to Fig. 4 in the low valve lift state Diagram showing control shaft cam profile The figure which shows the profile of the cam of the control shaft which concerns on 2nd Embodiment The figure which shows the profile of the cam of the control shaft which concerns on 3rd Embodiment The figure which shows the profile of the cam of the control shaft which concerns on 4th Embodiment

Explanation of symbols

16 Intake valve (engine valve)
17 Variable valve mechanism 56 Control shaft 57 Cam C1 Foundation circle C2 Foundation circle C3 Foundation circle P1 First involute curve portion P2 Second involute curve portion R1 Radius R2 Radius R3 Radius

Claims (2)

The profile of the cam (57) provided on the control shaft (56) of the variable valve mechanism (17) for controlling the valve lift of the engine valve (16),
The profile includes at least two involute curve portions (P1, P2), and the radius (R2, R3) of the base circle (C2, C3) defining the involute curve portion (P2) on the side where the valve lift is small is the valve lift. The cam profile of the variable valve mechanism, wherein the cam profile is smaller than the radius (R1) of the base circle (C1) that defines the involute curve portion (P1) on the larger side. The profile is continuously formed by involute curve portions (P1, P2) in which the radii (R1-R3) of the basic circles (C1-C3) gradually decrease as the valve lift increases from the larger side to the smaller side. The cam profile of the variable valve mechanism according to claim 1, wherein:

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