WO2017146002A1

WO2017146002A1 - Variable cam phase mechanism in valve operating device for internal combustion engine

Info

Publication number: WO2017146002A1
Application number: PCT/JP2017/006212
Authority: WO
Inventors: 一範野々山
Original assignee: 武蔵精密工業株式会社
Priority date: 2016-02-26
Filing date: 2017-02-20
Publication date: 2017-08-31
Also published as: JP2017150453A

Abstract

Provided is a valve operating device variable cam phase mechanism that utilizes the centrifugal force of a centrifugal weight to change the phase of a valve operating cam according to a change in engine speed, wherein: a second cam shaft (20) equipped with a second cam (20c) is relatively rotatably supported by a first cam shaft (10) equipped with a first cam (10c); a centrifugal weight (50) is supported by a cam drive wheel (30) via a pivot pin (32) so as to be able to rock between a reduced diameter position and an expanded diameter position; a return spring (51) for biasing the centrifugal weight to the reduced diameter position is connected to the centrifugal weight; a driven flange (21) connected to the cam drive wheel (30) and the centrifugal weight are connected via a drive pin (22) passing through a through hole (31) of the cam drive wheel; a driving force can be transmitted by the drive pin from the centrifugal weight to the driven flange so that both camshafts rotate relative to each other in conjunction with the swing of the centrifugal weight; and the drive pin is disposed radially outward of the cam drive wheel from the pivot pin. The weight and size of a centrifugal mechanism is thereby reduced.

Description

Cam phase variable mechanism in valve gear for internal combustion engine

The present invention relates to a cam phase variable mechanism in a valve operating apparatus for an internal combustion engine in which the valve camshaft is rotated in conjunction with a crankshaft of the internal combustion engine via a cam drive wheel (for example, a cam sprocket, a cam drive pulley, etc.) In particular, the present invention relates to a cam phase variable mechanism that uses the centrifugal force of a centrifugal weight to change the phase of a valve-operating cam on a cam shaft in accordance with a change in engine speed.

The cam phase variable mechanism is conventionally known as shown in Patent Documents 1 and 2, for example, and in this mechanism, a cam drive wheel is supported by a driven flange (or cam shaft) fixed to the cam shaft so as to be relatively rotatable. The centrifugal weight is supported on the cam drive wheel (or driven flange) via a pivot pin so that the centrifugal weight can swing between the diameter-reduced position and the diameter-enlarged position. A return spring that is biased to the radial position is connected, and the centrifugal weight and the driven flange (or cam drive wheel) transmit driving force from the centrifugal weight to the driven flange (or cam drive wheel) in conjunction with the swing of the centrifugal weight. It is connected via a drive pin that can be transmitted. In this variable mechanism, as the engine speed increases, the centrifugal weight swings from the reduced diameter position to the enlarged diameter position by centrifugal force, thereby rotating the cam drive wheel and the driven flange (cam shaft) relative to each other. The cam phase is changed.

Japanese Unexamined Patent Publication No. 8-254108 Japanese Utility Model Publication No. 55-108203

By the way, in the conventional cam phase variable mechanism shown in Patent Documents 1 and 2, a plurality of cams are integrally formed on the camshaft, and all of the plurality of camshafts on the camshaft are rotated by relative rotation between the camshaft and the cam drive wheels. These cams simultaneously change the cam phase (advance or retard). Therefore, it is not possible to change the phase of only a part of the cams with one cam phase variable mechanism. For example, the phase of only the intake valve (or exhaust valve) is changed without changing the phase of the exhaust valve (or intake valve). In an internal combustion engine having two intake valves in one cylinder, it is not possible to change the phase of only the second intake valve without changing the phase of the first intake valve. Therefore, it is difficult to apply when it is desired to change the phase of only some cams according to the required characteristics of the internal combustion engine.

Further, in the cam phase variable mechanism of Patent Document 1, the swinging force due to the centrifugal force of the centrifugal weight is such that the arm length L1 between the pivot pin and the drive pin connected to the cam drive wheel and the arm length L2 between the drive pin and the cam shaft. Is amplified by the lever ratio (L2 / L1) and transmitted to the driven flange. Therefore, even if L2 is set longer to obtain a larger lever ratio in order to reduce the weight and size of the centrifugal mechanism, the conventional mechanism is more radially inward than the pivot pin connected to the prescribed position of the cam drive wheel. Since the drive pin is arranged on the side, it is difficult to set L2 sufficiently long because of the interference with the pivot pin. Therefore, an even larger lever ratio cannot be obtained, and the arrangement structure is disadvantageous in terms of reducing the weight and size of the centrifugal mechanism.

The present invention has been made in view of such circumstances, and is a cam in a valve gear for an internal combustion engine that can solve the above-described problems and contribute to the reduction in the weight and size of the centrifugal mechanism, and hence the size of the valve gear. An object is to provide a phase variable mechanism.

In order to achieve the above object, according to the present invention, a first camshaft integrally having a first cam is integrally connected to a cam drive wheel that rotates in conjunction with a crankshaft of an internal combustion engine, and the second cam is integrally formed. A second camshaft is supported by the first camshaft so as to be relatively rotatable, and a driven flange adjacent to the cam drive wheel is integrally connected to the second camshaft. Is supported via a pivot pin so that a centrifugal weight disposed on the opposite side of the driven flange across the cam drive wheel can swing between a predetermined reduced diameter position and an enlarged diameter position. In addition, a return spring that biases the centrifugal weight to the reduced diameter position is connected to the centrifugal weight, and the driven flange and the centrifugal weight are connected via a drive pin that passes through a through hole provided in the cam drive wheel. Interconnected and driven The driving force can be transmitted from the centrifugal weight to the driven flange so that the driven flange rotates relative to the first camshaft in conjunction with the swing of the centrifugal weight. The drive pin has a hole shape that allows the drive pin to rotate around the pivot pin in association with the swinging of the cam drive wheel, and the drive pin is more outward in the radial direction of the cam drive wheel than the pivot pin. Arrangement is the first feature.

Further, according to the present invention, in addition to the first feature, the phase change angle of the second cam at the time of the relative rotation is the same from the contact position of the drive pin with one inner surface of the through hole. The second feature is that the amount of the through hole is restricted by the amount of movement to the contact position with the other inner surface.

According to the present invention, in addition to the first or second feature, the center of the pivot pin and the center of the pivot pin can be seen when viewed from a projection plane orthogonal to the first cam shaft when the centrifugal weight is in the reduced diameter position. A third feature is that the drive pin is arranged on a virtual straight line connecting the center of one camshaft.

In addition to the first to third features of the present invention, the centrifugal weight includes a plate-like base portion and a weight portion thicker than the base portion that is connected to the base portion. The driven flange is thicker than the base portion of the centrifugal weight, fixes the base end portion of the drive pin, the tip end portion of the drive pin is fitted and connected, and the cam A fourth feature is that a connecting hole formed of a long hole in the radial direction of the drive wheel is provided in the base portion of the centrifugal weight.

According to the first feature of the present invention, the centrifugal weight connected to the cam drive wheel that rotates integrally with the first camshaft with the first cam via the pivot pin is provided in the engine of the internal combustion engine. The centrifugal weight swings from the reduced diameter position to the enlarged diameter position as the rotational speed increases, and accordingly, the centrifugal weight causes the driven flange (and hence the second cam shaft with the second cam) to move through the drive pin to the first. Since it rotates relative to the camshaft, only the phase of the second cam of the first and second cams (and thus the opening / closing timing of the engine valve linked to the second cam) is linked to the swing of the centrifugal weight. Therefore, it is possible to change (i.e., advance or retard) according to changes in the engine speed, and therefore, it is convenient when only the second cam is desired to change in phase according to the required characteristics of the internal combustion engine. In addition, since the drive pin is disposed radially outward from the pivot pin and the arm length L2 between the drive pin and the first cam shaft can be secured sufficiently long without being obstructed by the pivot pin, The lever ratio (L2 / L1) between the arm lengths L1 and L2 between the drive pins can be made sufficiently large, and the swinging force of the centrifugal weight can be efficiently amplified and transmitted to the driven flange. Since the driven flange can be driven strongly even by a small centrifugal force, it is possible to contribute to the light weight and size reduction of the centrifugal mechanism including the centrifugal weight.

In addition, the centrifugal weight is disposed on the opposite side of the driven flange across the cam drive wheel, and the cam drive wheel is provided with a through hole through which the drive pin passes. As the drive pin has a hole shape that allows the drive pin to rotate around the pivot pin, the cam phase is variable compared to the structure in which both the driven flange and the centrifugal weight are arranged outside the cam drive wheel in the axial direction. The extension of the mechanism in the axial direction from the outer end of the first cam shaft can be suppressed as much as possible, which can contribute to the reduction in the axial direction of the valve gear.

According to the second feature of the present invention, the phase change angle of the second cam during the relative rotation between the driven flange (second cam shaft) and the first cam shaft is such that the drive pin is one of the through holes. Since the amount of movement of the drive pin, which is regulated by the through hole, is controlled by the amount of movement from the contact position with the inner surface to the contact position of the other inner surface. It corresponds directly to the limit value. Thereby, the setting accuracy of the phase change angle can be increased, and the phase change angle limit defining means (that is, the stopper means for restricting the swing limit of the centrifugal weight) need not be specially provided. Simplification is achieved.

Further, according to the third feature of the present invention, when the centrifugal weight is at the reduced diameter position, the virtual weight connecting the center of the pivot pin and the center of the first cam shaft is viewed from the projection plane orthogonal to the first cam shaft. Since the drive pins are arranged on a straight line, the length of L1 with respect to the specified L2 is minimum at the reduced diameter position (that is, the initial swing position) of the centrifugal weight. This makes it possible to increase the maximum value of the lever ratio in combination with the above-described effect of ensuring L2 sufficiently long, so that the drive responsiveness of the driven flange by the drive pin is effectively enhanced. Can do.

According to the fourth aspect of the present invention, the driven flange is configured to be thicker than the relatively thin plate-like base portion of the centrifugal weight, and the base end portion of the drive pin is fixed. Support rigidity for the drive pin by the flange can be increased. In addition, since the distal end of the drive pin is inserted and connected, and a connection hole constituted by a long hole extending in the radial direction of the cam drive wheel is provided at the base of the centrifugal weight, the connection is made when the centrifugal weight is swung. The difference between the turning radius of the hole around the pivot pin and the turning radius of the drive pin around the center of the first cam shaft is reasonably due to the sliding of the drive pin in the long connecting hole (long hole) in the radial direction. Therefore, the swinging force of the centrifugal weight can be smoothly transmitted to the drive pin through the connection hole.

FIG. 1 is a longitudinal sectional view of an essential part of the valve gear according to the first embodiment. FIG. 2 is a view taken in the direction of arrow 2 in FIG. FIG. 3 is a relationship diagram between the cam lift and the phase according to the first embodiment. FIG. 4 is a longitudinal sectional view (corresponding to FIG. 1) of the main part of the valve gear according to the second embodiment. FIG. 5 is a view taken in the direction of arrow 5 in FIG. FIG. 6 is a relationship diagram of cam lift and phase according to the second embodiment (corresponding to FIG. 3). FIG. 7 shows the principal part of the valve gear according to the third embodiment. In particular, FIG. 7 (A) is a partial correspondence diagram of FIG. 1 and FIG. 7 (B) is a correspondence diagram of FIG. FIG. 8 is a variation of the first embodiment, and is a relationship diagram between cam lift and phase (corresponding to FIG. 6) when the exhaust cam is advanced in a high speed range. FIG. 9 is a variation of the second embodiment, and is a relationship diagram between cam lift and phase (corresponding to FIG. 3) when the intake cam is retarded in a high speed range.

10... First cam shaft 10 c... Exhaust cam (first cam)
20... Second cam shaft 20 c... Intake cam (second cam)
21... Followed flange 22... Drive pins 22 a and 22 b...
31... Through hole 32... Pivot pins 35 and 36 .. One inner surface and other inner surface 50 of the through hole...

Centrifugal weights

50a and 50b. , Weight part 51 ... Tension coil spring (return spring)
52... Connection hole 60... Torsion spring (return spring)

Embodiments of the present invention will be described below with reference to the accompanying drawings.

First embodiment

First, a first embodiment of the present invention will be described with reference to FIGS. 1 and 2, a cylinder head 5 of an SOHC type single cylinder internal combustion engine as an internal combustion engine mounted on a vehicle such as a motorcycle has a plurality of valve cams (that is, intake and

exhaust cams

20c and 10c). A cam phase variable mechanism is provided that changes only the cam phase of a part of the engine (that is, the intake cam 20c) in accordance with the increase in the engine speed. Next, an example of the cam phase variable mechanism will be specifically described.

The first camshaft 10 that rotates in conjunction with a crankshaft (not shown) of the internal combustion engine via a chain transmission mechanism 33 is rotatably supported on the cylinder head 5 via bearings B1 and B2. An appropriate fixing means (for example, a bolt and a non-rotating means not shown) is provided at one end of the first camshaft 10 so that the cam sprocket 30 having sprocket teeth 30t on the outer periphery rotates integrally with the first camshaft 10. Etc.), etc.). A chain transmission mechanism 33 is constituted by the cam sprocket 30, a drive sprocket (not shown) fixed to the crankshaft, and an endless chain 34 wound between the two sprockets. The cam sprocket 30 constitutes the cam drive wheel of the present invention.

An exhaust cam 10c as a first cam is integrally formed on the outer periphery of the first cam shaft 10. An exhaust side rocker arm 6 that is pivotally supported by the cylinder head 5 and engages with an exhaust valve (not shown) is slidably contacted with the exhaust cam 10c. As the engine rotates, the exhaust cam 10c opens and closes the exhaust valve via the exhaust side rocker arm 6.

A cylindrical second camshaft 20 integrally having an intake cam 20c as a second cam in parallel with the exhaust cam 10c is provided on the outer periphery of the first camshaft 10 via bearings B3 and B4. It is movably fitted and supported. An intake side rocker arm 7 that is pivotally supported by the cylinder head 5 and engages with an intake valve (not shown) is slidably abutted on the intake cam 20c. As the engine rotates, the intake cam 20c opens and closes the intake valve via the intake side rocker arm 7.

In the present embodiment, a part of the plurality of bearings B1 and B2 that rotatably support the first camshaft 10 is the outer peripheral portion of the second camshaft 20 on the side of the intake cam 20c. The first camshaft 10 is rotatably supported via the second camshaft 20 and the bearings B3 and B4.

A disc-shaped driven flange 21 adjacent to the inner side surface (the right side surface in FIG. 1) of the cam sprocket 30 is provided at the outer end portion of the second cam shaft 20 with appropriate fixing means (for example, press-fitting means or spline fitting). Etc.).

In the cam sprocket 30, a centrifugal weight 50 adjacent to the outer side surface (the left side surface in FIG. 1) projects to a predetermined reduced diameter position (solid line position in FIG. 2) and radially outward from the reduced diameter position. It is supported by a pivot pin 32 so as to be swingable so that it can swing between the enlarged diameter position (chain line position in FIG. 2). The base end portion 32a of the pivot pin 32 is fixed to the cam sprocket 30 by appropriate fixing means (in this embodiment, press-fitting). The centrifugal weight 50 is connected to one end of a tension coil spring 51 as a return spring that urges the centrifugal weight 50 to the reduced diameter position, and the other end of the spring 51 is locked to the tip 32b of the pivot pin 32. The

Thus, the centrifugal weight 50 is disposed on the opposite side of the driven flange 21 with the cam sprocket 30 in the axial direction (more specifically, on the outer side in the axial direction when viewed from the cam sprocket 30). is there. Then, the centrifugal weight 50 and the driven flange 21 are connected via the drive pin 22 so as to be relatively rotatable. The drive pin 22 is driven from the centrifugal weight 50 so that the driven flange 21 (and hence the second cam shaft 20) rotates relative to the first cam shaft 10 in conjunction with the swing of the centrifugal weight 50 around the pivot pin 32. A driving force can be transmitted to the flange 21. Moreover, the drive pin 22 is disposed outward in the radial direction of the cam sprocket 30 with respect to the pivot pin 32.

In the present embodiment, when the centrifugal weight 50 is in the reduced diameter position, the center of the pivot pin 32 and the center of the first cam shaft 10 are viewed from the projection plane orthogonal to the first cam shaft 10 (that is, FIG. 2). Drive pins 22 are arranged on a virtual straight line connecting the two. In the present invention, if the drive pin 22 is located on the radially outer side of the cam sprocket 30 with respect to the pivot pin 32 as described above, the drive pin 22 is disposed at a position slightly shifted from the imaginary straight line. Also good.

By the way, the centrifugal weight 50 includes a plate-like base portion 50a and a weight portion 50b thicker than the base portion 50a connected to the base portion 50a, and has an arc shape along the circumferential direction of the cam sprocket 30. It is formed. The base portion 50a is formed with a particularly wide base end portion 54 in the radial direction.

The driven flange 21 is configured to be thicker than the base portion 50a of the centrifugal weight 50, and the base end portion 22a of the drive pin 22 is fixed to the thick base portion 50a (in this embodiment, press-fitted and fixed). The

Also, the wide base end portion 54 of the centrifugal weight 50 has a coupling hole into which a bearing hole 53 for rotatably penetrating and supporting an intermediate portion of the pivot pin 32 and a distal end portion 22b of the drive pin 22 are inserted and connected. 52 are juxtaposed. Among them, the bearing hole 53 is formed as a circular hole, and the connection hole 52 is formed as a long hole extending in the radial direction of the cam sprocket 30.

The cam sprocket 30 is provided with a through hole 31 through which an intermediate portion of the drive pin 22 passes. The through hole 31 is formed in a hole shape that allows the drive pin 22 to rotate around the pivot pin 32 accompanying the swinging of the centrifugal weight 50 (that is, an arc hole shape along the rotation locus of the drive pin 22). The Thus, as will be described later, the phase change angle of the second cam 20c when the second camshaft 20 (and hence the second cam 20c) is rotated relative to the first camshaft 10 is determined by the drive pin 22. It is regulated by the amount of movement from the first contact position that contacts one inner side surface 36 of the arc-shaped through hole 31 to the second contact position that contacts the other inner surface 35 of the hole 31.

Thus, when the drive pin 22 is in the first contact position, the swing position of the centrifugal weight 50 is defined as a predetermined reduced diameter position against the elastic force of the tension coil spring 51 as a return spring. When the drive pin 22 is in the second contact position, the swing position of the centrifugal weight 50 is defined as a predetermined diameter-enlarged position against the centrifugal force of the centrifugal weight 50.

Next, the operation of the first embodiment will be described. Since the centrifugal force acting on the centrifugal weight 50 is small when the internal combustion engine is in the low speed operation region, the centrifugal weight 50 is held at a predetermined reduced diameter position (solid line position in FIG. 2) by the elastic force of the tension coil spring 51. Is done. Further, when the rotational speed of the internal combustion engine increases, the centrifugal weight 50, which increases the centrifugal force with it, swings from the reduced diameter position toward the enlarged diameter position (chain line position in FIG. 2).

Thus, the centrifugal weight 50 is swung from the reduced diameter position to the enlarged diameter position by centrifugal force as the engine speed of the internal combustion engine increases, and accordingly, the centrifugal weight 50 is driven via the drive pin 22 to the driven flange 21 ( Accordingly, since the second cam shaft 20 with the intake cam 20c is rotated relative to the first cam shaft 10, the phase of the intake cam 20c in particular among the intake and

exhaust cams

20c, 10c (and hence the intake cam 20c is inhaled). Only the intake valve opening / closing timing linked via the side rocker arm 7 can be changed (advanced) in response to the increase in the engine speed in conjunction with the swing of the centrifugal weight 50. Thus, for example, only the intake cam 20c can be advanced (see FIG. 3) during high-speed operation of the engine, so that the overlap period between the intake valve opening and the exhaust valve opening is lengthened to improve the scavenging efficiency and High-speed driving performance can be improved.

In addition, the drive pin 22 of the present embodiment is disposed outward in the radial direction of the cam sprocket 30 with respect to the pivot pin 32, and the arm length L2 between the drive pin 22 and the first cam shaft 10 is set to the pivot pin. Therefore, the lever ratio (L2 / L1) between the arm length L1 between the pivot pin 32 and the drive pin 22 and the L2 can be sufficiently increased. As a result, the swinging force of the centrifugal weight 50 can be efficiently amplified and transmitted to the driven flange 21, so that the driven flange 21 can be driven strongly by the relatively small centrifugal force of the centrifugal weight 50, The included centrifugal mechanism can be reduced in weight and size.

Further, the centrifugal weight 50 of the present embodiment is disposed on the opposite side of the driven flange 21 with the cam sprocket 30 interposed therebetween, and the cam sprocket 30 is provided with a through hole 31 through which the drive pin 22 passes. 31 has a hole shape (in this embodiment, an arc-shaped long hole) that allows the drive pin 22 to rotate around the pivot pin 32 in accordance with the swinging of the centrifugal weight 50. As a result, the axial extension of the cam phase variable mechanism from the outer end of the first camshaft 10 is suppressed as much as possible, compared to the structure in which the driven flange 21 and the centrifugal weight 50 are both arranged on the axially outer side of the cam sprocket 30. The axial movement of the valve gear can be reduced.

Moreover, the phase change angle of the intake cam 20c during the relative rotation between the driven flange 21 (therefore the second cam shaft 20 integrated therewith) and the first cam shaft 10 is such that the drive pin 22 is one of the through holes 31. Since the amount of movement of the drive pin 22 restricted by the inner wall of the through hole 31 is restricted by the amount of movement from the contact position with the inner side surface 36 to the contact position with the other inner side surface 35, the intake cam This directly corresponds to the limit value of the phase change angle of 20c, and the setting accuracy of the phase change angle can be improved.

Further, in the present embodiment, when the centrifugal weight 50 is in the reduced diameter position, the center of the pivot pin 32 and the center of the first cam shaft 10 are viewed from the projection plane (FIG. 2) orthogonal to the first cam shaft 10. Since the drive pin 22 is arranged on the imaginary straight line to be connected, the length of L1 with respect to the specified L2 is minimum at the diameter reduction position (that is, the swing initial position) of the centrifugal weight 50. This makes it possible to set the maximum value of the lever ratio (L2 / L1) in combination with the above-described effect that L2 can be secured sufficiently long, so that the drive response of the driven flange 21 by the drive pin 22 is achieved. Sexually enhanced.

Furthermore, the driven flange 21 of the present embodiment is configured to be thicker than the relatively thin plate-like base portion 50a of the centrifugal weight 50, and the base end portion 22a of the drive pin 22 is fixed. The support rigidity with respect to the drive pin 22 can be increased. In addition, since the distal end portion 22b of the drive pin 22 is inserted and connected, and the connection hole 52 formed by a long hole in the radial direction of the cam sprocket 30 is provided in the base portion 50a of the centrifugal weight 50, the centrifugal weight 50 The difference between the turning radius of the connecting hole 52 around the pivot pin 32 and the turning radius of the drive pin 22 around the center of the cam sprocket 30 is within the connecting hole 52 (long hole) that is long in the radial direction. Thus, the sliding force of the centrifugal weight 50 can be smoothly transmitted to the driving pin 22 through the connecting hole 52.

Second embodiment

Next, a second embodiment of the present invention will be described with reference to FIGS. In the first embodiment described above, the first cam on the first cam shaft 10 is the exhaust cam 10c, and the second cam on the second cam shaft 20 is the intake cam. However, the second embodiment The first cam 10c on the first cam shaft 10 is an intake cam, and the second cam 20c on the second cam shaft 20 is an exhaust cam. Therefore, the intake side rocker arm 7 is in sliding contact with the first cam 10c (intake cam), and the exhaust side rocker arm 6 is in sliding contact with the second cam 20c (exhaust cam).

Other configurations are basically the same as those in the first embodiment, and the same reference numerals as those in the first embodiment are given to the respective constituent members. However, in the second embodiment, the mutual arrangement (that is, relative positional relationship) of the centrifugal weight 50, the drive pin 22, and the pivot pin 32 is different from that of the first embodiment, that is, each member shown in FIG. This arrangement form is in a mirror image relationship with the arrangement form of each member shown in FIG. Thus, as the centrifugal weight 50 swings from the reduced diameter position to the enlarged diameter position, the centrifugal weight 50 moves the driven flange 21 (second cam shaft 20) relative to the first cam shaft 10 via the drive pin 22. When the engine is rotated (that is, when the engine speed increases), the phase of the second cam 20c (exhaust cam) can be retarded (see FIG. 6) in conjunction with the swing of the centrifugal weight 50. .

Thus, according to the second embodiment, the centrifugal weight 50 oscillates from the reduced diameter position to the enlarged diameter position by the centrifugal force according to the increase in the engine speed of the internal combustion engine, and via the drive pin 22. When the driven flange 21 (second camshaft 20) is rotated relative to the first camshaft 10, the phase of the exhaust cam as the second cam 20c (and thus the exhaust cam via the exhaust-side rocker arm 6). Only the exhaust valve opening / closing timing that is linked) is changed (retarded) according to the increase in the engine speed, so that, for example, the scavenging efficiency in the high-speed operation region of the internal combustion engine can be improved and the high-speed operation performance can be improved. . Therefore, it is particularly suitable for an internal combustion engine that requires an increase in exhaust efficiency.

Other operational effects of the second embodiment are basically the same as those of the first embodiment.

Third embodiment

Next, a third embodiment will be described with reference to FIG. In the present embodiment, the return spring that repels the centrifugal weight 50 in the diameter reducing direction is constituted by a torsion spring 60 interposed between the centrifugal weight 50 and the cam sprocket 30.

One end of the torsion spring 60 is connected to the centrifugal weight 50 via a first locking pin 61 fixed to the base 50 a of the centrifugal weight 50, and the other end of the spring 60 is fixed to the cam sprocket 30. The cam sprocket 30 is locked via the locking pin 62. Further, the intermediate coil portion 63 of the torsion spring 60 is surrounded by the periphery of the pivot pin 32, and therefore, the reluctance of the spring intermediate portion is suppressed.

Thus, the centrifugal weight 50 is held in the reduced diameter position (solid line position in FIG. 7B) during normal times by the torsional force of the torsion spring 60. Further, the centrifugal weight 50 swings against the torsional force of the torsion spring 60 toward the diameter-enlarged position (the chain line position in FIG. 7B) by centrifugal force in accordance with the increasing change in the engine speed. Move.

Other configurations of the third embodiment are basically the same as those of the first embodiment, and the same reference numerals as those of the first embodiment are given to the respective constituent members. In addition, the said 3rd Embodiment also achieves the effect similar to 1st Embodiment fundamentally.

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 above-described embodiment, one of the first and

second cams

10c and 20c is an exhaust cam and the other is an intake cam. However, in the present invention, the first and second cams are used. Both the

cams

10c and 20c may be intake cams (ie, first and second intake cams), or both the first and

second cams

10c and 20c are exhaust cams (ie, first and second exhaust cams). It is good.

In the above embodiment, the single-cylinder engine is used as the internal combustion engine provided with the valve gear, but the present invention may be applied to a multi-cylinder (for example, two-cylinder) engine. In this case, the cam phase variable mechanism of the present invention is provided for each cylinder.

In the above embodiment, the SOHC engine is used as the internal combustion engine provided with the valve gear, but the present invention may be applied to a DOHC engine. In this case, the cam phase varying mechanism of the present invention is provided on at least one of the intake camshaft and the exhaust camshaft provided for each intake valve and exhaust valve.

In the above embodiment, an internal combustion engine for a motorcycle is shown. However, the present invention may be applied to an internal combustion engine mounted on a vehicle other than a motorcycle, or an internal combustion engine for a purpose other than a vehicle (for example, a stationary engine). The present invention may be applied to an internal combustion engine of the type.

In the above embodiment, the centrifugal weight 50 is disposed on the opposite side of the driven flange 21 with the cam drive wheel (cam sprocket 30) interposed therebetween, in particular, on the outer side in the axial direction of the cam drive wheel 30. In the present invention, the centrifugal weight 50 may be disposed on the inner side in the axial direction of the cam driving wheel 30. In this case, the centrifugal weight 50 is disposed between the driven flange 21 disposed on the outer side in the axial direction of the cam driving wheel 30 and the first cam shaft 10. May be integrally coupled with a connecting arm that penetrates the cam drive wheel 30 loosely.

The optimum relationship between the engine speed (particularly the vehicle speed in the case of an internal combustion engine for vehicles) and the opening / closing timings of the intake and exhaust valves can be variously set depending on the structure and specifications of the internal combustion engine. For example, in the above-described embodiment, the control example in which the valve timing is changed in the high speed operation range has been described. However, for example, the valve timing may be changed in the medium speed operation range. Further, in the first embodiment shown in FIG. 3, the intake cam as the second cam is advanced in the high speed operation range, but conversely, the exhaust cam is advanced (see FIG. 8) to close the exhaust valve. The timing may be advanced, and in this case, the valve overlap period can be shortened to prevent the unburned gas from being blown out, and the hydrocarbon in the exhaust gas can be reduced. Further, in the second embodiment shown in FIG. 6, the exhaust cam as the second cam is retarded in the high speed operation range, but conversely, the intake cam is retarded (see FIG. 9) to close the intake valve closing timing. In this case, the intake efficiency can be improved by the inertia supercharging effect.

Claims

A first camshaft (10) integrally having a first cam (10c) is integrally connected to a cam drive wheel (30) that rotates in conjunction with a crankshaft of an internal combustion engine,
A second cam shaft (20) integrally having a second cam (20c) is supported on the first cam shaft (10) so as to be relatively rotatable, and the second cam shaft (20) is driven by the cam. A driven flange (21) adjacent to the ring (30) is integrally connected;
The cam drive wheel (30) has a centrifugal weight (50) disposed on the opposite side of the driven flange (21) across the cam drive wheel (30), and has a predetermined reduced diameter position and an enlarged diameter position. A return spring (51, 60) is connected to the centrifugal weight (50) and biased to the reduced diameter position. ,
The driven flange (21) and the centrifugal weight (50) are connected to each other via a drive pin (22) that passes through a through hole (31) provided in the cam drive wheel (30). A driven pin (22) is driven from the centrifugal weight (50) to the driven flange so that the driven flange (21) rotates relative to the first camshaft (10) in conjunction with the swing of the centrifugal weight (50). (21) can transmit the driving force,
The through hole (31) has a hole shape that allows the drive pin (22) to rotate around the pivot pin (32) accompanying the swing of the centrifugal weight (50),
The cam phase variable in the valve gear for an internal combustion engine, wherein the drive pin (22) is disposed outward in the radial direction of the cam drive wheel (30) with respect to the pivot pin (32). mechanism.
The phase change angle of the second cam (20c) during the relative rotation is such that the drive pin (22) penetrates from the contact position with one inner surface (36) of the through hole (31). 2. The cam phase varying mechanism in the valve gear for an internal combustion engine according to claim 1, wherein the cam phase varying mechanism is regulated by an amount of movement to a contact position with the other inner side surface of the hole.
When the centrifugal weight (50) is in the reduced diameter position, the center of the pivot pin (32) and the center of the first cam shaft (10) are viewed from the projection plane orthogonal to the first cam shaft (10). The cam phase varying mechanism in the valve gear for an internal combustion engine according to claim 1 or 2, wherein the drive pin (22) is arranged on a virtual straight line connecting the two.
The centrifugal weight (50) includes a plate-like base (50a) and a weight part (50b) thicker than the base (50a) connected to the base (50a).
The driven flange (21) is configured to be thicker than the base (50a) of the centrifugal weight (50), and fixes the base end (22a) of the drive pin (22),
The distal end portion (22b) of the drive pin (22) is inserted and connected, and a connection hole (52) constituted by a long hole in the radial direction of the cam drive wheel (30) is provided in the centrifugal weight (50). The cam phase varying mechanism in the valve gear for an internal combustion engine according to any one of claims 1 to 3, wherein the cam phase varying mechanism is provided at the base (50a).