JPH084504A - Valve system for engine - Google Patents

Abstract

PURPOSE:To increase air intake efficiency and exhaust efficiency without increasing the amount of valve opening and lift, and also reduce the bending moment and shearing force acting on a lifter. CONSTITUTION:In a valve system for engine provided with a valve opening and closing mechanism in which intake valves 13 and exhaust valves 14 are opened and closed along specified lift curves, the form of an exhaust valve cam lift part 22 is set so that an average valve opening speed is increased more so as to make the lift curves asymmetrical of which maximum lift positions are deflected to advance and lag sides, respectively. Also a lifter 18 and a cam shaft 20 are positioned at an offset so that the lifter 18 is shifted to the side where the opening side part 22a of the exhaust valve cam lift part 22 is made in contact with the lifter 18, and the exhaust valve 14 is positioned at an offset in the same direction as the lifter 18 set at an offset.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve operating system for an engine.

[0002]

2. Description of the Related Art A valve operating system for an engine is for opening and closing an intake valve and an exhaust valve along a predetermined lift curve. This lift curve shows the relationship between the lift amount of the intake valve and the exhaust valve and the crankshaft rotation angle (camshaft rotation angle). Conventionally, the lift curve is generally shown by the broken line in FIG. 5, for example. In the figure, the horizontal axis represents the camshaft rotation angle, and the vertical axis represents the lift amount or valve speed of the intake valve and the exhaust valve. The conventional exhaust valve lift curve EX ′ and intake valve lift curve IN ′ are symmetrical with respect to the maximum lift cam angle θm ′, and the exhaust valve open side cam angle θEXO
′ = Closed side cam angle θEXC ′, intake valve open side cam angle θI
NO '= cam angle θINC' on the closing side. From the lift curves EX 'and IN', it is understood that in the conventional valve operating device, both the intake valve and the exhaust valve have the maximum opening at the center of the valve opening period. Also, it can be seen that the opening-side and closing-side average valve speeds are set to be the same.

[0003]

By the way, in order to improve the engine output, it is necessary to improve the charging efficiency. For that purpose, it is effective to increase the intake valve opening area or the lift amount. However, there is a limit in increasing the intake valve opening area due to the restriction on the space for forming the valve opening determined by the cylinder bore diameter. Therefore, for example, if the intake valve opening is made large, the exhaust valve opening must be made small, and there is a concern that exhaust efficiency will be reduced. Further, if the lift amount is increased, it is necessary to form a large relief at the top of the piston in order to prevent the valve heads of the intake valve and the exhaust valve from interfering with the piston at the time of the above overlap, which is a constraint for securing the compression ratio. There's a problem.

Therefore, the applicant of the present application has proposed an asymmetrical lift curve in which the maximum lift position is biased toward the advance side or the retard side as a valve operating device capable of improving the intake efficiency and the exhaust efficiency without increasing the valve opening and the lift amount. Are developing something that has. For example, in the case of an exhaust lift curve, the maximum lift position is advanced so that a high blowdown pressure can be obtained, and exhaust efficiency can be improved while reducing the exhaust valve opening. It is possible to improve the filling efficiency.

In the above exhaust lift curve, in order to advance the maximum lift position and secure a lift amount equivalent to that of the conventional one, it is necessary to increase the opening side speed of the exhaust valve, which causes the exhaust cam lift. There is a concern that the moving distance of the contact point between the open side portion of the portion and the lifter becomes large, and the exhaust lifter will have a large diameter as it is. In order to solve this problem, it is effective to dispose the exhaust lifter in an offset manner so as to be displaced to the side where the opening side portion comes into contact with the cam shaft.

However, if the lifter is arranged offset with respect to the cam shaft, a bending moment and a shearing force act on the lifter, which is disadvantageous in securing the strength of the lifter, and causes a problem in reducing the weight of the lifter.

The present invention has been made in view of the above circumstances, and it is possible to improve the intake efficiency and the exhaust efficiency without increasing the valve opening and the lift amount, and reduce the bending moment and shearing force acting on the lifter. It is an object of the present invention to provide a valve operating device for an engine that is made possible.

[0008]

According to a first aspect of the present invention, there is provided an engine valve operating system including a valve opening / closing mechanism for opening / closing an intake valve and an exhaust valve along a predetermined lift curve. The lifter mounted on the valve shaft is a direct-acting type configured so as to be pressed by the cam lift portion, and the shape of at least one of the intake valve and the exhaust valve cam lift portion is set to an average valve opening speed. By setting the average valve closing speed to be different from the average valve closing speed, the lift curve has an asymmetrical shape in which the maximum lift position is biased toward the advance side or the retard side, and the average valve speed of the cam lift portion is The lifter and the cam shaft are offsetly arranged so that the lifter is displaced on the side where the large portion and the lifter come into contact with each other, and further, the valve is offsetly arranged in the same direction as the offsetly arranged lifter. To have.

According to a second aspect of the present invention, in the first aspect, by setting the shape of the cam lift portion so that the curvature of the open side portion and the curvature of the close side portion are different sizes, the average valve opening It is characterized in that the speed and the average valve closing speed have different magnitudes.

According to a third aspect of the present invention, in the first or second aspect, the shape of the exhaust cam lifting portion is set so that the curvature of the open side portion is smaller than the curvature of the closed side portion. The average valve opening speed is made higher than the average valve closing speed, and the exhaust valve lift curve is made asymmetrical with the maximum lift position biased toward the advance side. It is characterized in that the lifter and the exhaust valve cam shaft are offsetly arranged so that the lifter is displaced on the side where the lifter comes into contact, and the exhaust valve is offsetly arranged on the same side as the exhaust valve lifter.

The invention of claim 4 relates to claims 1 to 3.
In any of the above, by setting the shape of the intake cam lift portion so that the curvature of the closed side portion is generally smaller than the curvature of the open side portion, the average valve closing speed of the intake valve is made larger than the average valve opening speed, The intake valve lift curve has an asymmetrical shape in which the maximum lift position is deviated to the retard side, and the lifter is deviated to the side where the closed side portion of the intake valve cam lift portion contacts the intake valve lifter. As described above, the lifter and the intake valve cam shaft are arranged offset from each other, and the intake valve is further arranged offset to the same side as the intake valve lifter.

Here, in each of the above inventions, the fact that the curvature of the open side portion is made smaller than that of the closed side portion has the following meaning. That is, the cam lift portion in the present invention is composed of the cam lobe following the base circle and the cam nose constituting the maximum lift portion, but in particular, the curvature in the cam lobe is not constant but continuously changes. This means that the curvature of the open side portion is reduced as a whole, but the curvature of the open side portion may be large when viewed locally. The same applies to making the curvature of the closed side portion smaller than that of the open side portion.

[0013]

According to the engine valve operating system of the first aspect of the present invention, the exhaust valve lift curve or the intake valve lift curve has an asymmetrical shape in which the maximum lift position is biased toward the advance side or the retard side. Therefore, by appropriately selecting this asymmetrical shape, it is possible to suppress the decrease in exhaust efficiency while reducing the exhaust valve opening, and improve the charging efficiency.

In order to make the lift curve asymmetrical, the lifter and the cam shaft are arranged so that the lifter is biased on the side where the portion of the cam lift having a large average valve speed contacts the lifter. Since the offset arrangement is adopted, it is possible to widen the range of movement of the contact point between the cam lift portion and the lifter without increasing the lifter diameter, thereby increasing the valve lift speed and ensuring the required lift amount.

When the lifter is offset with respect to the cam shaft, the intake valve or the exhaust valve is offset in the same direction as the offset lifter. Since the valve shaft is positioned so as to support the contact point, the bending moment acting on the lifter can be suppressed or eliminated, and the disadvantage of the strength of the lifter can be avoided.

According to the third aspect of the invention, the exhaust valve lift curve has an asymmetrical shape in which the maximum lift position is biased toward the advance side. Therefore, the exhaust valve has the maximum opening degree when the combustion gas pressure is high in the explosion stroke. The high blowdown pressure can be obtained by opening it to the exhaust gas, the combustion gas can be surely discharged, and the exhaust efficiency can be improved.

According to the third aspect of the invention, the lifter and the exhaust valve cam shaft are arranged so that the lifter is biased to the side where the open side portion of the exhaust valve cam lift portion and the exhaust valve lifter come into contact with each other. Since the exhaust valve is offset, and the exhaust valve is offset on the same side as the exhaust valve lifter, the intake lifter is biased to the closed side and the intake valve is biased in the same direction. Therefore, the valve lift speed can be increased by increasing the range of movement of the contact point between the cam lift and lifter without increasing the diameter of the lifter and suppressing or eliminating the bending moment and shearing force acting on the lifter. can do.

[0018]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 to 6 are views for explaining an engine valve operating system according to an embodiment (first embodiment) of the invention of claims 1 to 7, and FIG. 1 is a front view of the engine of this embodiment,
2 is a sectional front view of the valve gear, FIG. 3 is a sectional side view of an exhaust valve portion, FIG. 4 is a sectional plan view showing a valve opening, FIG. 5 is a schematic diagram showing an exhaust cam lift portion, and FIG. 6 is a lift curve. FIG.

In the figure, reference numeral 1 denotes a water-cooled 4-cycle 4-cylinder 5-valve engine. In this engine 1, a crankcase 3 and an oil pan 4 are laminated and fixed on a lower mating surface of a skirt portion 2a of a cylinder block 2, The cylinder head 5 is fastened to the upper mating surface with head bolts,
Has a structure in which the head cover 6 is attached to the upper mating surface of the.

Pistons 7 are slidably inserted into the cylinder bores 2b arranged in parallel with the cylinder block 2, and the pistons 7 are connected to the crankpin 9b of the crankshaft 9 via the connecting rod 8. It is connected. The crankshaft 9 extends in the arrangement direction of the cylinder bores 2b.

A combustion recess 5a forming a combustion chamber is provided in the cylinder block 5 mating surface of the cylinder head 5, and the combustion recess 5a has an axis X of the cylinder bore 2b as shown in FIG. And one center intake valve opening 10 located on a straight line perpendicular to the axis of the crankshaft 9.
a, and three intake valve openings consisting of two side intake valve openings 10b, 10b located on the left and right sides thereof, and two exhaust valves arranged adjacent to the side intake valve openings 10b, 10b. Openings 10c and 10c are formed.

Here, the center intake valve opening 10a, the side intake valve opening 10b, and the exhaust valve opening 10c are located substantially on the circumference along the inner peripheral surface of the cylinder bore 2b. The diameters d1 and d of the valve openings 10a, 10b and 10c
2 and d3 are set to have a relationship of d2>d3> d1.

The diameters of the valve openings 10a to 10c are set in the above relationship for the following reason. That is, the aim is to introduce as much air as possible into the cylinder bore from the portion closer to the cylinder bore axis X in the direction of the cam axis in the direction of the bore axis X. Side intake valve opening 1
0b is made as large as possible, and then the center intake valve opening 10
Regarding b, the diameter was set relatively small in order to arrange it as close to the bore axis X as possible. Further, the exhaust valve opening 10c has a smaller diameter than the side intake valve opening 10b in order to avoid interference with the enlarged side intake valve opening 10b.
The decrease in exhaust efficiency due to the reduction in diameter of the exhaust valve opening 10c is suppressed by making the lift curve asymmetrical, which is a feature of the present invention, as described in detail below.

Center and side intake valve openings 10a, 1
0b are led outward by the center intake port 11a and the side intake port 11b, respectively.
The merging intake ports 11 of a and 11b are opened on one side wall of the cylinder head 5. Further, the exhaust valve opening 10c is led out to the outside by the exhaust port 12a, and these port 1
The merged exhaust port 12 of 2a is opened to the other side wall of the cylinder head 5.

Center and side intake valve openings 10a, 1
0b is the center, the side intake valves 13, the valve head 13a of the 13,
The exhaust valve opening 10 can be opened and closed by 13a '.
c is openable and closable from the valve head 14a of the exhaust valve 14. The valve shaft 13b of the intake valve 13 and the valve shaft 14b of the exhaust valve 14 extend obliquely upward so as to spread outward at a predetermined angle.

Retainers 15 are detachably attached to the upper ends of the intake valves 13 and the exhaust valves 14, respectively. A valve spring 16 is arranged in a compressed state between each retainer 15 and a spring seat 5b formed on the cylinder head 5, whereby each of the valves 13 and 14 is compressed.
Is urged to close the valve openings 10a to 10c.

An intake lifter 17 is attached to the upper end of the intake valve 13 so as to surround the upper portions of the retainer 15 and the valve spring 16, and the upper end of the exhaust valve 14 has the retainer 15 and An exhaust lifter 18 is mounted so as to surround the upper portion of the valve spring 16. The intake and exhaust lifters 17 and 18 are slidably guided and supported by guide holes 5c formed in the cylinder head 5. These intake and exhaust lifters 17 and 18 are cylindrical with their upper ends closed, and the shim 1 arranged and fixed on the inner surface of the closed wall.
7a and 18a are in contact with the upper ends of the valve shafts 13b and 14b.

Then, the intake lifter 17 and the exhaust lifter 1
8, an intake camshaft 19 and an exhaust camshaft 20 are arranged in parallel with the crankshaft 9, and are freely rotatable by a bearing portion formed on the upper mating surface of the cylinder head 5 and a cam cap attached to the bearing portion. Supported by. Although not shown, the intake cam shaft 19 and the exhaust cam shaft 20 are connected to each other by meshing gears attached to their ends, and either one of the cam shafts is It is connected to the crankshaft 9 by a gear or a chain or the like. Due to the gear coupling, the intake camshaft 1
9 rotates counterclockwise in FIG. 2, and the exhaust cam shaft 20 rotates in clockwise direction in FIG.

In this embodiment, the intake / exhaust valve 1 described above is used.
3 and 14, intake / exhaust lifters 17/18 and intake / exhaust cam shafts 19/20, and the shape of the intake / exhaust cam lifts 21 and 22 (cam profile) are characteristic. I will describe.

When viewed in the cam shaft direction, the intake lifter 17 is arranged such that its axis c is parallel to the intake valve axis b, as shown in FIG. It is arranged so that it is displaced by A in the direction perpendicular to the side closer to the cylinder bore axis X. The intake camshaft 19 and the center and side intake valves 13, 13 are arranged so that the camshaft axis a and the intake valve axis b intersect.

When viewed in the cam shaft direction, the exhaust lifter 18 is arranged such that its axis f is parallel to the exhaust valve axis e, and the exhaust valve 14 is connected to the exhaust cam shaft 20 as shown in FIG. It is arranged so as to be displaced by B in the direction perpendicular to the anti-cylinder bore axis X side.

On the other hand, the exhaust valve 14 is arranged so as to deviate from the exhaust cam shaft 20 in the direction perpendicular to the exhaust lifter 18 by a distance C to the side opposite to the cylinder bore axis X. The deviation amount B is set to be larger than 18.

Further, when viewed in the direction perpendicular to the cam axis, as shown in FIG. 3, the exhaust cam lift portion 22 and the exhaust valve 14 are not displaced, but the exhaust lifter 18 is displaced outward by D. are doing. This ensures the wall thickness between the lifter guide holes 5c and allows the exhaust lifter 18 to rotate about its axis.

Here, when the exhaust valve 14, the exhaust camshaft 20, and the exhaust lifter 18 are offsetly arranged, the inclination angle and position of the exhaust valve 14 are first set from the viewpoint of ensuring an ideal combustion chamber shape. It is desirable to set the positions of the exhaust lifter 18 and the exhaust cam shaft 20 based on the exhaust valve 14 according to the deviation amount. The same applies to the intake valve 13. On the other hand, when the position of the exhaust valve 14 is used as a reference, the interval between the cam shafts may not match the interval determined by the transmission gear diameter or the like. Therefore, the exhaust valve 14 and the exhaust lifter 18 are referenced based on the position of the cam shaft. It is also possible to determine In this case, the exhaust lifter 18 may be close to the exhaust port side, which may cause a problem in heat load. In this case, it is effective to dispose the water cooling jacket 5d outside the exhaust lifter 18 to reduce the heat load.

Further, the cam lift portion 2 of the intake cam shaft 19 is also provided.
The top surface T of No. 1 is formed so as to project from the base circle 19a at a height corresponding to the maximum lift amount, and is located on the valve opening lift portion 21a located on the front side in the rotation direction and on the rear side in the rotation direction. It is composed of a valve-closing lift portion 21b, and the cam profiles of the lift portions 21a and 21b are asymmetrical. That is, the radius of curvature R of the valve closing lift 21b
c is set to be larger than the curvature radius Ro of the valve opening lifter 21a, and the cam angle θINC of the valve lifter 21b is set.
Is set to be smaller than the cam angle θINO of the valve lift 21a. As a result, the intake valve 13 is connected to the intake camshaft 1.
The rotation of the large cam angle θINO of 9 results in the maximum opening at a lower average opening speed than the conventional symmetrical head, and the rotation of the small angle θINC results in full closing at a higher average closing speed.

On the other hand, the cam lift portion 2 of the exhaust cam shaft 20.
The top surface T of 2 is formed so as to project from the base circle 20a to a height corresponding to the maximum lift amount, and is located on the valve opening lift portion 22a located on the front side in the rotation direction and on the rear side in the rotation direction. It is composed of a valve-closing lift portion 22b, and the cam profiles of both lift portions 22a and 22b are asymmetrical. That is, the radius of curvature R of the valve opening lift portion 22a
o is set to be larger than the radius of curvature Rc of the valve closing lift 22b, and the cam angle θEXO of the valve opening lift 22a.
Is set to be smaller than the cam angle θEXC of the valve closing lift 22b. As a result, the exhaust valve 14 becomes
The rotation of the small cam angle θEXO of 0 results in the maximum opening at a higher average speed than that of the conventional symmetrical head section, and the rotation of the large cam angle θEXC causes the full opening at a lower average speed.

Here, the valve-opening lift portions 21a and 22a and the valve-closing lift portions 21b and 22b are respectively formed by the base circle 1
It is composed of a cam lobe portion following 9a and 20a and a cam nose portion near the top surface T. In particular, the radius of curvature of the cam lobe portion is not constant but changes substantially continuously. Therefore, the radii of curvature Rc and Ro are not radii of curvature when viewed locally, but radii of curvature when averaged as a whole. The radius of curvature Ro usually takes a positive value, but it may also take a negative value. In addition, considering the case where the radius of curvature changes from positive to negative, it changes from positive infinity to negative infinity, and at first glance it seems that there is no continuity, so in the scope of the claims of the present application, the curvature I decided to use curvature instead of radius. Therefore, when the radius of curvature is large, it means that the curvature is small.

Next, the function and effect of this embodiment will be described. First, the operation of the exhaust valve 14 will be described. The exhaust cam shaft 20 rotates clockwise in FIG. 2 as the crankshaft 9 rotates. When the piston 7 descends to near the expansion bottom dead center, the valve opening lift 22a of the exhaust cam lift 22 starts sliding contact with the upper surface of the exhaust lifter 18 at the sliding contact C1 (see FIG. 5), and the exhaust valve 14 opens. Start (lift curve E in Figure 6
See X). Subsequently, when the piston 7 starts to rise and enters the exhaust stroke and the exhaust cam shaft 20 rotates by the angle θ EXO from the sliding contact start position of the valve opening lift portion 22a, the exhaust cam lift portion 2
The top surface T of 2 is in sliding contact with the sliding contact Co on the upper surface of the lifter, and the exhaust valve 14 has the maximum opening. When the exhaust cam shaft 20 further rotates, the valve closing lift 22b of the exhaust cam lift 22 starts sliding contact with the upper surface of the lifter, and the exhaust valve 14 starts closing. When the exhaust cam shaft 20 makes an angle θ EXC from the sliding contact start position (Co) of the valve closing lift 22b, the base circle 20a starts sliding contact, the exhaust valve 14 is fully closed, and the piston 7 is exhausted to the top dead center. After that, it starts descending and enters the intake stroke. in this case,
Lifter 18 of valve lift 22a of exhaust cam lift 22
The sliding contact with C changes from D1 from C1 to Co, while the sliding contact with the lifter 18 of the valve closing lift 22b is C.
Only D2 from o to C2 changes, and D1> D2.

In the opening / closing operation of the exhaust valve 14 as described above, in this embodiment, the radius of curvature Ro of the valve opening lift 22a of the exhaust cam lift 22 is set large, that is, the curvature is set small, and the cam angle θEXO thereof is set. Since the exhaust lift curve EX is set to be narrow, the maximum lift angle θm has an asymmetric shape in which the maximum lift angle θm is deviated to the advance side. Incidentally, the conventional exhaust lift curve EX 'has a symmetrical shape about the maximum lift angle θm'. Therefore, the exhaust valve 1 of this embodiment
The maximum lift angle θm of 4 is the conventional maximum lift angle θm ′.
It is more advanced and reaches its maximum opening earlier than before. In this case, the valve lifting lifter 22 of the cam lifter 22 is opened.
The smaller the cam angle θ EXO of “a”, the larger the advance angle, and the earlier the maximum opening is reached.

Here, in FIG. 6, a curved line VEX indicated by a one-dot chain line shows a change in speed of the exhaust valve 14 in this embodiment, and a curved line VEX 'shown by a two-dot chain line shows a change in speed of a conventional exhaust valve. As is apparent from the figure, in the case of the conventional exhaust lift curve EX ', which has a symmetrical shape, the valve speed at the time of opening the valve and the valve speed at the time of closing the valve are both the maximum speed and the average speed. It is the same, so the velocity curve is also symmetrical. On the other hand, in the case of the present embodiment, the valve speed at the time of opening the valve is higher than the valve speed at the time of closing both the maximum speed and the average speed. As a result, the maximum lift amount equivalent to the conventional one is secured while advancing the maximum lift angle.

Next, the operation of the intake valve 13 will be described.
The intake camshaft 19 rotates counterclockwise in FIG. 2 as the crankshaft 9 rotates. When the piston 7 rises to near the exhaust top dead center, the valve opening lift 21a of the cam lift 21 of the intake camshaft 19 starts sliding contact with the upper surface of the intake lifter 17 and the intake valve 13 begins to open (see FIG. 6). See lift curve IN). Then, the piston 7 starts descending to enter the intake stroke, and when the intake camshaft 19 rotates θINO from the sliding contact start position with the lifter 17 of the valve opening lifter 21a, the top surface T of the cam lifter 21 is lifted. It comes into sliding contact with the upper surface, and the intake valve 13 has the maximum opening. When the intake camshaft 19 further rotates, the valve closing lift 21b of the cam lift 21 starts sliding contact with the upper surface of the lifter, and the intake valve 13 starts closing. And intake camshaft 19
When θINC is rotated from the sliding contact start position of the valve closing lift portion, the base circle 19a starts sliding contact, the intake valve 13 is fully closed, and the piston 7 starts rising up through the suction bottom dead center and enters the compression stroke. . The diameters of the base circles 20a and 19a are set so that a slight clearance is generated between the base circles 20a and 19a. Strictly speaking, the two are not in sliding contact with each other,
For convenience of explanation, it is expressed as sliding contact.

In the opening / closing operation of the intake valve 13 as described above, in the present embodiment, the radius of curvature of the valve opening lift portion 21a of the intake cam lift portion 21 is set small, that is, the curvature is set large, and the cam angle θINO is wide. Since it is set,
The intake lift curve IN has an asymmetrical shape in which the maximum lift angle θm is deviated to the retard side. Incidentally, the conventional intake lift curve IN 'is symmetrical about the maximum lift angle θm'. Therefore, the maximum lift angle θm of the intake valve 13 of this embodiment is retarded from the conventional maximum angle θm ′, which is later than the conventional maximum opening angle. In this case, the wider the cam angle θINO of the valve lifting portion 21a of the cam lifting portion 21, the larger the retard angle, and thus the later the maximum opening degree.

In the present embodiment, since the exhaust valve opening 10c is set to have a relatively small diameter, it is possible to secure a larger total area of the intake valve opening, and the air introduction amount is increased as the total area of the intake valve opening is increased. Can increase. In order to increase the total area of the intake valve openings, the two side intake valve openings 1
Since 0b is set to be larger than one center intake valve opening 10a, a larger part of the increased air is introduced from the side intake valve opening 10b located near the cylinder bore axis X in the cam axis direction. Therefore, a larger amount of air is introduced from the vicinity of the center of the cylinder bore in the X direction of the cylinder bore axis, so-called tumble (longitudinal vortex) in the forward direction.
Is likely to occur.

Since the center intake valve opening 10a is located on the outer side of the cylinder bore when viewed in the cam axis direction, the air introduced from the center intake valve opening 10a is introduced from the side intake valve opening 10b. There is a tendency to generate so-called reverse tumble that cancels air. In the present embodiment, since the center intake valve opening 10a is set to have a smaller diameter than the side intake valve opening 10b, the amount of air from the center intake valve opening 10a is relatively small, and the above-mentioned reverse tumble is suppressed. Center intake valve opening 1
Since 0b is set to a small diameter, this center intake valve opening 10
a can be arranged closer to the cylinder bore axis X side, so that the air flow from the center intake valve opening 10a tends to be the same as the air flow from the side intake valve opening 10b. The reverse tumble can be suppressed.

On the other hand, since the exhaust valve opening 10c is set relatively small in order to secure a large total area of the intake valve opening, there is a concern that the exhaust efficiency will decrease. On the other hand, in this embodiment, the maximum lift angle θm in the exhaust lift curve EX is deviated to the advance side, so that the exhaust valve 14 opens to the maximum opening when the combustion gas pressure is high in the explosion stroke. Which results in a high blowdown pressure. Therefore, when the diameter d2 of the side intake valve opening 10b is set large as in the present embodiment and the diameter d3 of the exhaust valve opening 10c is set relatively small in order to avoid interference with the side intake valve opening 10b. Can reliably discharge the combustion gas and ensure exhaust efficiency. Moreover, since the blowdown pressure is high, the scavenging efficiency at the time of overlap is improved, and the filling efficiency is improved accordingly.

Further, in this embodiment, since the exhaust efficiency is high as described above, the exhaust lift curve EX is moved toward the retard side as a whole as compared with the conventional symmetrical lift curve EX '. It is possible to delay the opening start timing of the valve 14 to near the expansion bottom dead center (see the lift curve EXo in FIG. 6). In this case,
The expansion ratio can be increased to allow the combustion pressure to sufficiently act on the piston, and the exhaust loss can be reduced by the amount of exhaust after the exhaust gas temperature is lowered.

In this embodiment, the intake lift curve IN
Since the maximum lift angle θm of the above is deviated to the retard side, the opening degree of the intake valve 13 becomes maximum when the piston 7 descends to near the bottom dead center of the intake stroke and the negative pressure in the cylinder bore increases. . Therefore, the intake flow velocity is improved, the inertial effect is enhanced, and the intake air amount is increased.

Further, in this embodiment, since the intake efficiency is high as described above, the intake valve is moved by advancing the intake lift curve IN as a whole as compared with the conventional symmetrical lift curve IN '. It is possible to accelerate the closing timing of 13 to near the suction bottom dead center (lift curve I in FIG. 6).
No.), in this case, it is possible to prevent blowback in the low speed rotation range.

Further, in this embodiment, the exhaust lift curve EX
Since the maximum lift angle θm of the intake valve is moved to the advance side and the maximum lift angle θm of the intake lift curve IN is moved to the retard side, the exhaust valve 14 and the intake valve at the time of overlap at the exhaust top dead center The lift amount L1 of 13 is smaller than the conventional lift amount L2. Therefore, the escape for avoiding the interference with the exhaust valve 14 and the intake valve 13 formed at the top of the piston 7 can be reduced or eliminated. As a result, the compression ratio can be increased.

Furthermore, in the present embodiment, as shown in FIG. 6, the maximum valve opening speed and the average valve opening speed of the exhaust valve 14 are made larger than the maximum valve closing speed and the average valve closing speed, so that the exhaust lift curve EX is Although it is asymmetrical, it is possible to secure the same lift amount as in the case of the conventional symmetrical lift curve EX '. As shown in the figure, the opening speed and closing speed of the intake valve 13 are line-symmetric with respect to the exhaust valve speed with the exhaust top dead center as the axis of symmetry, and the positive and negative sides are reversed. Similar to the case of the valve, the same lift amount as in the case of the conventional symmetrical lift curve can be secured.

Here, as in the present embodiment, the exhaust cam lift section 2
When the radius of curvature Ro of the valve opening lift portion 22a of No. 2 is set to be larger than the curvature radius Rc of the valve closing lift portion 22b, the contact point of the valve opening lift portion 22a with the upper surface of the lifter is C1 as shown in FIG. There is a concern that the lifter diameter will increase when the cam shaft axis and the lifter axis intersect with each other as in the conventional case. Therefore, in this embodiment,
The axis f of the lifter is moved from the axis d of the exhaust camshaft 20 to the side where the valve opening lift 22a rotates, that is, the exhaust camshaft 2
Since the distance B was offset to the upstream side (the right side in FIGS. 2 and 5) in the rotational direction of 0, the lifter diameter was D1 as shown in FIG.
It may be set to be slightly larger than + D2. As described above, it is possible to widen the movement allowable range of the contact point between the cam and the lifter without increasing the diameter of the lifter, and it is possible to increase the valve lift speed and secure the necessary lift amount. Incidentally, in order to obtain the same lift curve without displacing the lifter position, the lifter diameter needs to be slightly larger than 2 × D1.

The points related to the moving distance of the contact point between the cam lift and the lifter in the exhaust valve 14 are related to the intake valve 13
The same applies to the case where the intake lifter 17 is connected to the intake camshaft 19
Therefore, it is possible to widen the movement allowable range of the contact point between the cam lift portion 21 and the lifter 17 without increasing the diameter of the intake lifter 17, and to increase the valve lift speed. It is possible to secure the required lift amount.

When the maximum lift position of the exhaust lift curve EX is advanced to accelerate the rise of the valve opening speed and the exhaust camshaft 20 and the exhaust lifter 18 are deviated as in this embodiment, The contact point of the exhaust cam lift portion 22 with the exhaust lifter 18 at the time when the valve acceleration at the initial stage of valve opening becomes large moves to the outside of the axis line f of the exhaust lifter 18 (anti-cylinder bore axis side, right side in FIG. 5). As a result, bending moment and shearing force act on the exhaust lifter 18, which is disadvantageous in securing the strength of the lifter.

Therefore, in the present embodiment, the exhaust valve 14 is arranged so that its axis e is further offset from the axis f of the exhaust lifter 18. Therefore, when the exhaust cam lift 22 contacts the exhaust lifter 18 outside the axis f of the exhaust lifter 18, the exhaust valve 14 is positioned so as to face the contact point. It is possible to suppress the generation of bending moment and shearing force, and to avoid the disadvantage of securing the strength of the exhaust lifter 18.

FIG. 7 shows a modified example in which the generation of the bending moment and the shearing force can be more surely avoided, and the same reference numerals as those in FIG. 2 indicate the same or corresponding portions. In this modification, the exhaust valve 14 is displaced from the exhaust cam shaft 20 by a dimension C, and the radius of the valve shaft 14b of the exhaust valve 14 is set to the above-described dimension C. As a result, the exhaust cam lift unit 2
Most of the moving range of the lifter contact point of 2 is exhaust valve shaft 14b
Is supported from below, so that the bending moment and shearing force generated in the exhaust lifter 18 can be more reliably avoided.

In the above embodiment, the intake valve 13 is arranged so that the axis of the intake camshaft 19 intersects with the intake camshaft 19, but the intake valve 1 is arranged to suppress the generation of bending moment.
3, the intake camshaft 19 and the intake lifter 17 can also be offset. In this case, in FIG. 2, it is effective to dispose the intake valve 13 so that the axis b of the intake valve 13 is located closer to the cylinder bore axis X side than the axis c of the intake lifter 17, whereby a bending moment is applied to the intake lifter 17. Occurrence can be suppressed or avoided.

Further, by advancing or retarding the asymmetrical lift curve in the above embodiment while keeping its shape, depending on the operating condition of the engine, the valve opening start time,
Also, the closing timing of the valve closing can be changed. Figure 8
This is an example in which the intake lift curve is advanced according to the engine operating state. In the figure, the same reference numerals as those in FIG. 6 indicate the same or corresponding portions.

In the example of FIG. 8, the intake lift curve INo is advanced by θ MOD to the lift curve IN when the engine rotation speed becomes higher than a predetermined speed. Various conventional valve timing mechanisms have been proposed for advancing or retarding the lift curve.
For example, a conventionally known mechanism that changes the relative angle between the cam shaft and the timing gear can be adopted.

In the above example, the intake lift curve INo is
The maximum lift angle θm is an asymmetric type in which the maximum lift angle θm ′ in the conventional lift curve IN ′ is retarded. Therefore, the angle θMOD to be advanced according to the operating condition of the engine is the conventional symmetrical lift type. Curve INo '
In this case, the angle may be smaller than the angle θSTD to be advanced.
Therefore, the load on the timing varying mechanism described above can be reduced.

[0060]

According to the engine valve operating system of the first aspect of the present invention, the exhaust valve lift curve or the intake valve lift curve has an asymmetrical shape in which the maximum lift position is biased toward the advance side or the retard side. Therefore, by appropriately selecting this asymmetrical shape, it is possible to improve the filling efficiency while suppressing the decrease in exhaust efficiency while reducing the exhaust valve opening.

In order to make the lift curve asymmetrical, the lifter and the cam shaft are arranged so that the lifter is biased to the side where the portion of the cam lift having a large average valve speed contacts the lifter. Since it is arranged offset, it is possible to widen the range of movement of the contact point between the cam lift and lifter without increasing the lifter diameter, which has the effect of increasing the valve lift speed and ensuring the required lift amount. is there.

When the lifter is offset with respect to the cam shaft, the intake valve or the exhaust valve is offset in the same direction as the offset lifter. Since the valve shaft is positioned so as to support the contact point, the bending moment and the shearing force acting on the lifter can be suppressed or eliminated, and the disadvantage of the strength of the lifter can be avoided.

According to the third aspect of the invention, the exhaust valve lift curve has an asymmetrical shape in which the maximum lift position is biased toward the advance side. Therefore, the exhaust valve has the maximum opening degree when the combustion gas pressure is high in the explosion stroke. Since it opens to a high level, a high blowdown pressure can be obtained, the combustion gas can be reliably discharged, and the exhaust efficiency can be improved.

According to the third aspect of the invention, the lifter and the exhaust valve cam shaft are arranged so that the lifter is biased to the side where the open side portion of the exhaust valve cam lift portion and the exhaust valve lifter come into contact with each other. Since the exhaust valve is offset, and the exhaust valve is offset on the same side as the exhaust valve lifter, in the invention of claim 4, the intake lifter is biased to the closed side and the intake valve is biased in the same direction. , It is possible to increase the valve lift speed by increasing the range of movement of the contact point between the cam lift and lifter without increasing the diameter of the lifter, and suppress or eliminate the bending moment and shearing force acting on the lifter. There is an effect that can be.

[Brief description of drawings]

FIG. 1 is a front view of an engine including an apparatus according to an embodiment of the present invention.

FIG. 2 is a sectional front view of the apparatus of the above-described embodiment.

FIG. 3 is a cross-sectional side view of an exhaust valve portion of the apparatus of the above embodiment.

FIG. 4 is a cross-sectional plan view showing a valve opening of the apparatus of the above embodiment.

FIG. 5 is a schematic view of an exhaust cam lift portion of the apparatus of the above embodiment.

FIG. 6 is a diagram showing a lift curve of the apparatus according to the embodiment.

FIG. 7 is a sectional front view showing a modified example of the exhaust valve portion of the apparatus of the above embodiment.

FIG. 8 is a diagram showing a lift curve when a variable valve timing device is added to the device of the embodiment.

[Explanation of symbols]

 1 engine 13 intake valve 13b intake valve shaft 14 exhaust valve 14b exhaust valve shaft 17 intake lifter 18 exhaust lifter 21 intake cam lift part 21a valve opening lift part (open side part of intake cam lift part) 21b valve lift part ( 22) Exhaust cam lift section 22a Valve opening lift section (Open side of exhaust cam lift section) 22b Valve closing lift section (Close side section of exhaust cam lift section) EX Exhaust lift curve IN Intake lift curve Ro Radius of curvature at open side Rc Radius of curvature at closed side

Claims (4)

[Claims] 1. A valve operating system for an engine, comprising a valve opening / closing mechanism for opening / closing an intake valve and an exhaust valve along a predetermined lift curve, wherein the valve opening / closing mechanism is a lifter cam mounted on a valve shaft. A direct-acting type configured to be pressed by, and at least one of the intake valve and the exhaust valve cam lift portion has a shape in which the average valve opening speed and the average valve closing speed are different from each other. By setting the lift curve to an asymmetrical shape in which the maximum lift position is biased toward the advance side or the retard side, and the side where the average valve speed of the cam lift portion and the lifter come into contact with each other. An engine valve operating system characterized in that the lifter and the cam shaft are offset so that the lifter is displaced, and the valve is offset in the same direction as the offset lifter. 2. The average valve opening speed and the average valve closing speed are set by setting the shape of the cam lift portion so that the curvature of the opening side portion and the curvature of the closing side portion are different from each other. An engine valve operating device characterized in that and are different sizes. 3. The average opening speed of the exhaust valve according to claim 1 or 2, wherein the shape of the exhaust cam lift portion is set such that the curvature of the open side portion is substantially smaller than the curvature of the closed side portion. It is set higher than the valve closing speed, and the lift curve for the exhaust valve is made asymmetrical with the maximum lift position biased toward the advance side,
The lifter and the exhaust valve cam shaft are arranged in an offset manner so that the lifter is displaced on the side where the open side portion of the exhaust valve cam lift and the exhaust valve lifter come into contact with each other. A valve operating system for an engine, which is arranged on the same side as the lifter for the engine. 4. The average closing valve of the intake valve according to claim 1, wherein the shape of the intake cam lift portion is set such that the curvature of the closed side portion is substantially smaller than the curvature of the open side portion. The intake valve lift curve is made asymmetrical with the maximum lift position biased toward the retard side, and the intake valve lift curve is close to the closed side part of the intake valve cam lifter and the intake valve lifter. An engine valve operating device characterized in that the lifter and the intake valve camshaft are offsetly arranged so that the lifter is displaced on the contact side, and the intake valve is offsetly arranged on the same side as the intake valve lifter. .