JPH04339115A - Valve system for four-cycle engine - Google Patents

Abstract

PURPOSE:To improve engine performance by reducing moment of inertia of a rocker arm. CONSTITUTION:There are provided a rocker shaft 11 forming an eccentric large diameter part, the first rocker arm 7 which is fitted directly around the same shaft and forms branching tip parts 7b, the second and the third rocker arms 8 and 9 which are fitted around the eccentric large diameter part on both sides of the first rocker arm and the first-the third cams to drive the first-the third rocker arms, and tip parts 8b and 9b of the second and the third rocker arms and the branching tip parts of the first rocker arm are superposed vertically upon each other. Furthermore, in one of a support part 7a of the first rocker arm and support parts 8a and 9a for the second and the third rocker arms, screw support parts 37 and 38 in which play adjusting screws 39 and 40 are installed are formed, and in the other, a screw receiving part 36 with which the tip parts of the play adjusting screws can be brought into contact is formed, and further, on the outer periphery of the support part for the first rocker arm, plural number of positioning projection parts 43A-43C capable of coming into contact with the side surfaces of the support parts for the second and the third rocker arms are formed.

Description

[Detailed description of the invention]

[Object of the invention]

0002

[Industrial Application Field] The present invention relates to a valve train for a four-stroke engine that can change the lift amount and opening timing of intake and exhaust valves depending on operating conditions, and in particular, it relates to a valve train for a four-cycle engine that can change the lift amount and opening timing of intake and exhaust valves according to operating conditions. The present invention relates to a reduced valve train for a four-stroke engine.

0003

2. Description of the Related Art Generally, a four-stroke engine installed in a vehicle such as an automobile or a motorcycle has intake and exhaust valves disposed above a combustion chamber, and these valves are driven by a valve train. That is, the valve operating device includes a camshaft that is interlocked with the crankshaft of the engine, and uses a cam formed on the camshaft to move the intake and exhaust valves up and down at predetermined timing.

0004

[Problems to be Solved by the Invention] By the way, the above-mentioned 4-cycle engine has the ability to obtain high output within a wide rotation speed range from low rotation speed to medium and high rotation speed, that is, the power band is wide. is desirable.

However, in conventional valve train systems, the opening/closing timing and lift amount of the valves are fixed, so an output characteristic that only has a peak value in a specific engine speed range can be obtained, and therefore, it is possible to obtain an output characteristic that has a peak value in a specific engine speed range. You are forced to choose whether to focus on output characteristics or to focus on output characteristics in the medium and high rotation speed range.

[0006] The present invention was made in consideration of the above-mentioned circumstances, and it is possible to improve the output within a wide rotation speed range, and also to improve engine performance by reducing the moment of inertia of the rocker arm. The purpose of this invention is to provide a valve train for a four-stroke engine. [Structure of the invention]

[0007]

[Means for Solving the Problems] The present invention provides a rocker shaft that is rotatably supported and is formed with an eccentric large diameter portion, and a rocker shaft that is directly inserted into the rocker shaft and has a branched tip portion. 1 rocker arm, second and third rocker arms disposed on both sides of the first rocker arm and fitted into the eccentric large diameter portion, and the first, second and third rocker arms, respectively. first, second, and third cams, the tips of the second and third rocker arms and the branched tips of the first rocker arm are vertically overlapped, and the second and third cams are vertically overlapped. and a third cam is formed with the same cam profile, the cam profile of the first cam being formed differently from the cam profile, and a support portion of the first rocker arm and the second and third rocker arms. A screw holding part for mounting the play adjusting screw is formed on one side of the support part of the first part, and a screw receiving part on the other side is formed to which the tip of the play adjusting screw can come into contact. The present invention is characterized in that a plurality of positioning protrusions that can come into contact with the side surfaces of the support parts of the second and third rocker arms are formed on the outer periphery of the support part of the rocker arm.

[0008]

[Operation] Therefore, according to the valve operating system for a four-cycle engine according to the present invention, by rotating the rocker shaft by a predetermined angle and rotating the eccentric large diameter portion, the cam floor surfaces of the second and third rocker arms are rotated to the first position. 1 Change the position of the rocker arm relative to the cam floor surface in the vertical direction. When the cam floor surfaces of the first and third rocker arms are moved downward relative to the cam floor surface of the first rocker arm, the contact between the second and third rocker arms and the second and third cams is released, and the first rocker arm and the first cam are in contact with each other, and the valve of the four-stroke engine is driven by this first cam.

Furthermore, when the cam floor surfaces of the second and third rocker arms are moved substantially upwardly or to the same position relative to the cam floor surface of the first rocker arm,
The contact between the rocker arm and the first cam is released, the second and third rocker arms are brought into contact with the second and third cams, and the valves of the four-stroke engine are operated by the second and third cams. . By rotating the rocker shaft and selecting a cam in this manner, engine output can be improved over a wide rotational speed range.

Furthermore, since the positioning protrusion is formed on the support portion of the first rocker arm, the second and third rocker arms are provided between the support portion of the first rocker arm and the support portions of the second and third rocker arms. There is no need to install a positioning washer to prevent the supporting part of the rocker arm from shifting from the eccentric large diameter part.

[0011] This positioning washer
Since it is formed to have a larger diameter than the supporting part of the rocker arm, either the screw holding part or the screw receiving part is formed to extend around the large diameter positioning washer to the other side. For this reason, the distance between the center of the support portion of the rocker arm and the screw holding portion or the screw receiving portion becomes large.

In contrast, in the present invention, the positioning protrusion is formed on the support portion of the first rocker arm to position the second and third rocker arms, so the above-mentioned positioning washer is not required. Therefore, the distance between the screw holding part or the screw receiving part and the center of the support part of the rocker arm can be set small, and the moments of inertia of the first, second, and third rocker arms can be reduced. As a result, the followability of the first, second, and third rocker arms to the first, second, and third cams is improved, and the valve train operates normally up to a high engine speed range. Engine performance can be improved.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment of the valve train for a four-cycle engine according to the present invention, FIG. 4 is a plan view showing the valve train in FIG. 1, and FIGS. 5 and 6 are the same as in FIG. FIG. 3 is an operating state diagram showing the action of the valve train.

[0015] This valve train is disposed on the intake side and the exhaust side of one cylinder of the engine, respectively. The valves 1, 2 shown in FIGS. 1, 5 and 6 are therefore arranged for intake or exhaust.

This embodiment includes a low-speed cam 3 as a first cam, and medium-high speed cams 4 as second cams disposed on one side and the other side of the low-speed cam 3, respectively.
and a camshaft 6 (FIG. 3, FIG. 5, FIG. 6) having a medium-high speed cam 5 as a third cam, and a low speed rocker arm as a first rocker arm located below each of the cams 3, 4, and 5. rocker arm 7 for medium and high speeds as a second rocker arm, rocker arm 9 for medium and high speeds as a third rocker arm, and supporting parts 7a, 8a and 9a of these rocker arms 7, 8 and 9.
is fitted and inserted, and the camshaft bearing part 21 (Figs. 2 and 3
), the rocker shaft 11 is rotatably supported by a rocker shaft 11.

The tip of the low-speed rocker arm 7 is branched into two directions, and both of these branched tips 7b are in contact with the stem heads of the valves 1 and 2, which open and close the combustion chambers of the engine (not shown), respectively. In addition, low speed rocker arm 7
The support portion 7a is directly fitted onto the rocker shaft 11 and is rotatably provided.

The support portion 8a of the rocker arm 8 for medium and high speeds is
It is rotatably fitted into the rocker shaft 11 via an eccentric bush 12 having a larger diameter than the rocker shaft 11 . As shown in FIGS. 5 and 6, the eccentric bush 12 has an axis eccentric from the center O of the rocker shaft 11, and is detachably fixed to the rocker shaft 11 by a retaining pin 10. Therefore, this eccentric bushing 12 functions as an eccentric large diameter portion of the rocker shaft 11.

Further, as shown in FIG. 4, the support portion 9a of the medium/high speed rocker shaft 9 also has an eccentric bush 13 having the same shape as the eccentric bush 12 and eccentric in the same direction.
It is rotatably fitted into the rocker shaft 11 via the. This eccentric bush 13 is also detachably fixed to the rocker shaft 11 by a retaining pin 10, and functions as an eccentric large diameter section.

Furthermore, rocker arms 8 and 9 for medium and high speeds
The bottom surface of each of the tip portions 8b and 9b is attached to one and the other branch tip portions 7b of the low-speed rocker arm 7 with a shim 14a.
are brought into contact with each other via. The contact point between the branched tip 7b of the low-speed rocker arm 7 and the tips 8b and 9b of the medium-high speed rocker arms 8 and 9 is set approximately on the axis of the valves 1 and 2.

Therefore, as shown in FIG. 5, when the low-speed cam 3 pushes down the cam floor surface 7c of the low-speed rocker arm 7 and lowers each branch tip 7b (when the low-speed cam 3 is activated) , the distal ends 8b and 9b of the rocker arms 8 and 9 descend following the branched distal end 7b due to gravity. On the other hand, as shown in FIG. 6, when the medium and high speed cams 4 and 5 push down the cam floor surfaces 8c and 9c of the medium and high speed rocker arms 8 and 9, respectively (when the medium and high speed cams 4 and 5 are activated), these rocker arm 8
and 9 push down each branched tip 7b of the low-speed rocker arm 7, so that these branched tips 7b are forcibly lowered.

The shim 14a is a T-shaped shim in longitudinal section, and is connected to both branched tips 7 of the low-speed rocker arm 7.
b from above. Further, the valve stem heads of the valves 1 and 2 are covered with a capped cylindrical shim 14b, and the lower surface of the branched end portion 7b of the low-speed rocker arm 7 abuts on this shim 14b. These shims 14a and 14
b is used for adjusting the tappet clearance of valves 1 and 2.

Further, among the cams 3, 4 and 5, the medium and high speed cams 4 and 5 have the same cam profile, and the low speed cam 3 has the same cam profile as these medium and high speed cams 4 and 5.
has a different cam profile than the cam profile of That is, the cam profile of the low-speed cam 3 is set so that the valve lift amount and valve opening/closing timing suitable for when the engine is operated in a low rotational speed range are obtained. Further, the cam profiles of the medium and high speed cams 4 and 5 are set so as to obtain a valve lift amount and valve opening/closing timing suitable for when the engine is operated in a medium and high speed range.

The above valve lift amount is
The stroke length corresponds to the cam lift amount. Figure 9
, the cam profile of the low speed cam 3 is shown by a solid line A (cam lift amount la), and the cam profile of the middle and high speed cams 4 and 5 is shown by a broken line B (cam lift amount lb). As is clear from FIG. 9, the medium and high speed cam 4
and 5 have their cam profiles set so that a larger valve lift amount than the low speed cam 3 can be obtained.

Note that the two-dot chain line C in FIG. 9 indicates the state in which the low-speed cam 3 is operated (see FIG. 5) shows the cam profiles of medium and high speed cams 4 and 5.

As shown in FIGS. 1 to 3, the rocker shaft 11 is rotated by a hydraulic cylinder 15 operated by hydraulic pressure from the engine. A rack 16 is connected to a piston (not shown) of the hydraulic cylinder 15, and the rack 16 is engaged with a pinion 17 formed at one end of the rocker shaft 11. Further, the hydraulic cylinder 15 is provided with a low-speed hydraulic port 18 and a high-speed hydraulic port 19, respectively, and hydraulic pressure from the engine is selectively guided to the respective ports 18 and 19.

When the engine speed is in the low speed range, hydraulic pressure is supplied to the low speed hydraulic port 18, and the rack 1
6 is pulled back, and the pinion 17 is rotated in the direction of arrow M. Then, as shown in FIG. 5, the eccentric bushes 12 and 13 rotate so that their thick tops 12a and 13a are positioned diagonally forward, and as described above, the low-speed cam 3 touches the cam floor surface of the low-speed rocker arm 7. By pressing 7c, this low speed cam 3 is activated. Further, when the engine speed is in the medium/high speed range, hydraulic pressure is supplied to the medium/high speed hydraulic port 19, the rack 16 is pushed out, and the pinion 17 is rotated in the direction of arrow N. Then, as shown in FIG. 6, the eccentric bushes 12 and 13
a and 13a are rotated so that they are positioned diagonally rearward, and as described above, the middle and high speed cams 4 and 5 press the cam floor surfaces 8c and 9c of the middle and high speed rocker arms 8 and 9, respectively, and High speed cams 4 and 5 are activated.

In this way, the rocker shaft 11 is operated so that the thick tops 12a and 13a of the eccentric bushes 12 and 13 are always tilted diagonally from the front in the upper half of the rocker shaft 11 due to the operation of the hydraulic cylinders 15, 16, and 17. It is configured to rotate around the rear range.

The rocker shaft 11, hydraulic cylinder 15, etc. as described above are arranged in a cylinder head 20 shown in FIGS. 2 and 3. A total of four rocker shafts 11 are arranged, one on each side of the vehicle, one on each side of the cylinder head 20, and are arranged to extend in the left-right direction of the vehicle. Each rocker shaft 11 is rotatably supported by a camshaft bearing portion 21 formed in the cylinder head 20. A lower half bearing hole 22 for supporting the camshaft 6 is formed in the upper part of the camshaft bearing part 21 . Also, this lower half bearing hole 2
A valve guide 23 (FIG. 2) is arranged near 2, and a stud bolt insertion hole 24 is formed therein. Further, the upper part of the cylinder head 21 has a mating surface 2 with the head cover 27.
5 is formed, and a cam chain chamber 26 is formed at the center position of the cylinder head 21 in the left-right direction of the vehicle.

A hydraulic cylinder 15 and a rack 16 are arranged within this cam chain chamber 26. This rack 16 is configured to mesh with the pinion 17 of the rocker shaft 11 from above. Further, two sets of the low-speed rocker arm 7 and the medium-high speed rocker arms 8 and 9 are installed on one rocker shaft 11. Each set of low-speed rocker arm 7 and medium-high speed rocker arms 8 and 9 is controlled by a positioning spring 29 interposed in the rocker shaft 11.
Its position is regulated together with the rocker shaft 11.

In FIG. 3, reference numeral 30 denotes a bearing housing, and an upper half bearing hole 31 formed in this bearing housing 30.
A camshaft 6 is rotatably supported by the lower half bearing hole 2 and the lower half bearing hole 2.

A lubricating oil passage 32 is formed in the bearing housing 30 in parallel with the camshaft 6. The lubricating oil that has lubricated the camshaft 6 is guided into the lubricating oil path 32 via a lubricating oil supply path 33 . The lubricating oil in the lubricating oil passage 32 is supplied downward from the lubricating oil filler port 34 to the low speed cam 3 and the low speed rocker arm 7; as well as the medium and high speed cams 4 and 5 and the medium and high speed rocker arms 8 and 9.
is lubricated. Note that the lubricating oil in this lubricating oil path 32 is
It is used again for lubricating the camshaft 6 via the lubricating oil return path 35.

Now, as shown in FIGS. 1 and 4, a screw receiving portion 36 is integrally formed in the support portion 7a of the low-speed rocker arm 7. The screw receiving portions 36 extend in a direction opposite to the branch tip portion 7b with respect to the support portion 7a, and are provided in pairs on the left and right in the branching direction of the branch tip portion 7b.

On the other hand, adjusting arms 37 and 38 as screw holding parts are integrally molded into the support parts 8a and 9a of the medium and high speed rocker arms 8 and 9, respectively. These adjustment arms 37 and 38 are
It extends in a direction opposite to the tip portions 8a and 9b with respect to the support portions 8a and 9a, and is bent in the direction of the screw receiving portion 36 midway. Adjustment screws 39 and 40 as play adjustment screws are screwed onto the tips of each of these adjustment arms 37 and 38, and lock nuts 41 and 42 are screwed into the adjustment screws 39 and 40, respectively.

By loosening the lock nuts 41 and 42 and moving the adjustment screws 39 and 40 forward and backward, the clearance between the tips of the adjustment screws 39 and 40 and the screw receiving portion 36 can be adjusted. When the engine is in a low rotational speed range, as shown in FIG. When the upper surface of the receiving portion 36 comes into contact with the tips of the adjustment screws 39 and 40, the tips 8b and 9b of the medium and high speed rocker arms 8 and 9 rotate toward the branched tip 7b of the low speed rocker arm 7. Rocker arms 8 and 9 for medium and high speeds
is synchronized with the movement of the low-speed rocker arm 7. In this way, the occurrence of hitting noise between the medium and high speed rocker arms 8 and 9 and the medium and high speed cams 4 and 5 is prevented.

Furthermore, as shown in FIGS. 1, 4, and 7 in particular, three positioning protrusions 43A, 43B, and 43C are integrally molded on both sides of the outer periphery of the support portion 7a of the low-speed rocker arm 7. be done. Of these, positioning protrusion 4
3A is formed on the upper surface of the support portion 7a, that is, on the same side as the cam floor surface 7c. Furthermore, the positioning protrusion 43B is integrally molded with an arm extending from the support portion 7a to the branch tip portion 7b. Further, the positioning protrusion 43c is formed as the base end portion of the adjustment arms 37, 38.

These positioning protrusions 43A, 43B,
As shown in FIGS. 5 and 6, 43C is set to protrude from the outer periphery of the support parts 8a and 9a of the medium and high speed rocker arms 8 and 9, and comes into contact with the side surfaces of these support parts 8a and 9a. configured as possible. Therefore, as shown in FIG.
, 43B and 43C and the camshaft bearing portion 21, and its position is regulated. Further, the medium/high speed rocker arm 9 has a positioning washer 44 interposed between the medium/high speed rocker arm 9 and the positioning spring 29.
and the positioning protrusions 43A, 43B, and 43C, and its position is regulated.

Further, as shown in FIG. 2, semicircular notches 4 are formed in the outer walls at both left and right ends of the cylinder head 20 when the lower half bearing hole 22 is formed in the camshaft bearing portion 21.
5 is formed. A semicircular plug 46 (FIGS. 3 and 8) that closes this processed notch 45 is fitted into this processed notch 45. Note that the semicircular plug 46 is attached to the head cover 2.
Some are integrally molded with a gasket 47 interposed between the cylinder head 7 and the mating surface 25 of the cylinder head 20.

Further, as shown in FIG. 2, as the layout of the cylinder head 20 becomes more elaborate as engines become smaller, bolt notches 4 are formed in the camshaft bearing 21.
8 may be formed and a bolt may be placed in this bolt notch 48. In this embodiment, the bolt is a rocker shaft stopper bolt 49 (FIG. 3) that regulates the rotational position of the rocker shaft 11.
If the rocker shaft does not rotate, this rocker shaft 1
It may be a bolt for fixing 1 to the cylinder head 20, or a bolt for fixing the cylinder head 20 to a cylinder (not shown).

Furthermore, a groove 50 is formed between the camshaft bearing portion 21 in which the bolt notch 48 is formed and the outer wall of the cylinder head 20. As shown in FIGS. 2 and 8, the groove 50 is formed in a substantially semicircular shape along the lower half bearing hole 22, and is provided in communication with the bolt notch 48. A lubricating groove 51 is formed on the inner surface of the lower half bearing hole 22, and engine oil collects along the lubricating groove 51 in the bolt notch 48 and the groove 50. Therefore, the ability to retain engine oil in the camshaft bearing portion 21 is improved, and the camshaft 6 can be satisfactorily lubricated even immediately after the engine is started after being stopped for a long time when engine oil tends to be insufficient.

Note that the groove 50 has a shape as shown in FIG.
It functions to lock the positioning flange 52 formed on the semicircular plug 46. Furthermore, since the mutually communicating bolt notches 48 and grooves 50 have a large capacity, the engine oil applied to the lower half bearing hole 22 and the camshaft 6 can be reliably stored when the engine is assembled. Engine oil can be prevented from overflowing to the outside of the cylinder head 20.

Next, the operation will be explained.

When the engine is in a low rotational speed range, the rocker shaft 11 is rotated in the direction of arrow M by the operation of the hydraulic cylinder 15, and the thick tops 12a and 13a of the eccentric bushes 12 and 13 are positioned diagonally forward. (Figure 5). As a result, the cam floor surfaces 8c and 9c of the medium and high speed rocker arms 8 and 9 move downward relative to the cam floor surface 7c of the low speed rocker arm 7. Therefore, the peripheral surfaces of the medium and high speed cams 4 and 5 and the cam floor surfaces 8c and 9 of the medium and high speed rocker arms 8 and 9
A gap is formed between the medium and high speed cams 4 and 5, and as a result, the medium and high speed cams 4 and 5 idle.

Also, at this time, the low-speed rocker arm 7 is constantly pushed upward about the axis of the rocker shaft 11 by the biasing force of the valve spring 53, so that its cam floor surface 7c touches the periphery of the low-speed cam 3. come into contact with the surface. Therefore, when the camshaft 6 rotates,
The valves 1 and 2 move up and down based on the lift characteristic A of the low speed cam 3 shown in FIG. In other words, valves 1 and 2 open and close the combustion chamber while ensuring a valve lift amount suitable for a low engine speed range.

On the other hand, when the engine is in the medium to high speed range, the rocker shaft 11 rotates in the direction of arrow N due to the operation of the hydraulic cylinder 15, and the eccentric bushes 12 and 1
Thick-walled top portions 12a and 13a of No. 3 are located diagonally rearward (FIG. 6). As a result, the cam floor surfaces 8c and 9c of the rocker arms 8 and 9 for medium and high speeds move approximately upward or to the same position relative to the cam floor surface 7c of the rocker arm 7 for low speeds, and the cam floor surfaces 8c and 9c of the rocker arms 8 and 9 for medium and high speeds move to the same position, respectively. contact with the circumferential surfaces of the cams 4 and 5.

As shown in FIG. 9, the medium and high speed cams 4 and 5 are formed to have a larger cam lift than the low speed cam 3, so the camshaft 6 rotates under the conditions shown in FIG. In this case, the low speed cam 3 idles, and on the other hand,
Medium and high speed cams 4 and 5 drive valves 1 and 2 via medium and high speed rocker arms 8 and 9, respectively, based on lift characteristic B shown in FIG. As a result, valves 1 and 2 open and close the combustion chamber while ensuring a valve lift amount suitable for the middle and high engine speed ranges.

According to the above embodiment, the low speed cam 3 has a cam profile suitable for the low engine speed range, and the medium and high speed cams 4 and 5 have cam profiles suitable for the medium and high engine speed range. After the profile is formed, the medium and high speed rocker arms 8 and 9 are rotatably fitted into the eccentric bushes 12 and 13 of the rocker shaft 11, respectively, and the low speed rocker arm 7 is fitted directly into the rocker shaft 11, thereby forming the rocker shaft 11. By rotating, it is possible to select the contact between the low speed cam 3 and the low speed rocker arm 7, and the contact between the medium and high speed cams 4 and 5 and the medium and high speed rocker arms 8 and 9. cam 3
Alternatively, it can be selectively driven by medium and high speed cams 4 and 5. Therefore, the output of the four-stroke engine can be improved over a wide engine speed range from low engine speeds to medium and high engine speeds.

Furthermore, since the selection of the low-speed cam 3 and the medium-high speed cams 4 and 5 is performed by rotating the eccentric bushes 12 and 13, large stress is not generated in each part when selecting the cams 3, 4, and 5. There is no. For this reason, cam 3
, 4, and 5 can be selected smoothly.

Furthermore, the support portion 7 of the low-speed rocker arm 7
Since the positioning protrusions 43A, 43B, and 43C are formed at the position a, the positioning washer 44 shown in FIG. It is not necessary to arrange the positioning washer 54 having the same shape as shown in FIG. Since this positioning washer 54 is formed to have a larger diameter than the supporting parts 8a and 9a of the medium and high speed rocker arms 8 and 9, the adjusting arms 37 and 38 of the medium and high speed rocker arms 8 and 9 bypass this positioning washer 54. and extends toward the screw receiving portion 36 side of the low-speed rocker arm 7. For this reason, the positioning washer 5
4, the center of the support parts 8a and 9a of the rocker arms 8 and 9 for medium and high speeds and the adjust arm 3
The respective distances L' from the tip portions 7 and 38 become large. The rocker arms 8 and 9 for medium and high speeds are
Since the rocker shaft 11 makes a reciprocating circular arc movement, as the distance L' increases, the moment of inertia of the low-speed rocker arm 7 and the medium-high speed rocker arms 8 and 9 also increases.

In contrast, in this embodiment, positioning protrusions 43A, 43B are provided on the support portion 7a of the low-speed rocker arm 7.
and 43C are formed to position the medium and high speed rocker arms 8 and 9, so the positioning washer 54 is no longer necessary. For this reason, the center of the support parts 8a and 9a of the rocker arms 8 and 9 for medium and high speeds and the adjustment arm 3
The distance L between the tips 7 and 38 can be set smaller than the distance L'. As a result, the moment of inertia of the low-speed rocker arm 7 and the medium-high speed rocker arms 8 and 9 can be reduced, and these rocker arms are connected to the cams 3, 4, and 5.
It follows the engine speed well and operates normally even in the high engine speed range, improving engine performance.

Furthermore, since the bolt notches 48 formed in the camshaft bearing portion 21 and the grooves 50 formed in the vicinity of the outer wall of the cylinder head 20 are configured to communicate with each other, these bolt notches 48 The engine oil can be sufficiently stored in the groove 50, and the engine oil holding capacity can be increased. Therefore, good lubrication of the camshaft 6 can be maintained especially when the engine is started after being stopped for a long time.

In the above embodiment, the case was described in which the cam profiles of the medium-high speed cams 4 and 5 were as shown by the broken line B in FIG. 10 or the broken line B'' in FIG. 11, the lifts of the valves 1 and 2 at medium and high engine speeds may be changed.

Further, in the above embodiment, a pair of screw receiving portions 36 are formed on the support portion 7a of the low speed rocker arm 7, and adjustment arms 37 and 38 are formed on the support portions 8a and 9a of the medium and high speed rocker arms 8 and 9, respectively. As described above, the low speed rocker arm 7
Adjustment arms 37 and 38 are formed in the support portions 7a of the middle and high speed rocker arms 8 and 9, and screw receiving portions 36 are formed in the support portions 8a and 9a of the medium and high speed rocker arms 8 and 9, respectively. It may be configured to abut against the lower surface of.

[0054]

As described above, according to the valve train for a four-stroke engine according to the present invention, an eccentric large-diameter portion is formed in the rotatably supported rocker shaft.
Since the second and third rocker arms are fitted into this eccentric large diameter portion, and the first rocker arm is arranged between the second and third rocker arms and fitted directly into the rocker shaft, rotation of the rocker shaft is possible. By selecting the above-mentioned cam according to the above, it is possible to improve the engine output over a wide rotation speed range.

[0055] Further, a screw holding portion for mounting a play adjustment screw is formed on one of the support portion of the first rocker arm and the support portion of the second and third rocker arms, and a screw holding portion for mounting a play adjustment screw is formed on the other side. A screw receiving portion is formed on which the distal end portion of the screw can abut, and
Since a plurality of positioning protrusions that can come into contact with the side surfaces of the support parts of the second and third rocker arms are formed on the outer periphery of the support part of the rocker arm,
Since it is not necessary to arrange a large diameter positioning washer between the rocker arms, the axial length of the screw holding part or the screw receiving part can be shortened. Therefore, the moment of inertia of the rocker arm can be reduced, and engine performance can be improved.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of a valve train for a four-stroke engine according to the present invention.

FIG. 2 is a plan view of a cylinder head to which the valve train of FIG. 1 is applied.

FIG. 3 is a sectional view taken along line III-III in FIG. 2;

FIG. 4 is a plan view showing the valve train of FIG. 1;

FIG. 5 is an operational state diagram of the valve train of FIG. 1 in a low engine speed range.

FIG. 6 is a diagram showing the operating state of the valve train in FIG. 1 in an engine medium to high engine speed range.

7 is a side view showing a low-speed rocker arm of the valve train of FIG. 1 together with a part of a medium-high speed rocker arm; FIG.

8 is a perspective view showing the periphery of a camshaft bearing in the cylinder head of FIG. 2. FIG.

FIG. 9 is a diagram showing a cam profile of the cam of FIG. 3;

FIG. 10 is a diagram showing a first modification of the cam profile shown in FIG. 9;

FIG. 11 is a diagram showing a second modification of the cam profile shown in FIG. 9;

12 is a side view corresponding to FIG. 7 when a positioning washer is disposed between a low-speed rocker arm and a medium-high speed rocker arm; FIG.

[Explanation of symbols]

1, 2 Valve 3 Low speed cam 4, 5 Medium and high speed cam 7 Low speed rocker arm 7a Low speed rocker arm support part 7b Low speed rocker arm branch tip 8, 9 Medium and high speed rocker arm 8a, 9a Medium and high speed rocker arm support Part 8b, 9
b Tip part 11 of rocker arm for medium and high speeds Rocker shafts 12, 13 Eccentric bush 36 Screw receivers 37, 38 Adjustment arms 39, 40 Adjustment screws 43A, 34B, 43C positioning protrusion A Cam profile of low speed cam

Claims (1)

[Claims] Claims: 1. A rocker shaft rotatably supported and formed with an eccentric large diameter portion; a first rocker arm that is directly fitted onto the rocker shaft and has a branched tip; second and third rocker arms disposed on both sides of the rocker arm and fitted into the eccentric large diameter portion; first and second rocker arms that respectively drive the first, second and third rocker arms;
and a third cam, wherein the distal ends of the second and third rocker arms and the branched distal ends of the first rocker arm are vertically overlapped, and the second and third cams are vertically overlapped. are formed to have the same cam profile, the cam profile of the first cam is formed different from the cam profile, and the support portion of the first rocker arm and the support portions of the second and third rocker arms are formed to have the same cam profile. A screw holding part for mounting a play adjusting screw is formed on one side, a screw receiving part is formed on the other side to which the tip of the play adjusting screw can come into contact, and further, the outer periphery of the support part of the first rocker arm is formed. A valve operating device for a four-stroke engine, characterized in that a plurality of positioning protrusions are formed that can abut on the side surfaces of the support portions of the second and third rocker arms.