JPH04321707A - Valve system for four cycle engine - Google Patents

Abstract

PURPOSE:To remove a foreign substance in the hydraulic oil in a hydraulic actuator by forming a dust chamber communicated to the interior of a cylinder under the cylinder formed in an actuator body. CONSTITUTION:A hydraulic actuator 15 is operationally connected to a rocker shaft 11, and the rocker shaft 11 is rotationally moved by oil pressure of hydraulic oil. In the hydraulic actuator 15, pistons 25 connected to the rocker shafts 11 are received in a cylinder 23 formed in an actuator body 24, and a dust chamber 55 communicated to the interior of the cylinder 23 is formed under the cylinder 23. Hereby, a foreign substance such as iron powder in the hydraulic oil flows down into the dust chamber by gravity during flowing of hydraulic oil and deposits, and hence the foreign matter remaining in the cylinder 23 can be remarkably reduced.

Description

[Detailed description of the invention]

[Object of the invention]

0002

[Field of Industrial Application] This invention relates to a valve operating system for a four-cycle engine that can change the valve lift amount, valve opening timing, etc. of intake and exhaust valves according to operating conditions.
In particular, the present invention relates to a valve train for a four-stroke engine with an improved structure of a hydraulic actuator that rotates a rocker shaft.

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 that 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 only 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.

The present invention has been made in consideration of the above-mentioned circumstances, and is capable of improving engine output within a wide rotation speed range, and also removes foreign matter from the hydraulic fluid of a hydraulic actuator. An object of the present invention is to provide a valve train for a four-stroke engine that can improve the performance of a four-stroke engine. [Structure of the invention]

[0007]

[Means for Solving the Problems] The present invention includes a rocker shaft that is rotatably supported and is formed with an eccentric large diameter portion, a first rocker arm that is directly fitted into the rocker shaft, and a first rocker arm that is directly fitted into the rocker shaft. second and third rocker arms disposed on both sides of the first rocker arm and fitted into the eccentric large diameter portion;
and first, second, and third cams that respectively operate a third rocker arm, and a hydraulic actuator that is operatively connected to the rocker shaft and rotates the rocker shaft using hydraulic pressure of hydraulic oil. , the second and third cams are formed with the same cam profile, the cam profile of the first cam is formed different from the cam profile, and the hydraulic actuator has a cam profile formed in the actuator body. A piston connected to the rocker shaft is housed therein, and a dust chamber is formed below the cylinder and communicated with the inside of the cylinder.

[0008]

[Operation] Therefore, according to the valve operating system for a four-stroke 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 surface of the second and third rocker arms is is changed relative to the cam floor surface of the first rocker arm 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, hydraulic oil flows into and out of the cylinder of the hydraulic actuator, causing the piston to slide, thereby rotating the rocker shaft in forward and reverse directions. During this flow of hydraulic oil,
Foreign matter such as iron powder in the hydraulic fluid flows down into the dust chamber due to its weight and accumulates therein. Therefore, foreign matter such as iron powder remaining in the cylinder can be significantly reduced, so that the piston can slide smoothly and wear between the piston and the cylinder can be reduced.

[0011]

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

FIG. 2 is a perspective view showing an embodiment of a valve train for a four-stroke engine according to the present invention, FIG. 6 is a partial plan view of a cylinder head to which the valve train of FIG. 2 is applied, and FIG.
7 is a cross-sectional view taken along line II in FIG. 6. FIG.

[0013] This valve train is disposed on the intake side and exhaust side of one cylinder of the engine, respectively. The valves 1, 2 shown in FIGS. 2 to 5 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 (FIGS. 4 and 5) having the same medium-high speed cam 5 as a third cam, and cams 3, 4, and 5.
A low-speed rocker arm 7 as a first rocker arm, a medium-high speed rocker arm 8 as a second rocker arm, and a medium-high speed rocker arm 9 as a third rocker arm located below each of the rocker arms 7, 8, and 9. The rocker shaft 11 is fitted with support parts 7a, 8a, and 9a, and is rotatably supported by a rocker shaft bearing part 18 (FIG. 6), which will be described later.

The tip of the low-speed rocker arm 7 is branched into two directions, and both branched tip portions 7b abut 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 speed use 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 FIG. 4, the eccentric bush 12 has an axis eccentric from the center of the rocker shaft 11, and is detachably fixed to the rocker shaft 11 by a bush pin 10. Therefore, this eccentric bushing 12 functions as an eccentric large diameter portion of the rocker shaft 11.

As shown in FIG. 3, the rocker arm 9 for medium and high speeds
The support portion 9a is also rotatably fitted into the rocker shaft 11 via an eccentric bush 13 which has the same shape as the eccentric bush 12 and is eccentric in the same direction. This eccentric bush 13 is also detachably fixed to the rocker shaft 11 by the bush pin 10, and functions as an eccentric large diameter section.

Further, the lower surfaces of the distal end portions 8a and 9a of the middle and high speed rocker arms 8 and 9 abut against one and the other branched distal end portions 7b of the low speed rocker arm 7 via shims 14a, respectively. 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. 4, when the low-speed cam 3 presses down the cam floor surface 7c of the low-speed rocker arm 7 and lowers each tip 7b of the low-speed rocker arm 7 (when the low-speed cam 3 is activated), In this case, the tips 8b and 9b of the rocker arms 8 and 9 are not pressed down together with the branch tip 7b. On the other hand, as shown in FIG.
and 5 push down the cam floor surfaces 8c and 9c of the rocker arms 8 and 9 for medium and high speeds (when the cams 8 and 9 for medium and high speeds are activated), the tips 8b and 9b of these rocker arms 8 and 9 Since each branch tip 7b of the locker arm 7 is pressed down, the branch tip 7b is forcibly lowered.

Note that this 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 shim 14b in the shape of a closed cylinder, 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 1
4b 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.

[0022] The above valve lift amount is
The stroke length corresponds to the cam lift amount. Figure 1
5 shows the cam profile of the low-speed cam 3 as a solid line A (cam lift amount la), and also shows the cam profile of the low-speed cam 3 with a solid line A (cam lift amount la), and the cam profile of the low-speed cam 3 with
The cam profile is shown by a broken line B (cam lift amount lb). As is clear from FIG. 15, the cam profiles of the medium and high speed cams 4 and 5 are set so that a larger valve lift amount can be obtained than that of the low speed cam 3.

The two-dot chain line C in FIG. 15 indicates when the rocker shaft 11 is rotated to position the thick tops 12a and 13a of the eccentric bushes 12 and 13 diagonally forward as shown in FIG. The cam profiles of medium and high speed cams 4 and 5 are shown during operation of cam 3 for medium and high speeds.

By the way, the rotation of the rocker shaft 11 is as follows.
As shown in FIG. 2, this is accomplished by a hydraulic actuator 15 that operates using engine oil as hydraulic fluid. As shown in FIG. 6, this hydraulic actuator 15 is installed in a cam chain chamber 17 located at the center of the cylinder head 16 in the left-right direction of the vehicle.

Further, a total of four rocker shafts 11 are arranged, one on each side of the vehicle, one on the front and rear of the cylinder head 16, and one on each side, and each rocker shaft 11 is arranged to extend in the left-right direction of the vehicle. Each rocker shaft 11 is rotatably supported by a rocker shaft bearing portion 18 formed in the cylinder head 16. One rocker shaft 11 has two rocker arms 7 for low speeds and rocker arms 8 and 9 for medium and high speeds.
They will be installed in groups. Each set of low-speed rocker arm 7 and medium-high speed rocker arms 8 and 9 is connected to the rocker shaft 1
A positioning spring 19 interposed in the rocker shaft 11 regulates its position together with the rocker shaft 11.

Note that the reference numeral 20 in FIG. 6 is a lower half bearing hole that is formed in the upper part of the rocker shaft bearing portion 18 and supports the camshaft 6. Further, reference numeral 21 is a valve guide, and reference numeral 22 is a stud bolt insertion hole.

As shown in FIGS. 1, 7, 11 and 12, the hydraulic actuator 15 has an actuator body 24 in which two cylinders 23 are arranged side by side, and two actuators are housed in each cylinder 23. The actuator body 24 includes a piston 25 and a lid 26 that covers the top of the actuator body 24. This lid 26 is fixed to the actuator body 24 using lid attachment bolts 44.

The piston 25 is slidably provided within the cylinder 23, and has a rack 27 integrally formed at its tip. This rack 27 is engaged with a pinion 28 formed at the end of the rocker shaft 11. Further, in the upper part of the actuator body 24, as shown in FIG. 1, FIG. 6, and FIG. Low-speed oil passages 29 are formed in communication with both ends of each of the oil passages 23 . A low-speed hydraulic port 31 communicating with the low-speed oil passage 29 and a medium-high speed hydraulic port 32 communicating with the medium-high speed oil passage 30 are formed in the lid 26, respectively.

On the other hand, as shown in FIG. 1, an oil passage switching solenoid valve 33 is installed in a head cover 33A that covers the cylinder head 16. The oil passage switching solenoid valve 33 selectively supplies hydraulic pressure to the low-speed hydraulic port 31 or the medium-high speed hydraulic port 32 via the low-speed hydraulic hose 34 and the medium-high speed hydraulic hose 35.

The hydraulic switching solenoid valve 33 has a spool valve 37 disposed within a valve body 36, and is slid by energizing and demagnetizing an electromagnet 38. The valve body 36 is further formed with an oil supply port 39 into which engine oil pressurized by an oil pump (not shown) flows as hydraulic oil. Also, the valve body 36 has a relief port 4.
0 is formed, and a low-speed oil supply port 41 and a medium-high speed oil supply port 42 are also formed. Low speed oil supply port 41 and low speed hydraulic port 31 of hydraulic actuator 15
and are connected by a low-speed hydraulic hose 34. Also,
The medium/high speed oil supply port 42 and the medium/high speed hydraulic port 32 of the hydraulic actuator 15 are connected by a medium/high speed hydraulic hose 35 .

Excitation and demagnetization of the electromagnet 38 is controlled based on the engine speed. In other words, when the engine speed increases, the engine speed is, for example, about 9500r. p
．． m. The electromagnet 38 is excited in the low rotation speed range below, and the
00r. p. m. In the medium and high rotation speed range above, this electromagnet 38
is demagnetized.

When the electromagnet 38 is energized, the spool valve 37 moves in the direction of arrow Q in FIG. do. Therefore, the hydraulic oil is introduced from the oil supply port 39 to the low-speed oil passage 29 via the low-speed oil supply port 41, the low-speed hydraulic hose 34, and the low-speed hydraulic port 31, and the piston 25 is pushed back in the direction of arrow M shown in FIG. As a result, the pinion 28 rotates in the direction of arrow O. As a result, as shown in FIG. 4, the thick tops 12a and 13a of the eccentric bushes 12 and 13 move obliquely forward, and the low-speed cam 3 moves to the low-speed rocker arm 7.
operate.

When the electromagnet 38 is demagnetized, the spool valve 37 is moved to the position shown in FIG. 1 by the biasing force of the solenoid return spring 43, and as a result, the oil supply port 39 and the medium/high speed oil supply port 42 communicate with each other. In addition, the low-speed oil supply port 41 and the relief port 40 communicate with each other. Therefore, the hydraulic oil is introduced from the oil supply port 39 to the medium and high speed oil passage 30 via the medium and high speed oil supply port 42, the medium and high speed hydraulic hose 35, and the medium and high speed hydraulic port 32, and the piston 25 The pinion 28 is pushed out in the N direction and rotates in the arrow P direction. As a result, as shown in FIG.
2a and 13a move diagonally rearward, and the middle and high speed cams 4 and 5 actuate the middle and high speed rocker arms 8 and 9.

Now, as shown in FIGS. 1 and 7, the actuator body 24 of the hydraulic actuator 15 is attached to the cylinder head 16 via a mounting plate 45.
Fixed. As shown in FIGS. 13 and 14, this mounting plate 45 is a substantially rectangular thick plate, and bolt insertion holes 46 are passed through four bulged corners. Plate mounting bolts 47 (FIGS. 1 and 7) are inserted into the bolt insertion holes 46 to fix the mounting plate 45 to the cylinder head 16.

The mounting plate 45 also has pin holes 4 for installing positioning pins 48 (FIGS. 1 and 7).
9 are provided at point-symmetrical positions as shown in FIG. Furthermore, the mounting plate 45 has a plurality of bolt holes 50 arranged in parallel at the center position in the left and right width direction, and a female thread 51 is formed on the inner periphery of each of these bolt holes 50.

On the other hand, as shown in FIGS. 1, 7 and 8, a positioning hole 5 is provided on the lower surface of the actuator body 24.
2 is formed. Further, as shown in FIGS. 6, 8, 10, and 11, a plurality of bolt insertion holes 53 are provided at the center position of the actuator body 24 in the left-right direction along the axis.
It is drilled in a penetrating state.

Therefore, when assembling the hydraulic actuator 15, the pin hole 4 of the mounting plate 45 must be
After positioning the positioning pin 48 implanted in the actuator body 24 by inserting it into the positioning hole 52 of the actuator body 24,
The hydraulic actuator 15 is assembled to the cylinder head 16 by inserting a mounting bolt (not shown) into the bolt insertion hole 53 of the actuator body 24 and screwing the tip of the mounting bolt into the female thread 51 of the bolt hole 50 in the mounting plate 45. .

Further, the actuator body 24 of the hydraulic actuator 15 has a recess 54 formed in its lower part, as shown in FIGS. 1, 7, 8, 10 and 12. After the hydraulic actuator 15 is assembled, the opening of the recess 54 is covered by the mounting plate 45 to form a dust chamber 55. This dust chamber 55 is communicated with the axial center position of the two cylinders 23 through a dust hole 56 . The dust chamber 55 is provided so that foreign matter such as fine iron powder in the hydraulic oil flowing into and out of the cylinder 23 through the dust hole 56 accumulates due to its weight.

[0039] It should be noted that the dust chamber 56
The hydraulic oil that has flowed into the interior flows into the dust chamber 55 through the gap between the actuator body 24 and the mounting plate 54.
Only foreign matter oozes out and accumulates inside the dust chamber 55.

Next, the functions and effects will be explained.

When the engine is in a low rotational speed range, the piston 25 of the hydraulic actuator 15 is pushed back in the direction of arrow M by the excitation of the oil passage switching solenoid valve 33, as shown in FIG. When the eccentric bushes 12 and 13 are rotated in the O direction, the thick top portions 12a and 13a of the eccentric bushes 12 and 13 are located diagonally forward as shown in FIG. 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, gaps are formed between the circumferential surfaces of the medium and high speed cams 4 and 5 and the cam floor surfaces 8c and 9c of the medium and high speed rocker arms 8 and 9, and as a result,
The middle and high speed cams 4 and 5 idle.

Furthermore, at this time, the low speed rocker arm 7 is constantly pushed upward about the axis of the rocker shaft 11 by the urging force of the valve spring 57 (FIG. 4), so that the cam floor surface 7c of the low speed contact with the circumferential surface of the cam 3 for use. 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/high rotation range, the piston 25 of the hydraulic actuator 15 is pushed out in the direction of arrow N by demagnetization of the flow path switching solenoid valve 33 shown in FIG. When rotated in the direction of arrow P, thick top portions 12a and 13a of eccentric bushes 12 and 13, respectively, are located diagonally rearward as shown in FIG. As a result, the rocker arm 8 for medium and high speed
The cam floor surfaces 8c and 9c of the low-speed rocker arm 7 move approximately upward or to the same position relative to the cam floor surface 7c of the low-speed rocker arm 7, and the cam floor surfaces 8c and 9c correspond to the peripheral surfaces of the medium-high speed cams 4 and 5, respectively. comes into contact with.

As shown in FIG. 15, 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. When the low speed cam 3 idles, the medium and high speed cams 4 and 5 drive the valves 1 and 2 via the medium and high speed rocker arms 8 and 9, respectively, based on the lift characteristic B shown in FIG. 15. 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 directly fitted and inserted into 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.

Further, the hydraulic actuator 15 that rotates the rocker shaft 11 in the forward and reverse directions uses engine oil as hydraulic oil, and guides this hydraulic oil into the cylinder 23 via the hydraulic switching solenoid valve 33 to cause the piston 25 to slide. However, this hydraulic oil contains foreign matter such as fine iron powder. Since a dust chamber 55 is formed in the actuator body 24 of the hydraulic actuator 15 and surrounded by the recess 54 and the mounting plate 45,
Due to the weight of the foreign matter in the hydraulic oil, the foreign matter passes through the dust hole 56 and accumulates in the dust chamber 55 together with the hydraulic oil. Therefore, the amount of foreign matter such as iron powder remaining in the cylinder 23 of the hydraulic actuator 15 can be reduced.
The piston 25 can be slid smoothly. As a result, wear between the cylinder 23 and the piston 25 can be reduced, and the performance of the hydraulic actuator 15 can be improved.

In the above embodiment, the cam profiles of the medium and high speed cams 4 and 5 are as shown by the broken line B in FIG. 15. 16 dashed line B' or Figure 1
7, the lifts of the valves 1 and 2 during medium and high engine speeds may be changed.

[0049]

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.

Further, the hydraulic actuator, which is operatively connected to the rocker shaft and rotates the rocker shaft by the hydraulic pressure of the hydraulic oil, has a dust pipe connected to the lower part of the cylinder formed in the actuator body. Since the chamber is formed, foreign matter such as fine iron powder in the hydraulic oil flows from inside this cylinder into the dust chamber and accumulates therein. Therefore, foreign matter in the hydraulic oil in the hydraulic actuator can be removed, and wear between the cylinder and the piston can be reduced, so that the performance of the hydraulic actuator can be improved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view taken along line II in FIG. 6, showing a hydraulic actuator operated to operate a medium-high speed cam.

FIG. 2 is a perspective view showing an embodiment of a valve train for a four-stroke engine according to the present invention.

FIG. 3 is a plan view of the valve train shown in FIG. 2;

FIG. 4 is an operating state diagram showing a low-speed cam operating state of the valve train of FIG. 2;

5 is an operating state diagram showing the operating state of the medium-high speed cam of the valve train shown in FIG. 2; FIG.

6 is a partial plan view of a cylinder head to which the valve train of FIG. 2 is applied, with intake/exhaust valves and valve springs omitted; FIG.

FIG. 7 is a sectional view showing the hydraulic actuator in FIG. 1 operated to operate a low-speed cam.

8 is a rear view showing the hydraulic actuator of FIG. 7. FIG.

9 is a right side view of the hydraulic actuator of FIG. 7. FIG.

FIG. 10 is a sectional view taken along line XX in FIG. 9;

11 is a sectional view taken along the line XI-XI in FIG. 9. FIG.

FIG. 12 is a sectional view taken along line XII-XII in FIG. 11;

13 is a plan view showing the mounting plate of FIGS. 1 and 7. FIG.

14 is a sectional view taken along the line XIV-XIV in FIG. 13. FIG.

FIG. 15 is a graph showing the cam profile of the cam of FIG. 2;

FIG. 16 is a graph showing a first modification of the cam profile shown in FIG. 15;

FIG. 17 is a graph showing a second modification of the cam profile shown in FIG. 15;

[Explanation of symbols]

1, 2 Valve 3 Low speed cam 4,5 Cam for medium and high speeds 7 Low speed rocker arm 8, 9 Rocker arm for medium and high speeds 11 Rocker shaft 12, 13 Eccentric bushing 15 Hydraulic actuator 23 Cylinder 24 Actuator body 25 Piston 27 Rack 28 Pinion 45 Mounting plate 54 Recess 55 Dust chamber 56 Dust hole

Claims (2)

[Claims] Claims: 1. A rocker shaft rotatably supported and formed with an eccentric large diameter portion; a first rocker arm directly fitted into the rocker shaft; and a rocker shaft disposed on both sides of the first rocker arm. second and third rocker arms that are fitted into the eccentric large diameter portion, first, second and third cams that actuate the first, second and third rocker arms, respectively; and the rocker shaft. a hydraulic actuator operatively connected to a hydraulic actuator for rotating the rocker shaft by hydraulic pressure of hydraulic fluid, the second and third cams having the same cam profile, and a cam of the first cam The hydraulic actuator has a profile different from the cam profile, and the hydraulic actuator has a piston connected to the rocker shaft housed in a cylinder formed in the actuator body, and a piston connected to the rocker shaft communicates with the cylinder downwardly. A valve train for a four-stroke engine, characterized in that a dust chamber is formed. 2. The valve train for a four-stroke engine according to claim 1, wherein the dust chamber is surrounded by a mounting plate for installing the actuator body on the cylinder head and the actuator body.