JPH03286111A - Valve system of four-cycle engine - Google Patents

Abstract

PURPOSE:To prevent the rotation of a low speed cam at a speed higher than its limited rotational speed surely by setting an engine speed for cutting ignition based on the rotational position of a rocker shaft for selecting the operation of low speed and medium/high speed rocker arms. CONSTITUTION:A sensor oil ON/OFF groove 37, which is formed along the axial direction of a rocker shaft 11, is formed in such a way as to communicate with a sensor oil supplying passage 36 in a position where the rocker shaft 11 makes turning motion and stops so that a medium/high speed cam may drive a medium/high speed locker arm. Therefore sensor oil in the sensor oil supplying passage 36 is introduced through the sensor oil ON/OFF groove 37 to a sensor oil ring groove 38 and a sensor oil operation passage 39 to set a push sensor 40 ON only when the rocker shaft 11 stays in a position in a medium/high speed rotational speed area. The engine speed for cutting ignition can be increased higher than a limited rotational speed of a low speed cam during the operation of the medium/high speed rocker arm, so that it is possible to surely prevent the rotation of the low speed cam at a speed higher than its limited rotational speed.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention provides a four-stroke engine that can change the lift amount, valve opening timing, etc. of intake and exhaust valves according to operating conditions. Regarding the valve train of the
This invention relates to a valve train for a cycle engine.

(Prior Art) Generally, in a four-stroke engine installed in a vehicle such as an automobile or a motorcycle, intake and exhaust valves are 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.

(Problem 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 rotational speed range from low rotational speed to medium and high rotational speed, that is, has a wide power band. is desirable.

However, in conventional valve train systems, the valve opening/closing timing and lift amount are fixed, so output characteristics that only have a peak value in a specific engine speed range can be obtained, and therefore the output characteristics in the low engine speed range cannot be obtained. You are forced to choose whether to focus on the engine or the output characteristics in the medium and high rotation speed range.

This invention was made in consideration of the above-mentioned circumstances, and it is possible to improve the output within a wide range of rotation speeds, and also to reliably prevent the rotation of the low-speed cam above the limit rotation speed, thereby improving the performance of the device. An object of the present invention is to provide a valve train for a four-stroke engine that can avoid failures.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a rocker shaft rotatably supported and formed with an eccentric large diameter portion, and a low speed rocker shaft that is directly inserted into the rocker shaft and has a branched tip portion formed therein. a rocker arm for medium and high speeds placed on both sides of this rocker arm for low speeds and fitted into the eccentric large diameter portion, and a low speed cam and a cam for medium and high speeds that drive the low speed and medium and high speed rocker arms, respectively. , wherein the tip of the medium-high speed rocker arm is overlapped with the branched tip of the low-speed rocker arm, and the cam profile of the medium-high speed cam is different from the cam profile of the low-speed cam. Furthermore, when the rocker shaft rotates, the low-speed rocker arm and medium-high speed rocker arm are selectively activated, and a position sensor detects the rotational position of the rocker shaft, and when the medium-high speed rocker arm is activated, the ignition is cut. It is characterized in that the rotational speed is increased to a limit rotational speed or more of the low-speed cam.

(Function) 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 surfaces of the second and 30th lever arms are rotated to the first position. 10 Change the position of the arm relative to the cam floor surface in the vertical direction.

When the cam floor surfaces of the second and 30th claw arms are moved downward relative to the cam floor surface of the 10th claw arm, the second and 30th claw arms and the second and third
The contact with the cam is released, the 10th lever arm contacts the first cam, and the valve of the 4-cycle engine
Driven by a cam.

Further, when the cam floor surfaces of the second and 30th lever arms are moved substantially upwardly or to the same position relative to the cam floor surface of the 10th lever arm, the contact between the 10th lever arm and the first cam is released, and the cam floor surface of the 10th lever arm is released. And the 30th hook arm and the second and third cams are in contact with each other, and the 4th
The valves of the cycle engine are actuated 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, the operating status of the medium-high speed rocker arm can be determined based on the detection signal from the position sensor that detects the rotational position of the rocker shaft. Since the rotation speed is increased above the limit rotation speed, the ignition cut rotation speed does not rise above the limit rotation speed of the low speed cam while the low speed rocker arm is in operation. As a result, it is possible to prevent the low-speed cam that drives the low-speed rocker arm from rotating at a rotation speed higher than the limit rotation speed, thereby avoiding a failure of the valve train.

(Example) Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 5 is a perspective view showing an embodiment of a valve train for a four-stroke engine according to the present invention, and FIG. 2 is a partial plan view of a cylinder head to which the valve train of FIG. 5 is applied.

This valve train is disposed on the intake side and the exhaust side of one cylinder of the engine, respectively. Therefore, the fourth
The valve 1.2 shown in FIGS. 8-8 is arranged for intake or exhaust.

This embodiment includes a camshaft 6 (FIG. 3,
8), low-speed rocker arms 7, medium-high speed rocker arms 8 and 9, and supports 7a and 8a of these rocker arms 7.8 and 9, respectively, located below the cams 3.4 and 5 and a rocker shaft 11 into which the rocker shaft 9a is fitted and rotatably supported by a rocker shaft bearing portion 28 (FIG. 3), which will be described later.

The tip of the low-speed rocker arm 7 is branched into two directions, and both of these branch tip portions 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, the support portion 7a of the low-speed rocker arm 7
is directly fitted onto the rocker shaft 11 and is rotatably provided.

The support portion 8a of the medium/high speed rocker arm 8 is rotatably fitted onto the rocker shaft 11 via an eccentric bushing 12 having a larger diameter than the rocker shaft 11. As shown in FIG. 7, this eccentric bushing 12 is precisely eccentric from the center 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.

As shown in FIG. 6, the support portion 9a of the medium/high speed rocker shaft 9 also rotates relative to the rocker shaft 11 via an eccentric bush 13 that has the same shape as the eccentric bush 12 and is eccentric in the same direction. Possibly inserted. This eccentric bushing 13 is also attached to the rocker shaft 11 by the retaining pin 10.
It is removably fixed to the shaft and functions as an eccentric large diameter section.

In addition, each tip portion 8b of the rocker arms 8 and 9 for medium and high speeds is
The lower surfaces of 9b and 9b abut on one and the other branch tip portions 7b of the low-speed rocker arm 7 via shims 14a, respectively. The contact points between the branch portion 7b of the low-speed rocker arm 7 and the tips 8b and 9b of the medium-high speed rocker arms 8 and 9 are set approximately on the axes of the valves 1 and 2.

Therefore, as shown in FIG. 7, when the low-speed cam 3 presses down the cam floor surface 7C of the low-speed rocker arm 7 and lowers each branch tip 7b, the tip 8b of the rocker arms 8 and 9 and 9b descends following this branch tip 7b due to gravity. On the other hand, 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, as shown in FIG. presses down each branch tip 7b of the low-speed rocker arm 7, so that the branch tip 7b is forcibly lowered.

The shim 14a is a T-shaped shim in longitudinal section, and is fitted into both branched tips 7b of the low-speed rocker arm 7 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 14b are connected to valves 1 and 2.
Used for tappet clearance adjustment.

Also, among the cams 3.4 and 5, the medium-high speed cam 4
and 5 have the same cam profile, and the low speed cam 3 has a different cam profile from the cam profile of these medium and high speed cams 4 and 5. In other words,
The cam profile of the low-speed cam 3 is set so that an appropriate valve lift amount and valve opening/closing timing can be obtained when the engine is operated in a low rotational speed range. Also,
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 of pulps 1 and 2, and matches the cam lift amount. In Fig. 9, the cam profile of the low-speed cam 3 is shown as a solid line A (cam lift amount p
a), and the cam profiles of the medium and high speed cams 4 and 5 are shown by a broken line B (cam lift amount ib). As is clear from this FIG. 9, medium and high speed cams 4 and 5
The cam profile is set so that a larger valve lift amount than the low speed cam 3 can be obtained.

In addition, the chain double-dashed line C in FIG. 9 indicates the middle and high speed cam when the rocker shaft 11 is rotated and the thick tops 12a and 13a of the eccentric bushings 12 and 13 are positioned diagonally forward (FIG. 7). 4 and 5 are shown.

By the way, as shown in FIGS. 2, 3, and 5,
The rocker shaft 11 is rotated by a hydraulic cylinder 15 operated by oil pressure from the engine. A rack 16 is attached to the piston (not shown) of this hydraulic cylinder 15.
The rack 16 is engaged with a pinion 17 formed at one end of the rocker shaft 11. The hydraulic cylinder 15 is also provided with a low-speed hydraulic port 18 and a high-speed hydraulic boat 19, and hydraulic pressure from the engine is selectively guided to each boat 18, 19.

When the engine speed is in the low speed range, hydraulic pressure is supplied to the low-speed hydraulic boat 18, the piston 27 is pushed back, the rack 16 is also pulled back, and the pinion 17 is rotated in the direction of arrow O in FIG. Eccentric bushes 12 and 1
3, as shown in FIG.
Rotate so that 3a is positioned diagonally forward. Further, when the engine speed is in the medium/high speed range, hydraulic pressure is supplied to the medium/high speed hydraulic port 19 and the piston is pushed out.
The rack 16 is also pushed out, the pinion 17 is rotated in the direction of arrow P in FIG. 5, and the eccentric bushes 12 and 13 are moved so that their thick tops 12a and 13a are positioned diagonally rearward, as shown in FIG. Rotate.

In this way, the rocker shaft 11 is connected to the hydraulic cylinder etc.
5.16.17, the eccentric bushing 12.13
The thick top parts 12a and 13a of the rocker shaft 1 are always connected to the rocker shaft 1.
It is configured to rotate in the range from diagonally forward to diagonally backward on the upper half side of 1.

Rocker shaft 11 and hydraulic cylinder 1 as described above
5 etc. is the cylinder head 21 shown in FIGS. 2 and 3.
will be placed in A total of four rocker shafts 11 are arranged, one on each side of the vehicle, one on each side of the cylinder head 21,
It is arranged to extend in the left and right direction of the vehicle. Each rocker shaft 1
1 is rotatably supported by a rocker shaft bearing portion 28 formed in the cylinder head 21. A lower half bearing hole 22 for supporting the camshaft 6 is formed above these rocker shafts 11 . In addition, this lower half bearing hole 22
A valve guide 23 is arranged nearby, and a stud bolt insertion hole 24 is formed. Furthermore, the cylinder head 21
A mating surface 25 with the head cover 27 is formed at the upper part of the cylinder head 21, and a cam chain chamber 26 is formed at the center 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. As shown in FIG. 3, this rack 16 is configured to mesh with the pinion 17 of the rocker shaft 11 from above.

In addition, rocker arm 7 for low speed, rocker arm 8 for medium and high speed
and 9 are installed in two sets on one rocker shaft 11. Each set of low-speed rocker arm 7 and medium-high speed rocker arms 8 and 9 is connected to the rocker shaft 11 by a positioning spring 29 interposed in the rocker shaft 11.
Its location is also regulated.

In FIG. 3, reference numeral 30 denotes a bearing housing, and the camshaft 6 is rotatably supported by an upper half-moving receiving hole 31 and the lower half-bearing hole 22 formed in the bearing housing 30.

A lubricating oil passage 32 is formed in this bearing housing 30 in parallel with the camshaft 6. A lubricating oil supply path 33 is communicated with this lubricating oil path 32 , and the lubricating oil that has lubricated the camshaft is guided into the lubricating oil path 32 through this lubricating oil supply path 33 . The bearing housing 30 has a lubricating oil filler port 34.
It is formed in communication with the lubricating oil passage 32. The lubricating oil in the lubricating oil passage 32 is injected downward from this lubricating oil filling port 34,
The low speed cam 3 and the low speed rocker arm 7; as well as the medium and high speed cam 4.5 and the medium and high speed rocker arms 8 and 9 are lubricated. Furthermore, the lubricating oil in this lubricating oil path 32 reaches the upper half bearing hole 31 via a lubricating oil return path 35, and is used again for lubricating the camshaft 6.

As shown in FIGS. 1A and 1B and also in FIG. 4, a fail-safe mechanism is installed in the cylinder head 21. In other words, the cylinder head 21 has a lower half bearing hole 22.
A sensor oil supply path 36 having an upper opening is bored in the sensor oil supply path 36 .

This sensor oil supply path 36 extends vertically downward, and its lower opening reaches the circumferential surface of the rocker shaft 11. This sensor oil supply path 36 guides the lubricating oil that has lubricated the camshaft 6 toward the rocker shaft 11 as sensor oil.

This rocker shaft 11 has sensor oil ON/0FFFF.
The groove top 70 is carved along the axial direction of the shaft 11. This sensor oil ON/0FFFF groove upper 7 medium and high speed cam 4
and 5 are formed so as to communicate with the sensor oil supply path 36 at the position where the rocker shaft 11 rotates and stops in order to drive the medium and high speed rocker arms 8 and 9 (medium and high speed range position) (Fig. 1). (B)).

Furthermore, the cylinder head 21 includes a rocker shaft 11.
A sensor oil ring groove 38 is formed along the peripheral surface of the end portion. This sensor oil ring groove 38 communicates with the sensor oil ON/OFF groove 7 o'clock during rotation of the rocker shaft 11, and also communicates with the sensor oil operating path 39. This sensor oil operating path 39 is horizontally bored in the cylinder head 21 and guides the sensor oil to a bush sensor 40 as a position sensor screwed onto the cylinder head 21. Therefore, only in the middle and high rotational speed range positions of the rocker shaft 11, the sensor oil in the sensor oil supply path 36 flows over the sensor oil ON/OFF groove 7 and into the sensor oil ring groove 38 and the sensor oil operating path 3.
9 to turn on the bushing sensor 40.

The sensor oil ON-OFF grooves 37 described above are all formed at the ends of the four rocker shafts 11 on the left and right sides of the exhaust and on the left and right sides of the intake. Further, a sensor oil supply path 36, a sensor oil ring groove 38, and a sensor oil operating path 39 are also formed in the same manner near the top 7 of these sensor oil ON/0FFFF grooves. Furthermore, Bush sensor 4
A total of four o are arranged, one each on the left and right sides of the exhaust and the left and right sides of the intake of the cylinder head 21. Therefore, when all four bushing sensors 40 are turned ON, it is determined that all the medium and high speed rocker arms 8 and 9 have been operated by the medium and high speed cams 4 and 5, and at this point the ignition cut rotation speed is set to the low speed. The rotation speed of the cam 3 is set to be higher than the limit rotation speed.

Here, the low-speed cam 3 and the medium-high speed cams 4 and 5 have a large difference in acceleration due to the nature of the cams, and as a result, the limit rotational speed of the cams generally differs. For example, the limit rotation speed of cams 4 and 5 for medium and high speeds is approximately 15,000 rpm.
m, and the limit rotation speed of the low-speed cam 3 is approximately 111,000.
It is rp. Therefore, for example, if the ignition cut-off rotation speed is set to about 11100 rpm when the low-speed cam 3 is operated, the ignition cut-off rotation speed is set to about 1500 rpm when the four bushing sensors 40 are turned on.

Next, the effects will be explained.

When the engine is in the low rotation speed range, the hydraulic cylinder 15
When the rocker shaft 11 rotates in the direction of arrow O in FIG. 5 due to the operation of , the thick top portions 12a and 13a of the eccentric bushes 12 and 13 are located diagonally forward (FIG. 7). 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 9C of the medium and high speed rocker arms 8 and 9
A gap is formed between the two, 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 urging force of the valve spring 20, so that its cam floor surface 7C comes into contact with the circumferential surface of the low-speed cam 3. come into contact with 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 rocker shaft 11 rotates in the direction of arrow P in FIG.
Thick-walled top portions 12a and 13a, respectively, are located diagonally rearward (FIG. 8).

As a result, the cam floor surfaces 8C and 9C of the rocker arms 8 and 9 for medium and high speeds move toward the road 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 respectively contact with the circumferential surfaces of the cams 4 and 5.

Here, 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 is rotated under the conditions shown in FIG. In this case, the low-speed cam 3 idles, while the medium-high speed cams 4 and 5 operate the valve 1 via the medium-high speed rocker arms 8 and 9, respectively, based on the lift characteristic B shown in FIG.
and 2. As a result, valves 1 and 2 are
Opens and closes the combustion chamber while ensuring a valve lift suitable for the engine's medium and high speed range.

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. Furthermore, the rocker arm 8 for medium and high speeds is attached to the eccentric bushes 12 and 13 of the rocker shaft 11.
and 9 are rotatably inserted into each other, and the low-speed rocker arm 7 is directly inserted into the rocker shaft 11. As the rocker shaft 11 rotates, the low-speed cam 3 and the low-speed rocker arm 7 are brought into contact with each other, and the low-speed rocker arm 7 is inserted into the rocker shaft 11. Since the contact between the cams 4 and 5 and the medium-high speed rocker arms 8 and 9 can be selected, the valves 1 and 2 can be selectively driven by the low-speed cam 3 or the medium-high speed cam 4.5. .

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.

Further, since the selection of the low speed cam 3 and the medium and high speed cams 4 and 5 is carried out by rotating the eccentric bushings 12 and 13, no large stress is generated in each part when selecting the cams 3, 4.5. Therefore, the cams 3.4.5 can be selected smoothly.

Further, in the low engine speed range where the low speed cam 3 and the low speed rocker arm 7 operate, the rocker shaft 11 is in the low speed range position shown in FIG. 1(A), so the sensor in the sensor oil supply path 36 Oil is blocked by the circumferential surface of the rocker shaft 11.

Therefore, the bush sensor 40 is turned off.

On the other hand, in the engine medium and high speed range where the medium and high speed cams 4 and 5 and the medium and high speed rocker arms 8 and 9 operate,
The rocker shaft 11 is in the middle and high rotation speed range position shown in FIG. 1(B). As a result, the sensor oil supply path 36 and the sensor oil ON/OFF * 37 communicate with each other, and the sensor oil in the sensor oil supply path 36 is transferred to the sensor oil 0N-OFF groove 37, the sensor ura ring groove 38, and the sensor oil operating path 39. The push sensor 40 is turned on through the push sensor 40. When all four bushing sensors 40 are turned on, the ignition cut-off rotation speed is switched to a rotation speed higher than the limit rotation speed of the low-speed cam 3.

Therefore, the ignition cut rotation speed is switched as described above only while all medium-high speed cams 4 and 5 and medium-high speed rocker arms 8 and 9 are in operation, so that while low speed cam 3 and low speed rocker arm 7 are in operation, The rotational speed of the low-speed cam 3 does not change to a rotational speed higher than the limit rotational speed.

As a result, failure of the valve train can be avoided.

In addition, as described above, the ignition cut-off rotation speed does not switch to a rotation speed higher than the limit rotation speed of the low-speed cam 3 while the low-speed cam 3 and the low-speed rocker arm 7 are in operation. There is no need to set the rotation speed high.

Therefore, the limit rotational speed can be set high for the medium-high speed cams 4 and 5 and low for the low-speed cam 3, so that the performance difference between the low-speed cam 3 and the medium-high speed cams 4 and 5 can be made clear. As a result, engine characteristics can be optimized in both medium and high rotational speed ranges as well as low rotational speed ranges.

FIGS. 12 to 17 are diagrams showing fail-safe mechanisms in other embodiments of the valve train for a four-stroke engine according to the present invention. In this other embodiment, the same parts as those in the above embodiment are given the same reference numerals and the explanation will be omitted.

As shown in FIGS. 12 and 13, in the cylinder head 21, a sensor oil supply path 36 similar to that of the previous embodiment is provided at the end of the intake rocker shaft 11 and in the vicinity of this end. A groove, a sensor oil ring groove 38, a sensor oil operating path 39, and a bush sensor 40 are formed and installed. Therefore, Bush sensor 4
Two 0s are installed on the intake side of the cylinder head 21.

Further, as shown in FIG. 14, a sensor oil ring groove 41 is formed in the cylinder head 21 near the end of the rocker shaft on the exhaust side in the same manner as the sensor oil ring groove 38. A sensor oil communication path 42 that communicates the sensor oil ring groove 41 and the sensor oil ring groove 38 is formed in the cylinder head 21 as shown in FIGS. 15 to 17 (A) and (B). . Furthermore, a sensor oil ON/OFF groove 43 is provided at the end of the cylinder head 11 on the exhaust side.
A sensor oil drain passage 44 that can communicate with the sensor oil ON+1OFF groove 43 is bored in the cylinder head 21.

The sensor oil drain path 44 is formed such that its upper opening opens into the interior of the cylinder head 21 .

Also, the sensor oil 0N-OFF groove 43 is connected to the rocker shaft 1.
16 (A)) which communicates with the sensor oil drain passage 44 at the low rotation speed range position of the rocker shaft 11 (Fig. Figure (B)).

Therefore, the low speed cam 3 and the low speed rocker arm 7
In the low engine speed range where the engine operates, the sensor oil ON-0FFFF groove in the rocker shaft 11 on the intake side communicates with the sensor oil supply path 36, as shown in FIGS. 16(A) and 17(A). First, since the sensor oil 0N-OFF groove 43 in the rocker shaft 11 on the exhaust side communicates with the sensor oil drain path 44, no oil pressure acts on the bushing sensor 40, and this bushing sensor 40 is in the OF state.
F is operated.

On the other hand, in the engine medium and high speed range where the medium and high speed cams 4 and 5 and the medium and high speed rocker arms 8 and 9 operate,
Figure 16(B) and 17v! : As shown in J(B), the sensor oil ON-OFF groove 37 in the rocker shaft 11 on the intake side communicates with the sensor oil supply path 36,
Since the sensor oil ON/OFF groove 43 in the rocker shaft 11 on the exhaust side does not communicate with the sensor oil drain path 44 and is blocked by the circumferential surface of the rocker shaft 11, the sensor oil in the sensor oil supply path 36 is Oil ON/0F
FFF groove, sensor oil ring groove 38, sensor oil communication path 42
The oil reaches the bushing sensor 40 via the sensor oil operating path 39, and turns on the bushing sensor 40.

When the bushing sensors 40 installed one each on the left and right sides of the intake side of the cylinder head 21 are both turned on,
The ignition cut rotation speed is the same as in the above embodiment, and the low speed cam 3
The rotation speed can be changed to a rotation speed higher than the limit rotation speed.

Therefore, also in this other embodiment, the low speed cam 3
Since the ignition cut-off rotation speed is not switched to a rotation speed higher than the limit rotation speed of the low-speed cam 3 during operation, the same effect as in the embodiment described above is achieved.

Moreover, in this other embodiment, it is sufficient to install two bushing sensors 40 in the cylinder head 21, so that the cost can be reduced accordingly.

In both of the above embodiments, the cam profiles of the medium and high speed cams 4 and 5 are as shown by the broken line B in FIG. 9, but the cam profiles of the medium and high speed cams 4 and 5 are As shown by broken line B' in the figure or broken line B' in FIG. 11, the lifts of valves 1 and 2 at medium and high engine speeds may be changed.

〔Effect of the invention〕

As described above, according to the valve train for a four-cycle engine according to the present invention, the eccentric large diameter portion is formed in the rotatably supported rocker shaft, and the second and third
Since the 0th lever arm was fitted into this eccentric large diameter portion, and the 10th lever arm was placed between the 2nd and 30th lever arms and directly fitted into the rocker shaft, the rotation of the cam due to the rotation of the rocker shaft was Depending on the selection, the engine output can be improved over a wide rotation speed range.

In addition, when the rocker shaft rotates, the low-speed rocker arm and the medium-high speed rocker arm are selectively operated, and the position sensor detects the rotational position of the rocker shaft, and when the medium-high speed rocker arm is activated, the ignition cut rotation speed is detected. By increasing the rotation speed above the limit rotation speed of the low-speed cam,
It is possible to reliably prevent the low-speed cam from rotating at a rotation speed higher than the limit rotation speed, and to avoid failure of the valve train.

[Brief explanation of the drawing]

Figures 1 (A) and (B) are sectional views taken along line I-I in Figure 2, Figure 2 is a partial plan view of a cylinder head to which the valve train of Figure 5 is applied, and Figure 3 is a 2 is a sectional view taken along the line ■-■, FIG. 4 is a perspective view showing the oil passage of the fail-safe mechanism shown in FIGS. 1 (A) and (B), and FIG. 5 is a 4-cycle according to the present invention A perspective view showing an embodiment of the valve train of an engine, FIG. 6 is a plan view of the valve train shown in FIG. 5, and FIGS. 7 and 8 are operating states showing the operation of the valve train shown in FIG. Figure 9 is a diagram showing the cam profile of the cam in Figure 5,
10 and 11 are views showing respective modifications of the cam profile shown in FIG. 9, and FIG. 12 is a cylinder head to which another embodiment of the valve train for a four-stroke engine according to the present invention is applied. The partial plan views of FIGS. 13, 14, and 15 are taken along line XI-XI in FIG.
□A cross-sectional view taken along the □ line and the 4th line, Figures 16 (A) and (B) are operational diagrams showing the fail-safe mechanism in Figure 15, and Figures 17 (A) and (B) are the Figure 16 (A
) and (B) are perspective views showing the fail-safe mechanism in an operating state. 1.2...Valve, 3...Low speed cam, 4,5...
・Medium/high speed cam, 7...Low speed rocker arm, 8.9
... Rocker arm for medium and high speeds, 11... Rocker shaft, 12.13... Eccentric bushing, 36... Sensor oil supply path, 37... Sensor oil ON/OFF groove, 38...
...Sensor oil ring groove, 39...Sensor oil operating path, 4
o... Bush sensor, A... Cam profile of low speed cam, B... Cam profile of medium and high speed cam.

Claims (1)

[Claims] A rocker shaft is rotatably supported and has an eccentric large diameter portion, a low-speed rocker arm is directly fitted onto the rocker shaft and has a branched tip, and is arranged on both sides of the low-speed rocker arm. a medium-high speed rocker arm fitted into the eccentric large-diameter portion; a low-speed cam and a medium-high speed cam that respectively drive the low-speed and medium-high speed rocker arms; is overlapped with the branched tip of the low-speed rocker arm, and the cam profile of the medium-high speed cam is formed to be different from the cam profile of the low-speed cam, and the rotation of the rocker shaft causes the low-speed The rocker arm and the rocker arm for medium and high speeds are selectively activated, and the position sensor detects the rotational position of this rocker shaft, and when the rocker arm for medium and high speeds is activated, the ignition cut-off rotation speed is set to exceed the limit rotation speed of the low speed cam. A valve train for a 4-stroke engine, which is characterized by a mechanism for raising the valve.