JPH05179912A - Valve system of four-cycle engine - Google Patents

Abstract

PURPOSE:To enlarge the degree of freedom for the setting of valve lift and valve timing without entailing the promotion of large type in an actuator producing the tuning effort of a rocker shaft. CONSTITUTION:A low-speed rocker arm 32 being operated by a low-speed cam 27 is directly fitted in a rocker shaft 31. In addition, medium and high speed rocker arms 33, 34 being operated by medium and high speed cams 28, 29 are fitted in two eccentric large diametral parts 38, 39 of the rocker shaft. Moreover, both operations of the low speed rocker arm by the low speed cam and the medium and high speed rocker arm by the medium and high speed cam are selected by rotation of the rocker shaft. At the time of selection from the low speed cam to the medium and high speed cam, a turning motion of the medium and high speed rocker arm based on a turning motion of the rocker shaft makes an eccentric value in the eccentric large diametral part of a inlet side valve system 20IN set up in the leading direction to a rotational direction of the medium and high speed cam larger than that of the same part of an exhaust side valve system 20EX set up in the trailing direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve operating system for a four-cycle engine that switches the operation of a low speed cam and a medium and high speed cam by rotating a rocker shaft.

[0002]

2. Description of the Related Art A valve operating system for a four-cycle engine is a valve operating system in which a valve lift amount and a valve timing are changed according to the engine speed range so that high output characteristics can be obtained in the entire engine speed range. is there. In such a valve operating device, a low speed cam and a medium and high speed cam are provided adjacent to each other on the cam shaft, the rocker shaft is configured to be rotatable, and an eccentric large diameter portion is provided on the rocker shaft. A high-speed rocker arm is fitted to the eccentric large-diameter portion, a low-speed rocker arm is directly fitted to the rocker shaft, and the rotation of the rocker shaft causes the low-speed cam and the low-speed rocker arm to come into contact with each other, and the medium-high speed cam. The contact of the rocker arm for medium and high speed and the contact of the rocker arm for medium and high speed are selected alternatively, and the operation of the low speed cam and the operation of the medium and high speed cam are switched.

That is, by rotating the rocker shaft by a predetermined angle to rotate the eccentric large-diameter portion,
The cam floor surface of the medium-high speed rocker arm is vertically moved relative to the cam floor surface of the low-speed rocker arm. When the cam floor surface of the medium-high speed rocker arm is moved downward with respect to the cam floor surface of the low-speed rocker arm, the contact between the middle-high speed rocker arm and the middle-high speed cam is released, and the low-speed rocker arm and the low-speed cam And the intake / exhaust valve is driven by this low speed cam. Also, when the cam floor surface of the medium-high speed rocker arm is moved approximately above or at the same position as the cam floor surface of the low-speed rocker arm, the contact between the low-speed rocker arm and the low-speed cam is released, and the medium-high speed rocker arm is released. And the medium / high speed cam come into contact with each other, and the intake / exhaust valve is driven by the medium / high speed cam. By thus selecting the cam by rotating the rocker shaft, it is possible to improve the engine output over a wide rotation speed range.

[0004]

In such a valve train, the relative displacement in the vertical direction between the medium-high speed rocker arm and the low-speed rocker arm is increased by increasing the eccentricity of the eccentric large diameter portion with respect to the rocker shaft. Since the difference between the cam profiles of the low speed cam and the medium and high speed cams can be set to be large, the degree of freedom in setting the valve lift amount and the valve timing can be increased.

However, if the eccentric amount of the eccentric large-diameter portion is set to be large, the turning force of the rocker shaft must be increased, and the actuator for generating the rocker shaft turning force becomes large. Usually, this actuator is arranged in a narrow place such as a cam chain chamber, so that it is difficult to increase the size.

The present invention has been made in consideration of the above circumstances, and the degree of freedom in setting the valve lift amount and the valve timing can be expanded without increasing the size of the actuator that generates the rocker shaft turning force. An object of the present invention is to provide a valve train for a 4-cycle engine.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a valve operating device for driving intake / exhaust valves of a four-cycle engine has a low-speed cam and a medium-high speed cam arranged adjacent to a camshaft, and a rocker shaft. A low speed rocker arm that is directly fitted to the rocker shaft and is operated by the low speed cam, and a middle and high speed rocker arm that is fitted to the eccentric large diameter portion of the rocker shaft and that is operated by the middle and high speed cam. The operation of the low-speed rocker arm by the low-speed cam and the operation of the medium-high-speed rocker arm by the medium-high speed cam are switched by the rotation of the rocker shaft according to the engine speed. The rocker for medium and high speed based on the rotation of the rocker shaft at the time of switching from the cam for low speed to the cam for medium and high speed. The eccentricity in the eccentric large-diameter portion of the valve gear in which the rotation of the boom is arranged in the leading direction with respect to the rotation direction of the medium-speed cam is determined by the rotation of the medium-speed rocker arm. Is set to be larger than the eccentric amount in the eccentric large-diameter portion of the valve gear arranged in the trailing direction with respect to the rotation direction of the.

[0008]

Therefore, according to the valve operating system for a four-cycle engine according to the present invention, the rotation of the rocker shaft for medium and high speed based on the rotation of the rocker shaft is arranged in the leading direction with respect to the rotation direction of the cam for medium and high speed. The eccentric amount of the eccentric large diameter portion of the valve operating device is set to be larger than the eccentric amount of the eccentric large diameter portion of the valve operating device arranged in the trailing direction. In the valve device, the relative displacement amount between the medium-high speed rocker arm and the low-speed rocker arm can be increased without increasing the size of the actuator that generates the camshaft turning force and increasing the rocker shaft rotation required torque. As a result, it is possible to set a large difference between the cam profiles of the medium- and high-speed cams and the low-speed cams in the valve gears arranged in the leading direction, and increase the difference in the valve lift amount determined by the cam profiles of these cams. Therefore, the degree of freedom in setting the valve lift amount and the valve timing can be expanded.

[0009]

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

FIG. 1 and FIG. 2 are cross-sectional views showing operating states in a low engine speed range and an engine high engine speed range, respectively, in an embodiment of a valve operating system for a four-cycle engine according to the present invention. FIG. 3 is an overall side view showing a 4-cycle engine to which the valve operating system of FIGS. 1 and 2 is applied.

As shown in FIG. 3, the engine unit 1
Is configured to include a crankcase 2 and a cylinder 3 which stands upright on the crankcase 2 and extends in the vehicle width direction. The cylinder 3 is configured by sequentially combining a cylinder block 4, a cylinder head 5, and a head cover 6 from below.
One or more cylinders (not shown) are formed in the cylinder. In this embodiment, in-line four cylinders are formed in the cylinder block 4.

A combustion chamber 7 (FIGS. 1 and 2) is formed in each cylinder of the cylinder head 5, and two intake ports 8 and two exhaust ports 9 are opened in each combustion chamber 7. Further, in the cylinder head 5, an intake passage 10 and an exhaust passage 11 which are respectively connected to the intake port 8 and the exhaust port 9 are formed for each combustion chamber 7. In the intake passage 10 and the exhaust passage 11, the intake port 8,
Partition walls 12 and 13 are formed near the exhaust port 9, respectively.

At the upstream ends of the four intake passages 10 formed in the cylinder head 5, an intake pipe 14 shown in FIG.
The carburetor 15 and the air cleaner 16 are sequentially connected, and these 15 and 16 introduce the air-fuel mixture into the combustion chamber 7 through the intake passage 10.

Exhaust pipes 17 shown in FIG. 3 are connected to the downstream ends of the four exhaust passages formed in the cylinder head 5, respectively. Each exhaust pipe 17 is connected to the engine unit 1
Of the engine unit 1
After being connected to the collecting pipe 18 under the
Divide into and open to the rear.

By the way, as shown in FIG. 1 and FIG.
The intake boat 8 and the exhaust port 9 are opened and closed by an intake valve 21 and an exhaust valve 22, respectively. The intake valve 21 and the exhaust valve 22 are slidably inserted into a valve guide 23 provided on the cylinder head 5, and are constantly urged upward by a valve spring 24. These intake valve 21 and exhaust valve 22 are respectively driven by the intake side valve operating device 20IN and the exhaust side valve operating device 20EX which are also shown in FIG.

These valve operating devices 20IN and 20EX are
A camshaft 30, which is rotatably supported between a camshaft journal portion 25 of the cylinder head 5 and a camshaft journal housing (not shown), and includes a low speed cam 27 and medium and high speed cams 28 and 29, and a cylinder. A rocker shaft 31 rotatably fitted into the lower portion of the camshaft journal portion 25 of the head 5 to form an eccentric large-diameter portion, a low-speed rocker arm 32 directly fitted into the rocker shaft 31, and a rocker shaft. 31. Medium and high speed rocker arms 33 and 34 fitted on both sides of the low speed rocker arm 32 in the eccentric large diameter portion at 31 and a hydraulic cylinder 35 as a rocker shaft rotation drive actuator for rotating the rocker shaft 31. Is configured.

Two cam shafts 30 are arranged in front of and behind the vehicle of the cylinder head 5, a total of two cam shafts 30 extending in the vehicle width direction. The front cam shaft 30 is for driving the exhaust valve 22, and the rear cam shaft 30 is for driving. Is for driving the intake valve 21. Each cam shaft 30 is formed with one set of cam units in which medium speed cams 28 and 29 are arranged on both sides of the low speed cam 27 by the number of cylinders (that is, the number of combustion chambers 7). In this embodiment, four sets are formed. Each cam shaft 30 is rotated in the direction of arrow A in FIGS. 1 and 2 by a crank shaft (not shown) housed in the crank case 2 of the engine unit 1 via a cam chain (not shown).

The medium speed cams 28 and 29 are formed in the same cam profile. The low speed cam 27 has a cam profile different from the cam profiles of the middle and high speed cams 28 and 29. In other words, the cam profile for the low speed cam 27 is formed so that a suitable valve lift amount and valve lift timing can be obtained when the engine is operating in the low speed range.
The middle and high speed cams 28 and 29 are
The cam profile is formed so that an appropriate valve lift amount and valve lift timing can be obtained when operating in a high speed range.

A total of four rocker shafts 31 are arranged on the front and rear sides of the cylinder head 5 in the vehicle width direction, one on the left and right sides in the vehicle width direction. The rocker shafts 31 extend immediately below the camshaft 30 in the same direction as the camshaft 30. It is provided in place. Two sets of low speed rocker arms 32 and medium and high speed rocker arms 33 and 34 are installed on one rocker shaft 31. The positions of the low speed rocker arm 32 and the medium and high speed rocker arms 33 and 34 of each set are regulated together with the rocker shaft 31 by a positioning spring (not shown) interposed in the rocker shaft 31.

As shown in FIGS. 4 and 5, the tip end of the low speed rocker arm 32 is branched into two, and both branch tip ends 32b are brought into contact with the intake valve 21 or the exhaust valve 22 through a shim 37. It Further, the support portion 32a of the low speed rocker arm 32 is directly fitted into the rocker shaft 31, and the low speed rocker arm 32 has a cam floor surface 32c formed between the branch tip portion 32b and the support portion 32a.

Support part 33a of rocker arm 33 for medium and high speed
Is an eccentric bush 38 having a diameter larger than that of the rocker shaft 31.
It is rotatably fitted in the rocker shaft 31 via. As shown in FIGS. 1 and 2, the eccentric bush 38 is detachably fixed to the rocker shaft 31 by a positioning fixing pin 40 and functions as an eccentric large-diameter portion of the rocker shaft 31.

As shown in FIG. 5, the support portion 34a of the medium-high speed rocker arm 34 is also rotatably fitted to the rocker shaft 31 via an eccentric bush 39 having the same shape as the eccentric bush 38. The eccentric bush 39 is also detachably fixed to the rocker shaft 31 by the positioning fixing pin 40 (FIGS. 1 and 2) and functions as an eccentric large diameter portion.

The lower surfaces of the tip portions 33b, 34b of the medium- and high-speed rocker arms 33, 34 are provided on one side or the other side of the branch tip portion 32b of the low-speed rocker arm 32, respectively.
The shims 41 are brought into contact with each other. Medium and high speed cam 3
The cam floor surfaces 33c and 34c are provided between the tip portions 33b and 34b and the support portions 33a and 34a, respectively.
Is formed. The contact point between the branch tip portion 32b of the low speed rocker arm 32 and the tip portions 33b and 34b of the medium and high speed rocker arms 33 and 34 is the intake valve 21.
Alternatively, it is set substantially on the axis of the exhaust valve 22.

Therefore, as shown in FIG. 1, the low speed cam 27 is arranged on the cam floor surface 32c of the low speed rocker arm 32.
Is pressed down to lower the respective branch tip portions 32b, and when the low speed cam 27 is operated, the middle and high speed rocker arm 33 is operated.
The respective tip portions 33b and 34b of and 34 follow the branch tip portion 32b by gravity and descend. On the other hand, as shown in FIG. 2, when the middle and high speed cams 28 and 29 are actuated by pushing down the cam floor surfaces 33c and 34c of the middle and high speed rocker arms 33 and 34, respectively. Rocker arm 3
Since the tip ends 33b and 34b of 3 and 34 push down the respective branch tip portions 32b of the low speed rocker arm 32, the branch tip portions 32b are forcibly lowered.

The hydraulic cylinder 35 shown in FIG. 4 is installed in a cam chain chamber (not shown) in the cylinder head 5. The same number of pistons (not shown) as the rocker shaft 31 are housed in the hydraulic cylinder 35, and the rack 43 is connected to each piston. These racks 43
Is engaged with a pinion 44 formed at one end of the rocker shaft 31. Further, the hydraulic cylinder 35 is provided with a low-speed hydraulic port 45 and a medium-high speed hydraulic port 46, respectively, and the hydraulic pressure from the engine is selectively guided to the respective ports 45, 46, so that each piston, that is, the rack 43. Reciprocates.

When the engine speed is in the low speed range, hydraulic pressure is supplied to the low speed hydraulic port 45 and the rack 4 is driven.
3 is pulled back, the pinion 44 is rotated in the direction of arrow M (FIG. 4), and the eccentric bushes 38 and 39 have their thickened top portions 38a and 39a positioned at the center in the front-rear direction of the engine, as shown in FIG. To rotate. As a result, the cam floor surface 33 of the rocker arms 33 and 34 for medium and high speed
c and 34c move downward relative to the cam floor surface 33c of the low speed rocker arm 33, and the middle and high speed cam 2
Gaps are formed between the peripheral surfaces of 8 and 29 and the cam floor surfaces 33c and 34c of the rocker arms 33 and 34 for medium and high speeds. As a result, the middle and high speed cams 4 and 5 idle, and only the low speed cam 27 abuts on the cam floor surface 32c of the low speed rocker arm 32 and rotates. Therefore, the intake valve 21 and the exhaust valve 22 are operated by the low speed cam 27 and the low speed rocker arm 32 so that the intake port 8 and the exhaust port 9 have the valve lift timing and the valve lift amount suitable for the low engine speed range. Open and close each.

When the engine speed is in the medium-high speed range, hydraulic pressure is supplied to the medium-high speed hydraulic port 46 (FIG. 4), the rack 43 is pushed out, and the pinion 44 is in the direction of arrow N (FIG. 4). 1, the eccentric bushings 38 and 39 have their thickened top portions 38a and 39a positioned outward in the front-rear direction of the engine as shown in FIG.
Is rotated in the direction of arrow B. As a result, the cam floor surfaces 33c and 34 of the medium and high speed rocker arms 33 and 34 are
c moves relatively upward or to the same position relative to the cam floor surface 32c of the low speed rocker arm 32, and these cam floor surfaces 33c and 34c are respectively used for the middle and high speed cams 2
Abut the peripheral surfaces of 8 and 29. Here, since the cam lift amounts of the middle and high speed cams 28 and 29 are formed to be larger than that of the low speed cam 27, the low speed cam 2 in the above state.
7 idles, while the middle and high speed cams 28 and 29 are the cam floor surfaces 33c of the middle and high speed rocker arms 33 and 34.
And 34c, respectively, and rotate. As a result,
The intake valve 21 and the exhaust valve 22 are operated by the middle and high speed cams 28 and 29 and the medium and high speed rocker arms 33 and 34, so that the intake port 8 and the intake port 8 have a valve lift timing and a valve lift amount suitable for the middle and high engine speed range of the engine. The exhaust ports 9 are opened and closed respectively.

The eccentric bushes 38 and 39 mounted on the intake side valve operating device 20IN are connected to the exhaust side valve operating device 20.
The eccentric amount is set to be larger than that of the eccentric bushes 38 and 39 mounted on the EX. That is, FIG. 1 and FIG.
As shown in FIG. 6, when the center of the rocker shaft 31 is O, the axial centers QI of the eccentric bushes 38 and 39 mounted on the intake valve operating device 20IN are relative to the center O of the rocker shaft 31 as shown in FIG.

[Outer 1] The eccentric bushes 38 and 39 mounted on the exhaust side valve operating device 20EX are eccentric only, and the axis QE is the rocker shaft 3.
For center O of 1

[Outside 2] Only eccentricity is set so that eI> eE.

The eccentricity eI of the eccentric bushes 38 and 39 in the intake side valve operating device 20IN can be set to a large value by rotating the rocker shaft 31 in the direction of arrow B in FIG. When switching the operation of the cams to the operations of the high speed cams 28 and 29, the middle and high speed rocker arms 33 and 34 are used in the leading direction with respect to the rotation of the middle and high speed cams 38 and 39 in the direction of the arrow A. Between the high speed cam 28 and the cam floor surface 33C of the medium and high speed rocker arm 33, and between the middle high speed cam 29 and the cam floor surface 34C of the medium and high speed rocker arm 34.
The frictional force generated between the rocker arms 33 and 34 causes a self-servo, and this frictional force is generated.
This is because it acts to promote the rotation of the rocker shaft 31 in the B direction, and as a result, the rotation required torque of the rocker shaft 31 becomes smaller.

On the other hand, in the exhaust side valve operating apparatus 20EX, the rocker shaft 31 is rotated in the direction of arrow B to switch the operation of the low speed cam 27 to the operation of the middle and high speed cams 28 and 29. At this time, since the middle and high speed rocker arms 33 and 34 are used in the trailing direction with respect to the rotation of the middle and high speed cams 28 and 29 in the direction of arrow A, the middle and high speed cams 28 and the cam floor surface 33C of the middle and high speed rocker arms 33C. And between the middle-high speed cam 29 and the cam floor surface 34C of the middle-high speed rocker arm 34 are frictional forces generated respectively.
And 34 act to hinder the rotation of the rocker shaft 31 in the direction of the arrow B, and as a result, the rotation request torque of the rocker shaft 31 becomes excessive.

For example, as shown in FIG. 7, in the exhaust side valve gear 20EX in which the medium and high speed rocker arms 33 and 34 are used in the trailing direction, the eccentricity eE of the eccentric bushes 38 and 39 is set to a value of 1.3. When set to, the required rotation torque of the rocker shaft 31 becomes the value of T2 as shown by the solid line TE, and when the eccentricity eE is set to a value of 1.5 to 1.7, the required rotation torque of the rocker shaft 31 becomes T3
And becomes too large. On the other hand, in the intake side valve operating device 20IN in which the medium and high speed rocker arms 33 and 34 are used in the leading direction, the eccentric bushes 38 and 3 are used.
When the eccentricity eI of 9 is set to a value of 1.3, the required torque for rotation of the rocker shaft 31 is T1 as shown by the solid line TI.
Therefore, even if the eccentricity eI is increased and set to a value of 1.5 to 1.7, the required rotation torque of the rocker shaft 31 is T2.
Thus, the eccentric bush 38 is used in the exhaust side valve operating device 20EX.
And the eccentricity eE of 39 are substantially the same as the case of 1.3.

Here, the turning force (rotation required torque) of the rocker shaft 31 is generated by the hydraulic cylinder 35 even if it is the exhaust side valve operating device 20EX, the intake side valve operating device 20IN.
However, since the same value can be generated, the eccentricity eE of the eccentric bushes 38 and 39 is increased in the exhaust side valve operating device 20EX.
Is set to about 1.3 and the required rotation torque of the rocker shaft 31 is set to T2. In the intake side valve operating device 20IN, the eccentric bushes 38 and 39 are eccentric until the required rotation torque of the rocker shaft 31 reaches T2. Increase the amount eI, eI
= 1.5 to 1.7 is set.

Generally, when the eccentricity amounts eE and eI of the eccentric bushes 38 and 39 are set large, the relative displacement amount K by which the medium and high speed rocker arms 33 and 34 are displaced in the vertical direction in FIG. 6 with respect to the low speed rocker arms 32 is increased. it can. In FIG. 6, the positions of the medium and high speed rocker arms 33 and 34 for the middle and high engine speed range are shown by solid lines, and the positions of the medium and high speed rocker arms 33 and 34 for the low engine speed range are shown by two-dot chain lines. By increasing the relative displacement amount K, the difference H in the cam profile between the low speed cam 27 and the medium and high speed cams 28 and 29 can be set large, and as a result, the valve lift amount determined by the low speed cam 27 and the medium The difference from the valve lift amount determined by the high speed cams 28 and 29 can be enlarged. Therefore, the degree of freedom in setting the valve lift amount and the valve timing can be increased, and the valve lift amount and the valve timing can be set to optimum values for the engine speed.

In this embodiment, as shown in FIG. 8, the valve lift curve determined by the medium- and high-speed cams 28 and 29 of the intake side valve operating device 20IN and the exhaust side valve operating device 20EX is Sa (the valve lift amount). La) is a valve lift curve determined by the low speed cam 27 of the exhaust side valve operating device 20EX, and Sb (valve lift amount Lb) is a valve lift curve determined by the low speed cam 27 of the intake side valve operating device 20IN. Are set to Sc (valve lift amount Lc), respectively. In other words, in this embodiment, in the exhaust side valve operating apparatus 20EX, the difference between the valve lift amount La determined by the medium and high speed cams 28 and 29 and the valve lift amount Lb determined by the low speed cam 27 is h.
On the other hand, in the intake side valve operating apparatus 20IN, the difference between the valve lift amount La determined by the middle and high speed cams 28 and 29 and the valve lift amount Lc determined by the low speed cam 27 is hI. Is set. Where h
I> hE.

As described above, in the intake side valve operating apparatus 20IN, the difference hI between the valve lift amounts Lc and La determined by the low speed cam 27 and the medium and high speed cams 28 and 29 can be increased, so that the valve lift amount is increased. Also, the degree of freedom in setting the valve timing is expanded, and the valve lift curves Sc and Sa can be set to the optimum values for the engine speed.

According to the above embodiment, in the intake side valve operating apparatus 20IN in which the medium and high speed rocker arms 33 and 34 are used in the leading direction with respect to the rotation direction A of the medium and high speed cams 28 and 29, the eccentric bushes 38 and 39 are provided. Since the eccentricity eI is set to be larger than the eccentricity eE of the eccentric bushes 38 and 39 in the exhaust side valve operating device 20EX in which the medium and high speed rocker arms 33 and 34 are used in the trailing direction, the intake side valve operating device 20IN In the above, the relative displacement amount K of the medium and high speed rocker arms 33 and 34 with respect to the low speed rocker arm 32 can be increased. As a result, the low speed cam 27 and the medium and high speed cams 28 and 29 are provided.
The difference h between the cam profile of the valve lift and the cam profile can be increased to increase the difference hI between the valve lift amount La determined by the middle and high speed cams 28 and 29 and the valve lift amount Lc determined by the low speed cam 27. The degree of freedom in setting the volume and valve timing can be expanded.

Further, medium and high speed rocker arms 33 and 3
4 is used on the leading side for intake side valve device 20I
At N, the eccentricity eI of the eccentric bushings 38 and 39 is 1.
Since the large value of 5 to 1.7 is set, the torque required to rotate the rocker shaft 31 in the intake side valve operating device 20IN becomes T2, without increasing the size of the hydraulic cylinder 35. The ability of 35 can be exerted almost completely.

[0038]

As described above, according to the valve operating system for a four-cycle engine according to the present invention, when the low speed cam is switched to the medium and high speed cam, the rocker arm for medium and high speed is rotated based on the rotation of the rocker shaft. Of the eccentric large-diameter portion of the valve gear arranged in the leading direction with respect to the rotation direction of the medium-high speed cam, and the rotation of the medium-high speed rocker arm is the rotation direction of the medium-high speed cam. However, since the eccentric amount in the eccentric large-diameter portion of the valve gear arranged in the trailing direction is set to be larger than that in the trailing direction, the rocker shaft is arranged in the leading direction without increasing the size of the actuator that generates the turning force. In this valve operating device, the degree of freedom in setting the valve lift amount and the valve timing can be expanded.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an operating state in a low engine speed region of an embodiment of a valve operating system for a 4-cycle engine according to the present invention.

FIG. 2 is a cross-sectional view showing an operating state in an engine middle high rotation speed range in the above embodiment.

FIG. 3 is an overall side view showing a 4-cycle engine to which the valve operating system of FIGS. 1 and 2 is applied.

FIG. 4 is a perspective view of the valve gear shown in FIGS. 1 and 2.

5 is a plan view showing a part of the valve gear of FIG. 4 by cutting away.

6 is an enlarged view showing a part of the valve gear of FIG.

FIG. 7 is a graph showing the relationship between the rocker shaft rotation required torque and the eccentric amount of the eccentric bush when the cam is switched from the low speed cam to the medium high speed cam.

8 is a graph showing a valve lift curve of the valve train in FIGS. 1 and 2. FIG.

[Explanation of symbols]

 20IN intake side valve operating device 20EX exhaust side valve operating device 21 intake valve 22 exhaust valve 27 low speed cam 28,29 medium and high speed cam 30 camshaft 31 rocker shaft 32 low speed rocker arm 33,34 medium and high speed rocker arm 38,39 eccentric Bushing eI Eccentricity of eccentric bush in intake side valve operating device eE Eccentricity of eccentric bushing in exhaust side valve operating device

Claims (1)

[Claims] 1. A low-speed cam and a medium-high speed cam which are arranged adjacent to a cam shaft, and a low-speed cam and a high-speed cam which are arranged adjacent to a cam shaft, and a low speed cam which is directly fitted to a rocker shaft. A low-speed rocker arm operated by a low-speed cam, and a medium-high speed rocker arm fitted to an eccentric large-diameter portion of the rocker shaft and operated by the medium-high speed cam. The operation of the low-speed rocker arm and the operation of the medium-high speed rocker arm by the medium-high speed cam are configured to be switched by the rotation of the rocker shaft in accordance with the number of revolutions of the engine. The rotation of the rocker arm for medium and high speeds based on the rotation of the rocker shaft causes the rotation of the rocker arm for medium and high speeds at the time of switching from the cam for operation to the cam for medium and high speeds. The eccentricity of the eccentric large-diameter portion of the valve operating device arranged in the leading direction with respect to the rotation direction of the cam is determined by the rotation of the middle-high speed rocker arm in the trailing direction with respect to the rotation direction of the middle-high speed cam. The eccentric amount in the eccentric large-diameter portion of the operated valve gear is set to be larger than the eccentric amount.
Cycle engine valve system.