JP2769922B2 - Cam mechanism in valve drive of portable work machine engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a cam mechanism in a valve drive device of a portable working machine engine.

(Prior art) Portable engine driven working machines such as brush cutters and trimmers
As shown in FIG. 13, it is common to mount an engine 72 on one side and a work equipment 73 on the other end, facing the gripping portion 71 on the power transmission shaft 70. Although the power transmission shaft is not shown in detail in FIG. 13, a steel cable or a steel rod is rotatably held in a pipe through a clutch connected to an engine crankshaft to transmit work equipment such as a mowing blade. Is what you do. As for the holding posture of the working machine, as shown in FIG. 13, the worker 74 is generally located on the left side of the working machine when viewing the working machine from the engine side. In this case, in order to prevent the operator from being burned by the high-temperature exhaust gas of the engine, it is general to provide the exhaust muffler 75 on the side farther than the operator 74 and the intake port 76 of the carburetor on the side closer to the operator. . The engine used is mainly a two-stroke engine which is lightweight and has the above-mentioned geometrical arrangement. However, it is also necessary to install a four-cycle engine to reduce noise and purify exhaust gas. In this case, the size of the engine becomes large, which impairs the lightweight and compactness required of the portable work machine, which is a great obstacle to practical use. Hereinafter, the problems will be described with reference to practical examples.

That is, FIGS. 8 and 9 show an example of a conventional four-stroke engine, in which the cam gear 12d meshing with the crank gear 31d rotates in the opposite direction when the crank gear 31d fixed to the crank shaft 32d rotates, The intake cam 111d and the exhaust cam 112 linked to the rotation shaft of the cam gear 12d actuate the intake valve 52d and the exhaust valve 51d, while one end of the crankshaft 32d is connected to a power transmission line via a flywheel and a clutch. It conveys power.

At this time, if the intake cam 111d and the exhaust cam 112d are formed on one shaft, a mushroom tappet is normally used, so the arrangement of the push rods 41d and 42d is required in the axial direction of the crankshaft due to the umbrella part. Is required, and as a result, the dimension between the crankshaft and the flywheel is increased.

In particular, in the case of an engine for driving a portable work machine, it is necessary to reduce the length between the crankshaft and the flywheel as much as possible to reduce the size and weight of the engine and the work machine. In the structure of the valve drive device described above, there is a limit in reducing the length between the crankshaft and the flywheel.

According to another embodiment as shown in FIG. 14, in this embodiment, the cam shaft 81 is arranged on the side of the crankshaft 80, but the direction perpendicular to the power shaft increases. When the weight balance with respect to the power shaft is lost, the requirements for a portable work machine cannot be satisfied.

Further, in the cam mechanism in the conventional valve driving device as shown in FIG. 10, the cam shape is made symmetrical on the rising side and the falling side of the tappet, and the lift speed curve is as shown in FIG. It appears symmetrically about the point of, especially in the engine that drives a portable work machine, it is necessary to increase the rotation speed of the crankshaft and increase the output per weight. , For this,
For the exhaust valve, it is necessary to reduce the valve opening speed to effectively utilize the pressure of the combustion gas near the bottom dead center of the piston, and to increase the valve closing speed and increase the inertial effect when the intake valve is opened. And
The intake valve needs to increase the valve opening speed of the intake valve to effectively use the inertia effect of the exhaust valve closing circuit, and to reduce the valve closing speed to prevent the gas from returning. However, as a means for achieving this, it is necessary to separate the cams for driving the intake and exhaust valves and to form them separately, resulting in high costs.

Also, in the case of a four-stroke engine, there has been a strong demand for measures to prevent the above-mentioned workers from being burned.

(Problems to be Solved by the Invention) Accordingly, the present invention can reduce the length between the crankshaft and the flywheel in order to obtain a drive engine for a portable work machine having a small volume and a small weight. Furthermore, a valve drive device for a portable working machine engine in which the combination of the valve drive device and the intake / exhaust position is arranged at a position where the operator does not get burned, was developed. To develop a cam mechanism for a valve drive device of a portable working machine engine that can make the valve opening speeds of valves and exhaust valves different for the purpose and increase the output per weight. It is the purpose.

(Means for Solving the Problems) That is, the present invention relates to a cam mechanism in a valve drive device of an engine for a portable working machine, wherein an engine drive in which a working device is mounted on a power transmission unit connected to a crankshaft of the engine. A swing rotary lifter that abuts a cam on a work machine and swings on an axis parallel to the crankshaft in a plane including the crankshaft and the cylinder center line is operated by rotating the cam. Then, in the valve drive mechanism provided to open and close both the intake and exhaust valves by opening the exhaust valve and then opening the intake valve, the cam shapes on the push rod rising side and the descending side with respect to the maximum lift point are almost The intake and exhaust valves are opened and closed by a cam having a symmetrical shape and a pair of swing rotary lifters swinging about an axis parallel to the rotation axis of the cam and having a planar contact portion with the cam. I've done it By doing so, the above object is to be achieved.

In particular, in the swing rotary type lifter in the cam mechanism, the contact portion with the cam generally has a curved surface as shown in FIG. The contact part with the cam in the rotary lifter is
It is characterized by being planar.

(Operation) In the present invention constituted by the above means, the cam is rotated by rotating a crank gear or the like meshing with the gear portion of the cam, and one of a pair of swing rotary lifters abutting on the cam is rotated. Then, the exhaust valve is opened via the exhaust valve push rod. Next, when the cam is further rotated, the other swinging rotary lifter abutting on the cam is rotated, the intake valve is opened via the intake valve push rod, and the exhaust valve is closed at a predetermined time. The operation of the valve is completed by closing the intake valve. As a result, since the swing rotary type lifter is rotated by one cam, the length of the cam in the axial direction is reduced, and the weight can be reduced because only one cam is required.

At this time, in the valve driving device, a cam having a cam shape on the push rod ascending side and descending side with respect to the maximum lift point having a substantially symmetrical shape, and a pair of rockers swinging around an axis parallel to the rotation axis of the cam. When the cam mechanism using the swing rotary type is used, the following operation is performed, and the lift curves of the exhaust valve and the intake valve can be made different.

That is, in FIG. 7 (a), A is the rotation center of the cam 11, B is the rotation center of the swing rotary lifter 21, α is the rotation angle of the swing rotary lifter 21, and the rotation of the swing rotary lifter 21 is α. When the distance between the center B and the exhaust valve push rod 41 is L, the lift of the push rod 41 is Lα. R is cam
The base circle radius at 11, the X axis is the coordinate axis fixed to the cam 11,
θ indicates that the contact surface between the cam 11 and the swing rotary lifter 21 is the cam 11
Is the relative angle with the X-axis when moving on the contour of. In this case, θ is not the same as the rotation angle of the cam 11,
Is Φ. Swing rotary lifter 21 and cam 11
And P and Q are the contact points with. y is an amount derived by subtracting the base radius R of the cam 11 from the distance from the rotation center A of the cam 11 to the contact point Q, and is a function of θ. a is a contact point P between the oscillating rotary lifter 21 and the cam 11,
An amount indicating the distance between a line passing through Q and a line parallel to the line and passing through the rotation center B of the oscillating rotary lifter 21, and is a constant determined by the design of the oscillating rotary lifter 21.

Here, the distance between the contact points P and Q between the oscillating rotary lifter 21 and the cam 11 is dy / dθ according to the formula of mechanics, and the contact surface between the oscillating rotary lifter 21 and the cam 11 is Assuming that the rotation angle at the time of contact with the base circle is α ₀ and the distance between the rotation center B of the swing rotary lifter 21 and the rotation center A of the cam 11 is C, Csin (α + α ₀ ) = (R + y + a) α + α ₀ = sin ^-1 [(R + y + a) / C] Φ = θ + α dα / dΦ = (dy / dθ) / [dy / dθ + Ccos (α + α ₀ )] The lift speed of the push rod 41 is Ldα / dΦ, and dy Even when the absolute value of / dθ is the same, the lift speed of the push rod 41 is lower when the push rod 41 is raised than when it is lowered. The reason is that the value of dy / dθ is positive on an ascending road, and negative on a descending route. Therefore, in the case of a cam in which the cam shape is made symmetrical on the ascending side and the descending side of the push rod, the ascending speed is lower for the exhaust valve push rod as shown in FIG. Characteristics that are slower and superior to conventional engines are obtained.

Further, a push rod for an intake valve shown in FIG.
For 42, the rotational direction is relatively opposite to that in FIG. 7 (a), so that Csin (β + β ₀ ) = (R + y + a) β + β ₀ = sin ^-1 [(R + y + a) mC] Φ = θ −β Therefore, dβ / dΦ = (dy / dθ) / [− dy / dθ + Ccos (β + β ₀ )] Therefore, even if the value of dy / dθ is the same, the push rod 42
The lift speed of the push rod 42 becomes faster when the push rod 42 rises. In other words, in the case of a cam in which the cam shapes on the ascending side and the descending side of the push rod are made symmetrically,
As for the push rod for the intake valve, the speed at the time of ascending becomes higher than the speed at the time of the descending as shown in FIG. 12 (b), and characteristics superior to those of the conventional engine can be obtained.

According to various experiments, as a portable working machine engine, the ratio of the speed of the push rod at the time of the rise to the speed at the time of the rise of the push rod is 120% to 170% on the exhaust side, and 83% to 58% on the intake side. % Is appropriate.

(Example) To further clarify the gist of the present invention, an example will be described with reference to the drawings.

As shown in FIG. 1, the valve driving device E of the engine for a portable working machine includes one cam 11 and a pair of swinging rotary lifters 21 and 22 abutting on the cam 11, and the pair of swinging lifters 21 and 22. Both the dynamic rotary lifters 21 and 22 are configured to rotate about the lifter shaft 23. The gear portion 12 of the cam is formed so as to mesh with a crank gear 31 of the crank 3. One swing rotary lifter 21 is connected to an exhaust valve push rod 41 and the other swing rotary lifter 22. Is connected to the intake valve push rod 42. The pair of swing rotary lifters 21 and 22 are arranged such that when viewed from above, the two swing rotary lifters 21 and 22 are bent from the lifter shaft to the center as shown in FIG. The exhaust valve push rod 41 and the intake valve push rod 42 are disposed so as to be on the same plane.

The state of use of the valve driving device of the portable work machine engine will be described. The cam gear meshing with the crank gear 31 by rotating the crankshaft 32 of the crank 3 from the engine in the clockwise direction when the power is taken out from the engine. By rotating the portion 12, the cam 11 is rotated, and one of the pair of swing rotary lifters 21 and 22 abutting on the cam 11 is rotated, and the exhaust valve is opened via the exhaust valve push rod 41. Let Next, when the cam 11 is further rotated, the other swingable rotary lifter 22 that contacts the cam 11 is rotated, and the intake valve is opened via the intake valve push rod 42, and at a predetermined time. The operation of the valve is completed by closing the exhaust valve and closing the intake valve. As a result, the swing rotary lifters 21 and 22 are rotated by one cam 11, so that the length of the cam in the axial direction is reduced, and only one cam is required, so that the weight is reduced.

In the case of this embodiment, the intake valve opening timing before piston top dead center 20 ° crank rotation angle 20 ° intake valve closing timing after piston bottom dead center crank rotation angle 60 ° exhaust valve opening timing before piston bottom dead center crank rotation angle 60 ° exhaust Valve closing timing This is performed when the crank rotation angle is 20 degrees after the piston top dead center, and a pair of swing rotary lifters 21 and 22 and a cam
The angle formed by the contact surface with 11 is (180 + A + B) / 2 (degrees)
(A: angle of exhaust valve opening 60 degrees before bottom dead center, B: angle of intake valve opening 20 degrees before top dead center) In the case of this embodiment, (180 + 60−20) / 2 = 110 degrees.

When the valve drive device E shown in the above embodiment is used in an engine for a portable work machine, the state becomes as shown in FIG. 3, and by rotating the crankshaft 32, the exhaust valve 51 and the intake valve 52 are provided at predetermined times.
And the engine is operated to transmit the power to the work equipment on the right side in the figure. In this case, when the valve drive device E is at the position of the work machine drive side of the engine, and when the work equipment side is viewed from the engine side, the exhaust valve 51 is located on the right hand, the intake valve 52 is located on the left hand, and the crankshaft 32 Is rotated in the clockwise direction, and the camshaft 13 is formed so as to rotate in the counterclockwise direction. When the portable work machine engine is held in hand, the exhaust side does not come to the front side, and burns. Nothing.

Further, according to the present embodiment, the cam having a substantially symmetrical cam shape on the push rod ascending side and descending side with respect to the maximum lift point, and swings around an axis parallel to the rotation axis of the cam. Since the cam mechanism is constituted by a pair of swinging rotary lifters, based on the above operation, the lift curves of the exhaust valve and the intake valve are made different, the opening speed of the exhaust valve is reduced, and the closing speed of the exhaust valve is increased. The valve opening speed of the intake valve can be increased and the valve closing speed can be decreased, the rotation speed of the crankshaft of the engine driving the portable work machine can be increased, and the output per weight can be increased.

Next, a second embodiment will be described. As shown in FIGS. 4 and 5, the valve driving device F of the engine for a portable work machine has a simple configuration in which the swing rotary lifters 21 and 22 have a simple shape as compared with the first embodiment. And the contact surfaces of the pair of swing rotary lifters are slightly shifted in the cam direction. With this configuration, the cam manufacturing cost can be reduced.

Next, a third embodiment will be described. As shown in FIG. 6, the valve drive device G of the engine for a portable work machine is a case in which two shafts supporting the swing rotary type lifters 21 and 22 are provided, whereby the lifter shaft portions 231 and 232 are provided. However, as in the first embodiment, the swing rotary type lifter 21,
The push rods 41 and 42 for both intake and exhaust valves can be arranged on the same line in a plane perpendicular to the camshaft without bending the inward 22 inward, and the length of the engine crankshaft in the axial direction can be reduced. Can be shortened.

The present invention is not limited to the present embodiment, and can be arbitrarily changed within a range in which the above-described objects and effects of the present invention described above and effects of the invention described later are achieved. It goes without saying that the gist of the present invention is not changed.

(Effects of the Invention) As described in detail above, the present invention, a valve drive device for a portable working machine engine, includes a drive working machine that mounts working equipment on a power transmission unit connected to a crankshaft of an engine. A pair of oscillating rotary lifters which abut on the cam, oscillate on a plane parallel to the crankshaft and in a plane including the crankshaft and the cylinder centerline, are operated by rotating the cam, and an exhaust valve is provided. And then a valve drive mechanism that opens and closes both the intake and exhaust valves by opening the intake valve, so that the tappet arrangement does not require a predetermined length in the axial direction of the crankshaft as in the prior art, Therefore, the dimension in the axial direction can be reduced. Further, since one cam is formed, the manufacturing cost of the cam is reduced, and the manufacturing cost can be reduced.

Further, in the valve drive mechanism, a cam having a substantially symmetrical cam shape on the push rod ascending side and descending side with respect to the maximum lift point, and a pair of rockers swinging around an axis parallel to the rotation axis of the cam. When the intake and exhaust valves are opened and closed by the swing rotary lifter, the lift curves of the intake and exhaust valves are made different by a single cam. At the same time, the valve opening speed of the intake valve can be increased and the valve closing speed can be decreased, the rotational speed of the crankshaft of the engine driving the portable work machine can be increased, and the output per weight can be increased. .

[Brief description of the drawings]

Drawings show an embodiment of the present invention, FIG. 1 is a front view showing a valve driving device, FIG. 2 is a plan view showing the valve driving device, and FIG. 3 uses the valve driving device. FIG. 4 is a cross-sectional view of the valve driving device in the second embodiment,
FIG. 5 is a side sectional view showing a main part of the valve drive device of FIG. 4, FIG. 6 is a front view showing the valve drive device of the third embodiment, and FIG. (A) shows the operation of a swing rotary type lifter connected to an exhaust valve push rod, and (b) shows a swing rotary type connected to an intake valve push rod. It shows the operation of the type lifter. FIG. 8 is a front view showing a conventional valve driving device, FIG. 9 is a sectional view showing an engine using the conventional valve driving device, and FIG. 10 shows the operation of a cam mechanism in the conventional valve driving device. FIG. 11 is a graph showing a relationship between a lift and a lift curve with respect to a camshaft rotation angle of a cam mechanism in a conventional valve driving device.
FIG. 12 is a graph showing the relationship between the lift and the lift curve with respect to the camshaft rotation angle in the present invention. (A) shows the exhaust cam mechanism, and (B) shows the intake cam mechanism. , FIG. 13 is an explanatory view showing the use state of a conventional portable engine-driven working machine, FIG. 14 is a cross-sectional view showing an engine using a conventional valve drive device, and FIG. 15 is a conventional swing rotary lifter. FIG. E, F, G… Valve drive device 11… Cam 21, 22… Oscillating rotary lifter 23, 231, 232… Lifter shaft 32… Crank shaft 41… Exhaust valve push rod 42… Push rod for intake valve 51 …… Exhaust valve 52 …… Intake valve

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F01L 1 / 12,1 / 14 A01D 34/76

Claims (1)

(57) [Claims] 1. An engine-driven work machine, in which a work device is mounted on a power transmission portion connected to a crankshaft of an engine, abuts one cam and is located in a plane including a crankshaft and a cylinder center line and is connected to a crankshaft. A swing rotary type lifter swinging on a parallel axis was operated by rotating the cam to open the exhaust valve, and then opened and closed the intake and exhaust valves by opening the intake valve. In the valve drive mechanism, a cam having a substantially symmetrical cam shape on the push rod ascending side and descending side with respect to the maximum lift point, and swinging around an axis parallel to the rotation axis of the cam, A pair of oscillating rotary lifters whose contact parts are flat, the intake valve,
A cam mechanism in a valve drive device of a portable working machine engine, characterized in that the exhaust valve is opened and closed.