JPH04209905A - Valve driving device of engine for portable type working machine and cam mechanism in valve driving device - Google Patents

Abstract

PURPOSE:To reduce an axial size, manufacturing cost of a cam, a weight, and the like by operating a pair of oscillatary rotation type lifters by rotation of one cam, and providing a valve driving mechanism for opening/closing both intake/exhaust valves. CONSTITUTION:A valve driving device E consists of one cam 11 and a pair of oscillatary rotation type lifters 21, 22 abutting on the cam 11, and respective oscillatary rotation type lifters 21, 22 are rotated around a lifter shaft part 23. A gear part 12 meshed with a crank gear 31 is rotated to rotate the cam 11, and one way of each of oscillatary rotation type lifters 21, 22 is rotated so as to open an exhaust valve through an exhaust side push rod 41. On the other hand, the cam 11 is rotated to rotate one way of the oscillatary rotation type lifters 21, 22 so as to open an intake valve through an intake side push rod 42. It is thus possible to shorten the axial length of the cam 11 while make light a weight by rotating both oscillatary rotation type lifters 21, 22 by one cam 11.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention operates two lids with a difference in angle using a single cam, thereby opening and closing first the exhaust valve and then the intake valve. By using a mechanism to reduce the length of the engine in the crankshaft direction, it is possible to
The present invention relates to a valve drive device for a four-stroke engine for a portable working machine that can prevent workers from getting burnt by devising a combination of exhaust valve positions, and further includes:
The lift curves of the exhaust valve and intake valve are different, so that the opening speed of the exhaust valve is reduced and the valve closing speed is increased, while the opening speed of the intake valve is increased and the valve closing speed is reduced. The present invention relates to a cam mechanism in a valve drive device for a die working machine engine.

(Prior art) Portable engine-driven working machines such as brush cutters and trimmers are the first
As shown in FIG. 3, an engine 72 is placed on one end of the holding part 71 on the power transmission shaft part 70, and a work equipment 73 is placed on the other end of the holding part 71.
It is common to wear a Although the power transmission shaft is not shown in detail in Fig. 13, it holds a steel cable or steel rod rotatably within the pipe via a clutch connected to the engine crankshaft, and transmits power to a working device such as a mowing blade. It is something.

As shown in FIG. 13, when the work machine is held from the engine side, the person 74 is generally positioned to the left of the work machine. In this case, in order to prevent the worker from getting burned by the high-temperature exhaust gas from the engine, it is common to provide the exhaust muffler 75 on the side farther from the worker 74 and the intake lower part of the carburetor on the side closer to the worker. . In addition, the engine used is light); and the above-mentioned geometric arrangement is easy.
Cycle engines are mainly used. However, it is also necessary to install a 4-cycle engine to reduce noise and purify exhaust gas. In this case, the size of the engine becomes large, impairing the lightweight and compactness required of a portable working machine, which is a big impediment to practical use. The problems will be explained below using practical examples.

That is, FIGS. 8 and 9 show an example of a conventional 4-stroke machine, in which the crank gear 3 fixed to the crankshaft 32d
1d rotates, the cam gear 12d that meshes with the crank gear 31d rotates in the opposite direction, and the cam gear 12d
Intake cam 111d and exhaust cam 1 connected to the rotating shaft of
12d operates the intake valve 52d and the exhaust valve 51d,
On the other hand, one end of the crankshaft 32d transmits power to a power transmission element via a flywheel and a clutch.

In this case, if the intake cam 111d and the exhaust cam 112d are formed on one shaft, a back-type tappet is normally used, so the tappets 41d and 42d are arranged at the required length in the crankshaft direction due to the umbrella part. This results in an increase in the distance between the crankshaft and the flywheel.

This is especially true for engines that drive portable work equipment, where it is necessary to minimize the length between the crankshaft and flywheel to reduce the size and weight of the engine and work equipment. With the structure of a conventional valve drive device, there is a limit to reducing the length between the crankshaft and the flywheel.

Further, according to another embodiment as shown in FIG. 14, the camshaft 81 is disposed on the side of the crankshaft 8θ, but the direction perpendicular to the power shaft is larger.
Due to the loss of weight balance with respect to the power shaft, the requirements for a portable working machine cannot be met.

Furthermore, in the cam mechanism of a conventional valve drive device as shown in Fig. 1O, the cam shape is made symmetrically on the ascending and descending sides of the tappet, and the lift speed curve reaches the maximum lift as shown in Fig. 11. It appears symmetrically around the point, and in particular for engines that drive portable working machines, it is necessary to increase the crankshaft rotation speed and increase the output per weight. In order to achieve this, the exhaust valve should be opened at a low speed (to effectively utilize the combustion gas pressure close to the bottom dead center of the piston), and the valve should be closed at a high speed to maximize the inertia effect when the intake valve opens. It is necessary to
For the intake valve, it is necessary to increase the intake valve opening speed to effectively utilize the inertia effect when the exhaust valve is closed, and to reduce the valve closing speed to prevent gas from blowing back. However, as a means for this purpose, it is necessary to provide separate cams for driving the intake and exhaust response valves and to have separate shapes, which increases the cost.

Furthermore, in the case of four-cycle engines as well, there has been a strong demand for measures to prevent workers from suffering burns as described above.

(Problems to be Solved by the Invention) Therefore, the present invention is capable of reducing the length between the crankshaft and the flywheel in order to obtain a drive engine for a portable working machine that has a small volume and can be stacked easily. , furthermore,
We have developed a valve drive device for portable work equipment in which the combination of the valve drive mechanism and the intake/exhaust position is located in a position that will not cause burns to the worker. The object of the present invention is to develop a cam mechanism in a valve drive device for a portable working machine, which allows the valve speeds to be purposefully varied.

(Means for Solving the Problems) That is, the present invention provides an engine-driven work equipment in which an engine is mounted on one end of a power transmission shaft and a work equipment is mounted on the other end of the power transmission shaft. A portable work machine equipped with a valve drive mechanism that opens and closes both intake and exhaust valves by operating a swinging rotary lifter that swings above by rotating the cam to open an exhaust valve, and then by opening an intake valve. Further, in the valve drive device for a portable work machine engine, the valve drive mechanism is located at a position opposite to the work machine drive side of the engine, and
When looking from the engine side to the work equipment side, the exhaust valve is on the right.
The above objective is achieved by positioning the intake valve on the left hand, rotating the crankshaft clockwise, and rotating the camshaft counterclockwise.

Furthermore, the push rod rising side with respect to the maximum lift point,
a cam having a substantially symmetrical cam shape on the descending side;
A valve drive device for a portable working machine engine that opens and closes an intake valve and an exhaust valve using a pair of push rod lifters that swing around an axis parallel to the rotation axis of the cam and have a planar contact portion with the cam. By using a cam mechanism as described above, the above purpose is attempted to be achieved. In particular, in the above-mentioned cam mechanism, conventionally the contact portion with the cam is generally curved as shown in FIG. The feature is that the contact portion with the cam that swings around is flat.

(Function) In the present invention configured by the above means, the cam is rotated by rotating a crank gear or the like that meshes with the cam gear of the cam, and one of the pair of swinging rotary lifters that abuts the cam is rotated. Rotate to open the exhaust valve via the exhaust side push rod. Next, when the cam is further rotated, the other swinging rotary lifter in contact with the cam is rotated, opening the intake valve via the intake side push rod, and closing the exhaust valve at a predetermined time. Furthermore, valve actuation is completed by closing the intake valve. As a result, since the columnar rotary lifter is rotated by one cam, the length of the cam in the axial direction can be reduced, and since only a single cam is required, the weight can also be reduced.

At that time, in the valve drive device, a pair of cams having a substantially symmetrical cam shape on the upward and downward sides of the push rod with respect to the Kandai lift point, and a pair of cams that swing around an axis parallel to the axis of rotation of the cam are used. Using a cam mechanism with a bush rod lifter works as follows, making it possible to make the lift curves of the exhaust and intake valves different.

In other words, in Fig. 7 (a), A is the center of the camshaft, B
is the center of rotation of the swinging lifter, and the rotation angle of the swinging lifter is a
, when the distance between the center of rotation of the swing lifter and the push rod is L, the lift of the push rod is Lα. The X-axis is a coordinate axis fixed to the cam, and θ is the relative angle with the X-axis when the contact surface between the cam and the swinging lifter moves on the cam contour. In this case, θ is not the same as the rotation angle of the camshaft (the rotation angle of the camshaft is Φ.Here, the distance between the contact points P and Q with the cam is d y /
dθ, and the value of a when the contact surface touches the base circle is ao
If the distance between the rotation center of the swing lifter and the rotation center of the cam is C, then C3lN(a+cyol= (R+y
+a)a+ao=SIN-'[(R+y
+ at/CIΦ=θ ten (α+a o ) Therefore, d a / dΦ=(dy/dθL/[dy/dθ+c
cos (α+a, l) The lift speed of the pushrod is L dy / dΦ, so even if the absolute value of d y / dΦ is the same, when the pushrod is rising, the lift speed of the pushrod is slower than when it is falling. The reason is that while the value of dy/dΦ is positive when ascending, it becomes negative when descending.Therefore, the cam shape is symmetrical on the ascending and descending sides of the cam. In this case, as shown in FIG. 12(A), the upward speed of the exhaust side push rod is slower than the downward speed, and characteristics superior to those of the conventional engine can be obtained.

Furthermore, for the push rod shown in FIG. 7(b), the rotation direction is relatively opposite to that in FIG. 7(a), so C3lNfβ+βol= (R+ y + a )β+β
o = SIN −' [lR+ y + a l/C
]Φ=θ−(β180) Therefore, dβ/dΦ= (dy/dθ)/I−dy/dθ+c
costβ+β. )1 Therefore, even if the absolute value of d y /dΦ is the same, when the push rod is rising, the lift speed of the push rod is faster than when it is falling. In other words, in the case of a cam in which the cam shapes on the upward and downward sides of the push rod are made symmetrically, the speed of the upward movement of the push rod on the intake side decreases as shown in Figure 12 (b). hourly speed, and has characteristics superior to conventional engines.

According to various experiments, as an engine for a portable work machine, the ratio of the push rod's descending speed to its ascending speed is 120% to 170% on the exhaust side, and 83% to 58% on the intake side. % is appropriate.

(Example) In order to further clarify the gist of the present invention, one example will be explained using the drawings.

As shown in Fig. 1, a valve drive device E of an engine for a portable working machine
consists of one cam 11 and a pair of rocking rotary lifters 21.22 that are in contact with the cam, and both of the pair of rocking rotary lifters 21.22 rotate around a lifter shaft 23. It is configured as follows. The gear part l of the cam
2 is formed to mesh with a crank gear 31 of the crank 3.

Further, one swinging rotary lifter 21 is connected to an exhaust valve rod 41, and the other swinging rotary lifter 22 is connected to an intake valve rod 42. When the pair of swinging rotary lifters 21 and 22 are viewed from above, as shown in FIG. , the exhaust valve rod 41 and the intake valve rod 42 are arranged on the same plane.

To explain the usage state of the valve drive device of the above-mentioned portable working machine engine, by rotating the crankshaft 32 of the crank 3 in the counterclockwise direction when looking at the engine from the power extraction side, the cam engages with the crank gear 31. rotating the gear portion 12 of the cam 11,
A pair of swinging rotary lifters 21 that come into contact with the cam 11.
22 to open the exhaust valve via the exhaust side push rod 41. Next, when the cam 11 is further rotated, the other swinging rotary lifter 22 that is in contact with the cam 11 is rotated, and the intake valve is opened via the intake push rod 42, and the exhaust is discharged at a predetermined time. Close the valve, and
Complete valve actuation by closing the intake valve. As a result, since the swinging rotary lifter is rotated by one cam, the length of the cam in the axial direction can be reduced, and since only a single cam is required, the weight can also be reduced.

In this example, ■Intake valve opening timing Before piston top dead center Crank rotation angle 20 degrees ■Intake valve closing timing After piston bottom dead center Crank rotation angle 60 degrees ■Exhaust valve opening timing Before piston bottom dead center Crank rotation angle 60 degrees ■Exhaust valve closing timing 2922 rotation angle after piston top dead center 20 degrees.

The angle formed by the contact surfaces between the pair of swinging rotary lifters 21 and 22 and the cam is (180+A+B)/2 (degrees) (
A: exhaust valve opening angle 60 degrees before bottom dead center, B: intake valve opening angle 20 degrees before top dead center), so in the case of this example, f180+60-201/2=11
It becomes 0 degrees.

When the valve driving device E shown in the above embodiment is used in a portable working machine, it will be as shown in FIG. The engine is operated and the power is transmitted to the working machine side of the cloth in the figure. In this case, the valve drive mechanism is located opposite the work equipment drive side of the engine, and when looking at the work equipment side from the engine example, the exhaust valve is located on the right hand, the intake valve is located on the left hand, and the crankshaft is located clockwise. Rotates in the direction of the needle,
The camshaft is designed to rotate counterclockwise,
When you hold the portable working machine engine in your hand, the exhaust side is not toward you, so there is no chance of getting burned.

Furthermore, based on this embodiment, the cam has a cam shape that is almost symmetrical on the push rod raising side and lowering side with respect to the maximum lift point, and the cam swings around an axis parallel to the rotational axis of the cam. Since the cam mechanism is constituted by a pair of bush rod lifters, the lift curves of the exhaust valve and the intake valve can be made different based on the above-mentioned action.

Next, a second embodiment will be explained. As shown in FIGS. 4 and 5, the valve drive device F for a portable working machine engine has a lifter with a simpler shape than that of the first embodiment,
The contact surfaces of the cam and the pair of lifters are slightly shifted in the cam direction. With this configuration, the manufacturing cost of the cam can be reduced.

Next, a third embodiment will be described. As shown in FIG. 6, the valve drive device G for an engine for a portable working machine has two shafts that support the lifter, so that the lifter shaft portion 231. 232, but the lifter does not need to be bent inward as in the first embodiment.
Both rods can be disposed on the same line in a plane direction perpendicular to the camshaft, and the length of the engine in the crankshaft direction can be shortened.

The present invention is not limited to the present embodiments, and can be modified as desired within the scope of achieving the above-mentioned objects and effects of the present invention and the effects of the invention described below, and any of these modifications may be made without limitation. Needless to say, this does not change the gist of the present invention.

(Effects of the Invention) As described in detail above, the present invention, the valve drive device for a portable working machine engine, is suitable for use in an engine-driven working machine in which an engine is mounted on one end of a power transmission shaft and a working equipment is mounted on the other end. A pair of swinging rotary lifters that contact the cam and swing on an axis parallel to the power transmission shaft within a plane including the power transmission shaft and the inner diameter of the cylinder are operated by rotating the cam. , is equipped with a valve drive mechanism that opens and closes both the intake and exhaust valves by opening the exhaust valve and then opening the intake valve.
Unlike the conventional arrangement, the tappet does not require a predetermined length in the crankshaft direction, and therefore the axial dimension can be reduced. In addition, since the cam is formed from one piece,
The manufacturing cost of the cam is reduced, and the manufacturing cost can be reduced.

In addition, the valve movement mechanism is located opposite to the work side of the engine, and the work tank is located from the engine side! Looking at example i, if the configuration is such that the exhaust valve is located on the right hand, the intake valve is located on the left hand, the crankshaft rotates clockwise, and the camshaft rotates counterclockwise, then the type of portable work machine When you hold it in your hand, the exhaust side is not in front of you, so you won't get burned.

Further, a cam having a push rod rising example and a lower RfR cam shape having a substantially symmetrical shape with respect to the maximum lift point,
If the intake and exhaust valves are opened and closed by a pair of bush rod lifters that swing around axes parallel to the rotational axis of the cam, one cam will make the lift curves of the intake and exhaust valves true, and the exhaust valve will open and close. By increasing the valve opening speed and increasing the valve closing speed, the intake valve opening speed can be increased and the valve closing speed can be decreased, thereby reducing the crank rotation of the engine that drives the portable work equipment. It is possible to increase the speed and increase the output per weight.

[Brief explanation of the drawing]

The drawings show an embodiment of the valve drive device for a portable working machine according to the present invention, and FIG. 1 is a front view showing the valve drive device;
FIG. 2 is a plan view showing the valve drive device. FIG. 3 is a sectional view of an engine using the valve driving device, and FIG. 4 is a sectional view of the valve driving device in a third embodiment.
Fig. 5 is a side sectional view showing the main parts of the valve drive device in Fig. 4, Fig. 6 is a front view showing the valve drive device in the third embodiment, and Fig. 7 is an operation of the cam mechanism. It is an explanatory diagram for showing. (A) shows the action of the swinging rotary lifter connected to the exhaust rod, and part (1) shows the action of the swinging rotary lifter connected to the intake rod. FIG. 8 is a front view showing a conventional valve drive device, and shows W! FIG. 9 is a sectional view showing an engine using the conventional valve driving device. Fig. 10 is an explanatory diagram showing the action of the cam mechanism of a conventional valve drive device, and Fig. 11 shows the relationship between the lift and lift curve of the cam mechanism in the conventional valve drive device with respect to the camshaft rotation angle. FIG. 12 is a graph showing the relationship between the lift and the lift curve with respect to the camshaft rotation angle according to the present invention. (A) shows the exhaust side cam mechanism; (B) shows the Li warm-up example cam 81#lI; 111
FIG. 3 is an explanatory view showing how a conventional portable engine-driven work machine is used, and FIG. 14 is a sectional view showing an engine using a conventional valve drive device. FIG. 15 is a sectional view showing a conventional swinging rotary lifter. E, F, G---One valve drive device 11---One cam 12---One cam gear part 13---One cam shaft 21.22---One Swinging rotary lifter 23---
--- Lifter shaft portion 3 --- Crank 31 --- One cam gear 32 --- One cam shaft 41 --- Exhaust valve rod 42 --- −−−−−One intake valve rod 51−−−−−−−+Exhaust valve 52−−−−−−One intake valve patent applicant Ryobi Co., Ltd. Agent Patent attorney Fumi Nagaya
Male Figure 1 Figure 2 Figure 3 Figure 6 Figure 7 (B) Figure 8 Figure 9 Figure 13 Figure '3 Figure 11 Figure 12 (A) (B) Figure 15 March 1992 16th

Claims (1)

[Claims] 1. In an engine-driven working machine in which an engine is attached to one end of a power transmission shaft and a working device is attached to the other end, a cam that comes into contact with one cam and lies within a plane that includes the power transmission shaft and the center line of the inner diameter of the cylinder. A rocking rotary lifter that swings on a shaft parallel to the power transmission shaft is operated by rotating the cam to open the exhaust valve, and then the intake valve is opened to open both the intake and exhaust valves. A valve drive device for a portable working machine engine, characterized by comprising a valve drive mechanism that opens and closes. 2. When the valve drive mechanism is located on the opposite side of the engine from the work equipment drive side, and when looking from the engine side to the work equipment side,
2. The valve for a portable working machine engine according to claim 1, wherein the exhaust valve is located on the right hand, the intake valve is located on the left hand, the crankshaft rotates clockwise, and the camshaft rotates counterclockwise. Drive device. 3. A cam whose cam shapes on the upward and downward sides of the push rod are almost symmetrical with respect to the maximum lift point, and a contact portion with the cam that swings around an axis parallel to the axis of rotation of the cam. A cam mechanism in a valve drive device for a portable working machine engine, characterized in that an intake valve and an exhaust valve are opened and closed by a pair of flat push rod lifters.