JP2001263085A - Hand-held type four-cycle engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize an engine body, reduce weight, and enhance workability. SOLUTION: This engine is constituted of a cam shaft 26 for supporting a valve system 53 rotatably onto a cylinder head 8 to drive opening and closing for an intake valve 18 and an exhaust valve 19, and a dry type timing transmission 35 arranged in one outer side of the engine body 1 to interlock a crankshaft 13 to the cam shaft 26, and a centrifugal clutch 49 for taking out power is attached to the crankshaft 13 on the other outside of the engine body 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hand-held four-stroke engine mainly used as a power source for a trimmer and other portable work machines, and more particularly to a crankcase having a crank chamber, a cylinder block having a cylinder bore,
An engine body including a cylinder head having an intake port and an exhaust port; a crankshaft supported by a crankcase and housed in a crank chamber; a piston fitted into a cylinder bore and connected to the crankshaft; Intake and exhaust valves that open and close intake and exhaust ports, and a valve train mechanism that opens and closes intake and exhaust valves in conjunction with rotation of the crankshaft; And a power take-out mechanism provided at an end projecting from the engine.

[0002]

2. Description of the Related Art Such a hand-held type four-stroke engine is already known as disclosed in, for example, Japanese Patent Application Laid-Open No. 10-28801.

[0003]

The hand-held four-stroke engine has a relatively clean exhaust gas, which is effective not only in preventing environmental pollution but also in ensuring the health of the user carrying the engine. . However,
Because its structure is more complex than a two-stroke engine,
There is a disadvantage that it is difficult to reduce the weight. Weight reduction is one of the important issues in improving workability, especially for a hand-held four-stroke engine.

However, in the hand-held four-stroke engine disclosed in the above publication, a valve operating mechanism provided on the cylinder head for opening and closing the intake and exhaust valves is configured to use a push rod and a lower arm. Since the valve operating chamber accommodating the push rod and the camshaft for driving the push rod is formed on the side wall of the engine body, the engine body is inevitably increased in size, making it difficult to reduce the weight of the engine.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a hand-held four-stroke engine which is light in weight and has good workability by making the engine body compact. .

[0006]

In order to achieve the above object, the present invention provides an engine body comprising a crankcase having a crank chamber, a cylinder block having a cylinder bore, and a cylinder head having an intake port and an exhaust port. A crankshaft supported by the crankcase and housed in the crankcase; a piston fitted into the cylinder bore and connected to the crankshaft; an intake valve and exhaust mounted on the cylinder head to open and close intake and exhaust ports. A hand-held device including a valve, a valve operating mechanism for opening and closing an intake valve and an exhaust valve in conjunction with rotation of a crankshaft, and a power take-out mechanism provided at an end of the crankshaft protruding outward from the engine body. In a four-stroke cycle engine, the valve mechanism is operated by a cylinder to open and close the intake and exhaust valves. A camshaft rotatably supported by the crankshaft, and a dry-type timing transmission device that is disposed on the outer side of the engine body opposite to the power take-out mechanism and interlocks between the crankshaft and the camshaft. This is the feature of 1.

The power take-out mechanism corresponds to a centrifugal clutch described later.

According to the first feature, it is not necessary to provide a chamber for accommodating the timing transmission device on the side wall of the engine body, so that the engine body can be made thinner and more compact, and the entire engine can be significantly reduced in weight. Can be achieved. In addition, the timing transmission and power take-off mechanism mounted on both ends of the crankshaft, with the cylinder block in between, improve the weight balance at both ends of the crankshaft and move the center of gravity of the engine to the center of the crankshaft. And the workability of the engine can be improved in combination with the weight reduction. In addition, during engine operation, the load from the timing transmission and the drive shaft is distributed to both ends of the crankshaft to avoid concentration of the load on the crankshaft and its bearings, and to improve their durability. Can be.

The present invention, in addition to the first feature, further comprises a flywheel having a cooling vane for sending cooling air to the engine body and having a larger diameter than the power take-out mechanism, between the engine body and the power take-out mechanism. The second feature is that the motor is mounted on the crankshaft.

According to the second feature, the rotation of the cooling blades does not hinder the power take-out mechanism while minimizing the size of the engine by the flywheel as much as possible.
Cooling air can be accurately supplied to the engine body, and their cooling performance can be improved.

Further, according to the present invention, in addition to the first feature, an oil tank for storing lubricating oil for lubricating the inside of the engine body is arranged adjacent to the outside of the timing transmission device and supported by the engine body. Is a third feature.

According to the third feature, the oil tank covers at least a part of the timing transmission, so that the transmission can be protected. In addition, due to the opposed arrangement of the oil tank and the flywheel, the center of gravity of the engine can be closer to the center of the crankshaft, and the workability of the engine can be further improved.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on embodiments of the present invention shown in the accompanying drawings.

FIG. 1 is a perspective view showing an example of use of a hand-held four-stroke engine of the present invention, FIG. 2 is a longitudinal sectional side view of the four-stroke engine, FIG. 3 is an enlarged view of a main part of FIG. 3 is an enlarged longitudinal sectional view around the cam shaft, and FIG.
FIG. 6 is a lubricating system diagram of the engine,
7 is a sectional view taken along the line 7-7 in FIG. 3, FIG. 8 is a sectional view taken along the line 8-8 in FIG. 7, FIG. 9 is a bottom view of the head cover, and FIG. FIG. 11 is a sectional view corresponding to FIG. 7, showing a modified example of the oil feed conduit and the oil return conduit.

As shown in FIG. 1, the hand-held four-stroke engine E is mounted on a drive unit of the power trimmer T as a power source, for example. Since the power trimmer T is used with the cutter C oriented in various directions depending on the working state, the engine E is also tilted or inverted upside down each time, and the driving posture is not constant.

First, the overall configuration of the hand-held four-stroke engine E will be described with reference to FIGS.

As shown in FIGS. 2, 3 and 5, a carburetor 2 and an exhaust muffler 3 are attached to the front and rear of the engine body 1 of the hand-held type four-stroke engine E, respectively. An air cleaner 4 is mounted at the entrance of the road. A fuel tank 5 made of synthetic resin is attached to the lower surface of the engine body 1.

The engine body 1 includes a crankcase 6 having a crank chamber 6a, a cylinder block 7 having one cylinder bore 7a, and a cylinder head 8 having a combustion chamber 8a and intake and exhaust ports 9, 10 opening to the chamber.
The cylinder block 7 and the cylinder head 8 are integrally cast, and a crankcase 6 separately cast from the lower end of the cylinder block 7 is joined by bolts. This crankcase 6 has first and second case halves 6L and 6R divided into right and left parts at the center thereof.
The two case halves 6L and 6R are joined to each other by bolts 12. A large number of cooling fins 38 are formed on the outer circumference of the cylinder block 7 and the cylinder head 8.

Crankshaft 1 housed in crankcase 6a
3 is rotatably supported on the first and second case halves 6L and 6R via ball bearings 14 and 14 ', and is connected via a connecting rod 16 to a piston 15 fitted in the cylinder bore 7a. The first and second case halves 6L and 6R are provided with oil seals 17 and 17 'which are adjacent to the outer sides of the bearings 14 and 14' and are in close contact with the outer peripheral surface of the crankshaft 13.

The cylinder head 8 is provided with an intake valve 18 and an exhaust valve 19 for opening and closing the intake port 9 and the exhaust port 10, respectively, in parallel with the axis of the cylinder bore 7a. A spark plug 20 has an electrode connected to the combustion chamber 8a. Is screwed in close proximity to the center.

The intake valve 18 and the exhaust valve 19 are connected to a valve spring 2 in a valve operating cam chamber 21 formed in the cylinder head 8.
2 and 23 are urged in the valve closing direction. In the valve cam chamber 21, the heads of the intake valve 18 and the exhaust valve 19
Cam followers 24 and 25 pivotally supported on the cylinder head 8 are vertically overlapped with each other.
A camshaft 26 that opens and closes the intake valve 18 and the exhaust valve 19 via the crankshaft 13 is provided in parallel with the crankshaft 13.
It is rotatably supported via one left and right side wall ball bearings 27, 27 '. One side wall of the valve operating cam chamber 21 to which the one bearing 27 is mounted is formed integrally with the cylinder head 8, and an oil seal 28 which is in close contact with the outer peripheral surface of the cam shaft 26 is mounted on this one side wall. You. The other side wall of the valve operating cam chamber 21 is provided with an insertion port 29 for allowing the cam shaft 26 to be inserted into the chamber 21, and after the cam shaft 26 is inserted, a side wall cap 30 for closing the insertion port 29 is provided. The other bearing 27 'is mounted. This side wall cap 3
Numeral 0 is fitted to the insertion port 29 via the seal member 31 and is connected to the cylinder head 8 by bolts.

As clearly shown in FIG. 3 and FIG.
Reference numeral 6 denotes a side on which the oil seal 28 is located, and one end of which protrudes outward from the cylinder head 8. On the same side, the crankshaft 13 also has one end protruding outward from the crankcase 6, and has a toothed drive pulley 32 at one end.
The driven pulley 33 having two teeth is fixed to one end of the cam shaft 26. And
A toothed timing belt 34 is wound around both pulleys 32 and 33 so that the crankshaft 13 can drive the camshaft 26 with a reduction ratio of 1/2. The valve train 5 is driven by the camshaft 26 and the timing transmission device 35.
3 are configured.

Thus, the engine E is of the OHC type, and the timing transmission 35 is of a dry type disposed outside the engine body 1.

Engine body 1 and timing transmission 35
Between them, a belt cover 36 made of a synthetic resin fixed to the engine body 1 with bolts 37 is arranged so as to avoid the influence of the radiant heat of the engine body 1 on the timing transmission device 35.

Further, an oil tank 40 made of a synthetic resin, which is arranged to cover a part of the outer surface of the timing transmission 35, is fixed to the engine body 1 by bolts 41.
Further, a recoil starter 42 (see FIG. 2) is attached to the outer surface of the oil tank 40.

Referring again to FIG. 2, the other end of the crankshaft 13 opposite to the timing transmission 35 also projects outward of the crankcase 6, and a flywheel 43 is fixed to one end of the crankcase 6 with a nut 44. You. The flywheel 43 integrally has a large number of cooling blades 45 on its inner surface to also serve as cooling blades. A plurality of mounting bosses 46 (one of them is shown in FIG. 2) are formed on the outer surface of the flywheel 43, and a centrifugal shoe 47 is pivotally supported on each of the mounting bosses 46 in a swingable manner. Is done. The centrifugal shoe 47 constitutes a centrifugal clutch 48 together with a clutch drum 48 fixed to a drive shaft 50 described later. When the rotation speed of the crankshaft 13 exceeds a predetermined value, the centrifugal shoe 47 starts centrifugal rotation of its own. The force comes into pressure contact with the inner peripheral wall of the clutch drum 48 to transmit the output torque of the crankshaft 13 to the drive shaft 50. The flywheel 43 has a larger diameter than the centrifugal clutch 48.

The engine cover 51 for covering the engine body 1 and the accessory is divided into a first cover half 51a on the flywheel 43 side and a second cover half 51b on the starter 42 at the timing transmission device 35. And are fixed to the engine body 1 respectively. First cover half 51a
, A bearing holder 75 having a truncated cone shape coaxially aligned with the crankshaft 6 is fixedly mounted on the cutter C.
The bearing holder 75 is provided with an air intake port 52 so as to take in outside air into the engine cover 51 as the cooling blades 45 rotate. I have. A pedestal 54 that covers the lower surface of the fuel tank 5 is fixed to the engine cover 51 and the bearing holder 75.

Since the timing transmission 35 for interlocking the crankshaft 13 and the camshaft 26 is of a dry type and is disposed outside the engine body 1, the side wall of the engine body 1 has There is no need to provide a special chamber for accommodating the device 35. Therefore, the engine body 1 can be made thinner and more compact, and the entire engine E can be significantly reduced in weight.

Further, with the cylinder block 7 interposed therebetween, a timing transmission device 35 is provided at both ends of the crankshaft 13.
And the centrifugal shoe 47 of the centrifugal clutch 48 are connected, so that the weight balance at both ends of the crankshaft 13 is good, and the center of gravity of the engine E can be brought as close as possible to the center of the crankshaft 13 to reduce the weight. Together, the workability of the engine E can be improved. In addition, during the operation of the engine E, the timing transmission 35 and the drive shaft 50
Will act on both ends of the crankshaft 13 so as to avoid concentration of the load on the crankshaft 13 and the bearings 14 and 14 'that support it.
Their durability can also be improved.

Since the flywheel 43 having a larger diameter than the centrifugal shoe 47 and having the cooling blades 45 is fixed to the crankshaft 13 between the engine body 1 and the centrifugal shoe 47, the size of the engine E is increased by the flywheel 43. Of the air intake port 5 without being hindered by the centrifugal clutch 48 by the rotation of the cooling blade 45
The outside air can be sucked in from the cylinder block 2 and accurately supplied around the cylinder block 7 and the cylinder head 8, and their cooling performance can be improved.

The engine body 1 further includes an oil tank 4
0 is mounted adjacent to the outside of the timing transmission 35 so that the oil tank 40
Of the transmission 35, and can cooperate with the second cover half 51b covering the other part of the transmission 35 to protect the transmission 35. Moreover, the engine body 1 of the oil tank 40 and the flywheel 43
, The center of gravity of the engine E can be closer to the center of the crankshaft 13.

Next, referring to FIGS.
The lubrication system will be described.

As shown in FIG. 3, one end of the crankshaft 13 is in close contact with the oil seals 39 and 39 'mounted on the inner and outer side walls of the oil tank 40, while the oil tank 40 is closed.
A through-hole 55 is provided in the crankshaft 13 for communicating between the inside of the oil tank 40 and the crank chamber 6a. Lubricating oil O is stored in the oil tank 40. The amount of the stored oil is such that the opening end of the through hole 55 into the oil tank 40 is always above the liquid level of the oil O regardless of the operating posture of the engine E. Set to be exposed.

In the oil tank 40, an oil slinger 56 is attached to the crankshaft 13 and a nut 5 is attached to the crankshaft 13.
7 is fixed. The oil slinger 56 is a crankshaft 1
The two blades 56 extending radially from each other from the central portion fitted to the third member 3 and bent toward the opposite side in the axial direction.
When the oil il slinger 56 is rotated by the crankshaft 13, at least one of the two blades 56 a and 56 b stores the oil in the oil tank 40 regardless of the operating posture of the engine E. O is scattered to generate oil mist.

3, 6 and 7, the crank chamber 6a is connected to the valve operating cam chamber 21 via an oil feed conduit 60, and the oil feed conduit 60 has a crank chamber 6a.
A one-way valve 61 is provided to allow flow in only one direction from the valve operating cam chamber 21 side. The oil feed conduit 60 is formed integrally with the belt cover 36 along one side edge thereof, and the lower end of the oil feed conduit 60 is formed in the valve chamber 62. The belt cover 36 is integrally formed with an inlet pipe 63 projecting from the valve chamber 62 to the back side of the belt cover 36, and the inlet pipe 63 is connected to a connection hole 64 at the lower part of the crankcase 6 so as to communicate with the crank chamber 6 a. Seal member 6
5 are fitted. The one-way valve 61 is provided in the valve chamber 62 so as to allow a one-way flow from the inlet pipe 63 to the valve chamber 62. The one-way valve 61 is a reed valve in the illustrated example.

The belt cover 36 is integrally formed with an outlet pipe 66 projecting from the upper end of the oil feed conduit 60 to the back side of the belt cover 36, and this outlet pipe 66 communicates with the valve operating cam chamber 21. , Is fitted into the connection hole 67 on the side of the cylinder head 8.

The valve cam chamber 21 communicating with the oil feed conduit 60 is provided with a lateral hole 68a provided in the cam shaft 26.
And a breather chamber 69 in the side wall cap 30 through a gas-liquid separation passage 68 comprising a vertical hole 68b, and the breather chamber 69 connects the breather pipe 70 to the air cleaner 4.
Communicated within.

As shown in FIGS. 4 and 9, a head cover 71 that closes the open upper surface of the valve cam chamber 21 is joined to the cylinder head 8 via a seal member 72.
A plurality of orifices 73, 73,.
A suction chamber 74 is formed which communicates with the valve operating chamber 21 through the suction chamber 74. The suction chamber 74 has a flat shape along the upper surface of the valve cam chamber 21, and four orifices 73 are formed at four corners of the bottom wall. On the bottom wall, two long and short suction pipes 74 and 75 projecting into the valve cam chamber 21 are formed integrally with each other at a central portion thereof at intervals in a direction perpendicular to the axis of the camshaft 26. These are provided with orifices 73, 73.

As shown in FIG. 6 to FIG.
On the other hand, is communicated with the inside of the oil tank 40 via an oil return conduit 78. The oil return conduit 78 is formed integrally with the belt cover 36 along the other side edge opposite to the oil feed conduit 60. The belt cover 36 is integrally formed with an inlet pipe 78 projecting from the upper end of the oil return conduit 78 to the back side of the belt cover 36, and this inlet pipe 78 is connected to the head cover 71 so as to communicate with the suction chamber 74. The formed outlet tube 80 is connected via a connector 81.

The belt cover 36 is integrally formed with an outlet pipe 82 projecting from the lower end of the oil return conduit 78 to the back side of the belt cover 36.
The oil tank 4 is connected so as to communicate with the oil tank 40.
0 is fitted in a return hole 84 provided in the hole. The open end of the return hole 84 is arranged near the center of the oil tank 40 so as to be exposed on the oil level in the oil tank 40 in any operating posture of the engine E.

A driven member 84 driven by the recoil starter 42 is fixed to the tip of the crankshaft 13 projecting outward from the oil tank 40.

During the operation of the engine E, when the oil slinger 56 scatters the lubricating oil O in the oil tank 40 due to the rotation of the crankshaft 13 to generate an oil mist, the crank chamber 23 is moved up by the piston 15 to move up. When the pressure is reduced, the oil mist is sucked into the crank chamber 6a through the through hole 55 and the crankshaft 13 piston 15
Lubricate around. Next, when the pressure in the crank chamber 6a is increased by the downward movement of the piston 15, the one-way valve 61 opens and the oil mist is supplied to the valve operating cam chamber 21 through the oil feed conduit 60 together with the blow-by gas generated in the crank chamber 6a. , Cam shaft 26 and cam followers 24 and 25
Lubricate etc.

When the oil mist and blow-by gas in the valve cam chamber 21 enter the gas-liquid separation passage 68 of the rotating camshaft 26, the gas and liquid are centrifuged in the passage 68, and the liquefied oil The blow-by gas is returned to the valve cam chamber 21 through the lateral hole 68 a of the separation passage 68, but is blown into the engine E through the breather chamber 69, the breather pipe 70 and the air cleaner 4 in order during the intake stroke of the engine E. .

Since the valve cam chamber 21 communicates with the air cleaner 4 through the gas-liquid separation passage 68, the breather chamber 69 and the breather pipe 70 as described above,
The pressure in the valve operating cam chamber 21 is maintained at atmospheric pressure or slightly lower.

On the other hand, since only the positive pressure component of the pressure pulsation is discharged from the one-way valve 61, the crank chamber 6 a is in a negative pressure state on average, and the negative pressure is released through the through hole 55 to the oil tank 40. To the suction chamber 74 via the oil return conduit 78, so that the suction chamber 74
The pressure in the oil tank 40 is lower than that in the suction chamber 74 and the pressure in the oil tank 40 is lower than in the valve cam chamber 21. As a result, a pressure shift occurs from the valve operating cam chamber 21 to the suction chamber 74 through the suction pipes 75, 76 and the orifices 73, 73... And further to the oil tank 40 through the oil return conduit 78. Oil mist in 21,
Oil liquefied and accumulated in the valve operating chamber 21 is sucked into the suction chamber 74 through the suction pipes 75, 76 and the orifices 73, 73,.
To the oil tank 40.

At this time, as described above, four orifices 73, 73,... Are formed at the four corners of the bottom wall of the suction chamber 74, and project from the central portion of the bottom wall into the valve operating cam chamber 21 to form a cam. Orifice 73, two long and short suction pipes 74, 75 arranged at intervals in the direction perpendicular to the axis of shaft 26
As shown in FIG. 10, the engine E is not only in the upright state (A) but also in the leftward tilted state (B) as shown in FIG.
Regardless of the driving posture such as the rightward tilting state (C), the leftward rolling state (D), the rightward rolling state (E), and the inverted state (F), six oils are accumulated in the valve operating cam chamber 21. Any of the orifices 73, 73... Is soaked, and the oil can be sucked into the suction chamber 74.

Thus, the oil mist in the oil tank 40 is supplied to the crank chamber 6a of the OHC type four-cycle engine E and the valve operating cam by utilizing the pressure pulsation of the crank chamber 6a and the function of the one-way valve 61. The oil is supplied to the chamber 21 and returned to the oil tank 40, so that the engine E can be reliably lubricated by the oil mist in any operation posture of the engine E, and the exclusive use for the circulation of the oil mist is provided. No oil pump is required, and the structure can be simplified.

In addition to the oil tank 40 made of synthetic resin, an oil feed conduit 60 connecting between the crank chamber 6a and the valve operating cam chamber 21, and an oil return conduit 78 connecting between the suction chamber 74 and the oil tank 40 are provided by the engine. Body 1
Since it is arranged outside, it does not hinder the thinning and compactness of the engine body 1 at all, and can greatly contribute to the weight reduction of the engine E. In particular, since the oil feed conduit 60 and the oil return conduit 78 disposed outside are hardly affected by heat from the engine body 1, overheating of the lubricating oil O can be avoided. Further, the integration of the oil feed conduit 60 and the oil return conduit 78 with the belt cover 36 can contribute to a reduction in the number of parts and an improvement in assemblability.

FIG. 11 shows a modified example of the oil feed conduit 60 and the oil return conduit 78. In this case, the oil feed conduit 60 and the oil return conduit 78 are made of a flexible material such as rubber separated from the belt cover 36. It is composed of a tube made of a conductive material. Since other configurations are the same as those of the previous embodiment, the same reference numerals as in the previous embodiment denote the same parts in the drawing, and a description thereof will be omitted.

According to this modification, the oil feed conduit 60
Regardless of the location where the oil return conduit 78 is connected, the piping can be freely laid by appropriately bending these conduits 60 and 78, and the layout flexibility can be expanded.

The present invention is not limited to the above embodiment, and various design changes can be made without departing from the scope of the gist. For example, instead of the one-way valve 61, a rotary valve that operates so as to conduct the oil feed conduit 60 when the piston 15 descends and shut off when the piston 15 rises in conjunction with the crankshaft 13 may be provided.

[0052]

As described above, according to the first aspect of the present invention, an engine body including a crankcase having a crank chamber, a cylinder block having a cylinder bore, a cylinder head having an intake port and an exhaust port, and a crank are provided. A crankshaft supported by a case and housed in a crank chamber; a piston fitted into a cylinder bore and connected to the crankshaft; and an intake valve and an exhaust valve mounted on a cylinder head for opening and closing an intake port and an exhaust port. A hand-held mechanism including a valve operating mechanism for opening and closing an intake valve and an exhaust valve in conjunction with rotation of the crankshaft, and a power take-out mechanism provided at an end of the crankshaft protruding outward from the engine body. In a four-stroke cycle engine, a cylinder head is used to open and close the valve mechanism and the intake and exhaust valves. A cam shaft rotatably supported,
The engine body consists of a dry-type timing transmission device that is located outside the power take-off mechanism on the side opposite to the power take-off mechanism and interlocks between the crankshaft and the camshaft. Therefore, it is not necessary to provide the engine body, so that the engine body can be made thinner and more compact, and the entire engine can be significantly reduced in weight. In addition, the timing transmission and power take-off mechanism mounted on both ends of the crankshaft, with the cylinder block in between, improve the weight balance at both ends of the crankshaft and move the center of gravity of the engine to the center of the crankshaft. As much as possible, coupled with weight reduction,
The workability of the engine can be improved. In addition, during engine operation, the load from the timing transmission and the drive shaft is distributed to both ends of the crankshaft to avoid concentration of the load on the crankshaft and its bearings, and to improve their durability. Can be.

According to a second feature of the present invention, a flywheel having cooling blades for sending cooling air to the engine body and having a larger diameter than the power take-out mechanism is provided between the engine body and the power take-out mechanism. Since it is mounted on the crankshaft, the rotation of the cooling blades allows the cooling air to be accurately supplied to the engine body without being hindered by the power take-out mechanism, while minimizing the size of the engine due to the flywheel.
Their cooling properties can be increased.

Further, according to the third feature of the present invention, the oil tank for storing the lubricating oil for lubricating the inside of the engine body is disposed adjacent to the outside of the timing transmission device and is supported by the engine body. The oil tank covers at least a part of the timing transmission, so that the transmission can be protected. In addition, due to the opposed arrangement of the oil tank and the flywheel, the center of gravity of the engine can be closer to the center of the crankshaft, and the workability of the engine can be further improved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of use of a handheld four-stroke engine of the present invention.

FIG. 2 is a vertical side view of the four-stroke engine.

FIG. 3 is an enlarged view of a main part of FIG. 2;

FIG. 4 is an enlarged longitudinal sectional view around a cam shaft of FIG. 3;

FIG. 5 is a sectional view taken along line 5-5 of FIG. 3;

FIG. 6 is a lubricating device system diagram of the engine.

FIG. 7 is a sectional view taken along line 7-7 of FIG. 3;

FIG. 8 is a sectional view taken along line 8-8 in FIG. 7;

FIG. 9 is a bottom view of the head cover.

FIG. 10 is an explanatory diagram of a suction operation of the accumulated oil in a cylinder head in various operating postures of the engine.

FIG. 11 is a sectional view corresponding to FIG. 7, showing a modified example of the oil feed conduit and the oil return conduit.

[Explanation of symbols]

 E ····· Engine 1 ····· Engine body 6 ····· Crankcase 6a ···· Crankcase 7 ····· Cylinder block 7a ···· Cylinder bore 8 ···· Cylinder head 9 ... intake port 10 ... exhaust port 13 ... crankshaft 15 ... piston 18 ... intake valve 19 ... exhaust valve 26 ... cam Shaft 35: Timing transmission device 40: Oil tank 43: Flywheel 45: Cooling blade 49: Power take-out mechanism (centrifugal clutch) 53: Valve mechanism

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02B 63/00 F02B 63/00 AD F02F 1/24 F02F 1/24 R (72) Inventor Koji Kasai Saitama 1-4-1, Chuo, Wako City, Japan F-term in Honda R & D Co., Ltd. (Reference) 3G015 AA03 AA05 AB03 BB01 BC00 BD02 BD11 BD24 BE03 BF05 BF07 CA06 CA12 DA02 DA11 DA12 EA26 EA27 3G016 AA02 AA07 AA19 BA22 BA46 BA49 BB12 CA19 CA41 CA44 CA51 CA57 FA27 GA01 3G024 AA18 AA19 AA73 BA23 DA03 DA04 DA09 GA26

Claims (3)

[Claims] 1. A cylinder case (6) having a crank chamber (6a), a cylinder block (7) having a cylinder bore (7a), and a cylinder head (8) having an intake port (9) and an exhaust port (10). An engine body (1), a crankshaft (13) supported by a crankcase (6) and housed in a crankcase (6a);
A piston (15) fitted in a cylinder bore (7a) and connected to a crankshaft (13), and an intake valve mounted on a cylinder head (8) to open and close an intake port (9) and an exhaust port (10). (18) and the exhaust valve (1
9), a valve operating mechanism (53) for opening and closing the intake valve (18) and the exhaust valve (19) in conjunction with the rotation of the crankshaft (13), and the engine body (1) of the crankshaft (13). And a power take-out mechanism (49) provided at an end protruding outward of the hand-held type four-stroke engine. The valve train (53) is driven to open and close the intake valve (18) and the exhaust valve (19). A camshaft (26) rotatably supported on a cylinder head (8) and a crankshaft (13) and a cam arranged outside the engine body (1) on the side opposite to the power take-out mechanism (49). Shaft (2
6) Dry type timing transmission device (35) for interlocking between
And a hand-held four-stroke engine. 2. The hand-held four-stroke engine according to claim 1, further comprising a cooling vane (45) for sending cooling air to the engine body (1), and a power take-out mechanism (4).
9) A handheld four-stroke engine characterized in that a flywheel (43) having a larger diameter is mounted on a crankshaft (13) between the engine body (1) and a power take-off mechanism (49). 3. The hand-held four-stroke engine according to claim 1, wherein an oil tank (40) for storing a lubricating oil for lubricating the inside of the engine body (1) is arranged adjacent to the outside of the timing transmission (35). And a hand-held four-stroke engine characterized by being supported by the engine body (1).