JP2015068313A - Engine and engine work machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine and an engine work machine with an automatic decompression device, simple in configuration and capable of preventing an increase in device size.SOLUTION: An engine with a flywheel 40 includes a cam 46 moving outward of an outer circumference of the flywheel 40 by a centrifugal force at a low engine speed, and a convex portion 46a of the cam 46 contacts a valve open/close lever 54, thereby automatically actuating a decompression device 50 communicating a combustion chamber with outdoor air. At a high engine speed, the convex portion 46 does not contact the valve open/close lever 54 since an arm 45 is moved toward the outer circumference and the convex portion 46a is moved inward. The decompression device 50 is fixed to a fixing boss 12 for an ignition coil, and bypass passages (12a, 12b) communicating with the combustion chamber are formed using the fixing boss 12.

Description

  The present invention mainly relates to an engine for a hand-held engine working device such as a brush cutter or a chain saw and an engine working machine, and more particularly to an improvement of a decompression device for reducing pressure in a cylinder of the engine.

  In small working machines such as brush cutters and chain saws, small engines are widely used as power sources. FIG. 6 is an external view of a brush cutter as an example of a conventional engine working machine 101. As shown in FIG. 6, an engine work machine 101 equipped with a small two-cycle engine 110 passes a drive shaft (not shown) through a pipe-shaped main pipe 104, and this drive shaft is provided at one end of the main pipe 104. By rotating at 110, the rotary blade 103 provided at the other end of the main pipe 104 is rotated. Near the lower part of the engine 110, a fuel tank 127 for storing a mixed fuel of gasoline and oil is provided. The rotary blade 103 can be attached to and detached from a spindle (not shown) provided on the gear unit 102, and a scattering protection cover 105 is provided in the vicinity of the rotary blade 103 for preventing the scattered grass from scattering. . The engine work machine 101 is operated while suspending a hook 113 by a shoulder belt (not shown), and a handle having a substantially U-shape in front view for operation by an operator near the longitudinal center of the main pipe 104. 106 is attached. Resin grips 107 a and 107 b are provided at the tip of the handle 106. The rotational speed of the engine is controlled by the operator by a throttle lever 109 attached in the vicinity of the grip 107a. The throttle lever 109 is operated while pulling the lock lever 112, and the pull amount is transmitted to the carburetor of the engine 110 through the wire 128.

  The engine 110 used in the engine working machine 101 is a general-purpose engine that is small and light and can obtain a large output, and can work for a long time by supplying fuel. Many engine tools represented by brush cutters, chain saws, and the like are required to have high output, small size, and light weight, and are therefore often manually started by a recoil starter. The engine 110 is provided with a starter handle 129. In recent years, in order to reduce the burden on the operator when pulling the starter handle 129, a manual decompression device has been provided so that the pressure in the combustion chamber can be released. There is a problem that it is necessary to operate every time, and there is a possibility of forgetting the operation. Therefore, Patent Document 1 proposes an engine in which an operation lever or the like is moved using the rotational force of the crankshaft, and thereby the decompression device is automatically operated.

JP-A-6-50116

  Patent Document 1 discloses a mechanism that automatically opens and closes a decompression device via a link mechanism or the like by utilizing rotation of a crankshaft. This is very useful because it can prevent forgetting operation of the decompression device at the time of starting. . However, the technique of Patent Document 1 inevitably increases the size of the apparatus, and there is a problem of an increase in weight, and there is a problem that it is difficult to employ the engine for an engine working machine that is small and portable. It was. In addition, when applying the technique disclosed in Patent Document 1, there are many components that need to be changed with respect to a conventionally used engine, leading to an increase in cost, and the operator opens and closes each time. The problem that it was necessary and the operability was poor, and the problems of durability and maintainability remained.

The present invention has been made in view of the above background, and an object of the present invention is to realize an engine with an auto decompression mechanism and an engine working machine that are automatically operated without requiring an operation by an operator.
Another object of the present invention is to provide an engine with an automatic decompression mechanism and an engine working machine that have a simple configuration, are small and light, and suppress an increase in manufacturing cost.
Still another object of the present invention is to provide an engine with an auto decompression mechanism and an engine working machine that are highly durable and easy to maintain.

The characteristics of representative ones of the inventions disclosed in the present application will be described as follows.
According to one aspect of the present invention, a crankcase, a cylinder fixed to the crankcase to form a combustion chamber, a piston that reciprocates inside the cylinder, a crankshaft, and a cooling fan connected to the crankshaft are provided. In an engine having a combined flywheel and decompression device, the decompression device has a movable valve for extracting a part of the compression of the combustion chamber and an operation lever for the movable valve, and the flywheel is operated only when the rotational speed of the crankshaft is low. A flywheel is provided with a centrifugal opening and closing device having a convex portion that moves radially outward of the wheel, and the decompression device is disposed at a position where the operation lever contacts when the convex portion moves outward. The decompression device is configured to be in an operating state during low-speed rotation. With this configuration, the pressure in the combustion chamber when the operator pulls the recoil starter is automatically released, so that the operator can pull the starter lightly and can easily start the engine.

  According to another feature of the present invention, the centrifugal opening / closing device is disposed near the outer periphery of the flywheel, and the convex portion is moved outward by centrifugal force when the flywheel is less than the set rotational speed, and is greater than or equal to the set rotational speed. In some cases, it was moved inward in the radial direction by centrifugal force so that the amount of outward protrusion was reduced. The centrifugal opening / closing device has an arm portion supported so as to be swingable in a radial direction around a swing shaft, and a cam that rotates integrally with the arm portion, and the convex portion is formed in the cam. The arm portion is biased by an elastic member so as to be pulled in the inner circumferential direction of the flywheel when the flywheel is stopped or rotated at a low speed. For this reason, the engine rotation speed is sufficiently low during the first rotation when the operator pulls the recoil starter, so that the centrifugal force acting on the arm portion is small, and the convex portion that protrudes outward without swinging the cam is formed. Contact the decompression valve opening / closing lever. As a result, the movable valve of the decompression device opens the bypass passage, so that the combustion chamber and the outside air automatically communicate with each other.

  According to another aspect of the present invention, the engine has an ignition coil that generates a high-voltage current supplied to the spark plug, and the flywheel is provided with a magnet that acts on the ignition coil. Is arranged on the flywheel at a position where the rotational balance is achieved. In this way, since the centrifugal switchgear is mounted so as to face the power generation magnet of the ignition coil, it can be used as a substitute for a balancer (mass body) for adjusting the rotational balance of the magnet, and a flywheel (magnet rotor) It is possible to suppress an unnecessary increase in weight. Also, because of the ignition timing, the magnet is arranged so that the piston passes through the ignition coil in the vicinity of TDC. However, if the decompression device is in the vicinity of the ignition coil, the valve of the decompression device opens when the piston is in the vicinity of BDC. Therefore, the decompression device can be arranged at an efficient position in terms of operation timing. Since fins for generating an air flow for cooling the cylinder are integrally provided on the flywheel, the present invention can be easily realized simply by changing the shape of the conventional magnet rotor with fins.

  According to another feature of the present invention, the cylinder is provided with a fixing boss extending radially outward of the cylinder to fix the ignition coil, and a communication hole communicating with the combustion chamber is formed in the fixing boss. The decompression device was attached to the fixing boss so that Since the bypass passage communicating the combustion chamber and the outside air is formed inside the fixing boss in this way, a dedicated boss is separately provided for the decompression device by providing a decompression device between the cylinder and the ignition coil. There is no need, and an engine with an automatic decompression device can be easily realized without significantly changing the conventional structure. The fixing boss portion extends in a direction perpendicular to the moving direction of the piston, and a mounting hole for mounting the decompression device is formed in the direction parallel to the moving direction of the piston from the middle of the fixing boss portion. Since it is attached, the decompression device can be mounted by effectively using the space between the outer peripheral side of the flywheel and the fixing boss. Further, the decompression device has a movable valve and a valve opening / closing lever for moving the movable valve. Since the moving direction of the movable valve is substantially perpendicular to the communication hole and the radial direction of the flywheel, the decompression device is connected via a push rod or the like. It is not necessary to operate the device indirectly, and the decompression device can be directly operated by the centrifugal opening / closing device, and the operation reliability is improved. Since the valve opening / closing lever of the decompression device is configured so that the contact surface with the convex portion is curved, it reduces wasteful stress and improves durability by hitting smoothly when the convex portion contacts the valve opening / closing lever. be able to.

  According to still another feature of the present invention, when the rotational speed of the crankshaft is high, the convex portion moves in the inner diameter direction of the flywheel and does not contact the valve opening / closing lever. Therefore, the operator can always pull the starter handle from a light state. When the engine is started, the movable valve is closed by the explosive force of the combustion chamber, and at the same time, the rotational speed is increased, so that the arm portion moves in the outer circumferential direction of the cooling fan by the centrifugal force. As the arm moves, the cam rotates, and the amount of protrusion of the cam from the outer periphery of the cooling fan decreases, so that it does not contact the decompression valve opening / closing lever, and the engine can be used normally. Further, when the engine is stopped, the rotational speed gradually decreases and the centrifugal force decreases, so that the arm portion moves in the cooling fan inner diameter direction, and the amount of protrusion of the cam convex portion to the outer peripheral side increases. Since the protrusion amount of the convex portion is increased, it again comes into contact with the valve opening / closing lever of the decompression device, so that the combustion chamber and the outside air can be brought into communication with each other. And next time, when the operator pulls the starter handle, it can be pulled with a low load from the beginning, and fatigue can be reduced. Even if the valve is not opened due to some malfunction, the valve is surely opened when the recoil is pulled.

  According to still another aspect of the present invention, the centrifugal switchgear is disposed between the ignition coil and the cylinder when viewed in the axial direction of the crankshaft of the engine. Therefore, the decompression device can be effectively arranged by making good use of the space between the cylinder and the flywheel, and the increase in size of the engine due to the installation of the decompression device can be prevented.

  According to the present invention, it is not necessary for the operator to operate the decompression device at the time of starting the engine, and the simple and highly durable automatic decompression device is provided without increasing the size of the engine or significantly increasing the weight. The engine was realized. In addition, in order to attach a decompression device to a conventional engine, the modification part can be changed by changing the shape and machining of part of the cylinder and changing the flywheel (magnet rotor). Since no processing or changes are required, the present invention can be easily implemented with a slight modification to the conventional engine.

  The above and other objects and novel features of the present invention will become apparent from the following description and drawings.

It is a longitudinal cross-sectional view of the engine working machine which concerns on the Example of this invention. It is a rear view of the flywheel 40 single-piece | unit of FIG. It is a longitudinal cross-sectional view of the decompression apparatus 50 of FIG. It is the figure which showed the principle of operation of the decompression apparatus 50 by the flywheel 40 (at the time of very low speed rotation). It is the figure which showed the principle of operation of the decompression apparatus 50 by the flywheel 40 (at the time of high speed rotation). It is a perspective view which shows the whole structure of the conventional engine working machine 101. FIG.

  Embodiments of the present invention will be described below with reference to the drawings. In the following drawings, the same portions are denoted by the same reference numerals, and repeated description is omitted. Further, in the present specification, description will be made assuming that the front and rear directions and the up and down directions are directions shown in the drawing. FIG. 1 is a longitudinal sectional view of an engine portion of an engine work machine 1 according to an embodiment of the present invention, and is a sectional view passing through a cylinder axis 18a and a crank axis 18b. In this embodiment, the engine working machine 101 shown in FIG. 6 is realized by improving only a part of the engine, and the configuration other than the improved part is the same as the structure shown in FIG.

  FIG. 1 is a longitudinal sectional view showing the internal structure of the engine working machine according to the present embodiment. The engine (main body) 10 is a two-cycle small engine and is housed in a synthetic resin housing such as a fan case 6 and a top cover 7 in this embodiment. The engine 10 has a crankshaft 15 that pivotally supports a counterweight 16 disposed coaxially with a main pipe 104 (see FIG. 6), a cylinder 11 disposed so as to extend substantially vertically upward from the crankcase 17, and a connecting rod. The piston 13 pivotally supported by 14 reciprocates in the cylinder 11 in the vertical direction. A combustion chamber 19 is formed by the cylinder 11 and the piston 13. The high voltage current generated by the ignition coil 23 is transmitted to the spark plug 25 via the ignition cord 24. A fuel tank 127 (see FIG. 6) is provided below the crankcase 17 of the engine 10, and a mixed fuel of gasoline and oil for two cycles is placed and sent to a carburetor (not shown).

  An end portion of a drive shaft (not shown) is connected to the front side (output side) of the crankshaft 15 via a clutch shaft 36 via a centrifugal clutch mechanism 30 having a clutch shoe 32. On the rear side of the flywheel 40 to which the centrifugal clutch mechanism 30 is attached, a blade 41 for cooling the engine is integrally formed. Although the flywheel 40 and the blade | wing 41 can be manufactured by integral molding with metals, such as an aluminum alloy, for example, you may manufacture with a material and shape other than that. The centrifugal clutch mechanism 30 is a known clutch mechanism in which a clutch shoe (swinger) 32 is connected to a clutch drum 34 by centrifugal force when the rotational speed of the crankshaft 15 reaches a certain level or more. The clutch shaft 36 is rotatably held on the fan case 6 by two sets of bearings 35. The driving force of the engine 10 is transmitted to the clutch drum 34 via the centrifugal clutch mechanism 30 fixed to the flywheel 40 attached to the crankshaft 15, and further from there, a shaft (not shown) provided in the main pipe 104. To the gear unit 102 and the rotary blade 103 (see FIG. 6).

  A manual recoil starter (not shown) is provided as a starting device in the vicinity of the rear end portion of the crankshaft 15 (indicated by the arrow 38). The recoil starter is a crank on which a clutch drum 37 is fixed by rotating a starter rope wound around a reel with a starter handle 129 (see FIG. 6) to rotate it at a high speed and applying a centrifugal clutch by the rotational force. This is a known manual starter in which the shaft 15 is rotated.

  The cylinder 11 of this embodiment is an air-cooling type, and a plurality of heat radiation fins for heat radiation are formed. The cylinder 11 is cooled when the air flow generated by the blades 41 hits the heat radiating fins of the cylinder 11 by the housing of the fan case 6 and the top cover 7. The cylinder 11 is formed with a fixing boss 12 that extends in a direction perpendicular to the moving direction of the piston 13 in order to fix the ignition coil 23 with a screw 26. The fixing boss 12 is manufactured by integral molding with the cylinder 11, and is manufactured by, for example, an aluminum alloy. A screw hole 12e is formed at the end of the fixing boss 12 away from the piston 13, and the ignition coil 23 is brought close to the outer periphery of the cooling fan of the cylinder 11 by screwing a screw 26 into the screw hole 12e. Arranged and fixed so as to. Since the fixing boss 12 in the conventional engine is provided only for forming the screw hole 12e, the size of the boss, particularly the cross-sectional size, is small, but in this embodiment, the tip of the screw hole 12e ( A further narrow passage (through hole 12a) is formed between the end near the piston) and the combustion chamber 19, and a bypass passage for communicating the combustion chamber 19 with the outside air is formed. Here, in addition to the conventional drilling of the screw hole 12e from the front to the rear with respect to the fixing boss 12, a hole having a diameter smaller than that of the screw hole 12e is formed at the bottom (near the rear end) of the screw hole 12e. ) To the combustion chamber, the through hole 12a can be formed by machining. The end of the through hole 12 a is blocked by attaching the ignition coil 23 with the screw 26.

  The decompression device 50 is attached to the fixing boss 12 in which the through hole 12a is formed. The decompression device 50 is a decompression mechanism, and releases a part of the pressure in the combustion chamber 19 to the outside air when the engine 10 is started to facilitate the compression work by the piston 13 and make it easier to start the engine 10. Device. In this embodiment, a valve opening / closing lever 54 for operating the decompression device 50 is provided near the lower end of the decompression device 50, and the valve opening / closing lever 54 is pushed in (moved upward) to pass through the bypass passage. A part of the pressure in the combustion chamber 19 can be released to the atmosphere. The valve opening / closing lever 54 of the decompression device 50 is disposed so as to be movable substantially parallel to the direction of the cylinder axis 18a. When the valve opening / closing lever 54 is pushed in, the decompression device 50 is activated. When the piston 13 moves in the cylinder 11 and the first combustion (first explosion) occurs while the decompression device 50 is in operation, the movable valve (described later) of the decompression device 50 is automatically restored to its original state due to the pressure fluctuation. It returns to the position (the initial position where the decompression device 50 is not activated), and the communication state between the combustion chamber and the outside air by the bypass passage is released. The valve opening / closing lever 54 is an operation member having a curved surface formed in an arc shape formed integrally or separately at the lower end of the movable valve, and the operation is performed by a cam 46 described later.

  FIG. 2 is a rear view of the flywheel 40 alone of the engine working machine. The flywheel 40 is an inertia body that is fixed to one end side of the crankshaft 15 with a bolt and rotates at the same speed as the crankshaft 15. The flywheel 40 has a certain amount of mass, and the engine torque fluctuates rapidly. In some cases, the inertial mass serves to moderate fluctuations in the rotational speed (rotation speed) of the engine. The magnitude of this moment of inertia is designed to be optimal according to the displacement of the engine 10, output characteristics, and work equipment such as the rotary blade 103. The flywheel 40 in the engine 10 according to the present embodiment serves as a component (magnet rotor) that constitutes a mechanism (magneto) that generates a high-voltage alternating current using a magnet (permanent magnet). A role as a cooling fan for generating an air flow for cooling the engine, a role as a part for attaching the centrifugal clutch mechanism 30 for transmitting or blocking the rotational force of the engine 10, and a part for attaching the centrifugal switchgear 43 As a role.

  In order to generate electric power with the ignition coil 23, two magnetic bodies 42 a and 42 b and a magnet are arranged on the flywheel 40 on the radially outer side. On the other hand, a centrifugal opening / closing device 43 for operating the decompression device 50 is provided on the side separated from the magnetic body 42 by about 180 degrees in rotation angle. The centrifugal opening / closing device 43 is a convex portion that protrudes radially outward from the outer periphery (outer edge portion) of the flywheel 40 when the rotational speed of the engine 10 is lower than a set value, for example, 2000 rpm or less. The cam 46 has a cam 46. When the cam 46 comes into contact with the valve opening / closing lever 54 of the decompression device 50, the decompression device 50 sets the combustion chamber 19 and the outside air in communication with each other. The centrifugal opening / closing device 43 includes a cam 46 supported so as to be rotatable or swingable about a swing shaft 44, and an arm portion 45 that rotates or swings integrally with the cam 46, and is an elastic member such as a compression spring. The end portion of the arm portion 45 is configured to be always pulled in the inner diameter direction of the flywheel 40 by 47. The centrifugal opening / closing device 43 is attached to a position facing the magnetic body 42 around the crankshaft 15 (a position that is substantially rotationally symmetric). Thus, when the engine 10 is stopped, the centrifugal opening / closing device 43 is rotatably supported by the cam 46 having the convex portion of the cam 46 protruding from the outer periphery of the flywheel 40, and the cam 46 rotates integrally with the cam 46. Since the arm portion 45 is provided so as to be pulled in by the elastic member 47 in the inner peripheral direction of the flywheel 40, the mass of the arm portion 45 and the spring constant of the elastic member 47 are appropriately designed. The opening / closing timing of the movable valve 53 of the decompression device 50 can be arbitrarily set by determining the design value of the engine rotation speed. Further, the flywheel 40 is normally manufactured from an aluminum alloy for weight reduction, and when the magnetic body 42 is inserted, an unbalance of rotation occurs. Therefore, a balancer (mass body) is inserted on the side opposite to the magnetic body 42 for balance, but in this embodiment, if the centrifugal switching device 43 is provided on the side opposite to the magnetic body 42 as a balancer, a fly It is not necessary to change the weight of the wheel 40. Since it comprised in this way, the component attached to the flywheel 40 can be mounted with sufficient rotation balance, preventing a weight increase.

  When the engine 10 stops or rotates at a very low speed, the cam 46 protrudes outward from the outer peripheral edge of the flywheel 40. The cam 46 is set so as to move the valve opening / closing lever 54 in contact with the valve opening / closing lever 54 of the decompression device 50 when protruding to the outer peripheral side. When the engine 10 has a rotational speed higher than the set value, the cam 46 rotates to move the portion (protrusion) that protrudes to the outer peripheral side in the inner diameter direction of the flywheel 40. As a result, the cam 46 opens and closes the valve. The lever 54 does not come into contact. Near the outer periphery of the flywheel 40, a plurality of blades 41 for generating cooling air are formed at substantially equal intervals in the circumferential direction, but only the blades 41 where the centrifugal opening / closing device 43 is installed are omitted. . Thus, since the centrifugal opening / closing device 43 is provided on the flywheel 40, the decompression device 50 can be set in the operating state by the low-speed rotation of the flywheel 40.

  FIG. 3 is a longitudinal sectional view of the decompression device 50, which is a sectional view passing through the central axis in the moving direction of the movable valve (decompression valve) 53 and perpendicular to the axial direction of the crankshaft 15. The decompression device 50 is mainly configured by a housing 51, a stopper base 55, a movable valve 53, and a valve opening / closing lever 54. The decompression device 50 is attached to the mounting hole 12c having a circular cross section formed perpendicular to the longitudinal direction of the fixing boss 12, and the substantially cylindrical housing 51 is fixed to the mounting hole 12c. This fixing method may be configured such that a male screw portion is formed on the outer peripheral surface of the housing 51, a female screw portion is formed on the inner peripheral surface of the mounting hole 12c, and these are screwed together with an O-ring 59 interposed. However, it may be fixed by other methods such as press-fitting, adhesion, and screwing. The fixing boss 12 is formed with a through hole 12 a serving as a horizontal hole in the vicinity of the upper portion passing through the central axis 58. As can be seen from FIG. 1, the through hole 12 a is a hole formed coaxially with the screw hole 12 e and opens into the combustion chamber 19 of the cylinder 11. A through hole 12b which is a vertical hole is formed downward from the through hole 12a, and the through hole 12a opens into the valve movement space 12d.

  A housing 51 of the decompression device 50 has a substantially cylindrical shape for realizing a valve mechanism by fitting a movable valve 53, and a through passage 51a is formed at the center, and is perpendicular to the through passage 51a. Two through passages 51b are formed. These through passages 51a and 51b form a bypass passage for communicating with the outside air from the combustion chamber 19 together with the through holes 12a and 12b. The bypass passage is opened and closed when the valve portion 53a of the movable valve 53 contacts or separates from the housing 51 on one end side (upper end side) of the through passage 51a. The upper end portion of the movable valve 53 is a valve portion 53a having a conical shape, and the shape of the upper end portion of the through-passage 51a is also formed in a funnel shape that fits closely with the valve portion 53a. The Note that the relative shape of the movable valve 53 and the housing 51 for realizing the valve operation is arbitrary, and is not necessarily limited to the shape shown in FIG. 3, but when the explosion occurs in the combustion chamber 19 (see FIG. 1), Since the inside of the moving space 12d is at a high pressure, it is important to have a shape that ensures that the movable valve 53 is kept closed at that high pressure.

  The through passage 51 a functions as a moving passage of the movable valve 53 in addition to the bypass passage, and is configured to be continuous with the through passage 55 a formed in the stopper base 55. The stopper base 55 is a member for holding a stopper mechanism that fixes the movable valve 53 that has moved downward so as not to move due to pressure fluctuations in the combustion chamber, and moves in a direction perpendicular to the central axis 58. A space for accommodating the two steel balls 56 is formed. The steel ball 56 is housed inside a horizontal hole portion 55 b having a circular cross-sectional shape formed on the stopper base 55 and is urged by a spring 57 in a direction approaching the movable valve 53. A part of the movable valve 53 is formed with a recess 53c that is recessed inward so as to be continuous in the circumferential direction. The recess 53c is formed at a position where the movable valve 53 makes good contact with the steel ball 56 when closing the bypass passage, and the cross-sectional shape is semicircular or close to that, and the movable valve 53 can be moved by the first explosion of the engine 10. When a high pressure is applied to the valve 53 due to combustion, the movable valve 53 moved downward is held. The stopper base 55 is preferably configured to be divided into two on a plane including the central axis 58, and it is advantageous in manufacturing if the cross-sectional position is set to be perpendicular to the moving direction of the steel ball 56. . The housing 51 and the stopper base 55 are fixed by an arbitrary fixing method.

  A valve opening / closing lever 54 is attached to an operated end portion 53b on the lower end side (side closer to the centrifugal opening / closing device 43) of the movable valve 53. The valve opening / closing lever 54 serves as an abutting portion that comes into contact with the cam 46 of the centrifugal opening / closing device 43, and in order to reduce contact resistance with the cam 46, the rotation direction of the flywheel 40 It is formed to bend in a direction parallel to the. The direction of the curved surface is formed so as to draw R on the opposite side of the outer peripheral surface of the flywheel 40. The reason why the contact surface of the valve opening / closing lever 54 with the cam 46 is curved is to smoothly apply the contact surface with the cam 46 to reduce useless stress and improve durability. The valve opening / closing lever 54 and the movable valve 53 may be configured by integrally molding metal, or may be configured as separate parts manufactured and joined together.

  Next, the operation of the decompression device of this embodiment will be described with reference to FIG. FIG. 4 is a view when the engine is stopped or when the flywheel 40 is rotating at an extremely low speed, and shows a state in which the cam 46 is in contact with the valve opening / closing lever 54. A swing shaft 44 is fixed near the outer edge of the flywheel 40, and a cam 46 is attached coaxially with the swing shaft 44. The cam 46 is fixed so as not to rotate relative to the arm portion 45, or is integrated. To be manufactured. Since one side located on the outer peripheral side of the arm portion 45 is pivotally supported by the swing shaft 44, when the flywheel 40 rotates at a high speed, the other end side (inner peripheral side) of the arm portion 45 is moved outward by centrifugal force. Move to. In order to prevent this movement, one end (end portion on the outer peripheral side) of an elastic member 47 such as a compression spring is fixed to the other end side of the arm portion 45. The other end (the inner peripheral end) of the elastic member 47 is fixed to the flywheel 40 by the fixing portion 48. Accordingly, the movement of the arm portion 45 outward in the radial direction stays at a place where the centrifugal force and the spring force of the elastic member 47 are balanced. At the time of stopping where the centrifugal force is hardly generated or at the time of extremely low speed rotation, the end portion of the arm portion 45 away from the swinging shaft 44 (the vicinity where the mounting portion 45a is formed) moves to the innermost side by the action of the elastic member 47. It will be in the state. In this state, as shown in FIG. 4, the convex portion 46 a of the cam 46 fixed to the arm portion 45 moves outward (radially outward as viewed from the flyhole 40), and the outer peripheral surface of the flywheel 40 or outside Since it protrudes by a predetermined amount outward from the peripheral edge, when the flywheel 40 rotates in the protruding state, the convex portion 46 a of the cam 46 comes into contact with the valve opening / closing lever 54. It is important to set the protruding amount so that the movable valve 53 can be moved by contacting the valve opening / closing lever 54. Since the valve opening / closing lever 54 has a curved surface that curves in the opposite direction to the outer peripheral surface of the flywheel 40, the valve opening / closing lever 54 is pushed, and the movable valve 53 moves in the direction of the arrow to bypass the combustion chamber 19 and outside air. It will be in the state connected by a channel | path. At this time, the contact state between the concave portion 53c and the steel ball 56 is released, but the steel ball 56 continues to press the vicinity of the lower portion of the concave portion 53c of the movable valve 53 by the spring 57, so that the movable valve 53 is moved upward. It will be held as it is.

  In this embodiment, the valve opening / closing lever 54 of the decompression device 50 and the cam 46 of the centrifugal opening / closing device 43 are in contact with each other. Therefore, when the flywheel 40 falls below a predetermined rotational speed immediately before the engine 10 is about to stop, Thus, the valve opening / closing lever 54 is pushed upward, the decompression device 50 is activated, and the combustion chamber 19 communicates with the outside air via the bypass passage. Even if the movable valve 53 does not reach the release position just before the engine 10 is stopped, when the operator pulls the starter handle 129 (see FIG. 6), the first cam 46 and the valve opening / closing lever 54 face each other. , The valve opening / closing lever 54 is pushed, and the decompression device 50 is in an operating state, so that the operator can pull the starter handle with a light load. In this way, unlike the conventional manual decompression device, the decompression device 50 is automatically turned on, so that it is not necessary for the operator to bother operating the decompression device, and forgetting to operate the decompression device 50 can be prevented. The engine with good startability can be realized. Further, the decompression device 50 is provided in the fixing boss 12 for fixing the ignition coil 23, and the bypass passage is also formed by using the fixing boss 12, so that a part of the existing cylinder 11 is slightly changed. Thus, the present embodiment can be realized, and the present embodiment can be realized with a slight increase in cost without increasing the size of the engine.

  Next, when the engine 10 makes an initial explosion, the movable valve 53 of the decompression device 50 is pushed downward, and the valve portion 53a of the movable valve 53 closes the through passage 51a. The communication state with is canceled. On the other hand, when the rotation of the engine 10 rises and rises above a certain set rotational speed, centrifugal force is applied to the arm portion 45 of the centrifugal opening / closing device 43, so that the arm portion 45 moves in the outer circumferential direction of the flywheel 40. When the arm portion 45 moves to the outer peripheral side, the cam 46 rotates about the swing shaft 44 serving as a rotation support portion, and thus the convex portion 46a of the cam 46 moves to the inside in the radial direction of the flywheel 40. That is, the protrusion amount of the convex portion 46a from the outer peripheral edge of the flywheel 40 to the radially outer side becomes small. Thus, when the rotational speed is higher than the set rotational speed, the convex portion 46a of the cam 46 does not come into contact with the valve opening / closing lever 54, so that the decompression device 50 is not put into operation. Further, since the convex portion 46a and the valve opening / closing lever 54 are not in contact with each other, there is no adverse effect on the normal operation of the engine 10. FIG. 5 shows a state in which the convex portion 46a and the valve opening / closing lever 54 are not in contact with each other. When the flywheel 40 is at a predetermined rotational speed or higher, the arm portion 45 moves radially outward, so the cam 46 rotates about the swing shaft 44 (clockwise in FIG. 5), and the cam 46 protrudes. The portion 46a is retracted to the innermost side from the outermost peripheral position of the flywheel 40 (here, the outer peripheral position of the magnetic body 42) or to a position where it hardly protrudes. The flywheel 40 is provided with a stopper 49 for restricting the rotation of the arm portion 45 and the cam 46, and the arm portion 45 is held at a position where the side surface of the cam 46 is in good contact with the stopper 49. Therefore, high-speed rotation of engine 10 (normal rotation for operating the work machine) is performed well.

  When the operator stops the engine 10, the rotational speed of the flywheel 40 decreases, and when the rotational speed is lower than a certain set value, the arm portion 45 is pulled in the inner diameter direction of the flywheel 40, Since the convex portion 46a of the cam 46 projects greatly outward from the periphery in the radial direction, the cam 46 contacts the valve opening / closing lever 54, the valve portion 53a of the movable valve 53 is opened, the bypass passage is released, and the combustion chamber 19 and the outside air are opened. Is in a communication state. As a result, when the operator pulls the starter handle 129 (see FIG. 6) next time, the decompression device 50 is in an operating state, so that it can be pulled lightly from the beginning. Even when some malfunction occurs and the movable valve 53 of the decompression device 50 is closed, when the starter handle 129 starts to be pulled, the decompression device 50 is immediately put into operation, so that the operator is always light. Can be pulled in state.

  The rotational speed (set rotational speed) at which the convex portion 46a of the cam 46 moves radially outward from the outer peripheral edge of the flywheel 40 can be arbitrarily set, but the normal maximum rotational speed 10000 rpm and idling rotational speed 3000 rpm. In the case of the 20 to 60 cc general-purpose engine, the cam 46 and the valve opening / closing lever 54 may be set in contact with each other at a rotational speed of 500 to 2000 rpm or less, for example.

  As described above, according to the present embodiment, a two-cycle engine that automatically opens and closes the movable valve 53 of the decompression device 50 without reducing the burden on the operator at the start of the engine and increasing the size and weight. realizable. In this embodiment, since the centrifugal opening / closing device 43 is arranged on the flywheel 40, the centrifugal force of the flywheel 40 can be reliably used for the opening / closing device for the movable valve, and a new component is added to the crankshaft 15. Therefore, the present invention can be realized without impairing the downsizing of the engine required for a hand-held engine working machine. In addition, since the centrifugal opening / closing device 43 is disposed near the outer periphery of the flywheel 40, the decompression device 50 that needs to be provided in the vicinity of the combustion chamber 19 in an engine in which the outer periphery of the flywheel 40 passes near the combustion chamber 19 is provided. It is suitable for arrangement, and the downsizing of the engine can be maintained. Further, in the configuration of this embodiment, unlike the configuration in which the centrifugal switchgear is attached to the crankshaft 15, it is not necessary to use a push rod or a complicated link mechanism, so the configuration is simple and the durability is improved. Is possible.

  As mentioned above, although this invention was demonstrated based on the Example, this invention is not limited to the above-mentioned Example, A various change is possible within the range which does not deviate from the meaning. For example, in the above-described embodiment, the convex portion 46a for moving the valve opening / closing lever 54 of the decompression device 50 is realized by the cam mechanism that moves in the arc direction, that is, swings, but the valve opening / closing lever 54 is moved. It is also possible to realize a member of any shape that can be realized by a mechanism that moves in a curved line or linearly outward in the radial direction by centrifugal force. Furthermore, although the example of the brush cutter has been described as an example of the engine working machine, the type of the working device is not limited to the mowing device, and the same applies to other working machine engines such as a chain saw, a cutter, and a cultivator. Applicable to.

1 Engine working machine 6 Fan case 7 Top cover 10 Engine 11 Cylinder 12 Fixing boss 12a Through hole (horizontal hole) 12b Through hole (vertical hole)
12c Mounting hole 12d Valve movement space 12e Screw hole 13 Piston 14 Connecting rod 15 Crankshaft 16 Counterweight 17 Crankcase 18a Cylinder axis 18b Crankshaft line 19 Combustion chamber 23 Ignition coil 24 Ignition cord 25 Spark plug 26 Screw 30 Centrifugal clutch mechanism 32 Clutch Shoe 34 Clutch drum 35 Bearing 36 Clutch shaft 37 Clutch drum 40 Flywheel 41 Blades 42, 42a, 42b Magnetic body 43 Centrifugal opening / closing device 44 Oscillating shaft 45 Arm portion 45a (Arm portion) mounting portion 46 Cam 46a (Cam ) Protruding portion 47 Elastic member 48 Fixed portion 49 Stopper 50 Decompression device 51 Housing 51a, 51b (passage of housing) 53 Moveable valve 53a Valve portion 53b End 53c Recess 54 Valve open / close lever 55 Stopper base 55a (through the stopper base) Through passage 55b Lateral hole part (in the stopper base) 56 Steel ball 57 Spring 58 (Decompression unit) Central shaft 59 O-ring 101 Engine working machine 102 Gear unit 103 Rotating blade 104 Main pipe 105 Splash prevention cover 106 Handles 107a, 107b Grip 109 Throttle lever 110 Engine 112 Lock lever 113 Hook 127 Fuel tank 128 Wire 129 Starter handle

Claims (12)

An engine having a crankcase, a cylinder fixed to the crankcase to form a combustion chamber, a piston that reciprocates inside the cylinder, a crankshaft, a flywheel connected to the crankshaft, and a decompression device. And
The decompression device has a movable valve for releasing a part of the compression of the combustion chamber, and an operation lever for the movable valve,
The flywheel is provided with a centrifugal opening / closing device having a convex portion that moves outward in the radial direction of the flywheel only when the rotational speed of the crankshaft is low,
An engine characterized by placing the decompression device at a position where the operation lever contacts when the convex portion moves outward, thereby bringing the decompression device into an operating state during low-speed rotation of the flywheel.   The centrifugal opening and closing device is disposed near the outer periphery of the flywheel, and the convex portion moves outward by centrifugal force when the flywheel is less than a set rotational speed, and by centrifugal force when the flywheel is above the set rotational speed. 2. The engine according to claim 1, wherein the amount of protrusion to the outside decreases by moving radially inward.   The centrifugal opening / closing device includes an arm portion supported so as to be swingable in a radial direction around a swing shaft, and a cam that rotates integrally with the arm portion, and the arm portion is configured by an elastic member to support the flywheel. 3. The engine according to claim 2, wherein the engine is biased so as to be drawn in an inner circumferential direction of the flywheel when the engine is stopped or rotated at a low speed, and the convex portion is formed on the cam. Having an ignition coil for generating a high-voltage current supplied to the spark plug;
A magnet that acts on the ignition coil is provided on the flywheel,
The engine according to claim 3, wherein the centrifugal opening and closing device and the magnet are disposed on the flywheel at a position where a rotational balance is achieved.   The engine according to claim 4, wherein blades for generating an air flow for cooling the cylinder are provided integrally with the flywheel. The cylinder is provided with a fixing boss extending radially outward of the cylinder in order to fix the ignition coil.
The engine according to claim 5, wherein a communication hole communicating with the combustion chamber is formed in the fixing boss, and the decompression device is attached to the fixing boss so as to be connected to the communication hole. The fixing boss portion extends in a direction perpendicular to the moving direction of the piston,
Forming a mounting hole for mounting the decompression device in the direction parallel to the moving direction of the piston from the middle of the fixing boss part;
The engine according to claim 6, wherein the decompression device is attached to the attachment hole.   The decompression device includes a movable valve and a valve opening / closing lever that moves the movable valve, and the moving direction of the movable valve is substantially perpendicular to the communication hole and the radial direction of the flywheel. Item 8. The engine according to Item 7.   The engine according to claim 8, wherein when the rotation speed of the crankshaft is high, the convex portion moves in an inner diameter direction of the flywheel and does not contact the valve opening / closing lever.   The engine according to claim 9, wherein the centrifugal opening / closing device is disposed between the ignition coil and the cylinder.   The engine according to claim 10, wherein a contact surface with the cam is curved at a valve opening / closing lever of the decompression device.   An engine working machine that drives a work machine using the engine according to any one of claims 1 to 11.

Images