ANTI-OVERRUNNING DEVICE FOR AN INTERNAL COMBUSTION ENGINE

Abstract: An anti-overrunnning device for a internal combustion engine comprising a vibrating pump (41) for generating pneu­ matic pressure by vibrations of the engine; an actuator (81) having a rod (92) for urging a throttle valve (27) lever in a direction of closing a throttle valve by virtue of the pneumatic pressure of said vibrating pump; and a vibra­ tion sensor (101) positioned in the middle of a passage (23) for communication between said vibrating pump and a pressure chamber (85) of said actuator to open said passage by virtue of the vibrations of the engine during overrunning thereof.

Description: The present invention relates to an anti-overrunning device for an internal combustion engine as defined in the introductory portion of patent claim 1. Portable working machines generally use a two-stroke engine as a power source. Particularly, a diaphragm type carbureter is employed to thereby make it posssible to operate a machine in all attitudes. So, the two-stroke engine is used for a chain saw, a brush cutter, etc.. It is usual that such a portable working machine is operated with the lightweight, small-size and high-output internal combustion engine fully loaded in order to enhance the working properties. However, in the chain saw or the brush cutter, when a throttle valve of a carbureter is totally opened where a load torque at the time of unloaded operation is small, the engine brings forth a so-called overrunning by which an allowable number of revolutions exceeds before cutting work takes place to sometimes damage the engine. The overrunning operation likewise occurs also after the cutting work has been completed. The overrunning may be avoided if the throttle valve is restored every time of interruption of the work so as not to affect the no-load running when the throttle valve is totally opened. However, because the intermittent work is repeatedly carried out, the operator often fails to do so, thus resulting in damages of and shortening of life of the engine. In the past, a measure has been taken to supply a mixture rich in fuel when a throttle valve is fully opened and nearly fully opened in order to prevent overrunning under the no-load running. However, this measure increases a consumption quantity of fuel. An ignition plug becomes easily fogged, and an exhaust fume increases. Tar or the like tends to be stayed in a muffler. The present inventor has proposed an anti-overrunning device as disclosed in Japanese Patent Application Laid-Open No. 1835/1986. In this device, a vibrating pump is normally driven to directly supply pressure air to an actuator, and therefore, a diaphragm of the vibrating pump is always unsteady due to the vibrations of the engine; the operating stability is poor; and it is difficult to set an actuating point at which a throttle valve is closed by an actuator during overrunning of the engine. Furthermore, the vibrating pump is provided with a spring to force back the diaphragm, and therefore the amplitude of the diaphragm is restriced. A vibrating pump has to be increased in size in order to obtain a sufficient pump capacity. A similar anti-overrunning device has been disclosed in JP-A-60 261 940. While in this device the vibrating pump is not provided with a return spring, the diaphragm suffers from similar drawbacks as explained above. It is therefore an object of the present invention to provide a new anti-overrunning device for an internal combustion engine may be run at a reasonable consumption amount of fuel in all running conditions, and in an overrunning condition (running in ecxess of a set number of revolutions), a throttle valve is automatically actuated in a closing direction to reduce an amount of mixture of the engine, in order to overcome the aforementioned problems. The present invention achieving this object has been defined and characterized in patent claim 1. In the device of the present invention a weight is mounted to the diaphragm of the vibrating pump. A return spring is not present. Accordingly the present invention provides an anti-overrunning device which is small but has sufficient pump capacity. Moreover, since the vibration valve is provided between the vibrating pump and the actuator, it is possible to suitably set the maximum number of revolutions of the engine according to the formulation of the vibration valve. According to the present invention, during the overrunning of the engine, the opening degree of the throttle valve of the carbureter is automatically reduced to reduce the flow rate of the mixture taken into engine. Therefore, there is provided a new anti-overrunning device which is positive in operation, may be run at a substantially reasonable fuel cost (rate of fuel consumption) in all running levels of the engine, is free of spark plug from a fog, is less in exhaust fume, and is less tar stayed on the muffler. Furthermore, since the operator can perform his work while a throttle handle is left fully opened because of actuation of the anti-overrunning device, the working properties may be enhanced, and the damage of and the shortening of life of the engine may be avoided. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side view showing the structure of an anti-overrunning device for an internal combustion engine according to the present invention; Fig. 2 is a horizontal sectional view of a carbureter provided on the anti-overrunning device; Fig. 3 is a side sectional view of the internal combustion engine provided with the anti-overrunning device; Fig. 4 is a side sectional view showing the state where the anti-overrunning device according to one embodiment of the present invention is mounted on the carbureter; and Fig. 5 is a side sectional view showing the state where the anti-overrunning device according to a second embodiment of the present invention is mounted on the carbureter. (Embodiments of the Invention) In the internal combustion engine 10, as shown in Fig. 3, a cylinder 16 having cooling fins 15 is closed at its upper end by a cylinder head 13 having cooling fins 12, and a crank case 21 is connected to the lower end thereof. A piston 14 fitted in the cylinder 16 and a crank shaft 19 supported on the crank case 21 are connected by a connecting rod 20. When the piston 14 is up a mixture ( a mixture of fuel and air) is taken into the crank case 21 from an intake port 17. The mixture is supplied to a chamber between the cylinder head 13 and the piston 14 when the piston 14 is down. As the piston 14 moves up, the mixture is compressed, and fuel is fired near the top dead center. The piston 14 is moved downward by the explosive force, and simultaneously the combustion gas is exhausted outside via the muffler 11 from an exhaust port 18. A carbureter 24 is connected to the intake port 17 through a heat insulating pipe 22. An air cleaner, not shown, is connected to an end wall 26 of a body 35 of the carbureter 24. As shown in Fig. 2, a throttle valve 27 is supported by the valve shaft 28 on a venturi 34 formed on the body 35, and fuel is supplied to the venturi 34 by negative pressure of air passing through the venturi 34. Such a fuel supplying mechanism is known, for example, in U.S. Patent No. 3,378,623 and directly has nothing to do with the gist of the present invention, and will not be further described. An upper end of the valve shaft 28 is rotatably supported on the body 35 by means of a bearing sleeve 38, and an inverted-L shaped throttle valve lever 29 is secured to the upper end. One end of a spring 36 wound around the valve shaft 28 is placed in engagement with the throttle valve lever 29 and the other end thereof placed in engagement with the bearing sleeve 38. Also, a boss portion of the lever 25 is slipped over the bearing sleeve 38, and one end of a spring 32 wound around the boss portion is placed in engagement with the lever 25 whereas the other end is placed in engagement with a pin 31 of the body 35. An engaging portion 37 of the throttle valve lever 29 is projected downwardly so that it may engage with the edge of the lever 25. In Fig. 1, the throttle valve lever 29 is pivotally urged counterclockwise by the force of the spring 36 to cause the engaging portion 37 to abut against the lever 25. The lever 25 is pivotally urged clockwise by the strong force of the spring 32 to close the throttle valve 27. When the lever 25 is rotated counterclockwise against the force of the spring 32 by a trigger wire 30, the throttle valve lever 29 also follows the lever 25 to increase an opening degree of the throttle valve 27. The anti-overrunning device for the internal combustion engine according to the present invention is composed of a vibrating pump 41, a vibration sensor 101 and an actuator 81 for reducing an opening degree of the throttle valve 27 by the throttle valve lever 29. The vibrating pump 41 has a diaphragm 58 sandwiched between cup-like housings 57 and 55 to form an atmospheric chamber 45 and a pressure chamber 46. Pad plates 42 and 51 are placed on both surfaces of a diaphragm 58, and a weight 44 is connected by means of a rivet 43. The pressure chamber 46 is provided with passages 56 and 47, to which port members 53 and 50, respectively, are connected. The port member 53 is provided with a check valve 54 to allow a flow of air from the passage 56 to a passage 52. The port member 50 is provided a check valve 48 to allow a flow of air from an atmospheric opening 49 to the passage 47 through a strainer 60 (refer to Fig. 4). The passage 52 is connected to a passage 103 of the vibration sensor 101 by a pipe 23. The vibration sensor 101 is so designed that a closure 105 having a passage 106 is connected to the end of a cuplike housing 102, and a ball 107 is urged against the end of a passage 103 by means of a spring 104 accomodated the housing 102. The actuator 81 has a diaphragm 84 sandwiched between cuplike housings 82 and 83 to form a pressure chamber 85 and a second chamber 86. An inlet 90 of the pressure chamber 85 is communicated with a passage 106 of a vibrating sensor 101 by means of a pipe 80. Pad plates 87 and 88 are placed on both surfaces of the diaphragm 84, the plates being connected by the base end of a rod 92. The rod 92 slidably inserted into a hole 91 of the housing 83 is retracted by means of a spring 89 surrounding the rod 92 and interposed between the pad plate 88 and the housing 83. The fore end of the rod 92 is placed into abutment with the aforementioned throttle valve lever 29. The pressure chamber 85 and the second chamber 86 are provided with orifices 93 and 94 in communication with atmosphere respectively, whereby the extreme operation of the actuator 81 may be restricted. The above-described vibrating pump 41 and vibration sensor 101 are preferably integrally connected to the lower end wall of the body 35 of the carbureter 24, and the actuator 81 is connected to the upper end wall of the body 35, as shown in Fig. 3. The vibration sensor 101 and the actuator 81 are connected by the pipe 23. However, the vibrating pump 41 and the vibration sensor 101 may be mounted suitably on the engine 10. Fig, 4 is an enlarged view showing an embodiment wherein a vibrating pump, a vibration sensor and an actuator are mounted on the body of a carbureter. It is to be noted that the diaphragm 58 of the vibrating pump 41 can be formed from a ground-fabric contained rubber plate, a thin resin plate and a thin metal plate other than a rubber plate. The shape of the diaphragm can be of a convolution type and a bellow-phragm type other than the flat plate. The weight 44 may be mounted interiorly of the pressure chamber 46 or mounted interiorly of both atmospheric chamber 45 and pressure chamber 46. The actuating point of the vibration sensor 101 may be suitably set by varying the diameter and weight of the ball 107, the set load of the spring 104, the inside diameter of the seat portion of the passage 103 and the like. A configuration may be made so that the ball 107 is urged against the passage 106 by means of a spring. When the vibrating pump 41 mounted on an engine 10 is subjected to vibrations of the engine, the weight 44 as well as a diaphragm 58 supporting the weight 44 vibrate, outside air is taken into a pressure chamber 46 via a check valve 48, and air in the pressure chamber 46 is fed toward the actuator 81 via a check valve 54. However, in the normal running condition of the engine, a pipe 23 is closed by a ball 107 subjected to the force of a spring 104 in the vibration sensor 101 and therefore a rod 92 of the actuator 81 is retracted by the force of a spring 89. In the overrunning condition, the vibration of the engine becomes violent, the ball 107 of the vibration sensor 101 grows restive against the force of the spring 104, and a passage of the pipe 23 is opened. Accordingly, positive or negative air is supplied from the vibrating pump 41 to a pressure chamber 85 of the actuator 81, and the rod 92 is projected. A throttle valve lever 29 as well as a valve shaft 28 are rotated by the rod 92 to reduce an opening degree of a throttle valve 27. In this manner, a quantity of the mixture supplied to the engine is reduced, as a consequence of which the number of revolutions of the engine is lowered and the overrunning is automatically prevented. In the following, the operation of the anti-overrunning device for the internal combustion engine according to the present invention will be described. Since in the state where the engine is less than a predetermined number of revolutions, the intensity of the vibrations of the engine is weak, the vibration sensor 101 is in its closed state, that is, the passage 103 is closed by the ball 107. Upon receipt of the vibration of the engine, the vibrating pump 41 vibrates up and down by the weight 44 supported on the diaphragm 58. When the diaphragm 58 is inflated upwardly, pressure of the pressure chamber 46 lowers, and therefore the check valve 48 opens to take air into the pressure chamber 46 from the atmospheric opening 49. Subsequently, when the diaphragm 58 is inflated downwardly the air of the pressure chamber 46 causes the check valve 54 to open and is discharged toward the pipe 23. However, since the passage 103 remains closed, when the pressure in the pressure chamber 46 is higher than the atmospheric pressure, the vibration of the diaphragm 58 is controlled. When the engine is in a level above a predetermined number of revolutions, that is, in an overrunning state, the ball 107 of the vibration sensor 101 vibrates against the force of the spring 104 to open the passage 103. The diaphragm 58 of the vibrating pump 41 is greatly vibrated by the weight 44, the air in the pressure chamber 46 is supplied to the pressure chamber 85 of the actuator 81 through the vibration sensor 101, and the rod 92 is forced down against the force of the spring 89. Thus, the throttle valve lever 29 is rotated along with the valve shaft 28, as shown by the chain lines in Fig. 4, and the opening degree of the throttle valve 27 is reduced. The flow rate of the mixture taken into the engine is reduced, and the number of revolutions of the engine decreases. When the number of revolutions of the engine decreases, the intensity of the vibrations transmitted from the engine to the vibration sensor 101 is weakened (the amplitude is small), and therefore again the passage 103 is closed by the ball 107. Then, the air in the pressure chamber 85 of the actuator 81 gradually flows outward, and the rod 92 is raised upward by the force of the spring 89. The throttle valve lever 29 is rotated counter-clockwise by the force of the spring 36, and the engaging portion 37 impinges upon the edge of the lever 25. In this manner, the opening degree of the throttle valve 27 increases, and again the number of revolutions of the engine increases. The opening degree of the throttle valve 27 is determined depending on the rotated position of the lever 25 operated by the trigger wire 30. When the number of revolutions of the engine again increases and exceeds a predetermined number of revolutions, the vibration sensor 101 again opens, and the opening degree of the throttle valve 27 is decreased by the actuator 81. The operation as described above is repreated whereby the engine is maintained less than a predetermined number of revolutions and the overrunning of the engine is automatically prevented without the operator's operation of the trigger wire 30 according to the variation of load. In the embodiment shown in Fig. 5, an actuator 181 connected to the upper end wall of the body 35 of the carbureter 24 is actuated by negative pressure supplied from a vibrating pump 141 through a vibration sensor 201. Members corresponding to those shown in Fig. 4 are indicated by reference numerals to which 100 are added. Provided in an atmospheric opening 149 of the vibrating pump 141 is a check valve 154 to allow a flow of air from a pressure chamber 146 to outside. On the other hand, provided on a passage 152 is a check valve 148 to allow a flow of air from the vibrating sensor 201 to the pressure chamber 146. The vibration sensor 201 is designed so that a ball 207 is urged against the end of a passage 152 by means of a spring 204 accomodated in a housing integral with a port member 150. A passage 206 is communicated with an inlet 190 of an actuator 181 through a pipe 180. The actuator 181 has a diaphragm 184 sandwiched between housings 182 and 183 to form a second chamber 186 and a pressure chamber 185, the second chamber 186 and pressure chamber 185 being communicated with atmosphere by orifices 194 and 193, respectively. A rod 192 connected to the diaphragm 184 is retracted by the force of a spring 189. When the engine exceeds a predetermined number of revolutions to increase vibrations, the diaphragm 158 is vibrated up and down by the weight 144 of the vibrating pump 141, and a ball 207 of the vibration sensor 201 grows restive against the force of the spring 204 to open the passage 152. Accordingly, air in the pressure chamber 185 of the actuator 181 is taken into the pressure chamber 146 through the pipe 180, the vibration sensor 201 and the check valve 148 and thence discharged from the pressure chamber 146 through the check valve 154. In this manner, the pressure chamber 185 is negative in pressure, the rod 192 is urged down against the force of the spring 189 only the throttle valve lever 29 is rotated clockwise, the opening degree of the throttle valve 27 is reduced, and the number of revolutions of the engine decreases. Thereafter, the overrunning of the engine is prevented in a manner similar to that of the embodiment shown in Fig. 4.

Claims: An anti-overrunning device for an internal combustion engine comprising a vibrating pump (41; 141) for generating pneumatic pressure by vibrations of the engine (10); an actuator (81; 181) having a rod (92; 192) for urging a throttle valve lever (29) in a direction of closing a throttle valve (27) by virtue of the pneumatic pressure of said vibrating pump; and a vibration valve (101; 201) positioned in the middle of a passage for communication between said vibrating pump (41; 141) and a pressure chamber (85; 185) of said actuator to open said passage by virtue of the vibrations of the engine during overrunning thereof, said vibrating pump comprising an atmospheric chamber (45; 145) and a pressure chamber (46; 146) which are defined within a housing by a diaphragm (58; 158), characterized by said diaphragm (58; 158) being provided with a weight (44; 144). An anti-overrunning device for an internal combustion engine according to claim 1, wherein said vibration valve (101; 201) comprises a ball (107; 207) received within a housing and urged by means of a spring (104; 204) in a direction of closing said passage. An anti-overrunning device for an internal combustion engine according to claim 1 or 2, wherein said actuator (81; 181) comprises a pressure chamber (85; 185) and a second chamber (86; 186) which are defined within a housing by a diaphragm (84; 184) supporting said rod (92; 192) and further comprises a spring (89; 189) for urging the rod connected to said diaphragm in a direction of opening said throttle valve (27). An anti-overrunning device for an internal combustion engine according to claim 3, wherein said pressure chamber (85; 185) and said second chamber (86; 186) of said actuator (81; 181) are provided with orifices which communicate with the exterior (93, 94; 193, 194). An anti-overrunning device for an internal combustion engine according to any of claims 1 to 4, wherein said vibrating pump (41) comprises a check valve (48) to allow flow of air from the exterior into the pressure chamber (46), and a check valve (54) to allow flow of air from the pressure chamber (46) into said actuator (81). An anti-overrunning device from an internal combustion engine according to any of claim 1 to 4, wherein said vibrating pump (141) comprises a check valve (148) to allow flow of air from said actuator (181) into the pressure chamber (146), and a check valve (154) to allow flow of air from the pressure chamber (146) to atmosphere.

Inventors: SEJIMO, YOSHIMI, TOBINAI, TERUHIKO, TSUBAI, TOSHIAKI
Applicants: WALBRO FAR EAST, INC.
Application year: 1988
Main classification: F02D17
IPC codes: F02D17, F02D11, F02D9