JP2012077640A - Two-cycle engine, and portable working machine including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stratified scavenging two-cycle engine which is excellent in startability and acceleration performance, and can clean exhaust gas.SOLUTION: A solenoid valve 12 is arranged on the upstream side relative to a check valve 11 of a leading air passage 10 connected to a scavenging passage 9 for connecting a scavenging port 8 of this stratified scavenging two-cycle engine to a crank chamber 1a. The opening/closing of the solenoid valve 12 is controlled by a solenoid valve drive device 17. The solenoid valve drive device 17 narrows down the solenoid valve 12 in start and acceleration by information of an engine revolution detection sensor 18, improves startability and acceleration performance, opens the solenoid valve 12 in rated operation, and reduces harmful substances of exhaust gas by increasing an air-fuel ratio.

Description

  The present invention relates to a two-cycle engine, and more particularly to a two-cycle engine capable of controlling the leading air flow rate for scavenging, improving startability and acceleration, and purifying exhaust gas, and a portable operation including the same. Related to the machine.

  2. Description of the Related Art In general, a two-cycle engine that is easy to achieve light weight and downsizing is widely used in a portable working machine such as a brush cutter for cutting plants and a chain saw for cutting trees. Further, an engine is known in which a governor device is provided as shown in Reference 1 so that the rotational speed does not increase too much.

  Further, in the above-described two-cycle engine, there is a problem that a mixed fuel of lubricating oil and gasoline is discharged as it is as unburned gas during scavenging. On the other hand, as shown in Reference 2, there is known a technique for suppressing unburned gas from being discharged to the outside as it is by separately taking leading air that pushes out combustion gas in advance instead of mixed fuel. ing.

JP-A-57-97035 JP 2008-14209 A

  However, since the governor device in the above-described prior art is configured to control the fuel in the intake passage to suppress the increase in the engine speed, in a two-cycle engine using a mixed fuel of gasoline and lubricating oil, lubrication is performed together with the fuel. Stopping the oil supply could reduce the life of the engine.

  Further, in the stratified scavenging type two-cycle engine, the cylinder chamber 2a can be sufficiently scavenged with air, and the air-fuel ratio of the air-fuel mixture (that is, the weight of air / the weight of fuel) is reduced. Although the amount of hydrocarbon (HC) and nitrogen oxide (NOX) emissions in the exhaust gas is reduced by making it larger than the fuel ratio (the air-fuel mixture is thin), the startability and acceleration are improved due to the large air-fuel ratio. There is a problem of being bad. To solve this problem, the air-fuel ratio should be reduced (the air-fuel mixture is thicker), but this will increase the emissions of hydrocarbons and nitrogen oxides in the exhaust gas and increase fuel consumption and fuel consumption. was there.

  The present invention has been made in view of the above problems, and the object of the present invention is to improve scavenging characteristics and to suppress engine overspeed while improving output and reducing exhaust gas. An object of the present invention is to provide a two-cycle engine and an engine working machine including the same.

  Of the inventions disclosed in the present application, typical features will be described as follows.

  According to one aspect of the present invention, a cylinder in which a piston can be moved up and down, a combustion chamber formed by a top surface, a ceiling wall, and a side wall of the piston in the cylinder, and a crank to which the piston is connected. A crank chamber in which a shaft is rotatably accommodated, a scavenging passage communicating the combustion chamber and the crank chamber, an intake passage having one end connected to the carburetor and the other end connected to the crank chamber, and the crank A two-cycle engine having a leading intake passage communicated between a fuel path extending from a combustion chamber to the combustion chamber via the scavenging passage, wherein the leading intake passage has an opening / closing valve for controlling an open / close state of the passage And the leading intake passage is throttled when the rotational speed of the crankshaft exceeds a first threshold value.

  According to still another feature, the portable work machine includes the above-described two-cycle engine.

  According to invention of Claim 1, the cylinder in which a piston is provided so that a vertical motion is possible, the combustion chamber formed in the said cylinder by the top surface of the said piston, the ceiling wall, and the side wall, The crankshaft to which the said piston is connected A crank chamber in which the combustion chamber is rotatably connected, a scavenging passage for communicating the combustion chamber and the crank chamber, an intake passage having one end connected to the carburetor and the other end connected to the crank chamber, and the crank chamber In a two-cycle engine having a leading intake passage communicated between a fuel path extending from the scavenging passage to the combustion chamber, an opening / closing valve for controlling an open / close state of the passage is provided in the leading intake passage. The ratio of the fuel in the air-fuel ratio of the fuel supplied to the combustion chamber by reducing the opening area of the leading intake passage when the rotation speed of the crankshaft exceeds a first threshold Increased, the air-fuel ratio of the mixture is reduced, it is possible to suppress an increase in rotational speed, it is possible to operate as a governor.

  According to the invention of claim 2, the on-off valve restricts the leading intake passage in the start operation region and the acceleration operation region and opens the passage in the rated operation region, so that at the time of start and acceleration, Inflow of air into the scavenging flow path is suppressed, the air ratio of the mixture is reduced, starting performance and acceleration are improved, and the air ratio of the mixture is increased during rated operation, and carbonization in the exhaust gas is performed. The discharge amount of hydrogen and nitrogen oxide can be reduced.

  According to the invention of claim 3, the second threshold value based on the rotation speed of the crankshaft is provided between the start operation region, the acceleration operation region, and the rated operation region, so that the optimum operation according to the operation region is achieved. Control can be performed.

  According to a fourth aspect of the present invention, the on-off valve is an electromagnetic valve including an electromagnet that is driven when a control current flows, and includes an engine speed detection sensor that detects an engine speed, and detects the engine speed. A highly responsive control can be performed by configuring an electromagnetic valve driving device that controls opening and closing of the electromagnetic valve in accordance with a signal of the device.

  According to the fifth aspect of the present invention, the leading intake passage includes a check valve that allows inflow from the leading air passage to the crank chamber and prevents backflow from the crank chamber to the leading air passage. In addition, the number of operations of the on-off valve can be reduced and the control can be simplified.

  According to the invention of claim 6, by providing the above-described two-cycle engine, it is possible to improve scavenging characteristics, and to suppress engine overspeed while realizing improvement in output and reduction in exhaust gas. An engine working machine including a cycle engine can be provided.

1 is an overall view of a portable work machine equipped with a stratified scavenging two-cycle engine of the present invention. The figure which shows a solenoid valve closed state in the layered scavenging two-cycle engine of this invention. The figure which shows a solenoid valve open state in the layered scavenging two-cycle engine of this invention. The figure which shows an example of control of electromagnetic valve opening / closing.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is an overall view of a portable working machine equipped with a stratified scavenging two-cycle engine to which the present invention is applied, FIG. 2 is a diagram showing a closed state of an electromagnetic valve in the stratified scavenging two-cycle engine of the present invention, and FIG. FIG. 4 is a diagram showing an example of control of opening / closing of the solenoid valve, in a state where the solenoid valve is open in the stratified scavenging two-cycle engine.

  The portable work machine shown in FIG. 1 includes an air-leading two-cycle engine 1003 and is configured as a brush cutter 1001. The portable work machine shown in FIG. A drive shaft that is rotatably supported is provided. The engine 1001 is configured as a two-cycle engine, and is particularly configured as an air-leading stratified scavenging two-cycle engine. The cutting blade 1002 is rotatably attached to a cutting blade mounting portion 1006 (gear case) at the tip of the operation rod 1004, and a cutting blade cover 1007 is attached to the worker side so that the cut grass is not scattered. . While the engine 1003 is driven, the brush cutter 1001 grips the gripping part attached to the end of the arm part extending in the left-right direction of the handle 1005 attached to the operation rod 1004 with both hands, and is provided in one gripping part. By operating the throttle lever, a carburetor (not shown) is operated via a throttle wire that passes through the handle 1005, thereby adjusting the throttle valve opening of the carburetor and adjusting the fuel supply amount. . When the opening of the throttle valve exceeds a predetermined value, sufficient fuel is ejected from the carburetor, the rotational speed of the engine 1003 is increased, a centrifugal clutch (not shown) is connected, and the cutting blade is rotated by the generated power. It is configured to work.

  FIG. 2 is a view showing a two-cycle engine 1003 of the present invention. A crankcase 1 is provided below the cylinder 2 in which a piston 5 connected to the crankshaft 4 by a connecting rod 6 reciprocates, and a scavenging passage 9 is provided so as to communicate from the crankcase chamber 1a to the cylinder chamber 2a. The mixture supply system including the carburetor 16, the throttle valve 14, and the check valve 13 communicates with the crankcase chamber 1 a, and the air supply system for supplying air communicates with the scavenging passage 9. In the cylinder chamber 2a, a scavenging port 8 leading to the scavenging flow passage 9 is opened, and an exhaust port 7 for exhausting combustion gas is opened.

  In the two-cycle engine 1003 configured as described above, when the piston 5 rises, the pressure in the crankcase chamber 1a starts to drop and the scavenging port 8 and the exhaust port 7 are closed. For this reason, the air-fuel mixture enters the crankcase chamber 1a where the pressure has decreased, and the air also enters the crankcase chamber 1a through the scavenging flow path 9. When the piston 5 reaches near the top dead center, the air-fuel mixture in the cylinder chamber 2a is ignited by the spark plug 3, and the piston 5 descends. Then, the pressure in the crankcase chamber 1a starts to rise, and the exhaust port 7 and the scavenging port 8 are opened. For this reason, the combustion gas is discharged from the exhaust port 7, and the air accumulated in the scavenging passage 9 is jetted from the scavenging port 8 to the cylinder chamber 2 a, and the combustion gas is forcibly discharged from the exhaust port 7. Then, after the air, the air-fuel mixture passes through the scavenging flow path 9 and enters the cylinder chamber 2a. Also, the piston 5 starts to rise, and the cycle as described above is repeated again.

  The engine speed changes by operating the throttle lever 15 to adjust the opening of the throttle valve 14 and controlling the flow rate of the air-fuel mixture flowing into the crankcase 1a.

  A check valve 11 is provided at the outlet of the leading air passage 10 to the scavenging flow path 9. An electromagnetic valve 12 is provided in the leading air passage 10 upstream of the check valve 11 and adjusts the air flow rate according to the engine speed, as will be described later.

  The solenoid valve 12 is provided in the leading air passage 10, and when electricity is not flowing through the electromagnet 12c, the solenoid valve 12 is pushed down by the spring 12b to close the leading air passage 10 (FIG. 2). When the electromagnet 12c is energized, the valve 12a is pulled up and the leading air passage 10 is opened by the passage interval a (FIG. 3).

  Based on the information obtained from the engine speed detection sensor 18, the solenoid valve drive device 17 instructs the opening and closing of the solenoid valve 12 based on the engine speed through the engine speed determination unit.

  Since the number of revolutions during idling operation and rated operation varies depending on the engine, the operation will be described with reference to FIG. First, in the case of 0 to 3,000 revolutions, it is determined that the engine is idling from the start (starting operation region), and the solenoid valve 12 is throttled. Since the engine is easier to start when the air-fuel ratio of the air-fuel mixture is smaller, the solenoid valve 12 is throttled to block the inflow of the leading air that causes the air-fuel ratio to increase. Next, in the case of 3,000 to 7,000 revolutions, the acceleration valve is determined to be in the acceleration operation region and the solenoid valve 12 is throttled. Since the acceleration performance is better when the air-fuel ratio is smaller, the solenoid valve 12 is throttled to block the inflow of the leading air that causes the air-fuel ratio to increase. Next, in the case of 7,000-10,000 rotations, it judges that it is a rated operation area | region and opens the solenoid valve 12. FIG. When the solenoid valve 12 is opened, the leading air passes through the leading air passage 10 and flows into the scavenging passage 9, and the exhaust gas value is improved by the air leading stratified scavenging. Finally, when the rated rotational speed exceeds 10,000, it is determined that the engine is overrun and the solenoid valve 12 is throttled. Overrun increases vibration and noise and shortens engine life. Therefore, when the rated rotational speed (rated rotational range) is exceeded, the electromagnetic valve 12 is throttled to reduce the air-fuel ratio, thereby suppressing the influence of overrun.

  As in the above example, the electromagnetic valve driving device 17 instructs the electromagnetic valve 12 to perform an operation most appropriate for the engine operating state based on information from the engine speed detection sensor 18.

As described above, in the configuration of the stratified scavenging two-cycle engine, the leading air that has previously pushed the burned gas in the cylinder bore and the air-fuel mixture that flows into the cylinder bore following the leading air slightly mix with the air in the cylinder. In view of the above, the air / fuel ratio is adjusted to be the optimum in that state. Therefore, by adjusting the inflow amount of the leading air by the electromagnetic valve 12, the mixing ratio can be adjusted so as to be an appropriate mixing ratio according to the rotational speed. In the present invention, the mixing ratio is adjusted in accordance with the rotational speed, and in particular, it is possible to suppress a further increase in the rotational speed by controlling the mixture to be in an excessive fuel state at the time of overrun. In addition, since the supply of mixed fuel containing lubricating oil does not stop,
Further, an electromagnetic valve 12 that controls the flow rate of air from the leading air passage 10 toward the scavenging passage 9, an engine speed detection sensor 18 that detects engine rotation, and information from the engine speed detection sensor 18 A solenoid valve drive device 17 that controls the opening and closing of the solenoid valve 12, and the solenoid valve drive device 17 determines, based on information from the engine speed detection sensor 18, whether the engine is starting, accelerating, or in rated operation. It is possible to improve the scavenging characteristics by opening the solenoid valve 12 during rated operation and opening the solenoid valve 12 during startup and acceleration, thereby improving output and reducing exhaust gas.

  As mentioned above, although demonstrated based on embodiment which shows this invention, this invention is not limited to the above-mentioned form, A various change is possible within the range which does not deviate from the meaning.

  For example, in this embodiment, the leading air passage is opened and closed by a solenoid valve, but a mechanical configuration that opens and closes the leading intake passage in conjunction with the engine speed may be used.

  In addition, the threshold values for the start operation region, the acceleration operation region, and the rated operation region are controlled by the number of revolutions, but depending on the operation state by the throttle lever, the time after the start, the load acting on the crankshaft, etc. The judgment may be made in a timely manner.

  Further, in this embodiment, an air leading method is adopted in which a leading intake passage that introduces outside air in accordance with the fuel passage is separately employed, but the fuel passage from the carburetor is branched to be divided into a thin fuel and a dense fuel, corresponding to air A light and dark scavenging system that performs the same control with a thin fuel to be used may be used.

  Further, the rotational speed of opening and closing of the solenoid valve 12 is not fixed, but may be determined so as to be able to operate smoothly according to the engine to be used, and the rotational speed may be changed by raising and lowering. Further, the electromagnetic valve 12 may be opened and closed gradually so that there is little shock when the electromagnetic valve 12 is opened and closed, and the passage interval a of the electromagnetic valve 12a may be switched linearly according to the rotational speed.

  Moreover, in this embodiment, the power supply of the engine speed detection sensor 18 and the solenoid valve drive device 17 uses the electric power generated by the magnet supplied to the spark plug 3, but the reverse current not used in the ignition. May be used. There is also a method using a battery or a capacitor.

  In the present embodiment, the leading air passage is opened when a current flows through the electromagnet, and the leading air passage is closed when the supply of current is stopped. However, the configuration may be reversed. That is, the leading air passage can be closed only when a current flows through the electromagnet, and in this way, for example, in an operation in which the rated operation state continues for a long time, current consumption can be reduced. .

1: Crankcase 1a: Crank chamber 2: Cylinder 2a: Cylinder chamber 3: Spark plug 4: Crankshaft 5: Piston 6: Connecting rod 7: Exhaust port 8: Scavenging port 9: Scavenging passage 10: Leading air passage
11: Check valve 12: Solenoid valve 12a: Valve 12b: Spring
12c: Electromagnet 13: Check valve 14: Throttle valve 15: Throttle lever 16: Vaporizer 17: Engine speed detection sensor 18: Speed discrimination section

Claims (6)

A cylinder provided with a piston movable up and down;
A combustion chamber formed in the cylinder by the top surface of the piston, a ceiling wall and a side wall;
A crank chamber in which a crankshaft to which the piston is connected is rotatably housed;
A scavenging passage communicating the combustion chamber and the crank chamber;
An intake passage having one end connected to the carburetor and the other end connected to the crank chamber;
A two-stroke engine comprising: a leading intake passage communicating between a fuel path from the crank chamber to the combustion chamber via the scavenging passage;
The leading intake passage is provided with an open / close valve that controls the open / close state of the passage,
A two-cycle engine characterized by narrowing the opening area of the leading intake passage when the rotational speed of the crankshaft exceeds a first threshold value. 2. The two-cycle engine according to claim 1, wherein the on-off valve restricts the leading intake passage in a start operation region and an acceleration operation region, and opens the passage in a rated operation region. 3. The two-cycle engine according to claim 2, wherein a second threshold value based on a rotational speed of the crankshaft is provided between the start operation region and the acceleration operation region and the rated operation region. The on-off valve is an electromagnetic valve provided with an electromagnet that is driven when a control current flows;
Equipped with a rotational speed detection sensor for detecting the rotational speed of the engine,
4. The electromagnetic valve driving device configured to control opening and closing of the electromagnetic valve in accordance with a signal of the engine speed detection device is configured. 5. 2 cycle engine. The leading intake passage further includes a check valve that allows inflow from the leading air passage to the crank chamber and prevents backflow from the crank chamber to the leading air passage. The two-cycle engine according to any one of claims 1 to 4. A portable work machine comprising the two-cycle engine according to any one of claims 1 to 5.