JP2018009538A - Bush cutter driven by internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress occurrence of vibration caused by the combustion state of an engine at the time of deceleration.SOLUTION: When deceleration is detected, misfire control is executed (S1). When the engine speed reaches 5,000 rpm or less (S2), switching is made to normal ignition timing control (S4). Since the combustion state becomes unstable during deceleration of an engine, sudden and relatively large vibration occurs. The vibration can be suppressed by executing the misfire control. When restarting the operation of the engine, vibration at the time of restarting the operation does not occur in a region in which the engine speed is 4,500 rpm to 5,500 rpm (62). By restarting the operation when the engine speed is 5,000 rpm, it is possible to suppress the occurrence of vibration at the time of restarting the operation.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a brush cutter driven by an internal combustion engine.

  The brush cutter is one of portable work machines, and has a drive source, that is, an engine or an electric motor connected to one end of a power transmission shaft, and a working unit connected to the other end of the shaft. It has a handle that traverses an operating tube that surrounds the shaft (Patent Document 1). The working unit is illustrated as a metal cutting blade rotating in the brush cutter of Patent Document 1, but is not limited thereto. The cutting blade may be a synthetic resin cord (referred to as “nylon cord”). Moreover, although the brush cutter of patent document 2 is provided with the cutting blade which reciprocates like a hedge trimmer, you may comprise the working part of a brush cutter with this reciprocating cutting blade.

  An engine type brush cutter is generally equipped with a single-cylinder two-stroke engine. The fuel supply mechanism for the engine may be a carburetor, or may be an electromagnetic fuel injection valve instead of the carburetor (Patent Document 3). A centrifugal clutch is interposed between the engine output shaft and the power transmission shaft. When the engine speed reaches a predetermined speed, the centrifugal clutch is engaged and the engine output is transmitted to the power transmission shaft. The operator can proceed with the work by holding the handle with both hands and moving the working part (cutting blade) to the left and right by swinging the arm to the left and right. The engine output can be controlled by the operator operating the throttle lever arranged on the handle.

  That is, the engine type brush cutter has a throttle valve in its intake system, and this throttle valve is linked to the throttle lever. The operator can open the throttle valve and increase the engine output by pulling the throttle lever. Conversely, when the operator releases the throttle lever, the throttle valve is fully closed (idle state), and the engine output is reduced.

  Patent Document 1 discloses in detail a mechanism for generating a high voltage to be supplied to an engine (ignition plug) of an engine type brush cutter, and also discloses an engine speed sensor in detail.

  The brush cutter is preferably mounted with a vibration absorber as means for mitigating unpleasant vibration caused by fluctuations in the combustion state of the engine (Patent Documents 4 to 6). However, for example, particularly when decelerating, the working unit tends to continue to operate due to inertia, so the drive unit does not immediately decelerate, and the time required for decelerating increases.

JP 2011-190732 A US 6,735,873 B2 JP 2013-119861 A JP 2005-168339 A JP 2009-261340 A WO2011 / 048697 (PCT / JP2009 / 068264)

  The engine type brush cutter has a problem that vibration is likely to occur during deceleration when the combustion state becomes unstable. That is, during deceleration, combustion in each cycle becomes unstable. Therefore, for example, when the throttle lever is released, that is, when the throttle valve is greatly displaced from the fully open state (full throttle) to the fully closed state (idle state), the engine decelerates toward the idle operation state. However, sudden and comparatively large vibrations easily occur due to intermittent ignition in the process of transient deceleration toward the idling operation.

  The operator adjusts the degree of the throttle lever drawing so as to achieve a desired steady-state engine speed for performing the work. That is, for the purpose of realizing a desired engine speed, the throttle lever is appropriately adjusted to adjust the drawing. During this adjustment, if the engine speed is too low, the operator pulls the throttle lever slightly. On the other hand, if the engine speed is too high, the operator slightly relaxes the force for pulling the throttle lever. In this fine adjustment process, the engine speed increases or decreases. Even in the deceleration process in the steady operation, sudden and relatively large vibrations may occur.

  In addition, the brush cutter often works in partial operation with the throttle valve half open. That is, the brush cutter does not always work at full throttle, but often works in partial operation.

  In the brush cutter, since the rotational inertia of the working part (cutting blade) is large, the reduction in the engine speed is delayed as the rotational force accompanying the inertia of the working part is transmitted to the downstream end of the power transmission shaft during deceleration. . That is, the brush cutter has a relatively slow decrease in engine speed, and the time required for deceleration is relatively long compared to a working machine such as a chain saw having a small inertial force.

  Although the engine combustion state becomes unstable during deceleration, vibration generated by the unstable combustion state is transmitted to the operator through the handle, which is uncomfortable for the operator. Further, even with a brush cutter equipped with the vibration absorbing device disclosed in Patent Documents 4 to 6, there is a case where the vibration absorbing device cannot absorb vibration during deceleration.

  An object of the present invention is to provide a brush cutter that can suppress the occurrence of vibration due to the combustion state of the engine during deceleration on the premise of a brush cutter driven by an internal combustion engine.

According to the present invention, the above technical problem is
A throttle valve that is an output control valve;
An internal combustion engine with a spark plug;
A throttle lever mechanically connected to the throttle valve for controlling the output of the internal combustion engine and operable by an operator;
A power transmission shaft having one end connected to the output shaft of the internal combustion engine;
A cutting blade connected to the other end of the power transmission shaft;
A throttle position sensor that is positioned in relation to the throttle valve or the throttle lever and detects an opening of the throttle valve;
Misfire control means for misfiring the internal combustion engine when it is detected that the internal combustion engine is in a deceleration state based on a signal from the throttle position sensor;
Ignition resumption control means for stopping the misfire control and resuming normal ignition timing control when it can be assumed that the rotation speed of the internal combustion engine has reached a predetermined return rotation speed,
The return rotational speed is achieved by providing a brush cutter that is set in a no-vibration region that does not generate vibration when the misfire control is stopped and switched to normal ignition timing control.

  Specific examples of the “misfire control” in the present invention include (1) control for stopping the application of a high voltage to the spark plug and (2) control for greatly delaying the ignition timing. Further, in the “ignition resumption control means”, it can be considered that the rotational speed of the internal combustion engine has reached a predetermined return rotational speed based on a predetermined time from the start of misfire control or a predetermined rotational speed of the engine output shaft. Of course, an engine speed sensor may be prepared, and the engine speed detected by the engine speed sensor may be regarded as having reached a predetermined return speed.

  The effects and other objects of the present invention will become apparent from the detailed description of the following examples.

It is a perspective view of the brush cutter of an Example. It is sectional drawing of the connection part of the engine and power transmission shaft which are included in an Example, and is a figure for demonstrating that the vibrational absorption apparatus exists in this connection part. It is a block diagram which shows the whole outline | summary of the electronic controller of the brush cutter of an Example. It is a diagram related to vibration that is likely to occur when the amount of change in the closing direction of the throttle valve is large and the change is rapid, in the region where sudden vibration occurs in the deceleration process and when ignition of the engine is restarted It is a figure for demonstrating the area | region which a vibration does not generate | occur | produce. FIG. 6 is a flowchart for explaining a first control example suitable for preventing vibration that is likely to occur when the throttle valve changes rapidly from a fully open state to a fully closed state as a typical example; 6 is a flowchart for explaining a second control example that is a modification of the first control example of FIG. 5. 12 is a flowchart for explaining a third control example suitable for preventing vibrations that are likely to occur when the throttle valve opening is finely adjusted in order to achieve a desired engine speed. It is explanatory drawing for demonstrating detecting a deceleration state using the 1st, 2nd threshold value which adjoins. FIG. 12 is a flowchart for explaining a fourth control example suitable for preventing vibrations that are likely to occur when the throttle valve opening is finely adjusted to achieve a desired engine speed. FIG. 10 is a flowchart for explaining a fifth control example suitable for preventing vibration that is likely to occur when the throttle valve opening is finely adjusted to achieve a desired engine speed. 12 is a flowchart for explaining a sixth control example suitable for preventing vibrations that are likely to occur when the throttle valve opening is finely adjusted in order to achieve a desired engine speed. FIG. 10 is a flowchart for explaining a seventh control example suitable for preventing vibrations that are likely to occur when the throttle valve opening is finely adjusted to achieve a desired engine speed. It is a figure for demonstrating the 1st example of the ignition timing control map used for control at the time of the steady driving | operation employable for the brush cutter of an Example. It is a figure for demonstrating the 2nd example of the ignition timing control map used for control at the time of the steady driving | operation employable for the brush cutter of an Example. It is a graph which shows the state of the vibration which generate | occur | produces at the time of partial driving | running | working in the conventional brush cutter. Here, the vertical axis represents the engine speed. It is a graph which shows the state of the vibration which generate | occur | produces at the time of partial driving | running | working in the conventional brush cutter. Here, the vertical axis is the vibration value. It is a flowchart for demonstrating the ignition timing control of the map switching in a steady driving state.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a portable brush cutter 100 to which the present invention is applied. The brush cutter 100 includes a driving unit 2, a cutting blade 4 that constitutes a working unit, and a power transmission shaft 6 that couples the driving unit 2 and the cutting blade 4. The power transmission shaft 6 has one end connected to the drive unit 2 and the other end connected to the cutting blade 4.

  The drive unit 2 typically includes a two-cycle internal combustion engine 8, a fuel tank 10, and the like, and further includes a microcomputer 12 (FIG. 3) for engine control. The microcomputer 12 controls the ignition timing of the ignition plug 54 (FIG. 3) of the engine 8.

  Returning to FIG. 1, the power transmission shaft 6 is surrounded by the operation tube 14. A handle 16 is detachably attached to the operation tube 14. The handle 16 extends across the operation tube 14, and grips 18 are attached to the left and right ends, respectively. That is, the handle 16 has a right grip 18R and a left grip 18L, and an operator operates the brush cutter 100 while holding the grips 18R and 18L with left and right hands.

  A throttle lever 20 for manually controlling engine output is attached to the right grip 18R. As is well known, the throttle lever 20 is mechanically linked to a throttle valve, typically by a wire. An operator can control the opening degree of the throttle valve by operating the throttle lever 20 as an operation unit. As a result, the output of the engine 8 can be controlled.

  Details of the connecting portion between the engine 8 and the power transmission shaft 6 are shown in FIG. In FIG. 2, reference numeral 8 a indicates an output shaft (crankshaft) of the engine 8. The output shaft 8 a is connected to the power transmission shaft 6 via the centrifugal clutch 30 and the vibration absorbing device 32. The vibration absorbing device 32 has a torsion coil spring 34, and the torsion coil spring 34 absorbs vibration. The vibration absorbing device 32 illustrated in FIG. 2 is described in detail in Patent Document 5 (Japanese Unexamined Patent Application Publication No. 2009-261340), and thus detailed description thereof is omitted. The vibration absorber 32 may have the configuration disclosed in Patent Document 4 or the configuration disclosed in Patent Document 6. The vibration absorber 32 is not necessarily essential. The vibration absorbing device 32 may be omitted from the brush cutter 100 and the centrifugal clutch 30 and the power transmission shaft 6 may be directly connected.

  The above-described configuration of the brush cutter 100 described with reference to FIGS. 1 and 2 is conventionally known. Since this general outline is described in Patent Documents 1 and 2, detailed description thereof is omitted.

  FIG. 3 shows an overall outline of the electronic control unit 40 of the brush cutter 100. The electronic control device 40 has a control unit 42 including the microcomputer 12 described above. Ignition timing control is executed by the control unit 42.

  A signal from the engine speed sensor 44 is input to the control unit 42. The engine speed sensor 44 has a function of detecting the speed of the engine 8. The control unit 42 also receives a signal from a throttle position sensor 46 related to the opening of the throttle valve. The throttle position sensor 46 outputs a signal related to the opening of the throttle valve.

  Specific examples of the throttle position sensor 46 include: (1) a fully open (WOT) detection switch that detects that the throttle valve is fully open and outputs an ON or OFF signal; and (2) the throttle valve is in an idle position (fully closed state). ) Idle detection switch that outputs an ON or OFF signal and (3) a partial (POT) detection switch that detects that the throttle valve is in a predetermined half-open state and outputs an ON or OFF signal (4) A throttle opening linear sensor that linearly detects the opening of the throttle valve from fully closed to fully open can be exemplified.

  The (1) fully open (WOT) detection switch, (2) idle detection switch, and (3) partial (POT) detection switch are devices whose output is inverted under a predetermined condition. It is arranged in the vicinity of the throttle lever 20 or the throttle valve shaft. When the operator fully pulls the throttle lever 20, the fully open (WOT) detection switch outputs an ON signal. When the operator releases the throttle lever 20, the idle detection switch outputs an ON signal. When the operator pulls the throttle lever 20 to a predetermined pulling / drawing position, the partial (POT) detection switch outputs an ON signal.

  The throttle opening linear sensor (4) is arranged, for example, on the throttle valve shaft or handle 16 or its relay portion, and the opening degree of the throttle valve from the fully closed position (idle position) to the fully open position (full throttle position). Is detected linearly.

  When, for example, a throttle opening linear sensor is employed as the throttle position sensor 46, the above-mentioned full open (WOT) detection switch, partial (POT) detection switch, and idle detection switch can be omitted.

First control example (FIGS. 4 and 5) :
FIG. 4 shows that in a conventional brush cutter, sudden and relatively large vibrations that are likely to occur when the opening of the throttle valve is changed quickly and largely from full throttle (fully open position) to fully closed (idle position). It is a figure for demonstrating. When the throttle valve changes in the closing direction, the engine speed decreases. In the process of decreasing the engine speed, sudden and relatively large vibrations are generated in the first region 60 up to a speed slightly higher than 5,000 rpm. The numerical value of 5,000 rpm is merely an example. Of course, there are variations depending on the model. The reason why sudden and comparatively large vibration is generated in the deceleration process is considered that the combustion state of the engine 8 during deceleration becomes unstable.

  More specifically, the deceleration process is considered to be because a cycle in which an explosion occurs in the combustion chamber is sometimes mixed with a cycle in which the explosion hardly occurs in the combustion chamber. This is considered to be a cause of sudden vibration.

  Therefore, in the first region 60, if the control that does not cause an explosion in the combustion chamber is added, the cause of the sudden and relatively large vibration described above can be eliminated. That is, during the deceleration process, in the first region 60, it is possible to fundamentally prevent the occurrence of sudden and relatively large vibrations by executing control that does not cause an explosion in the combustion chamber. Controls that do not cause an explosion in the combustion chamber are called “misfire control”. As misfire control, (1) control to stop applying high voltage to the spark plug, and (2) control to greatly retard the ignition timing. be able to.

  If misfire control is executed in the deceleration process, then it is necessary to stop misfire control and return to normal ignition timing control. However, when resuming ignition, it is desirable to suppress the occurrence of vibrations associated therewith.

  Continuing to refer to FIG. 4, it was experimentally discovered that the second region 62 including 5,000 rpm does not generate vibration even when ignition is resumed. This second region 62 is referred to as a “no vibration region”. Specifically, the engine speed of the non-vibration region 62 is 4,500 rpm to 5,500 rpm. If the engine speed defines the preferred timing for stopping the misfire control and switching to the normal ignition timing, after the misfire control is stopped, the normal ignition timing control is resumed at an engine speed of 4,500 rpm to 5,000 rpm. Is good. This 4,500 rpm to 5,000 rpm is higher than the engine speed (3,500 rpm) at which the centrifugal clutch 30 is engaged. That is, the return timing to the normal ignition timing control is preferably set to an engine speed higher than the engine speed of the clutch in the centrifugal clutch 30. In the non-vibration region 62, even when the misfire control is switched to the normal ignition timing control, no vibration is generated at the time of this control switching, but in the third region 64 below this, vibration accompanying the return is generated. The return vibration generation region 64 includes 3,500 rpm at which the centrifugal clutch 30 (FIG. 2) is engaged, and further corresponds to a region up to 2,500 rpm, which is the idling speed.

  That is, during the deceleration process, when the ignition was restarted (returned to the normal ignition timing control) in the region where the rotational speed was lower than 4,500 rpm, the accompanying vibration was observed. Based on this fact, in the deceleration process, the timing for stopping the misfire control and returning to the normal ignition timing control is preferably set in the non-vibration region 62 described above, that is, the vicinity region including 5,000 rpm. By setting the “return speed” in the non-vibration region 62 and reaching the return speed, the misfire control is stopped and the normal ignition timing control is resumed, thereby generating vibrations accompanying the return of the ignition. Can be suppressed.

  FIG. 5 is a flowchart of the first control example. An idle detection switch is prepared to implement the first control example. When the throttle lever 20 is released and the throttle valve is in the fully closed position, that is, in the idle position, the idle detection switch is turned on. With reference to the flowchart of FIG. 5, it is determined in step S1 whether or not the idle detection switch is ON. If Yes in step S1, it is determined that the throttle valve 20 has been displaced to the fully closed position because the operator has released the throttle lever 20, and the process proceeds to step S2 to determine whether the engine speed is equal to or less than the “return speed”. Is determined. If No at step S1, the routine proceeds to step S4 where normal ignition timing control is executed.

  Here, the “return speed” is set to an arbitrary engine speed in the non-vibration region 62 (FIG. 4) in which no vibration is generated even when ignition is resumed. Specifically, in this embodiment, 5,000 rpm is set as the “return speed”.

  When the current engine speed is larger than the “return speed” in step S2, the process proceeds to step S3 because of No, and misfire control is executed. As described above, the misfire control can be exemplified by (1) control for stopping application of a high voltage to the spark plug and (2) control for greatly delaying the ignition timing. By executing the misfire control, combustion and explosion in the engine combustion chamber can be substantially prevented.

  If it is determined in step S2 that the current engine speed is equal to or less than the “return speed”, the process proceeds to step S4 to stop misfire control and switch to normal ignition timing control.

  The first control example occurs when the throttle valve is rapidly displaced in the closing direction and the amount of change is relatively large, typically when the throttle valve is rapidly displaced from the fully open position to the fully closed position. This is effective in preventing sudden and comparatively large vibrations that are easily generated.

Second control example (FIG. 6) :
The second control example of FIG. 6 is also a modification of the first control example (FIG. 5). Accordingly, the same steps as those in the first control example are denoted by the same reference numerals, and the description thereof is omitted.

  In S2, when the current engine speed is equal to or lower than the “return speed”, the process proceeds to step S4, where the misfire control is stopped and the control is switched to the normal ignition timing control, as in the first control example (FIG. 5). It is. However, in this second control example, before stopping the misfire control and returning to the normal ignition timing control, it is determined in step S5 whether or not it is a cycle for returning from the misfire control. When it is a cycle to return from the control, the routine proceeds to step S6, and the retard angle control is executed during n cycles before returning to the normal ignition timing control. That is, an ignition timing delayed by a predetermined angle from the normal ignition timing is set, and ignition is performed based on this retarded ignition timing. This retard angle control is intended to make the instability larger than the combustion state by ignition at the normal ignition timing.

  As described above, in step S6, immediately before returning from the misfire control to the normal ignition timing control, an ignition timing is set by retarding the ignition timing of the normal ignition timing control by a predetermined angle. Since the combustion state becomes unstable when ignition is performed at a retarded ignition timing rather than normal ignition timing control, the recovery of the engine output becomes slower. That is, ignition is performed n times based on the ignition timing that is relatively difficult to burn, and then the normal ignition timing control is restored.

  Thereby, for example, the engine speed adjacent to or entering the third area 64 below the second area 62 can be set as the “return speed”. In other words, as indicated by an arrow A in FIG. 4, the second region, that is, the non-vibration region 62 can be substantially expanded downward (in the direction in which the engine speed decreases).

Third control example (FIG. 7) :
In partial operation, in order to achieve a desired engine speed, the adjustment of the throttle lever 20 is often finely adjusted. If it becomes higher than the desired engine speed, the grip of the throttle lever 20 is loosened and the throttle valve is displaced in the closing direction. On the contrary, if the engine speed is lower than the desired engine speed, the throttle lever 20 is strengthened to displace the throttle valve in the opening direction. By repeating this, a desired engine speed is realized. Vibration is likely to occur during this operation. Specifically, vibration is likely to occur when the throttle lever 20 is loosened, that is, when the throttle valve is slightly displaced in the closing direction. This vibration is sudden and relatively large. This third control example is suitable for suppressing the occurrence of this vibration. A third control example will be described based on the flowchart of FIG.

  In the vibration generation prevention control during deceleration according to the flowchart of FIG. 7, it is most preferable to employ a throttle opening linear sensor as the throttle position sensor 46. That is, it is preferable to execute the vibration prevention control using a sensor that can linearly detect the opening degree of the throttle valve.

  Referring to FIG. 7, when it is detected in step S11 that the throttle valve is changing in the closing direction, the process proceeds to step S12 to check whether the throttle valve opening has passed a threshold value, that is, a predetermined opening. A determination is made. When the opening degree of the throttle valve is larger than the predetermined opening degree, the routine proceeds to step S13 and normal ignition timing control is performed. In step S12, when the opening of the throttle valve passes the threshold value and changes to an opening smaller than the threshold value, the threshold value passage is reset in step S14, and then the process proceeds to step S15 to control misfire. Is executed. This misfire control is intended to substantially prevent ignition in the engine combustion chamber as described in the first control example (FIG. 5).

  In the next step S16, it is determined whether or not the current engine speed detected by the engine speed sensor 44 is equal to or greater than the “return speed” described above. If "No" is determined in step S16, it means that the engine speed is lower than the return speed, so that the routine proceeds to step S17 and the normal ignition timing control is returned. That is, the misfire control so far is stopped, and normal ignition timing control is executed instead. As a result, combustion and explosion in the engine combustion chamber are resumed. Since the combustion / explosion is resumed in the above-described region 62 (FIG. 4), there is almost no vibration associated with the resumption of ignition.

  If it is determined in step S16 that the current engine speed detected by the engine speed sensor 44 is equal to or greater than a predetermined return speed, the process proceeds to step S18 to determine whether the throttle valve opening has increased. Is determined. That is, it is determined whether or not the operator has performed an operation of pulling down the throttle lever (an operation of increasing the engine output). If "No" in step S18, the process returns to step S15 and misfire control is continued. On the other hand, if “Yes” in step S18, it is determined that there is a possibility that the operator is requesting to increase the engine output, and the process proceeds to step S19.

  In step S19, when the change in the opening of the throttle valve, that is, the amount of change in the direction in which the opening of the throttle valve increases, is greater than a predetermined value, it is determined that the operator is seeking to increase the engine output, and step S17 is performed. Proceed to step 4 to perform combustion and explosion in the engine combustion chamber. That is, the conventional misfire control is switched to the normal ignition timing control (ignition restart). In step S19, when the change in the opening of the throttle valve is slight, it is determined that the operator does not seek to increase the engine output, and the routine proceeds to step S20, where the misfire control is continued. This misfire control is continued until the "return speed" described above is reached (S21).

  As a modification of the third control example, the retard angle control (S6) of FIG. 6 may be added before returning from the misfire control to the normal ignition timing control in step S17.

Fourth control example (FIGS. 8 and 9) :
As in the third control example (FIG. 7), this fourth control example finely adjusts the grip of the throttle lever 20 (throttle valve opening) in order to achieve a desired engine speed. It is suitable for preventing vibrations that sometimes occur.

  The outline of the fourth control example will be described with reference to FIG. 8. As a typical example, when the operator loosens the force of pulling the throttle lever 20, the throttle valve is displaced in the closing direction. Along with this, the engine 8 is decelerated (the engine speed decreases). When the throttle valve is half open, two adjacent openings are set as “first threshold value A” and “second threshold value B”. The valve opening degree of the first threshold value A is larger than the valve opening degree of the second threshold value B (first threshold value A> second threshold value B). Therefore, by detecting that the opening of the throttle valve becomes smaller than the first threshold A and then smaller than the second threshold B over time, the engine is now You can know that you are in the deceleration process.

  When the opening of the throttle valve becomes smaller than the second threshold value B, the misfire control described above is executed. The timing at which misfire control is released, that is, when normal ignition timing control is resumed, is defined by counting up the number of revolutions N of the engine output shaft 8a in the fourth control example (FIG. 9). When the engine output shaft 8a rotates 30 times after the misfire control is started, the misfire control is stopped and normal ignition timing control is resumed (ignition restart). The number of times of 30 is less than about 1 second in terms of time, and ignition is restarted before the operator notices the execution of this control.

  In the misfire control performed during engine deceleration and the subsequent start of the normal ignition timing control, the engine speed (return speed) when starting the normal ignition timing control is described above with reference to FIG. It is preferably within the range of the non-vibration region 62 (FIG. 4). For this purpose, it is preferable that the number of rotations N (30 in the above example) of the engine output shaft 8a can be arbitrarily changed until the ignition is restarted. Further, the timing at which misfire control is released, that is, when normal ignition timing control is resumed, may be defined by time instead of the number of rotations N of the output shaft 8a. That is, when a predetermined time has elapsed from the start of misfire control, the misfire control may be stopped and normal ignition timing control may be started. It is preferable that the predetermined time can be arbitrarily changed.

  That is, also in the fourth control example, the engine speed when the misfire control is stopped and the normal ignition timing control is resumed is a value included in the non-vibration region 62 (about 5,000 rpm: FIG. 4). Is preferred.

  A fourth control example will be described based on the flowchart of FIG. In the fourth control example, two partial (POT) detection switches are prepared as the throttle position sensor 46. That is, the inversion of the output signal of the first partial (POT) detection switch detects that the opening of the throttle valve is the first threshold value A, and the inversion of the output signal of the second partial (POT) detection switch Thus, it is detected that the opening degree of the throttle valve is the second threshold value B. Of course, by employing a throttle opening linear sensor as the throttle position sensor 46, the first and second partial (POT) detection switches can be omitted.

  In step S31 of FIG. 9, it is determined whether or not the opening degree of the throttle valve has passed the first threshold value A. If Yes, the opening degree of the throttle valve has passed the first threshold value A. Proceed to step S32. In step S32, it is determined whether or not the opening of the throttle valve has passed the second threshold value B. If No, the routine proceeds to step S33, assuming that the vehicle is not decelerating, and normal ignition timing control is executed. The

  If Yes in step S32, it is determined that the vehicle is decelerating, and the passage of the first threshold value A and the second threshold value B is reset in step S34. Then, the process proceeds to step S35 and "misfire control" is executed. Is done. This misfire control is intended to prevent the air-fuel mixture from substantially burning as described above. In the next step S36, it is determined whether or not the number of rotations of the engine output shaft 8a from the start of misfire control is less than N times. The N times define a period during which misfire control is executed, and for example, 30 times is set.

  Even if the throttle valve opening change (in the direction in which the throttle valve opening increases) during the misfire control and the throttle valve opening change passes the second threshold B, the first threshold Unless passing through A, the process proceeds from step S38 to step S39. Then, misfire control is executed in step S39, and it is determined whether or not the number of rotations of the engine output shaft 8a accumulated since the start of misfire control in the next step S40 is less than N times. When the cumulative number of rotations of the engine output shaft 8a has reached N times, the routine proceeds to step S41, where misfire control is stopped and normal ignition timing control is resumed (ignition restart).

  A case where the throttle lever 20 is operated during the deceleration process will be described. Even if the opening degree of the throttle valve passes the second threshold value B and becomes larger than the second threshold value B, the process proceeds to step S39 as long as the first threshold value A is not passed, and misfire control is performed. Is executed as described above. When the opening of the throttle valve passes the second threshold value B and also passes the first threshold value A, it is determined that the operator is requesting an increase in engine output, and the routine proceeds to step S41, where normal ignition is performed. Timing control is executed. In step S42, the passage of the first and second threshold values A and B is reset.

  As a modification of the fourth control example, the retard angle control (S6) of FIG. 6 may be added before returning from the misfire control to the normal ignition timing control in step S41.

Fifth control example (FIG. 10) :
In the fifth control example, as in the third control example (FIG. 7) and the fourth control example (FIG. 9), the control of the throttle lever 20 is adjusted to achieve a desired engine speed. This is suitable for preventing vibrations that are likely to occur during fine adjustment. The fifth control example is also a modification of the fourth control example (FIG. 9). In the fifth control example, a throttle opening degree linear sensor is adopted as the throttle position sensor 46, and the opening degree of the throttle valve is detected linearly.

  In step S51 in FIG. 10, it is determined whether or not the opening of the throttle valve is being reduced. If yes, it is determined that the vehicle is decelerating and the process proceeds to step S52. In step S52, it is determined whether or not the opening of the throttle valve has passed the threshold value. If No, the routine proceeds to step S53, where normal ignition timing control is executed.

  If Yes in step S52, it is determined that the opening of the throttle valve has passed the threshold value, the passage of the threshold value is reset in step S54, and then the process proceeds to step S55 to perform misfire control. In the next step S56, it is determined whether or not the number of rotations of the engine output shaft 8a from the start of misfire control is less than N times. The N times define a period during which misfire control is executed, and for example, 30 times is set.

  It is determined whether or not there is a change in the direction in which the throttle valve opening increases during the misfire control (S57). As long as there is no change in which the opening of the throttle valve increases, the misfire control in step S55 is continued. When the number of rotations of the engine output shaft 8a from the start of misfire control reaches a predetermined N times (for example, 30 times), the process proceeds to step S61 to stop misfire control, and normal ignition timing control is resumed (restart ignition). ). It is desirable to set the predetermined N times so that the engine speed when the ignition timing control is resumed is a speed that belongs to the non-vibration region 62 (FIG. 4), for example, 5,000 rpm. Thereby, generation | occurrence | production of the vibration accompanying engine operation resumption can be suppressed.

  A case where the throttle lever 20 is operated during the deceleration process will be described. If there is a change that increases the throttle valve opening during misfire control, if the change in opening is greater than or equal to a certain value in step S58, it is determined that the operator is seeking to increase the engine output and the process proceeds to step S61. To resume normal ignition timing control. On the other hand, when the change in which the opening degree of the throttle valve increases is smaller than the predetermined value in step S58, it is determined that the operator does not seek to increase the engine output, and the process proceeds to step S59 where misfire control is executed. The Then, in the next step S60, it is determined whether or not the number of rotations of the engine output shaft 8a accumulated since the start of misfire control is less than N. When the accumulated number of rotations of the engine output shaft 8a reaches N times, the process proceeds to step S61, the misfire control is stopped, and the normal ignition timing control is resumed.

  As a modification of the fifth control example, the retard angle control (S6) of FIG. 6 may be added before returning from the misfire control to the normal ignition timing control in step S61.

Sixth control example (FIG. 11) :
The sixth control example is another modification of the fourth control example (FIG. 9). In this sixth control example, it is preferable to prepare two partial (POT) detection switches as the throttle position sensor 46. That is, the inversion of the output signal of the first partial (POT) detection switch detects that the opening of the throttle valve is the first threshold value A, and the inversion of the output signal of the second partial (POT) detection switch Thus, it is detected that the opening degree of the throttle valve is the second threshold value B.

  In FIG. 11, in step S71, it is determined whether or not the opening degree of the throttle valve has passed the first threshold value A. If Yes, the opening degree of the throttle valve has passed the first threshold value A. Then, the process proceeds to step S72. In step S72, it is determined whether or not the opening of the throttle valve has passed the second threshold value B. If No, the routine proceeds to step S73, assuming that the vehicle is not decelerating, and normal ignition timing control is executed. The

  If Yes in step S72, it is determined that the vehicle is decelerating, and the passage of the first threshold value A and the second threshold value B is reset in step S74. Then, the process proceeds to step S75 and misfire control is executed. . In the next step S76, it is determined whether or not the current engine speed detected by the engine speed sensor 44 is equal to or greater than a predetermined “return speed”. As described above, the “return speed” is set in the non-vibration region 62 (FIG. 4) in which there is almost no vibration associated with the resumption of ignition when switching from misfire control to normal ignition timing control (typical). 5,000rpm).

  The misfire control is continued until the decreasing engine speed reaches the return speed (S77, S75). When the current engine speed reaches the return speed, the routine proceeds to step S81, where the misfire control is switched to the normal ignition timing control (ignition restart).

  Even if the throttle valve opening change (in the direction in which the throttle valve opening increases) during the misfire control and the throttle valve opening change passes the second threshold B, the first threshold Unless passing through A, the process proceeds from step S78 to step S79. In step S79, misfire control is executed, and in the next step S80, it is determined whether or not the engine speed is equal to or higher than a predetermined “return speed”. When the engine speed reaches the return speed, the routine proceeds to step S81 where the misfire control is switched to the normal ignition timing control.

  As a modification of the sixth control example, the retard angle control (S6) of FIG. 6 may be added before returning from the misfire control to the normal ignition timing control in step S81.

  A case where the throttle lever 20 is operated during the deceleration process will be described. Even if the opening degree of the throttle valve passes the second threshold value B and becomes larger than the second threshold value B, the process proceeds to step S79 as long as the first threshold value A is not passed, and misfire control is performed. Is executed as described above. When the opening of the throttle valve passes the second threshold value B and also passes the first threshold value A, it is determined that the operator is requesting the engine output to be increased, and the routine proceeds to step S81 and normal ignition is performed. Timing control is executed. In step S82, the passage of the first and second threshold values A and B is reset.

Seventh control example (FIG. 12) :
This seventh control example is suitable for preventing vibrations that are likely to occur when the throttle valve opening is finely adjusted to achieve the desired engine speed, and this seventh control example is implemented. One partial (POT) detection switch is prepared for this purpose. In FIG. 12, it is determined in step S91 whether or not the POT detection switch is ON. If it is determined Yes in step S91, it is determined that the engine 8 is in a decelerating state, and whether the current engine speed detected by the engine speed sensor 44 is a predetermined value, for example, 6,000 rpm or more, in step S92. It is determined whether or not. If it is determined Yes in this step S92 (6,000 rpm or more), the process proceeds to the next step S93, and misfire control is executed for a predetermined period. Here, the predetermined period may be defined as a predetermined time from the start of misfire control, or may be the number of rotations (for example, 10 times) of the engine output shaft 8a when counted up from the start of misfire control. . This predetermined period may be arbitrarily changed.

  After the misfire control is executed for a predetermined period in step S93, the misfire control is switched to the normal ignition timing control in step S94. Then, in the next step S95, it is determined whether or not the current engine speed detected by the engine speed sensor 44 is a predetermined value (for example, 6,000 rpm) or more.

  When the current engine speed is greater than or equal to the predetermined value, the process returns to step S91. On the other hand, when the current engine speed is smaller than the predetermined value, the routine returns to step S94 and normal ignition timing control is continued.

  As a modified example of the seventh control example, the retard angle control (S6) of FIG. 6 may be added before returning from the misfire control to the normal ignition timing control in step S94.

  In the foregoing, a plurality of control examples have been described for the misfire control and the return to the normal ignition timing control that are executed when the throttle valve is displaced in the closing direction and the engine 8 is decelerated. Of course, each step included in the plurality of control examples can be replaced with each other in each control example. That is, the steps included in each control example may be arbitrarily combined in order to prevent the occurrence of vibration that is likely to occur during deceleration.

  Next, a control example that is preferably added to the embodiment of the present invention will be described.

Vibration suppression control during steady operation (FIGS. 13 to 17) :
FIG. 13 is a diagram for explaining an ignition timing control map during steady operation. The vertical axis in FIG. 13 represents the angle before the top dead center (BTDC). The broken line in FIG. 13 shows a conventional control map.

  With reference to the conventional ignition timing control of the broken line in FIG. 13, the conventional ignition timing control in the steady operation is, for example, that the ignition timing is gradually increased as the engine speed (rpm) increases from about 3,000 rpm to about 8,000 rpm. It has the characteristic of advancing (the BTDC value increases as the rotational speed increases). The problem with this conventional ignition timing control during steady operation is the periodic vibration that occurs during partial operation.

  FIG. 15 and FIG. 16 show the state of vibration that occurs during partial operation (about 7,000 rpm) in a conventional brush cutter. The vertical axis in FIG. 15 indicates the engine speed, and the vertical axis in FIG. 16 indicates the vibration value. It can be seen from the vibration value data in FIG. 16 that a relatively large vibration was generated in the conventional brush cutter in the partial operation state. The cause can be inferred that the resonance state of the operation tube 14 is generated in the partial operation.

  Returning to FIG. 13, the solid line and the two-dot chain line in FIG. 13 indicate the ignition timing control map in the steady operation that can be adopted by the brush cutter 100 of the embodiment. The solid line in FIG. 13 shows an ignition timing control map (WOT ignition timing when fully open) in steady operation when the throttle valve is fully open (full throttle). A two-dot chain line in FIG. 13 shows an ignition timing control map (POT ignition timing at the time of partial) in the steady operation in which the throttle valve is in the partial state.

  As can be seen immediately from FIG. 13, the WOT ignition timing (solid line) when the throttle valve is fully open (full throttle) is set to advance from BTDC approx. 10 ° to BTDC approx. 30 ° at a low speed (3,000rpm). Has been. According to the control based on the WOT ignition timing map in the throttle valve fully opened steady operation, a good load response of the engine can be realized.

  On the other hand, the control based on the POT ignition timing map in the partial steady operation where the throttle valve is half-opened (the two-dot chain line in FIG. 13) is at a stroke from about 10 ° BTDC to about 30 ° BTDC at a high engine speed of about 8,000 rpm. It is set to advance.

  A modification of the POT ignition timing map in the partial steady operation is shown in FIG. In FIG. 14, the control based on the POT ignition timing map in the partial steady operation where the throttle valve is half-opened (the two-dot chain line in FIG. 14) is gradually increased from about 10 ° BTDC at about 8,000 rpm to about 30 ° at about 10,000 rpm. The ignition timing advanced to is set. The ignition timing at each engine speed between about 8,000 rpm and about 10,000 rpm should be set to a value that does not cause vibration by experiment.

  FIG. 17 is a flowchart for explaining ignition timing control in a steady operation state. Assuming that the brush cutter 100 is in a steady operation state, in step S101, the throttle position sensor 46 determines whether or not the throttle valve is fully open. In this embodiment, a full open (WOT) detection switch is employed as the throttle position sensor 46. This WOT switch is designed to supply an ON signal to the control unit 42 when the throttle valve is fully open. If it is determined in step S101 that the throttle valve is fully open, the process proceeds to step S102 where a WOT ignition timing map (solid line in FIG. 13) is set, and ignition timing control is executed based on this WOT ignition timing map. The The load response of the engine can be improved by executing the control based on the WOT ignition timing map.

  On the other hand, if it is determined in step S101 that the throttle valve is not fully open, it is determined that the throttle valve is in the partial operation state, and the process proceeds to step S103 where a POT ignition timing map (two-dot chain line in FIG. 13 or FIG. 14) is set. The ignition timing is controlled based on the POT ignition timing map. Since the POT ignition timing map at the time of partial has a characteristic capable of suppressing the generation of vibration, it is possible to suppress the vibration in the partial steady operation.

  Referring to FIG. 3, the control unit 42 has a memory 50, and the ignition timing map is stored in the memory 50. That is, the fully open WOT ignition timing map (solid line) and the partial POT ignition timing map (two-dot chain line) described with reference to FIG. 13 or FIG. 14 are stored in the memory 50. The control unit 42 supplies an ignition timing control signal generated based on the WOT ignition timing map or the POT ignition timing map to the ignition circuit 52 during steady operation. The ignition timing control of the spark plug 54 is executed by the ignition circuit 52.

  In the vibration preventing control at the time of deceleration of the brush cutter 100 according to the embodiment, the vibration absorber 32 (FIG. 2) can be omitted from the brush cutter 100 by adding control for switching the ignition timing control map in the steady operation.

DESCRIPTION OF SYMBOLS 100 Brush cutter of Example 2 Drive part 4 Cutting blade 6 Power transmission shaft 8 Cycle internal combustion engine 8a Engine output shaft 12 Microcomputer 20 Throttle lever 30 Centrifugal clutch 32 Vibration absorber 42 Control unit 44 Engine speed sensor 46 Throttle position sensor 54 Spark plug 62 Non-vibration area

Claims (13)

A throttle valve that is an output control valve;
An internal combustion engine with a spark plug;
A throttle lever mechanically connected to the throttle valve for controlling the output of the internal combustion engine and operable by an operator;
A power transmission shaft having one end connected to the output shaft of the internal combustion engine;
A cutting blade connected to the other end of the power transmission shaft;
A throttle position sensor that is positioned in relation to the throttle valve or the throttle lever and detects an opening of the throttle valve;
Misfire control means for misfiring the internal combustion engine when it is detected that the internal combustion engine is in a deceleration state based on a signal from the throttle position sensor;
Ignition resumption control means for stopping the misfire control and resuming normal ignition timing control when it can be assumed that the rotation speed of the internal combustion engine has reached a predetermined return rotation speed,
A brush cutter in which the return rotational speed is set in a non-vibration region in which no vibration is generated when the misfire control is stopped and switched to normal ignition timing control.   The brush cutter according to claim 1, wherein after the misfire control is stopped, normal ignition timing control is resumed at an engine speed of 4,500 rpm to 5,000 rpm.   The delay angle control is executed to retard the normal ignition timing and slow the recovery of the engine output immediately before stopping the misfire control and restarting the normal ignition timing control. The brush cutter as described.   The brush cutter according to any one of claims 1 to 3, wherein the throttle position sensor is a throttle opening linear sensor that linearly detects an opening of the throttle valve from a fully closed position to a fully opened position.   The brush cutter according to any one of claims 1 to 3, wherein the throttle position sensor is a full open detection switch capable of detecting that the throttle valve is in a full open state.   The brush cutter according to any one of claims 1 to 3, wherein the throttle position sensor is a fully closed detection switch capable of detecting that the throttle valve is in a fully closed state.   The brush cutter according to any one of claims 1 to 3, wherein the throttle position sensor is a partial detection switch capable of detecting that the throttle valve is in a predetermined half-open state. The throttle position sensor is composed of first and second partial detection switches,
The opening of the throttle valve that can be detected by the first partial detection switch is different from the opening of the throttle valve that can be detected by the second partial detection switch.
The brush cutter according to claim 7, wherein a deceleration state of the internal combustion engine is detected by the first and second partial detection switches. An engine speed sensor for detecting the speed of the internal combustion engine;
The ignition resumption control means stops the misfire control and resumes normal ignition timing control when the engine speed detected by the engine speed sensor reaches the return speed. A brush cutter according to claim 1.   A time from the misfire control until the normal ignition timing control is restarted is set, and when a predetermined time has elapsed from the start of the misfire control, it is considered that the rotational speed of the internal combustion engine has reached the return rotational speed. Item 9. A brush cutter according to any one of Items 1 to 8.   If the number of rotations of the output shaft of the engine reaches a predetermined number between the misfire control and the restart of the normal ignition timing control, it is considered that the rotational speed of the internal combustion engine has reached the return rotational speed. The brush cutter according to any one of claims 1 to 8. The ignition timing during steady operation has a first map set during full throttle operation and a second map set during partial operation,
The first map is set to advance at a stretch at low engine speed,
The brush cutter according to any one of claims 1 to 11, wherein the second map is set to advance at a stroke or gradually at a high engine speed. A centrifugal clutch interposed between the output shaft of the internal combustion engine and the power transmission shaft;
The brush cutter according to claim 12, wherein the centrifugal clutch is directly connected to the power transmission shaft.

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