Engine work machine

Abstract

To provide an engine work machine capable of smoothly decelerating an engine.SOLUTION: An engine work machine includes: an internal combustion engine having a piston which can reciprocate in a cylinder, and a combustion chamber which is defined by the piston; an ignition plug for igniting air-fuel mixture of the combustion chamber; a detection unit for detecting an engine speed of the internal combustion engine; and a control unit which controls an ignition timing of the ignition plug by the detected engine speed, can execute feedback control for determining the ignition timing by difference between a target engine speed and the detected engine speed, and executes the feedback control when the detected engine speed satisfies a prescribed deceleration condition.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an engine-driven working machine that controls the engine speed. [Background technology]

[0002] There is known engine control that detects deceleration in a region below the clutch-in rotation speed and adjusts the rotation speed to the retard side in order to transition to an idle rotation speed during deceleration (see, for example, Patent Document 1).

[0003] There is known engine control that detects deceleration at an engine speed equal to or higher than the clutch-in engine speed and adjusts the engine speed to the retard side in order to transition to an idle engine speed during deceleration (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 9,109,569 [Patent Document 2] U.S. Patent No. 9,188,066 Summary of the Invention [Problem to be solved by the invention]

[0005] The conventional engine control described above retards the timing when deceleration is detected. However, the engine speed is prone to fluctuate during deceleration, making it difficult to smoothly decelerate the engine in response to the fluctuations in engine speed.

[0006] The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide an engine working machine that can be smoothly decelerated. [Means for solving the problem]

[0007] The engine working machine according to the present invention has the following features: an internal combustion engine having a piston reciprocally movable within a cylinder and a combustion chamber defined by the piston; A spark plug for igniting the mixture in the combustion chamber; A detection unit that detects a rotation speed of the internal combustion engine; The present invention is provided with a control unit that controls the ignition timing of the spark plug based on the detected rotation speed, and when the detected rotation speed satisfies a predetermined deceleration condition, switches from map control, which controls based on a map value, to feedback control, which determines the ignition timing from the deviation between a target rotation speed and the detected rotation speed, and returns to the map control when the rotation speed of the internal combustion engine satisfies a predetermined rotation speed condition. Effect of the Invention

[0008] The engine can be decelerated smoothly. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram showing the configuration of an internal combustion engine 10 according to an example of the present embodiment. [Diagram 2] 4 is a flowchart showing an engine control process according to an example of the present embodiment. [Diagram 3] 4 is a flowchart showing an engine control process according to an example of the present embodiment. [Figure 4] 4 is a time chart showing the state of the engine when the fuel is lean (lean come down) according to the example of this embodiment. [Diagram 5] 5 is a time chart showing the state of the engine when the fuel is rich (rich come-down) according to the example of this embodiment. [Figure 6] 5 is a time chart showing the state of the engine when PI control of the ignition timing toward a target reduced rotation speed is performed according to the example of this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] <<First embodiment>> According to the first embodiment, an internal combustion engine having a piston reciprocally movable within a cylinder and a combustion chamber defined by the piston; A spark plug for igniting the mixture in the combustion chamber; A detection unit that detects a rotation speed of the internal combustion engine; There is provided an engine working machine comprising: a control unit that controls the ignition timing of the spark plug based on the detected rotation speed, the control unit being capable of executing feedback control that determines the ignition timing from the deviation between a target rotation speed and the detected rotation speed, and the control unit executing the feedback control when the detected rotation speed satisfies a predetermined deceleration condition.

[0011] The control unit controls the ignition timing of the spark plug based on the detected rotation speed. The ignition timing is determined by feedback control. The feedback control determines the ignition timing based on the deviation between a target rotation speed and the detected rotation speed. The control unit executes the feedback control when the detected rotation speed satisfies a predetermined deceleration condition.

[0012] The ignition timing may be determined by map control. In map control, a control map is used that stores a relationship between the engine speed and the ignition timing. The ignition timing is determined by referring to the control map based on the detected engine speed.

[0013] Because feedback control is performed during deceleration, even during deceleration when engine speed is prone to change, the ignition timing can be determined accurately in response to the change in engine speed, allowing for sufficiently smooth deceleration. In this case, in particular, it eliminates delays in the supply of fuel and air to the combustion chamber (response), helping to optimize engine behavior.

[0014] When the detected rotation speed satisfies a predetermined deceleration condition, feedback control is executed. This feedback control includes cases where the control is switched from map control, or where the control is switched from the first type of feedback control to the second type of feedback control among multiple types of feedback control (such as a first type of feedback control and a second type of feedback control).

[0015] <<Second embodiment>> The second embodiment is the same as the first embodiment, except that The specified deceleration conditions include the detected rotation speed being smaller than a specified rotation speed (e.g., the assist upper limit rotation speed described below) or being within a specified rotation speed range (e.g., the deceleration assist range described below).

[0016] When it is determined that the rotation speed is lower than the predetermined rotation speed, the control can be switched quickly. When it is determined that the rotation speed is within the predetermined rotation speed range, the determination can be made accurately while being less susceptible to the effects of rotation speed fluctuations and signal noise. The predetermined rotation speed may be determined so as to detect an operation by an operator to intentionally set the engine to idle. For example, in response to deceleration due to load fluctuations, a predetermined deceleration condition is not satisfied so that feedback control is not initiated.

[0017] <<Third embodiment>> The third embodiment is the same as the first or second embodiment, The control unit 200 executes the feedback control when the detected rotation speed is higher than a predetermined clutch-in rotation speed.

[0018] This allows for earlier detection of deceleration rather than after the clutch is engaged, enabling feedback control.

[0019] <<Fourth embodiment>> The fourth embodiment is the same as the first to third embodiments, The feedback control is performed to achieve a target rotation speed.

[0020] By targeting the target RPM, it is possible to determine the appropriate ignition timing according to the detected RPM.

[0021] <<Fifth embodiment>> The fifth embodiment is the same as the fourth embodiment, The target rotation speed is a target idle rotation speed.

[0022] <<Sixth embodiment>> The sixth embodiment is the fourth embodiment, The target rotation speed is a target reduced rotation speed.

[0023] <<Seventh embodiment>> The seventh embodiment is the same as the first to sixth embodiments, The feedback control includes a PI control.

[0024] An appropriate ignition timing can be determined according to the detected rotation speed.

[0025] <<Eighth embodiment>> The eighth embodiment is the same as the first to seventh embodiments, The control unit cancels the feedback control when the detected rotation speed becomes smaller than a predetermined threshold value during execution of the feedback control.

[0026] The feedback control makes it possible to reduce the rotation speed appropriately and then terminate the feedback control.

[0027] <<Ninth embodiment>> The ninth embodiment is the same as the first to seventh embodiments, The control unit releases the feedback control when at least one of the following conditions is satisfied during execution of the feedback control: a predetermined time has elapsed since the detected rotation speed became smaller than a predetermined threshold value, or a predetermined engine rotation amount has been reached.

[0028] After the threshold value is reduced below a predetermined threshold value, the operation can be stabilized sufficiently more than during idling before being released.

[0029] <<Tenth embodiment>> The tenth embodiment is the eighth or ninth embodiment, When the detected rotation speed becomes greater than an upper idle speed after the feedback control is released, the control unit increases the amount of fuel supplied to the combustion chamber.

[0030] An optimal amount of fuel is delivered to the combustion chamber to allow the engine to run at low RPMs below the upper idle speed.

[0031] <<<Internal Combustion Engine 10>>> 1 is a block diagram showing a configuration of an internal combustion engine 10 according to an example of the present embodiment. The internal combustion engine 10 according to the example of the present embodiment is a two-stroke gasoline engine.

[0032] The internal combustion engine 10 of this embodiment mainly includes a carburetor 110, a spark plug 120, a combustion chamber 130, a cylinder 140, a crankshaft 142, a piston 144, and a control device 200.

[0033] <<Carburetor 110>> The carburetor 110 has a throttle valve 113 that adjusts the amount of the mixture flowing into the internal combustion engine 10, and a fuel valve 112 that adjusts the amount of fuel. The throttle valve 113 is operated by an operator. The fuel valve 112 is driven by a solenoid (not shown). The throttle valve 113 and the fuel valve 112 are conventionally known. Note that the fuel valve 112 according to this embodiment is normally closed when no current flows through the solenoid (normal state). The mixture that passes through the throttle valve 113 and the fuel valve 112 is drawn into the combustion chamber 130 by the operation of the piston 144.

[0034] The spark plug 120 is disposed at the top of the cylinder 140. The internal combustion engine 10 has an ignition device (not shown) that activates the spark plug 120. The ignition device burns the air-fuel mixture drawn into the combustion chamber 130 through spark discharge from the spark plug 120. The increase in the volume of the air-fuel mixture due to combustion moves the piston 144 downward, and the motion of the piston 144 is transmitted to the crankshaft 142 and converted into the rotational motion of the crankshaft 142.

[0035] <<Cylinder 140, crankshaft 142, piston 144>> A piston 144 is disposed in the cylinder 140 and is connected to a crankshaft 142. During a compression stroke of the internal combustion engine 10, the piston 144 rises to top dead center. At a predetermined ignition timing before the piston reaches top dead center, the air-fuel mixture is combusted, providing downward thrust to the piston 144.

[0036] <<<Control device 200>>> A control device 200 as an example of this embodiment has a CPU (central processing unit) 210, a ROM (read only memory) 220, a RAM (random access memory) 230, an input / output bus 240, as well as a rotation speed counter 250, an ignition plug driving circuit 260, and a fuel valve driving circuit 270.

[0037] The above-mentioned input / output bus 240 is connected to the ROM 220, the RAM 230, and an ignition plug driving circuit 260. The ignition plug driving circuit 260 is a circuit for driving the ignition plug 120. The input / output bus 240 inputs and outputs data signals or address signals to and from the CPU 210.

[0038] When an ignition control command issued by the CPU 210 is supplied to the ignition plug 120, the ignition plug 120 is ignited and the air-fuel mixture drawn into the combustion chamber 130 is burned.

[0039] When a valve control signal issued from CPU 210 is supplied to fuel valve drive circuit 270, fuel valve drive circuit 270 supplies a drive signal to the solenoid of fuel valve 112. Fuel valve 112 opens in response to the valve control signal.

[0040] A crankshaft reference position detection device 280 is provided near the crankshaft 142. The crankshaft reference position detection device 280 is connected to the input / output bus 240. The crankshaft reference position detection device 280 generates one reference pulse signal when the crankshaft 142 reaches a predetermined reference position, for example, when the piston 144 is located at the top dead center. The reference pulse signal is supplied to a revolution counter 250. The revolution counter 250 outputs a revolution speed signal indicating the revolution speed of the crankshaft 142 of the internal combustion engine 10.

[0041] The ROM 220 stores a program for executing an engine control processing routine in accordance with the flowcharts described with reference to FIGS.

[0042] <<<Engine control processing>>> In the following, it is assumed that the internal combustion engine 10 has completed startup processing such as initialization and is operating steadily. Figures 2 and 3 are flowcharts showing engine control processing according to one example of this embodiment. Figures 4 and 5 are time charts showing engine states according to one example of this embodiment.

[0043] Figure 4 is a time chart for lean fuel (lean come down). The chart shows the change in engine speed (Figure 4(a)), the change in ignition timing (Figure 4(b)), and the change in fuel increase (Figure 4(c)) when the engine speed exceeds the upper idle limit after the engine is decelerated by map control and then adjusted toward the target idle speed by PI control of the ignition timing and then returned to map control.

[0044] Figure 5 is a time chart for when the fuel is rich (rich come-down). The chart shows the change in the engine speed (Figure 5(a)), the change in the ignition timing (Figure 5(b)), and the change in the increase in fuel (Figure 5(c)) when the engine speed becomes lower than the lower limit of idle speed after the engine is decelerated by map control and then adjusted toward the target idle speed by PI control of the ignition timing and then returned to map control.

[0045] In addition, in FIG. 4 and FIG. 5, the same parts are denoted by the same reference numerals.

[0046] The CPU 210 of this example embodiment first detects the rotation speed signal from the rotation speed counter 250 and determines whether the internal combustion engine 10 is decelerating (step S211).

[0047] For example, if the absolute value of the amount of decrease in the rotational speed of the crankshaft 142 within a predetermined time period becomes larger than a predetermined value, it is determined that the internal combustion engine 10 is decelerating. The determination process may be performed not only once, but also multiple times in succession. It is possible to determine that the engine is decelerating appropriately while preventing the effects of noise, vibration, etc. This decrease in the rotational speed corresponds to the area R1 in the time charts of Figures 4(a) and 5(a).

[0048] When the CPU 210 determines that the internal combustion engine 10 is not decelerating (NO), the CPU 210 returns the process to step S211.

[0049] When the CPU 210 determines that the internal combustion engine 10 is decelerating (YES), it detects the rotation speed signal from the rotation speed counter 250 and determines whether the internal combustion engine 10 is accelerating (step S213).

[0050] The deceleration of the internal combustion engine 10 may be due to an increase in load. The deceleration of the internal combustion engine 10 due to an increase in load is a temporary deceleration, and then, when the load decreases, the internal combustion engine 10 accelerates (see region R2 in FIG. 4(a)).

[0051] In the above-mentioned determination process of step S213, it is determined whether or not the internal combustion engine 10 has accelerated after decelerating.

[0052] When the CPU 210 determines in the determination process of step S213 that the internal combustion engine 10 has accelerated (YES), the CPU 210 returns the process to step S211.

[0053] On the other hand, when the CPU 210 determines in the determination process of step S213 that the internal combustion engine 10 has not been accelerated (NO), that is, when deceleration has been caused by the operator's operation, it determines whether or not the deceleration control start condition has been satisfied (step S215).

[0054] The deceleration control start condition is that the rotation speed of the crankshaft 142 is lower than the assist upper limit rotation speed for deceleration control (see FIG. 4(a)) or is included in the deceleration assist range for deceleration control (see FIG. 4(a)) (see region R3 in FIG. 4(a) and FIG. 5(a)). The assist upper limit rotation speed is a rotation speed higher than the clutch-in rotation speed. In this way, deceleration caused by the operator's operation can be determined and optimal ignition control can be started at an early stage.

[0055] The deceleration of the internal combustion engine 10 can be mainly caused by the operation of the operator or by an increase in the load. When the rotation speed becomes smaller than the assist upper limit rotation speed, it is determined that the deceleration is caused by the operation of the operator. The deceleration caused by the operation of the operator is a stop operation, and the internal combustion engine 10 decelerates monotonically.

[0056] When the deceleration control start condition is determined to be that the rotation speed is lower than the assist upper limit rotation speed, the control can be switched quickly. On the other hand, when the deceleration control start condition is determined to be that the rotation speed is within the deceleration assist range, it is possible to accurately determine whether the deceleration control start condition is met without being affected by the rotation fluctuation of the crankshaft 142 or noise in the rotation speed signal.

[0057] When the CPU 210 determines in the determination process of step S215 that the deceleration control start condition is not satisfied (NO), the CPU 210 returns the process to step S213.

[0058] On the other hand, when the CPU 210 determines in the determination process of step S215 that the deceleration control start condition is satisfied (YES), it switches to PI control (step S217). By the processes of steps S217 and S217, PI control of the ignition timing toward the target idle speed shown in Fig. 4(a) based on the normal ignition map (not shown) is started.

[0059] In addition, when it is determined that the deceleration control start condition is satisfied (YES), by the processing of steps S217 and S218, PI control of the ignition timing toward the target deceleration (change in rotation speed over a predetermined time) (target deceleration rotation speed) may be performed as shown in FIG. 6.

[0060] PI control (Proportional-Integral Controller) is a type of feedback control. PI control uses proportional control (P control) and integral action (I action) to control the input value based on the deviation between the output value and the target value and the time during which the deviation occurs. Ignition timing is determined by PI control.

[0061] Note that instead of PI control, PID control (Proportional-Integral-Differential Controller) may be used. The input value is controlled based on the deviation between the output value and the target value, the time during which the deviation occurs, and the rate of change of the deviation over time.

[0062] Furthermore, PI control or PID control may be selected according to the fluctuation of the rotation speed, etc. Also, the ignition timing may be determined by a feedback control other than the PI control or the PID control.

[0063] By using feedback control such as PI control, the ignition timing is determined based on the deviation between the actual engine speed and the target engine speed, so that the ignition timing during deceleration, when the engine speed is relatively unstable, can be determined more appropriately than with map control. Also, by using feedback control, the optimal ignition timing can be determined and ignition can be performed whether the engine is running lean cum down or rich cum down.

[0064] The map control is a control that determines the ignition timing using a reference table (not shown) that stores in advance the correspondence between the rotation speed of the internal combustion engine 10 and the ignition timing. The reference table is searched based on the rotation speed detected by the rotation speed counter 250, and the ignition timing corresponding to the detected rotation speed is determined.

[0065] When the process switches to PI control in step S217, the ignition timing corresponding to the rotation speed at that time is obtained from the reference table of the map control as an initial value, and the spark plug 120 is fired. From the next rotation onwards, the obtained ignition timing is used to determine the ignition timing at that time by PI control so as to achieve the target rotation speed.

[0066] In the time charts shown in FIGS. 4(a) and 4(b), before time T1, the ignition timing is determined by map control so as to result in normal ignition curve 1 (FIG. 4(b)).

[0067] When the map control is switched to the PI control in the process of step S217 (time T1 in FIG. 4(a)), the ignition timing is determined by the PI control so as to achieve the target idle speed. In this case, during the PI control, the upper limit timing θmax and the lower limit timing θmin are set as shown in FIG. 4(b) so as not to cause the ignition timing to be excessively delayed or advanced.

[0068] Next, the CPU 210 judges whether the internal combustion engine 10 has accelerated (step S219). That is, even when the internal combustion engine 10 is decelerating by PI control (area R3 in Fig. 4(a) and Fig. 5(a)), the CPU 210 judges whether the internal combustion engine 10 has accelerated (area R4 in Fig. 4(a)). The judgment of acceleration here is also for excluding deceleration due to an increase in load.

[0069] When the CPU 210 determines that the internal combustion engine 10 has accelerated (YES), it cancels the PI control (step S225) and returns the process to step S211, whereby the map control is started again.

[0070] When the CPU 210 determines in the determination process of step S219 that the internal combustion engine 10 is not accelerating (NO), it determines whether or not the deceleration control start condition is satisfied (S221). When the CPU 210 determines that the deceleration control start condition is not satisfied, that is, that the rotation speed is equal to or higher than the assist upper limit rotation speed (NO), it cancels the PI control (step S225) and returns the process to step S211. This restarts the map control.

[0071] If the deceleration control start condition is met in the determination process of step S221, that is, if it is determined that the rotation speed is less than the assist upper limit rotation speed (NO), the CPU 210 determines whether or not the deceleration control end condition is met (step S223).

[0072] The deceleration control end condition is that the rotation speed of the crankshaft 142 becomes smaller than the assist lower limit rotation speed for deceleration control (see FIG. 4(a)) or falls outside the deceleration assist range for deceleration control (see FIG. 4(a)). In other words, it is determined whether the rotation speed of the crankshaft 142 is no longer subject to PI control. In this case, a condition that a predetermined time has passed since the rotation speed becomes smaller than the assist lower limit rotation speed may be added as a deceleration control end condition. In this case, the target idle rotation speed will be approached even closer, making the idle operation even more stable.

[0073] When the CPU 210 determines that the deceleration control end condition has been satisfied (YES), it sets the normal ignition curve 2 for map control (see FIG. 4(b)) (step S227) (time T2 in FIG. 4(a)). The normal ignition curve 2 for map control is data that defines a target value for determining the ignition timing by map control. The ignition timing is determined by map control so that the ignition timing becomes the normal ignition curve 2 shown in FIG. 4(b).

[0074] Next, the CPU 210 switches the engine control from the PI control to the map control (step S229), thereby releasing the PI control.

[0075] Next, the CPU 210 determines whether or not the idle speed monitoring time has elapsed since the control was returned to the map control (step S311).

[0076] When the CPU 210 determines that the idle rotation speed monitoring time has not elapsed (NO), it determines whether the rotation speed of the internal combustion engine 10 has become equal to or higher than the idle upper limit rotation speed (step S313). In this embodiment, the assist lower limit rotation speed and the idle upper limit rotation speed are the same rotation speed. The assist lower limit rotation speed and the idle upper limit rotation speed may be different rotation speeds.

[0077] When the CPU 210 determines in the determination process of step S313 that the rotation speed of the internal combustion engine 10 has reached or exceeded the upper idle limit rotation speed (YES) after returning to map control, it increases the amount of fuel supplied to the combustion chamber 130 (step S315) (see time T3 in FIG. 4(c)). In the case of lean come-down, if the rotation speed reaches or exceeds the upper idle limit rotation speed within the idle rotation speed monitoring time, the amount of fuel is increased. In this way, an optimal amount of fuel is supplied into the combustion chamber 130, and the rotation speed of the internal combustion engine 10 is reduced to below the upper idle limit rotation speed (region R6 in FIG. 4(a)).

[0078] When the CPU 210 determines in the determination process of step S313 that the rotation speed of the internal combustion engine 10 is less than the idle upper limit rotation speed (NO), it determines whether the rotation speed of the internal combustion engine 10 has become equal to or less than the idle lower limit rotation speed (step S317).

[0079] When the CPU 210 determines in the determination process of step S317 that the rotation speed of the internal combustion engine 10 has fallen below the lower limit idle rotation speed (YES), it selects an advance map ignition curve and performs map control (step S319) (see time T4 in FIG. 5(a) and FIG. 5(b)). In the case of rich come-down, when the rotation speed falls below the lower limit idle rotation speed within the idle rotation speed monitoring time, the rotation speed of the internal combustion engine 10 is increased by map control using the advance map ignition curve (region R7 in FIG. 5(a)).

[0080] The CPU 210 judges whether the rotation speed of the internal combustion engine 10 is equal to or higher than the upper idle limit rotation speed (step S321). If the rotation speed of the internal combustion engine 10 is lower than the upper idle limit rotation speed, the process returns to step S321. In this manner, even if the idle rotation speed monitoring time has elapsed, the ignition timing is determined by map control using the advance map ignition curve until the rotation speed becomes equal to or higher than the upper idle limit rotation speed (time T5 in FIG. 5).

[0081] When the CPU 210 determines in the determination process of step S317 that the rotation speed of the internal combustion engine 10 is greater than the lower limit idle rotation speed (NO), the CPU 210 returns the process to step S311.

[0082] When the CPU 210 determines in the judgment process of step S311 that the idle speed monitoring time has elapsed (YES), when the CPU 210 executes the process of step S315, or when the CPU 210 determines in the judgment process of step S321 that the speed of the internal combustion engine 10 is greater than the upper idle speed limit (YES), it assumes that the speed of the internal combustion engine 10 has reached the idle speed, starts normal map control (step S323), and ends this subroutine.

[0083] <<<<<Scope of this embodiment>>>> As described above, the present invention has been described with reference to the present embodiment, but the description and drawings forming a part of this disclosure should not be understood as limiting the present invention. The present invention includes various embodiments not described herein. [Explanation of symbols]

[0084] 10. Internal Combustion Engine 120 Spark plug 200 Control device

Claims

1. an internal combustion engine having a piston reciprocally movable within a cylinder and a combustion chamber defined by the piston; A spark plug for igniting the mixture in the combustion chamber; A detection unit that detects a rotation speed of the internal combustion engine; an engine working machine comprising: a control unit that controls the ignition timing of the spark plug based on a detected rotation speed, and when the detected rotation speed satisfies a predetermined deceleration condition, switches from map control, which controls based on a map value, to feedback control, which determines the ignition timing from the deviation between a target rotation speed and the detected rotation speed, and returns to the map control when the rotation speed of the internal combustion engine satisfies a predetermined rotation speed condition.

2. 2. The engine-driven work machine according to claim 1, wherein the predetermined deceleration condition includes a condition in which the detected rotation speed is lower than a predetermined rotation speed, or a condition in which the rotation speed of the internal combustion engine is within a predetermined rotation speed range.

3. 3. The engine-driven working machine according to claim 1, wherein the control unit executes the feedback control when the detected rotation speed is higher than a predetermined clutch-in rotation speed.

4. 4. The engine-driven work machine according to claim 1, wherein the feedback control is performed toward a target rotation speed.

5. 5. The engine work machine according to claim 4, wherein the target rotation speed is a target idle rotation speed.

6. The engine-driven work machine according to claim 4 , wherein the target rotation speed is a target reduced rotation speed.

7. The engine-driven work machine according to claim 1 , wherein the feedback control includes a PI control.

8. 8. The engine-driven work machine according to claim 1, wherein the control unit cancels the feedback control when the detected rotation speed becomes smaller than a predetermined threshold value during execution of the feedback control.

9. 8. The engine-driven working machine according to claim 1, wherein the control unit cancels the feedback control when at least one of the following conditions is satisfied during execution of the feedback control: a predetermined time has elapsed since the detected rotation speed became smaller than a predetermined threshold value, or a predetermined engine rotation amount has been reached.

10. 10. The engine working machine according to claim 8, wherein the control unit increases the fuel supplied to the combustion chamber when the detected rotation speed becomes higher than an upper idle speed after the feedback control is released.

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