Engine work equipment

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 work 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 slower side in order to transition to an idle rotation speed during deceleration (see, for example, Patent Document 1).

[0003] There is known an engine control that detects deceleration at an engine speed equal to or higher than the clutch-in engine speed and adjusts the timing 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-driven working machine that can be smoothly decelerated. [Means for solving the problem]

[0007] The engine-powered working machine according to the present invention is characterized by the following features: an internal combustion engine having a piston reciprocally movable within a cylinder and a combustion chamber defined by said piston; a spark plug that ignites the mixture in the combustion chamber; a detection unit that detects the rotation speed of the internal combustion engine; A control unit 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, the control is switched from map control, which controls based on a map value, to feedback control, which determines the ignition timing based on the deviation between a target rotation speed and the detected rotation speed, and when the rotation speed of the internal combustion engine satisfies a predetermined rotation speed condition, the control is switched back to map control. At the same time, when the detected rotation speed becomes smaller than a predetermined threshold value during the execution of the feedback control, the feedback control is cancelled. and a control unit. [Effects of the Invention]

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

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

[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 said piston; a spark plug that ignites the mixture in the combustion chamber; a detection unit that detects the rotation speed of the internal combustion engine; An engine working machine is provided that includes a control unit that controls the ignition timing of the spark plug based on the detected rotational speed, and is capable of performing feedback control that determines the ignition timing from the deviation between a target rotational speed and the detected rotational speed, and that executes the feedback control when the detected rotational 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 the 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, which uses a control map that stores a relationship between the engine speed and the ignition timing in advance. 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 fluctuate, the ignition timing can be determined accurately in accordance with the fluctuations in engine speed, allowing for sufficiently smooth deceleration. In this case, in particular, delays in the supply of fuel and air to the combustion chamber (response) are eliminated, 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, among multiple types of feedback control (such as first type feedback control and second type feedback control), the control is switched from first type feedback control to second type 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 upper assist rotation speed described below) or being within a specified rotation speed range (e.g., the deceleration assist range described below).

[0016] When determining that the rotation speed has fallen below a predetermined value, control can be switched quickly. When determining that the rotation speed has fallen within a predetermined range, the determination can be made accurately, with less influence from rotation fluctuations and signal noise. The predetermined rotation speed may also be determined so as to detect when an operator intentionally operates the engine to idle. For example, when deceleration is caused by a load fluctuation, the predetermined deceleration condition is not satisfied, and 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 than after the clutch is engaged, enabling feedback control.

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

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

[0021] <<Fifth embodiment>> The fifth embodiment is 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 PI control.

[0024] It is possible to determine an appropriate ignition timing 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 can be terminated after the rotation speed is reduced appropriately.

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

[0028] After the threshold value is reduced below a predetermined threshold value, the engine can be released after the engine operation is stabilized to a level greater than that during idling.

[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] The optimum amount of fuel is delivered to the combustion chamber, allowing the engine to run at low RPMs below the upper idle speed limit.

[0031] <<<Internal Combustion Engine 10>>> 1 is a block diagram showing the configuration of an internal combustion engine 10 according to one example of the present embodiment. The internal combustion engine 10 according to this 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] <<Vaporizer 110>> The carburetor 110 has a throttle valve 113 that adjusts the amount of the air-fuel mixture that flows 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, that is, closed when no current flows through the solenoid (normal state). The air-fuel 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 movement of the piston 144 is transmitted to the crankshaft 142 and converted into rotational movement of the crankshaft 142.

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

[0036] <<<Control device 200>>> The control device 200 of one 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 drive circuit 260, and a fuel valve drive circuit 270.

[0037] The above-mentioned input / output bus 240 is connected to the ROM 220, RAM 230, and spark plug drive circuit 260. The spark plug drive circuit 260 is a circuit for driving the spark 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 from the CPU 210 is supplied to the spark plug 120, the spark 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 a reference pulse signal when the crankshaft 142 reaches a predetermined reference position, for example, when the piston 144 is located at top dead center. The reference pulse signal is supplied to a revolution counter 250. The revolution counter 250 outputs a revolution 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 when the fuel is lean (lean comedown). 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 limit of idle speed after slowing down using map control, adjusting the ignition timing to the target idle speed using PI control, and then returning to map control.

[0044] Figure 5 is a time chart for when the fuel is rich (rich come-down). The chart shows the changes in engine speed (Figure 5(a)), ignition timing (Figure 5(b)), and fuel increase (Figure 5(c)) when the engine speed falls below the lower limit of idle speed after deceleration using map control, adjustment to the target idle speed using PI control of ignition timing, and then returning 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 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. Note that this 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 rotational speed corresponds to the region 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 process returns 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 the 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 determination process of step S213 described above, it is determined whether 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 judgment process of step S213 that the internal combustion engine 10 has not been accelerated (NO), that is, if the deceleration was caused by the operator's operation, it determines whether the deceleration control start condition has been met (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 FIGS. 4(a) and 5(a)). The assist upper limit rotation speed is a rotation speed higher than the clutch-in rotation speed. This makes it possible to determine deceleration due to the operator's operation and start optimal ignition control at an early stage.

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

[0056] When the deceleration control start condition is determined to be that the rotation speed has fallen below 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 has fallen within the deceleration assist range, it is possible to accurately determine whether the deceleration control start condition is met without being affected by rotation fluctuations in 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 process returns 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 is started toward the target idle speed shown in Fig. 4(a) based on the normal ignition map (not shown).

[0059] Furthermore, when it is determined that the deceleration control start condition is met (YES), 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 by the processing of steps S217 and S217, 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. PI control determines the ignition timing.

[0061] 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 and controlled depending on fluctuations in the rotation speed, etc. Also, the ignition timing may be determined by feedback control other than PI control or 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 the ignition timing can be determined more appropriately than with map control during deceleration when the engine speed is relatively unstable. Also, by using feedback control, the optimal ignition timing can be determined and ignition can be performed whether the engine is running lean or rich.

[0064] The map control is a control that determines the ignition timing using a look-up table (not shown) that stores in advance the correspondence between the rotation speed of the internal combustion engine 10 and the ignition timing. The look-up 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 first obtained from the lookup table of map control as an initial value, and the ignition timing is then used to ignite the spark plug 120. 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. 4A), 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. 4B so as not to cause excessive delay or advance of the ignition timing.

[0068] Next, the CPU 210 determines 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 FIGS. 4(a) and 5(a)), it determines whether the internal combustion engine 10 has accelerated (area R4 in FIG. 4(a)). The determination of acceleration here is also intended to exclude 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 restarted.

[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 CPU 210 determines in the determination process of step S221 that the deceleration control start condition is met, that is, that the rotation speed is less than the assist upper limit rotation speed (NO), it determines whether the deceleration control end condition is met (step S223).

[0072] The deceleration control termination condition is that the rotation speed of the crankshaft 142 has become smaller than the assist lower limit rotation speed for deceleration control (see FIG. 4(a)), or has fallen 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 has become outside the target range of PI control. In this case, a condition that a predetermined time has elapsed since the rotation speed became smaller than the assist lower limit rotation speed may be added as a deceleration control termination condition. In this case, the target idle rotation speed will be further approached, resulting in more stable idle operation.

[0073] When the CPU 210 determines that the deceleration control termination condition is 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 PI control to map control (step S229), thereby canceling the PI control.

[0075] Next, the CPU 210 determines whether or not the idle rotation speed monitoring time has elapsed since the return to 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 reached or exceeded 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. Note that 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 speed limit (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 comedown, if the rotation speed reaches or exceeds the upper idle speed limit within the idle speed monitoring time, the amount of fuel is increased. In this way, an optimal amount of fuel is supplied to the combustion chamber 130, and the rotation speed of the internal combustion engine 10 is reduced to below the upper idle speed limit (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 upper idle rotation speed (NO), it determines whether the rotation speed of the internal combustion engine 10 has become equal to or less than the lower idle 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 determines whether the rotation speed of the internal combustion engine 10 has reached or exceeded the upper limit of the idle rotation speed (step S321). If the rotation speed of the internal combustion engine 10 is below the upper limit of the idle rotation speed, the process returns to step S321. In this way, 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 reaches or exceeds the upper limit of the idle 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 process returns to step S311.

[0082] When the CPU 210 determines in the judgment process of step S311 that the idle rotation speed monitoring time has elapsed (YES), when it executes the process of step S315, or when it determines in the judgment process of step S321 that the rotation speed of the internal combustion engine 10 is greater than the upper idle rotation speed limit (YES), it determines that the rotation speed of the internal combustion engine 10 has reached the idle rotation 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 part of this disclosure should not be understood to limit 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 said piston; a spark plug that ignites the mixture in the combustion chamber; a detection unit that detects the 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 when the rotation speed of the internal combustion engine satisfies the predetermined rotation speed condition, returns to the map control, and when the detected rotation speed becomes smaller than a predetermined threshold while the feedback control is being executed, cancels the feedback control.

2. 2. The engine-powered implement 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-powered implement 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-powered implement according to claim 1, wherein the feedback control is performed to achieve a target rotation speed.

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

6. The engine-powered implement according to claim 4, wherein the target rotational speed is a target reduced rotational speed.

7. 7. The engine-powered implement according to claim 1, wherein the feedback control includes PI control.

8. 8. The engine-powered work 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 the detected rotation speed has reached a predetermined engine rotation amount.

9. 9. The engine-powered implement according to claim 8, wherein the control unit increases the amount of fuel supplied to the combustion chamber when the detected rotation speed becomes greater than an upper idle speed after the feedback control is released.

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