Handheld engine-driven working machine

Abstract

An engine-driven working machine includes a controller, which varies a control value of a solenoid valve so as to decrease or increase an opening degree of the solenoid valve when a rotating speed of an engine is within a predetermined high rotating speed range and the rotating speed of the engine is lower or higher than a predetermined rotating speed, respectively. When the control value of the solenoid valve is varied so as to decrease the opening degree of the solenoid valve and corresponds to a predetermined opening degree larger than a fully-closed state, the control value is set to a limitation value.

Claims

1. An engine-driven working machine comprising: an engine including an electronically controlled carburetor; and a controller connected to the electronically controlled carburetor; wherein the electronically controlled carburetor includes a solenoid valve for adjusting an amount of supplying fuel into the electronically controlled carburetor, wherein the controller is programmed to vary a control value of the solenoid valve so as to increase an opening degree of the solenoid valve when a rotating speed of the engine is within a predetermined high rotating speed range and the rotating speed of the engine is higher than a target rotating speed; wherein the controller is programmed to vary the control value of the solenoid valve to a control calculation value calculated so as to decrease the opening degree of the solenoid valve, when the rotating speed of the engine is within the predetermined high rotating speed range, the rotating speed of the engine is lower than the target rotating speed, and the control calculation value is nearer a fully-opened state than a single limitation value which corresponds to a predetermined opening degree larger than a fully-closed state, and wherein the controller is programmed to set the control value of the solenoid valve to the limitation value when the rotating speed of the engine is within the predetermined high rotating speed range, the rotating speed of the engine is lower than the target rotating speed, and the control calculation value equals to or is nearer the fully-closed state than the limitation value.

2. The engine-driven working machine according to claim 1, wherein the limitation value is determined by varying a control value determined in a completion operation by a predetermined value toward a direction of opening the solenoid valve.

3. The engine-driven working machine according to claim 1, wherein the engine-driven working machine is a chain saw, an engine cutter or a hedge trimmer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a side view of a chain saw according to the present invention in which a cover is omitted.

(2) FIG. 2 is a schematic view showing an internal structure of a carburetor in the chain saw according to the present invention.

(3) FIG. 3 is a flowchart showing a control method of the handheld engine-driven working machine according to the present invention.

(4) FIG. 4 is a graph showing an example of changes in the engine rotating speed and the control value with respect to time when an actual operation with load is performed with the chain saw according to the present invention.

(5) FIG. 5 is a graph showing changes in the engine rotating speed and the control value with respect to time around a time when the actual operation control value was determined in an example in which an actual operation with non-load of the chain saw was performed while the control described in the Patent Publication 1 was performed.

(6) FIG. 6 is a graph showing changes in the engine rotating speed and the control value with respect to time around a time when the actual operation control value was determined in an example in which an actual operation with load of the chain saw was performed while the control described in the Patent Publication 1 was performed.

DETAILED DESCRIPTION OF EMBODIMENTS

(7) Referring to the drawings, an embodiment of a chain saw according to the present invention will be explained.

(8) As shown in FIG. 1, a chain saw 10 has an engine 12 operated with gasoline fuel, and a controller 14 controlling the engine 12. The engine 12 has, at least, a cylinder block 16 and an electronically controlled carburetor 18. The carburetor 18 includes a solenoid valve 20 for adjusting an amount of supplying fuel into the carburetor 18, and the solenoid valve 20 is connected to the controller 14. Further, a detected object 22, such as a magnet, is attached to a flywheel 23, and the controller 14 is configured to detect the rotating speed of the engine 12 by using the detected object 22. Concretely, a period required for one rotation of the engine 12 is measured by detecting the detected object 22, and the rotating speed of the engine 12 is calculated per one rotation of the engine 12. In FIG. 1, chain blades are omitted.

(9) FIG. 2 is a schematic view showing an internal structure of the carburetor 18. As shown in FIG. 2, the carburetor 18 has a passage 24 including a Venturi section 24a, a throttle valve 26 provided in a passage downstream of the Venturi section 24a, a main fuel supply nozzle 27 disposed in the Venturi section 24a, and a slow-system (low speed) fuel supply port 28 disposed near the throttle valve 26. The main fuel supply nozzle 27 communicates with a metering chamber 32 through a first flow passage 30a and a fixed jet 30b, and communicates with a metering chamber 32 through a second flow passage 30c and the solenoid valve 20. The fuel supply port 28 communicates with the metering chamber 32 through a chamber 30d, a third flow passage 30e and the fixed jet 30f.

(10) Fuel is supplied at a predetermined rate by a negative pressure of the engine through the main fuel supply nozzle 27 and the slow-system (low speed) fuel supply port 28. By adjusting an opening degree of the solenoid valve 20, an amount of fuel supplied through the main fuel supply nozzle 27 can be controlled, so that the entire amount of supplying fuel can be adjusted. In the present embodiment, a control value corresponding to the opening degree of the solenoid valve 20 is determined so as to linearly change between 0 per mill (permillage) when the solenoid valve 20 is fully-opened and 1000 per mill when the solenoid valve 20 is fully closed.

(11) FIG. 3 is a flow chart showing an embodiment of a control method of the handheld engine-driven working machine according to the present invention, and a chain saw which is an embodiment of the handheld engine-driven working machine will be explained from here.

(12) In ST 10, a completion operation (with non-load) is performed in a manufacturing factory with chain blades removed from the chain saw, and a control value for completion operation V0 is determined. Since a control method for determining the control value for completion operation V0 is the same as that for determining an actual operation control value with non-load, an explanation of the former control method is omitted.

(13) In ST 20, an actual operation is started. Concretely, chain blades are attached to the chain saw, and under a circumstance where the working machine is actually used, the engine is started. As an initial value of the control value, the control value for completion operation V0 is used.

(14) In ST 22, it is determined whether or not the rotating speed of the engine 12 is within a predetermined high rotating speed range R1 (for example, 11000-14000 rpm). If the answer is NO, the control is not performed and is returned to ST 22. If the answer is YES, in ST 24, it is determined whether the rotating speed of the engine 12 is higher or lower than a target rotating speed R2 (for example, 12000 rpm).

(15) When the rotating speed of the engine 12 is higher than the target rotating speed R2 (for example, 12000 rpm), in ST 26, the control value is decreased by the result of the PI calculation, so that the opening degree of the solenoid valve 20 is increased, and then the control is moved to ST 34.

(16) When the rotating speed of the engine 12 is the target rotating speed R2 (for example, 12000 rpm), the control is moved to ST 34.

(17) When the rotating speed of the engine 12 is lower than the target rotating speed R2 (for example, 12000 rpm), in ST 28, it is determined whether or not a PI control calculation value VC, which is obtained by increasing the control value by the result of the PI calculation, is larger than a limitation value VL, which is a sum of the control value for completion operation V0 and a predetermined amount V1. When the PI control calculation value VC is smaller than the limitation value VL, in ST 30, the opening degree of the solenoid valve 20 is decreased by increasing the control value by the result of the PI calculation, and then, the control is moved to ST 34. When the PI control calculation value VC equals to or is larger than the limitation value VL, in ST 32, the control value is set to the limitation value VL, and then the control is moved to ST 34. The limitation value VL is smaller than 1000 per mill, preferably, smaller than 900 per mill. Namely, there is no chance for the solenoid valve 20 to be fully closed. Preferably, the predetermined amount V1 is 200 per mill.

(18) In ST 34, it is determined whether the control should be finishes or not. For example, for a certain number of continuous rotations (for example, 5000 rotations), when the fluctuation of the rotating speed of the engine 12 is within a predetermined range (for example, within 1000 rpm) and a number of times of the control implementations reaches a predetermined number of times (30 times), the control value at that time is determines as the actual operation control value, and then the control is finished. Otherwise, the control is moved to ST 22.

(19) FIG. 4 is a graph showing an example of changes in the engine rotating speed and the control value with respect to time when an actual operation was performed with load by using the chain saw according to the present invention.

(20) In FIG. 4, when the throttle was fully opened, the engine rotating speed was increased beyond 12000 rpm (C41). Then, when the chain saw 10 got started cutting wood and so on (with load), the engine rotating speed was decreased by an amount of load caused by the cutting operation, namely below 12000 rpm which is the target rotating speed, and remained below 12000 rpm during the cutting (C42). After the cutting is finished, the engine rotating speed was increased beyond 12000 rpm (C43), and when the throttle was returned, the engine, rotating speed was decreased to an idling rotating speed (C44). While the rotating speed of the engine 12 was within the predetermined high rotating speed range R1 (11000-14000 rpm, the PI control was performed (C45). Namely, according to whether the rotating speed of the engine 12 was smaller or larger than the predetermined rotating speed R2 (for example, 12000 rpm), the control value was increased (C46) or decreased (C47), respectively. When the control value was decreased, the control value was decreased by the result of the PI calculation. When the control value was increased and the PI control calculation value VC obtained by increasing the control value by the result of the PI calculation became larger than the limitation value, the control value was set to the limitation value VL (C48). In the third operation shown in FIG. 4, since the control value was continuously within the predetermined range (C47), the PI control was finished (C45), and the control value was determined as the actual operation control value. Thus, in the fourth operation shown in FIG. 4, the PI control was not performed. After that, in the fifth operation shown in FIG. 4, when the actual operation was performed with non-load, the engine stably rotated at around 13000 rpm, and no hunting phenomenon can be found (C48).

(21) Further, comparing the actual operation control values (the last control values) in FIGS. 4 and 6, the actual operation control value in FIG. 4 is restricted blow the limitation value VL, while the actual operation control value in FIG. 6 is relatively near 1000 per mill. Namely, the actual operation control value of the chain saw according to the present invention (FIG. 4) can be made closer to the actual operation control value to be determined with non-load than the actual operation control value of the chain saw according to prior art (FIG. 6).

(22) Further, comparing FIG. 4 using the chain saw 10 according to the present invention with FIG. 6 using prior art control, the fluctuations of the rotating speed with non-load are different from each other. Namely, in FIG. 4 using the chain saw 10 according to the present invention, the fluctuation is small and stable, while in FIG. 6 using the prior art control, the fluctuation is large. Thus, the chain saw according to the present invention does not provide an operator with uncomfortable feeling due to the fluctuation of rotation.

(23) As stated above, the limitation value VL (the upper limitation value) is a sum of the control value for completion operation V0 and the predetermined value V1. If the predetermined value V1 is too large, the control is not different from the prior art control. If the predetermined value V1 is too small, an effect of the control may be missed. For example, when a completion operation is performed at a lower ground level and an actual operation is performed at a higher ground level, an amount of supplying fuel is required to be reduced over the entire engine rotating speeds. In this connection, when the predetermined value V1 is too small, the amount of supplying fuel cannot be sufficiently reduced.

(24) Although an embodiment of the present invention has been explained, the present invention is not limited to the embodiment, namely, many kinds of modifications can be done within the scope of the present invention, and it goes without saying that such modifications fall within the scope of the present invention.