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. In case the controller determines that the engine-driven working machine gets started saw cutting, the controller stops varying the control value of the solenoid valve when the rotating speed of the engine is within the predetermined high rotating speed range and lower than the target rotating speed.

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 fuel supplied to the electronically controlled carburetor, wherein the controller is configured to determine whether or not the working machine is in a load state; wherein the controller is configured 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, the working machine is not in the load state, and the rotating speed of the engine is higher than a target rotating speed, wherein the controller is configured to vary the control value of the solenoid valve 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 working machine is not in the load state, and the rotating speed of the engine is lower than the target rotating speed, and wherein the controller is not configured to vary the control value of the solenoid valve when the rotating speed of the engine is within the predetermined high rotating speed range, the working machine is in the load state, and the rotating speed of the engine is lower than the target rotating speed.

2. The engine-driven working machine according to claim 1, wherein the controller is configured to vary the control value of the solenoid valve so as to increase the opening degree of the solenoid valve when the rotating speed of the engine is within the predetermined high rotating speed range, the working machine is in the load state, and the rotating speed of the engine is higher than the target rotating speed.

3. The engine-driven working machine according to claim 1, wherein the controller determines that the engine-driven working machine enters the load state when a changing value of the rotating speed of the engine for one rotation of the engine is lower than a predetermined threshold value more than a predetermined number of times per a predetermined number of continuous rotations.

4. The engine-driven working machine according to claim 1, wherein the controller determines that the engine-driven working machine enters the load state when a changing value of the rotating speed of the engine for one rotation of the engine is within a predetermined range more than a predetermined number of times per a predetermined number of continuous rotations.

5. 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 rotating speed with respect to time and determination of the saw cutting when an actual operation was performed with load by using a chain saw according to the present invention.

(5) FIG. 5 is a graph showing the engine rotating speed and its changing value during a period A shown in FIG. 4.

(6) FIG. 6 is a graph showing an example of changes in the engine rotating speed with respect to time and determination of the saw cutting state when an actual operation was performed with load by using a chain saw according to the present invention.

(7) FIG. 7 is a graph showing the engine rotating speed and its changing value during a period B shown in FIG. 6.

(8) FIG. 8 is a graph showing the engine rotating speed and its changing value when the actual operation was performed with non-load.

(9) FIG. 9 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.

(10) FIG. 10 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

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

(12) 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.

(13) 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.

(14) 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.

(15) 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.

(16) 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.

(17) 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.

(18) 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, 10500-14000 rpm). If the answer is NO, the control is not performed and is returned to ST 22. If the answer is YES, the control is moved to ST23.

(19) In ST 23, it is determined whether or not the chain saw is in a saw cutting state. When the answer is NO, the control is moved to ST 24.

(20) When the answer is YES, the control is moved to ST 25, The determination whether or not the chain saw is in the saw cutting state will be explained later in detail.

(21) When the chain saw is not in the saw cutting state, 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).

(22) 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.

(23) 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.

(24) When the rotating speed of the engine 12 is lower than the target rotating speed R2 (for example, 12000 rpm), in ST 30, the control value is increased by the result of the PI calculation so that the opening degree of the solenoid valve 20 is decreased, and then the control is moved to ST 34.

(25) When the chain saw is in the saw cutting state, in ST 25, it is determined whether the rotating speed of the engine 12 is higher or lower than the target rotating speed R2 (for example, 12000 rpm).

(26) When the rotating speed of the engine 12 is higher than the target rotating speed R2 (for example, 12000 rpm), in ST 31, 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.

(27) When the rotating speed of the engine 12 equals to or is lower than the target rotating speed R2 (for example, 12000 rpm), the PI control is not performed, and then, the control is moved to ST 34. Namely, when the chain saw is in the saw cutting state, the control value is not increase so that the opening degree of the solenoid valve 20 is not decreased.

(28) In ST 34, it is determined whether the control should be finished 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 reached a predetermined number of times (30 times), the control value at that time is determined as the actual operation control value, and then the control is finished. Otherwise, the control is returned to ST 22.

(29) Next, the determination whether or not the chain saw according to the present invention is in the saw cutting operation state will be explained in detail.

(30) FIG. 4 is a graph showing an example of changes is the rotating speed with respect to time and determination of the saw cutting state when an actual operation was performed with relatively large load by using a chain saw according to the present invention. FIG. 5 is a graph showing the engine rotating speed and its changing value during a period A shown in FIG. 4. The changing value of the engine rotating speed is a difference between the rotating speeds of the engine 12 per one rotation of the engine. Namely, when the rotating speed is faster than that in the previous rotation, the changing value is positive, and when the rotating speed is later than that in the previous rotation, the changing value is negative.

(31) In FIG. 4, when the throttle was fully opened, the engine rotating speed was increased approximately to 12000 rpm (C11). When the rotating speed of the engine 12 was in the predetermined high rotating speed range R1 (10500-14000 rpm) and until the chain saw became in a saw cutting state explained later, the PI control was performed (C12). Namely, according to whether the rotating speed of the engine 12 was smaller or larger than the predetermined rotating speed 112 (for example, 12000 rpm), the control value is increased or decreased, respectively.

(32) As shown in FIG. 5, when the throttle was fully opened, the chain saw 10 reached a fully-opened rotating speed with non-load (C13), and then, was operated at the rotating speed with non-load (C14). It has been found that when the chain saw 10 got started cutting wood and so on (with load) and the load was relatively large, the blades of the chain saw contacted an object to be saw cut so that the fluctuation of the changing value of the engine rotating speed became large toward a negative direction (C15), and then, the blades of the chain saw was moved into the object so that the blades of the chain saw became in a stable saw cutting state and the fluctuation of the changing value of the engine rotating speed became small (C16). During the period C15, when the changing value of the rotating speed of the engine per one rotation of the engine 12 became lower than a predetermined threshold value V1 (minus 90 rpm) more than a predetermined number of times (for example, three times) per a predetermined number of continuous rotations (for example, 10 rotations), it was determined that the chain saw 10 got started saw cutting (C17). The predetermined number of times per the predetermined times of continuous rotations and the predetermined threshold value V1 were appropriately defined so that whether or not the chain saw 10 got started saw cutting can be distinguished. After the determination of the starting of the saw cutting, the control of decreasing the control value so as to increase the opening degree of the solenoid valve 20 was maintained, but no control of increasing the control value so as to decrease the opening degree of the solenoid valve 20 was performed.

(33) As shown in FIG. 4, after the finishing of the saw cutting, the engine rotating speed was increased, to approximately 12000 rpm (C18), and then, when the throttle was returned, the engine rotating speed was decreased to the idling rotating speed (C19). When the engine rotating speed was decreased blow a predetermined rotating speed V2 (for example, 4000 rpm), it was determined that the saw cutting was finished (C20).

(34) FIG. 6 is a graph showing an example of changes in the engine rotating speed with respect to time and determination of the saw cutting state when the actual operation was performed with the chain saw according to the present invention with a relatively small load. FIG. 7 is a graph showing the engine rotating speed and its changing value during a period B shown in FIG. 6.

(35) In FIG. 6, when the throttle is fully opened, the engine rotating speed was increased beyond 12000 rpm (C31). While the rotating speed of the engine 12 was within the predetermined high rotating speed range R1 (10500-14000 rpm) and until it became in a saw cutting state explained below, the PI control was performed (C32). 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 or decreased, respectively.

(36) As shown in FIG. 7, when the throttle was fully opened, the chain saw 10 reached the fully-opened rotating speed with non-load (C33), and then, was operated at the rotating speed with non-load (C34). When the chain saw 10 got started cutting wood and so on (with load) and the load is relatively small, the blades of the chain saw 10 contacted an object to be saw cut, but since the fluctuation of the changing value of the engine rotating speed toward a negative direction was smaller than that in FIG. 5 (C35), it was not possible to determine whether or not the chain saw 10 got started saw cutting in the same way as that explained referring to FIG. 5. Then, it has been found that at the same time the blades of the chain saw 10 out into the object, the chain saw became in a stable saw cutting state and the fluctuation of the changing value of the engine rotating speed became small. In a period C36, when the changing value of the rotating speed per one rotation of the engine 12 is within a predetermined range R3 (for example, 30 rpm) more than a predetermined number of times (for example, 10 times) per a predetermined number of times of continuous rotations (for example, 10 rotations), it was determined that the chain saw 10 got started saw cutting (C37). The predetermined number of times per the predetermined number of continuous rotations is appropriately defined so that whether or not the chain saw 10 got started saw cutting can be distinguished. After the determination of the starting of the saw cutting, the control of decreasing the control value so as to increasing the opening degree of the solenoid valve 20 was maintained, but no control of increasing the control value so as to decrease the opening degree of the solenoid valve 20 was performed.

(37) As shown in FIG. 6, after the finishing of the saw cutting and then, when the throttle was returned, the engine rotating speed was decreased to the idling rotating speed (C39). When the engine rotating speed was decreased below the predetermined rotating speed V2 (for example, 4000 rpm), it was determined that the chain saw 10 is not in the saw cutting state (C40).

(38) FIG. 8 is a graph showing the engine rotating speed and its changing value when the actual operation was performed with non-load.

(39) As can be seen from FIG. 8, the changing value of the rotating speed of the engine was not within a predetermined value range R3 (for example, 30 rpm) and was larger than the predetermined threshold value V2 (for example, minus 90 rpm). Thus, the predetermined value range R3 and the predetermined threshold value V2 can be a reference for determining whether or not the chain saw is in the saw cutting state.

(40) As stated above, whether or not the chain saw gets started cutting is determined, and after the starting of the saw cutting, the control of decreasing the control value can be performed so as to increase the opening degree of the solenoid valve 20, but no control of increasing the control value is performed so as to decreasing the opening degree of the solenoid valve 20, so that the actual operation control value of the chain saw according to the present invention 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. Thus, the chain saw according to the present invention does not provide an operator with uncomfortable feeling due to the fluctuation of rotation.

(41) 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.