Patent Grant
9670837
This application claims priority from Japanese Patent Application No. 2013-272355 filed Dec. 27, 2013, the entire content of which is incorporated herein by reference.
The present invention relates to a portable work tool provided with a compact engine, such as a brush cutter.
A compact engine is employed as a power source in an electric generator and a portable work tool such as a grass-trimmer, a brush cutter, a blower, a chain-saw, and a power cutter.
Such a conventional engine includes a cooling fan provided on one end of a crank shaft for cooling a cylinder. Rotation of the crank shaft causes the cooling fan to rotate, thereby generating cooling air for cooling the cylinder.
Japanese Patent Application. Publication No. H06-123243 discloses a mechanism in which a wind governor is employed to utilize cooling air for controlling operational states (rotation speed) of an engine. Specifically, a governor plate is disposed on an air flow path of the cooling air within a fan case. The governor plate is connected to a throttle valve shaft of a carburetor that controls a throttle opening in the carburetor. The governor plate is pivotally movable about this throttle valve shaft.
Specifically, in this wind governor, the throttle valve shaft is caused to rotate to decrease the throttle opening when a load decreases, a rotation speed increases, and wind power of cooling air becomes stronger. Conversely, the throttle valve shaft is caused to rotate to increase the throttle opening when the load increases, the rotation speed drops, and wind power of cooling air becomes weaker.
This mechanism is easily configured by simply connecting a small-sized governor plate (wind governor) to the throttle valve shaft and is therefore effective in various types of portable engine-powered work tools that require compact engines.
The output of the engine in a working state can be controlled appropriately by the wind governor. However, control using the wind governor considerably suppresses an output of the engine that can be originally generated by the engine. That is, when the wind governor is employed, the output obtained from the engine is suppressed and is considerably smaller than in a case where the wind governor is not employed.
A larger engine output in the working state can still be obtained, even if the wind governor is employed, by improving the structure around the carburetor and the wind governor. In this case, however, because these structures become complicated, an advantage of the wind governor that the above-described control can be performed with a simple structure is impaired. Still further, an actuator or the like can be employed to perform the above-described controls. In this case, too, however, a complicated structure is needed, which is not desirable for a brush cutter and the like that needs to be small and lightweight.
It is thus difficult to improve an engine output in a portable work tool provided with a wind governor, through a simple configuration.
In view of the foregoing, it is an object of the present invention to provide a work tool provided with a wind governor capable of overcoming the above-described drawbacks.
In order to attain the above and other objects, the invention provides an engine-powered work tool including an air-cooled engine, an ignition system for igniting the engine, an output controller, a wind governor, a rotation speed detector and an ignition control unit. The air-cooled engine includes a crank shaft configured to rotate and a cooling fan fixed to the crank shaft and configured to rotate together with the crank shaft to generate cooling air. The output controller is configured to control an output of the engine, the output controller including a throttle valve shaft defining an axis and configured to make an angular rotation about the axis, the output of the engine being controlled based on the angular rotation of the throttle valve shaft. The wind governor is connected to the throttle valve shaft and includes a governor plate configured to move upon receipt of the cooling air thereon, the wind governor being configured to control the angular rotation of the throttle valve shaft based on an amount of the cooling air received by the governor plate. The rotation speed detector is configured to detect a rotation speed of the crank shaft. The ignition control unit is configured to control the ignition system based on the rotation speed of the crank shaft detected by the rotation speed detector to reduce the output of the engine when the rotation speed detector determines that the governor plate exceeds a predetermined position.
Preferably, the ignition control unit is configured to reduce the output of the engine by changing ignition timing for igniting the engine when the rotation speed detector determines that the rotation speed of the crank shaft exceeds a predetermined value corresponding to the predetermined position.
Preferably, the ignition control unit is configured to reduce the output of the engine by thinning out a frequency of ignition when the rotation speed detector determines that the rotation speed of the crank shaft exceeds a predetermined value corresponding to the predetermined position.
Preferably, the rotation speed detector is configured to detect the rotation speed of the crank shaft based on a position of the governor plate that moves in accordance with the amount of the cooling air.
Preferably, the ignition control unit is configured to control the ignition system to reduce the output of the engine when the governor plate moves to pass the predetermined position upon receipt of the cooling air.
Preferably, the wind governor is configured to determine a designated rotation speed of the crank shaft of the engine operating under no load, and the predetermined position is determined based on the designated rotation speed of the crank shaft determined by the wind governor.
Preferably, the rotation speed detector includes a position sensor configured to detect a position of the governor plate and to output information indicative of the position of the governor plate, and the ignition control unit is configured to control the ignition system based on the information outputted from the position sensor.
Preferably, the ignition system includes an ignition coil configured to generate spark current for igniting the engine, the ignition control unit being positioned adjacent to the ignition coil.
Preferably, the output controller includes a main body through which the throttle valve shaft penetrates, the throttle valve shaft having one end and another end opposite to each other, the governor plate being fixed to the one end of the throttle valve shaft, and the wind governor further includes: an arm fixed to the another end of the throttle valve shaft; and a governor spring connected to the arm to apply a biasing force to the throttle valve shaft.
Preferably, the engine-powered work tool further includes: an end tool configured to be driven in accordance with the rotation of the crank shaft; and a supporting shaft having one end provided with the end tool and another end provided with the air-cooled engine, the ignition system, the output controller, the wind governor and the ignition control unit.
In the drawings:
A brush cutter 310 as an example of an engine-powered work tool according to an embodiment of the present invention will be described with reference to
Descriptions used in the following description in relation to the brush cutter 310 will reference the state of the brush cutter 310 shown in
Referring to
Handles 13 for gripping by an operator are provided at respective left and right sides near a center portion of the shaft 20 in the front-rear direction. In
Further, a waist pad portion 21 is provided on the shaft 20 between the handles 13 and drive section 30 for facilitating operator's operations while holding the handles 13. Specifically, the waist pad portion 21 is formed by an elastic material provided on the shaft 20 to cover (surround) the same such that the waist pad portion 21 has an outer diameter larger than that of the shaft 20. The operator performs cutting work while gripping the handles 13 (grips 16) with his or her waist supported by the waist pad portion 21. Still further, an antiscattering cover 14 is provided below the cutting blade 11 for preventing cut grass and branches from being scattered toward the operator.
The drive section 30 includes the engine 40, a fuel tank 60, a protective cover 15, a carburetor 70, an air cleaner 50, a muffler 80 and a wind governor 90. The fuel tank 60 is fixedly provided below the engine 40 for storing fuel. Before using the brush cutter 310, the operator should remove a tank cap 61 (see
As illustrated in
Referring to
The carburetor 70 (an example of an output controller) is attached to the suction port provided on the left side (on the right side in
The muffler 80 is attached to the exhaust port provided to the right (on the left side in
In the engine 40, a crank case 44 is provided below the cylinder 43. The crank case 44 includes the crank shaft 42 thereinside. The crank shaft 42 is configured to rotate in association with a vertical reciprocating movement of the piston within the cylinder 43. The crank shaft 42 extends in the front-rear direction in
Once the engine 40 has started, the fuel is introduced (sucked) from the fuel tank 60 up to the carburetor 70 by a negative pressure generated at the time of air intake. However, before the engine 40 is started, the fuel needs to be manually taken up to the carburetor 70. To this end, a priming pump 62 is provided as shown in
While the fuel (mixed gasoline) is supplied from the fuel tank 60 to the carburetor 70, air is also introduced into the carburetor 70 through the air cleaner 50. An air-fuel mixture is generated in the carburetor 70 and is supplied to the engine 40.
A combination of an engine and a carburetor having similar configurations as the engine 40 and carburetor 70 can be used not only for an engine-powered work tool such as the brush cutter 310 of the present embodiment, but also be applicable to other machines, such as a motorbike. However, in case of a motorbike, an angle formed between its carburetor and the ground (horizontal plane) does not vary significantly while the motorbike is in operation (during driving). In contrast, in case of the brush cutter 310, an angle formed between the shaft 20 and the ground (horizontal plane) is often likely to change while the brush cutter 310 is being used. For example, the operator may hold the shaft 20 horizontally generally parallel to the ground, or may turn the shaft 20 into an orientation significantly inclined relative to the horizontal plane in order to adjust a cutting angle.
Although there are various types of carburetors, a diaphragm-type carburetor is effective for stably supplying fuel and generating air-fuel mixture even when the angle between the carburetor and the horizontal plane varies significantly. In the diaphragm-type carburetor, a fuel chamber formed within the carburetor is partitioned by a diaphragm formed of an elastic body, and fuel is sucked up into this fuel chamber and stored therein by a certain amount. This configuration allows stable supply of the air-fuel mixture irrespective of the angle of the carburetor relative to the horizontal plane. For this reason, the diaphragm-type carburetor is preferable as the carburetor 70 of the present embodiment.
The carburetor 70 is also a so-called butterfly-type carburetor and includes a throttle valve shaft 71 and a butterfly valve (not shown). The throttle valve shaft 71 is configured to angularly rotate about its axis extending in the front-rear direction in response to operations of the wind governor 90, as will be described later. The butterfly valve is configured to pivotally move within and relative to the throttle valve shaft 71 in accordance with the angular rotation of the throttle valve shaft 71. By how much the throttle valve shaft 71 angularly rotates and by how much the butterfly valve pivotally moves relative to the throttle valve shaft 71 in response to the angular rotation of the throttle valve shaft 71 determines a throttle opening of the throttle valve shaft 71 (or the carburetor 70). In the carburetor 70 of this structure, the throttle opening can be adjusted in accordance with the angular rotation of the throttle valve shaft 71. Generally speaking, such a butterfly-type carburetor is preferable as a carburetor for an engine-powered work tool. In other words, a diaphragm-type carburetor provided with a throttle opening adjusting mechanism using a butterfly valve is particularly preferable to be used in an engine-powered work tool, just as the carburetor 70 of the present embodiment.
A rotation speed (the number of rotations) of the engine 40 (output of the engine 40) is controlled based on an amount of the air-fuel mixture supplied from the carburetor 70. A rotating state of the engine 40 can be roughly divided into two: an idling state and a working state. In the idling state, the rotation speed of the engine 40 (output of the engine 40) is maintained low and the centrifugal clutch 46 is not connected to the drive shaft to prevent the cutting blade 11 from rotating. In the working state, the rotation speed of the engine 40 (output of the engine 40) is maintained higher than that in the idling state, and the centrifugal clutch 46 is connected to the drive shaft to permit the cutting blade 11 to rotate.
In order to realize switching between the idling state and working state, the operator pulls (grips) the throttle lever 17 provided near the right grip 16 (shown in
The throttle wire 100 is slideably movably provided inside an outer tube 101, as shown in
Cutting work is performed only in the working state. In the working state, first, in a no-load-applied condition, the rotation speed of the engine 40 is set to a prescribed rotation speed. Then, when the operator puts the rotating cutting blade 11 in contact with grass and branches, a large load is applied to the cutting blade 11, and hence the throttle opening needs to be increased to increase the engine output. After that, when the operator separates the cutting blade 11 from grass and branches in order to finish the cutting work, the load applied to the cutting blade 11 decreases rapidly. If the throttle opening has been increased in this state, the rotation speed may possibly increase rapidly. Hence, when no load is applied, the throttle opening needs to be decreased.
For controlling the throttle opening (angular rotation of the throttle valve shaft 71), the wind governor 90 is provided on the throttle valve shaft 71 of the carburetor 70, referring to
Specifically, the wind governor 90 includes a governor plate 91, a governor rod 92, a governor spring 93 and the arm 94.
The governor plate 91 is configured to receive the cooling air. As shown in
Further, on the distal end of the governor rod 92, a position-sensor sensed portion 96 is also provided. This position-sensor sensed portion 96 is configured to be sensed by a position sensor 97 that is fixed to the fan case 31. The position sensor 97 may be fixed to the cylinder 43.
Further, as shown in
That is, in
It should be noted that the torque applied to the arm 94 from the throttle return spring 105 is set to be larger than the torque applied to the arm 94 from the governor spring 93. Hence, as long as the throttle return spring 105 expands, the arm abutting portion 104 abuts on the right end portion of the arm 94 from below irrespective of the state of the governor spring 93. The throttle valve shaft 71 is thus biased in the counterclockwise direction in
When the operator grips the throttle lever 17, the throttle wire 100 is pulled downward in
At this time, in the working state, the wind governor 90 is used to perform control as described below with reference to
In
In the wind governor 90, when the cooling air applied to the governor plate 91 increases (a larger pressure is applied to the governor plate 91 from the cooling air), the throttle valve shaft 71 is caused to angularly rotate in a direction to reduce the throttle opening (i.e., clockwise direction in
Specifically, when the rotation speed of the engine 40 decreases and the strength of the cooling air is reduced as shown in
The designated rotation speed is determined by adjusting relationships among the wind governor 90 (the governor plate 91, a spring constant of the governor spring 93, etc.), the throttle valve shaft 71, and the like. For example, the designated rotation speed can be increased when tension (spring constant) of the governor spring 93 is increased, while the designated rotation speed can be decreased when this tension is reduced. Alternatively, for example, by changing an attachment position of the governor spring 93, too, the designated rotation speed or the engine output corresponding to the designated rotation speed can be made variable. These are possible example of designated rotation speed changing means that may be provided in the brush cutter 310 of the present embodiment.
Generally, in case of an engine without a wind governor, output of the engine is likely to become larger as the rotation speed is higher, at least in a rotation speed range lower than or equal to its designated rotation speed. Hence, by increasing the designated rotation speed, a larger output can be obtained from the engine in the working state. However, if the designated rotation speed is increased, vibrations, noises, or increase in fuel consumption will result even when cutting work is not actually performed in the working state. Thus, increasing the designated rotation speed is not preferable to obtain a larger output. Rather, it is desirable to obtain a larger engine output at a low rotation speed, without increasing the designated rotation speed.
To this end, in the brush cutter 310 of the present embodiment, due to provision of the wind governor 90, the above-described control to decrease or increase the output of the engine 40 is performed based on the movement of the wind governor 90, especially based on the movement of the governor plate 91 configured to move upon receipt of the cooling air to cause angular rotation of the throttle valve shaft 71. Further, in the brush cutter 310 of the present embodiment, the output of the engine 40 is also controlled to decrease by controlling ignition by the ignition coil (ignition system) 47, in addition to the control by the wind governor 90. Specifically, the control for reducing the output of the engine 40 is performed by the ignition control unit 471 when the governor plate 91 moves past a predetermined position (switching position). The switching position is determined depending on the designated rotation speed of the engine 40 under no load condition in the working state that is defined by the wind governor 90. Combining the output reduction control of the engine 40 with the operations of the wind governor 90 can realize faster control (accelerate control speed) over the rotation speed (output) of the engine 40 than a case where only the wind governor 90 is employed.
Specifically, as a method for controlling the ignition coil 47, either ignition timing control or ignition thin-out control may be performed.
In either ignition timing control or ignition thin-out control, the position sensor 97 is used for detecting the position of the position-sensor sensed portion 96 provided on the governor rod 92 of the wind governor 90, as shown in
First, the ignition timing control to decrease the engine output will be described with reference to
Because the cooling fan is fixed to the crank shaft 42, the strength of cooling air and the rotation speed have one-to-one correspondence in both of the idling state and the working state. Thus, the rotation speed of the engine 40 and the position of the governor plate 91 (the angle of the governor rod 92) also have one-to-one correspondence. Hence, the rotation speed in
According to the ignition timing control shown in
In this state, if the load applied to the cutting blade 11 is cancelled suddenly, the rotation speed of the engine 40 increases rapidly due to the large throttle opening. At this time, as described above, the throttle opening is controlled to decrease by the wind governor 90. In the present embodiment, if the rotation speed exceeds 7000 rpm (as a threshold), the ignition timing is also controlled to be retarded (BTDC is reduced to about 5° in case of the example of
Further, when the rotation speed becomes lower than or equal to 7000 rpm due to this operation, the throttle opening is increased by the wind governor 90 and, at the same time, as shown in
With the above-described ignition timing control, original performance of the engine 40 can be extracted efficiently. This point will be described below with reference to
A curve (1) in
Here, when the rotation speed is low, cooling air is weak and the governor plate does not move. Hence the wind governor does not function practically. Thus, in a low rotation speed range near the idling state, output of (2) is equivalent to that of (1). In a high rotation speed range higher than the designated rotation speed, the wind governor suppresses the engine output considerably, and thus the output of (2) is considerably reduced lower than that of (1). Note that the wind governor also functions in a rotation speed range lower than or equal to the designated rotation speed and, in this rotation speed range, the output of (2) is suppressed lower than that of (1). Specifically, in case of the curve (2) where the wind governor is employed, while the wind governor performs the above-described control based on the designated rotation speed of 7500 rpm, the wind governor starts controlling the engine output gradually from a low rotation speed much lower than 7500 rpm. Thus, the output of (2) is considerably lower than that of (1) even in the rotation speed range of approximately 6000 to 6500 rpm. As a result, in case (2) where the wind governor is provided, original output of the engine is considerably reduced low even in the rotation speed range lower than or equal to the designated rotation speed in the working state.
On the other hand, a curve (3) in
Incidentally, in case of (2), by increasing the designated rotation speed of the wind governor under no load, the output at the rotation speed around 6000 rpm can be increased. In this case, however, since the designated rotation speed of the engine under no load is made higher, fuel consumption increases even when cutting work is not performed actually. In case of (3), in contrast, the engine output in the working state can be increased without increasing the designated rotation speed under no load in the wind governor 90. That is, with the above-described configuration of the present embodiment, decrease in original output of the engine 40 in the working state can be suppressed, and the engine 40 can be used efficiently. Fuel consumption during performing cutting work can also be held low.
Next, the ignition thin-out control, which may be performed instead of the ignition timing control, will be described with reference to
In
On the other hand, when the rotation speed of the engine 40 exceeds 7000 rpm, the ignition control unit 471 controls such that ignition by the ignition plug is performed once every two cycles of the crank shaft 42. That is, a frequency of ignition is thinned out to one half. The output of the engine 40 is thus reduced.
With this configuration, when the rotation speed exceeds 7000 rpm, ignition is thinned out to reduce the output of the engine 40. Concurrently with this ignition thin-out control, the control by the wind governor 90 is also performed. Hence, the output characteristics as shown in
As a variation, the ignition timing control and ignition thin-out control can be performed concurrently. Similar effects can also be obtained in this case.
As described above, what is significant in the configuration of the brush cutter 310 of the present embodiment is that, two kinds of control are employed in combination for controlling the compact air-cooled engine 40: the wind governor 90 for appropriately controlling the throttle opening in the working state; and the ignition control of the engine 40. This structure can more reliably suppress over speed of the engine 40 under no load condition, and can increase the output of the engine 40 upon application of a load without changing the rotation speed. As a result, engine output obtained in the working state can be increased.
Further, the ignition control of the engine 40 is performed based on the rotation speed (number of rotations) of the engine 40 (crank shaft 42) in the present embodiment. To this end, the wind governor 90 and position sensor 97 are employed as the rotation speed detector for detecting the rotation speed of the engine 40. The rotation speed detector does not need to detect an accurate rotation speed in the entire rotation speed range, but only needs to detect whether the rotation speed reaches the rotation speed (threshold) at which the necessary ignition control is configured to be started. Further, the wind governor 90 itself (position-sensor sensed portion 96) constitutes a part of the rotation speed detector and thus the rotation speed detector can be made simple in structure.
Various modifications and variations are conceivable.
In the depicted embodiment, the throttle valve shaft 71 extends in the front-rear direction to penetrate a main body of the carburetor 70 therethrough, and the governor plate 91 and governor rod 92 are fixed to the one end (front end) of the throttle valve shaft 71, while the arm 94 and governor spring 93 are fixed to the another end (rear end) of the throttle valve shaft 71. However, all these components (governor plate 91, governor rod 92, arm 94, and governor spring 93) may be provided on the same end of the throttle valve shaft 71. In this case, the throttle valve shaft 71 does not necessarily penetrate the main body of the carburetor 70. However, the depicted configuration is particularly preferable to realize a simplified structure near the carburetor 70 and to ensure smooth operations.
Further, as described above, the designated rotation speed changing means may be employed to adjust the wind governor 90 for adjusting the designated rotation speed under no load condition in the working state. In this case, the ignition control unit 471 is configured to recognize settings of the designated rotation speed changing means, and the similar control as in the present embodiment is performed based on the switching position of the governor plate 91 that is set in accordance with the designated rotation speed.
Further, in the depicted embodiment, the ignition timing control or ignition thin-out control is performed in order to decrease the engine output at rotation speeds higher than or equal to the predetermined threshold. However, other means for decreasing engine output may be employed appropriately, provided that such means has no adverse effects on the engine 40.
Further, in the above-described example, the position sensor 97 recognizes the position-sensor sensed portion 96, by which the position of the governor plate 91 can be indirectly recognized. However, other structures may also be used for the similar control by the ignition control unit 471, as long as the position of the governor plate 91 can be recognized directly or indirectly. For example, the angle of the governor rod 92 may be detected for performing similar control by the ignition control unit 471. Such structure for detecting the angle of the governor rod 92 may be configured appropriately depending on the configurations of the wind governor 90 and/or the carburetor 70. In any case, it is clear that a simple-structured sensor is required.
Further, in the above-described example, the wind governor 90 (position-sensor sensed portion 96) and the position sensor 97 are employed as the rotation speed detector. However, the rotation speed (the number of rotations) of the crank shaft 42 may be detected or recognized by another configuration. If this is the case, it is unnecessary to accurately recognize the rotation speed at all rotation speeds, but it is only necessary to determine whether the rotation speed of the crank shaft 42 exceeds a predetermined value, just as in the determination of whether the governor plate 91 reaches the switching position. Hence, the rotation speed detector can have a simple configuration. Note that, the depicted structure of the present embodiment is especially preferable in configuring the rotation speed detector, since only the position sensor 97 is required in addition to the wind governor 90 that has been conventionally employed.
In the depicted example, the brush cutter is used as an example of the engine-powered work tool of the present invention. However, the present invention can also be applicable to other types of portable engine-powered work tools provided with air-cooled engines.
While the invention has been described in detail with reference to the above-described embodiments thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-272355 | Dec 2013 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 2835237 | Thorner | May 1958 | A |
| 3104657 | Rice | Sep 1963 | A |
| 3118433 | Lechtenberg | Jan 1964 | A |
| 3850155 | Thomas | Nov 1974 | A |
| 4662328 | Kronich | May 1987 | A |
| 4836167 | Huffman | Jun 1989 | A |
| 20090317262 | Gilpatrick | Dec 2009 | A1 |
| 20110226217 | Raasch | Sep 2011 | A1 |
| 20120304963 | Raasch | Dec 2012 | A1 |
| Number | Date | Country |
|---|---|---|
| H06-123243 | May 1994 | JP |
| Entry |
|---|
| U.S. Appl. No. 14/579,653, filed Dec. 22, 2014, Ikeda et al. |
| Number | Date | Country | |
|---|---|---|---|
| 20150184595 A1 | Jul 2015 | US |
