Portable engine working machine and rotary carburetor incorporated therein

Abstract

To improve responsiveness of fuel supply control, a rotary carburetor 100 has a nozzle 8 including a fuel discharge port 8a and a needle 10 disposed coaxially with the nozzle 8 and disposed with a portion inserted into the nozzle 8. The needle 10 can be displaced relative to the nozzle 8 to change an effective area of the fuel discharge port 8a. The rotary carburetor 100 has an electric motor 14 for displacing the needle 10 along an axis, and a drive mechanism component 12 interposed between the electric motor 14 and the needle 10 and converting a rotational movement of the electric motor into a linear movement.

Claims

1. A portable engine working machine comprising: a rotary carburetor disposed in an intake passage of the portable engine working machine; a rotatable valve main body included in the rotary carburetor, mechanically coupled to a throttle trigger operated by an operator, and rotated by an operation of the throttle trigger to change a throttle opening degree; a nozzle disposed on an axis of the rotatable valve main body and including a fuel discharge port supplying a fuel to an intra-carburetor air-fuel mixture passage; a needle disposed coaxially with the nozzle and disposed with a portion inserted into the nozzle, the needle being displaced relative to the nozzle to change an effective area of the fuel discharge port so as to control an amount of a fuel discharged from the fuel discharge port; an electric motor for displacing the needle along an axis; a drive mechanism component interposed between the electric motor and the needle and converting a rotational movement of the electric motor into a linear movement; and a control unit for zero-point adjustment adjusting an origin of the electric motor, wherein the control unit sets as the origin a position at which the needle is no longer displaceable upward or downward when the electric motor is driven out of a control range of displacement of the needle for controlling an amount of the fuel.

2. The portable engine working machine of claim 1, wherein the rotatable valve main body has a hollow throttle shaft extending on the axis of the rotatable valve main body, and a throttle lever coupled to the throttle shaft in a relatively non-rotatable manner and mechanically coupled to the throttle trigger, and wherein the drive mechanism component is received in the throttle shaft.

3. The portable engine working machine of claim 2, further comprising a vertical drive mechanism vertically displacing the rotatable valve main body when the rotatable valve main body is in rotational motion.

4. The portable engine working machine of claim 3, wherein the vertical drive mechanism includes a cam surface disposed on an end surface of the rotatable valve main body.

5. The portable engine working machine of claim 2, further comprising a drive gear or drive roller rotating in conjunction with an operation of the throttle trigger, and a position sensor for detecting a rotation of the drive gear or drive roller, wherein a throttle opening degree is detected by the position sensor through an intermediate gear or roller interposed between the position sensor and the drive gear or drive roller.

6. The portable engine working machine of claim 2, further comprising a position sensor disposed to surround a rotating member rotating in conjunction with an operation of the throttle trigger, wherein a throttle opening degree is detected by the position sensor.

7. The portable engine working machine of claim 6, wherein the rotating member is the throttle lever.

8. The portable engine working machine of claim 6, wherein the rotating member is the rotatable valve main body.

9. A rotary carburetor disposed in an intake passage of a portable engine working machine comprising: a rotatable valve main body mechanically coupled to a throttle trigger operated by an operator, the rotatable valve main body rotated by an operation of the throttle trigger to change a throttle opening degree; a nozzle disposed on an axis of the rotatable valve main body and including a fuel discharge port supplying a fuel to an intra-carburetor air-fuel mixture passage; a needle disposed coaxially with the nozzle and disposed with a portion inserted into the nozzle, the needle being displaced relative to the nozzle to change an effective area of the fuel discharge port so as to control an amount of a fuel discharged from the fuel discharge port; an electric motor for displacing the needle along an axis; a drive mechanism component interposed between the electric motor and the needle and converting a rotational movement of the electric motor into a linear movement; and a control unit for zero-point adjustment adjusting the origin of the electric motor, wherein the control unit sets as the origin a position at which the needle is no longer displaceable upward or downward when the electric motor is driven out of a control range of displacement of the needle for controlling an amount of the fuel.

10. The rotary carburetor of claim 9, wherein the rotatable valve main body has a hollow throttle shaft extending on the axis of the rotatable valve main body, and a throttle lever coupled to the throttle shaft in a relatively non-rotatable manner and mechanically coupled to the throttle trigger, and wherein the drive mechanism component is received in the throttle shaft.

11. The rotary carburetor of claim 10, further comprising a vertical drive mechanism vertically displacing the rotatable valve main body when the rotatable valve main body is in rotational motion.

12. The rotary carburetor of claim 11, wherein the vertical drive mechanism includes a cam surface disposed on an end surface of the rotatable valve main body.

13. The rotary carburetor of claim 9, wherein the rotary carburetor is applied to a stratified scavenging engine, and wherein the rotatable valve main body further includes an air passage supplying air to a scavenging passage of the stratified scavenging engine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a perspective view of a rotary carburetor mounted on an engine working machine of a first embodiment.

(2) FIG. 2 shows an exploded perspective view of the rotary carburetor of FIG. 1.

(3) FIG. 3 shows a longitudinal sectional view of the rotary carburetor of FIG. 1.

(4) FIG. 4 shows a schematic view for explaining a structure of a rotary carburetor mounted on an engine working machine of a second embodiment.

(5) FIG. 5 shows a view for explaining one method of zero-point adjustment of a motor and a zero-point is defined as a point at which a needle collides with a plane serving as a reference of a carburetor main body when the needle is extended.

(6) FIG. 6 shows a view for explaining another method of zero-point adjustment of a motor and a zero-point is defined as a point at which a step portion between a drive mechanism component and the needle collides with an end surface of a nozzle.

(7) FIG. 7 shows a view for explaining the other method of zero-point adjustment of a motor and a zero-point is defined as a limit value, i.e., a point at which the needle can no longer be raised, when the needle is continuously raised by an electric motor.

(8) FIG. 8 shows a flowchart for explaining one zero-point adjustment method.

(9) FIG. 9 shows a diagram for explaining the zero-point adjustment shown in FIG. 8 performed during deceleration.

(10) FIG. 10 shows a flowchart for explaining the other zero-point adjustment method.

(11) FIG. 11 shows a diagram for explaining the zero-point adjustment shown in FIG. 10 performed during acceleration.

(12) FIG. 12 shows a diagram for explaining one modification example of arrangement of a position sensor.

(13) FIG. 13 shows a diagram for explaining another modification example of arrangement of the position sensor.

(14) FIG. 14 shows a diagram for explaining another modification example of arrangement of the position sensor.

(15) FIG. 15 shows a diagram for explaining the other modification example of arrangement of the position sensor.

(16) FIG. 16 shows a diagram for explaining an outline of a rotary carburetor according to the present invention preferably applicable to a stratified scavenging engine.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

(17) Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. A rotary carburetor of the embodiments is incorporated in a portable engine working machine. Typical examples of the portable engine working machine include chain saws and bush cutters. Although a two-stroke engine is a typical example of an engine, the engine may obviously be a four-cycle engine.

First Embodiment (FIGS. 1 to 3)

(18) FIGS. 1 to 3 show a rotary carburetor mounted on a portable engine working machine according to a first embodiment of the present invention. FIG. 1 is a perspective view. FIG. 2 is an exploded perspective view. FIG. 3 is a longitudinal sectional view.

(19) Referring to FIGS. 1 to 3, a shown rotary carburetor 100 has a carburetor main body 2, and a columnar valve main body 4 is received in an axis-rotatable manner in the carburetor main body 2. This valve main body 4 is not displaced in the axial direction.

(20) As in the prior art, the carburetor main body 2 has two openings 2a opposed to each other. The cylindrical valve main body 4 has one through-hole 4a. This through-hole 4a forms an intra-carburetor passage 6 together with the two openings 2a, and an air-fuel mixture is generated in the intra-carburetor passage 6. Therefore, this intra-carburetor passage 6 will be referred to as an intra-carburetor air-fuel mixture passage in the following description.

(21) The axial rotation of the cylindrical valve main body 4 controls an effective passage cross-sectional area of the intra-carburetor air-fuel mixture passage 6, i.e., a throttle valve opening degree as in the prior art.

(22) The rotary carburetor 100 has a nozzle 8 fixed to the carburetor main body 2 as in the prior art (FIG. 3). The nozzle 8 extends upward on the axis of the valve main body 4 and penetrates the valve main body 4 into the carburetor air-fuel mixture passage 6. Therefore, the valve main body 4 is rotatable around the stationary nozzle 8. A tip portion of the nozzle 8 is provided with a fuel discharge port 8a in a circumferential surface thereof (FIG. 3) and, when fuel is discharged from the fuel discharge port 8a, the air-fuel mixture is generated in the intra-carburetor air-fuel mixture passage 6 and this air-fuel mixture is supplied to a crank chamber as in the prior art.

(23) A portion of a needle 10 is inserted in the nozzle 8 as in the prior art. Therefore, the needle 10 is arranged on the axis of the valve main body 4. In other words, the needle 10 is coaxial with the nozzle 8. The effective area of the fuel discharge port 8a is defined by a tip portion of the needle 10, and the needle 10 is vertically moved to control an amount of fuel supplied through the fuel discharge port 8a to the intra-carburetor air-fuel mixture passage 6.

(24) The needle 10 is provided with a drive mechanism component 12 vertically displacing the needle 10. The drive mechanism component 12 includes a conversion mechanism using, for example, a screw for converting a rotational movement to a linear movement. An electric motor 14 (FIG. 1) is coupled to the drive mechanism component 12. A typical example of the electric motor is a stepping motor.

(25) Reference numeral 18 shown in FIG. 2 denotes a return spring, and reference numeral 20 denotes a cover member. The carburetor main body 2 receiving the valve main body 4 is closed by the cover member 20. The return spring 18 is interposed between the cover member 20 and the valve main body 4.

(26) The valve main body 4 has a cylindrical throttle shaft 22 extending upward, and this throttle shaft 22 extends upward through the cover member 20. The throttle shaft 22 is rotatable relative to the cover member 20. The outer circumferential surface of the throttle shaft 22 has a non-circular irregular cross-sectional shape (FIG. 2).

(27) A throttle lever 24 and a position sensor 26 are arranged around the throttle shaft 22. A case of the position sensor 26 has a ring shape and is arranged coaxially with the throttle shaft 22. The case of the position sensor 26 has a shape surrounding at least a portion of the circumference of the throttle shaft 22 and is fixed to the cover member 20 by a fixing member 28 (FIG. 3) surrounding an upper end portion of the drive mechanism component 12, and first bolts 30. Although the fixing member 28 is not shown in FIG. 2, the drive mechanism component 12 is fastened to the fixing member 28 by second bolts 32 and the drive mechanism component 12 is received in the hollow throttle shaft 22.

(28) In the throttle lever 24, an opening receiving the throttle shaft 22 has an irregular shape complementary to the throttle shaft 22, so that the throttle lever 24 is integrated with the throttle shaft 22, i.e., the valve main body 4. Therefore, the throttle lever 24 is coupled to the throttle shaft 22 in a relatively non-rotatable manner. The throttle lever 24 is mechanically linked through a wire (indicated by W in FIG. 4) to a throttle trigger (indicated by Tt in FIG. 4) operated by an operator. When the operator operates the throttle trigger Tt, the movement of the throttle lever 24 interlocking with this operation causes the valve main body 4 to rotate around an axis so as to control the passage effective cross-sectional area of the intra-carburetor air-fuel mixture passage 6, i.e., the throttle valve opening degree.

(29) The ring-shaped position sensor 26 arranged around the throttle shaft 22 can detect the rotational position of the throttle lever 24. Therefore, the throttle valve opening degree of the rotary carburetor 100 can linearly be detected by the position sensor 26. In FIG. 1, reference numeral 34 denotes a control unit with a memory 36, and reference numeral 38 denotes a sensor for detecting a rotation speed of an engine.

(30) The throttle valve opening degree detected by the position sensor 26 is applied to the control of the fuel supply amount together with the engine rotation speed, for example. Specifically, the position sensor 26 can sense that the valve main body 4 is (i) located at an idle position, (ii) located at a fully open position, and (iii) located at a partial position, and (iv) a rotational speed of the valve main body 4, i.e., a throttle valve opening degree change speed, (v) a rotation amount of the valve main body 4, i.e., a throttle valve opening degree change amount, etc. These are applied to the control unit 34 to control the electric motor 14 (FIG. 1), i.e., the needle 10, so that the effective opening area of the fuel discharge port 8a of the nozzle 8 can directly be controlled. Thus, the optimization of fuel supply can be achieved with excellent responsiveness.

(31) This optimization of fuel supply is achieved without using a solenoid valve as in the prior art and therefore has no risk of causing the problem of using the solenoid valve, i.e., the problem that iron powder in fuel is accumulated and consequently clogs an intra-carburetor fuel passage.

(32) The position sensor 26 only needs to detect the rotation of the throttle shaft 22 within the rotational range of the valve main body 4 and therefore can have a shape defined by this detection range; however, in the case of the position sensor 26 having a ring shape, this sensor is easily arranged around the throttle shaft 22 of the valve main body 4, so that the rotary carburetor 100 including the position sensor 26 can be made compact.

Second Embodiment (FIG. 4)

(33) FIG. 4 shows a rotary carburetor 200 mounted on a portable engine working machine of a second embodiment. In the description of the rotary carburetor 200 shown in FIG. 4, the same elements as those of the first-mentioned rotary carburetor 100 are denoted by the same reference numerals. FIG. 4 is a view for explaining a main part of the rotary carburetor 200. The main part of the rotary carburetor 200 will be described with reference to FIG. 4. Although not shown in FIG. 4, the ring-shaped position sensor 26 described in the first embodiment may be disposed in the rotary carburetor 200.

(34) The valve main body 4 received in the carburetor main body 2 described with reference to FIG. 1 etc. rotates around an axis and is vertically displaced along the axis. Therefore, the rotary carburetor 200 has a vertical drive mechanism vertically moving the valve main body 4. The vertical displacement of the valve main body 4 is accompanied by a vertical motion of the needle 10. In other words, the valve main body 4 and the needle 10 rotate together and are vertically displaced together. On the other hand, the nozzle 8 is fixed to the carburetor main body 2 and therefore is not vertically displaced. The rotation of the valve main body 4 is induced by the throttle lever 24 mechanically interlocking through the wire W with an operator's operation of the throttle trigger Tt. The rotation of the valve main body 4 is accompanied by a vertical motion thereof and is also accompanied by a vertical motion of the needle 10. The vertical displacement of the needle 10 changes the effective area of the fuel discharge port 8a opened in the circumferential surface of the nozzle 8. Specific description will hereinafter be made with reference to FIG. 4.

(35) Referring to FIG. 4, the valve main body 4 has a cam 204 on an end face thereof, which is a lower end surface in this embodiment, and a cam surface 204a of the cam 204 is engaged with a support pin 206 fixed to the carburetor main body 2. When the valve main body 4 rotates around the axis, the cam 204 vertically displaces the valve main body 4. This vertical drive mechanism is the same as the rotary carburetor of Patent Document 4 cited above.

(36) The cylindrical throttle shaft 22 extending upward from the valve main body 4 extends upward through the cover member 20 and has an upper end fixed to the throttle lever 24.

(37) The rotary carburetor 200 of the second embodiment includes the needle 10 and the drive mechanism component 12 vertically driving the needle 10 with the electric motor 14 (FIG. 1), and the drive mechanism component 12 has an upper end portion fixed to the throttle lever 24 by the fixing member 28 and bolts 202.

(38) When the operator operates the throttle trigger Tt, this operation is transmitted through the wire W to the throttle lever 24, and the throttle lever 24 rotates. When the throttle lever 24 rotates, the throttle shaft 22 rotates. Therefore, the valve main body 4 rotates. This causes a change in the passage effective cross-sectional area of the intra-carburetor air-fuel mixture passage 6 (FIG. 1), i.e., the throttle opening degree.

(39) When the valve main body 4 rotates, the valve main body 4 is displaced upward or downward by the cam 204. This displacement is transmitted through the throttle shaft 22 and the throttle lever 24 to the drive mechanism component 12 and the needle 10 is displaced upward or downward together with the drive mechanism component 12. On the other hand, since the nozzle 8 is fixed to the carburetor main body 2 (FIG. 3), the effective area of the fuel discharge port 8a of the nozzle 8 changes due to the displacement of the needle 10.

(40) In the rotary carburetor 200 shown in FIG. 4, the effective area of the fuel discharge port 8a is mechanically controlled in conjunction with the operator's trigger operation. This can be used as a basis for applying electronic control using the electric motor 14. Therefore, a control amount of the optimum control of the fuel supply amount using the electric motor 14 has a corrective meaning, so that a small control amount thereof is sufficient. When the control amount is smaller, the responsiveness of the control becomes better, and consequently, the responsiveness of the optimum control of the fuel supply amount can further be improved.

(41) Zero-Point Adjustment (FIGS. 5 to 11):

(42) By adjusting the origin of upward or downward displacement of the needle 10 based on the rotation of the electric motor (stepping motor) 14, i.e., adjusting a zero-point, the accuracy of the fuel supply amount control can be ensured. This zero-point adjustment is performed by using a predetermined reference plane included in the rotary carburetors 100, 200 and the electric motor 14. Three examples of the zero-point adjustment will be described with reference to FIGS. 5 to 7.

(43) FIG. 5 is a view for explaining one example of the zero-point adjustment when the carburetor main body 2 has a concave portion under the needle 10 and a bottom surface 42 of this concave portion is used as the reference plane. Specifically, the zero-point adjustment is performed by defining as the origin, i.e., the zero-point, a point at which the needle 10 collides with the bottom surface 42 of the concave portion and causes the stepping motor 14 to step out when the needle 10 is deviated from a displacement range of control of the needle 10, i.e., a movable control range of the needle 10, and further displaced downward.

(44) FIG. 6 shows another example in which the drive mechanism component 12 is deviated from a movable control range of the drive mechanism component 12 and further displaced downward to cause a step portion 12a between the needle 10 and the drive mechanism component 12 to collide with an upper end surface of the nozzle 8. Therefore, FIG. 6 shows an example of the zero-point adjustment performed by defining as the origin, i.e., the zero-point, a point at which the step portion 12a abuts on the nozzle 8. Thus, the example of FIG. 6 is an example in which the upper end surface of the nozzle 8 is used as the reference plane.

(45) FIG. 7 shows the other example in which the zero-point is set as a point at which the needle 10 can no longer move upward, i.e., a point at which the needle 10 can no longer be retracted, when the needle 10 is displaced (retracted) upward to the maximum. Specifically, in FIG. 7, the zero-point adjustment is performed by defining as the origin, i.e., the zero-point, a point at which the needle 10 can no longer move upward when the needle 10 is deviated from the movable control range of the needle 10 and further displaced upward.

(46) The zero-point adjustment is preferably performed when the operation state of the engine is a predetermined operation state. The examples of FIGS. 5 and 6 include a step of completely closing the fuel discharge port 8a with the needle 10 and are therefore suitably performed at the time of deceleration. The example of FIG. 7 includes a step of completely opening the fuel discharge port 8a and is therefore suitably performed at the time of acceleration.

(47) The zero-point adjustment during deceleration will be described with reference to FIGS. 8 and 9. In FIG. 8, it is determined at step S10 whether a throttle operation is in a deceleration state. This determination is made based on the output of the position sensor 26. At next step S11, it is determined whether the throttle opening degree is at the idle position. This determination is also made based on the output of the position sensor 26. At next step S12, it is determined whether a change amount of the throttle operation is equal to or greater than a first threshold value. If all the steps of steps S10 to S12 are YES, it is determined that the current operation state corresponds to a region with zero-point adjustment shown in FIG. 9, and the zero-point adjustment is performed at step S13. This zero-point adjustment is performed by the method described with reference to FIG. 5 or 6. For example, in the example of FIG. 5, the needle 10 is displaced downward to collide with the bottom surface 42 of the concave portion. At next step S14, the position of the needle 10 abutting on the bottom surface 42 is set as the zero-point, and this value on the memory 36 (FIG. 1) is updated to zero.

(48) The zero-point adjustment during acceleration will be described with reference to FIG. 10. In FIG. 10, it is determined at step S20 whether a throttle operation is in an acceleration state. This determination is made based on the output of the position sensor 26 through the control unit 34 (FIG. 1). At next step S21, it is determined whether the throttle opening degree is at the fully open position. This determination is also made based on the output of the position sensor 26. At next step S22, it is determined whether a change amount. of the throttle operation is equal to or greater than a second threshold value. If all the steps of steps S20 to S22 are YES, it is determined that the current operation state corresponds to a region with zero-point adjustment shown in FIG. 11, and the zero-point adjustment is performed at step S23. This zero-point adjustment is performed by the method described with reference to FIG. 7. Specifically, the needle 10 is displaced upward to move the needle 10 to a position at which the needle 10 can no longer be displaced. At next step S24, the zero-point is set to the position at which the needle 10 can no longer be displaced upward, and this value on the memory 36 (FIG. 1) is updated to zero.

(49) Regarding the arrangement of the position sensor 26 in the first and second embodiments, since the position sensor 26 is for the purpose of detecting the throttle opening degree, the arrangement position of the position sensor 26 is arbitrary as long as this purpose is achieved, as illustratively shown in FIGS. 12 to 15.

(50) As shown in FIG. 12, a drive gear or drive roller 300 may be disposed on an output shaft of the electric motor 14. The position sensor 26 detects the rotation of the drive gear or drive roller 300 through an intermediate gear or roller 302 interposed between the position sensor 26 and the drive gear or drive roller 300.

(51) As shown in FIG. 13, the position sensor 26 may be attached to the carburetor main body 2, and this position sensor 26 may be arranged at a position where the rotation of the valve main body 4 can be detected.

(52) As shown in FIG. 14, the position sensor 26 may be disposed between the carburetor main body 2 and the cover member 20 to detect the rotation of the valve main body 4.

(53) As shown in FIG. 15, the valve main body 4 may be provided with a cylindrical part 306 extending downward from the lower surface thereof, and the position sensor 26 may be disposed around the cylindrical part 306.

(54) Although the first and second embodiments and modification examples thereof have been described, the present invention is not limited to a rotary carburetor having the one through-hole 4a (the intra-carburetor air-fuel mixture passage 6) in the valve main body 4. The present invention is also applicable to the stratified scavenging rotary carburetor disclosed in Patent Document 5 (U.S. Pat. No. 7,261,281 B2). FIG. 16 shows the valve main body 4 included in a stratified scavenging rotary carburetor 350 of a third embodiment. It should be understood that the other constituent elements of this stratified scavenging rotary carburetor 350 is substantially the same as the first and second embodiments. Referring to FIG. 16, the valve main body 4 has an air passage 352 in addition to the intra-carburetor air-fuel mixture passage 6. Air is supplied through this air passage 352 to a scavenging passage of a stratified scavenging engine. This scavenging passage is denoted by reference numerals 13, 14 in FIG. 2 of US 2014/0360467 A1 and U.S. Pat. No. 8,166,931 B2. In U.S. Pat. No. 8,833,316 B2, a specific configuration of the scavenging passage is disclosed in FIG. 3 (reference numeral 34). These disclosures of US 2014/0360467 A1, U.S. Pat. No. 8,166,931 B2, and U.S. Pat. No. 8,833,316 B2 are incorporated in this description. The air supplied to the scavenging passage is supplied as leading air to a combustion chamber of a two-stroke engine in a scavenging stroke thereof.

EXPLANATIONS OF LETTERS OR NUMERALS

(55) 100 rotary carburetor of first embodiment 200 rotary carburetor of second embodiment 350 rotary carburetor of third embodiment 2 carburetor main body 4 valve main body (rotating member) 6 intra-carburetor air-fuel mixture passage 8 nozzle 8a fuel discharge port 10 needle 12 drive mechanism component 14 electric motor 22 hollow throttle shaft 24 throttle lever (rotating member) 26 position sensor 34 control unit 36 memory 204a cam surface 300 drive gear or drive roller