DESCRIPTION

CARBURETOR

TECHNICAL FIELD

The present invention relates to a carburetor. More particularly, the present invention relates to a carburetor with an auto-choke mechanism used for an engine of a portable working machine such as a bush cutter.

BACKGROUND ART

A bush cutter for mowing weeds is conventionally known as a portable working machine. In such a bush cutter, a two-cycle engine or the like is used for driving a cutting blade or a nylon cutter provided at a tip end of an outer pipe. The engine is generally provided on a rear end side of the outer pipe. When the bush cutter is a knapsack type, the bush cutter is carried on the back of an operator by a suitable shouldering device (refer to, for example, Document 1 : Japanese Patent Laid-Open Publication No. HeilO-150825; and Document 2: Japanese Patent Laid-Open Publication No. Hei09-294441).

Recently, in order to improve startability of the engine, a bush cutter having an auto-choke mechanism has been developed. Though there are a variety of arrangements for the auto-choke mechanism, the inventor of the present invention has proposed an arrangement in which a solenoid valve (an electromagnetic valve) is provided integrally with a carburetor, and over-concentrated fuel (namely starting fuel) is supplied to an intake passage of the carburetor by opening the solenoid valve.

Most of the carburetors of this kind work in such a way that the auto-choke is effective (the auto-choke mechanism is operated) only when the temperature is equal to or lower than a predetermined value, i.e., when the engine is cold (refer to, for example, Document 3: Japanese Patent Laid-Open Publication No. 2002-339805).

However, in such a conventional carburetor, a supply passage for supplying the starting fuel from the fuel intake portion opened/closed by the solenoid valve to the intake

passage of the carburetor has a complicated shape restricted by the shape of a carburetor main body. Thus, pressure loss in the supply passage is increased, so that there are cases in which the fuel stagnate in the supply passage and thereby the fuel fail to easily reach the intake passage. Hence there arises a problem that startability of the engine is still not improved. Specifically, the number of the operation for rotating an output shaft of an engine, i.e., the number of cranking is increased when starting the engine.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a carburetor that can supply the optimal amount of the starting fuel to an engine when the engine is cold.

A carburetor according to an aspect of the present invention includes: an intake passage for making an intake air to an engine flow therethrough; a fuel storage section for storing a fuel from a fuel tank; a starting fuel supply passage for supplying a starting fuel from the fuel storage section to the intake passage; and a passage opening/closing section provided in the middle of the starting fuel supply passage, in which at least a part of the starting fuel supply passage between a portion opened/closed by the passage opening/closing section and the intake passage is formed in a straight line .

In the above arrangement, since at least a part of the starting fuel supply passage between the portion opened/closed by the passage opening/closing section and the intake passage is formed in a straight line, the pressure loss of the fuel between the portion opened/closed by the passage opening/closing section and the intake passage is suppressed, so that the fuel can be easily extracted to the intake passage by the negative pressure generated in the intake passage without stagnating. Accordingly, the optimal amount of the starting fuel can be supplied to the engine when the engine is cold, and a mixed gas having the optimal fuel concentration can be supplied to the engine, so that the startability of the engine can be secured.

According to another aspect of the present invention, it is preferred that in the aforesaid carburetor, the portion opened/closed by the passage opening/closing section is provided with a seat member having a seat face that abuts on the passage opening/closing

section when the portion is closed, the maximum seat diameter of the seat member being set to 1.0 mm.

In the above arrangement, if the seat diameter of the seat member provided in the portion opened/closed by the passage opening/closing section is set to be larger than 1.0 mm, excessive fuel will be supplied via the seat member and unburned fuel will be left in the engine, so that the startability will be deteriorated. In contrast, by setting the seat diameter to at most 1.0 mm, the startability of an engine can be prevented from being deteriorated. Accordingly, choke function of the carburetor can be sufficiently accomplished to a cooled engine, so that the startability of the engine can be maximized.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a cross section showing a carburetor of an embodiment of the present invention; and

Fig. 2 is an enlarged cross section showing a primary portion of the carburetor of the embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of the present invention will be described below with reference to the attached drawings. Fig. 1 is a cross section showing a carburetor 1 of the present embodiment. Fig. 2 is an enlarged cross section showing a primary portion of the carburetor 1.

As shown in Fig. 1 , the carburetor 1 includes a carburetor main body 2 and a solenoid valve 3 mounted on the carburetor main body 2. The solenoid valve 3 serves as a passage opening/closing section for an auto-choke of the present invention. The carburetor main body 2 is a device for mixing air with a fuel and has a conventional construction. Accordingly, when explaining the operation (the flow of the fuel) of the carburetor main body 2, the description of the conventional construction of the carburetor main body 2 will be briefly discussed.

Although not illustrated, the fuel from a fuel tank is supplied to a fuel storage section 22 through an inlet pipe 25 and an inner passage of the carburetor main body 2. A pump section is provided in the middle of the inner passage, which is actuated by a pressure change inside a crank case in accordance with the reciprocation of a piston, and the fuel is sent to the fuel storage section 22 by the pump section. The fuel of the fuel storage section 22 is also sent to a nozzle 23 communicated with the fuel storage section 22. The nozzle 23 is arranged coaxially with the rotation center of a rotary valve 24 that rotates interlocking with the operation of a throttle, and a tip end of the nozzle 23 projects into a through-hole 24A formed in the rotary valve 24. When the rotary valve 24 is rotated by the operation of the throttle, an intake air flow rate passing through the through-hole 24A increases, and the fuel in the nozzle 23 is extracted from an opening 23 A formed on the tip end of the nozzle 23 to the through-hole 24A by a negative pressure generated within the through-hole 24A. That is, since a needle 23B closing the opening 23 A moves in accordance with the rotation of the rotary valve 24 toward a direction in which the opening 23 A becomes more opened, the fuel from the nozzle 23 is extracted by the negative pressure.

On the other hand, since the fuel storage section 22 is separated from a diaphragm chamber 29A communicating with outside by a diaphragm 29, when the fuel is extracted from the nozzle 23, the diaphragm 29 moves toward the inside of the fuel storage section 22. Further, a hammer 29B provided at the center of the diaphragm 29 presses an arm 27A that is connected to a storage section needle 27 closing a communicating hole 28 provided between the fuel storage section 22 and a terminal portion 26 of the inner passage. Since the storage section needle 27 moves to open the communicating hole 28, the fuel is supplied to the fuel storage section 22, and therefore a predetermined amount of the fuel is constantly stored in the fuel storage section 22.

In the above manner, the fuel extracted to the through-hole 24A is mixed with the air, and the mixed gas is supplied to the engine through an intake passage 21 communicating with the through-hole 24A.

Incidentally, an inner diameter of the intake passage of the present embodiment, namely a venture diameter Dl, is set within a range of 10.5 to 12.5 mm. The carburetor 1 having the venture diameter Dl within the above range can be applied to a two-cycle engine having a displacement of 20 to 40 cc. The carburetor main body 2 is provided with a starting fuel supply passage 30 for auto-choke. The aforesaid solenoid valve 3 is provided to open/close the starting fuel supply passage 30.

The starting fuel supply passage 30 includes a fuel intake portion 31 that houses a tip end of a movable iron core 60 (which will be described later) of the solenoid valve 3 therein, a first supply passage 32 that supplies the fuel in the fuel storage section 22 to the fuel intake portion 31, and a second supply passage 33 that supplies the fuel passed through the fuel intake portion 31 to the intake passage 21.

A cylindrical seat member 38 is press-fitted into the fuel intake portion 31. The seat member 38 separates the fuel intake portion 31 into two spaces 31A, 31B respectively on the upstream side and the downstream side, and has a communicating path 31 C that intercommunicates the spaces 3 IA, 3 IB.

Of the first and second supply passages 32, 33, the second supply passage 33 is formed so as to allow the fuel intake portion 31 B and the intake passage 21 to communicate with each other in a straight line. By forming the second supply passage 33 in a straight line, the pressure loss of the fuel in the second supply passage 33 can be suppressed, so that the fuel can be easily supplied to the intake passage 21 without being stagnated in the second supply passage 33. Further, the second supply passage 33 can be formed, for example, by drilling from the side of the intake passage 21.

The solenoid valve 3 includes the movable iron core 60, a coil spring 61 that biases the movable iron core 60 downward as shown in the drawings, and a cylindrical coil 62 arranged outside the outer periphery of the movable iron core 60. As shown in Fig. 2, a conical abutting portion 6OA is formed at a tip end of the movable iron core 60, and a conical cap 6OB made of synthetic rubber is provided thereon to cover the conical abutting portion 6OA. In a state where the cylindrical coil 62 is not excited, since the conical cap

6OB abuts on a seat face 38A (an abutting portion of the seat member 38), the fuel does not flow through the communicating path 31 C. The conical cap 6OB is provided to improve the sealing performance. When the cylindrical coil 62 is excited, since the movable iron core 60 is moved against the biasing force of the coil spring 61 and thereby the conical cap 6OB leaves away from the seat member 38, the fuel intake portion 31 A and the fuel intake portion 3 IB communicate with each other, so that the fuel flows through the communicating path 31C.

In addition to the solenoid valve 3, the auto-choke mechanism of the present embodiment includes a temperature sensor for detecting a temperature of the engine, and a controller for controlling the solenoid valve 3 based on the result detected by the temperature sensor. By controlling the operation of the auto-choke mechanism so that the auto-choke mechanism operates when the temperature of the engine becomes equal to or lower than a predetermined temperature, the startability of the engine is improved.

When starting the engine, while activating the auto-choke, since the cylindrical coil 62 is excited and therefore the solenoid valve 3 is opened, the fuel from the fuel tank is supplied to the intake passage 21 of the carburetor main body 2 through the fuel intake portion 31 and the first and second supply passages 32, 33. Thus, an over-concentrated air- fuel mixed gas is supplied to the engine by the intake passage 21.

Herein, as shown in Fig. 2, a seat diameter D2 of the seat member 38 provided in the fuel intake portion 31 is set to at most 1.0 mm in order to prevent excessive fuel supply. If the seat diameter D2 is set to be larger than 1.0 mm, unburned fuel will be left in the engine, so that the startability will be deteriorated. In the present embodiment, in order to sufficiently accomplish the choke function to a cooled engine so as to maximize the startability of the engine, an optimized value for the seat diameter D2 is sought for. As a result, the seat diameter D2 is set to 0.6 mm.

It is to be understood that the present invention is not limited to the embodiment described above, but various modifications and improvements can be made as long as an object of the present invention can be achieved.

For example, although the solenoid valve 3 is used as the passage opening/closing section of the present embodiment, the present invention is not limited thereto, but any other arrangements such as an actuator using a piezoelectric motor can be used as the passage opening/closing section of the present invention. Further, although the first supply passage 32 for supplying the fuel in the fuel storage section 22 to the fuel intake portion 31 is not formed in a straight line in the present embodiment, the first supply passage 32 may also be formed in a straight line similar to the second supply passage 33.

Also, though the preferred configurations, methods and the like for carrying out the present invention are described above, the present invention is not intended to be limited thereto. In other words, though the present invention is mainly illustrated and described based on specific embodiment thereof, it should be understood that various modifications in the shape, material, quantity, and other details of construction can be made by those skilled in the art based on the embodiment described above without departing from the spirit and objects of technical characteristics of the present invention.

Accordingly, the description disclosed above, which gives specific shape, material and the like, is just an exemplary description to make the present invention well understood instead of being a definition of the limits of the invention, therefore the description based on a component name without part or all of the specific shape, material and the like is included in the present invention.

INDUSTRIAL APPLICABILITY

The present invention can be effectively applied to an engine using a carburetor having an auto-choke.