JPS62271954A - Variable venturi type carburetor - Google Patents

Abstract

PURPOSE:To prevent the mixture from being lean during acceleration, by disposing a valve which is opened when the venturi vacuum increases, in an auxiliary air-bleed passage in an air-bleed passage in a variable venturi type carburetor. CONSTITUTION:A needle 4 provided in a variable venturi piston 2 controls a main jet 21. An air-bleed passage 26 for a main fuel system is communicated with an auxiliary air-bleed passage extending from a passage 38 opened to a venturi section, and the passage i closed by a valve 39 which is opened by vacuum in a hole 24 opened to the venturi section, overcoming a spring 41. During acceleration, the venturi vacuum lowers so that the valve 39 is closed by the spring 41 and therefore, auxiliary air bleed is stopped, thereby it is possible to prevent the mixture from being lean.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a variable venturi type carburetor, and more particularly to a variable venturi type carburetor that controls the air-fuel ratio by air bleed. Regarding.

[Conventional technology]

A suction piston that changes the venturi area in response to the amount of intake air, a needle connected to the suction piston, a fuel passage extending in the axial direction of the needle so that the needle can enter, and a needle provided in the fuel passage. A variable venturi type carburetor is known which is equipped with a metering unit that cooperates with the fuel passage and an air bleed passage for supplying air into the fuel passage (Japanese Patent Laid-Open Nos. 58-140455 and 178858-1999). Public notices, etc.).

In the variable venturi type carburetor described in the above publication, the amount of fuel is metered in an annular gap between a needle that moves together with a suction piston and a metering jet, and the amount of fuel is further emptied by changing the amount of air bleed during warm-up, etc. The fuel ratio is now controlled. A flow control valve with a conical surface is used to control the amount of air bleed, and the passage area is continuously changed according to the temperature of the engine cooling water. It is designed to obtain the air-fuel ratio. Furthermore, the air-fuel ratio is controlled by additionally controlling the amount of air bleed depending on other operating conditions. For example, the above-mentioned JP-A-58-1
40455, the amount of air bleed is controlled by a throttle opening signal, and JP-A-58-178858 provides an air bleed control valve for feedback controlling the air-fuel ratio based on the output of an oxygen concentration sensor. ing.

[Problem that the invention seeks to solve]

When the amount of air bleed is multifaceted controlled by a plurality of parameters, the volume of the air bleed passage formed through the carburetor body immediately before the connection to the fuel passage increases. On the other hand, in a variable bencheri type carburetor, the venturi negative pressure is maintained almost constant at all times by the movement of the suction piston, but during acceleration when the throttle valve is suddenly opened, the venturi negative pressure temporarily becomes almost equal to the intake negative pressure. The value increases (in the negative direction). As a result, the pressure difference between the venturi negative pressure and the atmospheric pressure in the air bleed passage increases, causing a larger amount of air bleed air to be sucked out than was set assuming a constant venturi negative pressure. This causes the problem that the air-fuel ratio becomes lean even during acceleration. At this time, as mentioned above, if the volume of the air bleed passage just before the connection to the fuel passage is large, a large amount of air bleed air accumulated there will be sucked in, making the air-fuel ratio leaner. There was a problem with ki(naru).

Means for Solving Problem c] In order to solve the above problem, the variable venturi type carburetor according to the present invention includes a connecting passage that connects the F-bleed passage and the venturi for supplying air into the fuel passage. The invention is characterized in that the connecting passage is provided with a valve device that opens when the venturi negative pressure becomes greater than a predetermined value.

〔Example〕

Referring to FIGS. 1 and 2, 1 is the carburetor main body, 2 is an intake passage extending vertically, 3 is a suction piston that moves back and forth in the horizontal direction within the intake passage 2, and 4 is the tip end surface of the suction piston 3. 6 is a throttle valve installed in the intake passage 2 downstream of the suction piston 3, 7 is a float chamber of the carburetor, and a venturi is installed between the tip surface of the suction piston 3 and the wall of the carburetor body. 8 is formed. A hollow cylindrical casing 9 is fixed to the carburetor main body l.
A guide sleeve 10 is mounted inside the casing 9 and extends in the axial direction. A bearing 12 is located inside the guide sleeve 10.
is inserted, and the outer end of the guide sleeve 10 is fitted with a blind lid 13.
Closed by. On the other hand, a guide rod 14 is fixed to the suction piston 3, and the guide rod 14 is inserted into the bearing 12 so as to be movable in the axial direction of the guide rod 14. Since the suction piston 3 is thus supported by the casing 9 via the bearing 12, the suction piston 3 can move smoothly in its axial direction. The inside of the casing 9 is divided by the large diameter portion of the suction piston 3 into a negative pressure chamber 15 and an atmospheric pressure chamber 16 opposite thereto. A compression spring 17 is inserted. The negative pressure chamber 15 is connected to the venturi 8 through a suction hole 18 formed in the suction piston 3, and the atmospheric pressure chamber 16 is connected to the intake air upstream of the suction piston 3 through an air hole 19 formed in the carburetor body 1. It is connected within the passage 2.

On the other hand, a fuel passage 20 extending in the axial direction of the needle 4 is formed in the carburetor main body l so that the needle 4 can enter therein, and a metering jet 21 is provided within this fuel passage 20. The fuel passage 20 is connected to the float chamber 7 via a downwardly extending fuel pipe 22 upstream of the metering jet 21 , and the fuel in the float chamber 7 is sucked into the fuel passage 20 via this fuel pipe 22 . Further, a nozzle 23 having a hollow cylindrical shape and arranged coaxially with the fuel passage 20 toward the intake passage 2 is fixed. This nozzle 23 protrudes into the venturi 8 from the inner wall surface of the carburetor main body, and the upper half of the tip of the nozzle 23 further protrudes from the lower half toward the suction piston 3. Needle 4 is nozzle 23
and extends through the metering jet 21 , so that the fuel is metered by the annular gap formed between the needle 4 and the metering jet 21 and then supplied from the nozzle 23 into the intake passage 2 .

As shown in FIGS. 1 and 2, the fuel passage 20 and the metering jet 21 are formed by a cylindrical member, and this cylindrical member is fitted into a hole in the carburetor body together with a nozzle 23. . An open annular air passage (chamber) 24 is formed between this cylindrical member and the fitting hole, and this annular air passage 24
A plurality of air bleed holes 25 are formed through the metering jet 21 to communicate the inside of the metering jet 21 with the metering jet 21 . The annular air passage 24 is connected to an air bleed passage 26 formed within the carburetor body l.

Air is supplied to the air bleed 26 via a plurality of valve devices, and in the illustrated embodiment, air is supplied via a cold time control valve 27 and an electromagnetic control valve 28.

The cold time control valve 27 includes a bushing rod 30 having a conical surface that is actuated by wax 29, and an air bleed hole 31 is formed corresponding to the position of the conical surface of the bushing rod 30. The air intake hole 32 of this flow control valve is connected upstream of the venturi 8 in the intake passage 2. 33 and 34 are the inlet and outlet of engine cooling water. This cold time control valve 2
No. 7 is a well-known type that increases the amount of air bleed as the engine cooling water temperature rises. Therefore, when the engine cooling water temperature is low, the air-fuel ratio is set to be rich because the amount of air bleed from now on is small, and as the temperature rises and the amount of air bleed increases, the air-fuel ratio becomes lean.For example, when the cooling water temperature reaches about 80℃ The air bleed amount reaches its maximum constant value.

The electromagnetic control valve 28 is for feedback controlling the air-fuel ratio to a stoichiometric air-fuel ratio or a predetermined lean air-fuel ratio based on the output of an oxygen concentration sensor disposed in an exhaust passage of the engine (not shown). Such an electromagnetic control valve is also well known, and the valve member 35, which is controlled by an applied voltage, a duty signal, etc., continuously controls the passage area of the air bleed passage 36.

Therefore, as shown in FIG.
occupies a relatively large volume within the wall of the carburetor body 1 to flow from both the cold-time control valve 27 and the solenoid control valve 28 to the air bleed hole 25 which is the connection to the air-fuel passage 20. Note that an air bleed jet 37 is disposed in the air bleed passage 26 upstream of the point where the air bleed passage 36 for the electromagnetic control valve 28 joins the main air bleed passage 26 .

As shown in FIGS. 1 and 2, the air bleed jet 37 of the air bleed passage 26 and the air bleed hole 25
A connecting passage 38 is provided that connects the venturi 8 with a relatively large-volume portion between the connecting passage 38 and the venturi 8.
A valve device 39 is provided which opens when the venturi negative pressure becomes larger than a predetermined value (on the negative side). The valve device 39 includes a valve member 40 that slides in a cylinder bore formed in the wall of the carburetor main body 1 and blocks off the connecting passage 38 with its distal end surface, and a valve member that abuts the rear surface of the valve member 40. 40 in the closing direction, and the cap 42 fitted in the cylinder bore is pressed against the spring 41
The venturi negative pressure is applied to the rear surface of the valve member 40 by forming a spring seat for the valve member 40 and a small hole provided therein.

Further, a bypass fuel passage 43 is formed by branching from a position upstream of the metering jet 21 of the fuel passage 20, and this bypass fuel passage 43 receives air from an air bleed passage 44 and also has an idle adjustment screw 45.
The flow rate is controlled by 1111, bypassing around the nozzle 23 and opening above the throttle valve 6.

In the variable venturi type carburetor having the above configuration, the suction piston 3 moves in accordance with the amount of intake air to vary the passage area of the venturi 8. In other words, when the throttle valve 6 is wide (opened) and the amount of intake air increases, the flow velocity of the venturi 8 increases and the negative pressure increases, and this negative pressure enters the negative pressure chamber 15 from the suction hole 18 and moves into the suction piston. 3 to the left in Fig. 2. When the amount of intake air is small, the suction piston 3 moves to the right.

In this way, the negative pressure of the venturi 8 remains almost constant. For example, when the load is light and the opening amount of the throttle valve 6 is small, the opening amount of the suction piston 3 is also small, the intake negative pressure downstream of the throttle valve 6 is -11 g, and the negative pressure of the venturi 8 upstream of the throttle valve 6 is -11 g. 15msHg,
The negative pressure immediately before the air bleed hole 25 of the air bleed passage 26 is -3 ml/g. On the other hand, when the throttle valve 6 is opened under high load and the opening amount of the suction piston 3 is large, the intake negative pressure downstream of the throttle valve 6 is
The negative pressure in the venturi 8 upstream of the throttle valve 6 is -15 mm 1 g, and the negative pressure in the air bleed passage 26 is -3 mmHH. That is, regardless of the opening degrees of the throttle valve 6 and the suction piston 3, the pentieri negative pressure is always approximately constant, and therefore the negative pressure in the air bleed passage is also approximately constant.

However, when the throttle valve 6 is suddenly opened as during acceleration, there is a transient state between the above-mentioned light load state and high load state due to the opening delay of the suction piston 3, and at this time, the downstream of the throttle valve 6 The negative intake air is -40mm 11g as in the case of high load, but due to the opening delay of the suction piston 3, the negative pressure in the venturi 8 momentarily increases to around -4Qmsl1g.

As a result, as described above, the pressure difference between the venturi 8 and the air bleed passage 26 increases, and the air accumulated in the air bleed passage 26 is sucked out, resulting in a leaner air-fuel ratio.

In the present invention, when the negative pressure of the venturi 8 becomes large, the venturi negative pressure overcomes the setting force of the spring 41 and opens the valve member 40 of the valve device 39, causing the venturi negative pressure to flow into the air bleed passage 26. will be introduced. As a result, the venturi 8 and the air bleed passage 26 have the same pressure, and air from the air bleed passage 26 does not enter the fuel passage 20 from the air bleed hole 25. Therefore, the negative pressure of the venturi 8 is not weakened midway, and
It acts on the fuel in the fuel passage 20 and can further pump up fuel from the float chamber 7 below. In particular, when air bleeds to the metering jet 21, if the amount of air supplied from the air bleed hole 25 becomes excessive,
The narrow annular space between the metering needle 4 and the metering jet 21 is filled with air, causing a break in the fuel, which causes the air-fuel ratio to become lean. After the temporary transient state, the negative pressure in the venturi 8 returns to the aforementioned constant value.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to prevent the air-fuel ratio from becoming lean during acceleration.

[Brief explanation of drawings]

FIG. 1 is a partially enlarged view of FIG. 2, and FIG. 2 is a sectional view of a variable venturi type carburetor according to the present invention. l... Carburetor body, 3... Suction piston, 4
... Needle, 2o... Fuel passage, 26... Air bleed passage, 38... Communication passage, 39... Valve device.

Claims (1)

[Claims] A carburetor body having an intake passage, a suction piston that can move laterally into and out of the intake passage to form a variable area venturi, a fuel passage into which a needle attached to the suction piston can enter, and the fuel passage. a variable venturi carburetor having a metering jet disposed therein and cooperating with the needle, and an air bleed passage for supplying air into the fuel passage, the air bleed passage and the venturi being connected; Provide a connecting passage,
A variable venturi type carburetor, characterized in that the connecting passage is provided with a valve device that opens when the venturi negative pressure becomes larger than a predetermined value.