JPS6321355A - Air bleed device for variable venturi carburetor - Google Patents

Abstract

PURPOSE:To prevent blow back from an intake system and prevent variation in air fuel ratio by providing a buffering means consisting of a throttle and an expansion chamber on an air bleed passage of a variable venturi carburetor. CONSTITUTION:A variable venturi type carburetor having a suction piston 16 on the upper course side of a throttle valve 22 is fed with a fuel with a measured quantity measured by a measuring needle 26, from a float chamber 32 via a suction pipe 30 and a measuring jet 34. An air bleed passage 48 is connected to an annular chamber 46 around the measuring jet 34. An air bleed is controlled by each of an air fuel ratio control valve 54 which is controlled to a defined air fuel ratio by a control device 60 based on a signal from an air fuel ratio detector 62, a high land compensating valve 52, and a low temp. quantity increasing device 50, and supplied. A buffering chamber 70 consisting of a buffer jet 72 as a throttle and an expansion chamber is provided on its air bleed passage 49. And,blow back from a mixing chamber is buffered by this buffering chamber 70, without reaching air bleed control devices.

Description

[Detailed Description of the Invention] [Industrial Application Field] Is this invention an air bleed system for a variable venturi carburetor? I
Regarding the Il device.

[Conventional technology]

In a carburetor, it is necessary to variably control the air-fuel ratio in the rich direction or lean direction with respect to the Heas value for warm-up control, altitude control, and furthermore, feed hack control. Therefore, performing air bleed control is a well-known technique. When the carburetor is of the variable venturi type, air bleed is effected by opening an air bleed passage at the metering jet.

[Problem that the invention seeks to solve]

When introducing bleed air at the metering jet,
As the number of control items increases, for example, if warm-up control, altitude control, and feedback control are performed in one bleed passage, the volume of the bleed passage will inevitably increase.

If the bleed 1lll road volume 4Cj is large, a large amount of air will be bleed in the engine speed range of, for example, about 2000 to 3000 rpm, which resonates with the frequency of intake pulsation, and the air-fuel ratio will shift to the lean side. As a result, even if you try to control the power in this rotation speed range, the output air-fuel ratio cannot be set.In order to make it possible to set the output air-fuel ratio, if you take measures to make the metering needle thinner, the air-fuel ratio will change in the partial load range. The fuel becomes rich and the fuel consumption rate worsens.

[Means for solving problems]

According to the invention, there is provided a metering needle that is moved in the fuel passage so as to keep the venturi pressure constant, a metering jet that is formed in the fuel passage and that controls the amount of fuel in cooperation with the metering needle, and a metering jet that is formed in the fuel passage and controls the amount of fuel in cooperation with the metering needle. There is provided an air bleed device for a variable venturi carburetor, characterized in that it has an air bleed passage that is open to a jet and controls air bleed, and further includes a buffer means disposed in the air bleed passage.

〔Example〕

In FIG. 1, a variable venturi carburetor 10 includes a main body 14 defining an intake passage I2. A suction piston 16 is provided so as to be able to move in and out of the intake passage 12 in the lateral direction. A throttle valve 2 is located below the mixing chamber 18 formed between the suction screws 1 to 16 and the wall surface of the intake passage 12.
2 is located.

The pressure upstream of the throttle valve 22 acts on the left side of the piston 16, and the pressure downstream of the throttle valve acts on the left side of the piston 16, and the piston 16 moves left and right so that the differential pressure between the front and rear sides balances the set load of the compression spring 24. This provides the advantage of a variable venturi carburetor that the venturi pressure remains constant regardless of the throttle valve opening. A metering needle 26 is fixed to the suction piston 16, and the metering needle 26
extends into the fuel metering passage 28. The fuel metering passage 28 is closed at one end and opens into the mixing chamber 18 at the other end.

The upper end of the fuel suction pipe 3o opens into the fuel metering passage 28, and the lower end thereof extends below the fuel liquid level stored in the float chamber 32. In the downstream direction of the fuel flow in the metering passage 28, the inner surface of the metering passage is constricted and the metering jet 3
4 is formed. The portion of the metering needle 26 that extends through the metering passage 28 forms a tapered surface 28a, and this tapered surface 2
8a is the piston 1G by cooperating with the metering jet 34.
In other words, an amount of fuel is passed in accordance with the stroke, that is, the amount of intake air, and thereby a desired air-fuel ratio can be set. Upstream of the metering jet 34, the fuel passage 28 opens via a bypass passage 31, an annular chamber 38 and a passage 40 into the mixing chamber 18 upstream of the throttle valve but downstream of the venturi. An air bleed passage 42 opens into the bypass passage 31 . A portion of the fuel branched from the bypass passage 31 is introduced into the mixing chamber 18 in a mixed state with air introduced from the air bleed passage 42. The amount is metered and controlled by the mixing adjustment screw 44, and the idle speed can be adjusted.

An annular chamber 46 is formed around the metering jet 34, into which an air bleed passage 48 opens. In this embodiment, the air bleed passage 4B is the air bleed pipe 4.
9 to the low temperature increaser 50, the altitude compensation valve 52, and the air-fuel ratio control valve 54. The low temperature bulking device 50 is
It consists of a valve body 50a that opens and closes an air introduction passage 51 connected to the air bleed pipe 49, and a temperature sensing member 50c connected to the valve body 50a. The temperature sensing member 50c has a passage 50d.
When the temperature is low, the temperature sensing member 50 acts on the engine cooling water.
In case c, the valve body 50a is located on the right side, the amount of air introduced is small, and as a result, the air-fuel ratio is set richer than the base value.

After warming up, the valve body 50a moves to the left and the amount of air introduced increases, so the air-fuel ratio becomes the base value. In addition, Jet 50e
determines the effective diameter of the bleed passage of the low temperature bulking device.

The altitude compensation valve 52 controls the opening and closing of the air introduction passage 53, and the nine bellows 52b, which includes a bellows 52b filled with absolute pressure and a valve body 52C for controlling the amount of air introduced, contracts when traveling on flat ground and closes the valve. Since the body 52G is closed, the amount of air introduced is small and the air-fuel ratio is the base value. When traveling at high altitudes, the bellows 52b expands and the amount of air introduced increases. Since the air density is low when driving at high altitudes, there is not enough air and the engine becomes rich, but by introducing air, the air-fuel ratio is corrected to the appropriate level. Note that the jet 52d determines the effective diameter of the bleed passage of the altitude compensation valve.

The air-fuel ratio control valve 54 includes a valve body 54a that opens and closes an air introduction passage 55 to the air bleed pipe 49, and a solenoid 54b for driving the valve body 54a. The solenoid 54b is driven by a well-known air-fuel ratio control circuit 60. The air-fuel ratio control circuit 60 outputs an opening/closing signal for the air-fuel ratio control valve 54 based on the air-fuel ratio signal from the air-fuel ratio detector 62, which increases or decreases the amount of air introduced and feedback-controls the air-fuel ratio to the stoichiometric air-fuel ratio. operation is obtained. 54d determines the effective diameter of the bleed passage of the air-fuel ratio control valve.

As in this embodiment, three low-temperature increase control valves 50, altitude compensation valves 52, and air-fuel ratio control valves 54 are installed in the four air bleed pipes, and each performs necessary control. Performing such a large number of controls inevitably increases the volume of the air bleed system. FIG. 3 shows the air-fuel ratio characteristics with respect to the engine speed when the air bleed volume is large and when it is small. If the air bleed passage volume is large (dashed line), for example, 2000 to 3000 rpm
There is a problem that the air-fuel ratio deviates to lean in the engine speed range of . This seems to be because intake pulsation occurs when the throttle valve opening is large, and the frequency of this pulsation exactly resonates with the volume of the bleed passage, resulting in a significant increase in the amount of air bleed.

In this invention, in order to solve this problem, a buffer chamber 70 is installed in the air bleed pipe 49, and this buffer chamber 70
A diaphragm 72 is arranged on the metering agent side in close proximity to the diaphragm 72 . The dimensions of this throttle 72 are the jet 50e of the low temperature increase valve, the jet 52d of the altitude compensation valve, and the jet 54 of the air-fuel ratio control valve.
Select it so that it is equal to or somewhat larger than the sum of d.

As a result, the desired operation of the low temperature increaser valve 50, altitude compensation valve 52, and air-fuel ratio control valve 54 is not affected, and the necessary buffer operation can be obtained.

To explain the operation of the buffer chamber 70, in the partial load operating range, the intake pulsation of the mixing chamber 18 is small because the opening degree of the throttle valve 22 is small. Therefore, the pulsation applied to the air bleed jet formed in the metering jet 34 is also small. Therefore, the low temperature increase valve 50. Bleed air from the altitude compensation valve 52 and the air-fuel ratio control valve 54 can flow in smoothly.

When the throttle valve 22 opens wide, the intake pipe negative pressure weakens and the pulsation on the air bleed jet at the metering valve 34 opening into the mixing chamber 18 increases. At this time, the influence of pulsation is blocked by the cooperation between the buffer jet 72 and the buffer chamber 70. In this way, the air bleed amount characteristic shown by the solid line in FIG.
It is possible to prevent the lean deviation of the air-fuel ratio as shown by the broken line in the figure.

In another embodiment of the buffer chamber 70, as shown in FIG. 2, the negative side wall surface is formed by a diaphragm 80, and atmospheric pressure acts on one side of the diaphragm 80.

The diaphragm 80 can exert a strong buffering effect by being displaced in response to pressure pulsations.

〔effect〕

According to this invention, by providing a buffer chamber in the air bleed passage, even if there is pulsation in the intake pipe negative pressure, this influence can be blocked and the air-fuel ratio can be set appropriately.

In addition, if the engine stalls due to poor clutch engagement when starting, the air will blow back from the intake pipe.
If blowback from the intake pipe occurs due to a run-on, the installation of the buffer chamber 70 prevents a sudden increase in pressure and backflow of fuel, preventing high-pressure fuel from entering the control valve, which may cause initial startup failure. can be prevented.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of an embodiment of the present invention. FIG. 2 is a partial view showing a modified embodiment of the buffer chamber in FIG. 1. FIG. 3 is a schematic graph explaining air-fuel ratio characteristics in the prior art. 10... Carburizer 16... Suction piston 26... Metering needle 34... Metering jet 50... Low temperature increase device 52... High altitude compensation valve 54... Air-fuel ratio control valve 70... Buffer chamber 72...buffer jet

Claims (1)

[Claims] a metering needle moved in the fuel passage to maintain a constant venturi pressure; a metering jet formed in the fuel passage and cooperating with the metering needle to control the amount of fuel; and an air bleed opening in the metering jet. 1. An air bleed device for a variable venturi carburetor, comprising an air bleed passage for controlling the air bleed passage, and further comprising a buffer means disposed in the air bleed passage.