JPH07305656A - Film type carburetor - Google Patents

Abstract

PURPOSE:To stably supply fuel having a proper flow amount in an operating range extending from idling across the total load range regardless of the posture of a carburetor, particularly in its idling state. CONSTITUTION:A film type carburetor is provided with a first fuel passage 20 for supplying fuel whose amount is measured by solid jet 23 from a nozzle port 22 to the narrowest part of a venturi 3, and a second fuel passage 25 for supplying fuel regulated by a regulating valve 31 from low and intermediate speed ports 27, 28 to the side of a throttle valve 4 and for supplying fuel regulated by another regulating valve 33 from an idle port 29.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a membrane vaporizer for supplying fuel to a general-purpose engine that is a power source for agricultural or horticultural machines, small vehicles, etc., and more specifically, stable in use in any posture. The present invention relates to a membrane type carburetor having a fuel system capable of supplying stable fuel and performing stable engine operation from idling to full load, especially idling.

[0002]

2. Description of the Related Art A carburetor that supplies fuel to a general-purpose engine is generally of a membrane type because it takes various postures when used as compared with a carburetor that supplies fuel to a four-cycle engine such as an automobile engine. It is used. In addition, because the fuel flow rate is low, the rate of flow rate fluctuation is large due to the mounting position of the parts and the size or the quality difference, and the difference in the performance of each engine that receives the fuel supply makes it possible to adjust the fuel flow rate individually. Need to be adjusted.

Therefore, manual adjustment is performed by providing the effective areas of the main fuel passage from the constant fuel chamber where the fuel pressure is kept substantially constant by the diaphragm to the main nozzle, the idle port, and the low speed fuel passage to the slow port, respectively. By adjusting the valve, the fuel flow rate can be adjusted individually (see Japanese Patent Publication No. 47-21848).

The adjusting valve in the low speed fuel passage regulates the maximum flow rate of the fuel supplied from both the idle port and the slow port, and a smaller amount of fuel than the regulated maximum flow rate flows during idling. However, with machines such as brush cutters that are often used by turning over and upside down, it is unavoidable that the fuel pressure in the constant fuel chamber fluctuates considerably and the fuel is disturbed. If there is a significant change, the maximum flow rate of fuel regulated by the adjusting valve is supplied from the idle port, which may make the engine operation extremely unstable or stop it.

As a countermeasure, it is conceivable to reduce the effective area of the low-speed fuel passage, but the fuel flow rate is insufficient when the throttle valve begins to open, and the connection to the start of main fuel supply is not smooth, This causes the inconvenience that the engine operating performance in the partial load range deteriorates. As a further improvement measure, it is conceivable to increase the effective area of the main fuel passage to increase the fuel flow rate from the main nozzle, but the main fuel flow rate is increased over the entire supply operation range to reduce the fuel consumption. This leads to an increase and deterioration of the exhaust condition.

[0006]

The problem to be solved by the present invention is that the membrane vaporizer generally used in general-purpose engines is adapted to be used in various postures. Nonetheless, there is no fuel flow rate adjusting means capable of performing stable engine operation from the idling to the entire load range, and it is inevitable that the idling becomes unstable particularly depending on the posture.

[0007]

The present invention solves the above problems and includes a fuel system capable of performing stable engine operation in any posture from idling to full load, particularly idling. The purpose is to provide a membrane vaporizer.

That is, for this purpose, the present invention comprises two fuel passages extending independently of each other from the constant fuel chamber, the first fuel passage of which has a nozzle opening and a fuel metering opening which are open to the narrowest part of the venturi of the intake passage. Fixed jet is installed in the second fuel passage, and an idle port and a plurality of low / medium speed boats, which are opened side by side in the intake passage axial direction toward the throttle valve side portion of the intake passage, are provided in the second fuel passage. Low
The upstream side of the medium speed port and the inlet of the idle port are provided with manual adjusting valves for adjusting the effective passage areas separately.

[0009]

The fuel that has entered the second fuel passage when the engine is idling is metered by the adjusting valve for the idle, which is provided at the inlet of the idle port, and is supplied to the engine.
When the throttle valve opening is relatively small, the fuel that has entered the second fuel passage at low / medium speeds is metered by the adjustment valve on the upstream side of the low / medium speed port and supplied to the engine. The fuel that has entered is metered by a fixed jet and supplied to the engine. That is, the fuel flow rate can be accurately matched to the fuel demand amount at idling by the adjustment valve dedicated to idle, and the fuel demand at high speed is satisfied by the fuel supplied from the nozzle port, so that low / medium The fuel flow rate in the partial load range can be properly controlled by the adjusting valve on the upstream side of the high speed port. Further, since the fuel is throttled by the adjusting valve on the upstream side of the low / medium speed port, the fluctuation of the fuel flow rate in the second fuel passage due to the change of the posture becomes small, and as a result, the idling becomes stable.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. A fuel pump 5 is provided on one side surface of a body 1 having an intake passage 2 and a fuel pressure adjusting portion 12 is provided on the opposite side surface. It is provided.

In the fuel pump 5, the pressure pulse generated in the crankcase of the engine is introduced into the pulse chamber 6 to reciprocate the membrane 7, so that the fuel is sucked into the pump chamber 9 through the inlet check valve 8 and then the outlet. Communication path 11 via check valve 10
It is a well-known pump that delivers to.

The fuel pressure adjusting section 12 comprises a constant fuel chamber 13, a diaphragm 14, an atmosphere chamber 15 and a fuel valve 16.
When the amount of fuel in the constant fuel chamber 13 decreases, the diaphragm 14 is displaced toward the constant fuel chamber 13 and the lever 17 contacting the fuel valve 16 is rotated in the valve opening direction by overcoming the spring force of the valve closing spring 18. , Communicating the fuel sent from the fuel pump 5 to the communication passage 11
It is also well known that the fuel is introduced into the constant fuel chamber 13 to maintain the fuel pressure substantially constant.

Two fuel passages 20 and 25, which are independent of each other, are connected to the constant fuel chamber 13. The first fuel passage 20 is a cylindrical nozzle body 21 fitted and fixed to the body 1.
It has a nozzle port 22 that is formed to penetrate into the intake passage 2 and opens to the narrowest part of the venturi 3 and a fixed jet 23 for fuel measurement, and the constant fuel chamber 13 has a higher negative pressure than the venturi 3. In this case, a check valve 24 is provided to close the nozzle opening 22 and prevent back bleeding.

The second fuel passage 25 has a port chamber 26 at the end.
The low / medium speed ports 27, 28 that are open in the intake passage 2 side by side in the axial direction slightly downstream of the tail end of the venturi 3 and slightly upstream and downstream of the throttle valve 4 at the closed position. And an idle port 29 are provided in communication with the port chamber 26.

A needle-like adjusting valve 31 provided at the tip of a screw rod 30 screwed into the body 1 is inserted upstream of the two low / medium speed ports 27 and 28 of the fuel passage 25. The fuel flow rate from the constant fuel chamber 13 is measured by manually adjusting the effective area of the fuel passage 25, and the fuel sucked into the intake passage 2 from the low / medium speed ports 27 and 28 is controlled. There is. Further, a needle-like adjusting valve 33 provided at the tip of a screw rod 32 screwed into the body 1 is inserted at the inlet of the idle port 29, and the effective passage area of the inlet of the idle port 29 is manually adjusted. By measuring the fuel flow rate from the port chamber 26, the fuel sucked from the idle port 29 to the intake passage 2 is controlled.

In this embodiment having such a structure, the fuel that has flowed from the constant fuel chamber 13 to the port chamber 26 due to the flow rate regulation by the regulating valve 31 of the fuel passage 25 at the time of idling of the engine is another regulating valve. The flow rate is regulated by 33, and the fuel is sucked into the intake passage 2 from the idle port 29, and the required fuel for idling is supplied to the engine.

Further, the opening of the throttle valve 4 is relatively small and low.
At a medium speed, the flow rate of the fuel from the constant fuel chamber 13 is regulated by the adjusting valve 31 of the fuel passage 25 into the port chamber 26, and one of the fuels on the downstream side of the low / medium speed ports 27 and 28 is in accordance with the position of the throttle valve 4. It is sucked into the intake passage 2 from one or both of them, and supplies low / medium speed required fuel to the engine.

Further, when the throttle valve 4 has a large opening and at a high speed, a high negative pressure due to the intake air flow acts on the nozzle port 22 opening to the narrowest part of the venturi 3, and the constant fuel chamber 13 to the fuel passage. The fuel measured by the fixed jet 23 of 20 is sucked into the intake passage 2 and cooperates with the fuel from the low / medium speed ports 27 and 28 to supply the required fuel at high speed to the engine.

That is, the fuel flow rate at idling is controlled by operating the adjusting valve 33 for exclusive use of the idling provided at the inlet of the idle port 29, without considering the fuel flow rate at the off / idling time. Can be matched exactly.

Further, the fuel flow rate in the partial load range is that the fuel is supplied from the nozzle port 22 opened to the venturi 3 at the time of high speed, and therefore, the regulating valve provided upstream of the low / medium speed ports 27 and 28. The required amount can be accurately met by operating 31. And this adjusting valve 31
Since the effective area of the second fuel passage 25 can be adjusted without considering the fuel demand amount at the time of idling, not only can the low / medium speed operation be stably performed, but also the fuel in the full-open high speed operation can be performed. It is also possible to secure a flow rate. Further, since the nozzle port 22 is supplied with fuel at high speed and is filled with fuel sucked from the low / medium speed ports 27 and 28, the fixed jet 23
Thus, the effective area of the first fuel passage 20 can be set to be small so that the required fuel amount at high speed can be accurately matched without increasing the fuel consumption amount or deteriorating the exhaust state.

Therefore, the first fuel passage 20 by the fixed jet 23 and the second fuel passage 25 by the regulating valve 31 are also provided.
By appropriately setting the respective effective areas, it becomes possible to particularly accurately match the fuel demand amount in the operating region where the engine is heavily used, and it is possible to enhance the engine operating stability in the specific heavily operating region.

Further, since the fuel flow rate is regulated by the adjusting valve 31 on the upstream side of the low / medium speed ports 27 and 28, the constant fuel chamber 13 which affects the port chamber 26 even if the posture is largely changed.
The influence of the fuel pressure fluctuation on the idle port 29 is further reduced because the adjustment valve 33 is provided at the inlet portion of the idle port 29, and as a result, the influence of the fuel pressure fluctuation on the idle port 29 is further reduced. The fuel flow rate fluctuation to the idle port 29 is small, and stable idling can be performed.

[0023]

As described above, the first fuel passage for delivering the fuel metered by the fixed jet to the narrowest portion of the venturi from the nozzle port and the fuel adjusted by the adjusting valve to the side of the throttle valve are operated at low and medium speeds. According to the present invention, in which the second fuel passage for delivering the fuel which is delivered from the port and which is regulated by another regulating valve is delivered from the idle port is provided independently of each other, according to the present invention, the operating range from idling to full load in any posture. In particular, during idling, stable engine operation can be performed with little influence of fuel pressure fluctuations in the constant fuel chamber. Further, there is an advantage that fuel can be appropriately supplied at low, medium and high speeds, and the fuel connection between them can be smoothed.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an embodiment of the present invention.

[Explanation of symbols]

2 intake passage, 3 venturi, 4 throttle valve, 13
Constant fuel chamber, 20 first fuel passage, 22 nozzle opening, 23 fixed jet, 25 second fuel passage,
27, 28 low / medium speed port, 29 idle port, 31, 33 adjusting valve,

Claims (1)

[Claims] 1. A fuel jet having two fuel passages extending independently of each other from a constant fuel chamber, the first fuel passage being provided with a nozzle opening to a narrowest part of a venturi of an intake passage and a fixed jet for measuring fuel. The second fuel passage is provided with an idle port and a plurality of low / medium speed ports that are open side by side in the intake passage axial direction toward the throttle valve side portion of the intake passage. The low of the fuel passage
A membrane type carburetor, characterized in that a manual adjusting valve for adjusting the effective passage area separately is provided on the upstream side of the medium speed port and the inlet portion of the idle port.