JPS6246693B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing a piston in a variable vent lily type carburetor, in which the piston is actuated by negative pressure or mechanical operation to change the passage area of the vent lily portion. It is.

[Prior art and its problems] Conventionally, pistons used in variable bench lily type carburetors have been made of aluminum with an alumite treatment applied to the surface of the piston body to improve contact resistance and wear resistance. It is being However, in recent years, engine parts have become lighter and the carburetor body has also been changed from zinc to aluminum, so the cylinder of the carburetor body and the piston that fits into this cylinder are made of the same metal, which increases the amount of wear. The resulting fine aluminum powder re-adheres to the sliding parts of both pistons, increasing the sliding resistance of the piston and hindering its smooth operation. Especially when there is a high moisture content in the atmosphere, such as during rainy weather, the moisture in the intake air mixes with the aluminum powder adhering to the sliding surfaces of the piston and cylinder, turning into powder, which significantly reduces the piston's operating performance. In the worst case, this may cause the piston to stick to the cylinder of the carburetor body (hereinafter referred to as "sticking").
Particularly in motorcycles, if the vehicle stalls during deceleration, the deceleration will not occur as intended by the driver, making it difficult to maneuver.

In an attempt to overcome this drawback, it is known that the surface of an aluminum piston is coated with a fluorine-based synthetic resin with a low coefficient of friction to improve operability (Utility Model Application Publication No. 56-167766). However, since the coating layer is thin and has insufficient bonding strength with aluminum, it may peel off when used for a long time. If you use gasoline mixed with ethyl alcohol to save money, the ethyl alcohol will cause the coating layer to swell and become soft, making it more likely to peel off, which may eventually lead to malfunctions and stickiness as described above. be. Additionally, fluorine-based paints generate harmful gases during baking and drying during the coating process.
Since it worsens the working environment, it is necessary to have equipment to deal with it.

On the other hand, pistons in which the entire piston is made of a synthetic resin with a low coefficient of friction and high wear resistance are also known (see Utility Model Application Publication No. 53-21228); Synthetic resins generally have a large coefficient of linear expansion, that is, a large molding shrinkage rate, which results in poor dimensional stability during molding, and has the disadvantage that appropriate sliding clearance between the piston and cylinder cannot be stably secured.

In order to overcome this drawback and obtain the dimensional stability necessary for the piston of a variable bench lily type carburetor, synthetic resin is combined with fiber-based fillers such as glass fiber and carbon fiber, as well as calcium carbonate, mica, and talc. It is possible to mix an inorganic powder filler such as graphite. However, there is a drawback that the filler microscopically exposed on the surface of the synthetic resin molded product causes wear on the inner surface of the cylinder of the carburetor body, causing malfunction of the piston.

In this way, there is still no synthetic resin that can achieve the same level of dimensional accuracy as aluminum pistons, has a low coefficient of friction, and has excellent wear resistance. It has been considered difficult.

The present invention was made in view of the various circumstances mentioned above, and by skillfully combining multiple types of synthetic resins, it is lightweight, has high dimensional accuracy, has a low coefficient of friction, and has excellent wear resistance, and prevents piston malfunction. We aim to improve the quality, improve performance, and reduce the size and weight of variable bench lily carburetors by providing a piston that does not cause the sticking phenomenon semi-permanently and has excellent productivity.
Furthermore, the purpose is to improve the safety and reliability of motorcycles and automobiles.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a piston body of a variable bench lily type carburetor with a first material mixed with a filler to reduce the molding shrinkage rate. The main body is made of a synthetic resin, and the cylinder and the sliding portion on the outer periphery of the main body are made of a second synthetic resin that has a low coefficient of friction and excellent wear resistance.

Furthermore, when molding the piston, a tube or sheet formed of the second synthetic resin is fitted onto the inner surface of an outer mold that molds the outer surface of the piston, and then an inner mold that molds the inner surface of the piston is fitted. is polymerized into the outer mold, the first synthetic resin in a molten state is injected into the cavity between the outer mold and the inner mold, and the first synthetic resin is solidified to obtain the piston.

[Effect]

In the present invention, since the main body of the piston is made of the first synthetic resin with a small molding shrinkage rate, the dimensional accuracy of the piston after molding is high. Furthermore, since the sliding contact portion on the outer periphery of the piston is made of the second synthetic resin which has a low coefficient of friction and excellent wear resistance, the sliding force of the piston is reduced and the amount of wear of the piston is also suppressed.

Furthermore, since the sliding contact portion is formed of a tube or sheet, it can be formed thicker than when using a coating, and the connection between the piston body and the sliding contact portion is strong because it is a weld between resins. Therefore, there is no risk that the sliding contact portion will peel off. Furthermore, since the piston is obtained by molding, the productivity is extremely high.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings regarding a negative pressure piston type variable bench lily type carburetor.

In FIG. 1, a cylinder 14 is provided in a bench lily portion 13 on the upstream side of a throttle valve 12 in an intake passage 11.
A negative pressure piston 15 is fitted to be vertically slidable,
The upper part of the cylinder 14 is hermetically closed with a lid 16. A diaphragm 18 is attached to the upper end of the negative pressure piston 15 by an annular locking member 17.
The outer peripheral edge of this diaphragm 18 is connected to the cylinder 1.
4 and the lid 16, thereby forming a negative pressure chamber 19 and an atmospheric pressure chamber 20. The negative pressure chamber 19 is connected to the bench lily portion 13 through a negative pressure outlet hole 21 at the bottom of the negative pressure piston 15.
The atmospheric pressure chamber 20 communicates with an inlet 23 of the intake passage 11 via an air hole 22.

A needle 25 is located at the bottom of the negative pressure piston 15.
is installed, and the main nozzle 26 is moved up and down by the vertical movement of the needle 25 in conjunction with the negative pressure piston 15.
The amount of fuel jetted from the fuel chamber 27 to the bench lily portion 13 is measured by increasing or decreasing the annular area of the passage. A coil spring 29 is installed between the negative pressure piston 15 and the lid 16, and the spring force balances the negative pressure in the negative pressure chamber 19 to determine the vertical position of the negative pressure piston 15.

In this way, the negative pressure piston 15 adjusts the magnitude of the negative pressure of the bench lily portion 13, that is, the magnitude of the negative pressure of the bench lily portion 13.
The vertical position is determined according to the difference between the pressure of growing.

The negative pressure piston 15 is made of a combination of at least two types of synthetic resins, and as shown in FIG. The first synthetic resin is a synthetic resin with a small size and high dimensional accuracy during injection molding, and has excellent heat resistance, gasoline resistance, and weather resistance, such as polyphenylene sulfide (PPS). There is. As the filler, an inorganic filler such as calcium carbonate, mica, talc, graphite, etc. may be used.

The sliding contact portion 15b with the cylinder on the outer periphery of the main body 15a is made of a second synthetic resin having a low coefficient of friction, excellent wear resistance, and excellent heat resistance, gasoline resistance, and weather resistance, for example. , made of polytetrafluoroethylene (PTFE) or ethylenetetrafluoroethylene (ETFE).

In determining these materials, the inventors have conducted numerous research tests and found that the following specification values are most effective. That is, the molding shrinkage rate of the first synthetic resin forming the main body 15a is preferably 0.04 cm/cm or less, the fibrous filler contains 30% or more by weight, and the first synthetic resin forming the sliding contact portion 15b has a molding shrinkage rate of 0.04 cm/cm or less. The static friction coefficient of the synthetic resin No. 2 is preferably 0.06 or less, and the thickness of the forming layer is preferably 1 mm to 0.3 mm. Cylinder 14 in FIG. 1 into which the negative pressure piston 15 is fitted
The walls of the intake passage 11 and the intake passage 11 are all made of aluminum alloy, but may be made of other metals.

When manufacturing the negative pressure piston 15 having such a configuration, as shown in FIG.
Mold molding is performed using an outer mold 33 and an inner mold 34 that form the outer surface and inner surface of 5, respectively. First, an extruded tube or sheet 32 of a second synthetic resin, for example PTFE, for forming the sliding contact portion 15b is fitted into the outer mold 33, which has no draft on the inner surface, and the inner mold 34 is inserted into the outer mold 33. After polymerizing, a first synthetic resin for forming the main body 15a, such as PPS 36, is injected in a molten state into the cavity 35, and the PPS 36 is solidified to form the piston 1.
Mold 5. At this time, the tube or sheet 32 fitted into the outer mold 33 is strongly pressed onto the outer mold 33 by the PPS 36 injected into the cavity 35, and conforms to the outer mold shape, and even when the PPS 36 solidifies, the PPS shrinks during molding. Since the ratio is as small as 0.004cm/cm, there is almost no dimensional change. In addition, although there is no draft on the inner surface of the outer mold 33, that is, the portion 33a in contact with the PTFE 32, since the coefficient of friction of the PTFE 32 is small,
Mold cutting can be performed in the same manner as normal molding.

In the above configuration, the negative pressure piston 15 in FIG.
It is lightweight because it is made of synthetic resin. Further, since the sliding contact portion 15b of the negative pressure piston 15 is formed of the second synthetic resin with a low coefficient of friction, the sliding force of the negative pressure piston 15 is reduced, and the second synthetic resin has a high wear resistance. This also eliminates any increase in sliding resistance or staking caused by the adhesion of fine particles caused by wear. Therefore, in addition to the weight reduction, the negative pressure piston 15 slides smoothly, and the fuel injection amount can be increased or decreased in response to the operation of the throttle valve 12 shown in FIG. 1 quickly. In other words, the performance of the vaporizer is improved. In this embodiment, since the sliding contact portion 15b made of synthetic resin is made of a different material from the cylinder 14 made of metal, the amount of wear is further reduced.

Furthermore, since the sliding contact portion 15b is formed by the tube or sheet 32 shown in FIG. 3, it can be formed thicker than by coating, and the connection between the main body 15a and the sliding contact portion 15b is by welding the resins together. Therefore, since it is strong, there is no fear that the sliding contact portion 15b shown in FIG. 2 will peel off, and it has excellent durability.

Furthermore, since the negative pressure piston 15 is obtained by molding, its productivity is extremely good. Here, since the main body 15a of the negative pressure piston 15 is made of the first synthetic resin with a small molding shrinkage rate, the dimensional accuracy after molding is high, and the required outer diameter tolerance of several tens of microns is sufficiently achieved. be done.

Next, in order to prove the fact that the amount of wear decreases due to the reduction in frictional resistance mentioned above, Figures 4 and 5 were used.
The experimental results are shown in the figure. The experiment consisted of 4 cycles of 440c.c.
The test was carried out using a two-wheeled vehicle equipped with a two-cylinder engine. The carburetor cylinder inner diameter and piston outer diameter are 31 mm. In Figures 4 and 5,
A indicates the product of the present invention, in which 40% of the above-mentioned fibrous filler is added.
The case is shown in which a negative pressure piston 15 consisting of a main body 15a made of PPS and a sliding part 15b made of PTFE is used. B ₁ and B ₂ represent conventional examples; B ₁ is a case where the aluminum surface is subjected to an alumite treatment and coated with a fluorine-based paint; B ₂ is a case where only an alumite treatment is applied to the aluminum surface. C ₁ and C ₂ show comparative examples; C ₁ is a case in which the entire negative pressure piston is made of PPS containing 40% of the filler made of carbon fiber, and C ₂ is made of PPS containing 40% of the filler made of glass fiber. This is the case when it is formed with PPS that has been used. Additionally, the cylinder is made of aluminum. From FIG. 4, it can be seen that when the negative pressure piston according to the present invention is used, the amount of dimensional change in the inner diameter of the cylinder after running is small, and the wear of the cylinder is small.
Furthermore, from FIG. 5, it can be seen that the negative pressure piston itself according to the present invention has a small dimensional change in its outer diameter, and has little wear.

Furthermore, since the sliding resistance of the negative pressure piston 15 is reduced as described above, the negative pressure piston can be made smaller for the following reason. In other words, as shown in FIG. 6, if the inner diameter E of the cylinder 14 is sufficiently large relative to the width D of the intake passage 11, the angle formed between the tangent 36 of the corner 35 of the cylinder 14 and the axial direction 37 of the intake passage 11 Since θ is sufficiently large, even when the negative pressure piston 15 is strongly pressed toward the downstream side 38 by the fluid pressure of the intake air 30, the pressing force is sufficiently supported by the vicinity 39 of the corner 35, and the negative pressure piston 15 will not bite into the corner portion 35. On the other hand, as shown in FIG. 7, if the inner diameter E of the cylinder 14 is not very large with respect to the width D of the intake passage, the angle θ becomes small, causing a wedge effect and the pressing force of the intake air 30. This makes it easier for the negative pressure piston 15 to get caught in the corners. In particular, when the frictional resistance of the negative pressure piston 15 is large, the slippage between the negative pressure piston 15 and the cylinder 14 worsens, and the above-mentioned jamming becomes more likely to occur.

However, according to the present invention, the negative pressure piston 15
Since the frictional resistance is reduced, the above-mentioned biting becomes less likely to occur. Therefore, the inner diameter E of the cylinder 14, that is, the outer diameter F of the negative pressure piston 15, is
Even if the vacuum piston 15 is made smaller to some extent as shown in FIG. 7, malfunction of the vacuum piston 15 does not occur, and it is possible to provide a carburetor having a vacuum piston smaller than the conventional one with the same intake passage width D. Further, since the negative pressure piston 15 has low frictional resistance and is lightweight, the diameter of the diaphragm 18 can be reduced, and the cylinder 14 and the lid 16 can be made smaller, thereby making it possible to make the carburetor more compact.

FIG. 8 shows a carburetor having a negative pressure piston 15 that does not use a diaphragm. Pressure chamber 19
and an atmospheric pressure chamber 20. The negative pressure piston 15 also has a structure similar to that shown in FIG. Note that 42 in FIG. 8 is a chiyoke valve.

Furthermore, the present invention is not limited to a carburetor having a negative pressure piston that operates in response to negative pressure in the bench lily.
It can also be applied to a carburetor that is forcibly operated by a wire or rod linked to a throttle lever to change the passage area of the bench lily.

〔Effect of the invention〕

As explained above, according to the present invention, the negative pressure piston operates smoothly, so that the performance of the carburetor is improved. In addition, the durability of the negative pressure piston and the miniaturization of the carburetor have been realized, and productivity has also been dramatically improved.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention, FIG. 2 is a longitudinal sectional view showing the negative pressure piston of FIG. 1, and FIG. 3 is a longitudinal sectional view showing a method for manufacturing the same negative pressure piston. Fig. 4 is a characteristic diagram showing the amount of change in cylinder inner diameter dimension when the same negative pressure piston is used, Fig. 5 is a characteristic diagram showing the amount of change in outer diameter dimension of the same negative pressure piston, and Figs. 6 and 7 are FIG. 8 is a schematic plan view showing the operation of the present invention, and a longitudinal sectional view showing a modification of the negative pressure piston. 11... Intake passage, 13... Bench lily part, 14...
cylinder, 15... negative pressure piston, 15a... main body,
15b...Sliding contact part.

Claims (1)

[Claims] 1. In a variable vent lily type carburetor in which a piston that changes the passage area of the vent lily part is fitted into a cylinder provided in the vent lily part of the intake passage, the main body of the piston is mixed with a filler to reduce the molding shrinkage rate. The main body is made of a first synthetic resin with a low coefficient of friction and excellent wear resistance, and the sliding contact portion with the cylinder on the outer periphery of the main body is made of a second synthetic resin with a low coefficient of friction and excellent wear resistance.
In forming the piston from the synthetic resin, a tube or sheet formed from the second synthetic resin is fitted onto the inner surface of the outer mold for molding the outer surface of the piston, and then the inner mold for molding the inner surface of the piston is fitted into the inner surface of the outer mold for molding the outer surface of the piston. After polymerizing into the outer mold, the first synthetic resin in a molten state is injected into the cavity between the outer mold and the inner mold, and the first synthetic resin is solidified to obtain the piston. A method for manufacturing a piston for a variable bench lily type carburetor.