Structure of main nozzle in carburetor

Abstract: A carburetor comprises a jet needle (7) which has a taper portion gradually decreasing in diameter toward its head and which is inserted in a main nozzle (3) which is provided crossing with an intake pass and provided with a main jet (13) at its lower end. A gap between said main nozzle (3) and said jet needle (7) is allowed to change so as to control the flow of a fuel taken in from the head of the jet needle (7). The lower end of the main jet (13) fixedly provided on the head of said main nozzle (3) comprises a conical surface (16) and a planar portion (17). The main jet (13) has a plurality of downward oblique holes (18) boredly provided on said conical surface (16) in such a manner that the holes are equally spaced on the circumference at an inclined angle 30 to 90 ° to axial direction. The internal surface of said oblique holes (18) is made a rough surface (19).

Description: This invention relates to the improvement of a carburetor in engines using gasoline, light oil or the like as a fuel for, for example, automobiles, motorcycles and the like. Heretofore, a known structure of such carburetor is, for example, as shown in Fig. 1, such that it is provided with a throttle valve 6 which is moved in the direction crossing with an intake passage 2 communcating with an engine so as to form a variable venturi portion 5 in the intake passage 2; provided with a main nozzle 3 for controlling fuel inflow in a manner to cross with the intake passage 2 as with the throttle valve 6; and provided with a jet needle 7 which has a taper portion gradually decreasing in diameter toward its head, and whose base end is mounted to said throttle valve 6, and whose tapering head portion is inserted into the main mozzle 3. With the axial movement of the throttle valve 6, the gap between the main nozzle 3 and the jet needle 7 is allowed to change, whereby fuel proportional to the intake flow flowing through the venturi portion is taken in from the main nozzle 3 so as to control air-fuel ratio. Known head configurations of the jet needle 7 include the needle configuration in which its body tapers toward its head at a certain taper angle, and the conical configuration in which its body becomes conical at its head. A main jet 13 is threadingly connected to the lower end of the main nozzle 3. Such a carburetor is disclosed in the JP-A-4-66 760 which serves as the basis for the preamble of claim 1. An object of the invention is to provide a carburetor capable of reducing the area of the boundary layer in the pass of fluid such as fuel or air, or mixed gas, of improving fuel efficiency by optimizing air-fuel ratio and eliminating knock and short breath, and of making design and setting easy so as to improve usability. This object is achieved by the carburetor of claim 1. Namely, in the carburetor in which the jet needle 7 which has a taper portion gradually decreasing in diameter toward its head is inserted in the main nozzle 3 which is provided crossing with an intake passage and provided with the main jet 13 at its lower end, and with the axial movement of the throttle valve 6, the gap between the main nozzle 3 and the jet needle 7 is allowed to change so as to control the flow of a fuel taken in from the head of the jet needle 7; the lower end of the main jet 13 fixedly provided on the head of said main nozzle 3 comprises a conical surface 16 and a planar portion 17; the main jet 13 has a plurality of downward oblique holes 18 boredly provided on the conical surface 16 in such a manner that the holes are equally spaced on the circumference at an inclined angle 30 to 90 ° to axial direction; and the internal surface of said holes 18 is made a rough surface 19. Preferably, the internal wall surface of fuel intake holes following said plurality of downward oblique holes 18 of the main nozzle 3 is also provided with the rough surface 19. Preferably, an upward oblique hole 21 other than the downward oblique holes 18 is further provided. According to this invention, fuel flows smoothly, through the plurality of downward oblique holes 18 or the upward oblique hole 21 of the conical surface 16 on the lower end of the main jet 13 fixedly provided on the head of the main nozzle 3, into the nozzle. In the flow of the fuel, the presence of the rough surface 19 on a boundary layer occurring between the wall surface of the fuel supply pass and the fuel causes the area of the boundary layer to be decreased. That is, the fuel enters dents on the rough surface 19, on which the flow causes a slippage between fuel layers, whereby a fluid deceleration is not present on the portion in contact with the wall. This causes the flow of the fuel to closely resemble an ideal fluid flow, the fuel supply for producing mixing gas to become smooth, and the air-fuel ratio to be optimized. Fig. 1 is a section view of a carburator embodying the invention. Fig. 2 is a main jet of the invention. Fig. 3 is another embodiment of the main jet. Fig. 4 is still another embodiment of the main jet. The following is a description of Reference Codes: 1: Carburator assembly 2: Intake pass 3: Main nozzle 4: Throttle mechanism 5: Variable venturi portion 6: Throttle valve 7: Jet needle 8: Spring 9: Fuel tank 10: Fuel supply port 11: Float 12: Control valve 13, 13': Main jet 14: Large diameter hole 15: Small diameter hole 16: Conical surface 17: Planar portion 18: Downward oblique hole 19: Rough surface (in oblique hole) 20: Center line (of needle) 21: Upward oblique hole. With reference to Fig. I, a carburator in which the invention is embodied will be briefly explained. A carburator assembly 1 is formed with an intake pass 2 communicating with an engine G, and provided on the lower side of the intake pass 2 is a main nozzle 3 communicating with the intake pass 2. Formed on the upper side of the intake pass 2 is a throttle mechanism 4, and provided slidably in the throttle mechanism 4 is a throttle valve 6 which is moved in the direction crossing with the intake pass 2 so as to form a variable venturi portion 5 in the intake pass 2. Mounted on the lower end of the throttle valve 6 is a jet needle 7, and connected threadingly to the head of the jet needle 7 is a main jet 13. The throttle valve 6 is urged by a spring 8, so that the movement of the valve can be adjusted by a throttle lever (not shown). Formed on the lower side of the intake pass 2 is a fuel tank 9, into which fuel is supplied through a fuel supply port 10. Provided in the fuel tank 9 is a float 11, and the fuel supply into the fuel tank 9 is controlled by a control valve 12 connected to the float 11. Arrows A, E and F indicate the flow of intake, mixing gas and fuel, respectively. The fuel sucked by a negative pressure occurring by the intake A flowing from an upstream side P1 to a downstream side P2 of the intake pass 2 is first roughly measured by the main jet 13. Now, the invention relates to the composition of the main jet 13 in such carburator. Fig. 2 is a section view of the main jet 13 in connection with the invention. In the main jet 13, as shown in Fig. 2, the head of the main jet body is a planar portion 17, and said planar portion 17 is connected through a conical surface 16 to the body. Provided in the body is a hole for inserting the jet needle. The hole has a large diameter hole 14 and a small diameter hole 15 following the hole 14, and the head portion of the small diameter hole 15 has a plurality of downward oblique holes 18 boredly provided on the conical surface 16 in such a manner that the holes are equally spaced on the circumference and at an inclined angle  of 30 to 90° with respect to a center line 20 of the main jet 13. The number of the downward oblique holes 18 are preferably about three. Provided on the internal surface of the downward oblique holes 18 is a rough surface 19 having micro irregularities formed by blast treatment. The blast treatment is also preferably applied to the internal surface of the large diameter hole 14 and the small diameter hole 15 communicating with the downward oblique holes 18, though such treartment is difficult to apply. A main jet 13' of Fig. 3 is another embodiment, in which-although the composition of the vicinity of the the downward oblique holes 18 is just the same as that of Fig. 2 a lengh L2' of an intermidiate portion is made shorter. A main jet 13" of Fig. 4 is still another embodiment, in which in addition to the downward oblique holes 18, an upward oblique hole 21 is provided on the lower end of the samll diameter hole 15 at an obliquely upward angel  of 30 to 60° . As with said embodiment, the rough surface 19 is, of course, provided on the upward oblique hole 21. In this manner, the providing of the downward oblique holes 18 and the upward oblique hole 21 allows a smoother fuel supply. As described above, provided on the head of the main jet 13 are the plurality of downward oblique holes 18 equally spaced on the circumference or the upward oblique hole 21 in addition to the downward oblique holes 18, and provided in these oblique holes is the rough surface 19 formed by blast treatment. In this manner, the providing of the rough surface 19 causes the wall surface to be composed of the dints by blast shot and protrusions formed between dints. When the fuel flows in contact with the wall surface of the main jet, a boundary layer in which the fuel velosity is decelerated by friction resistance is present in the protrusion area, while in the dints area, the fuel flow causes a slippage between the fuel retained in the dints and the fuel flowing on the external side of the dints, that is, a slippage between fuels, whereby the condition of the fuel velocity becomes similar to that of ideal fluid. Accordingly, compared with a conventional, smooth surface passage providing no rough surface 19, the occupancy ratio of the boundary layer to the wall surface is significantly reduced, with the result that even where the gap is small, the fuel supply is subject to a little decelerating action of the boundary layer, and thus improved. This allows an air-fuel ratio leading to the increase in output to be obtained. The fuel is sucked from the plurality of downward oblique holes 18 equally spaced on the circumference or from the upward oblique hole 21 in which the rough surface 19 is provided, whereby the effect of the rough surface 19 in the individual oblique holes is doubled; the fuel supply is extremely improved: and the air-fuel ratio leading to the increase in output is allowed. Further, the rough surface 19 causes the passage resistance by air and fuel to be reduced, and the optimization of the air-fuel ratio allows horsepower to be improved and short breath to be eliminated. The fuel flow can be proportionally controlled, thereby making design and setting easy, and thus improving usability. Still further, the improvement of the fuel supply or intake allows the device to be made compact, and the weight and manufacturing cost to be reduced.

Claims: A carburetor in which a jet needle (7) which has a taper portion gradually decreasing in a diameter toward its head is inserted in a main nozzle (3) which is provided crossing with an air intake passage (2) and provided with a main jet (13) at its lower end, the jet needle (7) being mounted on the lower end of a throttle valve (6), which is disposed in the air intake passage (2) for axial movement therewith, whereby the gap between said main nozzle (3) and said jet needle (7) is allowed to change so as to control the flow of a fuel taken in from the head of the jet needle (7); the carburetor being characterized in that the lower end of the main jet (13) fixedly provided on the head of said main nozzle (3) comprises a conical surface (16) and a planar portion (17), the main jet (13) has a plurality of downward oblique holes (18) boredly provided on said conical surface (16) in such a manner that the holes are equally spaced on the circumference at an inclined angle 30 to 90° to axial direction, and the internal surface of said oblique holes (18) is made a rough surface (19). The carburetor as set forth in claim 1, wherein the internal wall surface of fuel intake holes following said plurality of downward oblique holes (18) of the main nozzle (3) is also provided with the rough surface (19). The carburetor as set forth in claim 1 or 2, wherein an upward oblique hole (21) other than the downward oblique holes (18) is further provided.

Inventors: OSHIMA MACHIKO, OSHIMA, MACHIKO, OSHIMA, MACHIKO, C/O K.K. KENSO
Applicants: KENSO KK, KABUSHIKI KAISHA KENSO
Application year: 1993
Main classification: F02M9
IPC codes: F02M19, F02M9