Patent Publication Number: US-3875267-A

Title: Carburetor float

Description:
D United States Patent l 1 m1 3,875,267  
 Seki et al. 1 Apr. 1, 1975 I CARBURETOR FLOAT 1,995,228 3/1935 Schimanek 261/70 x 3.263.975 8/1966 T -Y W 26l/DlGv 50 Inventors: Chlchltada Sekl; Takashl Hlsatoml, Hii gg V both of Yokohoma. Japan [73] Assignee: Nissan Motor Company, Limited,  
  Yokohoma,.lapan Primary Examiner-Frank W. Lutter Assistanl ExaminerWilliam Cuchlinski, Jr. [22] Flled&#39; 1973 Attorney, Agent, or Firm-Robert E, Burns; [21] Appl. No.: 424,082 Emmanuel J. Lobato; Bruce L. Adams [30] Foreign Application Priority Data Dec. 20, 1972 Japan 47-127098 ABSTRACT [52] U.S. Cl 261/70, 137/428, l37/434.  
  137/444, 251/231, 26l/DlG. 50 A generally triskelion shaped float with one of the legs [51] Int. Cl. F02m 5/02 extending downward pr s in r ased up ard for e [53] Field of Search 26l/DlG. 50, 70; l37/409, to close a fuel inlet valve when the carburetor or the 137/428, 434, 442, 444; 25l/l20. 231 fuel surface is tilted forward or backward to prevent overfilling of the float chamber under these condi- [56] References Cited liOnS- UNITED STATES PATENTS 1,186,164 6/l9l6 Benjamin 26l/70 5 Claims, 11 Drawing Figures PMENTEDAPR 1 I975 &#34;,B HLZBY sew 1 BF 3 F/g. F g- PRIOR ART PRIOR ART I4 I2 19 I2 I &#39;9 H 18 20 I6 IO \22 T i i 2| I7 EI. T1 l3 l3 F/g. 3 Fig. 4 PRIOR ART PRIOR ART iiTEtHEUAPR 119. 5 1875 .267  
 Fig. 5 F/g. 6  
 &#34;A&#39;Ill&#39;l IIIIIII I I&#39;EENTEUAPR 1 i975 DIFFERENTIAL MOMENT (/o) szzwsu g F fg. 9 F fg. /0  
  n so 40- Figs.2 8|5 387 FUEL SURFACE INCLINATION F lg.  
 CARBURETOR FLOAT The present invention relates to a carburetor float for an internal combustion engine, and more particularly to a carburetor float of a particular shape suitable for holding a needle valve in a closed position even if the carburetor or fuel surface is tilted forward or backward to prevent overfllling of the carburetor float chamber.  
  A float system of an internal combustion engine carburetor generally includes a float bowl or chamber and float and needle valve members accommodated in the float bowl to maintain a constant desired level of fuel. The float chamber is in communication with the atmosphere through an air vent and provided with a fuel outlet and a fuel inlet which is controlled by the needle valve. The needle valve operates in cooperation with the float which is supported on a free end of a hinged lever. More particularly, an upward moment resulting from floatation of the float is transmitted to the needle valve for closing the same, to control the flow of fuel into the float chamber through the fuel inlet to maintain the constant desired fuel level.  
  With a carburetor float system of the configuration described above, it is the general practice to employ a float of a simple rectangular shape as will be discussed more particularly below. A float of such a shape presents a difficulty in that the fuel inlet is erroneously opened due to a reduction in buoyant force acting on the float when the float chamber or fuel surface is inclined in a particular direction, as in acceleration, hillclimbing and turning of the vehicle. This causes the float chamber to overfill, and fuel may spurt out through the air vent and the main nozzle inviting acceleration failure or engine stoppage due to over supply of an air-fuel mixture to the engine.  
  It is therefore an object of the invention to provide a carburetor float for an internal combustion engine, which eliminates the difficulties mentioned hereinabove by holding a needle valve ofa fuel inlet of a float chamber in a closed position even if the float chamber or fuel surface is tilted forward or backward.  
  It is another object of the invention to provide a carburetor float having a generally triskelion profile with a downwardly extending lower leg which is normally immersed beneath the surface of fuel in the float chamber and two upper legs, both of which normally float on the surface of the fuel, but either one of which is immersed at least partially in the fuel when the fuel surface or float chamber is tilted forward or backward, as in accelerating, hill-climbing or turning of the vehicle, to securely hold the needle valve closed.  
  These and other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which directions such as left and clockwise refer to those as shown in the figures and in which:  
  FIG. 1 is a fragmentary vertical sectional view of an existing carburetor float system;  
  FIG. 2 is a vertical sectional view of the inner arrangement of the float chamber of the existing carburetor float system shown in FIG. 1&#39;,  
  FIGS. 3 and 4 are views similar to FIGS. 1 and 2, respectively, but show the surface of the fuel as inclined with respect to the float chamber;  
  FIG. 5 is a vertical sectional view of a float chamber incorporating a carburetor float embodying the present invention,  
  FIG. 6 is a horizontal section along a line A A of FIG. 5;  
  FIGS. 7 and 8 are vertical sectional views of the float chamber of FIG. 5 with the surface of the fuel inclined in opposite directions with respect to the float chamber;  
  FIG. 9 is a graph showing the variation of moment employing a float of the invention and a conventional float in dependence on the angle of inclination of the fuel surface; and  
  FIGS. 10 and 11 are elevational views showing modified configurations of floats according to the invention.  
  Referring to the accompanying drawings and first to FIGS. 1 and 2, there is shown an existing carburetor float system, which includes a float chamber II which communicates with the atmosphere through an air vent 12. The float chamber 11 is provided with a fuel outlet 13 for supplying fuel into the induction passage 14 of a carburetor of the engine through a main nozzle 15 which opens into a venturi portion 16 upstream of a throttle valve 17. The float chamber 11 is further provided with a fuel inlet 18 for receiving a fuel through a fuel supply passage 19 feeding thereinto. A numeral 10 represents the surface of the fuel in the float chamber 11. The amount of fuel which flows into the float chamber 11 is controlled by a fuel inlet valve or needle valve 20 which is supported on a hinge lever 21. The hinge lever 21 is pivotally supported at one end thereof on a normally horizontal pin 22. The opposite free end of the hinge lever 21 is connected to a float 23 in such a manner that upward moment produced by buoyant force acting on the float 23 is transmitted to the needle valve 20 by means such as shown to cause the same to close the fuel inlet 18 to maintain a constant fuel level in the float chamber 11. Fuel from the main nozzle 15 is sucked into the engine at a rate corresponding to the volume of air flowing through the venturi portion 16 in accordance with the throttle 17 position. If the fuel level in the float chamber 11 drops below a predetermined normal level, the needle valve 20 is opened due to a reduction in the buoyant force acting on the float 23 to introduce more fuel into the float chamber 11, thus maintaining the surface level of the fuel constant. It will be noticed that the float 23 is swingable in a normally vertical plane about the pin 22.  
  As mentioned hereinabove, a conventional carburetor float system employs a float of a simple rectangular parallelepiped shape as shown in FIG. 4. During accelerating, hillclimbing and turning of the vehicle, the surface 10 of the fuel in the float chamber 11 is inclined downward away from the pin 22 as shown in FIG. 3 or upward toward the pin 22 as shown in FIG. 4. When the fuel surface 10 is inclined as in FIG. 3, the needle valve 20 is kept closed by increased buoyant force on the float 23. However, when the fuel surface 10 is inclined as shown in FIG. 4, due to a reduction in the buoyant force on the float 23, the needle valve 20 is erroneously opened, allowing fuel to flow into the float chamber 11 and overfill it. This causes an excessively enriched airfuel mixture leading to acceleration failure and engine stoppage, both with fixed venturi carburetors and variable venturi carburetors.  
  These difficulties can be eliminated by employing a float 24 of the invention as shown in FIGS. 5 and 6,  
 having a generally triskelion profile. More particularly, the float 24 has a downwardly extending lower section 25 and two symmetrical upper sections 26 and 27. As show. the profiles of the lower and upper sections 25, and 26 and 27 are respectively triangular and trapezoidal. The upper sections 26 and 27 are spaced along the axis of the lever 21. The float 24 is formed of a plastic material such as foamed styrol having a specific gravity of about 0.2. As shown particularly in FIG. 5, the float 24 normally floats on the fuel or other liquid with the lower section 25 below the surface 10, and the upper sections 26 and 27 above the surface 10, one of the upper sections 26 and 27 is connected to the free end ofthe hinge lever 21 in the usual manner to control the position of the needle valve 20.  
  With a carburetor float system of the invention, if the surface 10 of the fuel or the float chamber 11 is rotated in the vertical swinging plane of the float 24 from a respective normally horizontal position as shown in FIGS. 7 or 8 during acceleration, hilLclimbing or turning of the vehicle, the lower section 25 and at least part of one of the upper sections 26 and 27 will be in contact with fuel so that the effective surface area of the float 24 in contact with the fuel will increase. and thereby increase the force applied by the float 24 to the lever 21 to close the valve 20 as shown in FIGS. and 6. Thus, when the surface 10 ofthe fuel in the float chamber 11 is inclined in either direction, an increased moment is imposed on the lever 21 due to the increased buoyant force acting on the float 24, holding the needle valve closed in a secure manner. As a result, it is possible to prevent fuel from the fuel supply passage 19 from flowing into the float chamber II to overfill the chamber 11.  
  In this connection, the force with which the needle valve 20 is pressed against its valve seat with a normal volume of fuel in the float chamber 11 may be expressed in terms of a differential moment between upward and downward moments imposed on the hinge lever 21 by the following equation, with reference to FIGS. 4. 5, 7 and 8:  
 Differential moment (7a) (Clockwise moment counterclockwise moment)/- (counter-clockwise moment) X 100 The clockwise moment is that imparted to the lever 21 by the buoyant force acting on the float 23 or 24 and the counter-clockwise moment is that imparted to the lever 21 by gravity and the pressure of fuel in the passage l9 acting on the needle valve 20. The differential moment thus represents the percentage by which the forces acting to close the needle valve 20 are greater than those acting to open the needle valve 20. This differential moment is preferred to be within a range of 20 to 40% in consideration of vibration of the surface 10 of the fuel within the float chamber 11, irregularities in performance of individual carburetor float systems, or fluctuations of the fuel pressure in the fuel supply passage l9. However, with a conventional float system, the differential moment becomes too large when the fuel surface I0 is inclined as shown in FIG. 3, as indicated by a solid line 28 in FIG. 9. On the other hand, when the fuel surface It] in the float chamber 11 inclined as shown in FIG. 4, the differential moment becomes negative and the needle valve 20 is opened, allowing fuel to flow into the float chamber 11 to overfill it. On the contrary, with a carburetor float 24 of the invention, the differential moment is maintained constant within the range of 20 to 40% due to the shape of the float 24, even when the fuel surface 10 within the float chamber 11 is inclined in either direction, as indicated by a broken line 29 in FIG. 9. In other words, a carburetor float 24 of the present invention can hold the needle valve 20 in its closed position with sufficient force, irrespective of the inclination of the surface 10 of fuel within the float chamber 11.  
  In the arrangement of FIGS. 5 to 8, the float 24 is symmetrical in cross section and size with respect to its vertical axis. However, it will be appreciated that the float 24 may be provided in an asymmetric form as particularly shown in FIGS. 10 or 11, taking into consideration the particular shape or size of the float chamber 11 and/or the particular requirements of the weight of the float 24. In FIGS. 10 and 11, the floats 24 have lower sections 25 and 25&#34;, and upper sections 26&#39; and 27&#39; and 26&#34; and 27&#34;, similar to the float 24 employed in the first embodiment shown in FIGS. 5 to 8. The function of the floats 24 with sections of different size is substantially the same as in the first embodiment, and thus a description is not given to avoid repetition.  
  It will be noted that the profiles of the sections 25&#34;, 26&#34; and 27&#34; of the float 24 shown in FIG. 11 are rectangular.  
 What is claimed is:  
  1. In combination; means defining a liquid float chamber, a float swingable in a normally vertical plane within said liquid float chamber, a normally horizontal pin about which said float is swingable;  
 a lever connecting said float to said pin; means defining a liquid inlet to said chamber; valve means connected to said lever to open and close said liquid inlet to the chamber;  
 said float having one lower section and two upper sections spaced along the axis of the lever;  
 said lower section being substantially below and said two upper sections being substantially above a predetermined normal level of liquid in the float chamber;  
 the effective surface area of said float in contact with liquid in the float chamber thus increasing as at least one of the float chamber and the surface of liquid in the float chamber is rotated in the nor mally vertical plane from respective normally horizontal positions, thereby increasing the force applied by said float to the lever in a direction to cause said valve means to close the fuel inlet.  
  2. A float as claimed in claim I, in which said lower section has a substantially triangular profile and said two upper sections have substantially trapezoidal profiles.  
  3. A float as claimed in claim I, in which said lower and said two upper sections have substantially rectangular profiles.  
  4. A float as claimed in claim 1, in which said two upper sections are of the same size.  
 5. A float as claimed in claim 1, in which said two upper sections are of different sizes.  
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