Automatic choking system for carburetor

Abstract: An automatic choking system designed to make a whole carburetor shorter and compact by comprising a case body (2) of nearly up-side-down L character shape; a thermo-element (3) housed in vertical portion (2a) of the case body (2), a thermister (4) attached to a thermally expanding wax side at the lower end of the thermo-element heated up by electric current to increase its own electric resistance with the heat; a piston (3b) projected from the top end of the thermo-element (3) by the thermal expansion of the wax; a link (6) housed in the top portion (2b) of the case body (2) and supported therein so as to move downward the one end (6b) of the link (6) with the other end (6a) of the link (6) being pushed up with the piston (3b); a moving part downward by being pushed down with the other end of the link; a starter valve (10) provided at the lower end of the moving part (7) to close a by-pass connected with main air passageway with the moving part (7) downward; and a needle (12) to close an auxiliary fuel passageway.

Description: This invention relates to a carburetor having an automatic choking system, said carburetor being provided for engines installed on motorcycles, motor scooters, etc. The automatic choking system for a carburetor installed on an engine is, as widely known, a system to increase fuel content at low temperatures of the engine in order to start the engine smoothly and to return the mixing ratio of the fuel with air automatically to a normal ratio for proper revolution of the engine with a rise in the temperature of the engine. Specifically, while a throttle valve of the carburetor is regulated by operating an accelerator lever, etc. to adjust the mixing ratio of a mixture of the fuel with the air in the main air passageway, a starter valve provided in a by-pass passageway by-passing the main air passageway and a needle provided in an auxiliary fuel passageway connected with the by-pass passageway are opened automatically at low temperatures of the engine to send a mixture richer than normal to the engine to start the engine smoothly. When the temperature of the engine goes up to reach the proper temperature, the starter valve closes the by-pass passageway automatically and the needle also closes the auxiliary fuel passageway automatically to return the mixing ratio of the fuel with the air to a normal ratio for proper revolution of the engine. US-A-4 815 427 on which the preamble of claim 1 is based discloses a fuel enrichment system for a multi-cylinder engine having a manifold balance line to deliver fuel to each of the cylinders as needed, including a valve located adjacent one of the carburetors to supply additional air/fuel mixture to approximately the center of the fuel balance line during the start-up of the engine. Figure 7 shows the outline of a conventional carburetor indicating main body 20 of the carburetor comprising main air passageway 21, by-pass passageway 22 by-passing the main air passageway 21, throttle valve 23 provided on the main air passageway 21, auxiliary fuel passageway 24 connected with the by-pass passageway 22, starter valve 25 and needle 26 forming the automatic choking system to open the by-pass passageway 22 and auxiliary fuel passageway 24 of the carburetor automatically while the engine is at low temperatures and to close these when the temperature was elevated. The Figure 7 omits to show the main fuel passageway provided on the main air passageway 21. The starter valve 25 and needle 26 are mounted on the tip end of moving part 28 being pushed by piston 27a of a thermo- element 27, and the thermo-element 27 and the moving part 28 are housed in case 29. Return spring 30 is to push back the moving part 28 and thermistor 31 is adhered to thermally expanding wax side of the thermo-element 27 as set out hereunder and to shut off an electric current due to an increase in the electric resistance due to the heat generated by the electric current. Wiring 32 is connected with thermistor 31 and connector 33 mounted on its tip end is connected with an electric circuit ( not shown ). Figure 8 is a cutaway drawing of the detail of the thermo-element 27 indicating thermally expanding and shrinking wax 27b made from paraffine and cupper powder housed in case 27c; diaphragm 27d made from nitrile rubber, etc. to confine the wax 27b in the case 27c; fluid 27e housed in guide tube 27f coupled with the opening of the case 27c by means of the diaphragm 27d; piston 27a movably inserted into guide tube 27f; gasket 27g provided between the guide tube 27f and the piston 27a; back-up ring 27h provided in the place surrounded by the gasket 27g, the guide tube 27f and the piston 27a; and bushing 27i provided between the guide tube 27f and the piston 27a to stop a swinging movement of the piston 27a. Figure 9 is a side view showing the automatic choking system 34 installed on the top surface 20a of the main body 20 of carburetor. Thermally insulated cover 40 is provided on the automatic choking system 34. Figure 10 is a partial side view of a motor cycle or a motor scooter 35 mounting the engine 36 on which the main body 20 of carburetor equipped with the automatic choking system 34 is installed and air cleaner 37 is also installed on the main body 20 of the carburetor. A conventional automatic choking system is constructed from the lower end to the upper end with the needle 26, the starter valve 25, the moving part 28, the thermo-element 27 and the thermistor 31 in that order, and all of them are housed in the case 29 of I character shape and therefore, as shown in Figure 9, the automatic choking system 34 is substantially tall and is mounted on the top surface 20a of the main body 20 of the carburetor and further the thermally insulated cover 40 is provided on the top of the automatic choking system 34. Under the circumstance, there is such a problem that a relatively extensive space must be provided above the main body 20 of carburetor. In addition, as the current motor cycle or motor scooter 35 is equipped with the engine 36 together with the main body 20 of carburetor having such a tall automatic choking system 34 underneath seat 38, the compartment 39 cannot be provided for a helmet or anything else underneath the seat because the tall automatic choking system projects into the compartment 39, and as it is impossible to make the main body 20 of carburetor equipped with an automatic choking system 34 a more compact unit, it is difficult to design a more compact motor cycle or motor scootor 35 and hence the designing freedom is substantially limited. A further problem is that, if the thermal insulation of the thermo-element of the automatic choking system 34 is poor, the thermally expanding wax in the thermo-element stays shrinked and the starter valve 25 and the needle 26 of the automatic choking system also stay to keep the by-pass passageway 22 and the auxiliary fuel passageway 24 open and hence the engine cannot be started again smoothly even in a few minutes after the engine is turned off and is still warm. In order to solve the above problems, the automatic choking system 1 for a carburetor according to this invention is constructed as set forth in Claim 1. Preferred embodiments may be gathered from the dependent claims. This invention is intended to make it possible to provide a relatively extensive space above the main body of carburetor by installing such an automatic choking system as described in claim 1 on the carburetor, to place the vertical portion of the case of the automatic choking system on a side of the carburetor and adjust the position of the vertical portion of the case on the carburetor to make the portion projected from the top of the carburetor as low as possible and, as a result, the height of the whole carburetor is lowered by installing this automatic choking system, and the carburetor can be constructed as a compact unit. Accordingly, an extensive space for the compartment of a motor cycle or motor scooter may be provided to design a larger compartment for a helmet, etc. underneath the seat and, as a whole, a compact motor cycle or motor scooter may be designed with an extended designing freedom. In addition, the thermal insulation of the thermo-element of automatic choking system is improved by employing such automatic choking systems for the carburetor as described in claims 2 and 3 to eliminate such a problem as a failure in the starting of engine due to poor thermal insulation of the thermo-element, despite the engine is still warm, because the thermally expanding wax of the thermo-element stays shrinked and the starter and the needle keep the by-pass and the auxiliary fuel passageway open even in a few minutes after the engine was turned off. With the automatic choking system for the carburetor as described in claim 4 the relationship between the upward stroke of the piston of the thermo-element and downward stroke of the moving part being pushed down with the other end of the lever may be either linear or variously curved and with the automatic choking system for the carburetor as described in claim 5 the stroke ratio between the upward stroke of the piston of the thermo-element and the downward stroke of the moving part being pushed down with the other end of the lever may be changed and hence the automatic choking system may be easily designed to further improve the starting of the engine. BRIEF DESCRIPTION OF THE DRAWINGS: Figure 1 is a cutaway drawing of the automatic choking system for the carburetor according to this invention. Figure 2 is a drawing indicating the condition prior to the operation of the automatic choking system for the carburetor according to this invention. Figure 3 is a drawing indicating the condition after the operation of the automatic choking system for the carburetor according to this invention. Figure 4 is a side drawing of the carburetor equipped with the automatic choking system according to this invention. Figure 5 is a side drawing looking from A as indicated by an arrow in figure 4. Figure 6 is a plane drawing of the carburetor equipped with the automatic choking system according to this invention. Figure 7 is a schematic drawing of a conventional carburetor. Figure 8 is a cutaway drawing indicating thermo-element in detail. Figure 9 is a side drawing of a carburetor equipped with a conventional automatic choking system. Figure 10 is a side drawing of a motor cycle or motor scooter on which a carburetor equipped with a conventional automatic choking system is mounted. DESCRIPTION OF THE PREFERRED EMBODIMENTS: The preferred embodiments of this invention are described hereunder by referring to accompanying drawings. Figure 1 is a cutaway view of this automatic choking system for the carburetor; Figure 2 indicates the condition before the automatic choking system is operated; and Figure 3 indicates the condition after the system started the operation. The automatic choking system for the carburetor is constructed as described hereunder. Case body 2 is made,for instance,from a plastics and of up-side-down L character shape; thermo-element 3 is housed in the vertical portion 2a of the up-side-down L case body 2; thermistor 4 is adhered to the thermally expanding wax 3a side provided on the lower end of the thermo-element 3 and is heated up by electric current to increase its own electric resistance to shut off the electric current; the first moving part 5 is to move upward by being pushed with piston 3b projected from the top end of the thermo-element 3 due to thermal expansion of the wax 3a; lever 6 is housed in the upper side portion 2b of the case and is supported by means of one end 6a being pushed up by the first moving part 5 and the other end 6b being pushed down; the second moving part 7 is to move downward by being pushed down by the other end 6b of the lever 6; by-pass 8 is connected with the main air passageway of the carburetor 9; starter valve 10 is provided on the lower end of the second moving part 7 and is inserted into the by-pass 8 from the top end 9a of the carbretor 9 to shut off the by-pass with the downward movement of the second moving part 7; and needle 12 is to close the auxiliary fuel passageway 11 connected with the by-pass 8. Supporting shaft 13 is to rotatably support the lever 6 and, by changing the supporting position of the supporting shaft 13, the stroke ratio between the upward moving stroke of the first moving part 5 being pushed up by the piston 3b projecting from the top end of the thermo-element 3, and the downward moving stroke of the second moving part 7 being pushed down by the other end 6b of the lever 6, may be regulated. In addition, by changing the respective shape of contact surfaces between the end 6a of the lever 6 and the first moving part 5 moving upward with the piston 3b projecting from the top of the thermo-element 3, namely the respective shape of the upper surface 5a of the first moving part 5 and the lower surface 6a'of the one end 6a of the lever 6, or by changing the respective shape of the lower surfacesof the other end 6b of the lever 6 and the upper surface of the second moving part 7, the relationship between the upward moving stroke of the first moving part 5 being pushed up by the piston 3b projecting from the top of the thermo-element 3, and the downward moving stroke of the second moving stroke, may be either linear or variously curved. Further the second moving part 7 is pushed up by means of spring 14 provided in the case body 2 and both of the starter valve 10 and the needle 12 are pushed down by means of spring 15 provided underneath the second moving part 7. Thermally insulated cover 16 is made from a plastics moulding as a mono-block on the outer surface of the vertical portion 2a of the case body 2 having the up-side-down L shape or separately provided, as set out hereunder and, in case that the thermally insulated cover 16 is provided separately, the cover is formed with a plurality of spaced circumferential walls and concave groove 16a is formed on upper inner surface of the cover and a plurality of convex salients 2a' are also formed on lower outer surface of the vertical portion 2a of the case body 2 and annular salient 2a''is also provided on upper outer surface of the vertical portion 2a of the case body 2. The thermally insulated cover 16 is put on from the lower side of the vertical portion 2a of the case body 2, for mating the concave groove 16a with the annular salient 2a'' and such an installation may give a space between the inner circumference of the thermally insulated cover 16 and the outer circumference of the vertical portion 2a of the case body 2 and as a result a better thermal insulation of the thermal-element of the automatic choking system is realised and a mono-block moulding of the thermally insulated cover 16 with the vertical part 2a of the case body 2 is possible as well. The reason for installing the thermally insulated cover 16 is, as referred to above, to remove the problem that if an engine, having a poorly insulated thermo-element 3 of the automatic choking system 1, is turned off, the engine may not be started again smoothly even while the engine is still warm in a few minutes after the turning-off because the wax of the thermal-element 3 is being shrinked to have the starter valve 10 and needle 12 in the automatic choking system keeping the by-pass 8 and the auxiliary fuel passageway 11 open. Rubber 17 is provided for vibration proof, insulation and dust proof for wiring cord 18 connected with the thermistor 4 and spring 19 is provided for pushing down the first moving part 5. Figure 4 is a side view of the automatic choking system 1 installed on carburetor 9 according to this invention. Figure 5 is a side view of the Figure 4 looking from A marked by an arrow and Figure 6 is a plane view of the system showing that the vertical portion 2a of the case body 2 of up-side-down L shape composing the automatic choking system is positioned by the side of carburetor 9 and, as a result, the portion projected from the top of the carburetor may be reduced, to make the carburetor 9 equipped with the automatic choking system a compact size and such a compact design gives a better thermal insulation of the thermo-element of the automatic choking system 1 and the thermally insulated cover 16 may be moulded into a mono-block with the vertical portion 2a of the case body 2. Further, as the space around the carburetor is available for the installation of the the automatic choking system 1, the position of the vertical portion 2a of the case body 2 of the up-side-down L shape may be easily adjusted in any way on a side of the carburetor. As the wiring cord 18 connected with the thermo-element is drawn from the lower end of the vertical portion 2a of the case body 2 of the automatic choking system, the wiring cord 18 may be shortened to eliminate an interference with the peripheral parts. The automatic choking system 1 for the carburetor of this invention is constructed as stated above and the throttle valve provided in main air passageway (not shown) is closed before the starting of the engine and the thermally expanding wax 3a, provided on the lower end of the thermo-element 3, is shrinked and, as a result, the piston 3b of the thermo-element 3 is lowered with the end 6a of the lever 6, and the other end 6b goes up to open the by-pass passageway 8 connected with the main air passageway of the carburetor 9 by means of the starter valve 10, and the needle 12 opens the auxiliary fuel passageway 11. Hence the starting of the engine can be improved by sending to the engine a mixture richer than normal because the fuel is mixed with the air in the by-pass 8 without regulating the throttle valve provided in the main air passageway. To start an engine, a key-switch is turned on to put on the thermistor 4, attached to the thermally expanding wax 3a at the lower end of the thermo-element 3, to thereby heat up and expand the wax 3a to push up the piston 3b from the top end of the thermo-element 3 and push up the end 6a of the lever 6 and lower the other end 6b to push down the moving part 7. Then the by-pass 8 is closed by means of the starter valve 10 provided at the lower end of the moving part 7 and the needle 12 closes the auxiliary fuel passageway 11 to return the mixing ratio of the fuel with the air automatically to normal of proper operation of the engine under an idling condition. When the engine reaches the idling condition, an electric resistance of the thermistor 4 is increased with the heat and, as a result, the electric current to the thermistor 4 is substantially reduced or shut off. However, it is to be understood that this invention is not limited thereto and that various changes and modifications may be made without departing from the the invention as defined in the appended claims.

Claims: A carburetor (9) comprising: a by-pass passageway (8) bypassing a main air passageway; an auxiliary fuel passageway (11) connected with said by-pass passageway; and an automatic choking system (1) comprising: a case body (2); a thermo-element (3) housed in a portion of the case body (2); a thermistor (4) attached to a thermally expanding wax (3a); a piston (3b) projected from an end of the thermo-element (3) by thermal expansion of the wax (3a) ; a starter valve (10) to shut off a by-pass passageway (8); and a needle (12) to shut off the auxiliary fuel passageway, characterized by: a lever (6) supported so as when one end (6a) is pushed up by the piston (3b), its other end (6b) is pushed down and pushes down a moving part (7) to operate the starter valve (10). The carburetor of claim 1 wherein a thermally insulated cover (16) is provided on an outer surface of a portion (2a) of the case body (2) by a mono-block moulding with the case body (2) or separately. The carburetor of claim 2 wherein the thermally insulated cover (16) is provided separately by means of a plurality of spaced circumferential walls of the cover (16), and a concave groove (16a) is formed on an inner surface of the cover (16) with a plurality of convex salients (2a') formed on a first part of an outer surface of the portion (2a) of the case body (2) and an annular salient (2a'') is also formed on a second part of the outer surface of the portion (2a) of the case body (2) and the thermally insulated cover (16) is put on from a first side of the portion (2a) of the case body (2) to mate the concave groove (16a) formed on the inner surface of the thermally insulated cover (16) with the annular salient (2a'') formed on the second part of the outer surface of the portion (2a) of the case body (2) so as to provide a space between the portion (2a) of the case body (2) and the thermally insulated cover (16). The carburetor of claim 1, claim 2 and claim 3 wherein the relationship between an upward moving stroke of the piston (3b) of the thermo-element (3) and a downward moving stroke of the moving part (7) being pushed down by the other end of the lever (6) may be linear or variously curved by changing the shape of respective contact surfaces (5a,6a') of the piston (3b) projecting from the thermo-element (3) and one end (6a) of the lever (6), or of respective contact surfaces of the other end (6b) of the lever (6) and the moving part (7). The carburetor of claim 1, claim 2, claim 3 and claim 4 wherein the stroke ratio between the upward moving stroke of the piston (3b) of the thermo-element (3) and the downward moving stroke of the moving part (7) being pushed down with the other end (6b) of the lever (6) is variable by changing the supporting position of the rotatably supported lever (6).

Inventors: MICHIHIRO SUDA, TAKAHIRO IWAKI, MICHIHIRO, SUDA, TAKAHIRO, IWAKI
Applicants: NIPPON THERMOSTAT KK, NIPPON THERMOSTAT CO., LTD.
Application year: 1993
Main classification: F02M1
IPC codes: F02M1