US3834677A

US3834677A - Automatic choke control

Info

Publication number: US3834677A
Application number: US00423982A
Authority: US
Inventors: Y Hosho
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1970-09-02
Filing date: 1973-12-12
Publication date: 1974-09-10
Anticipated expiration: 1991-09-10

Abstract

An automatic choke control for a carburetor in which the pivot of a bimetal for determining the degree of opening of a choke valve corresponding to the temperature of the engine is rotated in accordance with the variation in the running conditions of the engine at the time of cold starting, whereby the force for closing the choke valve is controlled in relation to the temperature of the engine.

Description

ilniieei States Patent liiosho 11] 3,834,677 Sept. 10, 1974 3,109,874 11/1963 Mennesson 261/39 B 3,159,692 12/1964 Kittler 261/39 B 3,253,781 5/1966 Scheffler 261/39 B 3,262,683 7/1966 Primary Examiner-Tim R. Miles Atzorney, Agent, or Firm-Craig & Antonelli ABSTRACT An automatic choke control for a carburetor in which the pivot of a bimetal for determining the degree of opening of a choke valve corresponding to the temperature of the engine is rotated in accordance with the variation in the running conditions of the engine at the time of cold starting, whereby the force for closing the choke valve is controlled in relation to the temperature of the engine.

10 Claims, 11 Drawing Figures mfimmsm'g" 3.34577 SHEEIIUFS INVENTOR Yumo HOSHO BY maa, aMtowww Hum- PATENTEDSEPI 0:914 3.834.677

sum 2 ur s INVENT OR YUKIO HOSHO BY Out MRL' .5 ATTORNEYS SHEEI 3 0F 5 FIG. 3

PATENTEDSEPI DISH 40 TEMPERATURE HC) INVENTOR Yuma HOSHO BY craul z uiowmi a H-KQQ ATTORNEYS m E wu mE 0250 6 E m ll l 5 m R T A G W F w m m m ..o P 6 k 2 E W m is 20.550 to G T 593 352m l s 0A F F 0 H m .0 Dr 9 w E Q T O I 4 Mn M\n m m JIIPITILM m E .052 $522 6 mm m m L a; 23 wzEnm F0 w $610 m C PATENTEUSEPI man SHEET '4 BF 5 FIG 7 FIG.8

. l""l""l""" I l n, w

INVENTOR YUKIO HOSHO BY mw 4, m

ATTORNEYS AUTOMATIC CHOKE CONTROL This is a continuation of application Ser. No. 175,431 filed Aug. 27, 1971 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carburetor for an internal combustion engine, and more particularly to an automatic choke control for a carburetor wherein the choke valve is automatically opened and closed in relation to the temperature of the engine.

2. Description of the Prior Art An automatic choke control of a carburetor is well known as a device which automatically controls the degree of opening of the choke valve in accordance with the temperature of cooling water or the like of the engine by the use of a bimetal deformed by the temperature variation. Since it is necessary to provide rich mixture gas at the time of cranking of the engine, the choke valve is completely closed at the time of cold starting by making the bimetal have a proper choke valve setting load. When the engine is cranked, an inlet suction of the engine acts upon the choke valve eccentrically and pivotally provided in a venturi and the choke valve is slightly opened to suck air against the choke valve closing load. After the self-cranking of the engine, the volume of inlet air required increases as the revolutions of the engine increases. Further, the fuel in the inlet manifold becomes liable to be evaporated as the temperature of the engine rises and the reduced pressure in the inlet manifold rises up. Accordingly, the mixture gas is required to be lean after self-cranking. Based on the above requirement, there has been provided a mechanism which gives a proper mixture ratio for continuing the warming up running of the engine after selfcranking by utilizing the reduced pressure in the inlet manifold to open compulsorily the choke valve against the choke valve setting load. (This mechanism will hereinafter be referred to as self-cranking compensation mechanism) The load working on the bimetal for closing the choke valve after self-cranking by the self-cranking compensation mechanism is the sum of the following two loads (1) and (2);

l. Choke valve setting load at the time when the choke valve is completely closed,

2. Load determined by multiplying the degree of opening of the choke valve at the time of self-cranking by the bimetal angle of deviation-load characteristic.

The former is 100 to 200 grams and the latter is several hundreds of grams, and at the time of selfcranking, the sum of the two works on the bimetal as a resisting force. Therefore, in the case that the engine is warmed up from a low temperature to a high temperature, the volume of harmful exhaust gas is extremely increased due to too rich mixture gas at a certain temperature and at another temperature the condition of the running engine becomes unstable due to too lean mixture gas.

SUMMARY OF THE INVENTION The primary object of the present invention is to provide an automatic choke control which varies the load acting on the bimetal according to the running condition of the engine so that the degree of opening of the choke valve at the time of cold starting of the engine may be controlled appropriately.

In accordance with the present invention accomplishing the object as stated above, the engine is smoothly warmed up and the harmful component in the exhaust gas is decreased.

The present invention has its feature in that the pivot of the bimetal controlling the choke valve is rotated according to the running condition of the engine, particularly, the variation in the reduced pressure in the inlet manifold between before and after self-cranking of the engine, whereby the resisting force action on the bimetal is varied and the degree of opening of the choke valve after self-cranking is made appropriate.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a front view partly in section of a carburetor having a conventional automatic choke control,

FIG. 2 is a side view of the carburetor of FIG. 1,

FIGS. 3 to 6 are graphic representations showing relationships between the temperature of the engine and the degree of opening of the choke valve, and the temperature of the engine and the closing force of the choke valve,

FIG. 7 is a vertical sectional view of the main portion of an embodiment of the automatic choke control in accordance with the present invention,

FIG. 3 is a sectional view taken along the line VIII VIII of FIG. 7,

FIG. 9 is a vertical sectional view of the main portion of a conventional automatic choke control of the electric heater type,

FIG. 10 is a front view partly in section of another embodiment of the automatic choke control in accordance with the present invention, and

FIG. 11 1 is a sectional view taken along the line XI XI of FIG. 10.

PREFERRED EMBODIMENTS OF THE INVENTION Referring first to FIGS. 1 and 2 showing a conventional automatic choke control, the reference numeral It shows a carburetor body having a primary mixing passage 2 and a secondary mixing passage 3. In the primary mixing passage 2 are provided a throttle valve 4, a choke valve 5, a venturi 6 and a main nozzle 7. The choke valve 5 is fixed to a choke shaft 8 which is, in turn, fixed to a choke lever 9. The reference numeral 10 shows a first idle cam which is rotatably supported on a counter shaft 12 together with a counter lever l 1 which is related to the first idle cam. 10 through a spring 113. The lever 11 is connected with the choke lever 9 through a rod 141. On the other hand, a throttle valve shaft 15 on which the throttle valve 4 is fixed is fixed to a throttle lever 16 the end of which is engaged with a cam surface 10 of the first idle cam 10. The choke lever 9 is further connected with the outer end of a coil bimetal 118 through a rod 17. The inner end of the bimetal 18 is fixed to a shaft 19 which is, in turn, fixed to a bracket 22 in a casing 21 mounted to an exhaust manifold 20. The choke lever 9 is provided with a groove 23. A lever 24 one end of which is engaged with said groove 23 is connected at the other end thereof with a diaphragm 26 of the self-cranking compensation mechanism 25. A chamber on the right side of the diaphragm 26 is connected to atmosphere and a chamber on the left side thereof is connected to the downstream of the throttle valve 4 in the primary mixing passage 2 through a pipe 27. The reference numeral 28 shows a spring which pushes the diaphragm 26 to the right under the state where the reduced pressure is small.

Now the operation of the above described conventional device will be described. Before the engine is started, the first idle cam 10 and the throttle lever 16 are in the position shown in the drawing. That is, according to the temperature at the time of starting of the engine, the deformation of the bimetal 18 is determined and accordingly the degree of opening of the choke valve is determined. Further, the degree of opening of the throttle valve 4 is determined by the position of engagement between the cam surface of the first idle cam and the throttle lever 16.

If the engine is started cranking under the above state, the choke valve 5 is slightly opened against the resisting force acting on the bimetal through the rod 17 by the pressure difference caused by eccentricity of the choke shaft 8 with respect to the choke valve 5, that is, difference in pressure receiving area between the opposite sides of the choke shaft. Thus, air is sucked through the choke valve and the fuel is sucked out through the main nozzle and a low speed fuel system (not shown) by the reduced pressure. The mixture ratio obtained at various temperatures is shown at zone A in FIG. 3. By this control of mixture ratio, the engine can be started. This range of mixture ratio is called cranking mixture ratio. This is selected according to all lever ratios, set position of the bimetal, temperature and spring characteristic so that the ratio may be controlled within the range between the upper and lower curves at every temperature.

Now the operation of the above conventional device will be described under the state where the engine is started and self-cranking is started. In this case, the mixture ratio is required to be within zone B shown in FIG. 3. This is controlled by the following mechanism. That is, when the engine starts self-cranking and the number of revolutions increases the reduced pressure downstream the throttle valve is abruptly increased. This reduced pressure works on the chamber on the left side of the diaphragm 26 through a pipe 27 having a reduced pressure take out port in the downstream of the throttle valve and pulls the diaphragm 26 toward the left side, and rotates the choke shaft 8 through the lever 24 and the choke lever 9 to increase the degree of opening of the choke valve 5. This is the self-cranking compensation mechanism.

At the same time when the choke valve is opened, the outer end of the bimetal is imparted with a force through the rod 17.

In the bimetal, there is a relation between the spring load and the angle of deviation of bimetal as shown in FIG. 4 that a force of kg is required to deviate the bimetal by one degree, namely W k 6g where W is a spring load and 0 is an angle by which the spring is deviated by the load W. And as shown in FIG. 5, there is a relation at 0 Ct where C is a degree of deviation of the bimetal per 1C of temperature rise. Considering these relations, the relation between the resisting force acting on the bimetal (force in the direction of closing the choke valve) at the time of cold starting for example at -C and the temperature rise according to the warming up and the degree of opening of the choke valve can be represented graphically in FIG. 6.

The choke valve closing force immediately after the self-cranking Fs is represented by PS Ws k0 where Ws is a setting load at the time when the choke valve is completely closed and 0 is the degree of opening of the choke valve at the time of self-cranking. In other words, in FIG. 6, the condition of the choke valve varies from the point A to B, C and D as the warming up advances. When the condition of the point C is reached, the bimetal is released and the choke valve is gradually opened by the pressure difference between the opposite sides of the choke shaft. From the viewpoint of the degree of opening of the choke valve, it is gradually opened to a full opened condition from the point L where the engine is in the condition immediately after self-cranking. Therefore, the time during which the choke is maintained open as it is opened at the time of self-cranking becomes very long, and during the long time a large amount of harmful exhaust gas is discharged. Further, if the valve is made to be opened faster, the engine becomes liable to stop.

If the choke valve should be operated as the engine is warmed up after self-cranking as L, M N 0 and P as shown in FIG. 6 and the point of N could be properly selected, the gradient of the opening curve after the choke valve begins to open can be made gentle and the most appropriate warming up characteristic can be easily obtained evading the exhaust gas and malfunc tion of the engine. In order to accomplish this valve characteristic, the choke valve is closed along the points A, C and D after self-cranking. In other words, the choke valve closing force is reduced by k6, immediately after self-cranking of the engine.

Now the present invention will be described in detail referring to the drawing showing preferred embodiments thereof. In FIGS. 7 and 8, a bimetal case 36 is secured to the exhaust manifold 20, and a lever 44 is fixed to a sleeve 43 slidably mounted on a bimetal shaft 40 fixed to a bracket 37 disposed within the case 36 by means of machine screws. The bimetal 42 is secured at the inner end thereof to the sleeve 43 as shown in FIG. 7, and mounted at the outer end thereof to the lower end of the rod 17 by means of a bush and a split pin or the like as in the conventional device. In such a construction, a diaphragm chamber 47 operated by the inlet reduced pressure together with a choke piston is provided as shown in FIG. 7. The reference numeral 46 indicates a bracket mounted to the

bimetal case

36, 48 indicates an inlet reduced pressure introducing conduit, 49 indicates a casing, 50 indicates a cover, 51 shows a diaphragm, 52 shows a spring, and the reference numeral 53 indicates a spring guide serving as a stopper. At the time of self-cranking of the engine, the diaphragm 51 is attracted to the left against the spring force of the spring 52 by the reduced pressure. By the lever 54 fixed to the diaphragm 51, the lever 44 is rotated in the counterclockwise direction through the rod 45 so that the pushing down force for the bimetal 42 coming from the rod 17 may be released. Thus, the point N can be selected at any position between the points L and N in FIG. 6. The point N in FIG. 6 shows the position which is determined in the case that the pivot of the bimetal is rotated by the bracket 44 by the angle corresponding to the degree of opening of the choke valve at the time of self-cranking.

In the embodiment as described above, a further diaphragm 51 other than the diaphragm 26 in the conventional automatic choke control shown in FIG. 1 is provided. However, the additional diaphragm 511 may be eliminated by making the diaphragm 26 in FIG. ll serve as a driving source to drive the lever 44 in the embodiment of the present invention shown in FIG. 7.

Although the present invention has been described in relation with an automatic choke control of the hotwell type, it will be understood that the present invention can be applied to a hot-water type choke control and the like in which the bimetal case is provided at a position separated from the body of the carburetor.

Now another embodiment of the present invention applied to a carburetor with an electric heater type automatic choke control will be described as an example of the device in which a bimetal case is directly mounted to the carburetor body.

FIG. 9 is a sectional view of a bimetal case portion of a conventional choke control, in which the reference numeral 55 shows a bimetal, 56 shows an insulator, 57 a heater coil, 58 a metal fixture for fixing the insulator, 59 a bimetal shaft and 64) indicates a bimetal. An end of the bimetal 6th is fixed to the bimetal shaft 59. When the engine starts, the outer end of the bimetal is pro vided with a compulsory force for rotating the bimetal pivot by the angle corresponding to the opening of the choke at the time of self-cranking by means of a rod in a self-cranking compensation mechanism as in the conventional device as shown in FIG. 1.

FIGS. and l l show an embodiment corresponding to the type of the conventional device as shown in FIG. 9, in which the reference numerals 55 to 60 indicate the same elements as those shown in FIG. 9. The reference numeral 61 shows a sleeve, 61 a lever integrally mounted to the

sleeve

61, 63 and 64- collars, 65 a rod, 66 and 67 terminals 62 connecting the electric power source for the

heater coil

57, and 68 indicates a boot for preventing invasion of dust.

In the construction as described above, the choke valve is opened to an extent corresponding to that of the self-cranking by the self-cranking compensation mechanism at the time of starting the engine. Simultaneously, the force acting on the bimetal 60 is able to be set to one equal to or about that acting at the time of completely closing the choke valve by the rod 65 connected to the lever of the choke piston, in the case shown in the drawing, by pushing up the rod 65.

Although this construction has been described with reference to an electric heater type case, it will be understood that this is able to be applied to a hot-air type in which the bimetal case is mounted to the carburetor body.

In the present invention, since the pivot of the bimetal is rotated by the angle corresponding to the degree of opening of the choke valve at the time of selfcranking simultaneously with the self-cranking of the engine to reduce the force acting on the bimetal, it becomes possible to easily maintain the optimum degree of opening of the choke valve as the warming up of the engine advances. And a stable running of the engine can be effected with a minimum volume of harmful exhaust gas discharged at the time of warming up. Further, it should be understood that the shaft of the bimetal can be rotated by various means other than that employed in the above-described embodiments.

What is claimed is:

1. Automatic choke apparatus for a carburetor of the type having a choke valve having a control linkage mechanism and a throttle valve having a control linkage mechanism in an intake passage, said apparatus comprising choke control means for controlling the movement of a choke valve, said choke control means including first temperature responsive control means for applying moving forces on said choke valve with choke valve opening moving forces decreasing with increasing temperature, second pressure responsive control means for moving said choke valve from a closed position to a first open position, and third control means connected to said first means for neutralizing changes in reactive forces on said first means resulting from movement of said choke valve to said first open position by said second means such that movement of said choke valve in respective opposite directions with respect to the first open position is controlled by said first means independent of reactive forces obtained by the action of said second means, said third means being connected to said first means independently and separately from the throttle valve control linkage mechanism so that neutralization of the changes in reactive forces on said first means is effected by said third means irregardless of the position and movement of the throttle valve.

2. An automatic choke control according to claim 1, wherein said first means includes a bimetallic coil responsive to temperature for producing the moving forces, said bimetallic coil having an inner end and an outer end, and linkage means acting between the control valve and the outer coil end for applying the moving forces to the choke valve.

35. An automatic choke control according to claim 1, wherein said second means is a self-cranking compensation means which includes a reduced pressure means for converting reduced pressure downstream of the throttle valve into moving forces acting on the choke valve at initial operation of the carburator.

4. An automatic choke control according to claim 2, wherein said third means includes a shaft means for rotatably supporting the inner end of said bimetallic coil and a vacuum diaphragm means directly connected to said shaft means for rotating the shaft means in response to reduced pressure.

5. An automatic choke control according to claim 4, wherein said second means is a self-cranking compensation means which includes a reduced pressure means for converting reduced pressure downstream of the throttle valve into moving forces acting on this choke valve at initial operation of the carburator.

6. An automatic choke control according to claim 5, wherein the reduced pressure means of the selfcranking compensation means is a vacuum diaphragm means.

7. An automatic choke control according to claim 6, wherein the vacuum diaphragm means of said selfcranking means is the vacuum diaphragm means of said third means.

An automatic choke control according to claim 4, wherein the vacuum diaphragm means rotates the shaft means by an angle proportional to the angle of rotation of the choke valve in said first position.

9. An automatic choke control according to claim 1, wherein the bimetallic coil is responsive to engine temperature.

Ml. An automatic choke control according to claim 1, wherein the bimetallic coil is responsive to temperature produced by an electric heater.

r =c l a:

Claims

3. An automatic choke control according to claim 1, wherein said second means is a self-cranking compensation means which includes a reduced pressure means for converting reduced pressure downstream of the throttle valve into moving forces acting on the choke valve at initial operation of the carburator.

6. An automatic choke control according to claim 5, wherein the reduced pressure means of the self-cranking compensation means is a vacuum diaphragm means.

7. An automatic choke control according to claim 6, wherein the vacuum diaphragm means of said self-cranking means is the vacuum diaphragm means of said third means.

8. An automatic choke control according to claim 4, wherein the vacuum diaphragm means rotates the shaft means by an angle proportional to the angle of rotation of the choke valve in said first position.

10. An automatic choke control according to claim 1, wherein the bimetallic coil is responsive to temperature produced by an electric heater.