US2796243A - Carburetor - Google Patents

Description

United States Patent CARBURETOR Archie D. McDuflie, Berkley, Micl1., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application May 16, 1955, Serial No. 508,561

3 Claims. (Cl. 261-41) This invention relates to carburetors for internal combustionengines, particularly for engines used in automotive vehicles, and relates primarily to carburetors having means for supplying fuel, for engine idling operation, at a point posterior to the mixture controlling throttle valve which is subject to the vacuum which is maintained in the engine manifold.

In devices of this character, when deceleration occurs, that is, when the carburetor throttle is closed, as when approaching a traffic light or upon going down grade, for example, the idling fuel supply passage is subjected to a very high vacuum because the engine is being driven by the vehicle and is operating during most of the deceleration' period at considerably more than idling speed. This results in providing the engine with more fuel than will be burned under the conditions referred to and causes a considerable amount of unburned fuel to be discharged through the exhaust conduit into the atmosphere. Also during deceleration, under some circumstances, fuel is supplied by the main nozzle before the throttle reaches its fullyclosed position which will not be entirelyburned. Obviously, a large amount of fuel is wasted and the atmos phere is contaminated by the unburned fuel which is discharged as described.

Devices have previously been designed to prevent the discharge of unburned fuel from the exhaust during acceleration and it is the primary purpose of the present invention to provide mechanism for accomplishing this result which is of novel construction, is entirely automatic in operation, is positive and efficient in action and can be produced at relatively low cost.

It is a further object of the invention to provide a device of'the character described which is particularly adaptable to compound carburetors having a plurality of intake passages, each of which has an idling fuel supply conduit associated therewith, and which device is so constructed that a single device is effective to prevent the discharge of fuel into the mixture passages during deceleration, by any and all of said idling fuel supply conduits. According to the present invention, these purposes are accomplished by the provision of means to communicate to the space above the fuel in the constant level fuel chamber, which supplies fuel to both the main and idling fuel supply conduits, a partial vacuum which is greater than the partial vacuum that is effective on the idle fuel supply conduit at idling or on the main fuel supply conduit under any operating condition, so that flow of fuel from both main and idling fuel conduits is prevented by the high vacuum maintained in said fuel chamber. The very high degree of vacuum which is maintained in the engine manifold and in the carburetor intake passages at points posterior to the throttle, and which would normally be effective to cause the excess fiow of fuel from the idling fuel supply passages during deceleration, previously referred to, is utilized to open a valve which is normally closed, to permit such high vacuum to be communicated to the fuel supply chamber during deceleration. This valve is reclosed when the period of deceleration is over to permit flow of fuel from the fuel supply conduits, so that the engine can resume operation under its own power.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

In the drawings, the single figure is a diagrammatic sectional view of a compound carburetor in which the present invention is embodied.

The carburetor is illustrated only diagramatically because the specific structural details of such carburetor are in no way material so far as the present invention is concerned, but the carburetor may be of substantially similar construction to that shown in the copending application of Elmer Olson et a1. Ser. No. 264,136, filed December 29, 1951, now Pat. No. 2,771,282, dated November 20, 1956. Such carburetor has four mixture passages, two of which are termed primary mixture passages and two of which are termed secondary mixture passages.

The primary passages function at all engine speeds and will be understood that there are two similar passages for supplying the other block.

The carburetor is composed of three castings'positioned above each other when the device is assembled, a throttle body casting 2 supported directly on the intake manifold, a casting 4, in which the fuel supply chamber and most of the fuel supply passages are formed, positioned above the throttle body casting and a third casting 6, in which the air inlet passages are formed, positioned above the casting 4. The several castings are separated by suitable gaskets.

The throttle body casting has two primary mixture outlets 8 and two secondary mixture outlets 10, only one of each being shown in the drawing. The primary outlets are controlled by primary throttle valves 12 secured to a manually operated shaft 14 rotatably mounted in the casting 2, while the secondary outlets 10 are controlled by secondary throttles 16 secured to a rotatable shaft 18, which is connected by means, not shown, to the shaft 14 so as to be operated therewith after a predetermined movement of the latter in a direction to open the primary throttles. As the throttle operating mechanism forms no part of the present invention, it is not shown herein.

In the casting 4 are primary mixing chambers 20 and secondary mixing chambers 22 which communicate with the outlets 8 and 10, respectively, and deliver a mixture of fuel and air thereto. Formed in the casting 6 and communicating with the mixing chambers 20 and 22, respectively, are primary air intake passages 24 and secondary air passages 26, both of which receive air from a single opening 28. Controlling the admission of air through passages 24 is a choke valve 30 secured to a rotatable shaft 32, the movement of which is generally automatically controlled by means (not shown) responsive to variations in temperature and engine suction. The passages 26 are unrestricted since such passages do not function except at relatively high engine speed and no restriction is necessary.

Coming now to the means for supplying fuel to the carburetor, there is formed in the casting 4 a constant level chamber 34 to which fuel is supplied from a main supply tank in any suitable manner and in which fuel is maintained at a substantially constant level by a float 36 which operates a valve of conventional construction, such as shown in the abovementioned application, for example. This chamber supplies both primary mixture passages A with fuel, and there is a second fuel chamber of generally similar construction, which is not shown but which supplies fuel to secondary mixture passages B.

The specific construction of the means for conveying fuel from tle chamber 34 to the mixture passage for idling and operation of the engine under load is not a part of the present invention. Any conventional construction could be employed and for convenience, there is shown herein a diagrammatic view of a fuel supply means which is substantially similar to that shown in the copending application of Olson et al. previously referred to. As shown, fuel flows from chamber 34 into a main fuel well 38 through a metering plug 40 which is screwed into the casting 4 and controls fuel flow in the conventional manner. This well is vented at the top by a passage 42 which connects with the mixture passage as indicated in the drawing, but the well could be vented to atmosphere, if desired.

Extending upwardly from the well 38 is a fuel supply tube 43 which supplies fuel to the main fuel inlet. This tube connects at its upper end with a passage 44 formed in a small casting 46 which is secured by any suitable means to a horizontal surface formed on the casting 4. The passage 44 connects with a small venturi tube 48 which constitutes the main fuel inlet and discharges a primary mixture of fuel and air adjacent the throat of a larger venturi tube 50, which forms the main mixing chamber 20.

Fuel for idling is supplied from an idling fuel well 52 to which fuel flows from the main well through an opening 54. A tube 56 extends downwardly into the well 52 from the casting 46 and connects at its upper end with a passage 53 with the mixture passage, as shown. The Well 52 is vented by a passage 47' in the same way as the main fuel well is vented. A passage 49 connects the passage 58 with a vertical passage 51 to convey idling fuel to the mixture passage, the passage 51 being formed partly in the casting 4 and partly in the casting 6, as indicated in the drawing.

At its lower end, the passage 51 connects with an idling fuel inlet 60 which connects with the mixture'passage A at a point posterior to the throttle and is controlled in the conventional manner by a manually adjustable valve 62. A small passage 64 connects the passage 51 at a point anterior to the throttle and serves as a bleed for the idling fuel passage, as is common in conventional carburetors. The tube 43 has a plurality of fuel inlet ports 53 at different levels which are progressively uncovered to admit air when the main fuel supply means is functioning and the chamber 34 is vented by a tube 68 which connects the upper part of the chamber with the air inlet passage 24.

As already stated, the described arrangement of fuel well and associated supply passages is substantially conventional and the operation is very simple. During idling, when the throttle is almost closed, fuel is supplied only by the idling fuel inlet 69, being drawn from the Well 52 through passages 58, 49 and 51, and mixed with some air which is admitted through the plug 45 and the passage 64. As the throttle is opened, the partial vacuum at inlet 60 decreases and that at passage 52 increases. At some point inthe opening movement of the throttle the vacuum at passage 44 becomes great enough to cause fuel to flow therefrom and this takes place before the idling inlet 60 has ceased to function. As the throttle continues to open, the flow from passage 44 increases and that from inlet 60 decreases until, ultimately, the inlet 69 ceases to function and all fuel is supplied by passage 44. After the passage 44 is functioning, if the throttle is moved to relatively wide open position and the speed is relatively high, the level of fuel in the well 38 may be lowered enough to permit air to enter the tube 43 through holes 53. This will prevent the mixture from becoming too rich at open throttle, high speed, as is well known in the art.

In the tube 48 the fuel from passage 44 is mixed with additional air to form a relatively rich mixture and this is discharged into the mixing chamber 20, which is in the form of a large venturi tube, and is there mixed with additional air to form a mixture of properly combustible proportions. A small venturi tube 70, which discharges into the mixing chamber 22 and is similar to the tube 48, constitutes the fuel inlet for each secondary mixture passage and the means for supplying fuel to the tube 70, which is not shown, may be of the same construction as above described, but there is no means for introducing fuel for idling operation in the secondary mixture passages. At idling only the primary mixture passages are effective.

It will be understood that in the above-mentioned application there is a separate fuel supply well and associated passages for each of the primary mixture passages, but it would be possible, if desired, to have a common well for supplying both primary mixture passages.

The mechanism which has been described constitutes no part of the present invention but is a description of one form of carburetor with which the present invention can be associated, and it is to be particularly understood that use of the present invention is in no sense limited to this particular carburetor. Such invention can be associated with substantially any conventional form of carburetor. Also, the invention, although it is particularly desirable with a compound carburetor, functions to accomplish its intended purpose with a single intake carburetor also.

As already indicated, there is a very high degree of vacuum, which may amount to 20 inches Hg or more, maintained for a time in the outlet passages '8, during deceleration, and unless means be provided to prevent such an action, this high vacuum would cause so great a flow of fuel from the passages 60 and under some circumstances from the main fuel supply passage 44, that there would be a discharge of unburned fuel from the exhaust into the atmospheric. Since the engine is being driven by the vehicle during deceleration, it is not necessary to supply fuel for operation of the engine under its own power and, in addition, it is desirable that self-operation of the engine be interrupted during deceleration so that the braking effect of the engine will be increased and fuel will also be saved. Accordingly, this invention comprises mechanism for completely stopping the how of fuel, both from the passage 60 and from the main fuel supply passage during deceleration until the engine Slows down to approximately normal idling speed and when this takes place, such mechanism becomes inoperative and flow of fuel from the passage 60 resumes. This is accomplished by maintaining in the space above the fuel in chamber 34, during deceleration, a suction or partial vacuum which is greater than that which is maintained at either the main or idling fuel inlet.

The mechanism for accomplishing this result includes a suction passage formed in the wall of the throttle body casting 2 and communicating with one end of a conduit 82 which, as shown, is a metal tube entirely outside the carburetor, the ends of which are connected to the castings 2 and 6 by any suitable means which will form a fluid-tight joint, as by coupling nipples 84 which are screwed into the castings. The other end of the tube 82 communicates with a chamber 86 formed in the casting 6. One wall of this chamber 1 is formed by a flexible diaphragm 88 of any suitable material, held against the face of the casting 6 with sufficient pressure to form a fluid-tight joint by a clamping ring 90 which is secured in position by any suitable means, such as screws 92, for example. A port 94 connects the chamber 86 with a passage 96 formed in casting 6, which connects with the vent tube 68 as shown in the drawing. The port 94 is controlled by a poppet valve 98 the stem of which is secured in any desirable way to the center of the diaphragm 88 and a spring 100 normally holds the valve in its closed position. The valve is opened when the vacuum communicated to the chamber 86 is greater than the force exerted by the spring 100 to hold the valve closed.

Positioned in the passage 96 and vent tube 68 are restricting plugs 102 and 104, respectively, having small passages 106 and 108 therethrough. The relative area of these passages determines the degree of vacuum or suction which will be communicated to the space in the chamber 34 above the level of fuel therein for any degree of vacuum maintained in the passage 8 at the point where the passage 80 connects therewith. -It should be apparent that if the passage 108 was not provided, the suction or partial vacuum which is communicated to the chamber 34 for any given suction in the passage would be greater than when the passage 108 is provided because the air admitted through the passage reduces, to an extent determined by the area of the passage, the suction maintained to the left of the restricting plug 102.

Therefore, by properly selecting the relative areas of the passages 106 and 108 substantially any desired result can be obtained, that is, by varying the size of passage 108 relative to passage 106, the degree of suction which it is necessary to maintain in passage 8 to produce enough suction in chamber 34 to prevent flow of fuel therefrom through passages 60 can be determined as desired, within limits. In other word-s, if the areas of passages 106 and 108 are properly chosen, the flow of fuel from passages 60 can be stopped when the suction in passage 8 is but little more than the idling suction, or the area of passage 108 relative to passage 106 can be increased, so that a greater degree of suction or partial vacuum will have to be maintained before the flow of fuel from passages 60 can be stopped. As a matter of fact, the sizes of the passages 106 and 108 can be so selected that the suction in the chamber 34 is not greater than that maintained at the main fuel inlet and the passage 60 but is slightly less than the suction maintained at such points. If the passages 106 and 108 are of a size to produce this result, the flow of fuel from the main and idling fuel supply passages would not be entirely stopped when the valve 98 is opened, but so little fuel would flow, due to the pressure of such suction in chamber 34, that all the fuel would be burned during deceleration.

The operation of the device should be obvious from which has already been said, but a very brief rsum of the operation follows. When the engine is idling, the suction or partial vacuum in the passages '8 is insufiicieut, because of the slow operating speed, to overcome the force of the spring 100 and open the valve 98, so that during idling, the pressure above the fuel in chamber 34 is approximately atmospheric and fuel is supplied by the passages 60 for idling operation. During deceleration the engine, being driven by the vehicle, is operating at considerably :higher speed and the suction in passages 8 will become considerably greater than the idling vacuum and will open the valve against the force of spring 104). Springs of different force can be used but it would be preferable to use a spring which will be overcome when the speed is not much above the idling speed so that the valve will not be reclosed until the speed drops, upon deceleration, nearly to the idling speed. Otherwise, the valve might close and the fuel chamber become subject to atmospheric pressure when the speed might still be such that excess fuel would be introduced into the passages 8, which would not be burned. When the valve '98 is open, suction is communicated through passage 96 and tube 68 to the top of chamber 34 and the passages 106 and 108 should be of such size that this suction is sufl'icient to prevent flow from the passages 60 when the suction in passages 8 is little more than the normal idling suction.

.As already indicated, the device disclosed is particularly adaptable to a compound carburetor of the type disclosed because, since there is only one chamber 34 which supplies both primary mixture passages, the single means for communicating suction to the chamber 34 will control the flow of fuel from the passages 60 which supply fuel to both the primary mixture passages of the carburetor. Obviously, however, the device is equally applicable to prevent flow of fuel during deceleration to a carburetor having a single intake or mixture passage. It should be apparent that instead of using the passage restricting plugs 102 and 104 in the passages 96 and 68, respectively, manually operated flow controlling valves adjustable from outside the carburetor housing could be employed to verbally control the effective area of the passages 96 and 68, as desired.

It should be understood that when the suction in the chamber 86 falls and becomes insufl'icient to overcome the force of spring100, the diaphragm is moved downwardly by the spring and creates a slight pressure on the fuel in the chamber 4. This tends to cause the normal fuel flow to be resumed more rapidly after the suction conduit has ceased to be effective. It is obvious that theetfect of the diaphragm varies with size and the larger herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. In a carburetor having a mixture passage adapted to supply a mixture of fuel and air to the engine, a throttle valve for controlling the quantity of mixture supplied to the engine, means for supplying fuel and air to said mixture passage including a fuel conduit for supplying fuel for idling to the mixture passage at a point posterior to the throttle valve, and a fuel supply reservoir from which said conduit receives fuel; means for preventing flow of fuel from said fuel conduit into the mixture passage during deceleration effected by a closing movement of the throttle, said last-named means comprising a chamber having a wall with an opening therein and a second wall formed by a flexible diaphragm, a suction passage communicating with said opening and extending to the fuel supply reservoir above the fuel therein, a valve controlling said opening and connected to said diaphragm, spring means normally biasing said valve to a position blocking communication between said passage and chamber, and a single suction conduit extending from said mixture passage posterior to the throttle and in communication at all times with said chamber, the vacuum in said chamber being sufficient only during deceleration with the throttle closed to actuate the diaphragm and valve to establish communication between said passage and conduit.

2. In a carburetor having a mixture passage adapted to supply a mixture of fuel and air to the engine, a throttle valve for controlling the quantity of mixture supplied to the engine, means for supplying fuel and air to said mixture passage including a fuel conduit for supplying fuel for idling to the mixture passage at a point posterior to the throttle valve, and a fuel supply reservoir from which said conduit receives fuel; means for preventing How of fuel from said fuel conduit into the mixture passage during deceleration effected by a closing movement of the throttle, said last-named means comprising a chamber having a wall with an opening therein and a second wall formed by a flexible diaphragm, a suction passage communicating with said opening and extending to the fuel supply reservoir above the fuel therein, a vent passage connecting with said suction passage and effective to admitair thereto, a valve controlling said opening and connected to said diaphragm, spring means normally biasing said diaphragm to a position in which said valve blocks communication between said passage and chamber, a single suction conduit extending from said mixture passage posterior to said throttle and in communication at all,

times with said chamber, said vent passage being efiective to communicate sufficient suction to said chamber to open said valve only during deceleration when the throttle is moved toward closed position, and means for controlling the effective area of the suction conduit and vent passage so as to control the degree of suction communicated to the fuel supply chamber.

'3. Ina carburetor having a mixture passage adapted to supply a mixture of fuel and air to the engine, a throttle valve for controlling the quantity of mixture supplied to the engine, means for supplying fuel and air to said mixture passage including a fuel conduit for supplying fuel for idling to the mixture passage at a point posterior to the throttle valve, a fuel supply reservoir from which said conduit receives fuel, and a casing adapted to enclose said reservoir; means 'for preventing flow of fuel from said fuel conduit into the mixture passage during deceleration effected by a closing movement of the throttle, said last-named means comprising a chamber formed in said casing, said chamber having a Wall with an opening therein and a second wall formed by a flexible diaphragm, said diaphragm forming a part of said reservoir and said casing, a suction passage communicating with said opening and extending to the fuel supply reservoir above the fuel therein, a valve controlling said opening and connected to said diaphragm, a spring means mounted intermediate said casing-and said diaphragm and normally biasing said valve to a position blocking communication between said passage and chamber, a single suction conduit at all times connecting said chamber with the mixture passage posterior to the throttle and effective to communicate sufficient suction to said chamher to move the diaphragm and open the valve when the suction in the mixture passage exceeds a predetermined value, said diaphragm being movable to increase the pressure on the fuel in the fuel chamber when the suction in said chamber falls below such predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS 1,948,135 Sands Feb. 20, 1934 2,547,873 Kittler Apr. 3, 1951 2,675,217 Slason Apr. 13, 1954 2,701,709 Brunner Feb. 8, 1955 FOREIGN PATENTS 191,140 Great Britain Jan. 4, 1923 973,711 France Sept. 20, 1950

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