US2982526A

US2982526A - Arrangement for varying air-fuel ratio

Info

Publication number: US2982526A
Application number: US783925A
Authority: US
Inventors: William D Preston
Original assignee: Sun Oil Co
Current assignee: Sunoco Inc
Priority date: 1958-12-30
Filing date: 1958-12-30
Publication date: 1961-05-02
Anticipated expiration: 1978-05-02

Description

May 2, 1961 w. D. PRESTON ARRANGEMENT FOR VARYING AIR-FUEL RATIO 2 Sheets-Sheet 1 Filed Dec. 30, 1958 I2 i Compressed Fig.

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May 2, 1961 w. D. PRESTON ARRANGEMENT FOR VARYING AIR-FUEL RATIO 2 Sheets-Sheet 2 Filed Dec. 50, 1958 Air- Fuel Ratio Fig. 5

Air-Fuel Ratio :8 .5 in: on 2 Eo=8m 3E uuj uuom |NVENTOR WILLIAM D. PRESTON a D. $/M

ATTORNEY United States Patent 6 ARRANGENIENT FOR VARYING AIR-FUEL RATIO William D. Preston, Swarthmore, Pa., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Filed Dec. 30, 1958, Ser. No. 783,925

4 Claims. (Cl. 261-72) This invention relates to internal combustion engines, and more particularly to a means for varying the ratio of air to fuel in the mixture fed to the cylinders of such engines.

It is rather desirable to be able to adjust or vary, from time to time, the air-fuel ratio in an internal combustion engine, this air-fuel ratio being known in common parlance as the richness or leanness of the mixture. For example, at full throttle, the maximum power output of the engine may be obtained at one particular value of air-fuel ratio, while at part throttle the maximum fuel economy (in miles per gallon) may be obtained at another, different value of air-fuel ratio; generally, the maximum power output will call for an air-fuel ratio considerably less (that is, a richer mixture) than that corresponding to the point of maximum fuel economy. It would be convenient if the engine could be adjusted, at diiferent times and as required or desired, for maximum power output or for maximum fuel economy. Again, variations or adjustments of the air-fuel ratio might become necessary, in order to optimize the operation, when the engine is operated at different altitudes, due to the variation in density of the air with altitude. Thus, the

, air-fuel ratio corresponding to say the point of maximum fuel economy would be different at sea level than at an elevation of 10,000 feet. There would be a similar difference (for dilferent altitudes or elevations) in air-fuel ratio, for maximum power output.

An object of this invention is to provide a novel arrangement for controlling and optimizing the performance of an internal combustion engine.

Another object is to provide a novel arrangement for varying the air-fuel ratio of the mixture fed to an internal combustion engine.

A further object is to perform the foregoing objects in.

a simple and eificient manner, necessitating only a minimum of modifications to a conventional internal combustion engine.

The objects of this invention are accomplished, briefly, in the following manner: the carburetor of an internal combustion engine is modified by providing a'conduit leading to the inside or interior of the float chamber thereof. By applying selectively subatmospheric, superatmospheric, or atmospheric pressure to this conduit, and hence to the interior of the float chamber, the air-fuel ratio of the mixture fed to the engine from the carburetor may be adjusted or varied. The subatmospheric and super-atmospheric pressures may be obtained, respectively, from a source of vacuum and from a source of positive pressure. The application of a subatmospheric pressure or vacuum (negative pressure) to the float chamber results in a mixture that is leaner (higher air-fuel ratio) than that resulting from the application of atmospheric pressure, while the application of a super-atmospheric pressure or positive pressure to the float chamber results in a mixture that is richer (lower air-fuel ratio) than that resulting from the application of atmospheric pressure.

A detailed description of the invention follows, taken in conjunction with the accompanying drawings, wherein:

Figure l is a diagrammatic illustration of an air-fuel ratio control system according to this invention; and

Figures 2-5 are various curves useful in explaining the operation of the invention.

Referring now to Figure 1, the float chamber portion of a carburetor for an internal combustion engine is illustrated schematically at 1. The carburetor itself operates in a conventional manner to feed a mixture of air and fuel (such as gasoline) to an internal combustion engine (not shown). The float chamber *1 includes a fuel inlet pipe 2, through which liquid fuel such as gasoline is pumped by means of a conventional mechanical fuel pump (not shown), and an outlet orifice indicated at 3, by way of which the fuel flows from the float chamber 1 to the metering jets of the carburetor. float chamber 1 controls or governs the level of the gasoline 5 in chamber 1 in such a way that the liquid level in this chamber is at all times maintained at a predetermined height.

In order to apply the arrangement of this invention in a practical manner to an internal combustion engine employing a carburetor, both of the vents which in a conventional carburetor transmit the air pressure from the downstream side of the air cleaner to the fuel in the float chamber 1 are plugged. Also, a hole is drilled through the air horn assembly of the carburetor into the float chamber 1, this hole being fitted with suitable tubing to provide a conduit 6 which thus leads to the inside or interior of the float chamber. The conduit 6 opens into the space above the fuel 5 in float chamber 1, that is, into the space normally unoccupied by fuel 5. The pressure applied to conduit 6 will therefore be effective on the fuel (gasoline) 5 in float chamber 1.

For experimental purposes only, and in order to test the arrangement of this invention in a modern automobile, a four-barrel carburetor was modified in the manner now to be described. Both of the vents in the primary system, which normally transmit the air pressure from the downstream side of the air cleaner to the fuel in the primary float chamber, were plugged. The passage in the primary float chamber, which links the primary and secondary float chambers together, was plugged; this passage is slightly above the normal fuel level and is ordinarily used to relieve excess fuel from either chamber,

if it becomes temporarily flooded. The fuel needle seat the air horn assembly of the carburetor into the primary float chamber, and this hole was fitted with one-eighth- 1 inch I.D. tubing, thus providing a conduit corresponding to that denoted by 6 in Figure l. The modifications described in this paragraph, in elfect, change the carburetor from a four-barrel one to a two-barrel one, and bring the air-fuel ratio of the mixture metered by the carburetor; completely under the control of any pressure brought to bear on the fuel (such as 5) in the primary float chamber (such as 1) by means of the conduit (such as .6).

An arrangement is provided for applying an adjustable pressure to conduit 6, and thereby also to the inside of carburetor float chamber 1, the pressure applied to such conduit thus being brought to bear on the fuel 5 in float chamber 1. The arrangement now to be described permits the selective application of sub-atmospheric (negative pressure or vacuum), atmospheric, or super-atmospheric (positive pressure) pressure to conduit 6, audio;-

Patented May 2, 1961 thermore permits adjustment of the value of the subatmospheric or super-atmospheric pressure so applied.

A branch conduit 7 is coupled to a suitable source of vacuum or negative pressure (that is, subatmospheric pressure), this branch conduit being coupled by way of a valve 8 to the main conduit 6. Valve 8 is arranged for manual operation, to couple at will the vacuum source to the conduit 6, and also to adjust the value of the vacuum or negative (subatmospheric) pressure applied to conduit 6. The vacuum may be conveniently obtained from the vacuum side of the mechanical fuel pump in the automobile, as indicated in Figure 1. If it is not convenient, or if for some reason the obtaining of the required negative pressure from the fuel pump is disadvantageous, a small, auxiliary vacuum pump may be utilized instead, taking its running power from the internal cornbustion engine.

A standard mercury manometer 9 is provided (one end of the U-tube being coupled to conduit 6 and the other end being open to the atmosphere), to measure the pressure applied to conduit 6 at any particular time. As previously stated, such pressure may be either negative, or zero, or positive, with respect to atmospheric pressure.

A branch conduit 10 is coupled to the main conduit 6, and is also coupled to the out side of a pressure regulator 11. The in side of pressure regulator 11 is coupled through a valve 12 to a small bottle 13 of compressed air. Bottle 13 comprises a source of positive or super-atmospheric pressure. By means of the manuallyoperated valve 12 and the manually-operated pressure regulator 11, the positive or super-atmospheric pressure source may be coupled at will to the conduit 6, and also, the value of the super-atmospheric or positive pressure so coupled or applied to conduit 6 may be adjusted. If desired, a small auxiliary pressure pump driven by the internal combustion engine may be utilized instead of the compressed air bottle 13, as a source of positive or superatmospheric pressure.

By suitably adjusting the

valves

8 and 12 and the pressure regulator 11, while observing manometer 9, it is possible to apply zero gauge pressure (that is, atmospheric pressure) to conduit 6, and thus also to the interior of float chamber 1. Likewise, it may be seen that it is possible to selectively apply various desired values of negative (subatmospheric or vacuum) pressure (obtained by way of branch 7 from the source of vacuum), or of positive (super-atmospheric) pressure (obtained from positive pressure source 13, by way of branch 10), to the conduit 6 and thereby also to carburetor float chamber 1. Obviously, the pressure being applied to conduit 6 at any particular time may be read (in inches of mercury, gauge) by means of manometer 9. It may be possible to simplify the arrangement illustrated in Figure 1, by designing a single valve construction which can be employed to supply either negative, zero, or positive pressure to conduit 6, at will, and to adjust the value of the positive or negative pressure so supplied.

Figure 2 is a set of curves obtained experimentally, using the apparatus of this invention. These curves were obtained with the internal combustion engine on a dynamometer test stand, and represent full-throttle and roadload conditions as legended, the speed being held at 2150 r.p.m. (O rn.p.h.). A so-called Orsat Analyzer, which functions to analyze the composition of the exhaust gas, was used to determine the air-fuel ratios delivered by the (experimental) carburetor, modified as described previously. From the values of the volume composition of the exhaust gas constituents (oxygen, carbon dioxide, carbon monoxide), the air-fuel ratio can be determined.

From Figure 2, wherein the values along the horizontal axis represent pressure in inches of mercury with respect to zero or atmospheric pressure, it may be noted that the air-fuel ratio goes down or decreases (that is, the mixture becomes richer) as the pressure applied to the conduit 6 and float chamber 1 increases positively from zero or atmospheric pressure. Conversely, the air-fuel ratio goes up or increases (giving a leaner mixture) as the pressure applied to float chamber 1 increases negatively from zero. The operation of this invention to vary the air-fuel ratio out of the carburetor does not depend upon the validity or invalidity of any particular theory. However, one explanation of the above-described action is as follows. The positive pressure, transmitted to the fuel 5 in float chamber 1, may actually force more fuel out of the float chamber into the main air stream, thus making the mixture richer. The negative pressure or vacuum, applied-to the fuel in the float chamber, may actually slow down the flow of fuel into the main air stream, making the mixture leaner.

It is desired to be pointed out that the conduit 6 is used only for pressure purposes, and no volume or flow of air is required. Therefore, only a -low-capacity vacuum source (or a small auxiliary vacuum pump capacity) and a small bottle of compressed air (or a lowcapacity pressure pump) are necessary.

Figure 3 is a curve illustrating the effect of air-fuel ratio on an internal combustion engine, under full throttle conditions. This curve indicates that the best air-fuel ratio, as far as brake horsepower is concerned, was 12:1 for a particular engine. The effect of air-fuel ratio on the brake horsepower may clearly be seen, from this figure. For this curve, engine power output was measured directly as brake torque on a laboratory dynamometer test stand, the brake horsepower being computed by conventional methods. The air-fuel ratio was obtained from an analysis of the exhaust gas, as in Figure 2.

Once the variable air-fuel ratio carburetor had been calibrated and the curves of Figmre 2 obtained, the internal combustion engine was installed in an automobile and road tests were made. Figure 4 is a curve illustrating the effect of air-fuel ratio on the time required to climb a hill, under certain conditions. To make this plot, the air-fuel ratio is determined by noting (by means of manometer 9) the pressure applied to float chamber 1, and then reading off the air-fuel ratio from the appropriate curve in Figure 2. In Figure 4, the time on the vertical axis is the time required to climb 0.387 mile of 6% grade at full throttle in fourth gear, from a 30 mph. start. By this method, the optimum air-fuel ratio was found to be 12.321.

Figure 5 is a curve illustrating the efiect of air-fuel ratio on the road-load fuel economy at 50 mph, the data being obtained from actual road tests, with the air-fuel ratios being obtained as in Figure 4. The roadload fuel economy of the car can be improved somewhat by leaner mixtures, which of course means a higher airfuel ratio. Such higher air-fuel ratios can be obtained (see Figure 2) by applying a negative pressure (vacuum) to the carburetor float chamber. The best reasonable airfuel ratio was found to be about 16:1, with about 17.5 m.p.g. available. This differs from the air-fuel ratio and the result in mpg. of the carburetor, as received from the manufacturer. As shown in Figure 5, richer mixtures than 14:1 will result in a considerable waste of fuel.

Summarizing, the curves in Figures 3, 4, and 5 clearly show the desirability of having an easily adjustable airfuel ratio. A convenient arrangement for providing such an adjustable air-fuel ratio has been disclosed, in accordance with this invention.

The invention claimed is:

1. In an internal combustion engine, a carburetor for feeding a mixture of air and fuel to said engine, said carburetor including a float chamber; a conduit leading to the inside of said chamber, and manually-operable means for selectively applying a subatrnospheric, an atmospheric, or a super-atmospheric pressure to said conduit, thereby to manually vary the effective pressure inside said chamber and thus to manually vary also the air-fuel ratio of the mixture fed to said engine, at the will of the operator.

2., The combination set forth in claim 1, wherein said means includes means for manually adjusting the value of the subatmospheric or super-atmospheric pressure ap plied to said conduit, thereby to enable manual variation of the air-fuel ratio of the mixture While the engine-is running.

3. In an internal combustion engine, a carburetor for feeding a mixture of air and fuel to said engine, said carburetor including a float chamber; a conduit leading to the inside of said chamber, a source of subatmospheric pressure, a source of super-atmospheric pressure, and manually-operable means for coupling at will either'said first-named or said second-named source, or neither, to said conduit, thereby to manually vary the effective pressure inside said chamber and thus to manually vary also 6, the air-fuel ratio of the mixture fed to said engine, at the will of the operator.

4. The combination set forth in claim 3, wherein said means includes means for manually adjusting the value of the subatmospheric or super-atmospheric pressure supplied from the respective source to said conduit, thereby to enable manual variation of the air-fuel ratio of the mixture while the engine is running.

References Cited in the file of this patent UNITED STATES PATENTS Sterner June 17, 1958