US1872490A - Carburetor - Google Patents

Description

Aug. 16, 1932. v F. c. MocK ET AL 1,872,490

CARBURETOR Filed March 24. 1930 Patented Aug. 16, 1932 UNITED STATES FRANK C. MOCK, CHARLES J'. GUSTAFSON, AND MILTON E. CHANDLER, OF CHICAGO,'

PATENT OFFICE ILLINOIS, ASSIGNORS TO BENDIX STROMBERG G ARBURETORI COMPANY, 0F SOUTH BEND, INDIANA, A CORPORATION 0F ILLINOIS CARBURETOB Application mei March 24, 1930. serial No.'43s,278.

The present invention relates to carburetors, particularly for airplane engines, and is a continuation in art of our copendin application, Serial o. 556,160, filed Ap 24, 1922.

In airplane carburetion practice, it is desirable to use as large a size of main carbureting passage as possible in order to .secure maximum volumetric efficiency and to draw in the greatest possible volume of air at high altitudes. The chief limitation on the size of main carbureting passage in the plain tube type of carburetor is the weak suction on the main fuel nozzle at low speeds and the lean spot in the transition from idle jet operation to main jet operation.

Heretofore, with the plain tube type of carburetor, any air inlet of Venturi tube size that was adequate for maximum power, caused too weak a suction for idling and low speed operation. Consequently, such carburetors were always equipped with separate idling jet systems and employed relatively small Venturi tubes, with the effect, as an apr proximate example, that the main nozzle in the Venturi tube would meter and deliver fuel down to about 600 R. l?. M. (if the maximum propeller speed was aboutv 1800 R. P. M.), or down to a throttle opening of 6 to 8. The idling speed was, however, only about 300 R. P. M. with a throttle opening 2 or 3. It was consequently necessary to control the mixture range between 300 R. P. M. and 600 R. P. M. or between 2 and 6 of throttle opening by passage of the throttle edge over the idling nozzle which was usually a circular hole.

With the general development of airplane engines, it was found that larger Venturi tubes were required for maximum power, with the result that the main nozzle of the Venturi tube would perhaps meter down to only 900 R. P. M., or 12 of throttle opening. A larger range of mixture delivery was thus demanded from the idling system, as it must deliver fuel feed from 300 R. P. M. to 900 R. P. M. or from 3 to 12 of throttle openin Afte considerable experimentation we found that this could not be done satisfactorily with idle nozzles having circular holes, due to a number of reasons. First, it was very difficult to determine exactly the right size and location of the hole. This could, ofV

course, be done, empirically for any individual carburetor, but due to manufacturing tolerances, it was impossible for quantity production methods. Second, it was necessary that the areaof the idle nozzle subject to manifold suction should be carefully proportioned to the opening and closing movements of the throttle with a circular opening in the idle nozzle, the areas successively uncovered and exposed to manifold suction by the opening movement of the throttle progressively increased, not as a linear function of throttle movement, but at a higher and varying rate. This made it impossible to proportion the change in idle nozzle area exposed to manifold suction to throttle movement and consequently the idle mixture could not be controlled throughout the idle range.

One ofthe objects of this invention is to provide a carburetor in which the idling range is increased to a speed where the main fuel j etcomes into positive and steady operation.

Another object of this invention is to provide a carburetor wherein thentransition from idle to main j et operation is perfectly blended so that no lean spots in the mixture occur therein.

A further object of this invention is t6 provide a carburetor in which the idle fuel nozzle is so related to the main throttle that the area of the former subject to manifold suctiony is synchronized with the opening and closing movements of the latter.

A still further object of this invention is toA In its present form, which is merely illustrative, our invention is embodied in the conventional type of idling device which is generally employed in plain tube carburetors and which is usually arranged to discharcfe in the immediate vicinity of the throttle. lt is -well known that in such carburetors there is a wide variation of suction on the main nozzle. ln the performance of an airplane carburetor, this eHect is extremely pronounced. Thus, from approximately onehalf speed down there is generally not enough suction on the main jet to accurately meter the mixture. Consequently, during this range the source of feed must be from the idling nozzle above, or at the upper edge of, the throttle. 4

From this it will be noted that during a considerable part of the running period, and over a considerable portion of the range of speeds, the idling nozzle is the primary source of fuel supply and should, therefore, meter` the proportions with substantially the same degree of accuracy as that required of the ordinary main nozzle. The control of speed during this portion of the range is obtained with a comparatively small movement of the throttle, which requires that the idling nozzle be located with certain exactness relative to 'the throttle in order to accurately control the range of suction at this nozzle 'during this comparatively small movement of the throttle.

Added to this is the further diliiculty that the suction above the throttle diminishes with the opening of the throttle owing to the greater volume of air admitted. This is the direct converse of what is desired, becausev during this time a higher suction is desirable at the nozzle for drawing the increased amount of fuel required for the greater volume of air. During the opening of the throttle there should be a gradual transition or blending from the operation of one nozzle to the other, otherwise lean charges may be admitted owing to the idling nozzle diminishing or discontinuing its feed before the main nozzle takes up operation. Hence, the idling nozzle should be capable of feeding an increased volume of fuel during a certain range of the throttle movement, despite the lowerin of the suction above the throttle.

. 's, or practically any other variation of idling nozzle feed, can be secured by utilizing differentially the relatively high suction existing above the throttle and the relatively low suction existing below it. For example, only a small portion of the nozzle orifice may 'be subjected to the suction above the throttle during very slow running, and with the opening movement of the throttle a greater portion of the nozzle orifice may be subjected to the' high suction above the throttle. The ccynguration of the nozzle orifice, how- Iover, should be such that for a given engine jected to suction above the throttle and decreases the proportion exposed to suction below the throttle. ln order, therefore, to obtain proper uniformity and control of the idling mixture, it is essential that the change in area of the idle nozzle exposed to suction above the throttle be carefully proportioned to the opening and closing movement of the throttle.

It will also be apparent that to obtain this accurate control of the idling nozzle feed a very accurate location of the nozzle relative to the throttle is essential. In the case of the ordinary butterfly throttle, when the throttle is in a closed or restricted position its edge contacts or moves toward the Wall of the carburetor barrel on an angle closely approaching a tangent. Consequently, any variation of even minute degree in the bore of the carburetor will result in the throttle edge, qcontacting .with the carburetor wall at a higher or lower point along the length of the wall. To take care of this condition it is necessary that relative adjustment be afforded between the throttle and idling nozzle if accuracy yof mixture proportion is to be obtained.

In'the present construction, and as broadly d1 sclosed in our copending application mentioned above, we have provided an arrangement of idling jet in which the outlet adjacent the throttle is in the form of a rectangular slot so that the area successively uncovered by the throttle and exposed to manifold suction is a function of the movement of the throttle throughout the small angle of movement in the idling range. We have also provided a form of idling jet which can be moved relative to the carburetor casting, preferably, but not necessarily, by rotation of the nozzle so as to selectively dispose the nozzle openin in different positions relative to the edge of the throttle. Thus, the .nozzle opening can be moved to withdraw-1t, or a portion thereof, from the influence of the suction above the throttle, or t o increase the area of the nozzle orifice subjected to this higher suction, or to confine to a greater or less extent the nozzle orifice to the di'erentialsuction existing at thev of the throttle. This conception of an i ling nozzle varying with the movement of the throttle and adjustable with respect to the influence of suction thereon, has the further possibility of permitting the nozzle opening to be shifted longitudinally of the .throttle valve, as we have -stated above, for

the purposeof increasing the area of the nozzle opening subjected to the suction of one side of the throttle and decreasing the area of nozzle opening subjected to the suction of the other side of the throttle.

While this is the preferred manner of accomplishing the objects set out above, it will be obvious that the same can be accomplished by other arrangements of the nozzle. In the drawing illustrating the present embodiment:

Figure 1 is a fragmentary sectional view of the carburetor embodying our invention, illustrating the relation ot: the idle nozzle plug and throttle as disclosed in our copending application Serial No. 556,160, iled April 24, 1922;

Figure 2 is a fragmentary sectional view on an enlarged scale of a modied construction shown in our same co-pending application Y Figure 3 is a side elevational view of our preferred form of nozzle plug;

Figure 4 is an elevational view on a still larger scale, of theface of the nozzle plug as viewed from the interior of the carburetor` barrel, the throttle being shown in closed position to indicate its relation to the slot in the plug; and

Figure 5 is a similar view to Figure 4, except that the throttle is shown in slightly open position so that the area of the slot above the throttle is greater than that below.

The particular form of carburetor illustrated in Figure 1 is selected forillustrating al typical embodiment of this invention simply because it forms the subject-matter of our above-mentioned copending application; it being obvious that the present invention is capable of embodiment in practically any type of carburetor. A specific description of this carburetor being available in said copending application, suiice it to say here that it comprises a body portion or casting 1, having an air intake 2 and a mixture outlet 3. A throttle 4 controls the mixture outlet 3, and a main nozzle 5 discharges into the innermost of two concentric Venturi tubes 6 and 7.

The idling nozzle, which is designated 8 in its entirety, discharges into the mixing chamber 9 in close proximity to the edge of the throttle 4. This idling nozzle draws fuel through a tube 10, which is secured at its lower end in a plug 11, the tube having a lateral hole 12 which also extends through the plug for admitting fuel to the tube. Fuel is supplied to botlrthe main nozzle and the idling nozzle from a float chamber 13 which discharges through a passageway 14 into the center of the main nozzle 5 and into an accelerating well 15 surrounding said nozzle. The idling nozzle 8 draws from this accelerating well through a passage 16.

ReferringV to the particular construction of the idling nozzle, it will be noted that the nozzle is arranged in a relatively large bore which extends through the side wall of `the caslting l adjacent the point where the lower lip ofthe throttle 4 comes into approximate Contact with the side wall of the chamber 9 when the throttle is in its closed position. This bore 17 has an enlarged counterbore 18 which is threaded at its outer end. Fitting in this bore .is a nozzle plug 19 having a reduced portion extending into the bore 17 and an enlarged portion disposed in the counterbore 18; This plug is backed up and held in any position in which it may be adjusted by a threaded closure plug 20 which screws into the threads in the end of the counterbore 18 and abuts the rear end of the nozzle plug 19. The nozzle plug 19 has a transverse bore 21 which communicates by way of the slot 22 with the mixing chamber 9 the slot 22 lying in proximity to the lip of the throttle valve 4 when the same is in closed or restricted position.

The exact size and shape of slot' 22 we have found to be extremely important'and it may be saidto constitute the heart of this invention. The slot is rectangular in shape and is relatively narrow compared rto its length. The shape of the slot and its relation to the lip of the throttle is clearly shown in Figures 3 and 4. Formerly when round holes were used as the orifices for idling nozzles, it was found impossible to properly control the mixture proportions throughout the idli'ng'range. This was due to the fact that the opening movement of the throttle sweeps the edge of its lip across the orice of the idling nozzle almost rectilinearly, as a tangent to a circle practically coincides with the are oit' the circle for a few degrees from the point of tangency, and if the orice of the idling nozzle is circular, the area successively uncovered by the edge of the throttle, as the throttle is opened, more than proportionately increases in size, since the segmental strips of a circle increase in width until the diameter of the circle is reached, when they decrease in width. This complex variation in size of the idling orifice with the opening of the throttle made it impossible to establish a definite and constant relation between the area of the idling orifice exposed to manifold suction and the movement of the throttle. Consequently, it was impossible to properly control the mixture proportions during the idling range.

I now a long narrow rectangular slot,

ysuch as is herein ,disclosed, be used as the orifice of the idling nozzle, it at once makes possible the establishment of a definite and constant relation between the area of the,

posed can be accurately proportioned to the opening movement of the throttle.

The plug 19 has a bore 23 through which the fuel mixture for idling passes on its way to the engine manifold. The plug also has a lateral recess 24 lying immediately above the tube 10, which tube may have a plug or restriction 25 in its upper end if desired. *A channel or annular space 26 is formed about the inner end of the plug 19, this channel forming an air space for air which is admitted by way of the port 27, valve port 28, and radial port 29 in the plug 19. A needle valve 30 is threaded into the hub of the plug 20 for controlling the amount of air which enters by way of the port 27, which air with the liquid fuel entering from the tube 10 forms a mixture for supplying the engine during idling.

When the throttle 4. is in its closed position with the lower lip thereof substantially intersecting the slot 22, as shown in Figure 4, it will be apparent that a certain rate of fuel feed will occur through the slot 22 depending upon the suction above the throttle,

Athe suction below the throttle, and the velocity of air around the throttle lip through the slot 22. It will be observed that by turning the plug 19, a greater or less area of the slot 22 is brought into alignment with the .lower lip of the throttle.` This brings a4 Igreater or lesser proportion of the slot area under the'iniluence of the suction existing around the edge of the throttle. Thus, by changing the angle of the plug 19 and its slot 22, different rates of fuel feed can be .obtained The channel or annular space 26 maintainscommunication with the upper end of the tube 10, so that fuel flow will be maintained even though the plug 19 is adjusted through a wide angle. The separate mounting of theplug 19 in the casting obviously .permits of this adjustment with little ditliculty, and after the plug has been properly adjusted it is 4secured firmly in position by screwing the closure plug 20 hard against it.

This practice of making the idling nozzle in a sepa-rate ,plug also possesses the advantage that the plugs may be easily substituted for plugs having larger or smaller or differently shaped orifices. Thus, while we have found that a rectangular orifice or slot gives bestaresults as a general rule, it by no means follows that in all cases the slot must be exactly rectangular in shape. It may, obviously take any shape desired provided it makes possible the establishment of a definite and substantiallv constant relation between the area of orice exposed to manifold suction and the opening movement. of the throttle.

In Figures 2 and 3 we have illustrated a modified construction. Here the adjustable and removable nozzle plug 31 is of relatively shallow depth and the fuellpassageway 32 enters the plug bore behind the Vplug 30. The fuel passes through a number of holes 33 into the interior of the outer closure plug 34, from whence it has communication to the slot 35 in the face of the nozzle plug 31 through an axial passageway 36 and transverse bore 37. The relative size, shape and relationship of slot 35, transverse bore 37 and axial passageway 36in the plug 3l are the same as the corresponding elements in the plug 19 illustrated in Figure 1. A needle valve 38 similarly controls the passageway 36. ln the modification illustrated in Figure 2, however, no air is admitted through the nozzle plug, as in Figure 1, but such air is admitted through a relatively7 small bleed hole 39 leading from the fuel passageway 32 to the outside of the carburetor.

The modification illustrated is only indicative of the large number of ways of carrying this invention into effect. They are all different manifestations of the one generic invention. The appended claims have been drawn with a view to covering these various methods of effecting the one invention, and such others as would naturally occur to one skilled in the art.

We claim:

1. Tn a carburetor, a cylindrical wall, said wall having a radial aperture therethrough, a valve seat member adapted to plug said aperture, said valve seat member comprising a cylindrical plug having a diametral rectangular slot at its inner end, said slot communicating with the interior of the carburetor, means for holding the valve seat plug in said aperture, and a needle valve co-operating with said valve seat member for controlling the iow of idling mixture in said carburetor.

2. In a carburetor, a mixing chamber having a throttle therein, the wall of said chamber having an aperture extending therethrough above and below said throttle when said throttle is' in closed position, an idling nozzle plug seated in said aperture, said plug having a fuel discharging slot extending diametrally thereof and a co-operating closure plug in back of said nozzle plug.

3. In a carburetor, an idling nozzle comprisino a substantially cylindrical member rotatable about its major axis and having an axial fuel passageway terminating in a diametral slot.

4. In a carburetor, a throttle valve, an idling nozzle having a fuel passageway terminating in a diametral slot, and means to adjust said nozzle and slot with respect to said throttlevalve for varying the mixture delivered by said idling nozzle.

5. In a carburetor, a mixing chamber having an outlet, a throttle valve controlling saidI outlet, an idling mixture nozzle having an orifice communicating with said chamber, means for varying the area of said orifice exposed to suction above said throttle in linear proportion tothe opening and closing movement of said throttle', and means for adjusting said nozzle with respect to said throttle for varying the composition of the mixture delivered by said nozzle.

6. In a. carburetor, a mixing chamber, a throttle valve in said chamber, and an idling mixture nozzle having an elongated orifice extending diametrically of the nozzle and m communicating with said chamber, said nozzle being rotatable to vary the relation of the orifice to the throttle.

7. In a carburetor, a mixing chamber, a throttle valve in said chamber, and a fuel 35 nozzle having an elongated orifice connecting With said chamber and extending diametrically of the nozzle above and below the edge of the throttle When the throttle is closed, said nozzle being rotatable to vary the rela- 2@ tion of the oriee to the throttle, and means associated with the nozzle for admitting air to be mixed with the fuel passing through the nozzle. V

In testimony whereof, We have hereunto signed our names.

FRANK C. MOCK. CHARLES J. GUSTAFSON. MILTON E. CHANDLER.

Images