US1796902A

US1796902A - Charge-forming device

Info

Publication number: US1796902A
Application number: US307748A
Authority: US
Inventors: Wilford H Teeter
Original assignee: Delco Products Corp
Current assignee: Delco Products Corp
Priority date: 1928-09-22
Filing date: 1928-09-22
Publication date: 1931-03-17
Anticipated expiration: 1948-03-17

Description

March 17, 1931. wA H, TEETER 1,796,902

CHARGE FORMING DEVICE Filed sept. 22, 192e Patented Mar. 17, 1931 UNITED STATES PATENT OFFICE WILFORD H. TEETER, OF DAYTON, OHIO, ASSIGNOR, BY MESNE ASSIGNMENTS, TO DLCO PRODUCTS CORPORATION, OF DAYTON, OHIO, .A CORPORATION OF DELAWARE CHARGE-mamme mvIcE Application led September 22, 1928. Serial No. 307,748.

This invention relates to charge forming devices for internal combustion engines and more particularly to devices of this type which include means for delivering a primary mixture of fuel and air to a plurality of secondary mixing chambers located near the engine intake ports, `and in which the primary mixture is mixed with additional air under certain operating conditions.

Devices of this character are shown in several earlier applications, for example, that of Fred E. Aseltine et al., Serial o. 288,683, filed June 10, 1928.

In the devices disclosed in certain of these earlier applications there has been some difculty observed in the formation of a mixture of the desired proportions throughout the operating range because ofthe presence of a velocity suctionat the fuel nozzles. It is, therefore, the object of the present invention, to provide a charge forming device, preferably one of the type above referred to, in .which the fuel is caused to ow into the mixing chamber by the effect of the static suction within the carburetor and in which the effect of a velocity head on the fuel flow is substantially eliminated.

Briefly, this object is accomplished by connecting the primary mixture passages, in which the fuel jets terminate, with the main air chamber so that approximately all the air passing through said primary mixture passage flows thereto from the said main air chamber. Anterior to the jets the primary mixture passages are enlarged and all terminate in a single chamber which is directly connected to the main air chamber and which is of greater size than the passage connecting said chamber and they main air chamber whereby the suction maintained in the said chamber is always substantially the suction of the main air chamber.

The fuel jets project upwardly into the horizontal mixture passages and each terminates within'a rectangular box having one open end anterior to the jet and communicating directly with the air chamber in which the primary mixture passages terminate. The other end of the box is closed except for a small orifice so that the velocity of air passing through the box adjacent the noz'- zle is always low and the suction therein is always substantially that of the main air chamber.

Further objects and 4'advantages of the present invention will be apparent from the following description, reference being had tothe accompanying drawings, wherein a preferred form of embodiment of the present invention is clearly shown.

In the drawings:

Fig. 1 is a vertical section through the carburetor unit and one outlet branch of the manifold.

Fig. 2 is a section on line 2-2jof Fig. 1.

Fig. 3 is a detail plan and Fig. 4 is a detail section of the shield or box surrounding the fuel jet.

The device disclosed herein comprises a main air manifold indicated in its entirety by the reference numeral 10. This manifold is provided with three outlet branches, only the middle branch 12 being shown herein. Each of these branches is adapted to be connected with one of the intake ports 14 of a multicylinder engine. Each of these ports serves two adjacent cylinders in the manner well known and fully illustrated in the copending application previously referred to.

The manifold is provided with an attaching flange 16 to which the main carburetor unit is secured. The carburetor comprises a main housing in the form` of a single casting 18 which is provided with an attaching flange 20, adapted to be secured by machine screws 22 to the flange 16 of the manifold. An air inlet horn 24, through which the flow of air is regulated in a manner later described, is secured in position over an air inlet opening in the top wall of said housing 18 and a casting 26, provided with certain dashpot chambers and fuel passages later described, is secured to the bottom wall of the main housing by any suitable means, for example, as disclosed in the copending case above referred to. AV sheet metal fuel bowl 28 is held tight against a shoulder 30 formed on the housing 18, by means of a screw 32, screwed into a post 34 depending from the casting 26, a gasket 36 bemg provided to prevent leakage around said screw. The fuel is supplied to said fuel chamber from a. main fuel su ply by means of a fuel line and connection o the same form as shown in the copending application referred to, and the level of fuel within the bowl 28 is maintained substantially constant by means of a float 38 which operates in the usual manner.

Fuel is conducted from the fuel bowl to a plurality of primary fuel nozzles 40 located in the primary mixing chambers 42 formedA in the central part of the main housing 18. That portion of the said housing 18 in which the primary mixing chambers are located, for convenience may be termed the distributor block. The construction of said distributor block and cooperating elements will be more fully described later. To enable the fuel to iiow from the fuel bowl 28 to the primary nozzles 40 the casting 26 is provided with a vertical fuel channel 44 which communicates at its upper end with a horizontal fuel canal 46, connect-ing with each of the nozzles through orifices 48. At low speed fuel flows from the fuel bowl to the channel 44 through metering orifice 50. All of the fuel flowing to the fuel nozzles up to a certain predetermined engine speed, for example, that corresponding to a vehicularspeed of 20-25 miles per hour passes through said metering orifice 50. For higher speeds than said predetermined speed fuel is also admitted to the fuel channel 44 through an orilice 52, controlled by a fuel valve 54 which is operated by means fully disclosed in the copending application above referred to and which need not be illustrated herein. The fuel admitted through the orifice flows through a horizontal channel 56 which con` nects with the lower end of the channel 44.

The fuel is lifted from the fuel bowl through the nozzles 40 to the primary mixing chambers by the suction maintained therein. When the throttle is moved toward closed position to reduce the engine speed there is a sudden reduction in suction effective on the vertical column of fuel between the fuel bowl and the nozzle. This reduction in suction might permit this column of fuel to drop sufliciently to cause a temporary fuel starving of the engine unless some means were provided to prevent such action. To this end acheck valve 58 is seated in an enlarged chamber 60 at the junction of the channel 44 and fuel canal 46, and on reduction of suc- A tion in the primary mixing chambers, said valve seats on the bottom of the chamber 60, preventing downward flow through the channel 44.

The metering orifice 50 is drilled in the casting 26 and the drill hole on the opposite side of the `fuel channel 44 is closed by a screw 62.

Each p'imary fuel nozzle is provided with a main el outlet 64 infthe top o f the ,noz-

zle and a secondary fuel outlet comprising two holes 66 and 68 formed in the Vertical wall of the nozzle near the bottom of the primary mixing chamber as disclosed in Fig. 1. At higher engine speeds suiiicient suction is maintained in the primary mixing chambers to draw fuel through the main fuel outlet 64 as well as from the holes 66 and 68. During idling or other operation at very low speed however, there is insufficient suction to lift the fuel to the top of the nozzle, the fuel at such time standing in the nozzle at a point somewhere between the top of said nozzle and the orifices 66 and 68, owing from said orifices by the action of gravity. Eachfuel nozzle is provided with a restricted fuel metering orilice 70.

There are three primary mixture passages 42 formed in the distributor block, such passages being close together and parallel to each other as indicated in Fig. 2. Each of these mixture passages communicates with a conduit which conveys the primary mixture to secondary mixing chambers formed in each branch of the manifold where such manifold branches connect with the engine intake ports, such structure being fully described in the copending application above referred to. Qnly one of the said primary mixture conduits is disclosed herein. This conduit is indicated by the reference character 72 and is connected to the middle one of the primary mixture passages 42 and con- Veys the primary mixture to the secondary mixing chamber formed in the middle outlet branch 12 of the air manifold. The inlet ends of the primary mixture passages 42 where the nozzles 40 project into such pas sages which are of greater diameter than the outlet ends thereof and between the nozzle and outlet end of each passage its cross sectional area is reduced as indicated at 74, for the purpose of reducing the velocity of iow through the said mixture passage adjacent the primary nozzle.

Flow of primary mixture through the passages 42 is controlled by a single throttle valve 76 which extends across all of said passa es 42 and has grooves 78 formed therein whlch register with the passages 42. This throttle valve is operated by means fully disclosed in the copending application referred to and a groove 80 is provided in the external surface of said throttle which cooperates with the inner end of a screw 82 adjustable in the casting to prevent longitudinal movement of said throttle.

All of the air entering the carburetor, with the exception of a small quantity of air which is supplied to carry the fuel when the choke mechanism is operated, Hows through the air horn 24, the flow being controlled by a main air valve 84 normally held against a seat 86 by a spring 88. The ai;` iows past said valve intoagmain air chamber 90 formed in scribed connects said air chamber with the` main air manifold 10 while a hole 94 in the floor of said air chamber permits the air to lflow therefrom into an auxiliary air chamber 96 which communicates directly with the inlet end of each primary mixture passage 42. When the carburetor is choked to facilitate starting of the engine the air valve 84 isheld closed and to provide sutlicient air to carry the starting fuel from nozzles 40 to the engine when said valve is closed, an air inlet 98 is provided in the form of an elongated slot cut through a plate 100 detachably secured to the housing 18 as shown in Fig. 1. The air valve 84 is adjustably secured on a stem 102 slidably mounted in a guide sleeve 104 fixed in the main housing 18. Surrounding the guide sleeve is a slidable sleeve 106 provided with a flange-108 at its lower end which is adapted to be engaged by a lever, not shown herein, to lift the sleeve into engagement with the air valve for the purpose of holding saidvalve against its seat to choke the carburetor. This sleeve may also be lifted partially by the choke mechanism as fully described in the 'above copending application, to vary the compression of the spring 88 which normally holds the valve closed.

Whenever the engine speed increases the suction below the air valve 84 is increased and said valve is opened against the closing force of the spring 88, and would admit enough to lean the fuel mixture unless means were provided to retard the opening movement of said valve. By retarding the opening of the valve, flut-tering of said valve as well as leaning of the mixture will be prevented. To retard the opening movement of said valve the lower end of the valve stem 102 has secured thereto a piston 110 which slides in a cylinder 112 formed inthe casting 26. Fuel is admitted to the cylinder through the bottom thereof by means fully disclosed in the above mentioned prior application and the construction of said cylinder and piston form no part of the present invention. The cylinder and piston constitute a dashpot which will retard any downward motion of the valve 84.

The flow of air from the air chamber 90 through the passage 92 to the secondary mixing chamber is controlled by two valves, va manually operated throttle 114 and a suction operated valve 116. The throttle is fixed on a shaft 118, journalled in the walls of the housing 18 and is operated concurrently with the throttle 76 in a manner hereinafter described.- The valve 116 is fixed to a shaft 120 which is positioned off center with respect to the valve, a greater portion of the valve being below the shaft than above. The shaft 120 is journalled in the housing 18 and the valve116 is operated primarily by engine suction, its opening movement being retarded for reasons later set forth.

The mode of operation and the functions of the two throttle valves are substantially as. follows: At engine speeds up to approximately that speed which correspondsv to a vehicular speed of 20-25 miles per hour on a level only the throttle 76 is open'and the primary mixture is of properly combustible proportions, and sufficient in quantity to meet the requirements of the engine. At speeds above the specific speed mentioned the capacity of the primary mixture passages is such that the velocity of flow therethrough would increase very rapidly. For reasons set forth hereinafter the throttle operating mechanism is so constructed that the air throttle begins to open at approximately the vehicular speed above mentioned, admitting air to the secondary mixing chambers and preventing such increase in velocity of flow through the primary tubes. The throttle operating mechanism is fully shown in the above application.

According to the present invention means are provided to prevent the formation of a velocity head at the fuel nozzles, and to communicate the static suction, i. e. static depression, of the air chamber 90 to said nozzles so that said static suction becomes the dominant factor in effecting the flow of fuel from said nozzles. The advantageous results produced by this construction will be best understood by a consideration of the difficulties caused by the presence of a velocity head in prior devices of this type, for instance that disclosed in the copending application previously referred to.

In the device disclosed in said application the restrictions formed at 74 in the primary mixture passages maintain a suficiently low air velocity at points anterior thereto to prevent the formation of a velocity head at the nozzles during operation at idling or under load at very low speeds. During operation at all other speeds, however, the air velocity past the nozzles is so great as to build up a velocity head. Owing to the presence of this velocity head at the nozzles, the metering jets which determine the fuel flow are calibrated somewhat smaller than they should be to give a fuel mixture ratio of the desired proportions for medium speeds. Up to an engine speed of approximately 1000 R. P. M., which is equivalent to a vehicle speed of 20- 25 miles per hour, the velocity head increases slowly and produces a flow which is approximately correct `to give the desired mixture ratio.

At higher engine speeds the velocity head builds up so rapidly that the fuel mixture becomes entirely too rich unless means are provided toreduce the velocity effect on the jets. To do this the secondary throttle corresponding to the throttle 114 of this device is timed to begin opening at an engine speed of approximately 1000 R. P. M. Owing to the large diameter of this throttle and consequent rapid increase in volume of air flowmg past the throttle per degree of rotation, the velocity of air flowing past the jets is very rapidly lowered after the air throttle begins to open, the velocity head being practically elimlnated at a little more than 1500 R. P. M. Since the fuel flow is determined by the velocity head and the jets are calibrated to (give a proper flow of fuel as the velocity hea increases up to 1000 R. P. M., the reduction in velocity head at higher speeds causes so great a reduction in fuel flow that the mixture becomes too lean to be properly combustible. This necessitates an additional flow of.- fuel, which is provided by opening a needle valve similar to the valve 54 and permitting fuel to fiow through an auxiliary fuel passage. This valve is opened by means of a cam, the contour of which is designed in the prior device, to begin openingxthe fuel valve at approximately 1000 R. P. M. and to continue opening said valve to admit just enough additional fuel to compensate for the loss in suction on the fuel jets due to reduction i the velocity head effective thereon.

In order to secure a fuel mixture of the desired proportions the two throttles must be accurately synchronized not only with relation to each other, but also to the needle valve. The cam which lifts the needle must be correct in contour, must be accurately located with reference to its follower and the latter must be also of exactly the right size and located in the right position. Since it is attempted to correct the velocity head which is a variable and unstable force by a mechanically operated means it is diflicult to obtain the synchronization of operation referred to, and if such synchronization is secured it will be disturbed by wear, or by dimensional variations, or by any of the parts becoming loose.

By eliminating the velocity head at the jets and employing metering jets calibrated to permit suflicientow of fuel to form a fuel mixture of the desired proportions when the fuel flow is governed by engine suction as determined by the spring held main air valve,

the variation in fuel flow on opening ofthe air throttle will disappear and there will be no need to open the needle valve to admit additional fuelexcept for full throttle operation. Therefore the need of accurate timing of operation of the two throttles relative to each other, or to the needle valve, will disappear.

This invention not only provides means for making the static suction, as determined by the air valve, the factor controlling the fuel flow, but also contemplates the opening of the main air throttle 114, merely for the purpose of increasing the quantity of mixture after the capacity of the primary vtubes becomes inadequate to meet the requlrements of the engine, and the cam operating needle valve 54 is designed to begin opening said valve at an engine speed corresponding to a vehicular speed of approximately 45-50 miles per hour on a level, only for the purpose of enriching the mixture at high speeds to produce the power necessary for such operation.

The means for preventing the formation of velocit head and making the static suction efectlve to draw fuel from the nozzles 40, comprises a'shield 122 which is secured in position around each of said nozzles. There are three of these shields 122, one of them being associated with each nozzle 40. The shield 122fis constructed in the form of a rectangular box which is positioned on the bottom of the primary mixture passage 42 85 immediately adjacent the inlet thereof. The bottom wall of said shield is provided with an orifice 124 through which the nozzle projects when the shield is secured in position. The bottom wall of said shield is formed with an extension 126 bent at right angles to the bottom wall and this extension is provided with an orifice 128 through which an attaching screw 130 extends. When the shield is in the position as shown in Fig. l the anterior or inlet end of said shield is entirely unrestricted while the posterior or outlet end of said shield is closed by a wall 132 provided with a minute outlet orifice 134.

The above described shield provides a supplementary passage immediately surrounding andl adjacent to the nozzle 40 and because of the particular construction'of said shield it serves to prevent any substantial increase in velocity of the air current flowing past the nozzle irrespective of the opening of the throttle valves. Because of the difference in sizes of the outlet orifice 134 and the totally unrestricted inlet end of said shield the velocity of the air flowing through said shield must always be small, too small in fact to create a velocity head at the nozzle. Moreover since the inletend of said shield is immediately adjacent the auxiliary air chamber 96 and substantially the same suction is 115 maintained in chamber 96 as in the main air chamber 90, the suction within the shield must be substantially that of the main air chamber 90.

The purpose of the supplementary air valve 116 and the mechanism retarding the opening movement thereof will now be briefly explained. Whenever the throttle valve 114 is opened to accelerate the speed, it is necessary to provide some enrichment of fuel mixture immediately in order to secure proper operation of an engine. In order to enrich the mixture in the specific form of charge forming device herein disclosed, a pump, hereinafter described, is provided to supply additional fuel, and at the same time the valve 116 is retarded in its opening movement to assist the action ofthe pump. It will be understood, however, lthat the retarding of the opening movement of valve 116 would assist in providing a rich mixture on opening of the throttle if the pump were not employed, and although particularly effective when used incombination with the pump its use is not limited to such combination.

The openin movement of the air valve is retarded for t e purpose of producing at all times, when the throttle 114 is opened, a suiicient pressure differential between the inlet and outlet. ends of the primary mixing tubes to create a velocity of flow through said tubes great enough to transport the primary mixture from the primary mixing chambers to the secondary mixing chambers almost immediately. In the device disclosed herein the aforementioned pump forces fuel for acceleration purposes into the primary mixing tubes to form a super rich mixture therein. If the air valve Were allowed to open freely the pressure differential between the two ends of the primary tubes would be too low to create a high air velocity therein and a perceptible interval of time would be required to carry this super rich mixture to the secondary mixing chambers. The secondary air entering through the main air passage would reach the secon ary chambers before this super rich mixture and would weaken the mixture therein instead of enriching it, thus entirely defeating the purpose of the fuel pump.- By retarding the opening movement of the valve 116 this diliculty is avoided. The suction at the outlet ends of the primary mixing tubes is maintained suficient to lproduce so high a velocity of air flow through the primary tubes that the super rich primary mixture reaches the secondary mixing chambers substantially simultaneously with the opening of the throttle. Of course, the retarding of the opening movement of the valve 116 also increases the time interval necessary for the air admitted on opening the throttle 114 to reach said secondary mixing chambers, so that this interval is substantially the same as that required for the rich primary mixture to reach said mixing chambers.

The air valve dashpot previously described operates as a pump to supply the additional fuel for acceleration to the primary mixing chambers. To this end a conduit 14() is connected through the wall of said dashpot cylinder near the bottom thereof and at its upper end said conduit connects with a fuel canal 142 formed in a block 144 secured in any desirable manner to the bottom of the distributor block. Formed in said block and communicating with the fuel channel 142 are three vertical fuel passages 146 the middle one of which is disclosed in Fig. 1. These passages communicate with three passages 148 formed in the oor of the distributor block and communicating with the three pri mary mixture passages 42. Air is admitted to the fuel channel 142 through two air passages 150 one of which is shown b'y dotted lines in Fig. 1. The air entering said passages forms an emulsion with the fuel in the channel 142 and said emulsion is drawn into the primary mixture -passage through the passages 148. The specific details of this pump form no part of the present invention, and therefore are only briey described herein, but fully described in the copending application previously referred to.

Each primary mixture conduit 72 conveys the primary mixture to a secondary mixing chamber which comprises a Venturi tube 160. There are three of these Venturi tubes which are identical in construction and are positioned in each outlet branch of the manifold 10, in such relation to the primary mixture conduits that the point of greatest suction in `each Venturi tube is immediately adjacent the outlet of the primary conduit associated therewith. Each Venturi tube is provided with an annular projecting rib 162 which fits,

when the manifold is attached to the engine block, both in the engine intake port and in a recess 164 in the end of the associated branch of the manifold, the rib being clamped between the shoulder 166 on the manifold and a corresponding shoulder 168 in the intake port. A channel 170 is formed in the outer wall of said Venturi tube, at the bottom of the element when the device is assembled, to permit any fuel which precipitates out of the mixture and collects on the wall of the manifold branch to iow into the larly effective to secure a fuel mixture of proper proportions in the specific charge forming device which is disclosed herein it is by no means limited in its use to this particular device but is adapted to be used in any form of charge forming device to secure a proper proportion of fuel and air in the combustible mixture formed by said device.

While the form of embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. A charge forming device for internal combustion engines comprising, a mixing cliamber, a fuel inlet therefor an air chamber for supplying air thereto, a throttle for controlling flow therefrom and means for making the static suction of the air chamber the dominant factor controlling the flow offuel from said fuel inlet, said means com rising a shield over the fuel inlet and means or maintaining within the shield a suction substantially equal to that of the air chamber.

2. A charge forming device for internal combustion engines comprising, a mixing chamber, a fuel inlet therefor an air chamber for suppl ing air thereto, a throttle for controlling ow therefrom and means for making the static suction of the air chamber the dominant factor controlling the flow of fuel from said fuel inlet, said means com rising a' shield over the fuel inlet and means or maintaining a substantiall constant velocity of air flow through the s ield under all operating conditions.

3. A charge forming device for internal combustion engines comprising, a mixing chamber, a fuel inlet therefor an air chamber for supplying air thereto, a throttle for controlling flow therefrom and means for making the static suction of the air chamber the dominant factor controlling the iiow of fuel from said fuel inlet, said means comprising a shield over the fuel inlet and forming a supplemental air passage immediately adjacent thereto, said shield having an outlet of considerably less area than the inlet thereof, whereby the velocity Aof flow through said shield is maintained substantially constant under all operating conditions.

4. A charge forming device for internal combustion engines comprising, a mixing A chamber, a fuel inlet therefor an air chamber for supplying air thereto, a throttle for controlling ilow therefrom and means for making the static suction of the air chamber the dominant factor controlling the flow of fuel from said fuel inlet, said means comprising a shield over the fuel inlet and forming a supplemental air passage immediately adjacent the nozzle, said passage havin an unrestricted inlet end and a closed out et end proinlet and forming a supplemental air passage immediately adjacent thereto, said passage having an inlet end communicating directly with said air chamber and of larger size than said outlet end whereby substantiall the same suction is maintained in the sai passage and air chamber.

6. A charge forming device for internal combustion en 'nes com rising a mixing chamber, a fuel inlet there or, an air chamber supplying air thereto, a throttle controlling the flow therefrom, and a shield over the fuel inlet and forming a supplemental air passage immediately adjacent thereto, said passage havin air unrestricted end communicatin direct y with said air chamber and a close outlet end provided with a small orifice therein whereby substantially the same suction is maintained in said passage as in said air chamber.

7. A. charge forming device for inte combustion engines comprising a mixing chamber, a fuel inlet therefor a main air chamber, a supplemental air chamber communicating therewith and supplying air toA said mixing chamber means for maintaining the same suction in said air chambers, a throttle controllingy the flow from said mixin chamber, and a shield over the fuel inlet an forming a supplemental air passage immediately adjacent thereto, said passage having an inlet end communicating directly -with said supplemental air chamber and of larger size than said outlet end, whereby substantially the same suction is maintained in the said passages and main air chamber.

8. A charge forming device for internal combustion engines comprising a secondary mixing chamber, a primary carburetor supplying fuel mixture thereto, a main air chamber supplying air to said secondary mixing chamber, a supplemental air chamber communicating with said main air chamber and supplying air to said primary carburetor, means for maintaining the same suction in said air chambers, a throttle'controllin the flow from said mixing chamber, and a s ield over the fuel inlet and forming a supplemental air passage immediately adjacent thereto, said passage havin an inlet end communicating directly wit said supplemental air chamber and of larger size than said outlet end, whereby substantially the same suction is maintained in the said passage and main air chamber.

In testimony whereof I hereto ailix my signature.

WILFORD H. TEETER.