US2017239A

US2017239A - Carburetor

Info

Publication number: US2017239A
Application number: US710689A
Authority: US
Inventors: Gerald John W Fitz
Original assignee: Briggs and Stratton Corp
Current assignee: Briggs and Stratton Corp
Priority date: 1934-02-10
Filing date: 1934-02-10
Publication date: 1935-10-15
Anticipated expiration: 1952-10-15

Description

@at 35 3935 J. w. Fn'z GER/M3 21,017,239

CARBURETOR Filed Feb. lO, 1934 4 Sheets--5heet l mmh am M27 W." .zigiy @Aww @et i5, 1935 .W. Fn'z GERALD CARBURETOR 4 Sheets-Sheet 2 Filed Feb. 10, 1954 'MJU/Aan' fm/25W@ C. 15,1935. 1 W FlTZ GERALD 2,017,239

` CARBURETOR 4 Sheets-Sheet 3 l Filed Feb.' lO, 1954 y@ @JJ @ci i5 3935- J. W. FlTz GERAL@ 2,6%?,23

CARBURETOR Filed Feb. 1o, 1954 4 Smets-sheet 4 Patented @et i5, E935 URETOR `lohn W. Fitz Gerald, Milwaukee, Wis., ignor to Briggs 8,: Stratton Corporation, Milwaukee, Wis., a corporation of Delaware Application February l0, 1934i, Serial No. 710,689

c claims. (ci. zei- 44) 'Ihis invention relates to improvements in carburetors, and refers more particularly to that type of carburetor forming the subject matter of the copending application of Werner E. Arml strong, Serial No. 589,116, led January 27th, 1932 customary, and it is a particular object of this invention to aiord a novel fuel discharge jet for this purpose.

Another objectof this invention is to provide improved and simplified means for metering the iiow of fuel from the discharge jet.

Another object of this invention is to meter the ow of fuel to the discharge jet directly from the motion of the variable Venturi forming members so as to insure proper coordination between the air and fuel supply.

Another object of this invention is to provide an adjustable connection between the fuel metering pin and one of the rotatable Venturi forming members whereby the relative positions of these elements may be readily regulated to aord an idling adjustment.

Another object of this invention is to provide a carburetor of the character described, in which a single adjustment affords not only the proper coordination between the air and fuel supply, but

also the idling adjustment.

Another object of this invention is to provide novel means for adjusting the volume of fuel to the discharge jet, which means embodies a connection to the throttle valve to be actuated in unison therewith for the purpose of increasing the supply of fuel as the throttle valve is opened.

A further object of this invention is to provide a carburetor of the character described, so constructed as to aiiord the optimum of simplicity and eiciency.

With the above and other objects in view, which will appear as the description proceeds, my invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the herein disclosed invention may be made as come within the scope of the claims.

In the accompanying drawings, I have illustrated three complete examples of the physical embodiment of my invention constructed according to the best modes I have so far devised for the practical application of the principles thereof, and 5 in which: i

Figure l is a side view with parts broken away and in section of a carburetor embodying this invention; f

Figure 2 is a. view taken on the plane of the 10 line 2--2 of Figure 1, showing the cover of the Venturi compartment broken away;

Figure 3 is a section view through Figure 1 on the plane of the line 3 3;

Figure 4 is an enlarged detail section view 15 through Figure 3 on the plane of the linelift, showing the fuel discharge jet andthe means for metering the ow of fuel thereto;

Figure 5 is a detail section view through Figure 4 on the plane of the line 5 5; 20

Figure 6 is a detail section view through Figure 4 on the plane of the line 6 6;

Figure '7 is a detail section view through Figure i on the plane of the line 'li-1;

Figure 8 is a detail section view through Figure 25 1 on the plane of the line 8 8;

Figure 9 is a view partly in section 'of a discharge nozzle of modified construction;

Figure 10 is a cross section view through Figure 9 on the plane of the line I -i; 30 Figure 11 is a section view through another modied form of fuel discharge nozzle, and the adjacent Venturi forming members; and

Figure l2 is a cross section through the discharge nozzle shown in Figure 11, said view be- 35 ing taken on the plane of the line l2-i2 of Figure 11.

Referring now more particularly 'to the accompanying drawings in which like numerals indicate like parts throughout the several views, 40 the numeral 5 designates the body of the carburetor which is preferably cast in one piece to form a cylindrical mixing chamber 6 and a oat chamber The mixing chamber 6 has a butterfly throttle valve 8 mounted therein, and as the car- 45 buretor illustrated is of the down-draft type, the throttle valve is located near the bottom of the mixing chamber.

The open tops of the float chamber and mixing chamber are closed by a cover unit 9 cast in one 50 piece and secured to the body 5 by screws lll.

. An air duct leading to the top of the mixing chamber is formed in the cover unit, and as is customary, a choke valve Il is mounted in the outer end portion of the air duct. The flat top 55 portion l2, of the cover unit, which covers the mixing chamber is provided with the customary fuel inlet fixture i3 embodying a needle valve (not shown) controlled by a oat Iii.

The upper portion of the mixing chamber is enlarged to afford two adjacent and side-by-side intersecting transverse cylindrical chambers l5. Freely rotatably mounted in the cylindrical chambers. l5 are complementary Venturi forming elements i6. These elements are journalled on trunnions carried by the partition wall l1 dividing the float chamber from the mixing chamber, and a coveri8 closing the open front of the cylindrical chambers i5. The speclc construction of these complementary Venturi forming elements forms no part of the present invention and is deiined in detail in the aforesaid copending application. Suilice it to say that each of these elements is provided with a semi-circular groove of gradually increasing depth so that simultaneous and opposite rotation of the elements adjusts the diameter oi the Venturi throat.

As also brought out in the aforesaid application, the function of the rotatable Venturi forming members is in response to changes in static pressure differential above and beneath the venturi.

Gears i9 carried by the Venturi forming members are in constant mesh to insure simultaneous and coordinated movement thereof and a coil spring 2D encircling and attached to a pin 2| on one of the Venturi forming members yieldably holds the members in their closed positions. The coil spring is enclosed in a removable protecting cap 22.

Disposed within the float chamber alongside the partition wall l1 is an insert 24 bored longitudinally to afford a fuel duct 25, which-is communicated through a restricted passage 26 with the interior of the float chamber so that fuel normally fills the duct-25.

The upper end of the duct communicates with the interior of a tubular stem 21 through a port 28 in the stem. The stem 21 passes through aligned openings 29 and 30 in the partition wall l1 and the upper end of the insert 24, with a shoulder 3| formed on the stem bearing against the inner face of the partition wall l1. The portion of the stem passing through the aligned openings 29 and 30 is flattened on opposite sides and the opening 30 is of corresponding shape so that the stem is held against axial rotation. The outer end of the stem is threaded and a nut 32 is applied thereon to clamp the insert 24 against the partition wall and to rigidly secure the stem in place. To hold the insert 24 against shifting about the axis of the stem, its lower end is provided with a pin 33, which is seated in a suitable recess in the bottom of the float chamber as clearly shown in Figure l.

`The tubular stem 21 projects forwardly from the partition wall I1 between the two complementary Venturi forming members on a plane slightly above their centers of rotation, to intersect the axis of the venturi. At the point of intersection, the tubular stem mounts a fuel discharge jet indicated generally by the numeral 34. This jet is of roughly tear-drop shape and consists of an upper cone-shaped section 35 with the apex thereof rounded and a lower cone shaped section 36, the apex of which is more pointed.

A centi-a1 fuel passage 31 extends down from aI transverse bore 38 in the upper section .in which the tubular stem 21 is received, to the plane of an annular channel 39 encircling the jet between the upperand lower sections, and

communicated with the bore or passage 31 through a plurality of radial ports 4l.

Directly beneath the transverse bore 33 there are two small air bleeds i2 leading from the passage or bore 31 to the outside surface of the jet to permit air to be drawn down into the passage 31 to pass down and out through the radial discharge ports together with the fuel issuing therefrom.

The fuel conducted to the discharge jet through the tubular stem 21 is metered by a pin i3 longitudinally slidable in the tubular stem 21, as best shown in Figure 4. Cut into the bottom of the inner end portion of the pin 43 is a V shaped groove 44 of gradually decreasing depth, so that the area of Acommunication between the tubular stem 21 and the passage 31 is finely adjustable by 'longitudinal shifting of the pin.

As will be hereinafter more fully brought out, longitudinal adjustment of the pin is directly coordinated with the adjustment of the Venturi area by actuating the pin from the rotation of one of the Venturi forming members. The rate of progression of the depth variation of the groove 44 or in other words, the shape of the longitudinal groove defined by the bottom of this thus carefully plotted with respect to the adjustment of the Venturi area so as to insure the proper fuel-air ratio for all operating conditions.

The opposite or outer end of the metering pin projects from the end of the tubular stem and is flattened at two opposite sides and externally threaded as at 45. This outer end portion of the -pin is slldably received in an opening 46 of the same cross sectional shape as the pin (see Figure 6), which opening is formed in the outer end of a sleeve 41 slidable on the tubular stem, so that the pin is constrained against any but longitudinal shifting with respect to the sleeve 41.

A lateral extension 4B extends down from the sleeve 41 to engage in a helical groove 49 formed in one of the rotatable Venturi forming members.

' The otherVenturi forming member has no groove for the extension 48, but the adjacent edge of the extension is shaped to conform to the curvature of the cylindrical surface of said other Venturi forming member so that the extensionis held in the groove 48 and the sleeve is restrained against any but axial longitudinal motion. A light coil spring 50 encircling the stem and confined between the inner end of the sleeve 41 and the discharge jet yieldably urges the sleeve outwardly and takes up any play in the fit of the extension 48 in the groove 49.

The threaded outer end of the metering pin projects beyond the outer end of the sleeve 41 and is threaded in a nut member 5| freely rotatably mounted at the outer end of the sleeve by a cap 52 threaded on the sleeve and secured against disengagement by solder or other suitable fastening means. A screw slotted head 53 on the nut member projects from the cap 52 to enable the application of turning force thereto. The adjusting nut member 5l is accessible from the exterior of the carburetor upon removal of a plug 54 closing an opening in the front wall Il. Inasmuch as the metering pin is held against rotation with respect to the sleeve 41, by reason of its sliding engagement in the opening 46, turning of the nut members 5I shifts the pin axially with respect to the sleeve 41. The metering pin is thus connected to the sleeve 41 so that upon axial shifting of the sleeve in response to motion on the part of the Venturi forming members, an adjustment of the area of communication between groove, isk

the tubular stem and the passage 31 in the discharge jet is effected.

The adjustability of the relative position of the pin with respect to the sleeve affords an idling adjustment for the carburetor.

As hereinbefore noted, the communication between the duct 25 through which the fu'el is conducted from the float chamber to the discharge nozzle, is through a restricted passage 26. The degree of communication afforded by the restricted passage 26 is sufficient for idling and slow running speeds. For higher speeds, the communication between the duct 25 and the oat chamber is augmented through the uncovering of a tapered port 55 in the lower end portion of the insert 26.

Normally, this port is closed, by a slide valve 56 pivotally mounted as at 51 and operable to uncover the tapered port starting at its narrow end, upon opening oi the throttle valve. The connection between the throttle valve and the slide valve v56 consists of a U-shaped link 55, whose` inner leg is slidable in a bore 59 in a boss formed in the oat chamber and `whose outer leg is slidable in a bore yt0 in an outer wall of the float chamber. The upper looped end of the link is received in a pocket or recess 6| cored in the cover member 9.

'I'he outer end portion 62 of the outer leg of the U-shaped link is loosely received in aligned openings in one blfurcated end 63 of a medlally pivoted lever ann 66. A thumb nut 65 threaded on the portion 62 is disposed between the two arms of the bifurcated end 63 to afford an adjustable connection between the lever arm @t and the l lilik.

The opposite end of the lever arm is also bifurcated and embraces a pin 66 fixed to a lever t1 secured to the shaft 68 cf the throttle valve, so that any actuation of the throttle valve imparts motion to the link 58 to transmit a. corresponding movement to the slide valve 56. The lever @il also engages suitable abutments carried by the body of the carburetor to define the limits of travel of the throttle valve as is customary.

Attention is particularly directed to the construction of the fuel dischargejet. The annular channel encircling the medial portion of the ,iet and the radial ports leading therefrom are of such relative sizes that the fuel issuing from the annular channel flows therefrom in a thin annular curtain and is readily atomized by the air owing through the venturi. The small air bleeds leading to the jet interior above the discharge oriiicesy assist in the atomization of the fuel and also preclude the possibility of siphoning the fuel from the float chamber.

While this specific construction of the jet has been found preferable, its primary features may be embodied in a modified construction as illustrated in Figures 9 and 10. In this embodiment, the general external shape of the jet is the same as that described, and as before, the central axial passage 31 is communicated with the tubular stem 21 through the port fili in the stem.

The lower end of the passage 31 leads to four discharge orifices 10, which openpthrough slight projections or bosses il. These bosses or projections are slotted at opposite `sides as at l2 to form .horizontal passages from which the fuel issues when the Venturi forming members are in their closed positions as during idling and slow running speeds.

Upon the opening of the venturi in response to acceleration produced by the opening of the throttle valve, the fuel not only discharges from the horizontal slots 12, but 'also directly from the mouths of the orifices 19. As in the embodiment hereinoefore described, an air bleed 42 leading to the upper portion of the passage 31 is also pro- 5 vided to facilitate atomization phoning.

Another modified embodiment of the fuel jet is illustrated in Figures 11 and 12. In this modication, the jet comprises a Venturi tube 13 1u mounted on the tubular stem 21 within the variable venturi formed by the rotatable elements, and provided with a stream-line shaped transverse cross bar 1l extending diametrically across the interior of the Venturi tube with the stem 21 15 passing therethrough.

Intersecting the longitudinal axis of the venturi, and the stem 21, the cross bar and the tubular stem are transversely bored as at 15 to afford two and prevent sidiametrically oppositely extending discharge ori- 20- flces leading to opposite sides of the cross bar so that the fuel issuing therefrom passes directly into the internal venturi 13 to enter the airl stream flowing therethrough.

To ail'ord adjustment of the eect of the air 25 current on the mouths of the fuel discharge oriflces, a cylindrical baille plate 15 is adjustabl-y mounted on the cross bar 1d as illustrated, to overlie the inlet of the venturi 1t. Adjustment of the baie plate toward and away from the venturi 30 regulates the effect of air stream on the fuel.

From the foregoing description taken in connection with the accompanying drawings, it will be readily apparent to those skilled in the art, that this invention aords an improved carburetor "J construction, and that it particularly provides novel means for discharging the fuel into the venturi.

What I claim as my invention is:

l. in a carburetor, the combination ofv compiementary rotatable Venturi forming members movable to vary the cross sectional area of the venturi, means on said Venturi forming members responsive to changes in static pressure diiierential at opposite ends of the venturi to eect adjustment of said members in response to changes in engine suction, a fuel discharge jet disposed within the venturi, a tubular stem. axially parallel with the axes of the rotatable Venturi forming members supporting the discharge jet and affordlng means for conducting fuel thereto, a metering pin slidable longitudinally in said stem to meter the volume of fuel flowing to the jet, and a motion transmitting connection between one of said complementary Venturi forming members and the metering pin whereby the metering pin is adjusted in accordance with changes in the cross sectional area of the venturi.

2. In a carburetor, the combination with complementary rotatable Venturi forming members to form a venturi variable in cross sectional area, and means to effect rotation of said members in response to changes in static pressure differential at opposite ends of the venturi, of a fuel discharge jet disposed within the venturi, means to conduct fuel to th'e jet, a metering -pin slidable longitudinally toward and away from the jet to meter the volume of fuel flowing to the jet, and means connected with the metering pin and hav- 70 ing an interengaging connection with one of the rotatable `Venturi forming members, said interengaging connection embodying a helical groove in said rotatable member and a follower slidable therein whereby rotation of said Venturiforming 7s liti member is translated into axial movement on the part of the metering nin. r l

.- 3. In a carburetor, the combination with complementary rotatable members forming a variable venturi, a fuel jet within the venturi and means to supply fuel to the jet, of a metering pin movable axially toward and from the jet to regulate the ow -of fuel to the jet, and means to actuate said pin in step with variations in the `area of the venturi, comprising an axially shiftable member, means adjustably mounting the metering pin from said member, and a cam follower on said member riding in a helical groove in one of said Venturi forming members to translate rotation of said memberinto linear motion on the part of the metering pin.

4. In a carburetor, a fuel discharge jet comprising, a multi-diameter body member vhaving' a-longitudinal bore from which discharge orifices lead to the exterior of the body member at its point of maximum diameter, a tubular stem angular to thelongitudinalaxis of the body member and connected thereto to mount the body member and conduct fuel to its longitudinal bore, the axes of the body member bore and the tubular stern ,intersecting and means movable` in said stem with a part arranged to cross the intersection of thebore in the body member and the tubular stem to adjust the degree of communication between said tubular stem and the bore of the body member, whereby to meter the volume of fuel flowing to the bore of the body member'. Y 5. In a carburetor, complementary rotatable members shaped to form a variable venturi, a fuel jet. disposed within the venturi with its axis substantially coinciding with that of the venturi and having an axial bore, a tube parallel with the axes of the complementary rotatable members and intersecting the bore of the jet and conm nected therewith to supply fuel to the jet, a metering pin movable in the tube across the intersection of the tube andjet bores'to regulate the flow of fuel to the jet, and means driven by one of the rotatable Venturi forming members to positively move the metering pin back and forth in said tube ,to effect its adjustment ln coordination with adjustment ofthe venturi.

6. In acarburetor, lcomplementary rotatable members forming a variable venturi, a fuel jet disposed withln the venturi, means to supply fuel to the jet, a metering pin movable to' regulate the flow of fuel to the jet, and means to positively move the metering pin in back and forth direction in accordance with adjustment of the Venturi forming members to at all times maintain a definite relationship between the volume of fuel flowing to the jet and the area of the venturi, said last named means comprising, connected to the metering pin and operable in a helical groove in one of the Venturi forming members 7. In a. carburetor, the combination with complementary rotatable Venturi members to form a 10 venturi variable in cross sectional area, and means to effect rotation of said members in response to changes in static pressure diierential at opposite ends of the venturi, of a fuel dischargejet disposed within the venturi, means to conduct fuel to the jet, a metering pin slidable longitudinally toward and away from the jet to meter the volume of fuel flowing to the jet, and a connection between the metering pin and one of the rotatable Venturi forming members through which rotation of said Venturi forming members is translated into longitudinal motion on the part of the metering pin, said connection comprising a helical cam track cut in one of the Venturi forming members and a cam follower connected with the metering pin and riding in said helical cam track.

8. In a carburetor, complementary members shaped to form a venturi and rotatable about axes lying in a plane normal to the axis of the venturi, a fuel jet axially disposed within the venturi and having an axial bore from which a discharge orifice leads, means to supply fuel to the jet including a tube connected with the jet with'the axis of its bore intersecting the axis of 35 the bore in the jet, a metering pin movable longitudinally on a line coinciding with the axis of the bore of the tube, one end portion of the pin having a progressively smaller cross section with its smallest cross section at the extreme end of 40 the pin so that endwlse movement of the pin towards the tube and across the intersection of its bore with that of the jet gradually decreases the flow of fuel to the jet, the progression of the reduction in cross section of said end portion of the pin bearing a definite relationship to the rate of change in the area of the venturi. and means driven by one' of the Venturi forming members to positively move the metering pin back and forth to maintain the supply oi fuel properly coordinated with the Venturi area at all times.

JOHN W. r'rrz GERALD.

a follower 5