US 3903215 A
In a preferred embodiment in an air valve carburetor, a throttle cam is rotatably disposed downstream of the air valve in an air inlet assembly having substantially rectangular cross-section. The surface profile of the cam generates a pair of convergent-divergent nozzles of the Laval type, whereby the air flow ambient the cam may pass through shock waves downstream of the throat for enhanced atomization of fuel droplets. Fuel is supplied anterior the throttle cam in proportion to inlet air flow by means of a metering rod responsive to the air valve position.
Claims available in
Description (OCR text may contain errors)
Sept. 2, 1975 United States Patent 1191 Cole et a1.
3,814,389 6/1974 261/DIG. 39
[ SONIC THROTTLE CARBURETOR  Inventors: Edward N. Cole, Bloomfield Hills; OTHER PUBLICATIONS Supersonic Inlet Diffusers and Introduction to Internal Aerodynamics;
Thomas P. Yasin, Rochester, both of Mich.
Dr. Rudolf Hermann; MinneapolisI-Ioneywell; Vanderhoff Ave.; Leaside, Toronto, Ontario,
General Motors Corporation, Detroit, Mich.
Canada; pp. 1-9.
22 Filed: Aug. 31, 1973 Primary E.\'aminer-Tim R. Miles Attorney, Agent, or FirmC. K. Veenstra Appl. No.: 393,397
 ABSTRACT In a preferred embodiment in an air valve carburetor,
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PMENTEU 21975 did MANIFOLD VACUUM IN. HG SONIC THROTTLE PERFORMANCE SONIC THROTTLE CARBURETOR BACKGROUND OFTHE INVENTION It has been well acknowledged that in multicylinder internal combustion engines of the carburetted type, homogeneous air-fuel mixtures are a practical necessity in obtaining satisfactory cylinder-to-cylinder charge distribution. Atomization, or the shearing,collapse and breakup of macroscopic or large-scale fuel droplets into microscopic or mist-like particles. is one of the conventional methods of providing this homogeneity. Not only is fuel vaporization aided by the increase in the surfacearea-to-volume ratio, with droplet sizes reduced to the order of microns, but the mist-like suspension of liquid particles in air is also a homogeneous mixture as desired. Especially in part-throttle operation, improvements infuel distribution, so-called driveability or vehicle performance. and cold starting capability should be realized with increased use of atomization in charge preparation for an engine.
One method of atomizing fuel droplets is to pass the fuelair mixture through an aerodynamic shock wave. In a shock wave the velocity and pressure of the flow change violently. These changes occur at the transition from a supersonic flow regime to a subsonic flow regime and disintegrate macroscopicfuel droplets.A fog or mist of atomized liquid fuel particles results, suspended in the air stream posterior or downstream of the shock wave.
The aforesaid shock waves are commonly found in the divergent section of a convergent-divergent nozzle of the Laval type. For such a nozzle, a shock wave will form whenever the ratio of upstream to downstream total (static plus dynamic) pressure exceeds a critical value. This critical value may be determined quantitatively from a knowledge of the mass rate of air flow, minimum flow area. and geometrical considerations in a carburetor by use of references such as Report 1 I35, Fquations, Tables, and Charts for Compressible Flow contained in the Thirty-Ninth Annual Report of the National Advisory Committee for Aeronautics; I953 At this critical pressure ratio, the flow .velocity at the point of maximum constriction or throat becomes sonic. Further decreases in downstream pressure cannot affect the flow upstream of this throat, for pressure signals cannot propagate upstream faster than the speed of sound. Downstream of the throat, however. further decreased pressure will cause theflow to accelerate to supersonic speeds. Then at some point downstream from the throat. a shock wave" is formed; the pressure is abruptly increased while the velocity is abruptly reduced.
PRIOR ART The present carburetor is an improvement over the carburetor described in US. Pat. No. l,l29.864 to C. A. Haas. datedMar. 2. I915. Haas depicts oppositely directed marginal flanges 3] with sides tapering toward the axis of the valve 29. the outer faces of the flanges being convexz" which suggests a description of l.aval type nozzles but shown in an air inlet having circular cross-section. U.S. Pat. No. l.l5 1.286 to A. F. Rowell. dated Aug. 24, I915. shows a movable choke sleeve 32 which. in combination with stationary throttle cone 3],, defines a conical convergirig-diverging nozzlefor throttling inlet air. However. the present invention provides means for maintaining an attached flow discontinuity SUMMARY OF THE INVENTION The purpose of this invention is to provide a novel carburetor having throttling means for generatinga shock wave in the air inlet as heretofore described, so that improved fuel atomization and other attendant benefits may be obtained thereby. Referring to the drawings; I
FIG. 1 shows a carburetor of the air valve type having a sonic throttle cam; I i i i FIG. 2 is a sectional view of the air inlet and top of the sonic throttle cam, taken along the line 22 indicated in 'FIG. l; and
FIG. 3 is a graph showing a'comparison of the performance of the sonic throttle cam and a conventional butterfly valve.
i The carburetor-throttle cam combination forming the subject matter of the present invention is made in a preferred embodiment from the air valve-type carburetor design described in *a copending application, Ser. No. 343,553; filed Mar. 21, 1973. Referring first to FIG. 1, the carburetorlO has a mixture conduit 12 including an air inlet 14 and a mixture outlet 16 which discharges to the engine. A throttle cam I8 is rotatably disposed in mixture outlet 16 on and is secured by screws 19 to a throttle shaft 20, for controlling engine air flow.
An air valve 22 is disposed in air inlet 14 on an air valve shaft 24. A spring 26 is hooked over the downstream edge 28 of air valve 22 or otherwise attached thereto and extends to a bracket 30 to bias air valve 22 to the position shown. 'A tang 32 reaches upwardly from air valve 22 and is connected by a link 34 to a diaphragm 36. A chamber 38, formed between the right side of diaphragm 36 and a cover member 40,.is connected by a tube 42 to a re,- gion 44 of mixture conduit 12 defined between air valve 22 and throttle l8.
A chamber 46, defined between the left side of diaphragm36 and a cover member 48, is subjected to substantially atmospheric pressure, present in air inlet 14 and in the air cleaner (not shown), through openings such as 50,52, and 54. (The air cleaner seats on a rim 56 disposed about the upper portion of carburetor 10.)
In operation, chamber 38 is subjected to the subatmospheric pressure created in region 44 as throttlecam I8 is opened. and diaphgram 36acts through link 34 to pull air valve 22 clockwise to an open position. Spring 26 is effective to balance. theopening force ofdiaphragm 36, thereby creatinga substantially constant subatmospheric pressure in region 44. By thus establishing. agenerally constant pressure drop across air valve 22, the flow area about air valve 22 and thus the rotative position of air valve 22 is determined by and is a measure of the rate of air flow through mixture conduit 12. H y
A tab 58 extends upwardly from air valve 22 and is connected through a link 60,to one end 62. of a lever 64. The opposite end 66 of lever 64 is pivoted about a pin 68. Intermediate ends 62 and 66, a hanger extends from lever 64 into the carburetor, fuel bowl 72.
The lower end 74 of hanger 70 has a hook 76 which is received in a recess 78 formed in a metering rod 80, to be described in further detail.
It may be noted that hanger 70 extends through an opening 82 in the cover 84 for fuel bowl 72. Opening 82 is restricted by a slider 86 which shifts horizontally during movement of hanger 70.
Metering rod 80 is disposed in a fuel passage 88 having its lower end 90 disposed to receive fuel from a well 92 formed in the bottom of fuel bowl 72. The upper end 94 of fuel passage 88 has an opening 96 through which fuel is discharged into the region 44 of mixture conduit 12, anterior of throttle cam 18, and posterior of air valve 22. It will be appreciated, therefore, that the fuel in fuel bowl 72 is subjected to a substantially constant metering head from the substantially atmospheric pressure in the upper portion of the fuel bowl to the generally constant pressure in region 44.
A metering jet or orifice 98 is disposed in fuel passage 88 around the top 99 of metering rod 80. Metering rod 80 has flat tapered surfaces 100 on opposite sides which, upon reciprocation of metering rod 80 in jet 98, varies the area available for fuel flow through jet 98.
In operation, as air valve 22 opens by clockwise rotation, link 60 rotates lever 64 in a clockwise direction. Lever 64 then lifts hanger 70 to move metering rod 80 generally upwardly and rightly in fuel passage 88. Thus as air valve 22 is opened to increase the area available for air flow through air inlet 14, metering rod 80 is shifted to increase the area available for fuel flow through metering orifice 98. By this means, a substantially constant air-fuel ratio may be maintainedthe precise proportion being controlled by the geometry of tapered surfaces 100 and of the linkage between air valve 22 and metering rod 80.
A spring 102 extends from a ledge 104 formed in fuel passage 88 to the lower end 106 of metering rod 80 to take up any slack in the linkage and to load metering rod 80 against jet 98.
It is noted that the foregoing linkage may be modified somewhat for more flexible operation, as in the manner set forth in a copending application, Ser. No; 343,553; filed Mar. 21, I973. The modifications comprise a slot in lever 62 for receiving link 60 (operatively connected to air valve 22), and operating condition responsive means controlling the position of link 60 in the slot whereby the length of the lever arm of lever 62 about pivot pin 68 may be varied to adjust the proportion of fuel flow to air flow in response to variations in the engine operating condition.
- As shown in FIG. 2, outlet 16 has a rectangular cross section formed by planar side walls 108 and planar end walls 110, and throttle cam 18 has a pair of flat side walls 112 disposed adjacent side walls 108. As shown in FIG. 1, throttle cam 18 has an upper surface 114 defined by a substantially flat portion 116 and a portion of circular cylindrical contour 118 and a lower surface 120 defined by a substantially flat portion 122 and a portion of circular cylindrical contour 124. The upstream or anterior end 180 of throttle cam 18 is rounded to afford a blunt leading edge opposing the inlet air stream so as to facilitate the separation of air flow streamlines thereabove, whereas the downstream or posterior end 18p of throttle cam 18 is a sharp trailing edge to facilitate the rejoining of air flow streamlines therebelow.
The convex airfoil shape of throttle cam 18, in combination with walls 110, defines an air flow path which is a pair of convergent-divergent passages or Laval Nozzles 126, with rectangular cross-section as shown in FIG. 2. The minimum flow area or throat of nozzles 126; can be noted in FIG. 2 as the area of the gaps between throttle cam 18 and end walls.
Screws 19 are countersunk in throttle cam 18, so that they do not perturb the air flow posterior of their position.
In operation, 'sonic flow occurs whenever the critical pressure ratio is exceeded at the minimum flow area point or throat. The critical pressure ratio, which indicates sonic flow at the throat, is dependent on the ratio of the exit area of the nozzle to the area at the throat. As the area ratio increases, the attendant critical pressure ratio decreases, so that less and less pressure differential (anterior and posterior throttle cam 18), is required for sonic flow. In the case of the present invention, the nozzle exit area is limited by the point at which the flow separates from the cam surface. Inasmuch as separation is not desirable from the standpoint of atomization, it has been a further object of the present invention to design the shape of throttle cam 18 to ensure attached sonic flow at manifold vacuums normally associated with road loads.
FIG. 3 shows a family of sonic throttle performance curves for use in evaluating the present invention and comparing it to conventional butterfly valves. Curves A and B show inlet air flow versus manifold vacuum at various constant throttle cam opening angles. It is apparent that inlet air flow becomes choked (flow limited), in the neighborhood of 8-10 inches Hg, and with manifold vacuums in excess of this nominal range, no greater air flow can be achieved. Curves C and D are curves of the aforesaid type for a conventional throttle, and it can be observed that choked flow does not occur. It can be further observed that for equivalent air flow at constant manifold vacuum, the present invention requires only about one-half the degree of throttle opening than that required by the conventional throttle valve.
Dashed curve E of FIG. 3 is the left-hand boundary for the so-called zone of silence, wherein noises downstream of throttle cam 18 cannot be propagated through the air flow past the throttle cam 18. For equivalent air flows, manifold vacuums to the left of curve E are insufficient to achieve the desired shock wave. Therefore, it is highly desirable to translate (shift) curve E leftward to broaden the range of manifold vacuums at which throttle cam 18 becomes effective. One of the design criteria imposed on throttle cam 18 is the selection of the largest radius of convex curvature for portions 118 and 124 of throttle cam 18 practicable in view of cam size and flow area considerations, thereby optimizing the aforesaid breadth of effectiveness of throttle cam 18.
It will be noted from the foregoing that the purpose of throttle cam 18 in combination with end walls is to provide by geometrical design a pair of convergent-divergent Laval-type nozzles interposed in mixture conduit 12 which generate a shock wave attached to but posterior throttle cam 18 to enhance the atomization of fuel droplets spilling from opening 96 of fuel passage 94.
What is claimed is:
I. An internal combustion engine carburetor cornprising a conduit for air flow to the engine. said conduit including a portion of substantially rectangular cross section having a pair of planar side walls and a pair of planar end walls. a throttle shaft extending through said conduit from one side wall to the other side wall, a substantially rectangular throttle cam disposed in said conduit on said shaft and being rotatable between closed and open positions for controlling flow therepast, said throttle cam having a pair of side wallsjuxtaposed with said conduit side walls, said throttle cam further having upper and lower surfaces. said upper surface having a substantially flat portion terminating in a leading edge adjacent one end wall and said lower surface having a substantially flat portion terminating in a trailing edge adjacent the other end wall, said upper surface further having a portion of circular cylindrical contour extending from said upper surface flat portion to said trailing edge, and said lower surface further having a portion of circular cylindrical contour extending from said lower surface flat portion to said leading edge, said leading edge being rounded from said upper surface flat portion to said lower surface contoured portion and said trailing edge being an angular intersection of said upper surface contoured portion with said lower surface flat portion. and means for introducing liquid fuel into said conduit upstream of said throttle cam, said contoured portions cooperating with said end walls to define converging-diverging nozzle means of substantially rectangular variable flow area therebetween for accelerating air and fuel flowing through said conduit to supersonic velocity and for decelerating said air and fuel through a shock wave to promote atomization of the fuel.
2. An internal combustion engine carburetor comprising a conduit for air flow to the engine, said conduit including a portion of substantially rectangular cross section having a pair of planar side walls and a pair of planar end walls, a throttle shaft extending through said conduit from one side wall to the other side wall, a substantially rectangular throttle cam disposed in said conduit on said shaft and being rotatable between closed and open positions for controlling flow therepast, said throttle cam having a pair of side wallsjuxtaposed with said conduit side walls, said throttle cam further having upper and lower surfaces, said upper surface having a substantially flat portion terminating in a leading edge adjacent one end wall and said lower surface having a substantially flat portion terminating in a trailing edge adjacent the other end wall, said upper surface further having a portion of circular cylindrical contour extending from said upper surface flat portion to said trailing edge, and said lower surface further having a portion of circular cylindrical contour extending from said lower surface flat portion to said leading edge, said leading edge being rounded from said upper surface flat portion to said lower surface contoured portion and said trailing edge being an angular intersection of said upper surface contoured portion with said lower surface flat portion, and means for introducing fuel into said conduit, said contoured portions cooperating with said end walls to define convergingdiverging nozzle means of substantially rectangular variable flow area therebetween for accelerating flow through said conduit to supersonic velocity to inhibit propagation of noise past said throttle cam.