US3317195A

US3317195A - Carburetor

Info

Publication number: US3317195A
Application number: US399991A
Authority: US
Inventors: James T Bickhaus; Forrest W Cook
Original assignee: ACF Industries Inc
Current assignee: ACF Industries Inc
Priority date: 1964-09-29
Filing date: 1964-09-29
Publication date: 1967-05-02
Anticipated expiration: 1984-05-02

Description

y 1967 J. T. BICKHAUS ETAL 3,317,195

CARBURETOR 3 Sheets-Sheet 1 Filed Sept. 29, 1964 INVENTORS T W. COO

FORRES AMES BY TICKHAUS AGENT J. T. BICKHAUS ETAL 3,317,195

CARBURETOR 5 Sheets-Sheet 5 Filed Sept. 29, 1964 FIG.4.

/ ENGINE SPEED F l G. 7.

inch displacement),

United States Patent Ofiice 3,3 1 7,195 Patented May 2, 1967 This invention relates to multi-stage, multi-barrel carburetors and particularly to a carburetor with modified performance characteristics compensating for the usual manner of automobile operator response which is not necessarily conducive to either smooth vehicle operation or fuel economy. Recently, the trend in motorcar development is toward a vehicle with smooth and seemingly effortless performance. Each new model boasts larger engines with increased torque and improved drive trains and suspensions to better isolate engine and road vibration and sound. The purpose of such developments is to improve vehicle potential in the above respects. This invention is primarily intended to promote the full potential in this trend, and it is one of the objects of this invention to provide a carburetor better adapted in performance characteristics to obtain efficiency and a throttle control for smoother engine response by an operator.

When multi-barrel, multi-stage carburetors were first introduced on motorcars, both primary and secondary barrels were about the same size, that is, approximately the same air flow capacity. Because high cruising speeds were possible on operation of the primary barrels alone, the secondaries became useful only in this upper range of engine speeds and, accordingly, the added performance of the secondaries had only a limited utility. This fact was realized by some quite early, and attempts were made to modify these carburetors to bring the secondary in at lower speeds.

As motorcar engines continued to increase in size (cubic the capacity of the secondaries was increased with respect to the primaries in order to match the increased breathing capacity of the larger engines. In the four barrel carburetor, this was accomplished by increasing the size of the secondaries so that each was larger than its corresponding primary. At low engine speeds, the oversized secondaries are useless because air stream velocity is too low to pull fuel out'of the secondary nozzles. Consequently, at cruising speeds for the motorcar and below, the automatic transmission was set to downshift if the throttle was opened far enough to open the secondaries. The increase in engine speed after the downshift so increased the air flow velocity in the secondaries that satisfactory operation of the carburetor was obtained. The downshift, of course, increased the torque transmitted from the automatic transmission and this was accompanied by the natural increase in torque from the engine which jumped to higher speeds. These two effects acting together often caused loss of traction of the driving wheels and, in all cases, a sudden startling bump. Of course, a bump in acceleration is incompatible with smooth effortless operation and obviously dangerous besides. Accordingly, the trend toward increasingly larger secondaries was arrested.

As pointed out above, the object of this invention is primarily intended to suit the trend toward smooth seemingly effortless operation in the motorcar which is now being emphasized, and to improve efiiciency, but these objects are obtained, according to the invention, by a carburetor with undersized primaries and oversized secondaries. This approach, in retrospect, seems least likely to succeed in view of prior experiences, but by adopting a modified control for the secondaries, an unexpected result has been attained. With this control, the secondaries no longer function to increase engine power solely in the upper end or the high speed range of an engine, instead the secondaries become available to increase power from the low end of the engine speed range on up. It is an- .other object of the invention therefore to provide a multistage carburetor with secondaries having a full range of action.

According to this invention, a multi-stage, multi-barrel carburetor is constructed with primaries which are relatively much smaller than the carburetor secondaries.

With smaller primaries, a soft smooth throttle response in the low speed, low power range of the engine is inherent because total flow capacity for air and fuel is limited when only the primaries are operating. Contrary to prior multi-stage practice, the secondaries are depended upon to supply the capacity for full engine power throughout substantially the full range of engine operation. This full range operation is attained by an automatic throttle means constructed to operate as a dominant conrol of engine power output and as an automatic control for air flow capacity in the secondaries in a manner depending on engine power output. The low speed operation of the secondaries is accomplished, in effect, by operating the high speed fuel nozzles in the secondaries, initially at least, on the same principle as the low speed or idle fuel system in the primaries. This combined operation is attained by an automatic throttle anterior of the main fuel nozzles in the secondaries.

With this invention, several distinct advantages in engine efiiciency and engine response are obtained. It cannot be denied that the rate of air and fuel flow to an engine determines its power output, nor, that in order to obtain the same power from a given engine with a small carburetor (a small size or capacity mixture conduit) as with a large carburetor (larger size or capacity mixture conduit) more throttle opening will be required. -It is also characteristic of engines that a richer mixture is required at idle speeds when the throttle is closed than in the so-called economy range of carburetor operation with the throttle in partially open positions. When taken together, these facts spell out the advantage of a small carburetor operating in the part throttle range over a larger carburetor operating in the idle range. The smaller the carburetor on a given engine, the greater the percentage of time of operation in the economy range. If this is true of carburetors generally, then it is also true of multi-stage carburetors having small primaries.

'Again, throttle position in the carburetor mixture conduit has a distinct effect on fuel distribution between cylinders. This effect is most adverse in the low range of throttle openings. The smaller the carburetor used on a given engine, the greater the throttle opening required for a given power output from that engine. Consequently, there is thus a, second gain in efiiciency in operating an engine in the part throttle range, or in using smaller primaries which require a comparatively greater throttle opening.

Good fuel mileage depends upon a steady throttle, but most operators continually over-control. Their usual operating procedure is to open the throttle too far, accelerate to greater speed than trafiic flow permits, and then apply the brake either too hard or too long and decelerate below the speed traflic flow permits. This in turn requires opening the throttle again to keep up with the traflic flow and a continuous repetition of applying the brake and opening the throttle. Only on multiple lane turnpikes with exceedingly low trafiic density does the usual operator achieve a steady throttle operation for any appreciable percent of his driving. A carburetor with smaller primaries requires greater throttle movement to obtain the same engine response as a carburetor with larger primaries. Furthermore, engine response at low speeds is softer, smoother and easier to control with the smaller primaries. These factors ll contribute to less frequent braking and better mileage from a multi-stage carburetor with smaller primaries.

Equally important to smooth effortless performance from an engine and good fuel mileage is the use of the automatic throttle of this invention in the over large secondaries. The over large secondaries provide the desired capacity for full power at top speed. The automatic throttle on the other hand takes up control automatically to supply the air and fuel to the engine at a rate providing best power at any engine speed at wide open throttle. This automatic throttle is dominant in its control even if the operator goes to the floor with the accelerator at low speeds as is often the case. Even if these occasions are of short duration, as they usually are, the automatic throttle prevents spectacular but useless waste of fuel.

The above explanation sets forth some of the technical advantages to be gained from this novel concept of a multi-stage carburetor with undersized primaries and oversized secondaries equipped with an automatic throttle located anterior to the fuel nozzles in the secondaries. With such a multi-stage carburetor, it is wholly unnecessary to synchronize secondary operation with a downshift in the transmission and, of course, this change in itself, if practiced, would eliminate the cumulative effect of synchronization heretofore described.

It is one of the objects of this invention to provide a multi-stage carburetor with a smooth transition from single stage to multistage operation regardless of the manner of throttle operation.

These and other objects of this invention will appear from the following detailed description which is in such clear, concise, and exact terms as will enable any person skilled in the art to make and use the same when taken in conjunction with the accompanying drawings, forming a part thereof, and in which:

FIGURE 1 is a top plan view of a carburetor incorporating this invention and mounted on the intake manifold of an internal combustion engine;

FIGURE 2 is a side elevational view of the carburetor of FIGURE 1;

FIGURE 3 is a sectional view of the carburetor of FIGURES 1 and 2 and taken along the section line 33 of FIGURE 1;

FIGURE 4 is a schematic illustration of the carburetor of FIGURES 1-3 similar to showing of FIGURE 3 and showing the carburetor with the parts in a position such as would be typical during operation of an automotive engine fully warmed up and running at road load in the range of 800-1200 r.p.m., wherein the air flow through the primary is in the range of 4-10 pounds per minute and the secondary is inoperative;

FIGURE 5 is a schematic illustration as in FIGURE 4 representing a condition in which the throttles are opened almost wide to accelerate at the low range of engine speeds in which the carburetor condition is depicted in FIGURE 2;

FIGURE 6 is a schematic illustration as in FIGURE 1 representing a condition taking place during further acceleration of the engine subsequent to the condition illustrated in FIGURE 5;

FIGURE 7 is a showing of operational characteristics of a carburetor incorporating the invention.

Turning to the drawings, the illustration in FIGURES l and 2 is a representation of a multi-barrel, multi-stage carburetor showing a body 11 formed with two primary mixture conduits .10 and 12 in side by side relation to two secondary mixture conduits 14 and 16, respectively. The primary mixture conduits are smaller than the secondaries.

As is well known in the art, the downstream or discharge ends of the mixture conduits are surrounded by a flange 18 forming a seat for the carburetor on the intake manifold M of an automotive engine E. Suitable studs projecting through the flange 18 secure the carburetor to the intake manifold, all in a well-known manner. Fuel is supplied by a fuel pump KP through a fuel line 19 from a fuel tank T to a fuel bowl 20 and a fuel bowl 22 on opposite sides of the carburetor through suitable passages through which the flow is controlled by suitable float valves to maintain a substantially constant fuel level in the fuel bowls 20 and 22. Each primary conduit is connected by a fuel passage from fuel bowls 20 and 22 respectively. Each fuel passage extends from a fuel metering inlet jet 24 submerged in the fuel of the respective fuel bowl and terminates in primary conduits 10 and 12 respectively in a nozzle structure 26, as indicated schematically in FIGURE 4. Fuel bowls 20 and 22 are also schematically shown in FIGURE 4. Fuel line 19 is connected to an inlet fitting 21. Similar structures are shown and described in detail in Patent 3,030,085 of L. B. Read of April 17, 1962 and this patent is incorporated into this disclosure by this reference.

The open end of each fuel nozzle 26 projects into the throat of a primary venturi 28 located at the throat of a main venturi 30 in the primary mixture conduits 10 and 12 respectively.

Metering restrictions

24 and 26 and

venturis

28 and 30 form together a fuel nozzle means discharging in each of the primary mixture conduits, 10 and .12, respectively.

The secondary conduits 14 and 16 are connected to fuel

bowls

20 and 22 respectively through fuel passages each including a metering jet inlet 33 located below the fuel level in the respective fuel bowls 20 or 22. The fuel passage terminates in nozzle structure 34 and 36 positioned across the secondary conduits 14 and 16 respectively in the region of a venturirestriction 15 in each conduit. The nozzle structures 34 and 36 are tubular and have axially arranged apertures 38 for discharging fuel into the secondary conduits 1-4 and 16, respectively. The metering jets 33 and nozzles 34 and 36 comprise fuel nozzle means discharging into the secondary mixture conduits 14 and 16.

Discharge of a fuel and air mixture from the primary mixture conduits 10 and 12 is under control of two manually operated throttle valves 40 and 42 positioned across the primary conduits 10 and 12 respectively and fixed to a common throttle shaft 44. Discharge of fuel and air mixture from the secondary mixture conduits 14 and 16 is under control of the

throttles

46 and 48 positioned across secondary conduits 14 and 16 respectively and fixed to the throttle shaft 50 rotatably journalled in the carburetor body 11. The

throttles

46 and 48 are unbalanced valves, so mounted that engine suction will tend to hold the valves tightly closed. The throttle valves are opened, first valves 40 and 42 in the primary conduits then, the

valves

46 and 48 in the secondary conduits by manual control through a suitable manually operated primary throttle control linkage 51 for sequentially operating the secondary throttles, in the manner shown in the Read patent. As further shown in the prior patented device, these throttles can be equipped with mechanism to lock the

secondary throttle valves

46 and 48 closed, while the primary throttles 40 and 49 are manually moved to wide open position.

The two primary conduits 10 and 12 are closed by a choke valve 52 rotatably mounted in the air horn portion '13 of the carburetor. The operation of the choke valve 52 will control the flow of air into the primary conduits. Choke valve 52 is eccentrically fixed for rotationable movement on a choke shaft 54 journaled in the upper portion of the air born 13 on the primary side of the carburetor. Choke shaft 54 in turn has fixed thereto a lever 55 which has its free end tied by a link 56 to a second lever 57 fixed to a secondary shaft 58 as indicated in FIGURE 3. Shaft 58 is also journaled in the upper portion of the carburetor and, as shown in FIGURE 1, extends through the carburetor casting and has fixed to this end thereof a lever 60 shown more clearly in FIGURE 2. The free endof lever 60 in turn is connected by a movable link 62 to a short lever 64 which is fixed to a shaft 66 rotatably jou-rnaled in the housing 32 of an automatic choke. The shaft 66 within the housing 32 of the choke has fixed thereto a multiple lever 68 having one arm 70 positioned in the path of movement of a thermostatic coil spring 72. Another arm 74 of lever 68 is connected by a link 76 to a piston '78 mounted for movement within a cylinder 80. The other end of cylinder 80 is closed but is connected by a passage 82 to the downstream end of the carburetor posterior to the throttle valve 40 and 42 in the mixture conduits and 12. The operation of this automatic choke structure is similar to that shown and disclosed in the above cited Read patent.

Briefly, however, the operation is as follows. The thermostatic coil when cooling, below a temperature in the middle 70s tends to unwind and move the end 73 of the coil in a clockwise direction as shown in FIGURE 2. As the coil unwinds in this direction, it contacts lever end 70 and rotates the shaft 66 in the same direction to raise the piston 78 to the upper portion of the cylinder 80, as shown in FIGURE 2. Simultaneously, through the several linkages and shafts described, the choke valve 52 is closed in a counter clockwise direction as viewed in FIGURE 3 to close oif the primary mixture conduits 10 and 12. However, upon starting of the engine and upon the opening of the primary throttles 40 and 42, air flow to the primary mixture conduits 10 and 12 will rotate the unbalance valve 52 in a clockwise direction as viewed in FIGURE 3 against the bias of the thermostatic spring 72, to permit sufiicient air to pass into the engine E for starting. With the engine running, increased manifold vacuum downstream of the throttles 40 and 42 operates through the air passage 82 upon the choke piston 78 to draw it to a predetermined position in the cylinder 80. This motion of piston 78 rotates shaft 66 and lever end 70 counter-clockwise, as viewed in FIG- URES 2 and 3, and against the closing tension of spring 72. This also tends to open the choke valve partially to provide a flow of air to the engine to lean out the starting air-fuel mixture and to provide air for idle operation. I

In a known manner during engine operation, warm air from the engine is brought in through an opening 84 in the choke housing to gradually heat up the thermostatic coil 72. As the coil 72 is warmed, it will wind up and the end 73 of the choke coil will move counter-clockwise, as viewed in FIGURE 2, to continuously reduce the bias on the lever arm 70 and permit the choke valve to gradually move to a wide open position to provide a progressively leaner air fuel mixture as the engine warms to operational temperatures. At this point, the choke coil ceases to influence the position of the choke valve and air flow through the primary conduits positions the choke valve 52, which is substantially vertical as viewed in FIGURE 3, to form a minimum amount of obstruction to air flow.

The larger secondary mixture conduits Hand 16 are provided with an automatically operated throttle consisting of an unbalanced air flow responsive valve 86 rotatably mounted anterior to the discharge of the fuel nozzle means 34 and 36 for closing the secondary mixture conduits 14 and 16. The unbalanced valve 86 is fixed to a rotatable shaft 88 journaled in the air horn 13 of the carburetor body and is biased by a coil spring 90 surrounding a portion of shaft 88 toward a closed position to substantially close the secondary mixture conduits 14 and 16. One end 91 of this spring 90 abuts against the under surface of valve plate 86, as shown in FIGURE 3, and the other end 92 is anchored through an aperture in the carburetor body. As will be hereinafter explained, the valve 86 acts as an automatic throttle controlling the rate of flow through the secondary mixture conduits whenever the manually operated

secondary throttles

46 and 48 are in an open, or partly open position.

The primary mixture conduits 10 and 12 are provided with a low speed or idle system shown in part in FIGURE 3. In each one of the mixture conduits 10 and 12 is a different low speed nozzle or port 94 opening above and below the respective throttle valve 40 and 42 from an idle mixture chamber 96, which is connected to a fuel passage 98 leading from the fuel bowls 20 and 22 through passages of the type shown in the prior patent to Read.

The positions of the parts in FIGURE 4 depict a typical operating condition of the carburetor after the engine has warmed up and is being operated at a steady speed at road load in which the flow of air in the primary of the carburetor has reached a steady rate, for example, in the range from 4-10 pounds per minute. This range is chosen because it is exemplary of the operation of a well known engine. In the example illustrated in FIGURE 4, engine speed would be in the range of 800-1200 r.p.-m. for this engine and this air consumption would indicate an engine horsepower output in the range of 35-83 H.P. With normal size primaries in a conventional carburetor, this range of 4-10 pounds per minute would require a throttle opening in what is termed the off-idle range only, but in the carburetor of this invention, with smaller primaries and larger secondaries, as illustrated here, the range of rate of air flow mentioned would require operation of the primaries in an intermediate or part-throttle range of throttle positions beyond the off-idle throttle range in order to have capacities of 4-10 pounds per minute of air flow. The degree of opening of the throttles in this part-throttle range, however, is less than that required to open the

secondary throttles

46 and 48, although it is much greater than the off-idle range of operation with larger primaries.

The wider open throttles, in the part-throttle range, provide a leaner mixture as less fuel is pulled out of the idle system than would result if the throttles were in off-idle position with a greater manifold vacuum. Leaner mixtures will operate the engine than in the idle range or full throttle range. Thus, the advantage of smaller primaries operating at part throttle follows logically by a comparison with bigger primaries operating in the idle range. The carburetor primaries can consequently be calibrated to deliver the optimum mixture ratio in the part-throttle range to suit the engine.

In the above example, any power demand above, HP. requires opening the secondary conduits 14 and 16 because the primaries just do not have capacity to supply the fuel-air mixture to produce more than a fraction of the available engine horsepower. Since the increase in engine output is small for a comparatively wide range in the primary throttle positions, when the primaries are used alone, there is a smaller change in engine output for a given throttle angular movement. This so-called fine control within the low range of horsepower output for the engine contributes to better efliciency regardless of the skill of the operator. Above the low range of horsepower output and for the greater range of engine power output and possibly as much as seventy-five percent of the available power, the engine is under the control of the automatic throttle or air valve 86 in the secondary side of the carburetor, the operation of which is described below.

As the primary throttles 40 and 42 are opened beyond the range of part throttle depicted in FIGURE 4, the throttle linkage 51 begins to open the

throttles

46 and 48 in the secondaries, and their full opening takes place within a very small range of angular movement of the primary throttles 40 and 42 to the condition shown in FIGURE 5. This inherently makes precise manual control of the opening of the secondary throttles diflicult. However, in this carburetor, power output above the economy range at wide open throttle is handled by the automatic throttle 86, which responds only to the rate of air flow through the larger secondary conduits 14 and 16. This rate of flow depends primarily on engine speed and not on manual throttle opening in the secondaries. FIG- URE indicates the condition of the carburetor at wide open throttle in the low range of engine speeds under heavy load. FIGURE 6 shows the condition of the carburetor at wide open throttle at a high range of engine speeds under which conditions the throttle 86 is open than under the conditions of FIGURE 5 and due to the greater flow of air through the carburetor. Consequently, the air valve throttle 86 is a throttling device of which the operator has no direct control.

In operation, above the economy range of engine operation, the engine may be under increased load due to acceleration, an increase in the grade of the road over which the vehicle is traveling, or an increase in the load carried by the vehicle. Under these conditions, all the throttles in the primary and secondary conduits may be wide open as indicated in FIGURE 5. The speed of the engine determines the manifold vacuum downstream of the automatic throttle 86, as the manifold vacuum is roughly proportional to engine speed. Thus, because of lower engine speed under load, the air valve 86 closes somewhat with the reduction in air flow through the carburetor. However, even with the reduced air flow, fuel will be pulled out of the secondary nozzles due to the sub-atmospheric pressure in the secondary conduits because of the restrictive or choking eliect of throttle 86. This increases engine power at low speeds with wide open throttles over what is possible with the venturi restrictions 15 alone.

The bias of spring 96 has a substantially constant rate over its operational range. Thus, although the amount of opening of valve 86 is roughly proportional to the air flow through the secondary conduits, the degree of opening is less at higher engine speeds, so that the restriction eifect of the air valve at increasing engine speeds is increasingly greater. Thus, the degree of depression in air pressure below atmospheric in the region of nozzles 34 and 36 is greater progressively at higher speeds, which results in a substantially constant fuel-to-air ratio of the mixture flow through the secondary conduits 14 and 16 respectively.

FIGURE 7 is a graphic representation of engine operating conditions with a carburetor of the type described with and without the use of the automatic throttle air fiow responsive valve 86. The horizontal axis of the graph represents engine speed increasing from left to right, while the vertical axis of the graph indicates the ratio of fuel-to-air, increasing from the bottom to the top. The curves A, B, and C represent the operation of the carburetor with wide open secondary and primary throttles at all times at varying engine speeds from low to high speed. These conditions are those which would be met when the vehicle is under heavy load at low speed due to rapid acceleration or to a steep grade or under heavy load. Under such conditions, it is desirable to have an enriched mixture to provide sufiicient power at all speeds for proper performance of the engine. Curve A represents a condition in which the air valve 86 was eliminated completely to show the effect of no restriction in the secondary conduit upstream of the secondary throttles. In fact, curve A was produced by holding the air valve wide open during all conditions of operation. The conditions represented by curve A are those in which the fuel-to-air ratio continuously changes relative to engine speed and does not tend to level off until maximum engine speed. Because curve A does not level off until at high speeds, it is difiicult to calibrate the carburetor to provide an optimum fuel-to-air ratio to the engine which would be acceptable at all speeds. Thus, a calibration giving an optimum fuel-air mixture at any engine speed would provide a richer mixture at high speeds with loss of economy and a lean mixture at lower speeds with loss of power.

Curve B of FIGURE 7 shows a characteristic operation of the carburetor utilizing the air valve 86 with a spring biasing the air valve toward a closed position and widerresponsive to air flow to the engine. With the secondary throttles at wide open position, air begins to flow through the secondary almost immediately. Because of the air valve operation which provides a restriction upstream of the nozzles 34 and 36, as described, the depression at the nozzles begins to suck fuel into the air flow to the engine. Curve B indicates how the fuel-air-mixture ratio goes up rapidly at low speeds and then tends to level off through an intermediate range of engine speed into the high speed region. This condition is more preferable than the condition indicated by curve A. The carburetor operating under the conditions of curve B provides a rich mixture at low engine speeds resulting in greater power for rapid acceleration or for heavy loads on the engine. Furthermore, the conditions of curve B enables the calibration of the carburetor to provide an optimum air and fuel mixture ratio close to the horizontal portion of curve B, which results in optimum engine operating conditions for a large range of engine speeds.

Curve C of FIGURE 7 illustrates a condition in which a stronger spring is used for biasing the air valve 86 of the carburetor toward a closed position. As would be expected, the stronger spring provides a greater resistance to air flow through the secondary side of the carburetor resulting in a greater depression in the region of the secondary nozzles 34 and 36. Thus, the fuel-to-air mixture ratio goes up very rapidly due to the immediate flow of fuel to the engine upon the initial flow of air to the engine. Furthermore, the fuel-to-air ratio reaches a maximum much more quickly and then begins to drop somewhat over an intermediate range of engine speeds to a lower point at high engine speeds. The drop in the fuel to air ratio is due to the fact that as the large air valve 86 opens it sweeps across the nozzle bar 34 and directs air flow more strongly against one nozzle port or the other of the nozzle bar. This illustrates the fact that the fuel-to-air mixture ratio to the engine is also dependent upon the configuration of the carburetor throat such as the number of nozzle aperturres 38 in the nozzle bars 34 for example, the closeness of the sweep of air valve 36 to the nozzle bars 34, the size of the secondary venturis, as well as other physical considerations which can all be modified to provide a type of air flow resulting in the fuel-to-air mixture ratio desired. Curve C also indicates that the carburetor can be calibrated to provide an optimum fuel-to-air mixture ratio close to the value reached at the outer end of the curve. Thus, at low engine speeds, a richer than optimum fuel-to-air mixture ratio can be supplied to the engine for power, with the mixture flowing to the carburetor dropping back toward an optimum value at higher engine speeds for economy.

Accordingly, the carburetor with such an automatic throttle is one which can be calibrated to select the proper degree of throttle opening in the secondary for best engine performance from the low range of output upward to full power and speed. This eliminates the waste of fuel caused by over control of the manually operated throttles. The automatic throttle is an improvement because it responds to engine requirements up to the limit set by the degree of opening of the manual throttles. For example, if the operator opens all of the throttles wide, or nearly wide, then the automatic throttle reacts as depicted in FIGURE 6. Automatic throttle 86 opens, but only an amount to supply the engine with the rate of mixture delivery which the engine can use to produce maximum torque at that particular engine speed. This may, or may not, be a full rich mixture. A full rich mixture might be neither the best for economy, nor for power, but the secondary nozzles 34 and 36 can be calibrated to deliver the best mixture for both at any engine speed. In this respect, improvement can be realized over direct manual control bearing no relation whatsoever to engine speed.

In previous four-barrel carburetors of a conventional type, weighted secondary velocity throttles were placed within the carburetor posterior to the secondary throttles for forming obstructions in the secondary conduits to prevent flow of air through the secondary side of the carburetor until the opening of the secondary throttles was sufficient to provide a great enough air flow to draw fuel from the nozzles by venturi action. These velocity throttles merely delayed the functioning of the secondary side of the carburetor, but once they were opened, the carburetor would function under conditions illustrated by curve A of FIGURE 7. Furthermore, since the weighted velocity throttles were downstream of the secondary nozzles they did not provide any drop in pressure or depression around the nozzles to draw fuel into the air stream when air flow into the secondaries was low and thus enrich the fuel and air mixture for power at low engine speeds.

It has also been known to utilize air valves in the secondary side of a carburetor upstream of the nozzles, but such air valves were also weighted, so that they merely offered a depression around the secondary nozzles at the early opening of the secondary throttles to provide an enriched mixture for the engine during the period of time that the air flow through the secondaries was building up to a point where it could draw fuel from the secondary nozzles by venturi action alone. Since these air valves of the prior art were weighted, they quickly were taken out of action as the weight would be swung in toward the axis of rotation of the valve, and thus provided no resistance to air flow after the initial opening action. The weighted air valves provided only a fuel enrichening effect at the first opening of the secondary side of the carburetor and were removed from action completely, until the secondary throttles were closed, at which time, the weighted air valves were also closed. Such valves provided no constant control of air flow through the secondaries at all engine speeds as provided by the air valve throttle of this invention.

The second stage of a conventional two stage carburetor operates more or less in an off or on condition. That is, the second stage is either closed, while the first stage or primary portion of the carburetor is utilized, or when the secondary throttles are opened, the secondary mixture conduits are opened almost immediately to a wide open condition to provide maximum power for acceleration or load conditions. However, in a conventional carburetor at wide open secondary throttle operation at low speeds when maximum power is required, the secondary side of the carburetor will lean out the fuel-air mixture as the venturi action on the secondary throttle drops rapidly because of decreased air flow at low engine speeds. Curve A compared with curve Band C illustrates the difficulty in realizing maximum power at low engine speeds with such conventional carburetor operation.

The invention thus provides the ability to utilize the secondary mixture conduits or a second stage of the carburetor more fully, so that it is not merely an off or on operation at wide open thottle but is a modulated operation under constant control of the air valve at all engine speeds.

The curves of FIGURE 7 point out that at low engine speeds at full open throttle, a much greater or maximum power can be obtained from the engine than can be obtained by conventional carburetors requiring a venturi action alone, in which the velocity of the flow of air through the secondaries is the determining factor in the provision of fuel flow from the secondary nozzles. The fact that with this invention the air valve 86 constantly provides a restriction upstream of the secondary nozzles enables a consistently richer mixture at all times for the low end of the operation curve. Also, as indicated by curves B and C of FIGURE 7 the enriched mixture enables the realization of the full or optimum capacity of the engine over a greater range of engine speeds.

The above described invention then permits the modification of a two stage carburetor from one which is a compromise between a primary mixture conduit that is oversize for part throttle operation and a secondary mixture conduit which is undersize for full power conditions. This invention allows reducing the size of the primary mixture conduit to one which provides a better or finer control within the low range of off-idle operation of the carburetor and yet one which is adequate for the low speeds at off idle. With this invention the secondary stage can be increased in size to provide maximum power up to the capacity of the engine by using a much larger amount of air flow to the engine, which would be impossible without the controlling feature of the air valve in the second ary.

In a typical four-bore, two stage carburetor, utilized at the present time for a well-known engine having a cubic inch displacement of 396 cubic inches, the ratio of the diameter of the primary mixture conduits at the primary throttle positions to the diameter of the secondary conduits at the secondary throttle positions is 26 to 27. In comparison, a carburetor incorporating this invention was designed for an engine having a total displacement of 429 cubic inches, in which the ratio of the primary mixture conduits at the primary throttle positions to the diameter of the secondary mixture conduits at the secondary throttle positions is 23 to 28. This indicates a degree to which it is practical to go with smaller primary mixture conduits and larger primary mixture conduits using the automatic air valve throttle in the secondary section.

In the operation of the carburetor of the type described above incorporating this invention, as the primary throttles are open from their closed position, the secondary throttles are prevented from opening by the manifold vacuum pulling on the unbalanced portion of the throttle valves. However, in one type of operation, when the primary throttles are opened between 63 and 67 degrees from the horizontal, the secondary throttles start to open through the lost motion linkage 51 and both the primary and secondary will be at wide open position simultaneously. The above limitations to the bore sizes as well as to the opening of the throttles successively are given by way of example only and are not meant to be limiting to the invention.

The bias of spring in resisting the opening of the automatic air valve 86 against the flow of air into the secondary conduits may be varied as set forth above, and for the type of performance desired by the manufacturer. The bias of the spring, of course, depends upon the size of the air valve 86 as well as the size of engine with which the carburetor is used.

With the invention described above, the carburetor utilizing an automatic throttle of the type shown in 86 is one which offers a much smoother operation of the engine as the secondary throttles start to open. This results from the fact that the automatic by spring 90, provides a depression in the air pressure downstream of the valve 86 in the neighborhood of the throttle nozzle ports 38 when the sec-ondary throttles open. This provides a fuel flow int-o the secondary mixture conduits even if the air flow through the secondary bores is small. This sub-atmospheric pressure in the neighborhood of the nozzle bars 34 provides immediate fuel flow at the start of the opening of the secondary throttles. The mixture flow to the engine is not leaned out as would occur with carburetors not using the air valve throttle 86 where the low air flow through the secondary venturis would be insuflicient to draw fuel out of the secondary nozzles. The use of air valve 86 provides a richer mixture upon opening of the secondary throttles which results in a smooth transition in engine performance from the closedsecondary throttle operation to open secondary throttle operation.

Normally the secondary throttles come into play during a demand for rapid acceleration or for increased power under load. Either condition would cause the engine to throttle 86, biased closed stumble if the mixture were not enriched, as described, upon opening of the secondary throttles. Thus, in spite of the larger size of the secondary mixture conduits, the air valve throttle 86 provides an improved engine performance upon the opening of the secondary mixture conduits and when air flow through the secondary side is a minimum. This minimizes the bump often felt in engine operation as thesecondaries open due to the leaning out of the mixture by the air flow through the secondaries without suflicient fuel. The air valve throttle 86 tends to provide a fuel flow from the nozzle passages 38 before the air flow through the secondary side begins to open the automatic throttle 86. The invention thus provides a secondary side for two stage carburetion, which is operative at all open positions of the secondary throttles and which thus provides suflicient fuel to the engine and realize optimum power at all conditions of engine operation. The operational advantages of this invention are in contrast to prior art structures which used weighted or biased valves to close off the secondary at low speeds so as to not lean out the air and fuel mixture to the engine, as they had no provision to provide fuel flow into the secondary side of the carburetor at the off-idle throttle positions, when the flow of air through the secondary side was so low as to be unable to draw fuel from the secondary nozzles. The carburetor of this invention provides a continuous control of the secondary carburetor side and does not require closing off the secondary at small off-idle positions of the secondary throttles.

We claim:

1. A multistage carburetor comprising a body structure having a pair of primary mixture conduits and a pair of secondary mixture conduits for the flow of an air and fuel mixture therethrough, said secondary conduits being larger than said primary conduits, means including a different open ended primary nozzle for providing fuel flow into each of said primary conduits, means including a different secondary nozzle having a plurality of openings for providing fuel flow into each of said secondary conduits, manually operable primary throttles and secondary throttles movably mounted respectively within each of said primary and secondary conduits and downstream respectively of said primary and secondary nozzles for controlling the flow of air-fuel mixture therethrough, control valve structure within said secondary conduits upstream of said respective secondary nozzles, shaft means eccentrically mounting said control valve structure for movement from a position closing said secondary conduits toward an open position in response to air flow through said secondary conduits, and a spring connected to said control valve structure normally biasing said control valve structure against said air flow toward said closed position to provide a pressure drop across said air valve structure, said spring being a coil spring surrounding said shaft means, and one end of said spring abutting a surface of said control valve with the other end thereof being anchored to said body structure.

2. A multistage carburetor comprising a body structure having a primary mixture conduit and a secondary mixture conduit for the flow of an air and fuel mixture therethrough, said secondary conduit being larger than said primary conduit, means including a primary nozzle having an open end for providing fuel flow into primary conduit and a secondary nozzle having a plurality of openings for providing fuel flow into said secondary conduit, manually operable means including a primary throttle and a secondary throttle movably mounted respectively within said primary and secondary conduits and downstream respectively of said primary and sec- ,0

ondary nozzles for controlling the flow of air-fuel mixture therethrough, a control valve within said secondary conduit upstream of said secondary nozzle, shaft means eccentrically mounting said control valve for movement from a position closing said secondary conduit toward an open position by air flow through said secondary conduit, a spring normally biasing said control valve against said air flow toward said closed position, said spring being a coil spring surrounding said shaft means, one end of said spring abutting a surface of said control valve with the other end thereof being anchored to said body structure, a choke valve within said primary conduit upstream of said venturi therein, means eccentrically mounting said choke valve for movement from a position closing said primary conduit to an open position, and temperature responsive means biasing said choke valve toward its closed position at an ambient temperature below a predetermined value.

3. A multistage carburetor comprising a body structure having a pair of primary mixture conduits and a pair of secondary mixture conduits for the flow of an air and fuel mixture therethrough, said secondary conduits being larger than said primary conduits, said conduits each having a venturi restriction between the ends thereof, means including a different primary nozzle opening at its end into the venturi restriction within each of said primary conduits for providing fuel flow therein, means including a different secondary nozzle having a plurality of openings for providing fuel flow into the venturi restriction within each of said secondary conduits, manually operable primary throttles and secondary throttles movably mounted respectively within each of said primary and secondary conduits and downstream respectively of said venturi restrictions for controlling the flow of air-fuel mixture therethrough, control valve structure within said secondary conduits upstream of said respective venturi restrictions therein, shaft means mounting said control valve structure for movement from a position closing said secondary conduits toward an open position in response to air flow through said secondary conduits, and a spring connected to said control valve structure normally biasing said control valve structure against said air flow toward said closed position to provide a pressure drop across said air valve structure, said spring being a coil spring surrounding said shaft means, one end of said spring abutting a surface of said control valve with the other and thereof being anchored to said body structure, said manually operable means including a throttle lever connected to said primary throttle and a lost motion linkage between said throttle lever and said secondary throttle, whereby upon operation of said throttle lever said primary throttle is opened first and then sequentially said secondary throttle, said secondary throttle being mounted eccentrically on said secondary shaft whereby manifold vacuum will hold said secondary throttle closed during engine operation when said lost motion linkage is not operative to open said secondary throttle.

References Cited by the Examiner UNITED STATES PATENTS 2,420,925 5/ 1947 Wirth. 2,793,844 5/ 1957 Olson. 2,821,371 1/1958 Stoltman. 2,832,576 4/ 1958 Henning. 2,836,404 5/ 1958 Carlson et al. 2,890,031 6/ 1959 Carlson et al. 3,030,085 4/ 1962 Read. 3,053,240 9/1962 Mick. 3,182,974 5/1965 Hill. 3,186,691 6/ 1965 Manning.

HARRY B. THORNTON, Primary Examiner.

RONALD R. WEAVER, Examiner.