Method and apparatus for varying fuel flow to compensate for changes in operating temperature

Abstract

In a carburetor having an induction passage, a variable venturi in the induction passage, a fuel bowl and means for metering fuel flow from the fuel bowl to the induction passage, the method of compensating for changes in temperature is disclosed as providing an auxiliary passage including variable restriction means therein communicating between the fuel within the fuel bowl and the induction passage, applying venturi generated vacuum to the auxiliary passage in order to thereby cause flow of fuel therethrough, varying the value of the venturi generated vacuum generally in response to volume rate of air flow through the variable venturi, and varying the effective flow area of the variable restriction means generally in accordance with temperature. A carburetor having an induction passage with a variable venturi and a fuel bowl has temperature controlled variable restriction means in combination with passage means communicating between the fuel within the fuel bowl and induction passage, vacuum generated by the variable venturi is applied to the passage means to cause a pressure differential across the fuel thereby resulting in fuel flow through the passage means, the temperature controlled variable restriction means is effective to vary the rate of fuel flow therethrough in response to said vacuum, and additional means responsive to the opening and closing movements of said variable venturi is effective to vary the magnitude of said vacuum generated by the variable venturi.

Description

BACKGROUND OF THE INVENTION

Theoretically, in order to achieve a proper fuel-air mixture discharged by the carburetor, the relationship sought is one where a particular mass of fuel (such as pounds of fuel per hour) is metered as to be mixed with a particular mass of air (also such as pounds of air per hour).

In doing this, carburetors employ either a fixed or variable venturi, or some such functionally equivalent structure, within the induction passage so that as air flows therethrough a reduction in the pressure (often referred to as venturi vacuum) of the air is achieved in the vicinity of the venturi throat. The value of the venturi vacuum is of a variable magnitude generally indicative of the rate of flow of such air through the venturi.

However, as is also well known, during cold starting and operation of an engine, fuel-air mixtures which are richer in terms of fuel, compared to normal engine operation, are required. The provision of such fuel enrichment to carburetors of the variable venturi type has been a constant problem which has not been solved by the prior art.

That is, where a required fuel enrichment curve has been empirically determined it has been found that prior art systems, in order to be sure that all requirements of such empirical curve were at least met, would have to supply greatly excessive fuel flows during certain ranges of the empirical curve. In other words, with prior art systems it is impossible to exactly match the enrichment fuel flow delivery curve of the carburetor to the required enrichment fuel flow curve of the cooperating engine. This, of course, results in greatly increased engine exhaust emissions.

Accordingly, the invention as herein disclosed and described is directed primarily to the solution of the above and attendant problems.

SUMMARY OF THE INVENTION

According to the invention, a method of providing enrichment fuel to an internal combustion engine from a carburetor having a body, induction passage means formed through said body for communicating with said engine, variable venturi means situated within said induction passage means, fuel reservoir means for containing fuel, fuel delivery means including fuel metering means communicating between the interior of said fuel reservoir means and said induction passage means, said fuel metering means being effective to meter the rate of fuel flow from said fuel reservoir means through said fuel delivery means and into said induction passage means in accordance with the volume rate of air flow through said variable venturi means, and auxiliary conduit means communicating between said fuel within said fuel reservoir means and said induction passage means for supplying auxiliary fuel flow to said induction passage means generally in accordance with sensed temperature, comprises the steps of creating a sub-atmospheric pressure within said auxiliary conduit means of a magnitude reflective of volume rate of air flow through said variable venturi means, and variably restricting the effective flow area of said auxiliary conduit means generally in accordance with said temperature as to more nearly close-off said effective flow area as said temperature increases.

While the invention is shown as embodied in a variable venturi carburetor, the invention or certain features thereof may be equally applicable to other carburetor types, such as certain air valve type carburetors.

Apparatus for carrying out the above inventive method may be described as a carburetor for an internal combustion engine, comprising a carburetor body, induction passage means formed through said body for communication with said engine, variable venturi means situated in said induction passage means effective for defining a variably operable venturi throat, a fuel reservoir, temperature controlled variably restriction means in combination with auxiliary passage means communicating between the fuel within said fuel reservoir and said induction passage means, said auxiliary passage means communicating with a source of vacuum generated by the flow of air through said variably operable venturi throat as to thereby cause a pressure differential across said fuel resulting in the flow of auxiliary fuel through said auxiliary passage means, said temperature controlled variable restriction means being effective to vary the flow of said auxiliary fuel through said auxiliary passage means in response to the magnitude of said vacuum, and additional means responsive to the opening and closing movements of said variably operable venturi throat for varying the effective magnitude of said vacuum communicated to said auxiliary passage means.

Various general and specific objects and advantages of the invention will become apparent when reference is made to the following detailed written description considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, wherein for purposes of clarity certain details and elements may be omitted:

FIG. 1 illustrates, in cross-section, a variable venturi carburetor constructed in accordance with the teachings of the invention; and

FIG. 2 is a graph illustrating characteristic operating curve of both the prior art and of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now in greater detail to the drawings, FIG. 1 illustrates a carburetor assembly 10 having body or housing means 12 with an induction passage 14 formed therethrough with such induction passage 14 having an inlet end 16 and an outlet or discharge end 18 leading to an inlet 22 of the interior 24 of an intake manifold 26 of an associated internal combustion engine. A variably positionable throttle valve 28, mounted as for rotation on a throttle shaft 30, is situated within the induction passage and effective for controlling the flow of a motive or combustible mixture from said induction passage 14 into the intake passage 24 of engine manifold 26. Generally, such combustible mixture will, of course, be comprised of atmospheric air admitted into inlet end 16 and fuel supplied to the induction passage 14 from an associated fuel reservoir or fuel bowl assembly 32.

The fuel bowl assembly 32 is illustrated as comprising a suitable bowl or housing structure 34 which may contain a float member 36 controlling an associated fuel inlet needle valve assembly (not shown but well known in the art) so as to maintain the level of the fuel 38 within the bowl 34 at a preselected level as at 40. The interior 39 of fuel bowl may be vented to the atmosphere as by vent means 41.

The related fuel metering means is shown as comprising a fuel well or conduit 44 with the lower end thereof being in communication with the fuel 38 as at 46.

Conduit 44 leads to a fuel discharge conduit or nozzle-like portion 48 which communicates with the induction passage 14 as at an outlet or discharge orifice 50. Preferably, the discharge orifice 50 is located as to be just below or downstream of the throat of a variable venturi arrangement as by having such opening formed in the fixed wall or fixed half 52 of the variable venturi.

As illustrated, the variable venturi may be comprised of a variably positionable venturi plate 54 which may be fixedly secured to a rotatable shaft 62 journalled in the housing means 12. The venturi arrangement may be such as to define a generally rectangular opening at the throat of the variable venturi when viewed, for example, in the direction of arrow 64. In fact, opposite walls, one of which is shown at 66, may define flat planar surfaces permitting the variable or moveable venturi plate 54 to be closely received therebetween for swingable motion about the centerline of rod or shaft 62. Such flat planar surfaces would terminate as at a boundary line 68 from which the continuing portion of the induction passage means 14 downstream thereof would transitionally change configuration until it became circular to accommodate the throttle valve 28.

A lever 70 is fixedly secured at one end to shaft 62, for rotation therewith, and has its swingable arm portion connected to a linkage rod 72 leading to a throttle valve actuating lever 74 fixedly secured to throttle shaft 30. Throttle actuating lever 74 is, in turn, connected as by linkage means 76 leading to a vehicle operator foot-controlled throttle pedal 78 which may be mounted for pivotal rotation as at a pivot 80. As throttle pedal 78 is rotated clockwise about pivot 80, throttle valve 28 is moved counter-clockwise in the opening direction about the centerline of shaft 30.

Generally, as throttle valve 28 is moved in the opening direction moveable venturi plate 54 is rotated counter-clockwise about the axis of shaft 62 thereby increasing the opening of the throat of the variable venturi as depicted by the dimension, D. As venturi plate 54 thusly moves toward and away from the opposite venturi section, a metering rod or valve 82, having a metering surface 84, is correspondingly moved toward and away from a cooperating metering orifice as provided by the restriction depicted at 86. Generally, as rod 82, which may be suitably pivotally connected to the venturi plate 54 as within a recess 88, moves toward restriction 86, the coaction of metering surface 84 and orifice member 86 results in a reduced effective flow area thereby correspondingly reducing the rate of flow of fuel supplied through conduits 44 and 48 and into induction passage 14.

FIG. 1 also illustrates, as being formed within housing means 12, a passage or conduit 90 having a member 92 situated therein and defining an orifice 94. A member 96, situated within a chamber 98, divides the chamber 98 generally into portions or conduit sections 100 and 102 with communication therebetween being established through an orifice 104 formed in member 96. A first interconnecting conduit or passage means 106 serves to complete communication between conduit 90 and conduit portion 102. A discharge or delivery conduit 108 has one end in communication with conduit section 102 and its other end terminating in a discharge orifice 110 opening into the induction passage 14, preferably, at a point downstream of the throat of the variable venturi. Although discharge orifices 50 and 110 are illustrated as being at different elevational levels, it should be apparent that such may in fact be at identical levels.

A metering rod or valving member 112, having a contoured metering surface 114 cooperating with orifice 94, is shown as being pivotally connected, as at 116, to an arm 118 which is operatively fixedly secured to venturi plate 54 so as to rotate therewith about the centerline of shaft 62. As venturi plate 54 is moved as to increase the throat dimension D, rod 112 is moved to the left causing the effective flow area, defined between metering surface 114 and orifice 94, to decrease.

A second valving member 120, having a body 122 slideably received within chamber 98, has a contoured metering surface 124 which, as shown, is adapted to coact with orifice 104 to define an effective flow area therebetween. Chamber 98 may be closed as by a wall member 126 which permits the passage therethrough of an extension portion 128 of valve member 120. Temperature responsive means (which as is well known in the art may be responsive to either or both engine and ambient temperatures) such as a bimetallic coil 130, having one end anchored as at 132, has a free end operatively connected to valve extension 128 as at 134. As shown, conduit portion 100 of chamber 98 is placed in communication with the fuel 38 as by conduit means 136.

OPERATION OF THE INVENTION

Generally, as has already been indicated, as throttle valve 28 is increasingly opened in order to provide a greater volume rate of flow of a fuel-air mixture to the engine intake 24, variable venturi throat, D, is increasingly opened to provide a greater flow area for the air passing through the induction passage. However, venturi vacuum is generated by the air flowing through the venturi throat and such venturi vacuum is employed in creating a metering depression or pressure differential across the fuel 38 and orifice 50 thereby causing fuel flow through the main or normal fuel delivery system comprised of conduit means 44, 48 and effective orifice or flow area of orifice member 86 as determined by the contoured metering surface 84 of metering rod 82. The main or normal fuel delivery system will function to provide a characteristic curve as depicted at 140 of FIG. 2 with such curve being determined by plotting the values of fuel-air ratio along the vertical axis and the volume rate of air flow along the horizontal axis. Curve 140 is illustrative of engine operation and fuel requirements during conditions of engine operation wherein the engine has attained a predetermined minimum operating temperature (often referred to as normal operating temperatures).

However, such metered fuel flow producing curve 140 is insufficient to maintain proper engine operation during periods of cold starting and cold engine operation. During such periods, because of the lower degree of fuel vaporization due to lower temperatures, additional quantities of fuel must be provided so that the overall quantity of vaporized fuel carried into the engine combustion chambers is sufficient to provide the required fuel-air ratio within such combustion chambers.

Prior art carburetors of the variable venturi, constant depression or air valve type merely employed an orifice, which was opened at below normal operating temperatures, in the fuel source and supplied fuel therefrom and through conduit means parallel to the main or normal fuel delivery system with such parallel system discharging into the venturi area. The problem, as previously indicated, with such prior art parallel systems is that they failed to provide proportional fuel enrichment over the entire range of volumetric air flow through the induction passage. A typical curve illustrating the performance of such prior art fuel enrichment systems is shown at 142 of FIG. 2.

With reference to FIG. 2, if dash-line 144 is considered as depicting a typical rate of air flow at curb idle (actually a fast idle situation during cold engine starting and operation) then point 146, the intersection of curve 142 and dash-line 144, represents a greatly over-rich (in terms of fuel) fuel-air mixture being supplied to the engine. Such prior art systems have been found to be so overly rich, as at point 146, as to cause engine stalling.

Further, if dash-line 148 is considered as depicting a typical air flow during typical periods of engine acceleration then point 150, the intersection of curve 142 and dash-line 148, represents a significantly too-lean (in terms of fuel) fuel-air mixture being supplied to the engine. Such excessively lean mixtures result in engine backfires.

In comparison to the typical performance of the prior art structures as depicted by curve 142, the structures constructed in accordance with the teachings of the invention are able to produce a resulting enrichment curve 152 which, for all practical purposes, provides the exact degree of fuel enrichment required for all corresponding air flows.

Generally, the elevation of curve 152, with respect to curve 140, and the shape of curve 152 is controlled and determined by the action of valving means comprised of apertures 104 and 94 coacting with metering surfaces 124 and 114.

For example, let it be assumed that the engine is running and that the various related elements are held in the position shown in order to maintain the effective bleed area between orifice 94 and metering suface 114 constant. Now if it is further assumed that the engine is cold thermostat 130 will be wound tighter causing valve member 120 to move to the left to some corresponding stop position as against wall member 126. Consequently, because of the movement of metering surface 124 to the left, the effective flow area through orifice 104 is at a maximum.

The air flowing through the venturi throat at this time is providing a metering or venturi vacuum for causing fuel to be metered and discharged from orifice 50 in accordance with curve 140. Additionally, the same air-flow generated venturi vacuum is applied to the parallel cold enrichment fuel system via port 110 and conduit means 118. Such reduced pressure or venturi vacuum is further communicated to passage means 102 through orifice means 104, chamber portion 100 and conduit 136 to the fuel contained therein. However, it should be made clear that the full magnitude of the venturi vacuum is not applied to the fuel within conduit 136 because of passages 106 and 90 communicating between a source of ambient atmospheric pressure and passage or conduit means 102. Such communication with the ambient permits a degree of atmospheric pressure to be bled into passage means 102 and the degree of atmospheric bleed is determined by the effective flow area through orifice 94.

In any event, the modified venturi vacuum, applied to the fuel within conduit means 126, causes fuel to flow upwardly through conduit 136, chamber portion 100, orifice 104, passage means 102, conduit means 108 and out of orifice or port 110 into the induction passage 14. The rate of flow of such additional fuel will depend on the pressure differential created across the fuel within conduit 136 by the modified venturi vacuum as well as the effective flow area through orifice 104. Consequently, it should be apparent that as thermostat 130 becomes progressively heated causing the end 134 thereof to generally unwind, valve 120 will be correspondingly moved to the right resulting in metering surface 124 further restricting the effective flow area through orifice means 104. In turn, of course, since one of the variables in determining the rate of flow of fuel through the auxiliary enrichment system is the effective area of orifice means 104, a reduction in the rate of flow auxiliary fuel is experienced.

Accordingly, it should be apparent that if, under the assumed conditions of curb-idle engine operation the enrichment system of the invention originally provided a fuel flow resulting in point 154 (the intersection of curve 152 with dash-line 144) then, with all other elements being maintained, as temperature increases the fuel-air ratio of the enrichment fuel will generally correspondingly change to leaner (in terms of fuel) fuel-air ratios as generally depicted by points 154a, 154b and 154c.

Similarly, every other point on curve 152 will also experience such changes resulting from increasing temperatures and the further restricting of the flow of enrichment fuel through orifice means 104. Therefore, as it should be apparent, as thermostatic means 130 is progessively warmed every point along curve 152 will be progessively displaced directly downwardly until such points coincide with curve 140. In view of the preceding, it can be said that the temperature responsive to controlled valving means is effective for raising and lowering curve 152 in accordance with temperature.

The above-described raising and lowering of the locus of points of curve 152 is in relation to the operation of temperature responsive means 120 with the air bleed valving means 94, 114 being maintained in any selected position.

Now, let it be assumed that the temperature responsive means 120 is maintained at any selected position and that the air bleed means 94, 114 is varied. It should, of course, be apparent that as throttle valve 28 is rotated in the opening direction, linkage means 70, 72 causes moveable venturi plate 54 to move generally counter-clockwise in the opening direction and that air bleed valve means 112 is thusly moved to the left. In so doing, valving surface 114 further restricts the effective flow area between itself and aperture 94. (This is assuming that valving surface 114 is contoured as to be progressively larger in cross-section in accordance with the distance from the left end of the valving surface 114 of such measured cross-section. However, in practice, the contour of valving surface 114 may be of any required configuration and may, in fact, be such as at times in cooperation with aperture 94 even increase the effective flow area therethrough as the moveable venturi plate 54 is moved in the opening direction).

In any event, as the effective flow area through aperture 94 is further restricted, the value of the vacuum within passage or chamber 102 increases thereby increasing the pressure differential across the effective flow area of orifice 104 and causing an increased rate of fuel flow therethrough and into induction passage 16.

Accordingly, if the contributions of the air bleed means and the temperature responsive means can be considered in their broad aspects, it can be seen that the air bleed means 94, 114, responsive generally to air flow demands of the engine, is effective for determining the shape of the curve 152 while the temperature responsive means 120 is effective for determining a family of such curves 152.

Although only one particular curve 152 has been depicted, merely for purposes of discussion, it should be clear and evident that in actual practice the shape of curve 152 may be of any desired configuration suitable for the particular requirements of any associated engine.

Further, it should be pointed out that in the preferred embodiment of the invention the fuel enrichment system is additive in the sense that whatever increase in fuel flow is required to raise the fuel-air ratio from, for example, point 154d on curve 140 to the value represented by point 154 on curve 152 is totally supplied by the enrichment system disclosed and that when all flow of fuel is terminated by virtue of orifice 104 being completely closed the fuel-air ratio becomes that depicted by curve 140 and determined by the main metering system, partially comprised of restriction 86 and cooperating valving surface 84.

Further, FIG. 1 also illustrates the concept of providing suitable manually positionable means 160 which may be employed, as with suitable motion transmitting means 162, for controlling the position of valving means 120. Such manual means 160 may, of course, be employed in combination with temperature responsive means 130 or, in the alternative, as a substitute therefor.

Although only one preferred embodiment of the invention has been disclosed and described, it is apparent that other embodiments and modifications of the invention are possible within the scope of the appended claims.

Claims

I claim:

1. A method of providing enrichment fuel to an internal combustion engine from a carburetor having a body, induction passage means formed through said body for communicating with said engine, variable venturi means situated within said induction passage means, fuel reservoir means for containing fuel, fuel delivery means including fuel metering means communicating between the interior of said fuel reservoir means and said induction passage means, said fuel metering means being effective to meter the rate of fuel flow from said fuel reservoir means through said fuel delivery means and into said induction passage means in accordance with the volume rate of air flow through said variable venturi means, and auxiliary conduit means communicating between said fuel within said fuel reservoir means and said induction passage means for supplying auxiliary fuel flow to said induction passage means generally in accordance with sensed temperature, comprising the steps of creating a sub-atomospheric pressure within said auxiliary conduit means of a magnitude reflective of volume rate of air flow through said variable venturi means, and variably restricting the effective flow area of said auxiliary conduit means generally in accordance with said temperature as to more nearly close-off said effective flow area as said temperature increases.

2. A method according to claim 1 wherein the step of creating a sub-atmospheric pressure within said auxiliary conduit means comprises the steps of communicating to said auxiliary conduit means a vacuum of a magnitude generated in accordance to the velocity rate of air flow through said variable venturi means, and variably venting such communicated vacuum generally in accordance with the degree to which said variable venturi means is moved toward a more nearly closed condition.

3. A carburetor for an internal combustion engine, comprising a carburetor body, induction passage means formed through said body for communication with said engine, variable venturi means situated in said induction passage means effective for defining a variably openable venturi throat, a fuel reservoir, variable restriction means in combination with auxiliary passage means communicating between the fuel within said fuel reservoir and said induction passage means, said auxiliary passage means communicating with a source of vacuum generated by the flow of air through said variably openable venturi throat as to thereby cause a pressure differential across said fuel resulting in the flow of auxiliary fuel through said auxiliary passage means, first additional means operatively connected to said variable restriction means to make said variable restriction means effective to vary generally in accordance with a parameter of temperature the rate of flow of said auxiliary fuel through said auxiliary passage means caused in response to the magnitude of said vacuum, and second additional means responsive to the opening and closing of said variably openable venturi throat for varying the effective magnitude of said vacuum communicated to said auxiliary passage means.

4. A carburetor for an internal combustion engine according to claim 3 wherein said first additional means comprises temperature responsive means.

5. A carburetor according to claim 3 wherein said variable restriction means is situated generally in said auxiliary passage means and comprises an aperture of fixed dimensions cooperating with a variably positionable valving member.

6. A carburetor according to claim 5 wherein said aperture of fixed dimensions is situated generally between said induction passage means and said fuel.

7. A carburetor according to claim 3 wherein said variable restriction means is situated generally in said auxiliary passage means and comprises an aperture of fixed dimensions cooperating with a variably positionable valving member for variably controlling the effective flow area of said aperture, and wherein said first additional means comprises temperature responsive means operatively connected to said valving member.

8. A carburetor according to claim 7 wherein said temperature responsive means comprises a bimetallic member.

9. A carburetor according to claim 3 wherein said second additional means comprises variable venting means operatively communicating between said auxiliary passage means and a source of substantially atmospheric pressure.

10. A carburetor according to claim 9 wherein said venting means comprises fixed aperture means cooperating with movable valving means, said movable valving means being effective to vary the effective flow area of said fixed aperture means.

11. A carburetor according to claim 10 wherein said movable valving means is operatively connected to a movable portion of said variably openable venturi means.