US2470742A - Density responsive device - Google Patents

Description

VMay 11, 1949.

E. A. HAAsE :my

DENSITY RESPONSIVE yDEVICE Filed Ilarch 6, 1944 wf/v 50. rais R14-Hansa .IIIIIIIIII lll l ATTMIVEY Patented May 17, 1949 DEN SITY RESPONSIVE DEvICE Elmer A. Haase and Jay A. Bolt, South Bend, Ind., assignors to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application March 6, 1944, SerlalNo. 525,278

A 2 claims. (ci. zas-'92) A V type may, for example, be used in a carburetor to control theV area of the fuel metering orifice to thereby control the fuel/air ratio; or it may be used to modify the air metering differential pressure used in regulating the fuel flow to thereby vary the fuel ilow and consequently the fuel/air ratio; or it may be used in other ways to control the ratio of fuel and air being supplied by the carburetor to the engine.

An object is to provide a density-compensat-- ing unit of the single bellows or capsule type having certain features of construction which result in improved performance characteristics.

Another and more specific object is Ato provide a density control capsule or bellows embodying a valve element which will be automatically moved to a safety position in the event of bellows failure.

Other objects and advantages will become apparent in view of the following description taken in commotion with the drawings, wherein:

Figure 1 is a view. principally in substantially central vertical section of an injection-type carburetor having the improved control unit of the present invention operatively applied thereto;

Figure 2 is a transverse vertical section of the control unit of Figure 1;

Figure 3 is a top plan of Figure 2; and

Figure 4 is an enlargement of the lower por- -tion of Figure 2.

The construction of the improved control unit per se will iirst be described, next the method of filling the same, and finally its adaptation to, and operation in connection with the injection type carburetor` of Figure 1.

Referring particularly to Figures 2, 3 and 4,

` 2 Il, abutting at its lower end against a shoulder I2-b forming part of member I2 and at its upper extremity against the'- top transverse wall I5 of cap II. The spring Il prevents 4collapse of the bellows when the latter is evacuated, as will be more fully hereinafter explained.

A combined dash-pot piston and guide member I6 is inserted in an opening formed in the end wall I5 of cap II and has a ange Il secured in leak-proof relation thereto. IThe lower extremity I6a of the member I6 has a sliding fit in the cylinder i3 and functions as a dash-pot piston with respect to said cylinder and also as a guide for the bellows, The member I6 is formed with a ll port I8 which connects-with a cross-port IBa communicating with the interior of the bellows I0, the upper extremity of the port I8 being enlarged and internally threaded to removably receive a sealing plug I8b. The-body of the piston I6a is preferably formed with a relieved portion indicated at I9 to facilitate lubrication of the side walls thereof.

The top wall I5 of head or cap II may be provided with a plurality of fins 20 which render the device more sensitive to changes in temperature In that they expedite transmission of heat to the wall I 5 and thence to the interior of the cap, the latter preferably being fllled or partlyfllled with a temperature-responsive medium other than air in a manner to be described. s

At its lower extremity, the cylinder I3 is formed with one or a plurality of restricted ports 2|, whereby oil or other damping fluid is permitted to pass from said cylinder into the bellows and return when the bellows is compressed and extended and relative reciprocatory movement ensues between the piston and cylinder, to thereby more effectively damp vibration of the bellows.

The parts this fardescribed constitute a bellows assembly which is carried by a housing 22, the latter at its lower extremity being threaded into a supporting bushing 23 provided with a lock nut 24, said `bushing having a lower projection or boss 25 adapted to be threaded into a socket provided therefor in a stationary support, such as the deck or top wall of a carburetor, note Figure 1.

A valve member or needle 26 is carried by the movable end of the bellows, said needle at its upper end being' secured to an annular disc 21 which rests on a retaining Washer 28 removably held in place by a resilient snap ring 29 adapted to engage in a groove formed in the inner wall of the member I2. A plunger 30 is inserted in a bore formed in the upper extremity of the needle 26 and is normally urged against the bottom wall of the member I2 by a spring 30a, to thereby resiliently maintain the said valve in its assembled position and permit self-alignment.

The needle valve 26 is preferably of the slab type and is slidable within a sleeve 3| having a press t in a bore formed inl the central portion of bushing 23, the lower end of the said needle preferably being tapered or beveled and cooperating with a transverse port or passage 32. An overtravel by-pass port or slot 33 is formed in one side of the needle and functions as a safety means in the event the bellows should break, as will be more fully hereinafter described.

A lock nut 34 is threaded over the cap lIl and contacts the upper end of housing 22, to ensure against displacement of the bellows and coacting parts.

A seat member 35 is provided at the lower end of the boss and has an external annular groove adapted to receive a sealing gasket when the unit Yis mounted as shown in Figure 1.

The unit herein illustrated is of the venturivented type, and accordingly the bushing 23 is formed with air-inlet vents or ports 36 which communicate the bellows with the main venturi of the carburetor, calibrated ports 36a in the upper extremity of the bellows housing communicating the bellows with the air scoop. This places the bellows in pressure communication with the air flowing through the venturi as well as the air in c the region of the carburetor deck whereby the loaded, and its spring rate per given size or unit capacity are factors which have an important bearing on the temperature and density compensating characteristics and accurate metering of the unit. Theoretically, a bellows with no spring force or effect exerted at any time would Aresult in substantially similar internal and external pressures and travel of the needle valve or element controlled thereby in direct relation to density for any temperature, but from a practical standpoint, this cannot be achieved. In the present invention, a bellows is used having a relatively low spring rate` per unit capacity or for a given stroke of the bellows, and the errorv remaining due to spring eifect is offset by predeterminedA evacuation. By stroke is meant the axial travel or movement of the bellows to carry the needle valve over the range of movement it -must have to properly control the valve port. Spring rate of the bellows is influenced primarily by the number of active corrugation per given stroke, wall thickness of the bellows, and type of material from which the bellows is made. The stroke that a given size bellows will have under load is directly proportional to nthe number of active corrugations and inversely proportional to some power of wall thickness. In the example illustrated in Figure 2 of the drawings, the bellows has eleven active corrugations with side walls of beryllium copper of single ply thickness. However, when spring rate is reduced beyond a certain point, a problem presents itself in that the bellows tends to become unstable in operation, particularly during the time it passes from a state of expansion and begins to contract, as where it moves from a high to a lower altitude. To more accurately control the travel of the bellows, a larger quantity of oil-or other damping fluid is used than is the case with bellows having less flexibility. This has a stabilizing imiuence and has given satisfactory results.

Another important factor to be considered is the degree of evacuation of the bellows. According to the present invention, the bellows is evacuated at ground level barometer to an internal pressure equivalent to some external pressure which prevails at a relatively high altitude, for example, to a pressure approximating those prevailing at an altitude of 20,000 feet and which would be in the neighborhood of 14" Hg absolute pressure. Thus, when abellows evacuated in this manner is used for a control on an aircraft carburetor, up until the time external pressures drop to a certain point, the internal gas pressure of the bellows is less than the external pressure thereon. When so evacuated and with coordinated spring loading, the major part of the effective stroke of the bellows will take place while the bellows is in compression and the minor part while the bellows is in tension. This may be controlled by greater or less evacuation with' coordinated spring loading, depending upon the installation or the type of airplane to which the unit is adapted. As long as the bellows operates in a state of compression, the error introduced by spring effect is negligible. It should be understood,v however, that a spring-loaded bellows evacuated at ground level to a pressure corresponding to that existing at some particular altitude will not necessarily have an internal pressure equal to such altitude pressure when that particular altitude is attained, since the internal volume of the bellows is constantly changing with changes in altitude. Hence, the internal pressure might be materially less than external pressure at 20,000 feet altitude, and the point where internal and external gas pressure become equal be considerably beyond such altitude.

Evacuation coordinated with spring rate and oil flll must be maintained within certain limits, else the unit will have insufllcient temperature response and there will be increased error in this direction. Furthermore, evacuation beyond a certain point requires an unduly heavy spring to maintain the bellows in the desired state of compression at ground level barometer which introduces an error in density compensation in the region of low altitudes. Experiments have indicated a lower limit of pressure within the bellows at ground level of within the neighborhood of 10 Hg absolute pressure.

Instead of considering the degree of evacuation in terms of internal absolute pressures, it maybe given as the amount of internal depression. Thus with a barometric pressure of 29.5" Hg, an internal depression of 12.0 Hg would correspond to 17.5" Hg absolute internal pressure, an internal depression of 15.75 Hg to 13.75" Hg absolute internal pressure, an internal depression of 22.5 to 7" Hg absolute internal pressure, etc.

As far as the upper limit is concerned, here the line need not be so sharply drawn. Obviously, the less evacuation, the less will be the range of bellows travel in compression and the more the range of travel in tension.

When a bellows is evacuated as above set forth,

u it becomes necessary to prevent undue collapse thereof, or to` maintain it in a predetermined state of compression. This is accomplished by the spring I4, which should be of such strength as to maintain the bellows in the desired condition '5 with a certain quantity of dampingiiuid, pref- 1o eiably a good grade of petroleum oil. lA certain ratio of dampingfluid and temperature-responsive gasmust be observed. AThe amount of fluid determines the enclosed gas volume, and since oil (if used) is affected by temperature, it will 15 tend to give additional temperature compensation in the compression travel of the bellows and less temperature compensation in the extension travel of the bellows.

Figure 1 illustrates an adaptation of the im-H20 proved control unit to an injection type carburetor, only such parts of the latter being shown as will permit an understanding of the operation of the unit. Briefly, the carburetor comprises a casing or housing, generally indicated at 31, having a main venturi 38 and a small or boost venturi 39. Air pressure differential chambers are indicated at 49, 4i and fuel pressure differential chambers at 42 and 43. Chambers 49 and 4| are separated by a flexible diaphragm 44, while chambers 42 and 43 are separated by like diaphragm 45. A rigid wall 46 separates chambers A4l and 42 and also serves to support a fuel-inlet valve assembly mounted for reciprocatory movement in the center of the respective chambers and adapted to move in relation to the movement of the diaphragms 42 and 43 to open a fuel-inlet port, not shown, for admitting unmetered fuel into the chamber 43, from which it flows to a regulator section, also not shown, through various meter- 40 ing orifices, not shown, to a discharge nozzle 49. The chamber 42 is subjected to metered fuel pressure, or in other words to the pressure of the fuel posterior to the metering orifices. The fuel metering differential pressure is thus applied 45 across the diaphragm 45.

The chamber 40 is connected to the air scoop by means of impact tubes 5 i, annular chamber.52,

passage controlled by needle valve 26, and thence by way of passage 53; and chamber 4I is 50 connected to boost Venturi 39 by means of passage 54. When the engine is in operation,- air is drawn in through the air scoop and thence through the venturis 38 and 39 and a differential pressure is created between the throat of venturi 55 39 and the air inlet which, at constant entering air density, is proportional" to the square root of the quantity7` of air flowing. These respective pressures are transmitted to chambers 49 and 4l and create a net force on diaphragm 44 tending 60 to move valve `assembly 41 to the right, or in a direction to open the valve. If this force were unopposed, the valve would move to the extreme right; however, when the valve opens, fuel under pressure flows into unmetered fuel `chamber 43,

through the metering orifices, and thence to the discharge nozzle 49 from which it is discharged into the air stream flowing to the engine. The fuel metering differential pressure across the metering orifice resulting from or accompanying the flow therethrough, is transmitted to chambers 43 and 42, and acts upon diaphragm 45 creat` ving a force tending to move the fuel inlet valve to the left, or in a direction to close the valve,

thus opposing the force created on diaphragm 16 6 44 by the air dierentlal pressure. The valve will therefore adjust itself to a point of equilibtrolledy by the rate of air flow, and a constant mixture of fuel and air obtained.

For a more comprehensive disclosure of the in- Y jection carburetor disclosed in Figure l, referencermay be had to the copending application of Frank C. Mock, Serial N o.'202,206, filed April 15, 1938, Patent No. 2,390,658.

Since the venturi to air scoop differential pressure increases for a given mass rate of air flow upon decrease in entering air density, the differential pressure across diaphragm 44 will tend to increase thereby increasing the fuel flow 4and richening the mixture. In order to prevent such enrichment with increase in altitude, the carburetor of Figure 1 is provided with a. calibrated bleed 56 interconnecting chambers 40 and 4i which is substantially ineffective to vary the pressures in chambers 40 and 4I at such times as the needle 26 is an open position, as at ground level, but which becomes increasingly effective in reducing the pressure in chamber 40 as the density responsive needle 26 progressively restricts passage 55 with increase in altitude. Asa consequence, for any given mass air ow the needle 26 will so restrict passage 55 with variation in altitude that the differential in pressures across diaphragm 44 remains constant notwithstanding that the differential in the pressures at venturi 39 `and impact tubes 5| increases with decrease in entering air density. By this means, automatic altitude compensation is obtained and the richness of the mixture is unaffected by variations in altitude, as is desired.

For example, as the density of the entering air decreases, as by an increase in altitude or rise in temperature, the air differential created by the main and boost venturis increases for a given weight of air and tends toward enrichment of the fuel mixture. However, such decrease in density acts onbellows I0, which expands and causes the needle valve to lower and restrict passage 55, thereby reducing the differential across the diaphragm 44 and the fuel valve tends to close and regulate fuel flow in proper ratio to mass air flow. Upon an increase in density, as where the plane descends from a high to a low altitude, the reverse takes place. The fuel mixture is thus maintained at all altitudes at the i proper richness or value.

Bellows failure is very rare, but should such occur, the needle valve 26 will immediately be projected to the position shown in Figure 4, where instead of closing off passage 55 from passage 53,

and thereby greatly leaning the mixture, the slot emergency setting which will give the pilot time to ground the plane without engine failure due to severe leaning out of the mixture.

It will be noted that the heat transfer ns 20 are located at a point where maximum heat transfer is desirable, viz., in the region of the cap containing the temperature-responsive fluid or nitrogen.

Although the invention has been described with reference' to a particular embodiment, it will be understood that certain changes in construction and design as well as in the steps of the method could be adopted without departing from the scope of the invention `as defined by the appended claims.

We claim:

1. A density-responsive control unit for actuating a regulating element such as a needle valve in accordance with changes in pressure and temperature over a certain altitude range including a corrugated bellows having a; movable end, means connected to said latter end mounting said element, a cap at the opposite end of the bellows, supporting means to which said cap is secured, a hollow cylinder located centrally of the bellows and fixed to said movable end, a piston member projecting from said cap into said cylinder, said bellows being partly evacuated to an internal pressure corresponding to a pressure existing at an altitude well above normal ground level, a spring in said bellows encircling said cylinder and piston and functioning to sustain the bellows against abnormal collapse at ground level barometer due to evacuation, a damping fluid partly iilling the bellows and a temperature-responsive inert gas filling the space above the damping fluid, said cylinder beingported to the interior of the bellows to provide a dash-pot action during extension and contraction of the bellows.

2. A density responsive device for controlling .a valve arrangedto regulate the flow of a fluid through a port, including a corrugated bellows having a movable end and a relatively xed end,

meanssupporting said valve member from said movable end, said bellows being evacuated to an internal depression such that the internal gas pressure thereof is less than external pressures over a substantial portion of the altitude range,

spring means of such force as to balance the REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 897,730 Fulton Sept. 1, 1908 1,251,214 Fulton Dec. 25, 1917 1,477,277 Milker Dec. 11, 1923 1,752,116 Smith Mar. 25, 1930 1,802,848 Summers Apr. 28, 1931 1,934,548 Kellogg Nov. 7, 1933 2,088,954 Gregg Aug. 3, 1937 2,112,750 Price Mar. 29, 1938 2,116,802 Shivers May 10, 1938 2,129,499 Landon Sept. 6, 1938 2,155,950 Nallinger Apr. 25, 1939 2,214,236 Seldon Sept. 10, 1940 2,250,932 Kittler July 29, 1941 2 297,231 Lichte Sept. 29, 1942 2,307,724 Anderson Jan. 5," 1943 2,316,417 Gregg Apr. 13, 1943 2,352,058 Wood et al June 20, 1944 2,361,227 Mock Oct. 24, 1944 2,376,711 Mock May 22, 1945 OTHER REFERENCES Automotive Industries, June 15, 1941, pages 620-624.

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