US2268807A - Aircraft fuel pump - Google Patents

Description

Jan. 6, 1942.

R. B. CURTIS AIRCRAFT FUEL PUMP Original Filed July 13, 1939 Z WI EWZQP' Russel! I'B. Cur h 5 Patented Jan. 6, 1942 AIRCRAFT FUEL PUMP Russell E. Curtis, Dayton, Ohio, assignor to Ourtis Pump Company, Dayton, Ohio, a corporation of Ohio Original application July 13, 1939, Serial No.

Divided and this application March 8, 1941, Serial N0. 382,315

3 Claims.

This invention is a division of my copending application, Serial No. 284,263, filed July 13, 1939, and relates to aircraft fuel pumps and more particularly to mechanism for maintaining at a constant value the pre-selected pressure on the discharge side of the pump.

Due to the fact that fuel tanks in aircraft are usually remotely located with respect to the fuel pump, it is inevitable that the various angles which the craft assumes in flying frequently alter the suction head on the intake side of the pump. Unless compensated for, this rise and fall in the suction head constantly influences the discharge pressure of the pump as regulated by the relief valve.

It is therefore an object of this invention to provide simple yet accurate compensating means whereby the negative loading of the relief valve due to increased suction on the low side will not affect. the pressure .on the discharge side for which the valve has been adjusted.

Another object of this invention is the provision of balancing means for a relief valve structure whereby variation in the suction does not add to or subtract from the forces tending to open the valve and therefore does not affect the discharge pressure of the fuel pump.

The novel features believed to be characteristic of the present invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organiza- (not shown) for rotatlvely supporting a rotor 26. The rotor is transversely slotted to slidably receive the three through blades 34, the cylinder bore and ends of the blades being so formed that the blade ends contact the cylinder wall at all points in their rotation. I

The cylinder 20 has slots 36 and 38 positioned to align with ports 40 and 42 in the body I2.

With rotation in the direction of the arrow '44, Figure 1, 40 becomes the suction port and 42 the discharge port, but by merely removing the screws (not shown) that connect the valve body I06 to the pump body I2 and turning the entire relief and by-pass valve structure through an angle of 180 on its vertical axis and reconnecting the valve and pump bodies, the pump will be adapted for rotation in a direction opposite to that of the arrow 44 whereupon 42 is the suction port and 40 the discharge port. No other change is required. Opposite hubs 48 are pipe threaded as at 49 for suction or discharge pipesas required. 4

A-suitable driving mechanism (not shown) is provided for driving connection with the rotor 26.

tion and manner of construction, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection withthe accompanying drawing, in which:

Figure 1 is a vertical cross-sectional view, with parts in elevation, of a fuel pump, illustrating the details of construction of th diaphragm and valve spring cup when the latter is at its lowermost limit of movement as taught by the present invention;

Figure 2 is a transverse cross-sectional view taken substantially in the plane of the joint indicated by the broken line IIII of Figure 1; and

Figure 3 is a fragmentary cross-sectional view of the diaphragm and valve spring cup arrangement similar to Figure l but showing the relation of parts when the cup is actuated to its uppermost limit of movement.

' As best shown in Figure l, the pump body I2 is bored intermediate its ends and concentrically supports the eccentrically bored pump cylinder 28 and is provided with front and rear journals The relief valve structure provided for maintaining the discharge pressure at a constant value is housed in the valve body I06 which is suitably secured to the pump body by means of screws or the like, and a valve head I08 secured to the main valve body I06 by the screws H0. 7

The relief valve proper is of the poppet type comprising the disk. II2 with stem II4 slidable in a hub I it of the main body I06, the disk being beveled at I I8 and having a corresponding angular seat in the body which divides the interior of the body I06 into a suction chamber I20 including all of the space above the disk H2 and a discharge chamber I22 below the disk.

Ducts I24 and I26 in the pump and valve bodies, respectively, connect the suction port 40 to the suction chamber I20, while ducts I28 and I30 in the valve body and pump body respectively connect the discharge chamber I22 to the discharge port 42.

- Depending from the valve head I08 into the suction chamber I20 is a long hub I32 internally chambered to contain a valve loading spring I84 and externally sized to slidably receive a valve spring cup I36, the bottom of which rests upon a small knob I38 on the upper side of the valve disk H2.

The valve spring adjusting means comprises an. adjusting screw I40 with a head I42 and a flange I44 intermediate the screw and head, the flange being of larger diameter than the headlower adjust! screw retaining washer Hi6 rests on a shoulder H03 and has a central opening through which the screw extends freely, the flange 5 resting on the upper face of the washer. The upper retaining washer I50 has a central o 'ng which passes over the screw head is 100: 'ld rests on the flange I44. A spring ring 452 is snapped into a groove at the upper edge of the Washer 551i, the groove being positioned to hold the two washers so spaced as to allow free turning movement of the flange I44 between them. A spring adjusting nut is tapped to fit the external threads of the screw I40 and has a peripheral key extending laterally into a keyway (not shown) on the valve head I08,

I not shown) similar to the key on the spring ad justing nut I56 and which extends into a keyway in the valve head I08 to hold the washer I50 from rotating.

The adjusting screw cap I10 when drawn against the spring to open the valve would be the discharge pressure, acting to raise the valve from below, plus the suction tending also to raise it but from above. Valves for use inthis situation are therefore provided with a balancing means whereby variation in the suction does not add to nor subtract from the forces tending to open the valve, and therefore does not affect the discharge pressure. The release valve balancing means herein provided comprises a diaphragm I14 of resilient synthetic rubber preferably with an intightly to the gasket I12, allows but a slight v clearance between the inside of the cap andthe' top of the locking bar W2 whereby the ba'ris retained in the notch in which-it has been placed as long as the cap is in position.

When an adjustment of the spring I34 is to be made, the cap IHi is first removed, then, by the simple insertionof a screwdriver into the slot I60, the locking bar I62 is made to rise out of the notch in the washer I50 and the screw may be rotated until the desired adjustment is obtained, whereupon the locking bar is pushed into the nearest notch and the cap I10 replaced. In a situation where it may be necessary to reach into close spaces to make this adjustment, the desirability of this simple manipulation is obvious.

Furthermore, where height is limited. as it is on pumps of this class, a small portion only of the available height is taken by the adjusting and locking means, leaving space for a longer and more flexible spring, whereby larger increments of adjustment may be made with smaller resulting variations in spring stress making the matter of adjusting for fine variation in discharge pressure not dependent upon skillful or careful manipulation of the adjusting means. The use of a longer and more flexible spring also results in less variation in the discharge pressure at the various speeds of rotation and rate of discharge encountered in the operation of aircraft.

Now, as is well known in the art, the suction head against which the pump operates varies from one instant to the next because of aircraft acceleration. or deceleration, or altitude, orthe fact that the fuel tank, when the aircraft climbs,

may be well below the pump. and when it dives it may be well above it, or vice versa, all depending upon the respective locations of the pump and tank. Consequently, if an ordinary springloaded release valve only were provided, this changing rise and fall of the pressure in chamber i520 would cause the discharge pressure to fluctuate, because of the sum total of the force acting ternal fabric layer (not shown) to give it additional strength. Around the edge of the central opening the material is thickened to provide a ring I16 around which the upper edge of the spring cup I36 is so closely rolled as to form an airtight joint at this point, and prevent the cup and diaphragm from pulling apart in operation.

The diaphragm is also made thicker at the outer edge to form the wedging ring I18, this ring and a small portion of the diaphragm being clamped between the valve body I06 and the valve head I08.

Since the material of the diaphragm is subject to cold flow under excessive pressure, the space between the body I06 and head I 08, which contains the outer edge, must be carefully made so thatwhen metal to metal contact of the body and head is made at I80, the diaphragm will be gripped tight enough to safely prevent pulling out under the suction pressure in operation, but not tight enough to cause cold flow.

The active portion I82 of thevdiaphragm is of U shaped cross section which loops downward between the outside of the cup I36 and the inner edge of the annular rib I84 in the body I 06.

Since the material composing the diaphragm swells'appreciably from gasoline absorption, the loop I 82 will drop downward more as the material swells. It will also be drawn upwardly farther as the valve rises to its maximum height. If then, the effective area of the diaphragm is to remain constant under both of these extremes, the sides of the U loop must be so supported as to maintain a constant width under all conditions.

This condition will be met when the drop in the loop I82 and the width of the rib I84 is such that the sides of the loop will be held parallel and to a uniform spacing with each other in all positions. In sucha structure, the effective area of the diaphragm will be constant for any valve lift and for any degree of swelling of the material, and the discharge pressure will be unaffected by these variations.

The relative positions of parts at the extreme limits of movement of the valve spring cup I30 are best illustrated in Figures 1 and 3.- As shown in Figure 1, the valve spring cup I36 is at its lowermost limit of movement in which it rests on the knob I38 of the valve disk I I2. In Figure 3, the valve spring cup I36 is illustrated as abutting the end of the chamber I86 in which it is in its uppermost limit of movement.

The diaphragm I14 is so shaped and positioned that the valve disk I I2 may rise to its maximum operating height a distance of approximately of an inch without causing change in the effective area of the diaphragm. The loop I82 of the diaphragm remains exposed to the suction chamher I20 as the valve disk H2 is raised and lowered. As the valve spring cup I36 rises, it effects a rolling action of the diaphragm loop I 82 in such a manner that the effective area thereof remains substantially constant.

the tapped opening I90, causing the fuel discharge pressure to increase directly with rise in manifold pressure.

Obviously, increased suction inthe chamber i20 will pull as much cup I36 as it does upwardly on the valve disk H2, and the valve closing pressure will be controlled entirely by the spring I34 independently of variations in suction heads A by-pass valve is usually incorporated in the relief valve body of the power pump of aircraft fuel systems, so that, in the event of sticking of the power pump rotor, or other powefmump failure, fuel may be forced through the power pump independently of its coupling elements, by means of an auxiliary hand pump provided for the purpose.

Heretofore, these by-pass valves have been made with ametal to metal seat, necessitating considerable initial spring pressure .to hold them closed when not operating, and have not been so placed as to provide the greatest freedom in the passages through them, whereby considerable hand pump efiort was required to overcome these innate resistances before hand pumping became effective. I

The by-pass valve I92 herein disclosedis of synthetic rubber to metal seat construction so that a very light spring holds it closed effectively against leakage, and it is so placed and its orifices so shaped, as to provide a substantially direct non-resisting passage for the flow of'the hand pumped fuel.

While the constructions of the locking arrangements for the adjustable spring, the rotary main pump and the by-pass valves have been described in more or less greater detail, it is to be understood that such constructions form no part of the invention claimed herein and are illustrated and described only for the purpose of more clearly definingtheir coaction in relation to. the adjustable spring cup and diaphragm. Any other types ofconstructions with the adjustable spring cup and diaphragm in a like manner may be used equally as well.

While a particular embodiment only of this invention has been illustrated, it will, of course, be understood that the invention should not be limited thereto, since many modifications may be made and, therefore, it is contemplated by the appended claims to cover all such modifica harder downwardly on the tubular portion said housing, a

which would coact 3 tions as fall within the true spirit and scope of the present invention.

I claim as my invention: 1. A diaphragm construction comprising a pair of spaced relatively movable members, a flexible diaphragm extending between the members and having legs adapted members and away from the members are moved-#relative to each other for maintaining the same exposed diaphragm area between the members for various relative positions of the members.

2. A diaphragm assemblycomprising a housing having a cylindrical inner wall, a cylindrical cup member slidable in said housing ,in spaced relation from said inner wall, a flexible diaphragm surrounding said cup member andbridging the space between the member and housing, said diaphragm having inner and outer marginal portions adapted to engage the cup member and the cylindrical wall respectively and to roll from such engaging position into bridging position between the housing and cup whereby theeffective exposed area of the diaphragm between the housing and cup remains constant for all positions of the cup in the housing while being defined by different portions of the diaphragm.

3. In a pump including a'housing defining a suction chamber between the inlet and discharge sides of the pump in communication with the inlet side of the pump, a relief valve in said housing betweensaid suction chamber and discharge side of the pump, and adjustable means for loading said relief valve, the improvements which comprise said housing having a tubular portion depending in said suction chamber into spaced relation from said relief valve and said being spaced from the walls of cup member slidably embracing said tubular portion and having a closed end between the adjustable loading means and,the relief valve, said loading means urxi-nz theclosed end of said cup against the relief valve, a flexible diaphragm surrounding said cup member and looped between the cup member and the housing to bridge the space therebetween. said div the housing and cup member for maintaining the same exposed diaphragm area'between the housing and cup member for various relative positions thereof.

' RUSSELL R. CURTIS.

to roll against one of then the other member as

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