US2456886A - Apparatus for dry sump lubrication of engines - Google Patents

Description

E. A. Mom 2,456,886 APPARATUSA FR'DRY SUMP LUBRICATION 0F ENGINES 2 Shets-Sheet 1 De.21,194s.

Filed Oct. 12, 1945 Dec. 21, 1948. E. A. MORI APPARATUS FOR DRY'SUMP LUBRICATION OF ENGINES 2 Sheets-Sheet 2 Filed Oct. 12, 1945 gvwQ/HM ERNST A. MORI Patented Dec. 21, -1948 APPARATUS FOR DRY SUMP LUBRICATION F ENGINES Ernest A. Mori, Pittsburgh, Pa., assignor to Gulf Research & Development Company, Pittsburgh, Pa., a corporation oi.' Delaware Application October 12, 1945, Serial No. 621,886

(Cl. 18d-,6)

Claims. 1

This invention relates to improvements in 'engine lubrication systems o1 the dry sump type. 'I'hese are so called because the oil supply, instead of being retained in the crankcase as in conventional automobileA engines, is contained in a separate tank from which it is pumped tc the engine, and thence is continuously returned to the supply tank as rapidlyas it drains into the crankcase. Inasmuch as the crankcase is substantially dry at all times the engine is not susceptible to i'iooding and fouling when operating in tiltedvpositions. whereas engines of conventional type in which the oil supply is selfcontained must operate in horizontal position, or one not departing greatly from horizontal, to avoid such eiiects. Engines embodying dry sump lubrication, therefore, have especial utility in lthe eld of aviation because they do not impose limitations on the maneuverability of an airplane.

In order to withdraw the oil normally draining to the crank case, as well as to accommodate sudden surges tending to overrun the sump, the scavenge pump -is designed with a capacity of at least 21/4 times the normal oil requirement of the engine. Fluctuating drainage of oil into the sump may be due to any or all of several causes, such as variations in engine speed, maneuvering of the airplane which requires the engine to assume changing positions and inclinations, and by intermittent actuation of hydraulic control devices drawing their supply of uid from the engine lubrication system, as for example mechanisms for changing propeller pitch. Thus, since the scavenge pump must be designed with a capacity suilicient to keep the oil in the sump at a low level under all operating conditions, the pump intake will at times be partly or wholly uncovered. As a result the scavenge pump sucks air or gas along with the oil during a considerable period of its operation, and the air becomes mechanically entrained in the oil returned to the supply tank, due in part to the beater action of the pump on the oil-air mixture. This presents a hazardous condition, for at high altitudes the entrained vair bubbles expand in the intake side of the pressure pump supplying oil to the engine due to the high ratio of absolute pressure in the oil supply tank to the absolute pressure in the pump gear teeth. AAt high altitudes the flow of oil to the engineis reduced to the danger 'point or'belowrdepen'ding upon the amount of air-entrainment,i since the oil delivery of the pressure pump is reduced -supply tank which permit in proportion to the volume of air present in the gear teeth.

Various expedients have been adopted to minimize or avoid air entrainment in the lubricating oil, mainly by mechanical means such as arrangements of ybaiiles and compartments in the the bubbles to separate from the body of oil. Another solution, and one of much practical value, is disclosed in the patent to Bruce R. Walsh, No. 2,373,360- This comprises a main scavenge pump drawing from the bottom of the sump and of a capacity suflicient to keep the oil therein at a low level under normal conditions, yet with its intake always and the auxiliary scavenge without entraining air submerged, and an auxiliary scavenge pump drawing from a higher level, above the normal one, and separately delivering to the upper part of the supply tank. Thus, the main scavenge pump handles only oil7 regardless of variations in the amount of oil draining to the crankcase,

pump normally discharges air through a separate pipe into the supply tank above the oil level therein so that the air is vented to atmosphere Without mixing with the oil, yet upon undue rise oi' oil in thel sump the auxiliary pump is primed and assists in discharging excess oil back to the supply tank to return the sump level to normal.

Such a system requires separate lines oi piping between the main and auxiliary scavenge pumps,v respectively, and the oil supply tank. Military necessity dictates that the amount of piping be reduced to minimize the chance that this vital part of the operating mechanism of an airplane might be punctured by a bullet, and `in both military and civilian use it is desirable to eliminate, in so far as possible, a multiplicity o! pipes which, if they should break, could cause a complete failure of engine lubrication with disastrous' consequences. AIt is accordingly one of the principal objects of my invention to provide a dry sump lubrication system which incorporates main and auxiliary scavenge pumps both of which deliver to an oil supply tank through the same` pipe, yet

in the oil so delivered, lrrespective of a iluctuating oil level in the sump. Other and further objects will be evident from the following description and drawings, in which: Figure l is a partly diagrammatic view of one form of my invention embodying main and auxiliary scavenge pumps, and pressure pump, inline.

lFigure'i-is also a. partly diagrammatic view' -of a modified arrangement wherein the main tank over the curved scavenge pump is mounted inside the engine crankcase and is driven by a shaft geared to the main drive shaft for the auxiliary scavenge pump and the pressure pump.

Referring more particularly to the drawings and rst to Figure l thereof, an engine crankcese I is provided with a sump il inits bottom to receive oil draining from the engine bearings. The oil for lubrication is delivered from tank i2, through pipe i3 and pressure pump IS, and thence throughY pipe i5 to the engine. A main scavenge pump IB and an auxiliary scavenge pump il are mounted in line with the pressure pump it, andl all are directly driven by shaft le which projects through the crankcase. The inlet pipe I9 of the main scavenge pump extends into sump ii at a low point, below the normal oil level 2li whereas the inlet pipe 2i oi the auxiliary scavenge pump terminates in the sump above the normal level, as indicated at 22.

The main scavenge pump discharges through pipe 23 and through either the upper or lower branch pipes 26 and 25 to the top or bottom of the supply tank, depending upon the position of the two-wayy valve 26. Thus, during the warm.- up period for the engine, oil returned to the supply tank may be directed through the lower adjacent to the inlet of pipe i3, whereby more direct circulation Following the initial warm-up period it is usually desirable to adjust valve 2t so that oil returning to the supply tank hows through the upper branch where heat may be extracted Iby a heat exchange cooler 2l prior to its discharge into the surface of baille 28 which assists in eliminating any air bubbles from the sheet of oil flowing thereover, and avoids agitation of the main body of oil such as would cause bubbles of air to form in it.

At extremely high altitudes the effect of the will open and permit the oil to take an alternative path by-passing the cooler.

Any sudden surge of oil collecting in the 'sump and tending to overrun it is drawn by pipe 2i into the auxiliary scavenge pump and discharged pipe 3d into the stream from pump. When this occurs the single pipe 28 serves both main and auxiliary scavenge pumps.` Normally, however, since the inlet of the auxiliary scavenge pump is entirely pump only air. For reasons out it is undesirable to mix air with the main oil stream. My invention, therefore, provides a spring-pressed check Valve 8i of two or three pounds pressure in the branch pipe 36and a restricted lbleeder tube 32 between the auxiliary scavenge pump and check valve, and iesirably near the check valve, leading back into the crankcase. So long as the intake of the auxiliary scavenge pump is uncovered, air which is pumped will merely be discharged back to the crankcase through the bleeder tube, since its pressure will be insulcient to overcome the pressure of oil behind the check valve plus the spring pressure tending to hold the valve closed. If the oil should rise in the sump to the level 22, or higher, the auxiliary scavenge pump will immediately prime itself because of the air vbleed in the dis,l charge side, and thereupon the check valve will* the auxiliary oil stream will join but will be discontinued abruptly open so that the main one when a low level is restored in the sump.-

of the warm.oil is obtained.

iat

engine and a pressure TheA assembly of vFigure 2 is similar in its operation. Here, however. the main scavenge pump 33 is mounted inside the crankcase andy is driven by a short shaft 3i connected to the drive shaft 36 by bevel gearing 36. As in the previously described embodiment, the main scavenge pump discharges through a pipe 31 to a supply tank 38. through either an upper branch 39 or a lower branch lid, controlled by a two-way valve 4|. Here, also. the upper branch has a cooler 42 and valve controlled lay-pass A33, while the lower branch entering the tank opens adjacent to the pipe M which supplies the pressure pump d5.

The connection between' the auxiliary scavenge pump it and the main oil line, as shown, comprises a short connecting pipe t? in which a spring pressed check valve il@ is mounted and which normally closes the passage. Thus. when the intake pipe di) of the auxiliary scavenge pump is uncovered, air which is pumped cannot enter the main supply pipe and therefore passes back to the crankcase through a small bleeder tube 50 which communicates with the pipe di between the auxiliary scavenge pump and the check valve. When the oil in the sump rises suiciently, to be picked up by the auxiliary scavenge pump, however, the check ,valve will open under the increased pressure exerted on it and the auxiliaryoil stream will thereupon join the main stream as the same is discharged by the main scavenge pump. In both this and the preceding embodiment it is to be noted. that the bleeder tube is of such small bore that although air is effectively vented back to the crankcase, only a negligible amount of oil can return by this route, due to greater resistance to the passage of the more viscous liquid, so that this discharge of oil from the auxiliary scavenge pump into the main oil stream is not appreciably reduced.

What I claim is:

l.` A dry sump lubrication system for engines comprising an oil supply tank separate from the engine and a pressure pump delivering oil therefrom to the engine, a main scavenge pump having an inlet which is submerged in oil retained in the engine sump. an auxiliary scavenge pump having an inlet which is norm-ally. above the level of oil in the sump, a common discharge pipe for both the main and auxiliary scavenge pumps leading to said supply tank, a valved connection between the discharge of said auxiliary scavenge pump and said common discharge pipe, and means for bleeding oi air which is normally pumped by said auxiliary scavenge pump.

2. A dry sump lubrication system for engines comprising an oil supply tank separate from the pump delivering oil therefrom to the engine, .a main scavenge pump having an inlet which is submerged in oil retained in the engine sump, an auxiliary scavenge pump having an inlet which is normally above the level of oil in the sump, a common discharge pipe for both the main and auxiliary scavenge pumps leading to said supply tank, a valved connection between the discharge of said auxiliary scavenge pump and said common discharge pipe normally closing communication therebetween when said auxiliary scavenge pump discharges air but adapted to establish communication therebetween when oil is pumped, and bleeder meansfor relieving air pumped by the auxiliary scavenge pump when the vvalved connection closes communication with the common discharge pipe.

3. In a dr'y sump lubrication system including Y main and auxiliary scavenge pumps drawing from audace different levels in the engine crankcase and dissure pump returning oil from the supply tank to the `engine, the improvement comprising a. com mon discharge pipe for both the main and auxiliary scavenge pumps leading to said supply tank, a valved connection between the discharge of said auxiliary scavenge pump and said common discharge pipe adapted to establish communication therebetween only when oil is being delivered by said auxiliary scavenge pump, and a bleedeifor air pumped by said auxiliary scavenge pump when communication with said common discharge pipe is blocked.

4. A dry sump lubrication system for engines comprising an oil supply tank separate from the engine and a pressure pump delivering oil therefrom to the engine, a main scavenge pump drawing oil from the engine crankcase at a low point therein, an auxiliary scavenge pump drawing from a higher level normally above any accumulation of oil in the crankcase, a common discharge pipe for said main and auxiliary scavenge pumps communicating with said supply tank, a connecting pipe between the outlet of said auxiliary scavenge pump and said common discharge pipe, a check valve therein adapted to open under pressure of liquid discharged by said auxiliary scavenge pump and a bleeder tube communicating with said connecting pipe between the outlet oisaid auxiliary scavenge pump and said check valve.

5. A dry sump lubrication system for engines comprising an oil supply tank separate from the engine and a pressure pump delivering oil therefrom to the engine, a main scavenge pump drawing oil from a sump in the engine erankcase and having an inlet'which is continuously submerged, an auxiliary scavenge pump drawing from a higher level. normally above the oil level in the 'charging to a separate supply tank, and a pres- 4 sump, a common discharge pipe for both the main and auxiliary scavenge pumps leading to said supply tank, a connection between the discharge of said auxiliary scavenge pump and the said common discharge pipe, a spring-pressed check valve in said connection, said check valve being normally closed when air is discharged .by said auxiliary scavenge pump, and means providing a restricted passage extending from said connection at a point adjacent said check valve at the uP- stream side thereof to relieve air discharged from said auxiliary pump during normal operation, said check valve opening and establishing communication between said auxiliary scavenge pump and common discharge pipe at such times as the inlet of the auxiliary scavenge pump becomes submerged in oil and the auxiliary scavenge pump primes itself due to the presence of the restricted passage between Vthe pump and check valve ,through which passage the pump can exhaust Ithe air entrapped in its pumping members, due -to .the oil submergenee at the inlet. l

` ERNEST A. MORI.

REFERENCES CITED i The vfollowing references are of record in the ille of this patent:

UNITED STATES PATENTS

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