US2425885A - Centrifugal compressor - Google Patents

Description

All@ 19, 1947 vl. c. JENNINGs A CENTRIFUGL COMPRESSOR Aug. 19, 1947.

l. C. JENNINGS CENTRIFUGAL COMPRESSOR Filed July 16, 1943 4 Sheets-5h00?. 2

M ,M J. 0 G. w W I Y AWN. \\W\\ a um l QN. ,0N .N |N\ f/ttorney l. C. JENNINGS CENTRIFUGAL COMPRESSOR Aug. 19, 1947.

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Filed July 16, 1943 Aug. 19, 1947- c.JENN|NGs 2,425,885

CENTRIFUGAL COMPRESSOR Filed July 16, 1943 4 Sheets-sheet 4 Inventor TRW/v6 aJav/v/A/Gs,

n Hfjorney Patented Aug. 19, 1947 UNITED STATES PATENT vOFFKIIE'.

v CENTRIFUGAL COMPRESSOR y Irving Callender Jennings, South Norwalk, Conn. Application July 16, 1943, seria1N0.495,o47

13 Claims.

This invention relates generally to a centrifugal compressor designed for an airplane cabin supercharger. It will ,be understood that the same device could readily be used for supercharging an internal combustion engine or generally for compressing air or producing a vacuum.

Centrifugal compressors for air or gases have the advantage of simplicity, compactness, and durability. Their design, however, heretofore has been limited to conditions where low pressure diierentials were required, except in large capacity, multi-stage units, which are heavy and cumbersome. This made them unsuitable for supercharging airplane cabins for higher altitudes, where a relatively small amount ofair at a relatively high differential pressure had to be handled. Also, for such applications this type of compressor requires an elaborate, cumbersometype of control to take care of the varied conditions resulting from the great change in density of the air when the plane is near the ground or when it is operating high above the earth.

One of the principal objects of the present invention is the construction of a centrifugal compressor and control which obviates all of the disadvantages above set forth.

The present invention consists of a centrifugal compressor and control capable of handling small amounts of air at a relatively high differential pressure, It is very compact and requires very y little horse power to operate.

These results are accomplished by the use of a small diameter impeller running at a much higher speed than has heretofore been thought possible. This makes the compressor very small and light and adds 'greatly to its efficiency, as the unavoidable leakage and the skin friction or drag of the impeller is greatly reduced due to its small diameter.

In order to run at these high speeds the impeller must be absolutely symmetrical. It is made of the strongest and lightest material, with both blade and central web sections narrowed from the hub to the periphery to develop uniform strength to resist the high centrifugal forces present. It is preferably of the open type, with radial blades in close running relation to the casing.

The impeller is preferably mounted on a shaft supported by ball bearings on each end. These bearings, and the high speed gear, are provided with novel means for cooling and lubrication to permit running at the extremely high speed required. Y

To obtain the high impeller rotation necessary,

ing an overall speed-up ratio in the order of say 25 to 1, or an impeller speed of approximately 70,000 revolutions per minute when the diameter of the impeller is about 41/2" and the main drive is running at about 2800 R. P. M.

Part of 'the invention resides in the vtype of speed control provided, which consists of a. hy-

'draulic coupling, known to* the art as a uid drive, mounted on the intermediate shaft or the high speed shaft and provided with an automatic device built into the compressor casing which alters'the speed of the compressor inversely as the density of the 'air'handled by regulating the fluid'level inthe coupling. This uid coupling has a. damping effect on thek vibrations set up by the high speed gearing land allows a greater degree of misalignment.

Oil pressure for operating this control, includt ing the supply of oil to the interior of the fluid coupling to restore the liquid level in the coupling and to take care of leakage through the seals and to lubricate and cool the bearings and gears, is supplied by. an oil pump, preferably mounted directly on the low speed or main drive shaft.

In an airplane, wherevibration is always present and reliability is very important, separate oil pipes and pipe COllplings are to be avoided. The invention is designed .without any ofthese appendages. The lpassages for oil andthe passages to transmit the cabin air'pressure to the control are drilled or cast in the structure and matched at the joints to form through conduits. 'I'here is no danger of compressor failure due to broken auxiliary piping. The design is suchthat the various parts of kthe casing can be readily disassembled.

In the drawings wherein like reference numerals and Fig. 2, showing details of the automatic control device. y

Fig. 5, along the lines m-m Fig. 3; Fig. 6, along 3 the lines a-g Fig'. 3; Fig,j.7, along the lines e-e Fig. 4; Fig. 8, along the lines It-.ty Fig. 4: and Fig. 9, along the lines l-lffFig.3, show details of the control and the control and lubricating piping.

Fig. is a. section through the fluid coupling along the lines j j, Fig. 1.

Figs. 11 and 12 are sections through the uid coupling along the lines f-f, Fig. 2, showing different positions. of the oil level regulating scoop.

Fig. 13 is a section through the lubricating oil pump along the imesh-ffm Fig.l l.

Fig. 14 is a view of the impeller in perspective, illustrating the construction'of `axial and radial blades.

Fig. 15 is a view of one blade of the. impeller showing the curved section.

In the drawings, A is used to indicate the cen-A trifugal compressor; B the intermediate structure containing the speed control and part of the uid drive, and part of the speed-up gearing; C and D are the structures containing the remainder of the gearing., the lubricating pump, and the main drive shaft S. I (Fig. 2) indicates the air inlet, and O (Fig.3) the air discharge.v

I is the impeller, preferablydouble suctionf splined and mounted on the shaft 2, which is supported by ball bearings 3'and'4. It revolves in a close fitting surrounding casing expanding into a volute passage 5 terminating -in the discharge pipe O. The impeller is driven'through step-up vgearing from main drive shaft S, which may be connected to an engine of the airplane or to other prime mover. The shaft Sis supported by ball bearings 6 and 1. On this shaft is mounted a gear 8, which meshes with a pinion-ll'r on an intermediate shaft I0. This shaft, supported by suitable bearings, is connected throng-hv afluid drive coupling I I to a shaft I2, also supported by bearings, on which is mounted a gear I3 meshing with the pinion I4, which is preferably machined directly on the shaft 2. x

The impeller is shown in section in Figs, 1 and 2; in the end view Fig. 3; in perspective in Fig. 14, and one of the blades is shown enlarged in Fig. 15. It will be noted that the impeller is perfectly symmetrical both around its transverse and longitudinal central axes., The central web I5 and the radial blades heavy in section near the hub land are then gradually curved to a narrow width at the periphery so as to equally stress `all parts of the impeller when it is subjected to centrifugal force. 'I'his makes the most economical use of material. By making the web and blade sections narrow at the periphery, their weight at this point isreduced, which greatly `reduces the centrifugal force, which, with the heavier'blade section near the hub, gives the necessary strength and permits the impeller to be run atextremely high speed. The impeller is preferably madeof ya very light. strong material such as Duralumin, forged to obtain the greatest strength,and then machined to the proper shape.

The impeller is further Vprovided with axial blades I1, which form inlet openings of equal area on each side of the impeller. These blades are shaped to form an acute angle with the direction of rotation to scoop in the air without shock and arethen curved to smoothly match the radial blades of the impeller. This double inlet eliminates axial thrust and permits smalldiameter inlet openings relative to the diameter `of the impeller, which adds to the efficiency,

I6 v are 4made relatively 4 The axial blades and the radial blades are closely surrounded by the casing, the walls of which are gradually curved and tapered to form passages I8 to conduct the air with a minimum loss of head smoothly through the impeller into the volute 5.

The axial fblades are shown as separate pieces splined to the shaft 2 and clamped against the impeller by means of the nut i9 through bushings 20, the inner races of ball bearings 3 and 4, and av shoulder 2I of the shaft 2. It will be readily understood, however, that the axial blades could be integral with the impeller.

The operation of the fluid coupling Il will be readily understood from Figs. l, 2, 10, 11 and 12. It consists of a. driving member 22, which is preferably mounted on the intermediate shaft I 0, and a driven member 23, which is mounted on the shaft I2. Members 22 and 23 are separated from each other only by a running clearance and their axes of rotation approximately coincide. Each member is provided with radial blades 24 forming buckets 25, with curved bottoms. When the coupling is filled with liquid and the driving member 22 is rotated rapidly, the liquid acquires the velocity of the driving member and liquid is circulated by centrifugal force around the bottom of these buckets into the buckets of driven member 23, causing this member to acquire a velocity approaching that of the driving member. Under these conditions the coupling is transmitting the maximum power, and very little slip occurs between the driving and driven members. If the liquid is partially removed from the coupling when under load, the driven member will run at a slower speed thanthe driving member, the difference in speed depending on the amount of liquid removed. When all the liquid is removed no motion will be transmitted between the driving and driven member. I'his action of fluid couplings, which is well understood in the art, is used to control the speed of the compressor.

The horsepower output of a fluid coupling varies about as the cube of the speed. By placing this coupling on the intermediate shaft or on the high speed shaft, both of which are running at high speed, the size of this coupling is greatly reduced. K

Oil is the preferred liquid to use in the fluid coupling as it is non-corrosive and may also be used to lubricate the moving parts.

Details of the control are as follows: Oil is fed into ,the interior of the coupling continuously in a small amount through an orifice 26 and the hollow shaft I Il. A curved pipe or scoop 21 is mounted on a hollow shaft 28, which is journalled in a stationary housing 29. On the shaft 23 is xed a segment of gear 30, which is in engagement with a rack 3i. The rack 3| is attached to a piston 32 in a cylinder 33 and is supported 0n the other end by a bearing 34. 'I'he piston 32 is raised fby oil pressure and is lowered by the spring 35 when the oil pressure is released. The oil pressure is regulated by a valve 36 controlled by automatic means responding to the absolute pressure in the cabin. Reciprocating the piston up and down causes the end of the scoop 21 to move in and out from the center of the coupling.

The scoop, being connected to hollow shaft 23, will remove any liquid in the coupling as long as its end is submerged, because it is stationary and is presented at an angle to the rapidly revolving liquid inl the coupling. An orifice 38 is provided in the end of the scoop to limit the rapidity with which the liquid is removed.

1n Fig. 11 the scoop is shown at its position nearest the center, where it has the least scoopV would continue to remove a certaincoupling hub and the Astationary piece 29, and 4l" along the bearing clearance of the hollow shaft 2B. Under this condition the coupling develops its full power and the compressor is running at its maximum speed. The automatic means for thus regulating the speed of the compressor, in addition to the oil control valve 36, consists of the following parts. All of these parts are mounted on detachable part 42 of the casing B so that they can be readily removed for repair or replace-v ment. Above the valve 36 are fixed two flexible Ibellows 43 and 44, separated by a plate 44'. A plate 45', fixed to the plate 44 by three posts 46', rests on the valve stem 41' of the valve 36.

The bellows 43 has been exhausted of air so that its interior has a pressure of approximately zero absolute. The bellows 44 is connected through passages 45, 46 and 41 (Figs. 3, 4, 6 and 9) to the discharge O of the compressor, which in turn is connected to the supercharged cabin. The force exerted by the bellows 44 in pounds will be substantially the absolute pressure of the supercharged cab-in times the area of the end of the bellows, as this area is relieved of all pressure by the bellows 43.

Springs 48, the tension of which may be adjusted by the nuts 49, compress the bellows 44 against the absolute cabin pressure, and if this pressure is insufficient the control valve 36 will. be opened by oil pressure from a pump or other source of supply and oil under pressure will be built up in the cylinder 33. Piston 32 will be forced unwards, the scoop 21 will be retracted from the periphery of the coupling, oil coming in through the discharge nozzle 26 will rapidly fill up the iiuid drive Il, which will then have less slip, the compressor will increase in speed, and more air will be delivered.

When the cabin pressure rises to the predetermined amount, the bellows 44 will be lexpanded and the plate 4-5 will force the value stem 41 against its seat, and the valve 36 will be closed. Leakage between the piston 32 and the cylinder 33 will permit the spring 35 to force the piston downward, which will extend the scoop 21 out further toward the periphery of the coupling. The oil will be scooped out of the revolving coupling by the scoop 21, and the compressor will slow up and furnish less air.

An arm 56 xed on a shaft, to which isfastened a lever 5l, is provided to increase manually the tension of the springs 48, if it is desired to increase the air discharge of the compressor, Stops 69 are provided to limit the travel of the lever 5I.

The oil under pressure for operating the piston 32 for the continuous supply to the interior of the fluid coupling and for cooling and lubricating the bearings and gears of the compressor, is supplied by a special oil pump 52 (Figs. 1 and 13). It is shown preferably as a gear type pump mounted directly on the slow speed main drive shaft S. It takes its oil from the bottom of the gear casing through an inlet passage 53 and discharges the oil under a moderate pressure into the passages 54 and 55. Passage -54 opens directly into the passage x56, whichV connects through a passage 58 to a passage running right through the compressor. The passage 58 conducts the oil into passage -59 and 60 (Fig. 7) into orifices 6I and 62, which furnishes a spray of oil directly on the cages of the ball bearings 3 and 4, and to the orifice 63, Figs. 1 and 4, which sprays the oil on to the high speed pinion I4'.

The oil passage 60,-, is preferably formed in a post which is attached to one side of the cylinder 33, both post and cylinder being cast integral with the casing B. This construction provides a rigid support for the orifices 6 IV and 63.

The passage also connects to the passage y54, (Figs. 4, 7 and 8), which supplies the oil to the speed control valve 36'.

A relief valve- 65 (Fig. 8), is provided to keep the oil pressure constant. The excess oil not used for lubrication and other purposes is discharged, falls to the bottom of the casing, and is returned to the suction of the oil pump.

Passages 55 and'66 (Fig. 1) conduct the oil to the oriice'26, which discharges it through a passage 61 in the center of the intermediate shaft l0 into the liuid coupling I l, to keep the coupling supplied continuously with oil.`

The oil which is being returned from the fluid drive and from the orifices. to lubricate and cool the bearings is all returned to the bottom of casing B, Fig. 1, and is again circulated by the gear pump 52. The passage 68 (Fig. 5), shows the means of returning the oil used to lubricate the bearing 4. Itis understood that jets could be provided for the lower speed bearings and gears, but in view of the fact that there is a mist of oil continually present due to the spray being thrown by the high speed gear and from the oil returning from the fluid drive, this may be dispensed with.

The oil in the bottom of the casing is kept away from the-gearV 8' by a projecting wall 69 in the casing D' (Figs. l, 2 and 13), which maires a joint withv the casing C, then extends up above the center line of the gear Dump as shown in Fig. 13. This forms a trough around the lower part of the gear 8' and prevents thegear' from throwlng oil around the casing, and thus allows a deeper well of oilin the bottom of the casing.

While the valve 36 is shown as being automatically controlled by the absolute pressure in the cabin, it willl readily be understood that it could be controlled by the volume or weight of air being handled by the compressor or by the absolute pressure of the inlet air or a combination of any of these, or otherv means, to satisfy some diierent condition.

Having thus fully. described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. The combination with a high speed centrifugal compressor, of a drive means therefor including a fluid coupling, pump means Afor continuously supplying the fluid coupling with fluid to compensate for leakage, and scoop means controlled by the pressure delivered by said compressor for removing fluid from the coupling in varying amounts to produce slippage for regulating the output Vof the compressor, said scoop means being independent of'sald pump means.

2. The combination with a high speed centrifugal compressor and a drive means therefor including a fluid coupling, of pump means for continuously supplying fluid `to said coupling, and

pressure controlled means separate from said pump means for removing fluid from the coupling automatically in varying amounts to proa bellows in communication with the discharge duce slippage for regulating the output of the side of the compressor, and an adjustable scoop compressor, said pressure controlled means inseparate from said pump means and automaticluding a bellows in communication with the discally controlled by said bellows for transferring charge side of the compressor, an adjustable motive uid from said coupling to vary the slip scoop automatically controlled by s-aid bellows in said coupling, and thereby vary the output for transferring fluid from said coupling, said speed of said coupling.

scoop being in the form o1' an arcuate tube hav- 7. In a unitary supercharging assembly including its discharge end pivotally mounted adjacent ing a driven shaft housing, a drive shaft housing, but to one side of the center of the coupling l0 and an intermediate shaft housing, a high speed whereby its inlet end is movable from a position centrifugal compressor mounted in the .driven adjacent the periphery of the coupling to aposishaft housing, a stepup power transmission for tion adjacent the center thereof, means for opersaid compressor including a iluid coupling and ating said scoop, said last mentioned means being gearing in the intermediate .shaft housing, means controlled by the pressure delivered by said comincluding a pump in the drive shaft housing for presser. supplying oil under pressure to said gearing to -3. 'Ihe combination with a high speed centriflubricate said gearing, and to said fluid coupling ugal compressor and a drive means therefor in t0 furnish Working liquid thereto. and means cluding a fluid coupling, of pump means for ccnbuilt into said housings and controlled autotinuously supplying fluid to said coupling, and matically by duid conditions at the outlet of said means controlled by the pressure-delivered by the compressor for automatically Controlling the compressor and separate from sai-d pump means amount of oil in said coupling independently of for automatically removing uid from the cou- Said Dump, whereby the slip in sald coupling is pling in varying amounts to produce slippage for regulated and the speed of said compressor is regulating the output of the compressor, said Valued.

pressure controlled means including a bellows in 8- 111 a 'Unit-'Hy Supercharglng assembly incommunication with the discharge side of the cluding a driven shaft houslng, a. drive shaft compressor, an adjustable scoop controlled autohousing, and an intermediate shaft housing, a matically by said bellows for transferring uid high Speed Centrifugal COmDIeSSOI mounted in from said coupling, said scoop being in the form th? Ciriven Shaft housing, a step-up power transof an arcuate tube having its discharge end pivmlsslfm for Said FOmlJfeSSOI including a fluid otally mounted adjacent but to one side of the' coupilng and geffmg 1n the intermediate Shaft center of the coupling whereby its inlet end is housing' leans mcluding a Dl'lmD 1H the drive movable from a position adjacent the periphery Shaft housing for Supplying 011 under pressure of the coupling tions at the outlet of said compressor for remov 'l from said coupling in varying amounts to 4. In a unitary supercharging assembly includmg 01 mg a driven shaft housing' a drive Shaft housing 40 produce slippageulby; ivhich the output of said and an intermediate shaft housing. a high speed compressor is reg a e 9. In a. unitary supercharging assembly intr fu com r or ounted -in the driven szleift1 hilsing Isteisaup Igearing for said comcluding a' driven .Shaft musing a' drive shaft said compressor for regulating the'eflective voli ume of uidm said ud coupling shaft housing for supplying oil under pressure to said gearing for lubricatio and to said fluid 5 The combination with a' hlgh speed centnf coupling as a working liquid, said means including s, hollow post formed integrally with the intermediate shaft housing, and having discharge transmission means between said drive shaft, and Onces adjacent unit/S of said gearing' and means said impeller shaft, and including a fluid coupling, a casing for said power transmission means adapted to contain motive liquid for said coupling, a pump operated from said drive shaft for pumping the motive liquid fromsaid casing, cono said pump to continuously supply motive liquid to said fluid coupling, and means independent of said pump controlled bythe pressure at the outlet 0f Said 9011119195501' f?? automatically Contr 011mg 65 gearing, a pump driven from said drive shaft for the Slip m '.Sald Coupling t0 Vary the Output Speed supplying motive oil tc the working chamber of 0f Said COUDling said coupling, and to said gearing to lubricate 6. Thecombination with ahigh speed centrifsaid gearing, and means for controlling the ugal compressor and a drive means therefor inamount of motive liquid in said coupling autocluding a uid coupling, of pump means vfor C011- 7 0 matically according touid conditions at the inllOUSly Supplying motive fluid to sidolipllng, outlet of said compressor to vary the output and pressure controlled means for 'removing fluid Speed of Said compressor.

from the coupling in varying amounts to produce 11. In combination, a high speed centrifugal slippage for regulating the output of the comcompressor including an impeller, a shaft for pressor. said pressure controlled means including said impeiler and bearings for said shaft, a drive of the coupling to a position adjacent the center i 35 to said gearing to lubricate it' am] to said uid shaft, a power transmission between said drive shaft and said impeller shaft including a fluid coupling, a pump driven from said drive shaft for continuously supplying motive oil to the working chamber of said coupling, conduit means leading from the outlet of said pump for delivering oil to said bearings to lubricate said bearings, and means automatically controlled by uid conditions at the outlet of said compressor for regulating the amount of liquid in said coupling independently of said pump to vary the slip in said coupling, and thereby vary the speed of said compressor.

12. In combination, a high speed centrifugal compressor including an impeller, a shaft for said impeller and a pair of spaced bearings for said shaft, a drive shaft, a power transmission between said drive shaft and said impeller shaft, including a fluid coupling and a transmission gearing, a pump driven from said drive shaft for supplying motive oi-l to the working chamber of said coupling, conduit means leading from the outlet of said pump for delivering lubricating oil to said transmission gearing and to said shaft bearings to lubricate said gearing and said bearings, and means automatically controlled by the pressure at the outlet of said compressor for regulating the amount of liquid in said coupling independently of said pump to vary the slip in said coupling, and thereby vary the speed of said compressor.

13. In combination, a high speed centrifugal compressor including an impe1ler a shaft for said impeller and bearings for said shaft, a drive shaft, a power transmission between said drive shaft and said impeller shaft including a fluid coupling and a transmission gearing, a pump driven from said drive shaft for continuously supplying motive oil to the working chamber of said coupling, means leading from the outlet of said pump for delivering oil to said bearings and to said gearingto lubrica-te said bearings and said gearing, an adjustable scoop for transferring motive ,oil from said coupling, said scoop being in the form of an arcuate tube having its discharge end pivotally mounted adjacent, but to one side of the center of the coupling, whereby its inlet end is movable from a position adjacent the periphery of the coupling to a. position adjacent the center thereof, and means automatically operable in accordance with the pressure at the outlet of said compressor for operatingr said scoop about its pivotal support.

` navNG CALLENDER JENNI'NGS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,187,656 Kiep et al. Jan. 16, 1940 2,187,667 Sinclair et al Jan. 16, 1940 2,223,715 Berger Deo. 3, 1940 2,313,205 Potez Mar. 9, 1943 1,097,729 Rice May 26, 1914 1,865,918 Junkers July 5, 1932 2,261,463 Garve Nov. 4. 1941 1,859,607 Sinclair May 24, 1932 2,187,656 Kief et al. Jan. 16, 1940 2,289,440 Kugel July 14, 1942 FOREIGN PATENTS Number Country Date 378,754 Great Britain Aug. 18, 1932 497,779 Great Britain 1938 445,005 Great Britain Apr. 1, 1936

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