US2344366A - Counterrotating supercharger - Google Patents

Description

Mmh14,1944.l VN, C, PME, 2,344,366

COUNTE RO'ITINGl SUERCHARGER Filed March 21, 1941 3 Sheets-Sheet l A NVE/1%'.

-March 14, 1944. v Y N, c, PRICE 2,344,366

COUNTER ROTATIING SUPERCHARGE Filed Marchl 21.v 1941 3 Sheets-Sheet 2 March 14, 1944. N. c. PRICE 2,344,366

COUNTER ROTATING SUPERCHARGER Filed March 21, 1941 s sheetssheet 5 atented Mar. 14, i944 I FFIC Y l2,344,366 COUNTERRDTATG SUPERCGER Nathan '0. Price, Hollywood, Calif., assigner to Lockheed Aircraft Calif.

Corporation',

.Bur-bank,

ApplicationV March zi, 1941, serial No. 384,539

(ci. 23o-131) Claims.

This invention relates to an improved centrifugal type of air compressor, or engine and pressure compartment supercharger, particularly .adapted to aircraft installations requiring a small volume of delivery at relatively high pressures.

In centrifugal compressors of this general type the tip speed of the impeller practically governs the pressure attainable, and is limited by the centrifugal forces generated in the material of the impeller. Such forces also prevent the use of other than straight radial vanes on the impeller. Thus for a high pressure and low volume impeller, an increase in its diameter requires a narrowing of the depth of the impeller to-maintain the same volume, and practical limitations, including eiliciency, limit such adjustments, so that a high shaft speed, approaching or exceeding 25,000 R. P. M., is common with small volume superchargers.

It is accordingly an object of this invention to provide an improved centrifugal compressor wherein the diffuser section is caused to'rotate counter to the rotation of the impeller. With this arrangement, the increased pressure rise, neglecting losses, will vary with the type of impeller. If the impeller is designed to produce all pressure rise in the diffuser section, the 'coun-` terrotation of the latter would theoretically be able to produce iive times as much pressure rise. In the more conventional case where half the pressure rise occurs in the impeller, the lcounterrotating diiuser would produce an additional two and a half times increase in pressure over a Xed diuser. Thesecomparisons are based on the assumption that the impeller tip speed is constant, the diffuser being rotated in the opposite direction at approximately the same rate of revolutions. y

The lower tip speeds resulting from the use of a counterrotating diffuser not only result in improved impeller form for a given pressure and volume, but reduce-the centrifugal stresses in the impeller and thus permit the use of curved and shrouded vanes built up rather than machined integral with the hub and disc.

It is accordingly an object of this invention to provide an improved supercharger of the centrifugal pump or compressor type wherein afgreatly increased pressure rise is obtainable at relatively low peripheral speeds of the impeller. I accomplish this result by rotating a diffuser elementv counter to the rotation of the impeller so that the \eiective peripheral speed of theimpeller isincreased to that corresponding to the relative motion between the diiiuser and the impeller, without increasing the centrifugal stresses in the rotating parts.

It is a further object of this invention to provide an improved and higher .pressure centrifugal pump or compressor wherein a diifuserenvelopes and rotates counter to the usual impeller,

the diiuser and impeller having a common drive and axis, which in one form may be a bevel gear drive with one driven member balanced against the other to *eliminate unbalanced forces in the drive.

It is also an object of this invention to providel invention will be apparent from the disclosures in the specication and the accompanying drawings.

This invention in its preferred form is illustrated in the drawings and hereinafter more fully described.'

In the drawings: l

Figure I is an inlet side plan or top view of a centrifugal supercharger embodying one form of the features of this invention; partly broken away to show the interior construction thereof.

Figure 1I is a section on the line II-II of Figure I, showing the step-up drive to the impeller and counterrotating diffuser.

Figure III is a fragmentary section of a larger engine supercharger embodying another form of step-up drive.

As shown:

An aircraft cabin supercharger has been chosen in Figures I and II to illustrate an embodiment of this invention, the particular supercharger being designed to pressurize a small cockpit for substratosphere ying, capable of delivering a maximum pressure of 5 to 6 pounds to the square inch. Since thevolume required is small, the example uses a 3% diameter impeller and a 41/2" diameter counterrotating diffuser, both driven at 27,000 R. P. M. through a step-up drive from a 10,000 R. P. M. motor. is therefore a high pressure low volume design, and it is to be understood that my invention can be adapted to other and widely varying requirements, including much higher capacity. A second example comprises an engine supercharger of much higher capacity, anda planetary gear drive has been shown therewith.

In Figures I and II a casing l0 and cover l I together define a centrifugal compressor housing The first example having a volute or snail type of collecting and diffusing 'passage I2 surrounding an impeller chamber I3, the passage I2 terminating in a cone type expansion outletl passage I4 which acts to convert a substantial part of the remaining velocity energy into pressure at the delivery end of the cone. An impeller I5 is axially journaled relative to the chamber I3 and has a counterrotating diffuser I'B coaxially journaled relative to the impeller I5.

The relatively small diameter of the impeller reduces the centrifugal forces in the material thereof to such an extent that the vanes I1 need not be machined from the solid impeller as radial members, as is necessary in conventional centrifugal compressors of this type, but instead can be separately formed of ,sheet material, with the most efficient curvatures and entrance angles, being assembled to the impeller disc by welding or furnace brazing. It also becomes practical to apply a shroud I8 in the same manner, which shroud reduces frictional losses, leakage, and eddy currents, thus further increasing the efficiency of the impeller. The diffuser I6 closely resembles the conventional diffuser, with vanes i9, but is mountedon a disc 20 for rotation in a direction opposite to the rotation of the impeller, so that if the two rotations are equal, the effect on the air leaving the impeller is to double the effective tip speed thereof, with a resulting increase in the pressure corresponding to the equivalent tip speed obtained.

The particular compressor chosen for this illustration was designed for supercharging a small cockpit in high altitude airplanes, the use requiring extraordinary precautions against contami-v nation of the air by the lubricating system of the step-up drive. Since the drive itself must have thoroughly adequate lubrication, the compressor is arranged at the top of a vertical drive shaft 26, so that the impeller and diffuser lie in horizontal planes, and the inlet to the impeller and housing is in the top surface of the cover II. Labyrinth seals 22, y 23 and 24 are formed between the diffuser and impeller discs and shrouds, and the mating surfaces in the case and cover, and a spaced screw pump type of seal 25 is provided between the inlet end of the impeller shroud and the central opening in the cover.

The impeller I5 is mounted on a shaft 26 embraced by a second shaft 21 on which the diffuser is threadingly mounted by means of an integral sleeve or hub 28;A the arrangement being such that a pocket is formed for an oil slinger 29 on the shaft 26. A ball bearing 38 supports the hub 2B from the housing I0, and a bevel gear pinion 3i is formed on the shaft 21, serving as an abutment for one side ofthe inner bearing race, the other side of the race clamping an oil slinger 32 against a shoulder on the hub 28. A second bevel gear pinion 33 is splined to the shaft 26 below the shaft 21 and carries a ball bearing 34 on an extension sleeve 35, the bearing 34 being supported by a diaphragm 36 forming the top of an oil reservoir 31 screwed into the bottom of the housing I0. The pinions- 3l and 33 are diametrically disposed relative to a. driving bevel gear 38 and are therefore driven in opposite directions thereby, also balancing the load thereon. The gear 38 is supported in a ball bearing 39 in a spacing housing 40, a hub 4I integral with the gear 38 beingin splined driven engagement with the shaft 42 of an'electric motor 43.

A positive circulation of lubricant from the reservoir 31 is provided by a threaded 'extension 88 of the shaft 26, which projects into a threaded pocket 69 in the reservoir and acts as a screw pump to pump oil from the reservoir through a passage 10 in the shaft 26 where it is discharged between the two shafts in the-neighborhood of the upper ball bearing `3l). Part of the oil works down between the shafts and to the pinion gear teeth through holes therebetween, while part works up the shaft 26 to the oil slinger 29 thereon, and thence is thrown outwardly through holes in the diffuser hub 28 and oil slinger 32 to pass through the upper ball bearing 30.

The gear chamber is exteriorly ventilated to prevent the pressure effect in the diffuser from working back into the gear chamber and thus forcing oil up the shafts into the suction areas of theimpeller and diffusez'. This venting comprises an airport 44 in communication with an annular groove 45 surrounding the sleeve or spacer 48, which sleeve has a series of perforations 46. The groove 45 is also in communication with the gear `chamber by means of a passage 41.

The second form of supercharger shown in Figure III is designed for supercharging an engine at high altitudes, and, therefore, requires a much higher volume of delivery to maintain engine power at such levels. An impeller 48 and diffuser 49 are carried by coaxial shafts 5D and 5I, the impeller shaft 58 having a sun gear 52 of a planetary gear set, while the diffuser shaft 5I carries an internal gear 53, planetary gears 54 meshing with both the sun and internal gears and being journaled on a stationary spider 55. The engine crankshaft 56 is fragmentarily shown at the top of the figure as driving an intermediate shaft 51 through step-up gearing 58 and 59, the shaft 51 in turn having a gear 60 engaging peripheral teeth 6I on the rim of the internal gear 53. The described planetary gear step-up rotates the diffuser shaft 5I in one direction while the sun gear and impeller shaft rotate in the opposite direction at increased speed. As an example, re-

ferring to crankshaft speed as unity, the diffuser may make 5.7 turns in one direction while the impeller turns 14.3 times the other way, the relative movement of the adjoining surfaces resulting in an equivalent impeller peripheral or tip speed of 1,390 ft. per second at rated engine speed.

In this form of my invention, lubrication of the gearing can utilize a pressure connectionv to the4 engine oil system at 62, which feeds oil along a central passage 63 in the impeller shaft 50, branch passages 64 leading to bushings 65 in the planetary gears 54, and other branches 66 feeding to the diffuser shaft 5I and thence to the front bearing 61.

It will thus be seen that I have invented an improved centrifugal compressor or supercharger wherein high pressures are attainable in small Vvolume and light weight assemblages, and in which the impeller tip speed can be held to safe values, involving lower gear ratios and greater freedom from trouble.

Having thus described my invention and the present preferred embodiments thereof, I desire to emphasize-'the fact that many modifications maybe resorted to.

I claim:

1.*In a centrifugal pump or compressor, in combination with a volute housing and an impeller rotating therein, a diffuser in the form of an annular vaned ring surrounding the periphery of said impeller inwardly of the-volute in said housing, coaxial shafts supporting said impeller and diffuser for relative rotation, a driving bevel gear, diametrically disposed bevel gear pinions, one pinion driving one' of said shafts in one direction and the other of said pinions driving the other shaft in the opposite direction, a lubricant reservoir, and lubricant circulating means therein associated with one of said shafts and adapted to deliver lubricant between said shafts and to the driving pinions thereon.

2. In a centrifugal pump or compressor including an impeller, a rotatable diffuser member surrounding and aligned with the periphery of said impeller, a passaged shaft supporting said impeller, a'sleeve coaxial with said impeller shaft and adapted to support said diffuser member for rotation relativevto said impeller, oil circulating means energized by movement of said shaft and adapted to deliver oil therethrough to,l

assist in said oil circulation while limiting the travel of oil to said impeller and diffuser,4 and means for simultaneously Vdriving said shaft and said sleeve in opposite directions.

3. In a centrifugal fluid compressor, the combination comprising a rotatable impeller having forwardly-inclined vanes with leading discharge edges and an adjacent coaxially positioned counter-rotatable diffuser rotor having rearwardly inclined vanes to receive fluid discharged from said impeller, and means to impart counterrotation between said impeller and diiuser rotor.

a. In a centrifugal uid compressor, the combination comprising a rotatable impeller having forwardly inclined vanes with leading discharge edges and an adjacent coaxially positioned counter-rotatable diffuser rotor having rearwardly inclined vanes with approximately tangentially directed leading edges to receive fluid dis'- charge from said impeller, and means to impart counter-rotation between said impeller and diffuser rotor.

5. In a centrifugal-fluid compressor, the com bination comprising a rotatable impeller having forwardly inclined vanes with leading discharge edges and an adjacent coaxially positionedA counter-rotatable diffuser rotor having vradially overlapping rearwardly inclined vanes to receive fluid discharged from said impeller. and means to impart counter-rotation between said impeller and diffuser rotor.

' rotatable diffuser rotor surrounding the peri.

phery of said impeller and containing rearwardly inclined v .anes inclosed in saidrotor tn receive fluid discharged from said impeller, Vand means to impart counter-rotation between said impeller and diffuser rotor.

8. In a centrifugal fluid compressor, the combination comprising 'a rotatable impeller having forwardly inclined vanes with leading discharged edges and a concentrical-ly positioned, counterrotatable diffuser rotor surrounding the periphery of said impeller and containing radially overlapping rearwardly inclined vanes inclosed in said rotor andforming elongated, rearwardly directed, divergent duid passages ltherethrough. to receive fluid discharged from said impeller. and means to impart counter-rotation between said impeller vand diffuser rotor.

9. In a centrifugal fluid compressor. the combination according to claim 3, and a volute discharge housing communicating with the discharge of said diffuser rotor.

10. In a centrifugal fluid compressor, the combination according to claim 3, and a volute discharge housingcommunicating with and encircling the periphery of said diffuser rotor.

NATHAN C. PRICE.

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