# US 2021/0172452 A1 · Centrifugal compressor impeller with nonlinear backwall > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0172452 A1 - Document ID: US20210172452A1 - Status: Published application - Kind: A1 - Application number: 16/709,442 - Filed: 2019-12-10 - Published: 2021-06-10 - Earliest claimed: 2019-12-10 - Assignees: Ingersoll-Rand Industrial U.S., Inc. - Applicants: Ingersoll-Rand Industrial U.S., Inc. - Inventors: Noel Blair - Web page: https://patentgrep.com/patent/US20210172452A1 ## CPC - F04D 29/2216: {Shape, geometry (F04D29/2211 takes precedence)} - F04D 29/281: {for fans or blowers} - F04D 17/10: for compressing or evacuating - F04D 29/266: {mounting compressor rotors on shafts} - F04D 29/284: {for compressors} - F05B 2240/301: Cross-section characteristics - F05B 2250/711: convex - F05D 2250/71: curved - F04D: NON-POSITIVE-DISPLACEMENT PUMPS (engine fuel-injection pumps F02M; ion pumps H01J41/12; electrodynamic pumps H02K44/02) - F05B: INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G - F05D: INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS ## Abstract A centrifugal compressor impeller includes a plurality of blades on a front side that extend from a first axial side to an outer radial end of the impeller. The centrifugal impeller includes a back side having a nonlinear backwall. The backwall can include a flat area hear a bore of impeller, a flat area near a tip of the impeller, and a convex surface between the flat areas of the bore and the tip. In some forms the impeller further includes a concave surface between the convex surface and the tip to form an s-shape. A transition or inflection point can denote the change from convex to concave. The convex and/or concave surfaces can take any variety of forms such as constant radius sections and/or compound curves. ## Claims ### Claim 1 An apparatus comprising: a centrifugal impeller having a blade side and a backwall side, the backwall side having a backwall and a hub region configured with a bore to be affixed to a rotatable shaft, the blade side including a plurality of impeller blades that extend from a first axial end to a first radial end of the centrifugal impeller, the plurality of impeller blades configured to receive a working fluid in the first axial end, compress the working, and discharge the working fluid through the first radial end when the centrifugal impeller is being operated, the backwall of the centrifugal impeller defined by: a flat area that extends inward from an outermost radial extent of the centrifugal impeller to a first location; a flat area in the hub region that extends outward from an outer diameter of the bore to a second location; and a compound curve located between the first location and the second location. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the compound curve is a curve having first radius of curvature in a radial inward region of the compound curve, and a curve having a second radius of curvature in a region radial outward of the radial inward region. ### Claim 3 (depends on 2) The apparatus of claim 2, wherein the compound curve is a convex curve at the first radius of curvature, and a concave curve at the second radius of curvature. ### Claim 4 (depends on 1) The apparatus of claim 1, wherein the compound curve includes an inflection point between a radial inward region of the compound curve and a radial outward region of the compound curve, the inflection point denoting a change in direction of the compound curve. ### Claim 5 (depends on 4) The apparatus of claim 4, wherein the inflection point occurs at a location greater than 50% of the distance from a rotational axis of the centrifugal impeller to the outermost radial extent of the centrifugal impeller. ### Claim 6 (depends on 5) The apparatus of claim 5, wherein the inflection point also marks a discontinuity between a radius of curvature of backwall as it transitions from the radial inward region to the radial outward region. ### Claim 7 (depends on 6) The apparatus of claim 6, wherein the compound curve provides a lower bore stress, lower tip deflection, and lower out of reference plane deflection than an impeller with identical geometry and mass properties but with a flat backwall instead of a compound curve. ### Claim 8 (depends on 1) The apparatus of claim 1, wherein the centrifugal impeller includes an inducer at the first axial end and an exducer at the first radial end, and wherein the compound curve is a convex curve. ### Claim 9 (depends on 1) The apparatus of claim 1, wherein the compound curve includes a concave curve at a location radially outward of the convex curve. ### Claim 10 An apparatus comprising: a centrifugal impeller having a plurality of blades on a first side and a backwall on a second side, the centrifugal impeller including an intake on a first axial end of the first side and an outlet on an outer radial end of the first side, the centrifugal impeller having a bore hole and a bore hole flat area on the back side surrounding the bore hole, the backwall also defined by a tip region flat area near the outer radial end, the backwall including a convex region defined by an outward projection of material located between the bore hole flat area and the tip region flat area. ### Claim 11 (depends on 10) The apparatus of claim 10, wherein the centrifugal impeller also includes a concave region located radially outward of the convex region. ### Claim 12 (depends on 11) The apparatus of claim 11, wherein at least one of the concave region and convex region is defined by a compound curve. ### Claim 13 (depends on 11) The apparatus of claim 11, wherein the convex region and concave region have different radius of curvatures proximate an inflection point that denotes the transition between the convex region and the concave region. ### Claim 14 (depends on 13) The apparatus of claim 13, wherein the inflection point is located at least 50% of the distance between an axis of rotation of the centrifugal impeller and a tip at the tip region flat area of the centrifugal impeller. ### Claim 15 (depends on 10) The apparatus of claim 10, wherein at least one of the bore hole flat area and tip region flat area is planar. ### Claim 16 (depends on 15) The apparatus of claim 15, wherein the centrifugal impeller also includes a concave region located radially outward of the convex region, and which further includes an inflection point denoting the transition between the convex region and concave region that is located at least 50% of the distance between an axis of rotation of the centrifugal impeller and a tip at the tip region flat area of the centrifugal impeller. ### Claim 17 (depends on 16) The apparatus of claim 16, wherein at least one of the convex region and concave region is a compound curve. ### Claim 18 (depends on 17) The apparatus of claim 17, wherein the compound curve provides a lower bore stress, lower tip deflection, and lower out of reference plane deflection than an impeller with identical geometry and mass properties but with a flat backwall instead of a compound curve. ### Claim 19 An apparatus comprising: a centrifugal compressor impeller having a plurality of blades disposed on a front side and a backwall disposed on a back side, the backwall having a central flat area surrounding a bore of the centrifugal compressor impeller and a convex shape extending from the central flat area toward a tip of the centrifugal compressor impeller. ### Claim 20 (depends on 19) The apparatus of claim 19, wherein the centrifugal compressor impeller also includes a flat area at the tip of the centrifugal compressor impeller.