# US 8,569,922 B2 · Electric motor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,569,922 B2 - Document ID: US8569922B2 - Status: Granted - Kind: B2 - Application number: 13/150,391 - Filed: 2011-06-01 - Published: 2011-12-08 - Granted: 2013-10-29 - Earliest claimed: 2010-06-04 - Assignees: ebm-papst St. Georgen GmbH & Co. KG - Applicants: Volker Rombach - Inventors: Volker Rombach - Web page: https://patentgrep.com/patent/US8569922B2 ## CPC - H02K 1/276: Magnets embedded in the magnetic core, e.g. interior permanent magnets [IPM] - H02K 15/03: having permanent magnets - H02K: DYNAMO-ELECTRIC MACHINES (dynamo-electric relays H01H53/00; conversion of DC or AC input power into surge output power {H03K3/53}) ## Abstract A novel electric motor rotor structure, particularly desirable for use with brittle rare-earth-magnets, offers improved resistance to rattling and axial shifting. This is achieved by forming the rotor with an annular central yoke connecting to a plurality of pole shoes along the periphery of the rotor and defining a magnet-receiving recess or pocket 160 between each pole shoe and the central yoke. Spaced circumferentially between adjacent magnets 38 are regions 146 of reduced magnetic conductivity, which include relatively thin metallic holding segments, which connect adjacent pole shoes to each other and to the central yoke. During manufacturing, tools are applied to upset or crimp the holding segments, and thereby form spring elements, to hold the magnets in stable positions and resist any tendency of the magnets to rattle or axially shift during motor operation. One obtains the same power level from a smaller, and therefore lighter, motor than was previously possible. ## Claims ### Claim 1 An electric motor comprising: a stator (28) having a stator lamination stack (27) defining a plurality of slots (126); a stator winding (U, V, W) arranged in said slots (126); a rotor (36) separated from the stator (28) by a magnetically effective air gap (39), which rotor includes, on its side facing toward said air gap (39), a plurality of salient poles (136A, 136B, . . . ) having pole shoes (136) facing toward said air gap (39), and on its side facing away from the air gap (39) a magnetic yoke (130) that is mechanically connected to the pole shoes (136) by respective holding segments (132, 134a, 134b); a respective recess (160) formed between the magnetic yoke (130) and a respective pole shoe (136), in which recess, in order to generate a magnetic flux in said pole shoe (136), at least one permanent magnet (38) is arranged, thereby defining a respective magnet/pole shoe boundary (138) at each transition from said permanent magnet to the associated pole shoe, and which recess (160) is adjoined, on each circumferential side of the at least one permanent magnet (38) by a region (146a, 146b) of poor magnetic conductivity that is contiguous, on its side facing toward the air gap (39), with one of the holding segments (134a, 134b), wherein the width (β), measured in a circumferential direction, of a pole shoe (136) decreases, at least locally, in a direction away from the magnet/pole shoe boundary (138) toward the air gap (39) in a transition zone to a point (142) of least pole shoe width, in said transition zone, a pole shoe (136) defines, on each of its sides facing toward the adjacent pole shoe (136), a flank (139), and the holding segments (134a, 134b) are configured as spring elements that mechanically urge the pole shoes (136) in a direction toward the associated permanent magnets (38), in order to retain said permanent magnets in the recesses (160) provided for them. ### Claim 2 (depends on 1) The motor according to claim 1, in which at least the majority of the holding segments (134a, 134b) configured as spring elements do not touch the flank (139), located respectively opposite them, of a pole shoe (136). ### Claim 3 (depends on 1) The electric motor according to claim 1, in which the width (β_M), measured in a circumferential direction, of a pole shoe (136) is greater at the magnet/pole shoe boundary (138) than its width (β_C) at a point (142) at which said width is smallest. ### Claim 4 (depends on 1) The electric motor according to claim 1, in which the at least one rotor magnet (38) that is arranged in the recess (160) provided between the magnetic yoke (130) and the pole shoe (136) has, on its side facing toward the yoke (130), an angular extent that is at least equal to 85% of a pole pitch (τ_P) of the rotor (36). ### Claim 5 (depends on 4) The electric motor according to claim 4, in which the angular extent is at least equal to 95% of a pole pitch (τ)_P) of the rotor (36). ### Claim 6 (depends on 1) The electric motor according to claim 1, in which the stator winding (U, V, W) comprises concentrated windings (128G). ### Claim 7 (depends on 1) The electric motor according to claim 1, which is implemented as an internal-rotor motor. ### Claim 8 (depends on 1) The electric motor according to claim 1, in which the at least one permanent magnet is implemented as a ceramic magnet (38). ### Claim 9 (depends on 1) The electric motor according to claim 1, in which a carrier part (132) is arranged between two adjacent rotor poles (135), which part extends toward the air gap (39) and from whose radially outer region there extends at least one holding segment (134a, 134b) to the pole shoe (136) of an adjacent rotor pole (135), which holding segment (134a, 134b) is formed with a notch (170, 172) to yield a spring member that mechanically urges said pole shoe (136) in a direction away from the magnetically effective air gap (39). ### Claim 10 (depends on 9) The electric motor according to claim 9, in which a holding segment (134a, 134b) extends from the radially outer region of the carrier part (132) to each of the two adjacent pole shoes (136), which holding segments (134a, 134b) are each formed with an indentation (170, 172) to yield a spring member that acts upon the associated pole shoe (136) in a direction away from the magnetically effective air gap (39). ### Claim 11 (depends on 8) The electric motor of claim 8, wherein a magnetically active constituent of said magnet is a rare earth metal. ### Claim 12 (depends on 11) The electric motor of claim 11, wherein said rare earth metal comprises neodynium.