Rotor balancing

Abstract: An improved arrangement for securing a counterweight to a rotor of an electric motor is disclosed wherein the counterweight includes a body portion disposed entirely on one side of a diametrical plane extending along the axis of rotation of the rotor and flange portions for securing said counterweight to the rotor are disposed on the other side of this plane.

Description: This invention relates to motor-powered machines, such as for example motor compressors, especially adapted for compressing refrigerant and more particularly to an improved balancing technique using a counterweight affixed to the motor rotor. In various types of rotary machines such as motor compressors which include a stator and a rotor connected to a drive shaft for rotatably driving same, it is common to provide a generally circumferentially extending counterweight to one or both ends of the rotor so as to balance the rotor/drive shaft assembly against asymmetrical forces encountered during operation of the rotary machine. Typically, for example in the compressor shown in our GB-A-2 194 291 which is a document only relevant as an intermediate publication, such counterweights extend axially outwardly from the rotor end face with the angular circumferential extension of each counterweight being no greater than 180°. Patent Abstracts of Japan, Vol 9, No 208 of JP-A-60 70953 discloses a counterweight in accordance with the prior art portion of claim 1. With this prior construction, the retaining means lie on opposite ends of a diametral plane through the rotor axis. The present invention, as defined in claim 1, provides better retention of the counterweight on a rotor since, contrary to prior beliefs, in case of counterweights having a relatively large axial length it has been discovered that the main load on fastening lugs received in the retaining means is not a shear load due to centrifugal forces on the counterweight but is a tension load which develops from the bending moment created by centrifugal force which tends to pull the counterweight from its securing lug. The present invention provides a larger moment arm by which to counteract the centrifugal forces acting to dislodge the counterweight, so that the magnitude of this dynamic loading is substantially reduced and the potential adverse effect thereof substantially eliminated at normal operating speeds of the crankshaft. Still better retention is provided where the counterweight is stepped, as defiled in claim 2, to reduce the centrifugally induced moment applying tension to the retaining means. Thus, it has been found that mounting the counterweight to the rotor by extending one or more lugs from the rotor through openings in the counterweight and then swaging the ends of such lugs to secure the counterweight in place, as in the preferred construction, provides a simple, inexpensive and yet satisfactory way to fabricate the assembly. The above and other advantages of this invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the following drawings. Brief Description of the Drawings Figure 1 is a section view of the lower portion of hermetic motor compressor assembly, such as a scroll-type compressor, showing a balanced rotor assembly embodying the principles of the present invention secured to a crankshaft, the section being taken along a radial plane extending along the axis of rotation of the crankshaft; Figure 2 is a fragmentary exploded perspective view of a portion of a rotor and its associated counterweight in accordance with this invention; Figures 3 to 5 are a top plan view, a side elevation view and a bottom plan view of the counterweight of Figure 2; Figure 6 is a section view of a portion of a securing flange portion, the section being taken along line 6-6 of Figure 3; and Figures 7 and 8 are a side view in section and a top plan view of the counterweight of Figure 2 shown in assembled relationship with a motor rotor. Description of the Preferred Embodiment Although the principles of the present invention may be applied to many different types of rotary machines having a crankshaft to which is secured a motor rotor, the discussion herein relates to a hermetic scroll-type machine which has specific utility in the compression of refrigerant for air conditioning and/or refrigeration machines, such as the machine shown in our above mentioned GB-A-2 194 291. The scroll-type machine 10 includes a crankshaft upper bearing 12, a pair of mated spiral scroll members for compressing gases (not shown), a crankshaft lower bearing 14, a vertically disposed rotatable crankshaft 16 journaled in the upper and lower bearings 12 and 14, an electric motor for driving the crankshaft including a rotor 18 heat shrunk onto the outer periphery of the crankshaft, a stator 20, and a shell 22 enclosing all of the above elements with the stator being press fit within the shell. Rotor 18 is generally of conventional squirrel cage construction and comprises a generally circular cylindrical body 26 having a bore 28 extending therethrough and includes at its opposite axial ends upper and lower end rings 30 and 32, a pair of circumferentially spaced integral securement lugs 34 extending from end ring 30, a first balancing counterweight 36 mounted by lugs 34 to upper end ring 30, and a second balancing counterweight 38 mounted to lower end ring 32. Upper end ring 30 has an axial end face 40 provided with a plurality of angularly spaced axially extending projections 42 which are adapted to generate gas turbulence for cooling as the rotor rotates. In accordance with this invention, first balancing counterweight 36 is stepped and comprises two semi-cylindrical C-shaped sections including an axially inner section 44 adapted to be received interiorly of end ring 30 and having circumferentially opposite end faces 46; an axially outer section 48 adapted to extend axially outwardly from end face 40 and having circumferentially opposite end faces 50 and a pair of opposite circumferentially extending flange portions 52 each including an opening 54 sized to receive one lug 34 in order to secure counterweight 36 to end ring 30. Sections 48 and 44 each have arcuate body portions between their respective end faces 50 and 46 each of which extends circumferentially through an arc of up to but not exceeding 180° so as to be disposed entirely on one side of a diametric plane "P" extending along the axis of rotation "A" of the rotor. Flange portions 52, on the other hand, extend circumferentially from the juncture of faces 50 and 46 of sections 48 and 44 to define an angular extension exceeding 180°. Thus, as assembled, the counterweight main body portions will be disposed on the opposite side of plane "P" from mounting lugs 34 and cooperating flange extensions 52. Surprisingly, the provision of a counterweight which has a main body portion extending circumferentially up to approximately 180° and a pair of securing flange portions extending circumferentially outwardly from opposite ends of this main body beyond 180° substantially reduces the loads on the securement means, and because of a full 180° is available also provides more space for the counterweight itself (i.e. it can be circumferentially longer, or it can be of less axial length for a given weight). For assembly, counterweight 36 is positioned above end ring 30 and inner section 44 inserted coaxially into the centre bore 28 of rotor 18 whereby lugs 34 are received in openings 54 of flanges 52. The axial end of each lug is then deformed (e.g., swaged) such that each lug is nonremovably mechanically locked in its opening.

Claims: A rotor for use in a rotary machine having a rotatable shaft (16) to which the rotor (18) is attached, the rotor including a counterweight secured to an end face of the rotor, the counterweight comprising: a main body portion (48) of substantial mass, said main body portion extending generally circumferentially along the end face (40) of the rotor (18) through an arc not exceeding 180° of said end face (40) and being positioned on one side of an imaginary plane (P) incorporating the rotor axis (A) and dividing the rotor into two imaginary halves; and mounting flanges (52) extending outwardly from opposite ends of said main body portion (48) and extending generally circumferentially along said end face (40) of said rotor, said flanges (52) including means (54) by which they are secured to the rotor end face (40) ; and wherein said main body portion comprises a section (48) which extends axially outwardly from said rotor end face (40) to beyond the flanges, characterised in that the flanges (52) extend to the other side of said plane (P), that said securing means are positioned on said other side of said plane (P) and that said securing means comprise an aperture (54) in each said mounting flange (52), each said aperture (54) receiving fastening means (34) securing said counterweight (36) to the end face (40) of said rotor (18) against axial and radial movement. A rotor as claimed in claim 1, wherein said section (48) of said main body portion is C-shaped and said main body portion is stepped to further comprise a C-shaped inner section (44) dimensioned to fit within a bore provided in said end face (40) of said rotor (18). A rotor as claimed in claim 1 or claim 2, wherein said flanges (52) extend outwardly from opposite circumferentially spaced ends (50) of said body. A rotor as claimed in any one of the preceding claims, wherein said fastening means are lugs (34). A rotor as claimed in claim 4, wherein the ends of said lugs (34) are swaged over to secure said flanges (52).

Inventors: ANDERSON GARY JUSTIN, BUSH JAMES WILLIAM, ANDERSON, GARY JUSTIN, BUSH, JAMES WILLIAM
Applicants: COPELAND CORP, COPELAND CORPORATION
Application year: 1988
Main classification: H02K7
IPC codes: F16F15, F04C18, F04C23, F16H15, H02K15, F04C29, H02K7