WO1995015025A1

WO1995015025A1 - An electric motor-hermetic compressor assembly

Info

Publication number: WO1995015025A1
Application number: PCT/BR1994/000041
Authority: WO
Inventors: Marcos Guilherme Schwarz; Egidio Berwanger
Original assignee: Empresa Brasileira De Compressores S/A. - Embraco
Priority date: 1993-11-23
Filing date: 1994-11-22
Publication date: 1995-06-01
Also published as: BR9304565A

Abstract

An electric motor-hermetic compressor assembly, said compressor comprising a case (2), inside which there is mounted a cylinder block (5, 10), carrying a bearing (6, 11) that supports a crankshaft (7), which carries a rotor (8, 20) of a motor, whose stator (4) is attached to the cylinder block (5, 10), said stator (4) being attached directly to the bearing (11), said rotor (20) being externally and concentrically disposed relative to the stator (4) and mounted to one of the ends of the crankshaft (7), through a connecting element (30).

Description

AN ELECTRIC MOTOR-HERMETIC COMPRESSOR ASSEMBLY

Field of the Invention

The present invention refers to a rotary electric motor-hermetic compressor assembly and, more particularly, to an assembly consisted of an electric motor, provided with an external rotor, and a hermetic compressor with a vertical shaft, of the type used in small refrigerating appliances, such as refrigerators, freezers, drinking fountains, etc.. Background of the Invention

A hermetic compressor for refrigerating appliances comprises, mounted inside a hermetic case, a motor- compressor assembly, in which the electric motor is supported by a cylinder block, onto which there is fixed a bearing supporting the crankshaft, which carries at the lower portion thereof the rotor of said electric motor. In this motor, which can be of the induction type or of the electronically commutated direct current type, the stator containing the windings is externally mounted in relation to the rotor. The electric motors with such construction present some inconveniences that limit the efficiency of these appliances, besides causing other deficiencies. One of the causes of efficiency limitation relates to the losses due to the existence in these motors of a large amount of magnetic material mass that is subjected to an alternated magnetic field. Another cause of efficiency limitation refers to the low ratio between the active and inactive conductors in said electric motors.

A solution for said efficiency limitation is obtained by increasing the height of said motors, in order to achieve optimum ratios, in terms of efficiency and cost. However, said solution cannot be applied to the electric motor of a refrigerating hermetic compressor, due to the limitation of height found in said appliances.

Another inconvenience in the construction of the electric motor with an internal rotor relates to the possibility of occurring variations in the rotational speed of the motor, which is prejudicial when said motor is running in low speeds, due to the presence of pulsating loads and to the limited inertial moment of the rotor. The motors with an internal rotor and of the electronically commutated type (ECM) , which carry magnets on the surface of the rotor, further present problems of structural resistance, resulting from the centrifugal force acting on said superficial magnet portions, which force may remove said magnets from the rotor surface. To minimize this problem, said motors require a special construction, reinforced by the use of composite materials or steel sleeves. The application of such type of motor in hermetic refrigerating compressors has a further inconvenient, which is the radial effort due to the magnetic interaction between the rotor and the stator of said motor, the latter being supported in these compressors by the cylinder block. This radial effort (illustrated in figure 1 in dashed lines) may cause problems of mechanical drag, with failures in the compressor due to the elasticity or lack of rigidity in the structure of said cylinder block (length of the tubular body and supporting arms) ; shaft elasticity; gap between the shaft and bearing; and flexibility in the plurality of the stator blades.

These deficiencies, resulting from the constructive form of the motor, may cause the contact of the stator and rotor parts, which become close to each other due to shape errors or deviations in the assembly thereof, causing the mechanical drag effect. Disclosure of the Invention

Thus, it is an object of the present invention to provide a rotary electric motor assembly, to be used in hermetic compressors, which does not present problems of mechanical drag in the compressor, redistributing the efforts on the structure of the motor-compressor assembly, in order to eliminate said efforts applied to the cylinder block, reducing the noise and further having a more economical dimension, compatible with the limited internal dimensions of the compressor.

A further object of the present invention is to provide an electric motor such as cited above, which minimizes the occurrence of variations in the rotational speed, when the compressor is working in low rotations. These and other objectives of the present invention are achieved through an electric motor-hermetic compressor assembly, said compressor comprising a case, inside which there is mounted a cylinder block, carrying a bearing that supports a crankshaft, which has an end portion carrying the rotor of a motor, whose stator is attached to the cylinder block, said stator being attached directly around an axial portion of the bearing, said rotor being externally and concentrically disposed relative to the stator and mounted to one of the ends of the crankshaft, through a connecting element having an internal portion fixed to the crankshaft and an external portion fixed to the rotor. The motor of the present invention, besides avoiding the above cited problems, increases its efficiency, since it reduces the magnetic material to be subjected to the alternated field, besides reducing the amount of inactive conductors, thus increasing the ratio between the active and inactive conductors of said motor. Moreover, the electric motors of the electronically commutated type need no more a reinforced construction to increase its structural resistance. In this construction, the efforts take place in the motor, thereby eliminating the mechanical efforts of the cylinder block, allowing the latter to have a lighter construction and avoiding the production of noise in the block due to deformations. Brief Description of the Drawings

The invention will be described below, with reference to the attached drawings, in which: Fig. 1 shows schematically and in a partial longitudinal sectional view the disposition of the stator and rotor of an electric motor in a hermetic compressor, according to the prior art; Fig. 2 shows schematically a longitudinal sectional view of a motor mounted to the cylinger block of a hermetic compressor, according to the prior art; and

Fig. 3 shows, as illustrated in figure 2, a longitudinal sectional view of a motor mounted to the cylinder block of a hermetic compressor, according to the present invention. Best Mode for Carrying Out the Invention

According to the figures, a motor-compressor assembly 1 of the prior art used in small refrigerating appliances is suspended inside a hermetic case 2 through supporting springs 3 (only one is illustrated) . The stator 4 of said motor is mounted to a cylinder 5 of the motor-compressor assembly 1, to which is fixed a bearing 6 for supporting a crankshaft 7, onto which lower portion is mounted the rotor 8 having an aluminum cage. The crankshaft 7 carries at an end adjacent to the bearing 6, an eccentric end portion 7a and, at the opposite end, an oil pump 9.

The motor of the motor-compressor assembly 1 can be of the direct current type or of the electronically commutated type (ECM) . In either type, the stator 4 of the prior art motor has the coil windings externally surrounding the rotor 8, the latter being in the form of a cylindrical tubular body with an internal contact surface 8a to allow the mounting thereof to the crankshaft 7, and an external surface 8b, which is kept slightly away from the adjacent internal surface 4a of the stator 4.

When the motor is of the ECM type, the external surface 8b of the rotor 8 carries a plurality of permanent magnets, which are adequately attached to said surface. In the prior art construction, the cylinder block 5 presents a structure, whose central portion is in the form of a tubular body, constituting the bearing 6, whereto is mounted the crankshaft 7, with a gap sufficient to allow the maintenance of a lubricant oil film between the adjacent walls of said crankshaft 7 and bearing 6. The cylinder block 5 extends radially through radial projections 5a, onto which peripheral edge are mounted the respective ends of the supporting springs 3. The radial projections 5a define a base, incorporating at the lower part thereof peripheral hanging supporting arms 5b, which carry the stator 4 of the motor. With this construction, the cylinder block 5 is submitted to structural efforts, such as illustrated in dashed lines in figure 2, when the motor is energized, said efforts enabling the generation of moments.

In this construction, the tubular body of the cylinder block 5 extends partially along the length of the crankshaft 7, at the adjacent portion of the latter where the eccentric end portion is mounted. To permit this assembly, at a portion of the internal face 8a of the rotor 8, there is provided a superficial recess 8c, defining a housing to receive the lower end of the bearing 6 of the cylinder block 5, with a minimum gap sufficient to avoid the rotor-cylinder block contact. The height of the superficial recess should be calculated so that the provision of the housing does not remove much magnetic mass from the rotor, at the same time that it gives stability to the mounting of said rotor to the crankshaft 7. Nevertheless, the small extension of the crankshaft 7 surrounded by the bearing 6 of the cylinder block 5 results in substantial shaft- bearing deformations during the compressor operation. In a preferred embodiment of the present invention illustrated in figure 3, the motor of the compressor has an external rotor 20, mounted to a portion of the opposite end of the crankshaft 7 that is not surrounded by the bearing 11 of the cylinder block 10, through a connecting element 30 in the form of an inverted flange, in order to allow said external rotor 20 to rotate with the rotational movement of the crankshaft 7. The connecting element 30 has a tubular body portion in the form of a central fixation ring 31, which is mounted so as to peripherally involve said opposite end of the crankshaft 7 and which has a lower edge, wherefrom a massive circular platform 32 is radially projected outwardly from said crankshaft 7, said platform being provided at the external edge 32a thereof with upper supporting arms 33, which are projected towards the external rotor 20 and which are attached to a cage portion 21 of said external rotor 20. The circular platform 32 is provided, adjacent to said external end edge 32a, with windows 34 that allow the passage of the lubricant oil pumped for the lubrication of the bearing and surroundings during the compressor operation, as well as the return of the oil to an oil sump (not illustrated) of said compressor, through the internal face of the connecting element 30. In another possible embodiment, the connecting element 30 is in the form of "U" shaped supporting bars, with an end mounted to the crankshaft 7 and the opposite end attached to a cage portion 21 of the rotor 20. In this construction, the lubricant oil reaches the sump through the gap located between said bars. A variant of this construction presents said bars projecting upperly or lowerly from the edge of the central fixation ring 31 mounted to the crankshaft 7. In any of the solutions above, the flange 30 connects the external rotor 20 to the crankshaft 7, adjacently to a free end of the bearing 11 projecting beyond the adjacent end edge of the stator 4 which, in this construction, has an axial extension shorter than the axial extension of the bearing 11.

The rotor-crankshaft connection can be achieved by attaching an end portion of said rotor to the crankshaft, when said rotor incorporates the connecting element 30 in a single piece. The larger axial extension of the bearing and the mounting of the stator 4 directly onto said bearing 11, surrounding the latter concentrically, results in a higher stability to the motor-cylinder block assembly, eliminating from the cylinder block the actuation of efforts due to the magnetic interaction between the rotor and stator.

In the preferred illustrated construction, the bearing 11 has a lower end 11a facing the end of the crankshaft 7 that carries the oil pump 9 externally to the adjacent lower edge of the stator 4.

This reduction of efforts permits the construction of a ligther cylinder block, since it does not require structural reinforcements and peripheral supporting arms to sustain the stator 4, as in the prior art. Besides the transfer of efforts, the construction of the present invention avoids that the forces acting on the rotor 20 originate moments capable of causing mechanical drag, as well as eliminates the noise produced by the cylinder block, since the latter is not submitted to efforts and, therefore, does not suffer deformations. Moreover, in this rotor construction, the amount of magnetic steel submitted to the alternated field is lower, resulting in a higher efficiency, due to the inherent reduction of energy losses. The extension covered by the conductors that form the coil heads is smaller, thereby reducing losses due to Joule effect, as well as costs. The motors of the electronically commutated type and with an external rotor have a higher moment of inertia, because they carry the magnets at a larger distance from the center of rotation. Said higher moment of inertia reduces speed variations when said motor is running in low rotations. The deformations and relative displacements between the parts, due to the shaft-bearing gap and resulting from the short bearing of the prior art, are reduced by using a longer bearing in the present invention.

Claims

1. An electric motor-hermetic compressor assembly, said compressor comprising a case (2) , inside which there is mounted a cylinder block (5, 10) , carrying a bearing (6, 11) that supports a crankshaft (7) , which has an end portion carrying a rotor (8, 20) of a motor, whose stator (4) is attached to the cylinder block (5, 10) , characterized in that the stator (4) is attached directly around an axial portion of the bearing (11) , said rotor (20) being externally and concentrically disposed relative to the stator (4) and mounted to one of the ends of the crankshaft (7) , through a connecting element (30) having an internal portion (31) fixed to the crankshaft (7) and an external portion (33) fixed to the rotor (20) .

2. Assembly, as in claim 1, characterized in that the bearing (11) of the cylinder block (10) has an axial extension larger than the axial extension of the stator (4) .

3. Assembly, as in claim 2, characterized in that the internal portion (31) of the connecting element (30) is mounted to the crankshaft (7) , adjacently to a free end of the bearing (11) of the cylinder block (10) projecting beyond the adjacent end edge of the stator (4) .

4. Assembly, as in claim 3, characterized in that the internal portion (31) of the connecting element (30) defines a central fixation ring, peripherally surrounding the adjacent end of the crankshaft (7) .

5. Assembly, as in claim 4, characterized in that the connecting element (30) is in the form of an inverted flange, a supporting platform (32) radially projecting from the central fixation ring (31) , said platform having an external end edge provided with axial projections that enable the assembly to the rotor (20) .

6. Assembly, as in claim 5, characterized in that the connecting element (30) is provided, adjacent to the external end edge thereof, with windows to allow the passage of lubricant fluid.