A PROCESS AND DEVICE FOR MOUNTING THE ROTOR OF AN ELECTRIC MOTOR

Abstract: A process and device for mounting the rotor of an electric motor, comprising a stator (70) affixed inside a motor housing (60), and a rotor (50) affixed to a crankshaft (30) journalled to a supporting block (10), said assembly being achieved by a control unit (120) commanding the radial displacements of an upper end of the crankshaft (30) having a lower end journalled to a lower bearing (80) mounted to the motor housing (60), each radial displacement being limited by a respective contact condition of the rotor (50) to a respective and adjacent portion of the stator (70), which condition is identified and registered, in order to allow the calculation of the center of the circumference which contains the contact conditions and the posterior displacement of the upper end of the crankshaft (30), until its geometric center is aligned with the calculated geometric center of said circumference.

Description: A PROCESS AND DEVICE FOR MOUNTING THE ROTOR OF AN ELECTRIC MOTOR Field of the Invention The present invention refers to a process and to a device for mounting a shaft-rotor assembly of an electric motor to a respective stator, which is already mounted inside a shell of a hermetic compressor used in a refrigeration system. Background of the Invention In a known construction of a reciprocating hermetic compressor mounted inside a shell, there is provided a supporting block journalling a crankshaft, which moves, through a connecting rod, a piston reciprocating inside a cylinder provided in an end portion of said supporting block, said crankshaft carrying, with no axial gaps, a rotor of an electric motor . The electric motor has a stator, which is tightly mounted inside a motor housing, usually in the form of a cup and in whose inside is concentrically positioned the rotor carried by the crankshaft, being provided, between the rotor and the stator, a certain radial gap which is calculated so as to avoid the contact between said parts during operation of the motor. The motor housing is mounted inside the compressor shell and affixes the supporting block. In this construction, the lower end of the crankshat is mounted to a lower bearing provided in a portion of the bottom wall of the motor housing, concentrically to the crankshaft axis . According to this construction, the assembly of the rotor to the stator occurs with the latter already affixed inside the motor housing, being difficult to make positioning adjustments of the rotor in relation to the stator. In this assembly, the rotor is already affixed to the crankshaft which, on its turn, is seated onto an axial upper bearing. To prevent the rotor from presenting contact points with the stator during operation of the compressor, one of the solutions is to produce the rotor and the stator with high dimensional precision and to make a precise assembly of said parts, said precision being defined so as to guarantee the alignment between the respective axes of both parts, avoiding the contact therebetween during the operation of the compressor. Another solution is to provide an increased radial gap between the rotor and the stator, which is obtained with the consequent mass reduction of at least one of these components, so that said gap compensates for eventual and usually common disalignments between the rotor and stator axes. However, increasing the air gap in this solution affects the motor efficiency. Disclosure of the Invention It is an objective of the present invention to provide a process and a device for mounting the rotor to the stator of an electric motor for a reciprocating hermetic compressor, which allow to achieve said assembly with a precise alignment of the axes of the involved parts, without requiring them to present high manufacturing dimensional precision or increased radial gap upon material being removed from either the rotor or the stator of the electric motor. This and other objectives are achieved by a process for mounting the rotor of an electric motor comprising a stator, which is affixed inside a motor housing having a bottom wall provided with a self-centralizing lower bearing; and a rotor affixed around a crankshaft, with a lower end journalled to the lower bearing and with an upper end journalled to a supporting block, which is attachable to an open upper end of the motor housing, said process comprising the steps of: a- retaining, in a determined position, the motor housing affixing the stator; b- introducing the supporting block-crankshaft-rotor assembly through the open upper end of the motor housing, until the lower end of the crankshaft is seated onto the lower bearing; c- submitting the upper end of the crankshaft to radial displacements, each being limited by a respective contact condition of the rotor to a respective and adjacent portion of the stator; d- identifying and registering each contact condition between the rotor and the stator; e- calculating the center of the circumference which contains the contact conditions, from their identification; f- conducting the crankshaft to a radial displacement, until its geometric center is aligned with the calculated geometrical center of said circumference; and g- affixing the supporting block to the motor housing. The device which carries out the process of the present invention comprises a mounting station provided with the motor housing affixing the stator; at least one conveying means, which is operatively connected to the mounting station, in order to convey the upper end of the crankshaft to radial displacements, each being limited by a respective contact condition of the rotor to a respective and adjacent portion of the stator; a control unit, which is operatively connected: to the mounting station, in order to receive therefrom the information about the presence of a motor housing positioned therein; and to the conveying means, in order to command each radial displacement of the upper end of the crankshaft; and sensor means, which are provided in at least one of the parts defined by the conveying means and by the mounting station and which are operatively connected to the control unit, in order to inform the latter about: the presence of a motor housing at the mounting station; the introduction of the crankshaft into said motor housing; and each contact condition of the rotor in relation to the stator, said control unit determining the geometric center of the stator from the information about the contact conditions informed by the sensor means and instructing the conveying means to displace the crankshaft, until the alignment of the crankshaft axis and the geometric center of the stator has been obtained. Brief Description of the Drawings The invention will be described below, with reference to the attached drawings, in which: Figure 1 shows, schematically and in a longitudinal sectional view, a hermetic compressor of the type having the rotor- stator assembly mounted inside a motor housing; Figure 2 shows, schematically and in an exploded perspective view, the supporting block journalling the crankshaft and the rotor to be mounted inside a motor housing affixing the stator; Figure 3 shows, schematically and in a perspective view, the supporting block journalling the crankshaft and the rotor mounted inside the motor housing affixing the stator of figure 2; and Figure 4 shows in a block diagram, the mounting operation of the supporting block journalling the crankshaft and the rotor mounted to the motor housing, of figures 2 and 3, according to the present invention . Description of the Illustrated Embodiment The present invention will be described in relation to a process for mounting an electric motor, for example of the type used in a hermetic compressor with a vertical crankshaft, such as that illustrated in figure 1, and which comprises a hermetic shell 1 defining a sump 2 of lubricant oil in the bottom thereof and lodging therewithin a supporting block 10 which carries, in an end portion, a cylinder 20 and which has, in a median portion, concentrically with a throughbore 11, an axial upper bearing 12 for supporting a crankshaft 30, which is vertical and has an eccentric 31 articulated through a connecting rod 40 to a piston 45 reciprocating inside the cylinder 20, as a function of the rotation of the crankshaft 30. The crankshaft 30 is provided, at its upper portion, with a flange portion 32 which is seated onto the bearing 12 of the supporting block 10 and, at its lower portion, with an oil pump 33 which takes oil from the sump 2 to the parts with relative movement and needing lubrication. The crankshaft 30 also carries, between the flange portion 32 and the oil pump 33, a rotor 50, of the electric motor of the compressor, affixed to said crankshaft 30 with no radial gaps . In this construction, the supporting block 10 is in the form of a chute having lateral walls 13 and a bottom wall 14 provided with a recess 15, which is concentric to the throughbore 11 and into which is lodged the axial upper bearing 12. The cylinder 20 has a pair of opposite lateral flanges, each being, for example, supported on an upper edge of an adjacent lateral wall 13 of the supporting block 10. The axial upper bearing 12 is in the form of a ring having a determined spherical shape, which permits the self-alignment thereof during movement of the crankshaft 30. According to this construction, the supporting block 10 is affixed to a motor housing 60 usually in the form of cylindrical cup, on whose upper edge 61 the supporting block 10 is seated in a position in which the axis of the crankshaft 30 is aligned with the axis of a stator 70 of the electric motor, avoiding contacts between the rotor 50 and the stator 70 during operation of the motor. The motor housing 60 is provided, on a bottom wall 62, with a central portion 63, which is inwardly projected and has a throughbore 64 concentric and aligned with the axis of the motor housing 60, to allow the passage of a lower end of the crankshaft 30 where is provided the oil pump 33. The central portion 63 defines, external to the motor housing 60, a housing for a lower bearing 80, which is self-centering and with a construction similar to that of the axial upper bearing 12 and which is affixed to the bottom wall 61 of said motor housing 60, in order to have its axis aligned with the axis of said bottom wall 62. In this construction, the stator 70 is mounted to the motor housing 60, internally and concentrically in relation to the latter, with no radial gaps, before receiving the rotor-crankshaft assembly. When mounting the electric motor, after affixing the stator 70 inside the motor housing 60 and affixing the lower bearing 80 to the latter, the crankshaft 30 carrying the rotor 50 is introduced inside the motor housing 60, until the lower end of said crankshaft 30 seats onto the lower bearing 80. In this compressor construction, the crankshaft 30, mounted inside the motor housing 60, is initially positioned through the throughbore 11 provided in the supporting block 10, this supporting block-crankshaft- rctor assembly being mounted to the stator, which is already affixed inside the motor housing 60. According to the present invention, a precise assembly of the rotor to the stator is achieved by a mounting process having the steps stated below. According to the present invention, the assembly of each crankshaft 30 carrying the rotor 50 to the stator 70 occurs with a device comprising a mounting station 100, which receives and retains the motor housing 60 and where each stator 70, conducted by a first conveying means 110, is introduced and retained in said motor housing 60, by instruction of a control unit 120, which is operatively connected to the first conveying means 110 and to the mounting station 100. After this assembly, a second conveying means 130, which is operatively connected to the mounting station 100, conducts to the latter the supporting block 10 carrying the crankshaft 30-rotor 50 assembly. The control unit 120 instructs the second conveying means 130 to position the lower end of the crankshaft 30 inside the lower bearing 80. Each operational movement of the second conveying means 130 is achieved as a function of the information received from the control unit 120, for example through sensor means, not illustrated, provided in at least one of the parts defined by the second conveying means 130 and the mounting station 100, in order to inform said control unit 120 about the presence of a motor housing affixed in the mounting station 100; and about the positioning of the lower end of the crankshaft 30 inside the lower bearing 80. The sensor means may include, for instance, pressure sensors, provided in the second conveying means 130 and acting on the motor housing 60, and presence sensors, provided in one of the parts defined by the mouting station 100 and first conveying means 110, in order to detect the presence of a motor housing in said mouting station 100. The control unit 120 further instructs, after the lower end of the crankshaft 30 has been journalled, the second conveying means 130 to impart, to the upper end of said crankshaft 30, radial displacements, each being limited by the contact of the rotor with a respective and adjacent portion of the stator 70, this contact condition being determined, for example, by pressure sensors of the sensor means . After each contact, the control unit 120 registers the contact position and instructs the second conveying means 130 to promote a subsequent radial displacement of the upper end of the crankshaft 30, so that a new contact condition may be obtained and registered, allowing the production of at least three different contact conditions . With the determination of the contact conditions, the control unit determines, mathematically, the geometric center of the stator, and also determines the movement to be instructed to the second conveying means 130, so that the latter may position the geometric center of the crankshaft 30 aligned with the geometric center defined for the stator 50. The alignment between the axes of the crankshaft 30 and the rotor 50 is defined so that the radial gap between said parts be substantially close to the desired minimum gap and be maintained circumferentially unaltered, avoiding undesirable contacts between said parts during operation of the compressor . Upon achieving the centralizing position of the crankshaft 30 in relation to the stator 50, the supporting block 10 is affixed by suitable means, such as welding or gluing, to the peripheral upper edge 61 of the motor housing, maintaining unaltered the obtained alignment condition.

Claims: CLAIMS 1. A Process for mounting the rotor of an electric motor, comprising a stator (70), which is affixed inside a motor housing (60) having a bottom wall (62) provided with a self-centralizing lower bearing (80); and a rotor (50) affixed around a crankshaft (30), with a lower end journalled to the lower bearing (80) and with an upper end journalled to a supporting block (10), which is attachable to an open upper end of the motor housing (60), characterized in that it comprises the steps of: a- retaining, in a determined position, the motor housing (60) affixing the stator (70); b- introducing the supporting block (10 ) -crankshaft (30)- rotor (50) assembly through the open upper end of the motor housing (60), until the lower end of the crankshaft (30) is seated onto the lower bearing (80); c- submitting the upper end of the crankshaft (30) to radial displacements, each being limited by a respective contact condition of the rotor (50) to a respective and adjacent portion of the stator (70); d- identifying and registering each contact condition between the rotor (50) and the stator (70); e- calculating the center of the circumference which contains the contact conditions, from their identification; f- conducting the crankshaft (30) to a radial displacement, until its geometric center is aligned with the calculated geometrical center of said circumference; and g- affixing the supporting block (10) to the motor housing (60). 2. Process, as in claim 1, characterized in that, in step "c", the upper end of the crankshaft (30) is submitted to at least three contact conditions, which are different and angularly separated from each other. 3. Device for mounting the rotor of an electric motor, comprising a stator (70), which is affixed inside a motor housing (60) having a bottom wall (62) provided with a self-centralizing lower bearing (80); and a rotor (50) affixed around a crankshaft (30), with a lower end journalled to the lower bearing (80) and with an upper end journalled to a supporting block (10), which is attachable to an open upper end of the motor housing (60), characterized in that it comprises: a mounting station (100) provided with the motor housing (60) affixing the stator (70); at least one conveying means (130), which is operatively connected to the mounting station (100), in order to convey the upper end of the crankshaft (30) to radial displacements, each being limited by a respective contact condition of the rotor (50) to a respective and adjacent portion of the stator (70); a control unit (120), which is operatively connected: to the mounting station (100), in order to receive therefrom the information about the presence of a motor housing (60) positioned therein; and to the conveying means (13), in order to command each radial displacement of the upper end of the crankshaft (30); and sensor means, which are provided in at least one of the parts defined by the conveying means (130) and by the mounting station (100) and which are operatively connected to the control unit (120), in order to inform the latter about: the presence of a motor housing (60) at the mounting station (100); the introduction of the crankshaft (30) into said motor housing (60); and each contact condition of the rotor (50) with the stator (70), said control unit (120) determining the geometric center of the stator (70) from the information about the contact conditions informed by the sensor means and instructing the conveying means (130) to displace the crankshaft (30), until the alignment of the axis of the crankshaft (30) and the geometric center of the stator (70) has been obtained . 4. Device, as in claim 3, characterized in that it comprises a first and a second conveying means (110, 130), which are operatively connected to the mounting station (100) and to the control unit (120), said first conveying means (110) conducting said motor housing (60) to said mounting station (100). 5. Device, as in claim 4, characterized in that it includes sensor means provided in the second conveying means (130) and operatively connected to the control unit (120), in order to inform the latter about each contact condition between the rotor (50) and the stator (70) . 6. Device, as in claim 5, characterized in that the sensor means are pressure sensors .

Inventors: FERNANDES JOSE LUIZ PALOMAR, FERNANDES, JOSE, LUIZ, PALOMAR
Applicants: BRASIL COMPRESSORES SA, FERNANDES JOSE LUIZ PALOMAR, EMPRESA BRASILEIRA DE COMPRESSORES S.A. - EMBRACO, FERNANDES, JOSE, LUIZ, PALOMAR
Application year: 1999
Main classification: H02K15
IPC codes: H02K15