Field of the Invention

The present invention refers to an axial bearing for hermetic compressors with a vertical shaft, of the type used in small refrigerating appliances. Background of the Invention

Hermetic compressors comprise, mounted inside a hermetically sealed shell, a cylinder block carrying a vertical crankshaft, by seating a portion of a peripheral flange for supporting said crankshaft onto an axial bearing provided between said flange and the main bearing of the cylinder block. In a conventional construction, the axial bearing is in the form of a supporting cylindrical ring, seated on an adjacent bearing surface of the cylinder block.

The crankshaft carries, at the median portion thereof, a rotor of the electric motor of the compressor and, at its bottom, a pump rotor which, during the operation of the compressor, takes lubricant oil from a sump provided at a lower portion of the compressor shell, up to the relatively moving parts, in order to form an oil film between said parts, avoiding the wearing contact therebetween. Between the peripheral flange of the crankshaft and the axial bearing, the oil film should assure the maintenance of a parallelism condition between the adjacent surfaces of said parts. There are, however, factors of mechanical nature which, during the compressor operation, cause loss of parallelism between said surfaces, one of said factors resulting from malformation of the contacting parts. Moreover, during the compressor operation, small inclinations of the crankshaft occur in function of the temporary build up of load over the eccentric of said crankshaft during the rotation thereof. This effect is mainly felt during compression, when the forces over the crankshaft are

much higher than the forces to which the latter is submitted during suction.

In the constructions in which the components do not have a geometry that is favorable to the formation of an oil film, the lubrication during the compressor operation will be deficient, allowing frictional contact to occur between the parts, causing mechanical losses in the compressor. Theoretically, though the bearings with parallel surfaces do not generate a hydrodynamic support, manufacture imperfections, thermal deformations or inclinations of the crankshaft during its rotation may give rise to an oil film between the annular surface of the axial bearing and the adjacent surface of the crankshaft, which however is not enough to guarantee an adequate operation of the bearing.

In order to obtain a convenient hydrodynamic force in axial bearings with parallel surfaces, it is necessary to provide said bearings with large surfaces, which, on the other hand, increases friction losses.

The patent application PI9301036 discusses constructions of an axial bearing, in which its top surface contacting the peripheral flange of the crankshaft is provided with superficial irregularities which improve the maintenance of the oil film between said axial bearing upper face and an adjacent contacting lower surface of the crankshaft peripheral flange, said irregularities being constructed so as to provide a hydrodynamic effect which increases the thickness of the oil film between said parts. Though this construction reduces the friction wear between the relatively moving parts, in order that the lubrication of said parts occurs satisfactorily mainly when they are submitted to efforts resulting from the compressor operation, the achievement of said parts requires a high level of precision, meaning high production costs.

The constructive inaccuracy or the disalignment between the parts to be lubricated may cause rupture of the oil film in regions of said parts where the axial force of the weight of both the motor and crankshaft acting vertically and downwardly over the bearing exceeds the compensating force of the oil film. Disclosure of the Invention

Thus, it is an object of the present invention to provide an axial bearing for a hermetic compressor which maintains substantially unaltered the thickness of an oil film between the peripheral flange of the crankshaft and the axial bearing during the compressor operation, minimizing friction losses between the respective contact surfaces, thereby increasing the efficiency of the compressor.

This and other objectives are attained with an axial bearing for a hermetic compressor of the type including a vertical crankshaft incorporating a peripheral flange which is supported, through an oil film, on the upper face of the annular bearing body, said bearing resting on a cylinder block, said bearing further comprising a supporting means which, at the lower portion thereof, is seated on the cylinder block and which carries, at its upper portion and in a fixed rotating form, the lower face of the annular bearing body, said supporting means causing during the compressor operation a downward oscillation of the annular bearing body around a diametral axis, said oscillation occurring over a circumferential portion of the supporting means submitted to an axial force, resulting from an oil film pressure over the respective circumferential portion of the annular bearing body higher than the oil film pressure over the diametrically opposite portion of the annular bearing body, said oscillation being sufficient to balance the oil film pressure in said circumferential portions.

Brief Description of the Drawings

Fig. 1 shows, schematically and partially, a median vertical sectional view of a hermetic compressor with a vertical crankshaft of the type used in the present invention;

Fig. 2 shows, schematically and in a longitudinal sectional view, an upper portion of a crankshaft-axial bearing assembly mounted to the cylinder block according to a constructive form of carrying out the present invention;

Fig. 3 shows, schematically and in a perspective view, the axial bearing illustrated in figure 2; and Fig. 4 shows, schematically and in a perspective view, another constructive form of the axial bearing of the present invention, to be mounted to the cylinder block. Best Mode of Carrying Out the Invention

According to figure 1, there is illustrated a hermetic compressor with a vertical shaft, comprising a hermetic shell 1, inside which is adequately suspended a motor- compressor unit formed by a cylinder block 3 to which is attached an electric motor, whose rotor 4 is fixedly mounted to a crankshaft 5 seated on a main bearing machined in the cylinder block 3. The crankshaft 5 has, at its upper portion, a peripheral flange 7 for supporting an eccentric end portion 8 of the crankshaft 5 and, at its lower portion, a pump rotor which carries oil from an oil sump 9 to the parts of the cylinder block 3 needing lubrication during the compressor operation . The rotation of the crankshaft 5 around its axis generates a relative movement, between the lower face of the peripheral flange 7 of said crankshaft 5 and the adjacent bearing surface which supports said peripheral flange 7, which movement, due to machining imperfections of the parts, thermal deformations or occurrence of small inclinations of crankshaft 5 during

its rotation, may cause rupture of the oil film, allowing visco-mechanical losses to occur in the compressor. In some constructions, crankshaft 5 is supported, through an oil film, by an axial bearing seated on the cylinder block 3.

In the condition of precisely obtained adjacent surfaces, the forces acting over the oil film and resulting from, e.g., the weight of the crankshaft 5, are equally distributed along the circumferential length of the upper surface of the axial bearing, thereby generating equal reaction forces of the oil and maintaining substantially constant the oil film thickness between the peripheral flange 7 of the crankshaft 5 and the axial bearing for supporting the same. Nevertheless, the existence of irregularities on at least one of the respective adjacent faces causes an increase of the compressive force over the oil film at the regions where said excess of force is found, causing rupture of the oil film in said region. According to the present invention, the reduction of the power losses of the compressor as cited above is achieved by using an axial bearing, comprising an annular bearing body 10, in whose upper face is seated a peripheral flange 7 of the crankshaft 5 through an oil film formed between said parts, and a supporting means 20, which is seated at its lower portion on the cylinder block 3 and which supports at its upper portion, in a fixed rotating manner, the lower face of the annular bearing body, said supporting means 20 causing during the compressor operation a downward oscillation of the annular bearing body 10 around a diametral axis, said oscillation occurring over a cicumferential portion of the supporting means 20 submitted to an axial force resulting from an oil film pressure over the respective circumferential portion of the annular bearing portion 10 higher than the oil film

pressure over a diametrically opposite portion of the annular bearing body 10, said oscillation being enough to equilibrate the oil film pressure in said diametrically opposite circumferential portions. In a constructive form of the present invention, the annular bearing body 10 is preferably constructed as the one described in Patent Application PI9301036 and has an annular cylindrical form, with an upper face shaped so as to act as a hydrodynamic wedge in the distribution of oil between the adjacent surfaces of the peripheral flange 7 of the crankshaft 5 and the upper face of the annular bearing body 10. In a form of carrying out the present invention, as illustrated in figures 2 and 3, the supporting means 20 is elastically deformable between an operative condition, defined when said supporting means 20 is submitted to different axial forces resulting from different oil film pressures along the circumferential extension of the annular bearing body 10, and an inoperative condition, defined when a pressure balance of the oil film exists along said circumferential extension of the annular bearing body 10. The contractive axial force reduces the oil film thickness at the circumferential portion where the force is acting, capable of causing rupture of said oil film in this region, with the consequences already discussed above.

In a preferred illustrated form of carrying out the invention, according to the constructive concept described above, the supporting means 20 is defined by at least a flexible annular element, illustrated in figure 3 and disposed concentrically to the crankshaft 5, in the form of a spring element, for instance. In another possible construction according to this inventive concept, the supporting means 20 comprises a plurality of flexible elements, such as vertical

springs, which are circumferentially and equally distributed between the cylinder block 3 and the annular bearing body 10, so that each flexible element be provided with a respective contact surface relative to the main bearing of cylinder block 3 and a contact surface with a lower surface of the annular bearing body 10.

According to another constructive concept of the present invention, as illustrated in figure 4, the supporting means 20 comprises a rigid ring 21, provided with a pair of lower saliences 22, diametrically opposite to each other, each lower salience 22 seating on an adjacent portion of the main bearing surface of cylinder block 3, defining an oscillating axis for the supporting means 20 around which said supporting means 20 and annular bearing body 10 oscillate to compensate the existence of axial forces resulting from an oil film pressure over the annular bearing body 10 as cited above. The compensation of the axial forces acting in any circumferential portion of the annular bearing body 10 occurs, in this construction, by providing at least another oscillating axis for the annular bearing body 10, preferably ortogonal to the oscillating axis cited above. In the preferred illustrated construction, this other axis is defined by providing a lower face of the annular bearing body 10 with a pair of lower projections 11, diametrically opposite to each other and each seating on a portion of the adjacent surface of the rigid ring 21. In another possible construction, the supporting means 20 has a plurality of rigid rings provided with lower saliences 22, diametrically opposite to each other and seated on a surface of an adjacent lower rigid ring, in order to avoid coplanarity of the oscillating axes . In these constructions, the dampening of the forces actuating on the annular bearing body 10 occurs by an

oscillating movement around the oscillating axes mentioned above.

In order to avoid that the oil, which is being pumped by the crankshaft during the rotation thereof, be radially expelled by the supporting means 20, the latter is mounted around a tubular axial extension 30 of the cylinder block 3 concentric to the annular bearing body 10 and with an axial height sufficient to prevent said oil from escaping. With the axial bearing constructions of the present invention, the compressive forces, which are circumferentially located over the oil film and which result from irregularities projecting from at least one of the adjacent surfaces of the peripheral flange 7 of crankshaft 5 and annular bearing body 10, are compensated by reaction forces of the supporting means 20, acting in an opposite direction to that of the compressive forces, in order to maintain substantially unaltered the oil film thichness existing in this region, minimizing the contact between the frictional surfaces during the compressor operation . While two preferred constructions for the axial bearing have been described and illustrated, other constructions are possible within the concept presented. In order to restore the pressure balance of the oil film between the peripheral flange 7 and annular bearing body 10, the supporting means 20 should have at least two dontact surfaces with said annular bearing body 10, angularly equidistant from each other, and at least two contact surfaces with cylinder block 3 angularly equidistant from each other.