OIL PUMP FOR A HERMETIC COMPRESSOR

Abstract: Hermetic refrigeration compressor for household and similar refrigeration appliances, comprising a sealed casing (12), whose bottom (10) forms a sump for the lubricating oil (14), in which there are housed both the actual compressor and the related driving motor (16) which share a hollow crankshaft (20) rotating about a vertical axis, pumping means (34, 36) for the lubricating oil being connected to the lower end portion of said crankshaft. Said pumping means comprise a sleeve (34), which is rigidly fixed at the lower end portion of the crankshaft (20), and a piston member (36) which is elastically connected to the stator (22) of the motor (16) and floats freely inside said sleeve.

Description: OIL PUMP FOR A HERMETIC COMPRESSOR DESCRIPTION The present invention refers to a hermetic refrigeration motoi compressor unit, in particular for use in household-type refrigeration appliances. The actual refrigeration compressor (which is usually of the reciprocating or rotary type) and the related electric driving motor are generally known to have a common shaft and to be enclosed m a sealed casing. Owing to the resulting impossibility foi any kind of maintenance to be earned out subsequently, it is imperative for an effective, continuous and reliable lubrication of the moving pails of such a hermetically sealed unit to be assured throughout the operating life span, which may amount to as many as more than 15 years, of the lefngeration appliance in which such a unit is mounted. To this puipose, the hermetic motor compressor unit comprises means that are adapted to ensure, during the operating periods thereof, an adequate flow of the oil that is filled in an appropriate quantity in the sealed casing at the end of the compressor manufacturing cycle, m such a manner as to enable it to not only lubricate said moving parts, but also prevent them from overheating. It is a genei ally known practice for the above mentioned means to be provided m the form of a downwaid extension of the shaft, that is longitudinally bored and shaped so as to be capable of drawing in the oil from the bottom of the sealed casing and diffusing it substantially by centrifugal effect, into the parts to be lubricated Such a construction is usually effective in the case of traditional hermetic motoi compressoi units that aie equipped with a single-phase two-pole induction motoi operating at 2700 to 3000 ipm Howevei , heimetic motor compressor units are increasingly being used since a few years now, which aie equipped with electnc direct-current brushless motors that are capable of operatmg at adjustable speeds varying from a maximum that may reach as many as 4000 ipm to a minimum that may on the contrary be as low as 1000 ipm or even less, to the puipose of optimizing the perfoimance of the related lefngeration appliance, particularly from an energy usage point of view Hermetic motoi compressoi units aie also known which are equipped with a four-pole induction motor operating at a speed of only 1500 ipm so that, for a same lenigeiation capacity oi output, a greatei displacement of the compressor is needed In both above cited cases, the traditional lubiication and cooling means as the afore mentioned ones aie laigely inadequate owmg to the fact that the low otational speeds of the shaft do not ensme any adequate delivery head and flow ate of the oil sucked m from the bottom of the sealed casing, or a thorough diffusion of the same oil to all parts that need to be lubricated In a heimetic motor compiessoi unit in which the electnc d vmg motor is arranged below the compressoi , it has been pioposed that a worm-screw mernbei be inserted with a slight I adial gap in the hollow shaft stalling from the lowei end theieof (see document WO 96/29516) The relative movement between the shaft and the woim-sciew member, which extends along the entire electric dnvmg motoi and is letamed by a support being fixed to the stator of the motoi , ensures the desued oil flow This solution has howevei a drawback m that the helical insert is completely contained inside the shaft and is affected by the heat tiansmitted by the motoi As a lesult mutual expansions tend to take place during the opeiation of the motoi compiessoi unit, which cause the ladial gap between the insert and the shaft to be altered, under corresponding variations m the lubrication performance It has been also proposed that a pumping chamber with a worm-screw member attached protrudmgly to the lower end portion of the shaft and a therewith associated stationary sleeve (see documents WO 93/22557 and EP-A-0 728 946) be provided m the motor compressor unit. This kind of solution causes a further radial gap to be created between the stationary sleeve and the inner surface of me rotating shaft, so that leakages unavoidably take place owing to oil seeping through said gap, with the lesult of a reduced flow rate of the oil bemg pumped Furthermore, a solution of this kind proves quite difficult and expensive to implement, smce caie shall duly be taken to ensure, between the two component parts of the pumping chambei , not only the afore mentioned circumferential gap, but also a gap on the horizontal plane between the sleeve and the lower end portion of the shaft in view of preventing said parts from undergoing a weardown effect brought about by fnction during operation It therefore is a main puipose of the present invention to provide, through the use of simple, leliable and low-cost means, an improved hermetic motoi compressor unit that is capable of ensuring an effective oil flow even at operating speeds thereof that may be as low as appiox 800 rpm As this will be bettei explained furthei on, this and further aims are leached in a hermetic motor compiessor unit provided with an oil suction arrangement featunng the chai acteπstics as I ecited m the appended claims Anyway, such featuies along with the advantages of the present invention, will be more readily undei stood from the description that is given below by way of non-limitmg example with lefeience to the accompanying drawings, m which - Figuie 1 is a ci oss-sectional view along a vertical plane of the lower portion of a heimetic motoi compressor unit compπsimg the oil suction arrangement according to the piesent invention, in a first embodiment theieof, - Figure 2 is a similai view as the one illustrated m Figure 1 , but showing only the oil sucnon arrangement in a second embodiment thereof; - Figure 3 is an exploded view of the component parts of the oil suction arrangement shown in Figure 2 With reference to Figure 1, it can be nohced that the items and details of the hermetic motor compressor unit that are of no relevance to the purposes of the present invention, starting from the actual compressor, are not shown since considered to be lai gely known to all those skilled in the art. A metal sealed casing 10 has a lower portion 12 that forms the sump m which the oil 14 collects which, filled in durmg compressor manufacturing, ensures the iubncation of the moving parts of an electric driving motor 16 and a compressor situated thereabove that may for instance be of the reciprocating type. In this particular embodiment, the motor 16 is of the direct-current brushless type with a permanent-magnet rotor 18 fixed to a vertical hollow shaft (which is common to the compressor situated thereabove) and a similar stator 22. The lower portion of the stator comprises a shroud 24 that supports (with the aid of a pair of slots that are not shown in the Figure for reasons of greater simplicity) the end portions 26 and 28 of a biacket 30 that is preferably made out of spring-steel rod. As it can be noticed, this bracket 30 is substantially in the shape of a U with a recessed central zone 32 Fixed to the lowei end portion of the hollow shaft 20 there is a sleeve 34 that extends further vertically into the sump 10 so as to be able to plunge mto and draw from the lubrication oil collected therein. The sleeve 34 is adapted to rotate jointly with the hollow shaft 20 Inserted inside the sleeve 34 there is an oil suction member 36 which is piovided, on its outer suiface, with a helical groove that advantageously extends thioughout, le covers the entne length of the same membei This groove, by cooperating with the inner wall of the sleeve 34 forms a channel ensunng the passage of the oil from the sump 10 to the interior of the shaft 20 The sleeve 34 and the fluted member 36 are preferably made of plastic material le a material with a lower heat conductivity than the one of the metal matenal used to make the hollow shaft 20 itself This solution is clearly simpler and less expensive as far as both the construction itself and the assembly are concerned It furthermore enables the pioblems associated to the mutual thermal expansion of the sleeve and the fluted member to be largely eliminated Conclusively, the performance and reliability characteristics of the whole hermetic motoi compressor unit are impioved, accrdrng to the actual purpose of the present invention The fluted membei 36 is sustained by the elastic biacket 30 whose central zone 32 inserts fieely m a notch piovided m the lowei head portion of the member 36 This type of elastic assembly enables the member 36 to float but not lotate, inside the sleeve 34 durmg the opeiation of the motor compressoi unit, thereby enabling possibly occurring misalignments of the shaft 20 and the oil suction arrangement to be compensated for A second embodiment of the piesent invention, which is based on the same peiatmg principle and ensures piactically the same level of effectiveness as the afore described embodiment, is illustrated in Figures 2 and 3, in which the same lefeience numeials aie used to indicated items and details coi responding to the ones illustiated in Figuie 1 As a lesult, to the lowei end portion of the shaft 20 there is again fixed a sleeve 34, in this case howevei via an extension 40 of the same shaft In the sleeve 34 there is inserted a floating piston member 36 that is sustained by the elastic biacket 30 whose end portions 26 and 28 aie connected to the shroud of the motoi 16, as this is shown m Figure 1 The constiuction-i elated diffeience lies m the fact that the floating member 36 (Figuie 2) is piovided in its outer surface with two axial and diametiically opposed lecesses 42 that coopeiate with coi responding apertmes 44 and 54 which are provided at lespective at lespective different levels and pass through the wall of the sleeve 34 Furthermore a undulated cam-profiled spring washer 46 is mounted between the membei 36 and the sleeve 34 This cam-profiled washer 46 is fixed to the sleeve 34, piefeiably by bonding, and is adapted to act against a cross extension 56 that is provided at the lower end portion of the member 36 This extension 56 is in turn provided with a downward open notch, in which the elastic bracket 30 sustaining the oil suction arrangement is able to insert freely The attachment of the extension 40 to the shaft 20 (see Figure 2) is brought about simply by pi ess-fitting the two parts together, thanks to the ability of the upper end portion of the extension 40 to deform owing to the presence of a notch 48, as well as to a button 50 engaging a recess 52 The button 50 and the recess 52 are provided on the outer surface of the extension 40 and the inner surface of the shaft 20, respectively During the operation of the unit, when the shaft 20 rotates jointly with the extension 40 and the sleeve 34, the cam-profiled washer 46 acts against the extension 56 and pushes the piston-like member 36 downwards against the action of the elastic bracket 30 that tends to bias, le push the member 36 upwards As a result, thanks to the combined effect of the curvature of the washer 46 and the elasticity of the biacket 30, the rotation of the shaft 20 is able to bnng about a reciprocating movement of the member 36 in a vertical direction The lubiicating oil is drawn in from the oil sump into the recesses 42 of the piston-like membei 36 when the sleeve 34 is rotated into the position m which it allowsthe lecesses 42 to communicate with the lower apertuies 44 This occurs during the downstioke of the membei 36 When the sleeve 34 is then rotated by an angle of appiox 90° with lepect to the above mentioned position, the oil is able to flow from the recesses 42 through the upper apertures 54 into the hollow shaft 20 This occuis during the upstroke of the membei 36 The descnbed solution theiefoie constitutes an effective positive-displacement piston pump without moving valves

Claims: CLAIMS 1. Hermetic motor compressor unit for household and similar refrigeration appliances, comprising a sealed casing (10), whose bottom (12) forms a sump for the lubricating oil (14), in which there are housed the actual compressor and the related driving motor (16) which share a common hollow crankshaft (20) rotating about a vertical axis, lubricating oil suction means (34, 36) being provided at the lower end portion of said crankshaft, characterized in that said oil suction means comprise a sleeve (34), which is rigidly fixed to the lower end portion of the crankshaft (20) and in which a fluted member (36) is inserted that is connected elastically with the stator (22) of the motor (16), said oil suction means extending downwards fully outside said hollow shaft (20). 2. Hermetic motor compressor unit according to claim 1, characterized in that said sleeve (34) and said fluted member (36) are made of a material having a lower thermal conductivity than the material of which the hollow shaft (20) is made. 3. Hermetic motor compressor unit according to claim 1 or 2, characterized in that said fluted member (36) is sustained by a substantially U-shaped bracket (30) formed by a metal wire or strip, whose intermediate zone (32) engages the lower end portion of the fluted member, and whose side aims (26, 28) are anchored to the stator (22) of the electric motor (16). 4. Hermetic motor compressor unit according to any of the claims 1 to 3, characterized in that said fluted member (36) is a member that is provided on its outei suiface with a helical groove foiming the channel for the compressor lubiication oil (14) to pass therethiough 5. Hermetic motor compressor unit according to any of the claims 1 to 3, characterized m that said fluted element (36) is a piston-like member that is provided on its outer surface with axial, mutually opposed recesses (42) that are adapted to coopeiate with corresponding radial apertures (44, 54) provided at respective drffei ent levels and passing through the wall of said sleeve (34) 6. Heimetic motor compressor unit according to claim 5, charactenzed in that at the lower end portion of said sleeve (34) there is fixed a undulated cam-profiled spring washer (46) that cooperates with a cross extension (56) of said piston-like membei (36)

Inventors: DELLBY FREDRIK, ZONTA CARLO, DELLBY, FREDRIK, ZONTA, CARLO
Applicants: DELLBY FREDRIK, ZANUSSI ELETTROMECC, ZONTA CARLO, DELLBY, FREDRIK, ZANUSSI ELETTROMECCANICA S.P.A., ZONTA, CARLO
Application year: 1999
Main classification: F04B39
IPC codes: F04B39