Reciprocating electric compressor

A reciprocating compressor includes a compressing unit placed over a motor unit. A crankshaft, which converts rotating action of the motor unit into reciprocating action of a piston of the compressing unit, has (a) a centrifugal pump provided at a lower section of the crankshaft, and (b) a pair of spiral pumps that communicate with the centrifugal pump and have leading grooves running in opposite directions to each other. The crankshaft also includes a pair of eccentric paths at its upper section. The eccentric paths open into an enclosed container and communicate with the spiral pumps respectively. This structure allows production of greater force for transferring lubricant oil regardless of the rotating direction of the crankshaft.

FIELD OF THE INVENTION

The present invention relates to reciprocating electric compressors to be used in refrigerating-cycle devices such as a refrigerator having a freezer, a vending machine, and an air-conditioner.

BACKGROUND OF THE INVENTION

A reciprocating electric compressor (hereinafter simply referred to as “compressor”) employed in refrigerating-cycle devices such as a refrigerator with a freezer, a vending machine, and an air-conditioner has been required to be highly efficient and reliable. In general, a conventional compressor is equipped with a crankshaft incorporating a lubricator, and a typical one is disclosed in Japanese Patent Publication No. S62-44108. The conventional compressor is described hereinafter with reference toFIG. 8.

FIG. 8is a sectional view of the conventional compressor. Compressor1is housed in enclosed container2, which accommodates frame3in the middle, motor unit4at a lower section, compressing mechanism5at an upper section. Crankshaft7extends through bearing6of frame3. On an outer wall of crankshaft7, rotor8of motor unit4is rigidly mounted. Crankshaft7has main shaft70and eccentric shaft9, and engages with slider11of piston10via eccentric shat9. Piston10is an element of compressing mechanism5.

Slant hole12(hereinafter referred to simply as “hole”) slantingly extends from the bottom of crankshaft7to the lower end of bearing6through crankshaft7, and opens onto the outer wall of shaft7. Hole12has a rather small diameter.

A part of crankshaft7rests within bearing6, and on this resting section, spiral pump14(hereinafter referred to simply as “pump”) is formed. Pump14comprises a single leading groove which communicates with lateral hole13at its lower end and vertical hole15formed in eccentric shaft9at its upper end. Vertical hole15opens into an inner space of container2at its upper end, and communicates with the slide face of thrust-bearing16at its lower end. Lubricant oil17is pooled in the lower section of container2, and crankshaft7dips therein at its lower end.

An operation of the foregoing conventional reciprocating compressor is described hereinafter. When motor unit4is turned on, rotor8starts spinning, which causes crankshaft7to rotate. Rotation of crankshaft7reciprocates piston10engaging with eccentric shaft9via slider11, so that compression is carried out. Lubricant oil17rises from the lower end of crankshaft7through slanted hole12due to centrifugal force, and moves upward via lateral hole13to pump14of main shaft70, which then transmits lubricant oil17to bearing16and eccentric shaft9, and then lubricant oil17is discharged into the space within container2.

As such, lubricant oil17rises through hole12, which extends slantingly and upward from the lower end of shaft7, due to centrifugal force, and pump14formed of the one-way leading groove from lateral hole13transfers lubricant oil17to the slide section of bearing16, where lubricant oil17performs lubricating action. A winding direction of the leading groove is determined on the premise that pump14operates in a given rotating direction. Therefore, if pump14operates in a direction opposite to the given one, a downward force is created by pump14, so that no lubricant oil is supplied to the upper section of bearing6. As a result, bearing6incurs abnormal abrasion, which causes a breakdown. For instance, in the case of a reciprocating compressor which employs a three-phase induction motor as the motor unit, it can be inversely rotated due to incorrect wiring. Thus a plugging relay needs to be integrated into the circuit for preventing the breakdown due to the reverse rotation; however, since the relay is so expensive, the cost of the compressor is obliged to increase.

There is another conventional reciprocating compressor which employs a single-phase and resistant-start induction motor using a PTC relay as a starter. In this compressor, when an instantaneous power interruption occurs, which does not give a recovery time to the PTC relay, the piston is pushed back due to the pressure of a compressed room. If the power is recovered during this reverse rotation, the compressor is kept rotating inversely. In this case, the lubricator does not work properly, and the slide section incurs a breakdown due to abrasion.

In order to overcome the problems discussed above, a reciprocating compressor equipped with both-way leading grooves has been proposed. This structure allows reversible operation; however, there is still no reciprocating compressor operable in both rotating directions and equipped with a compressing unit, which needs high pump-head for lubrication, over a motor unit.

SUMMARY OF THE INVENTION

The present invention provides a reciprocating compressor equipped with a compressing unit over a motor unit. Rotation of the motor unit is converted into reciprocation of a piston by a crankshaft. The crankshaft includes (a) a centrifugal pump disposed in a lower section, and (b) a pair of functionally independent spiral pumps having two leading grooves which communicate with the centrifugal pump and run in opposite directions to each other. The crankshaft opens into an enclosed container at its upper end, and has a pair of functionally independent eccentric paths (vertical holes) communicating with the spiral pumps respectively.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a sectional view of a reciprocating compressor in accordance with the first exemplary embodiment of the present invention.FIG. 2shows an enlarged view of a crankshaft of the compressor shown inFIG. 1.

Enclosed container18accommodates motor unit21comprising stator19and rotor20, and compressing unit22driven by motor unit21. Container18pools lubricant oil23at its lower section. Motor unit21is a three-phase induction motor which allows the compressor, powered by a three-phase power supply, to rotate in both directions regardless of wiring direction.

Compressing unit22is detailed now. Crankshaft24includes eccentric shaft25, sub-shaft section26and main shaft section27. Sub-shaft section26and main shaft section27sandwich eccentric shaft25vertically in a concentric manner. Cylinder block29includes compression chamber28, sub-bearing30and main-bearing31. Both of bearings30and31cross with an axis of compression chamber28at approximately right angles, and support sub-shaft section26and main-shaft section27respectively. Sub-bearing30can be disposed independently of cylinder block29and can be rigidly mounted to block29. This structure achieves high pump-head for lubrication and rotation in both directions.

Compression chamber28is equipped with piston32in a manner that piston32is slidable, and piston-pin33press-fit into piston32is linked to eccentric shaft25with a linking section, namely, connecting rod34. Valve-plate35includes an inlet valve and an exhaust valve (both are not shown), and is sandwiched by cylinder head36having an exhaust chamber (not shown) therein and cylinder block29. Suction muffler37having an inlet (not shown) is sandwiched by cylinder head36and valve plate35.

Main-shaft section27of crankshaft24has bottom hole38at its lower end. Cap41has throttle section40at its lower end and is press-fit into main-shaft section27. Suction hole39is prepared at the center of throttle section40. In main-shaft section27, slant path42extends slantingly and upward from bottom hole38such that the center of throttle section40is included within the inner wall of path42, which forms a hollow cylinder. Path42is placed such that its upper end reaches a lower section of main bearing31and approaches the outer wall of crankshaft24. As shown inFIG. 2, suction hole39has a diameter smaller than a diameter of the hollow cylinder of path42.

Main-shaft section27has spiral pumps43A,43B engraved on its outer wall. The pumps include leading grooves running counter to each other and forming helical grooves. Pumps43A and43B communicate with slant path42at communicating section44provided at a lower section of the main shaft. Sections other than communicating section44are disposed such that they are independent of each other and free from crossing with each other.

A pair of eccentric paths45A,45B stand vertically inside eccentric shaft25and sub-shaft section26and are independent of each other. Those two paths form vertical holes and communicate with upper ends of pumps43A,43B respectively at communicating sections46A,46B prepared in an upper section of the main shaft. Upper ends of paths45A,45B open on an upper end of sub-shaft section26and communicate with the inside of container18. Sub-shaft section26has a pair of spiral pumps48A,48B engraved on its outer wall, and those pumps form helical grooves communicating with each other via sub-shaft communicating sections47A,47B and paths45A,45B. Slant hole42has vent hole49at its end, and vent hole42communicates with the inside of container18and opens (via an upper opening) onto the upper end of main-shaft section27. As shown inFIG. 1, vent hole49includes a first part49athat extends upwardly along the rotation axis of the crankshaft24from an off-center position with respect to the rotation axis at an upper section of the hollow cylinder of path42, and a second part49bthat extends from an upper end of the first part to the upper opening located at the upper end of the main-shaft section27. Thrust bearing50is rigidly mounted to an end of sub-shaft section26, and forms a thrust bearing together with sub-bearing30.

An operation of the foregoing reciprocating compressor is demonstrated hereinafter. When stator19of motor unit21is powered, rotor20starts spinning. In this embodiment, rotor20spins along rotating direction51viewed down from a top of the compressor.

Rotation of crankshaft24causes eccentric shaft25to move eccentrically, which reciprocates piston32in compression chamber28via connecting rod34and piston-pin33. Refrigerant is sucked into chamber28via the inlet of suction muffler37, and compressed. The refrigerant passes through the exhaust valve, cylinder head36, the exhaust chamber, and is finally discharged to a refrigerating cycle (not shown) outside container18.

Next, the lubricating operation is demonstrated. Rotation of crankshaft24forces lubricant oil23to flow into cap41via suction hole39. Lubricant oil23then forms a parabolic free-surface in cap41due to centrifugal force and counter force to the gravity generated in throttle section40, and flows to slant path42via bottom hole38.

Since path42extends slantingly and upward from bottom hole38to form a centrifugal pump, lubricant oil23further rises to communicating section44due to this centrifugal force. As such, crankshaft24includes the centrifugal pump formed of the following two elements: (a) slant path42extending upward from the lower end of crankshaft24with its axis slanting toward the outer rim of crankshaft24, and (b) throttle section40leading to lubricant oil23. Thus lubricant oil23on the lower end of crankshaft24surrounded by throttle section40is subject to the centrifugal force due to the rotation of crankshaft24. Throttle section40receives the downward force generated by the centrifugal force, thereby increasing upward force. Further, the slant of path42efficiently increases the pump head of lubricant oil23. As a result, lubricant oil23can be transferred by the greater force regardless of the rotating direction.

Since eccentric shaft25rotates in direction51viewed down from a top of the compressor, lubricant oil23flows into pump43A from communicating section44. At this time, lubricant oil23will not flow into pump43B because a downward force of pump43B prevents lubricant oil23from flowing into pump43B.

Pump43A pushes lubricant oil23to rise, so that lubricant oil23further gains its pump head in path45A via communicating section46A, and then finally discharges and scatters from an upper opening of sub-shaft section26.

Part of lubricant oil23is supplied to eccentric shaft25by passing through path45A, and supplied to sub-shaft section26via communicating section47A. Part of lubricant oil23is also supplied to thrust bearing50via pump48A, so that respective sliding sections such as main-shaft section27, sub-shaft section26and eccentric shaft25are lubricated.

When rotor20rotates counter to rotating direction51, lubricant oil23flows into pump43B via communicating section44, and is pushed by pump43B upward, so that lubricant oil23passes through path45B via communicating section46B and gains its pump head in path45B, and then finally discharges and scatters from the opening at the upper end of sub-shaft section26. Lubricant oil23is supplied to sub-shaft section26via communicating section47B, and is also supplied to thrust bearing50from pump48B.

Lubricant oil23lifted by the centrifugal pump can thus be supplied to the respective sliding sections regardless of the rotating direction which can be changed by a wiring of the three-phase power supply. As a result, the reciprocating compressor has the compressing unit disposed at its upper section, and is compatible with both rotating directions.

Slant path42has hole49at its top end, and hole49opens onto the upper end of main-shaft section27to communicate with the inside of enclosed container18. This structure allows refrigerant gas generated from lubricant oil23to discharge into container18via hole49. As such, the refrigerant gas of lubricant oil23existing in the lubricating route of crankshaft24can be exhausted, so that obstruction of the lubrication due to gas is reduced. A larger height between the lubricant oil surface in slant path42and the opening of hole49can prevent lubricant oil23from flowing out from hole49, and this structure allows a relative increase of a pumping-up amount of lubricant oil23, thereby preparing a sufficient amount of lubricant oil.

Meanwhile, a conventional lubricating mechanism similar to this first embodiment is compared with the foregoing operation.FIG. 3is an enlarged view of a conventional crankshaft similar to that of the first embodiment. This similar one has the following two different points: (a) This similar crankshaft is engraved with leading grooves of bilateral directions such that spiral pumps43C and43D of the main shaft share their outlet. (b) There is one communicating section46C of the main shaft and there is one eccentric path45C.

Since pumps43C and43D generate pressure to transfer the lubricant oil upward, this similar structure, in which the lubricant oil rises through a single line, i.e.,46C-45C, can be designed as a matter of course. This similar structure, however, discharges substantially less amount of lubricant oil from the top end of crankshaft24.FIG. 4shows the comparison between this similar structure and the structure of the first embodiment, namely, the amounts of lubricant oil supplied to both the structures per minute at 50 Hz and 60 Hz of power-supply frequency are compared. The result tells that the structure of the first embodiment can supply much more lubricant oil than the similar structure at both the frequencies.

In this similar structure, leading grooves of bilateral directions communicate with each other at communicating section46C, so that a closed loop is formed such that parts of lubricant oil23drawn-up through a leading groove running along the rotating direction is restored toward the centrifugal pump through a leading groove running counter to the rotating direction. As a result, lubricant oil23supplied to eccentric path45C decreases.

As discussed above, the first embodiment provides a pair of pumps43A,43B and a pair of slant paths45A,45B, and those pairs form functionally independent systems. This structure allows any pumps active with respect to the rotating direction to transfer lubricant oil23upward free from interference from the lubricating paths regardless of rotating directions of crankshaft24. Thus the pressure for transferring the lubricant oil is not weakened.

Moreover, sub-shaft section26has a pair of pumps (helical grooves)48A,48B engraved on its outer wall. Pumps48A,48B are functionally independent. The pumps are communicated with paths45A,45B via communicating sections47A,47B. This structure allows sub-bearing30to keep holding the lubricant oil regardless of rotating direction.

FIG. 5shows a sectional view of a reciprocating compressor in accordance with the second exemplary embodiment of the present invention.FIG. 6is a circuit diagram of the compressor, andFIG. 7illustrates an operation of the compressor. The same elements as those in the first embodiment have the same reference marks, and the descriptions thereof are omitted here.

The second embodiment employs a motor unit different from that used in the first embodiment. Motor unit21A is a single-phase resistant-start induction motor comprising rotor52and stator53. As shown inFIG. 6, in stator53, main coil54and starter coil55are coupled with each other in parallel, and PTC relay56is coupled with starter coil55in series as a starter.

An operation of the foregoing reciprocating compressor is demonstrated hereinafter. Upon energization, starter coil55is energized with the resistance of an element of PTC relay56, and starting torque occurs in a given rotating direction for starting the operation. The element of PTC relay56sharply increases its resistance in one second after the start due to self-heating. Starter coil55is thus interrupted, and the current runs through only main coil54to keep the compressor operating. When the operation is halted, starter coil55needs to be energized for re-starting the operation. For that purpose, the element of PTC relay56needs cooling time57for reducing the resistance. If the cooling time is too short, the element of PTC relay56still remains in high-resistance state, and starter coil55cannot be energized, so that the compressor does not start.

In such a case, i.e., when the starter torque does not occur, if some external force is applied and it works as the starter torque, rotor52rotates along the direction of the external force. To be more specific, as shown inFIG. 7, instantaneous power interruption58shorter than one second happens. For instance, if piston32stops at a timing of just before the top dead center, piston32is pushed back by the pressure in compression chamber28, so that inverse rotation59occurs. During this inverse rotation, if energization60is restored, operation61is maintained with the inverse rotation kept going.

However, as described in the first embodiment, the reciprocating compressor in accordance with the present embodiment can achieve steady lubrication regardless of the rotating direction. Therefore, if the compressor falls into an abnormal operation as discussed above, it never incurs a breakdown due to abrasion, so that the compressor is proved highly reliable.

The foregoing discussion proves that the present invention can achieve steady lubrication regardless of the rotating direction, and provide a reliable compressor.