Motor of compressor and refrigeration cycle apparatus

A compressor includes: a stator core including a plurality of teeth around which an aluminum winding wire is wound in a concentrated manner; a rotor core disposed on an inner diameter side of the stator core and including a plurality of magnet insertion holes; and a plurality of ferrite magnets inserted in the magnet insertion holes, in which when a width of a winding wire portion formed in each of the teeth is represented as A, a length in an axis direction of the stator core is represented as L, and the number of slots is represented as S, the stator core has a shape that satisfies a relation of 0.3<S×A÷L<2.2.

CROSS REFERENCE TO RELATED APPLICATION

This application is a U.S. national stage application of International Patent Application No. PCT/JP2014/072755 filed on Aug. 29, 2014, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a motor of a compressor that, while converting a refrigerant subjected to a low temperature and a low pressure into a refrigerant subjected to a high temperature and a high pressure, and circulates the resultant refrigerant, and a refrigeration cycle apparatus including the compressor.

BACKGROUND

A conventional motor disclosed in Patent Literature 1 listed below has a configuration in which a cylindrical permanent magnet is disposed on an outer circumference of a rotor core and a magnetic tube made of stainless steel is further disposed on an outer circumference of the permanent magnet to prevent significant demagnetization of the permanent magnet due to a high temperature. Magnetic resistance of a magnetic circuit viewed from the permanent magnet is reduced by the magnetic tube provided between the permanent magnet and a stator, a residual magnetic flux density at an operating point of the permanent magnet at the time of armature reaction increases, and a magnetic flux reaching a stator core from the permanent magnet increases. Therefore, the conventional motor disclosed in Patent Literature 1 listed below can prevent demagnetization of the permanent magnet and prevent a reduction of its output even when the permanent magnet has a high temperature and armature reaction is exerted.

PATENT LITERATURE

However, because a magnetic permeability of stainless steel constituting the magnetic tube is lower than a magnetic permeability of silicon steel or Armco ion used for the rotor core and the stator core, the configuration taught by Patent Literature 1 is unsuitable for improving the motor efficiency. On the other hand, in a compressor, during one revolution of a rotor, a compression torque varies according to a rotational position of the motor, and the maximum value of the compression torque may be three times an average torque depending on an operation condition. In a motor of a compressor, demagnetization of a rotor magnet depends on a peak current flowing at the time of the maximum compression torque. Therefore, a motor of a compressor needs to conform to a specification with demagnetization resistance considered more significantly than a motor represented by Patent Literature 1 mentioned above, that is, a motor used for a mechanism including no load change.

SUMMARY

The present invention has been achieved in view of the above circumstances, and an object of the present invention is to provide a motor for a compressor that can improve demagnetization resistance while suppressing a reduction in motor efficiency.

In order to solve the above-mentioned problems and achieve the object, the present invention provides a motor of a compressor comprising: a stator core including a plurality of teeth and a plurality of slots formed between the teeth, an aluminum winding wire being wound around the teeth in a concentrated manner; a rotor core disposed on an inner diameter side of the stator core and including a plurality of magnet insertion holes; and a plurality of ferrite magnets inserted into the magnet insertion holes, wherein when a width of a winding wire portion formed in each of the teeth is represented as A, a length in an axis direction of the stator core is represented as L, and the number of the slots is represented as S, the stator core has a shape that satisfies a relation of 0.3<S×A÷L<2.2.

Advantageous Effects of Invention

According to the present invention, an advantageous effect is yielded in that it is possible to improve demagnetization resistance while suppressing a reduction in motor efficiency.

DETAILED DESCRIPTION

A motor of a compressor and a refrigeration cycle apparatus according to embodiments of the present invention will be described below in detail with reference to the drawings. The present invention is not limited to the embodiments.

First Embodiment

FIG. 1is a side view of a motor of a compressor according to a first embodiment of the present invention,FIG. 2is a sectional view of a stator and a rotor illustrated inFIG. 1taken along a line in the direction by arrows A-A, andFIG. 3is a configuration diagram of a refrigeration cycle apparatus having the compressor illustrated inFIG. 1mounted thereon.

A compressor100illustrated inFIG. 1includes a stator1disposed on an inner circumferential surface of a frame (not illustrated), a rotor2disposed on an inner diameter side of the stator1with a clearance8located therebetween, and a compression unit3to which a shaft7penetrating the rotor2is connected. Discharge holes3afor discharging a high-pressure refrigerant compressed by the compression unit3are formed on an upper portion of the compression unit3.

The stator1and the rotor2constitute a motor of the compressor100. The stator1is fixed to the inner circumferential surface of the frame (not illustrated) by press fitting, shrinkage fitting or freeze fitting. The shaft7is held in a state such that the shaft can rotate by bearings (not illustrated) provided on an upper part and a lower part of the compressor100.

The stator1illustrated inFIG. 2is composed of an annular stator core5constructed of a number of electromagnetic steel sheets each having been formed in a specific shape by a stamping process, and having been stacked on top of another in an axis direction, and an aluminum winding wire6to which external electric power is supplied.

The stator core5has an annular back yoke5a, and a number of teeth5bthat are arranged on an inner diameter side of the back yoke5aat regular intervals in a rotation direction and that extend from the back yoke5atoward a center of the stator core5.

Each of the teeth5bhas a winding wire portion5b1around which the aluminum winding wire6is wound, and an umbrella-shaped tooth end portion5b2that is formed on an inner diameter side of the corresponding tooth5band has a facing surface5efacing the rotor2, which extends in the rotation direction.

A number of slots5dare also formed on the stator core5, which are spaces delimited by the back yoke5a, the winding wire portions5b1and the tooth end portions5b2.

In the illustrated example, nine teeth5bare formed. The width in the rotation direction of the winding wire portion5b1is constant from the back yoke5ato the tooth end portion5b2. The aluminum winding wire6that generates a rotating magnetic field is wound around the winding wire portion5b1in a concentrated winding method. InFIG. 2, only the aluminum winding wire6that is wound around one winding wire portion5b1is illustrated and illustrations of the aluminum winding wire6on the other portions are omitted.

The rotor2includes a cylindrical rotor core2aformed by stacking a number of electromagnetic steel sheets each having been formed in a specific shape by a stamping process, and having been stacked on top of another in the axis direction, a number of magnet insertion holes2bprovided at regular intervals in the rotation direction in correspondence with the number of magnetic poles and having a curved shape protruding to a radially inner side, ferrite magnets2ceach having a shape corresponding to the shape of the magnetic insertion hole2band inserted into the magnetic insertion holes2b, respectively, and a shaft insertion hole2dformed at a center about a radial direction of the rotor core2a.

The shaft7is fixed to the shaft insertion hole2dby press fitting, shrinkage fitting or freeze fitting. The magnet insertion holes2bextend in the axis direction, and six ferrite magnets2care inserted into the magnet insertion holes2b, respectively, in the illustrated example.

The clearance8is formed between an outer circumferential surface of the rotor2and the tooth end portions5b2. When the aluminum winding wire6is subjected to electric conduction, a rotating magnetic field is generated between the rotor2and the stator1, and thereby the rotor2is rotated.

A refrigeration cycle apparatus30illustrated inFIG. 3includes the compressor100illustrated inFIG. 1, a control circuit31, a temperature sensor32, a condenser33, a decompression device34, an evaporator35, a bypass circuit36, an on-off valve37, and anther decompression device38.

The control circuit31controls the on-off valve37based on a detection result of the temperature sensor32. The temperature sensor32is provided near a gas outlet of the compressor100to detect a temperature of a refrigerant flowing through the gas outlet. The bypass circuit36constituted by the decompression device38and the on-off valve37that are connected in series is interposed between a liquid refrigerant outlet of the condenser33and a gas inlet of the compressor100. The refrigeration cycle apparatus30is suitable for an air conditioner.

An operation is described below. High-temperature and high-pressure refrigerant gas compressed by the compressor100exchanges heat with air and condenses to become a liquid refrigerant in the condenser33. The liquid refrigerant expands in the decompression device34to become low-temperature and low-pressure refrigerant gas. The low-temperature and low-pressure refrigerant gas sucked in the compression unit3illustrated inFIG. 1is compressed in the compression unit3based on rotation of the rotor2to have a high temperature and a high pressure again. The high-temperature and high-pressure refrigerant gas passes through the clearance8between the stator1and the rotor2or the slots5d, and is discharged from a discharge pipe (not illustrated) formed on the compressor100. In this manner, in the refrigeration cycle apparatus30, the refrigerant circulates through the compressor100, the condenser33, the decompression device34and the evaporator35in this order, and returns again to the compressor100.

FIG. 4is a chart illustrating variation in a compression torque of the compressor. Because the compressor100performs a compression operation, the compression torque changes while the rotor2rotates one revolution as illustrated inFIG. 4. Assuming that an average torque Ta is 100%, the maximum value of the compression torque may reach 300% that is three times the average torque Ta depending on an operation condition.

In the motor used in the compressor100, demagnetization of a rotor magnet depends on a peak current flowing at the time of the maximum compression torque. Therefore, the motor used in the compressor100needs to conform to a specification with demagnetization resistance considered more significantly than a motor used in a mechanism including no load change.

For the motor of the compressor100according to the first embodiment, the aluminum winding wire6that is a winding wire made of aluminum having a lower electric conductivity than a copper wire used as a generally used winding wire, and the ferrite magnets2chaving a positive temperature coefficient of coercive force are used to improve the demagnetization resistance.

FIG. 5is a chart illustrating rates of copper losses of a copper wire and an aluminum wire,FIG. 6is a chart illustrating relations between the magnet temperature and the coercive force,FIG. 7is a chart illustrating specific heats of the ferrite magnet and the rotor core,FIG. 8is an illustration representing heat transmitted to inside of the rotor core, andFIG. 9is a sectional view of a surface-magnet rotor.

As illustrated inFIG. 5, assuming that the copper loss of a copper wire is 100%, the copper loss of an aluminum wire reaches 160% that is 1.6 times that of the copper wire. Therefore, when a winding wire to be wound around the stator1is changed from a copper wire to an aluminum wire, heat corresponding to a difference in copper loss between the copper wire and the aluminum wire is generated in the stator1illustrated inFIG. 2.

Meanwhile, the temperature coefficient of coercive force of the ferrite magnets2cis positive while the temperature coefficient of coercive force of a rare-earth magnet is negative as illustrated inFIG. 6. That is, the ferrite magnets2chave characteristics that the coercive force increases with increases in magnet temperature. Because the resistance to a demagnetizing field is increased and the reliability is enhanced when the coercive force increases, it is desirable that the coercive force is higher.

A material having a lower specific heat than that of the ferrite magnets2cis used for the embedded-magnet rotor core2aas illustrated inFIG. 7. When a material having a lower specific heat is used for the embedded-magnet rotor core2a, heat generated by the aluminum winding wire6can be transmitted to the ferrite magnets2cmore effectively than a surface-magnet rotor core20aillustrated inFIG. 9.

This matter is described specifically. When a surface-magnet rotor20illustrated inFIG. 9is set in the stator1illustrated inFIG. 2, heat transmitted from the teeth5btransmits toward inside of the magnets20cgradually from outer circumferential surfaces on a radially outer side of the magnets20carranged on an outer circumferential surface of the rotor core20ain the rotor20. That is, because the heat from the teeth5btransmits only to the outer circumferential surfaces of the magnets20cin the rotor20, the heat is not easily transmitted to a radially inner side of the magnets20c.

A number of arrows “a” and “b” inFIG. 8schematically show paths of heat transmitted to the rotor core2a. First, inFIG. 2, heat generated by the aluminum winding wire6transmits to the rotor core2avia the facing surfaces5eof the tooth end portions5b2, the clearance8, and the outer circumferential surface of the rotor core2ain this order. Heat denoted by the arrows “a” inFIG. 8of the heat transmitting to the rotor core2atransmits to the ferrite magnets2cfrom portions on a radially outer side of the corresponding magnet insertion holes2b. On the other hand, heat denoted by the arrows “b” of the heat transmitting to the rotor core2apasses through between adjacent ones of the magnet insertion holes2band transmits to the ferrite magnet2cvia portions on a radially inner side of the magnet insertion holes2b.

In this manner, when a material having a lower specific heat than that of the ferrite magnets2cis used in the embedded-magnet rotor core2a, heat generated by the aluminum winding wire6can transmit to both the radially outer side and the radially inner side of the ferrite magnets2c. That is, while heat transmits only to the outer circumferential surfaces on the radially outer side of the magnets20cin the surface-magnet rotor core20a, heat can be transmitted to the entire outer circumferential surfaces of the ferrite magnets2cin the embedded-magnet rotor core2a. Therefore, the rotor2can increase the magnet temperature more effectively than the rotor20and accordingly the coercive force is enhanced in the rotor2with increase in the magnet temperature, thereby to improve the demagnetization resistance.

Because the degree of adhesion between the aluminum winding wire6and the stator core5is higher in the concentrated winding method, use of the concentrated winding method enables the magnetic temperature to be increased more.

A configuration for improving the demagnetization resistance by increasing the temperature of the ferrite magnets2chas been described above. However, because the aluminum winding wire6has larger loss than a copper wire, there is a concern of a reduction in motor efficiency. A configuration for improving the demagnetization resistance while suppressing a reduction in motor efficiency is described below.

FIG. 10is a partially enlarged view of the teeth, andFIG. 11is a sectional view of the teeth illustrated inFIG. 10taken along a line in the direction by arrows a-a. Because the resistance value of an aluminum wire is higher than that of a generally used copper wire as described above, it is important to shorten a winding length in one turn of the aluminum winding wire6to be wound around the teeth5b.

As illustrated inFIG. 10, the tooth end portion5b2of the tooth5bis formed in such a manner that a width B in the rotation direction of the facing surface5eis larger than a width A in the rotation direction of the winding wire portion5b1.

Because the magnetic flux from the rotor2enters the back yoke5athrough the tooth end portions5b2and the winding wire portions5b1, designs of the tooth end portions5b2and the winding wire portions5b1are important to effectively capture the magnetic flux into the back yoke5a.

If the width A of the winding wire portion5b1is too large, the cross-sectional area of the slots5dbecomes small and wire winding spaces are reduced. If a fine aluminum wire is used to ensure the number of turns of the aluminum winding wire6, the copper loss increases and the motor efficiency deteriorates.

The solid line illustrated inFIG. 11represents an outline of the winding wire portion5b1and the dotted line illustrated inFIG. 11represents an outline of the tooth end portion5b2viewed from a radially outer side of the stator core5toward a radially inner side thereof. InFIG. 11, there are represented the width A (mm) in the rotation direction of the winding wire portion5b1, the width B (mm) in the rotation direction of the tooth end portion5b2, and a length in the axis direction of the stator core5, that is, a stack thickness L (mm) of the stator core5are represented. InFIG. 11, stack thicknesses of the winding wire portion5b1and the tooth end portion5b2are regarded as the stack thickness L of the stator core5.

A winding length in one turn of a winding wire that is a length per one turn of the aluminum winding wire6wound around the winding wire portion5b1can be expressed as (A+L)×2. The amount of captured magnetic flux in the axis direction is increased when the stack thickness L of the stator core5is increased, but the amount of captured magnetic flux does not change even when the width A of the winding wire portion5b1is increased. Therefore, it is desirable that the width A of the winding wire portion5b1is narrower.

The ratio of the winding length in one turn to the stack thickness L can be defined as (A+L)×2÷L. Meanwhile, the number of the slots5dneeds to be designed to be adapted to the magnetic flux density of the width A of the winding wire portion5b1. Therefore, when the number of the slots5dis S, the number S of the slots5dhas an inverse relationship to the width A of the winding wire portion5b1. When this relationship is introduced into the above expression, S×A÷L is obtained.

FIG. 12is a chart illustrating a copper loss obtained by actual measurement. InFIG. 12, the vertical axis represents the loss increase index and the horizontal axis represents the value obtained by S×A÷L. As illustrated inFIG. 12, when the value obtained by S×A÷L is larger than 0.3 and smaller than 2.2, that is, when the stator core5has a shape that satisfies a relation of 0.3<S×A÷L<2.2, a winding length in one turn effective for capturing the magnetic flux is obtained. Therefore, even when the aluminum winding wire6is used, wasteful copper loss is reduced, and the demagnetization resistance can be improved while a reduction in the motor efficiency is suppressed.

Second Embodiment

FIG. 13is a side view of a motor of a compressor according to a second embodiment of the present invention. A compressor200illustrated inFIG. 13has an oil separator4that is installed on the shaft7passing through an upper surface side of the rotor core2aand is positioned to the upper surface side of the rotor core2a. The configuration other than the oil separator4is identical to that of the compressor100illustrated inFIG. 1. Parts identical to those of the first embodiment are denoted by like reference signs and descriptions thereof will be omitted, and only parts of the second embodiment different from those of the first embodiment are described below.

Dotted arrows illustrated inFIG. 13represent paths of a refrigerant and misty lubricant oil, and solid arrows represent paths of lubricant oil liquefied by the oil separator4. When the oil separator4illustrated inFIG. 13is provided, the refrigerant compressed by the compression unit3is scraped above the compression unit3at the time of an operation of the compressor200. The compressed refrigerant passes through the clearance8or the slots5dand reaches a discharge pipe (not illustrated). At this time, lubricant oil accumulated below the compressor200is scraped above the compression unit3in a misty state. The misty lubricant oil absorbs heat generated by the aluminum winding wire6when passing through the clearance8or the slots5das illustrated by the dotted arrows, and is liquefied by the oil separator4. The liquefied lubricant oil drops on an axial end face of the rotor2located below the oil separator4as illustrated by the solid arrows. Heat of the lubricant oil dropped on the axial end face of the rotor2transmits from the axial end face of the rotor2to the ferrite magnets2c. As a result, the heat generated by the aluminum winding wire6can be transmitted more effectively to the ferrite magnets2cand the demagnetization resistance is improved more.

Third Embodiment

FIG. 14is a side view of a motor of a compressor according to a third embodiment of the present invention, andFIG. 15is a sectional view of a rotor illustrated inFIG. 14. In a compressor300illustrated inFIG. 14, holes2eare formed in the rotor core2awhile the oil separator4is used. Parts identical to those of the first embodiment are denoted by like reference signs and descriptions thereof will be omitted, and only parts of the third embodiment different from those of the first embodiment are described below.

The hole2eis formed in a dent shape extending from a face on a side facing the oil separator4out of two axial end faces of the rotor core2atoward the compression unit3as illustrated inFIG. 14. The holes2eare provided at regular intervals in the rotation direction between adjacent ones of the magnet insertion holes2band between the magnet insertion holes2band the shaft insertion hole2d, as illustrated inFIG. 15.

The lubricant oil liquefied by the oil separator4infiltrates into the holes2eof the rotor core2alocated below the oil separator4and heat of the lubricant oil infiltrated into the holes2etransmits to the ferrite magnets2cfrom a radially inner side of the ferrite magnets2c. As a result, the heat generated by the aluminum winding wire6can be transmitted more effectively to the ferrite magnets2cand the demagnetization resistance can be improved more.

FIG. 16is a view illustrating a modification of the rotor illustrated inFIG. 14. In the compressor300illustrated inFIG. 16, holes2e-1penetrate both the axial end faces of the rotor core2a. Due to this configuration, the lubricant oil liquefied by the oil separator4can be infiltrated into the holes2e-1from their upper side to heat the ferrite magnets2c. Furthermore, the holes2e-1can also serve as flow passages of the refrigerant as shown by dotted line arrows. That is, the refrigerant infiltrated into the holes2e-1from their lower side passes through the holes2e-1toward their upper side and is discharged from a discharge pipe (not illustrated). As a result, the flow amount of the refrigerant in the compressor300is increased and the refrigeration capacity of the refrigeration cycle apparatus30can be improved.

The positions of the holes2eand the holes2e-1described in the third embodiment are not limited to positions between adjacent ones of the magnet insertion holes2band between the magnet insertion holes2band the shaft insertion hole2d. For example, a number of holes can be provided at regular intervals in the rotation direction between each of the magnet insertion holes2band the shaft insertion hole2d. Also in this configuration, the heat generated by the aluminum winding wire6can be effectively transmitted to the ferrite magnets2c. By mounting one of the compressors100,200and300according to the first to third embodiments on the refrigeration cycle apparatus30, the refrigeration cycle apparatus30with high efficiency and high reliability can be provided.

As described above, the compressors100,200and300according to the first to third embodiments include the stator core5in which the aluminum winding wire6is wound around the plural teeth5bin a concentrated manner, the rotor core2adisposed on an inner diameter side of the stator core5and having the plural magnet insertion holes2b, and the plural ferrite magnets2cinserted into the plural magnet insertion holes2b, in which when the width of the winding wire portions5b1formed in the teeth5bis represented as A, the length in the axis direction of the stator core5is represented as L, and the number of the plural slots5dis represented as S, the stator core5has a shape that satisfies a relation of 0.3<S×A÷L<2.2. Due to this configuration, heat generated by the aluminum winding wire6can be transmitted to the ferrite magnets2cto improve the coercive force. Furthermore, because a winding length in one turn effective for capturing the magnetic flux can be obtained, wasteful copper loss is reduced even when the aluminum winding wire6is used, so that the demagnetization resistance can be improved while a reduction in the motor efficiency is suppressed.

Furthermore, the compressors200and300according to the second and third embodiments have the oil separator4installed on the shaft7penetrating the upper surface side of the rotor core2aand positioned on the upper surface side of the rotor core2a. This configuration enables heat of lubricant oil liquefied by the oil separator4to be transmitted to the ferrite magnets2c, thereby effectively heating the ferrite magnets2c.

In the rotor core2aof the compressor300according to the third embodiment, the holes2eor2e-1that are formed between the magnet insertion holes2band the shaft insertion hole2dand open on the oil separator4side are formed. Due to this configuration, heat of lubricant oil liquefied by the oil separator4can be transmitted to the ferrite magnets2cfrom the radially inner side of the ferrite magnets2c, and the ferrite magnets2ccan be effectively heated.

Furthermore, the holes2e-1according to the third embodiment penetrate the both end faces of the rotor core2a. Therefore, the flow amount of a refrigerant in the compressor300is increased, and the refrigeration capacity of the refrigeration cycle apparatus30can be improved.

The configurations described in the above embodiments are only examples of the configuration of the present invention and can be combined with other publicly known techniques, and a part of the configurations can be omitted or modified without departing from the scope of the present invention.