Rotary electric machine

A rotary electric machine includes a rotor, a stator having coils wound to surround the rotor, a cylindrical ring member fixedly mounted on the stator by shrinkage fitting, and a frame disposed on the outside of the ring member with a gap created in between. The distance of the gap varies as a result of thermal expansion of the stator and the ring member. An outer surface of the ring member goes into contact with the frame when the stator and the ring member thermally expand, whereby the stator and the ring member are efficiently cooled.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a structure of a rotary electric machine and, more particularly, to a rotary electric machine capable of efficiently cooling a stator thereof and having excellent magnetic properties.

2. Description of the Background Art

A conventional AC motor includes a stator configured with a plurality of independent stator pieces on which stator coils are wound, the stator pieces being arranged in a ringlike structure, and a stator retaining ring having an opening in which the stator is fixed by press-fitting, wherein the stator retaining ring and a motor housing are fixed by screws. This kind of AC motor is described in Japanese Patent Application Publication No. 2001-025187, for example.

An example of a conventional rotary motor includes a cylindrical aluminum housing, a cylindrical iron sleeve fixedly arranged on a cylindrical inner surface of the housing, and a ring-shaped stator configured with a plurality of stator pieces made of a magnetic material that are fixedly arranged side by side along a circumferential direction on a cylindrical inner surface of the iron sleeve in close contact therewith. The iron sleeve is firmly fit in the housing by shrinkage fitting. Japanese Patent Application Publication No. 2003-284269 describes this kind of rotary motor.

Also, an example of a conventional cooled-casing-type rotary electric machine includes a stator frame in which a coolant passage is formed, the stator frame having an inner circumferential portion serving to retain a stator core. Japanese Patent Application Publication No. 1994-269143 describes this kind of rotary electric machine.

In the aforementioned conventional AC motor, the stator retaining ring and the motor housing are fixed by screws and there is formed a thick layer of air between an outer surface of the stator retaining ring and the motor housing. This AC motor therefore has a problem that the motor can not be sufficiently cooled when the temperature thereof has increased under operating conditions, because the stator and the stator retaining ring can not easily dissipate heat.

In the aforementioned conventional rotary motor, the iron sleeve is firmly fit in the housing by shrinkage fitting so that an outer surface of the iron sleeve and an inner surface of the housing are in close contact with each other. Therefore, the iron sleeve thermally expands when the rotary motor is run and the temperature thereof increases. As a consequence, contact pressure between the iron sleeve and the housing increases by compression, causing a compressive stress in the stator which is disposed in close contact with the inner surface of the iron sleeve. This develops a problem that iron loss in the stator increases under operating conditions, leading to deterioration of magnetic properties.

The aforementioned cooled-casing-type rotary electric machine has the stator frame in which the coolant passage is formed. Thus, the stator frame is cooled by a coolant while the stator thermally expands due to a temperature increase during operation of the rotary electric machine. For this reason, contact pressure between the stator frame and the stator remarkably increases under operating conditions and, as a consequence, there arises a problem that iron loss in the stator increases under operating conditions, leading to deterioration of magnetic properties.

SUMMARY OF THE INVENTION

Intended to solve the aforementioned problems of the prior art, the present invention has as an object the provision of a rotary electric machine capable of efficiently cooling a stator thereof and having excellent magnetic properties.

A rotary electric machine according to the present invention includes a rotor mounted rotatably about a rotary shaft, a stator having a coil wound to surround the rotor, and a frame disposed on the outside of the stator with a gap created in between. The gap has a distance which can vary as a result of thermal expansion of the stator caused by a temperature change, and an outer surface of the stator goes into contact with the frame and is cooled thereby when the stator thermally expands.

The rotary electric machine of this invention includes a rotor mounted rotatably about a rotary shaft, a stator having a coil wound to surround the rotor, and a frame disposed on the outside of the stator with a gap created in between, wherein the gap has a distance which can vary as a result of thermal expansion of the stator caused by a temperature change, and an outer surface of the stator goes into contact with the frame and is cooled thereby when the stator thermally expands. This structure of the invention makes it possible to efficiently cool the stator when the stator thermally expands due to a temperature change during operation of the rotary electric machine, suppress an increase in contact pressure between the stator and the frame and prevent an increase in iron loss in the stator.

First Embodiment

FIG. 1is a cross-sectional diagram illustrating the configuration of a rotary electric machine1according to a first embodiment of the present invention.

As depicted inFIG. 1, the rotary electric machine1includes a rotor3mounted on a rotary shaft2, a ring-shaped stator4arranged to surround an outer surface of the rotor3. The stator4essentially made of iron is a split-type stator including a plurality of stator pieces on which coils5are wound, the stator pieces being arranged in a ringlike structure. On the outside of an outer periphery of the split-type stator4, there is provided a cylindrical, thin-walled ring member6made of iron which is the same material as that of the stator4. The ring member6and the stator4are fixed on a common axis with the ring member6mounted on the stator4by shrinkage fitting. On the outside of an outer periphery of the ring member6, there is disposed a cylinder-shaped aluminum frame7having an inside diameter which is a little larger than an outside diameter of the ring member6. As the ring member6is fit inside the frame7, there is created a slight gap8between an inner surface of the frame7and an outer surface of the ring member6(refer toFIG. 2). There is formed a fluid passage71within a cylindrical body of the frame7for circulating a coolant. Heat generated by the coils5when the rotary electric machine1is run is dissipated by the coolant circulating through the fluid passage71via the stator4, the ring member6and the frame7.

Structures of the stator4, the ring member6and the frame7are described in detail below with reference toFIGS. 2 to 4.FIG. 2is a diagram depicting an enlarged view of a portion A circumscribed by broken lines inFIG. 1,FIG. 3is a perspective view depicting the structure of the ring member6, andFIG. 4is a perspective view depicting the structure of the frame7.

As already mentioned, there is provided the ring member6on the outside of the stator4. As the thin-walled ring member6is fixed on the stator4by shrinkage fitting, an inner surface of the ring member6and the outer surface of the stator4are in close contact with each other. Because the ring member6is thin-walled, the ring member6has a small thermal capacity and, thus, the ring member6has a high heating efficiency and can be heated by induction heating, for example. For this reason, the ring member6can be easily shrink-fit on the stator4within a short time, eliminating the need for a large-scale facility for performing shrinkage fitting. Since the stator4and the ring member6which are fixed together by shrinkage fitting are both made of iron, the two components have the same coefficient of thermal expansion. Therefore, the stator4and the ring member6similarly expand and shrink when subjected to temperature changes that occur under operating conditions of the rotary electric machine1, without creating any slack between joint surfaces of the two components. It is to be pointed out that although the stator4and the ring member6are both made of iron in the first embodiment, what is essential in this invention is that the two components are made of materials having substantially the same coefficient of thermal expansion. This would prevent the occurrence of a slack between the joint surfaces of the stator4and the ring member6as a result of thermal expansion and shrinkage of the two components caused by temperature changes that occur when the rotary electric machine1is run. Additionally, while the stator4and the ring member6are fixed together by shrinkage fitting in this embodiment, the two components may be joined by press fitting, for example.

The ring member6has hooking parts61which serve as supporting portions projecting radially outward from the outer surface of the ring member6, the hooking parts61being arranged in three rows in an axial direction of the ring member6by four columns located around a circumferential direction thereof. Each of the hooking parts61is formed by a cut-and-bend method in which part of a cylindrical wall of the ring member6is cut and bent radially outward. Specifically, each of the hooking parts61is formed by bending a cut part formed in the ring member6, the cut part having edges formed along three of four sides of a rectangle excluding one side located on an upper side of the ring member6(as illustrated inFIG. 3). The hooking parts61thus formed have a springy characteristic. More specifically, the ring member6is produced by forming the hooking parts61on a thin-walled iron plate, bending the iron plate into a cylindrical shape and, then, welding butt ends of the iron plate to form a welded joint62, for example. Incidentally, the number and locations of the hooking parts61are not limited to the above-described example but may be determined as appropriate in accordance with specific requirements. The shape of each hooking part may also be modified as necessary. It will be possible to form hooking parts having a complex shape by using the aforementioned method in which the ring member6is produced by forming the hooking parts61on an iron plate and bending the iron plate into a cylindrical shape.

In the inner surface of the frame7, there are formed recesses72which are located at positions corresponding to the hooking parts61of the ring member6. As the ring member6is inserted into the frame7, the hooking parts61fit into and become retained by the recesses72, whereby the ring member6and the frame7are correctly positioned in both the axial and circumferential directions at the same time. As the hooking parts61have the springy characteristic, end portions of the hooking parts61push against the recesses72in radial directions so that the ring member6is held within the frame7with the uniform gap8formed therebetween. The springy characteristic of the hooking parts61also serve to cancel out variations in dimensions of the ring member6and frame7, making it possible to easily match central axes of the ring member6and frame7. This structure serves to absorb vibrations and reduce acoustic noise during operation of the rotary electric machine1.

While the ring member6and the frame7are supported with the gap8formed in between during assembly of the individual components of the rotary electric machine1, such as the stator4, the ring member6and the frame7, as mentioned in the foregoing discussion, the distance of the gap8can vary as a result of thermal expansion of the stator4, the ring member6and the frame7caused by temperature changes during operation of the rotary electric machine1. The gap8is initially set to have such a dimension that the outer surface of the ring member6goes into close contact with the inner surface of the frame7, making it possible to cool the ring member6, when the individual components like the stator4reach temperatures falling within a temperature range in which heat built up in the individual components should be dissipated. Described below is how the distance of the gap8is preset.

Here, the distance of the gap8is discussed taking into consideration the amount of increase in interference between the ring member6and the frame7caused by temperature changes under conditions where the outer surface of the ring member6and the inner surface of the frame7are in mutual contact, that is, the two components are supported with the distance of the gap8set to zero, during assembly of the rotary electric machine1. The term “interference” used herein refers to the difference between the outside diameter of the ring member6and the inside diameter of the frame7. When the ring member6and the frame7are supported with the gap distance zero, the amount of the interference is equal to zero, and when the ring member6and the frame7thermally expand due to temperature changes, the amount of the interference increases. The following discussion presents examples of how the amount of increase in the interference is determined.

The amount of increase in the interference is determined using an example in which the rotary electric machine1is structured such that the stator4has an inside diameter of 173 mm and an outside diameter of 200 mm, the frame7has an inside diameter of 204 mm and an outside diameter of 216 mm, and the ring member6has a thickness of 2 mm. In this example, it is assumed that the coefficient of linear expansion of aluminum used as a material forming the frame7is 2.1×10−5/° C. and the coefficient of linear expansion of iron used as a material forming the stator4and the ring member6is 1.3×10−5/° C. It is also assumed that the temperature of the rotary electric machine1is 20° C. during assembly thereof and the temperature of the frame7is within a range of −30° C. to 40° C. while the rotary electric machine1is run.

FIG. 5is a diagram representing how diameters of the stator4and the frame7vary in relation to temperature changes. Here, a further assumption is made that the stator4and the ring member6remain at the same temperature because these components are made of the same material, i.e. iron and these components are fixed together by shrinkage fitting, and the amount of change in the diameter of the stator4includes that of the ring member6. The temperature 20° C. of the rotary electric machine1during assembly thereof is used as a reference temperature and either of the amount of change in the diameter of the frame7and that of the stator4is zero at 20° C. When the frame7is at 40° C. and the stator4is at 100° C., for example, there is a difference A of about 0.12 mm between the amount of change in the diameter of the former and that of the latter. Also, when the frame7is at −30° C. and the stator4is at 30° C., there is a difference B of about 0.24 mm between the amount of change in the diameter of the former and that of the latter.

Under the assumption that the ring member6and the frame7are supported with the gap distance zero during assembly as mentioned above, the difference between the amount of change in the diameter of the frame7and that of the stator4explained above referring toFIG. 5corresponds to the amount of increase in interference between the ring member6and the frame7caused by a temperature change.FIG. 6is a diagram indicating a relationship between temperature differences between the frame7and the stator4and the amount of increase in interference therebetween when the frame7is at −30° C. (shown by an upper solid line) and at 40° C. (shown by a lower solid line). Point C shown inFIG. 6indicates, for example, that the amount of increase in interference between the ring member6and the frame7is approximately 0.12 mm when the frame7is at 40° C. and the stator4is at 100° C. Also, point D shown inFIG. 6indicates that the amount of increase in interference is approximately 0.24 mm when the frame7is at −30° C. and the stator4is at 30° C.

Considering such properties as heat resistance of internal components of the rotary electric machine1, it is assumed that the rotary electric machine1is in a range wherein heat built up in the individual components should be dissipated when there is a temperature difference of 60° C. or more between the stator4and the frame7, a permissible upper limit of the temperature difference being 100° C. This range is represented by a hatched area inFIG. 6. Point C shown inFIG. 6is a point where the amount of increase in interference between the ring member6and the frame7is minimized within the hatched area ofFIG. 6. The amount of increase in interference is approximately 0.12 mm at point C ofFIG. 6when the frame7is at 40° C. and the stator4is at 100° C. as mentioned above.

On the basis of results of close examination of the above-described example, a maximum value of the distance of the gap8at which the outer surface of the ring member6goes into close contact with the inner surface of the frame7can be set at 0.12 mm in the temperature range wherein heat dissipation should be done according to the first embodiment. It follows that if the distance of the gap8is set to 0.12 mm or less, the outer surface of the ring member6goes into contact with the frame7having the internal fluid passage71for circulating the coolant, making it possible to efficiently cool the stator4and the ring member6within the entire temperature range in which it is expected that heat should be dissipated.

On the other hand, point E shown inFIG. 6is a point where the amount of increase in interference between the ring member6and the frame7is maximized within the hatched area ofFIG. 6in which it is expected that heat should be dissipated. At point E, the frame7is at −30° C., the stator4is at 70° C. and the amount of increase in interference is approximately 0.34 mm. What is represented by point E at which the amount of increase in interference is maximized is a situation where a contact pressure between the ring member6and the frame7is maximized.

A solid line shown inFIG. 7represents a relationship between the distance of the gap8during assembly and a circumferential stress that occurs in the frame7when the frame7is at −30° C. and the stator4is at 70° C. As the amount of increase in interference is approximately 0.34 mm at point E shown inFIG. 6, the circumferential stress occurring in the frame7is zero if the distance of the gap8during assembly is 0.34 mm. If the distance of the gap8during assembly is zero, a circumferential stress of approximately 100 MPa will occur in the frame7.

If the frame7is made of an aluminum die-cast (ADC) material, for example, the frame7has a yield strength of 180 MPa against the circumferential stress. In a case where the frame7is used at a safety factor of 2 or above, that is, when the circumferential stress occurring in the frame7is 90 MPa or less (shown by a broken line F inFIG. 7), the distance of the gap8during assembly should preferably be made equal to or larger than 0.03 mm.

If the distance of the gap8is initially set to 0.03 mm, a calculated compressive stress that will occur in an outer surface of the stator4when the frame7is at −30° C. and the stator4is at 70° C. is approximately 75 MPa. This compressive stress results from a combination of a contact pressure that occurs when the ring member6is shrink-fit on the stator4and a contact pressure exerted by the frame7as a result of thermal expansion of the individual components due to a temperature increase thereof.

The above-described structure of the present embodiment is further examined using a comparative example of a rotary electric machine in which a frame having an inside diameter of 200 mm and an outside diameter of 216 mm is directly shrink-fit on a stator having an inside diameter of 173 mm and an outside diameter of 200 mm. In this rotary electric machine, a circumferential stress that occurs in the frame when the frame is at −30° C. and the stator is at 70° C. is approximately 175 MPa (shown by a dot-and-dash line G inFIG. 7). It is recognized that the value of the circumferential stress that occurs in the frame7of the first embodiment when the gap distance is initially set to 0.03 mm is remarkably smaller than the value of the circumferential stress that occurs in the frame of the comparative example. Additionally, a calculated compressive stress that will occur in an outer surface of the stator of the comparative example is approximately 107 MPa. Thus, it is also recognized that the value of the compressive stress that will occur in the outer surface of the stator4of the first embodiment when the gap distance is initially set to 0.03 mm is much smaller than the value of the compressive stress that will occur in the stator of the comparative example. Incidentally, the compressive stress that will occur in the stator of the comparative example results from a combination of a contact pressure that occurs when the frame is shrink-fit on the stator and a contact pressure exerted by the frame as a result of thermal expansion of individual components due to a temperature increase thereof.

It is understood from the above that by presetting the distance of the gap8to 0.03 mm or more it is possible to prevent an increase in the compressive stress occurring in the outer surface of the stator4without producing an excessive circumferential stress in the frame7regardless of temperature increase.

It is appreciated from results of the aforementioned examination that if the distance of the gap8is set within a range of 0.03 mm to 0.12 mm in the structure of the first embodiment, the outer surface of the ring member6goes into contact with the inner surface of the frame7, making it possible to efficiently cool the individual components within the entire temperature range in which it is expected that heat should be dissipated. Additionally, this arrangement of the embodiment serves to prevent an increase in the compressive stress occurring in the outer surface of the stator4as a result of thermal expansion of the stator4, the ring member6and the frame7. If it is intended to set the gap distance to 0.03 mm in the structure of the first embodiment, for example, it is possible to create the gap8of 0.03 mm between the ring member6and the frame7by grinding the outer surface of the aforementioned 2-mm-thick ring member6by as much as 0.03 mm.

The foregoing discussion has been based on the assumption that the frame7is in a temperature range of −30° C. to 40° C. while the rotary electric machine1is run and it is expected necessary that heat built up in the individual components should be dissipated if the temperature difference between the frame7and the stator4falls within a range of 60° C. to 100° C. This assumption may however be altered as appropriate in accordance with operating conditions or the purpose of use of the rotary electric machine1, for instance.

An optimum thickness of the ring member6is now considered hereunder. As the ring member6is shrink-fit on the stator4in the above-described structure of the present embodiment, a contact pressure is exerted on the outer surface of the stator4. The contact pressure exerted on the stator4as a result of shrinkage fitting increases with the thickness of the ring member6. While the compressive stress that occurs in the outer surface of the stator4is approximately 75 MPa under conditions where the distance of the gap8is initially set to 0.03 mm, the frame7is at −30° C. and the stator4is at 70° C. in the structure of the first embodiment, this compressive stress results from the combination of the contact pressure that occurs when the ring member6is shrink-fit on the stator4and the contact pressure exerted by the frame7as a result of thermal expansion of the individual components due to a temperature increase thereof as mentioned earlier. Thus, the compressive stress occurring in the outer surface of the stator4increases as the contact pressure occurring as a result of shrinkage fitting increases. Taking this in mind, the compressive stress that occurs in the outer surface of the stator4has been determined under conditions where the thickness of the ring member6was gradually increased when the gap distance was initially set to 0.03 mm, the frame7was at −30° C. and the stator4was at 70° C. Consequently, it has been determined that the compressive stress that occurred in the outer surface of the stator4took the same value as in the aforementioned comparative example when the outside diameter of the stator4was 200 mm and the thickness of the ring member6was 5 mm, that is, when the thickness of the ring member6was 2.5% of the outside diameter of the stator4. This indicates that the optimum thickness of the ring member6is 2.5% or less of the outside diameter of the stator4.

As described in the foregoing, the rotary electric machine1of the first embodiment is structured such that the ring member6and the frame7are arranged with the gap8created in between, the distance of the gap8being variable as a result of thermal expansion of the ring member6caused by temperature changes, and the individual components are cooled as the outer surface of the ring member6goes into contact with the frame7as a result of a change in the gap distance therebetween.

Therefore, it is possible to efficiently cool the stator4and ring member6when heat built up in these components needs to be dissipated. Additionally, it is possible to prevent an increase in iron loss in the stator4by suppressing an increase in the compressive stress that occurs in the outer surface of the stator4as a result of thermal expansion of the stator4, the ring member6and the frame7and thereby improve magnetic properties of the rotary electric machine1. Durability of the rotary electric machine1is also improved as no excessive circumferential stress is produced in the frame7. Furthermore, the structure of the embodiment provides an advantage that the ring member6is kept from turning during operation of the rotary electric machine1because the outer surface of the ring member6goes into contact with the frame7.

Also, as the frame7is fit on the outside of the ring member6with the slight gap8created in between without using a shrinkage fitting or press-fitting technique, there is no need for any large-scale facilities for performing a shrinkage fitting or press-fitting process. This feature serves to reduce environmental load caused by manufacturing facilities.

Furthermore, as the ring member6is supported within the frame7with the aid of the hooking parts61provided on the ring member6constituting a springlike structure and the recesses72formed in the frame7, it is possible to support the ring member6within the frame7with the uniform gap8created in between with a simple structure. This structure facilitates mutual positioning of the ring member6and the frame7in both the axial and circumferential directions. The structure of the embodiment also serves to reliably prevent the ring member6from turning relative to the frame7while the rotary electric machine1is run.

Also, as the hooking parts61constitute the springlike structure as mentioned above, the hooking parts61serve to cancel out dimensional variations of the ring member6and the frame7due to poor machining accuracy thereof, making it easy to match the central axes of the ring member6and frame7. This structure also serves to absorb vibrations and reduce acoustic noise during operation of the rotary electric machine1.

While the hooking parts61provided on the ring member6hook into and become retained by the recesses72formed in the frame7in the above-described first embodiment, this structure may be modified such that the recesses72are not formed in the frame7and the ring member6is supported by the frame7only with an elastic restoring force exerted by the hooking parts61formed on the ring member6. Also, the invention is not limited to the above-described support mechanism employed for supporting the ring member6within the frame7. The rotary electric machine1may employ any kind of support mechanism in which a ring member is supported within a frame with such a gap formed in between that allows an outer surface of the ring member to go into contact with the frame as a result of thermal expansion of the former. For example, the rotary electric machine1may employ a support mechanism as depicted inFIG. 8in which a ring member6A having a flange portion61A which serves as a supporting portion projecting radially outward from an upper end of an outer surface of the ring member6A is inserted into a frame7A, and the flange portion61A is screwed or bonded to the frame7A so that the ring member6A is supported by the frame7A with a gap8A created in between.

In the above-described structure of the present embodiment in which the hooking parts61of the ring member6hook into and become retained by the recesses72formed in the frame7, pushing forces exerted by the hooking parts61of the ring member6may potentially produce a local stress in the frame7especially at the recesses72formed therein. One approach to prevent permanent deformation of the frame7due to such stress would be to strengthen the frame7by forming a cast-iron layer on the inner surface of the frame7, for example.

While the fluid passage71for circulating the coolant is formed within the cylindrical body of the frame7in the first embodiment, the location of the fluid passage71is not limited thereto. For example, a fluid passage for circulating the coolant may be formed on an outer surface of the frame or a fluid passage may be formed in such vicinity of the frame that is close enough to cool the frame. Also, while it is possible to cool the stator and the ring member quite efficiently if the fluid passage for circulating the coolant is formed within the cylindrical body of the frame, the fluid passage for the coolant need not necessarily be formed within the frame. This is because the frame is in direct contact with ambient air and the stator and the ring member can be cooled as long as the frame is in contact with the ring member.

Furthermore, although the stator4is a split-type stator in the foregoing first embodiment, the stator4need not necessarily be of a split-type. For example, it is possible to employ a structure in which a ring member is shrink-fit on a non-split-type stator configured with a single-structured ringlike iron core and then the ring member is supported within a frame with a slight gap formed in between. This structure also provides the same advantage as provided by the structure of the first embodiment.

It is to be pointed out that when employing a non-split-type stator configured with a single-structured iron core, it is possible to structure a rotary electric machine without any ring member. If the rotary electric machine is structured such that the stator is supported directly by the frame with a gap created in between without the provision of a ring member wherein an outer surface of the stator goes into contact with the frame when the stator expands due to a temperature change, it is possible to produce the same advantage as provided by the above-described structure of the first embodiment.

Second Embodiment

FIG. 9is a perspective view depicting the structure of a ring member6B of a rotary electric machine1B according to a second embodiment of the present invention. The ring member6B has a second hooking part63which serves as a supporting portion in addition to hooking parts61which are structured in the same fashion as those of the above-described first embodiment. The second hooking part63of the second embodiment which is located at an uppermost axial end (as illustrated) of the ring member6B is formed by cutting and bending part of the ring member6B along a direction deviating from a cut-and-bend direction of the hooking parts61by 90 degrees. A frame7B which supports the ring member6B is provided with a second recess in which the second hooking part63is retained at a location corresponding to the second hooking part63. The rotary electric machine1B is structured in otherwise the same fashion as the rotary electric machine1of the foregoing first embodiment, and elements like those of the first embodiment are designated by the same symbols and a description of such elements is not given here.

In this embodiment, the hooking parts61and the second hooking part63formed in different cut-and-bend directions fit into and become retained by the recesses72and the second recess formed in the frame7B, respectively, as described above. Therefore, the second embodiment provides, in addition to the aforementioned advantage of the first embodiment, such an advantage that the ring member6B is more securely kept from turning relative to the frame7B during operation of the rotary electric machine1B.

Third Embodiment

FIG. 10is a perspective view depicting the structure of a ring member6C of a rotary electric machine1C according to a third embodiment of the present invention. The ring member6C employed in this embodiment is a tolerance ring of which entire ring structure has a springy characteristic. Specifically, the ring member6C employed in the third embodiment is a tolerance ring having a plurality of protrusions64formed on an outer surface of the ring member6C to extend along an axial direction thereof. A frame7C employed in the third embodiment has a simple thin-walled cylindrical structure unlike the ring member6of the first embodiment in which the recesses72are formed. The plurality of protrusions64serve as supporting portions for supporting the ring member6C within the frame7C. To be more specific, the protrusions64serving as the supporting portions are in contact with an inner surface of the frame7C so that the ring member6C is supported on the inside of the frame7C with a slight gap created in between. The rotary electric machine1C is structured in otherwise the same fashion as the rotary electric machine1of the foregoing first embodiment, and elements like those of the first embodiment are designated by the same symbols and a description of such elements is not given here.

Since the ring member6C of this embodiment is a tolerance ring, the entire ring structure including the protrusions64which serve as the supporting portions has springiness as described above. Therefore, the third embodiment provides, in addition to the aforementioned advantage of the first embodiment, such an advantage that the springiness of the entire ring structure of the ring member6C cancels out variations in dimensions of the frame7C due to poor machining accuracy thereof, making it easy to match central axes of the ring member6C and frame7C. This also serves to facilitate assembly. In addition, the structure of the third embodiment serves to absorb vibrations and reduce acoustic noise during operation of the rotary electric machine1C.

Fourth Embodiment

FIG. 11is a perspective view depicting the structure of a ring member6D of a rotary electric machine1D according to a fourth embodiment of the present invention, andFIG. 12is a fragmentary cross-sectional view schematically depicting the structure of the ring member6D.FIG. 12shows a cross section taken along a surface at right angles to a rotary shaft2of the rotary electric machine1D, depicting in particular an enlarged view of the proximity of one of a plurality of stator pieces40constituting a stator4.

As illustrated in the Figures, the ring member6D of this embodiment differs from the ring member6of the foregoing first embodiment including the structure of the supporting portions thereof. Supporting portions65of the ring member6D are structured to have protruding parts each having an inverted trapezoidal cross section formed on an outer surface of the ring member6D, extending along an axial direction thereof, as well as dovetail grooves66formed in inside surfaces of the individual supporting portions65. The ring member6D having such supporting portions65can be formed by bending a thin-walled iron plate to produce protrusions having generally a trapezoidal cross-sectional shape, bending the iron plate into a generally cylindrical shape, and then welding butt ends of the iron plate to produce a welded joint62, for example. In this fourth embodiment, three such supporting portions65are formed in the above-described manner. In an inner surface of a frame7D of this embodiment, there are not formed any recesses like those of the first embodiment. The ring member6D is supported within the frame7D with a gap8D created in between as outermost surfaces of the individual supporting portions65of the ring member6D are in contact with the inner surface of the frame7D. The supporting portions65of this embodiment may be structured to provide a desired level of springiness by properly determining the angle of bending of the supporting portions65and/or the thickness of the ring member6D. The rotary electric machine1D is structured in otherwise the same fashion as the rotary electric machine1of the foregoing first embodiment, and elements like those of the first embodiment are designated by the same symbols and a description of such elements is not given here.

In this fourth embodiment, the supporting portions65provided on the outer surface of the ring member6D are shaped to have the dovetail grooves66formed in the inside surfaces of the protruding parts each having the inverted trapezoidal cross section extending along the axial direction of the ring member6D as described above. Therefore, the fourth embodiment provides, in addition to the aforementioned advantage of the first embodiment, such an advantage that the above-described structure of the present embodiment serves to keep compressive stresses exerted on the stator pieces40due to mechanical contact of the outermost surfaces of the supporting portions65and the frame7D from being transmitted directly to the respective stator pieces40and to distribute the compressive stresses over entire outer surfaces of the stator pieces40. For this reason, the structure of the embodiment makes it possible to prevent deterioration of magnetic properties of the rotary electric machine1D due to an increase in local compressive stresses.

Optionally, the structure of the embodiment may be such that elastic members are disposed in the dovetail grooves66formed in the inside surfaces of the individual supporting portions65in order to strengthen the supporting portions65and support the ring member6D within the frame7D more securely.

While one of the supporting portions65is depicted in an exaggerated fashion inFIG. 12to facilitate understanding of the structure of the supporting portions65, the gap8D is a slight gap like the one described in the foregoing first embodiment and, therefore, the outer surface of the ring member6D naturally goes into contact with the inner surface of the frame7D when the ring member6D thermally expands, making it possible to cool the ring member6D by way of the frame7D.

FIG. 12depicts one of cutouts41formed in the outer surfaces of the stator pieces40. These cutouts41are cutouts commonly used when arranging the plurality of stator pieces40in a cylindrical configuration. If the supporting portions65of the ring member6D are disposed at locations corresponding to the individual cutouts41, it will be possible to distribute the compressive stresses exerted on the stator pieces40due to mechanical contact of the outermost surfaces of the supporting portions65and the frame7D in a more reliable fashion.

Fifth Embodiment

FIG. 13is a fragmentary cross-sectional view schematically depicting the structure of a rotary electric machine1E according to a fifth embodiment of the present invention.FIG. 13shows a cross section taken along a surface at right angles to a rotary shaft2of the rotary electric machine1E, depicting in particular an enlarged view of the proximity of one of a plurality of stator pieces40constituting a stator4.

The structure of the fifth embodiment is one variation of the above-described structure of the fourth embodiment. A ring member6E of the fifth embodiment is structured in the same fashion as the ring member6D of the fourth embodiment. In this fifth embodiment, a frame7E has dovetail grooves73formed in an inner surface thereof for fitting supporting portions65formed on the ring member6E. When the individual supporting portions65are fit into the dovetail grooves73, the ring member6E is supported within the frame7E with a gap BE created in between.

In this fifth embodiment, the frame7E has the dovetail grooves73formed therein and the supporting portions65formed on the ring member6E are fit into the dovetail grooves73. Therefore, the fifth embodiment provides, in addition to the aforementioned advantage of the fourth embodiment, such an advantage that the ring member GE is securely kept from turning relative to the frame7E.

The rotary electric machine1E of the fifth embodiment may be varied as illustrated inFIG. 14, for example, in which a rotary electric machine1F is structured such that a gap8F is created also between dovetail grooves73F of a frame7F and supporting portions65of a ring member6F. In this variation of the fifth embodiment, the ring member6F can be supported within the frame7F by means of hooking parts like those of the first embodiment formed on an outer surface of the ring member6F, for example.

While the invention has been described with reference to the specific embodiments thereof, the above-described structures of the individual embodiments may be freely combined, modified or simplified as appropriate. In other words, various modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention, and it should be understood that this is not limited to the illustrative embodiments set forth herein.