COOLED MOTOR AND A METHOD OF MANUFACTURING ITS JACKET

Abstract: A jacket with passages (2) for cooling liquid is provided by extrusion of aluminum alloy billets. This product is used as a stator-cooling jacket, i.e. a motor casing (1). Front and rear cast-iron housings (4, 5) are fitted to the front and rear surfaces of the casing (1) with tie-bolts (10) to form a liquid-cooled motor. The flanges (14, 16) of the front and rear housings (4, 5) are provided with either holes for passing the tie-bolts (10) or female threads for receiving the male threads at the free end portions of the tie-bolts (10). The cross section of each lightening hole (11), formed during the casting of the casing (1) and utilized as a hole for passing the tie-bolt, is shaped so as to allow only the axial movement of the tie-bolt (10). The number of lightening holes (11) is four, for example, and they are positioned at regular intervals in the circumferential direction of the casing (1). The passages (2) for passing a cooling liquid through the interior thereof are provided on the left and right sides of each lightening hole (11), and a plurality of cooling fins (12) projecting inward are formed by precision machining in the lightening holes. Thus, the liquid-cooled motor and its jacket have improved reliability with respect to the leakage of the liquid, and an improved cooling efficiency. In addition, the number of manufacturing steps is decreased.

Description: LIQUID-COOLED MOTOR AND A METHOD OF MANUFACTURING ITS JACKET The present invention relates to a cooling structure of an electric motor such as an induction motor, and more particularly, to a jacket for cooling a stator and a method of manufacturing the same, and an improvement in the structure of a cooled motor using the jacket. For the purpose of enhancing the cooling efficiency in an electric motor and relieving the peripheral equipment from being adversely affected by heat dissipation, there has been proposed a liquid cooled motor which includes a casing 1 having liquid cooling conduits 2, which serves as a cooling jacket for a stator 3, as shown in Figs. 3 and 4. Such a motor is disclosed in FR-A-2 312 874. In this case, the casing 1 is usually sand-cast from aluminum alloy, and housings 4 and 5 are separately attached to the front and rear surfaces, respectively, of the casing 1 by ordinary bolts. Such housings are disclosed in JP-A-1-198 243. The following problems are encountered in such a motor: Due to characteristics of the casting, the wall portions of the casing 1, inevitably involve cavities 7 in the interior or on the surface thereof, which may cause liquid leakage if the casing 1 is used as the liquid cooling structure. In particular, the cavities 7 are liable to be exposed on the inner surface or the end surface which has been subjected to cutting operations, thereby causing leakage of the coolant. In order to fill the cavities 7, there may be needed, for example, a time-consuming and costly treatment requiring casing 1 to be dipped into a special sealing compound after being cast. It is also impossible to provide the sand-casting with deep holes and threaded holes having an accurate configuration by the sand-casting process alone. Hence, if they are needed, the sand-casting must be subjected to further cutting operation after casting. In addition, due to the impossibility of obtaining a higher dimensional accuracy, a fine or complicated sectional configuration is unable to be provided on the interior of the liquid cooling conduits 2. Further, at least eight ordinary bolts 6 must be used to fasten the front and rear housings to the casing 1, involving a large number of assembling steps which not only may cause an unevenness in the screw torque of the bolts 6 but also requires a greater precaution to ensure a uniform fastening. It is therefore the object of the present invention to provide a liquid cooled motor and its jacket presenting a higher reliability with respect to liquid leakage and less assembling steps and an improved cooling efficiency. According to a first aspect of the present invention there is provided a method of manufacturing a jacket for cooling a stator of a motor, characterised by the steps of: extruding a billet of aluminium alloy to provide the jacket and conduits therein for the passage of liquid coolant; and cutting said extruded billet into a desired length. According to a second aspect of the present invention there is provided a liquid cooled motor comprising a jacket for cooling a stator of the motor, the stator cooling jacket having provided therein a plurality of conduits intended for the passage of liquid coolant and having front and rear surfaces to which are attached front and rear housings respectively, characterised in that: the stator cooling jacket is formed of an extruded profile of aluminium alloy; and the jacket and the front and rear housings are fastened together by means of a plurality of tie bolts extending from the front housing to the rear housing. Preferably, the front and rear housings are made of cast iron and respectively include flanges having a plurality of holes through which the tie bolts are allowed to pass and a plurality of threaded holes for receiving threaded end portions of the tie bolts, respectively. Preferably, the jacket includes a plurality of thickness lightening holes formed, when extruding the jacket for cooling a stator, and used as holes through which the tie bolts are allowed to pass. Preferably, each of the plurality of thickness lightening holes has a sectional configuration a part of which permits only the axial displacement of the tie bolt inserted into the thickness lightening hole. Preferably, the plurality of thickness lightening holes are equally spaced in the circumferential direction of the jacket, and the plurality of conduits for the passage of coolant are arranged on both sides of each of the thickness lightening holes. More preferably, each of the plurality of conduits includes a multiplicity of inwardly protruding cooling fins. As described above, a casing which is of an extrusion molded material according to the present invention provides a stator cooling jacket made of aluminum alloy being free of cavities. Furthermore, the fastening by means of the tie bolts contributes to a reduction in the number of assembling steps and uniformity of the screw torque applied thereto. The sectional configuration of the thickness lightening holes permitting only the axial displacement of the tie bolts present effective measures for preventing a radial positional offset between the casing and the front and rear housings. Moreover, by capitalizing on the characteristics of the extruded profile that the wall portions will not form cavities and that a fine structure can be formed with a higher accuracy, the liquid cooling conduits may be configured to have a multiplicity of inwardly protruding cooling fins, thereby enhancing the cooling efficiency. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a sectional front elevation of a jacket for cooling a stator of a motor constructed in accordance with an embodiment of the present invention, taken along the line A-A in Fig. 2; Fig. 2 is a sectional view of the jacket taken along the line B-B in Fig. 1; Fig. 3 is a sectional front elevation of a conventional jacket for cooling a stator, taken along the line C-C in Fig. 4; and Fig. 4 is a sectional view of the conventional jacket taken along the line D-d in Fig. 3. Referring first to Figs. 1 and 2, there is depicted a frame for an induction motor constructed in accordance with the present invention, which comprises a casing 1, a front housing 4, and a rear housing 5, each being integrally combined with the others by means of tie bolts 10. The casing 1 serving as a cooling jacket for a stator 3 is formed by cutting a so-called extrusion molded material obtained by extruding a billet of aluminum alloy through a die designed for predetermined shape. The extrusion molded material is obtained in the form of a generally elongated tube having a cross section as shown in Fig. 2; each of its four corners having larger wall thickness is provided with a pair of conduits 2 and a thickness lightening hole 11 which are symmetrically arranged. The thickness lightening holes 11 are provided in order to regulate the wall thickness existing between the pair of conduits 2 in conformity to requirements in extrusion molding. The extrusion molding characteristics require the conduits 2 and the thickness lightening holes 11 to longitudinally extend through the extruded profiles. Thus, any casing 1 formed by radially cutting this material presents a section having the conduits 2 and thickness lightening holes 11 as shown in Fig. 2. The conduits 2 function as liquid cooling conduits 2, while the thickness lightening holes 11 longitudinally (or axially) receive the tie bolts 10. By utilizing inherent features of the extruded profiles that their walls are free from cavities and that fine structures can be formed with a higher accuracy, the liquid cooling conduits 2 according to this embodiment are high precision machined to have a multiplicity of inwardly protruding cooling fins 12 as depicted in Fig. 2. The thickness lightening holes 11 are respectively machined to have a sectional configuration allowing the tie bolt 10 extending therethrough to be displaced in only the longitudinal direction of the casing 1, while preventing its radial displacement in section. Therefore, such casing 1 formed by extrusion molding can be provided with both the conduits 2 having a higher cooling efficiency and the thickness lightening holes 11 having a circular sectional portion preventing the tie bolt from backlashing. On the other hand, the front and rear housings 4 and 5 for enclosing the stator 3 and a rotor (not shown) while permitting a rotor shaft to extend therethrough are made of a cast iron in consideration of the requirements for their configuration and strength. The front housing 4 comprises a circulating conduit 13 communicating with the liquid cooling conduit 2 located on the side of the casing 1, and a front flange 14 having through-holes for the tie bolts 10. The rear housing 5 comprises a lead-in/lead-out conduit 15 communicating with the liquid cooling conduit 2 resting on the side of the casing 1, and a rear flange 16 having threaded holes into which the threaded portions of the tie bolts 10 are screwed. In assembling this liquid-cooled motor, the stator 3 is first placed within the casing 1, and the front and rear housings 4 and 5 are respectively attached to the front and rear surfaces of the casing 1 in such a manner that the cooling conduit 2 of the casing 1 communicates with the circulating conduits 13 and 15 of the front and rear housings 4 and 5, respectively, through an O ring 17. Then, the tie bolts 10 are inserted by way of the bolt through-holes formed in four corners of the front flange 14 of the front housing 4 into the circular sectional portions of the thickness lightening holes 11 of the casing 1, their threaded end portions being firmly screwed into the threaded holes formed in four corners of the rear flange 16 of the rear housing 5 with the equal torque. Upon the actuation of the electric motor, a separately disposed pump is allowed to be connected with the lead-in/lead-out conduit 15 of the rear housing 5 so as to feed a cooling medium such as oil into the liquid cooling conduit 2 of the casing 1. The coolant circulates by way of the conduits of the casing 1 and the front and rear housing, and then from the rear housing 5 through a radiator back to the pump. The radiator is independently placed on the outside of the motor. During the circulation, the coolant absorbs heat of the stator 3 and the casing 1 for removing to the outside. The presence of the circular sectional portions in the thickness lightening holes 11, intended to receive the tie bolts 10, prevents the tie bolts 10 from being moved in the radial direction of the casing 1, thus preventing the casing 1 from being radially displaced relative to the front and rear housings 4 and 5 due to vibration of the motor during operation, thereby preventing the occurrence of offset between the stator shaft and the rotor shaft. The sectional configurations of the liquid cooling conduits 2 and the thickness lightening holes 11 are not limited to those shown in Fig. 2 as long as the above-described functions are ensured. The tie bolts 10 may be replaced with combinations of a tie bolt and a nut. In this case, the tie bolts can be secured by the nuts after being inserted through holes in the rear flange 16 of the rear housing 5.

Claims: A method of manufacturing a jacket (1) for cooling a stator (3) of a motor, characterised by the steps of: extruding a billet of aluminium alloy to provide the jacket (1) and conduits (2) therein for the passage of liquid coolant; and cutting said extruded billet into a desired lenght. A liquid cooled motor comprising a jacket (1) for cooling a stator (3) of the motor, the stator cooling jacket (1) having provided therein a plurality of conduits (2) intended for the passage of liquid coolant and having front and rear surfaces to which are attached front and rear housings (4,5) respectively, characterised in that: the stator cooling jacket (1) is formed of an extruded profile of aluminium alloy; and the jacket (1) and the front and rear housings (4,5) are fastened together by means of a plurality of tie bolts (10) extending from the front housing (4) to the rear housing (5). A liquid cooled motor according to claim 2, wherein said front and rear housings (4,5) are made of cast iron and respectively include flanges (14,16) one having a plurality of holes through which said tie bolts (10) are allowed to pass, and the other a plurality of holes for receiving threaded end portions of said tie bolts (10), respectively. A liquid cooled motor according to claim 3, wherein said holes for receiving the threaded end portions of the tie bolts (10), are themselves threaded. A liquid cooled motor according to claim 2, 3 or 4, wherein said jacket (1) includes a plurality of thickness lightening holes (11) which are formed when extruding said jacket (1) and which are used as holes through which said tie bolts (10) are allowed to pass. A liquid cooled motor according to claim 5, wherein each of said plurality of thickness lightening holes (11) has a sectional configuration a part of which permits only the axial displacement of said tie bolts (10) inserted into said thickness lightening holes (11). A liquid cooled motor according to claim 5 or 6, wherein said plurality of thickness lightening holes (11) are equally spaced in the circumferential direction of said jacket (1), and said plurality of conduits (2) for the passage of coolant are arranged on both sides of each of said thickness lightening holes (11). A liquid cooled motor according to any one of claims 2 to 7, wherein each of said plurality of conduits (2) includes a multiplicity of inwardly protruding cooling fins (12).

Inventors: KATSUZAWA YUKIO, MASUYA MICHI, NAKAMURA KOSEI, KATSUZAWA, YUKIO, MASUYA, MICHI, NAKAMURA, KOSEI, KATSUZAWA, YUKIO, 1915-5, FUNATSU, MASUYA, MICHI, FANUC DAI-3 VIRA-KARAMATSU, NAKAMURA, KOSEI, ROOM 11-601 FANUC MANSHION
Applicants: FANUC LTD
Application year: 1992
Main classification: H02K9
IPC codes: H02K5, H02K9