Coating material for armature coil of a motor for electrical equipment

Abstract: In a motor in which a copper armature coil (2) wound around an iron armature core (1) is fixed to the armature core (1) by coating a resin coating material (3) on the armature coil by impregnation, crack generation in the coating material is prevented. The coefficient of thermal expansion of the coating material is set to a value between the coefficient of thermal expansion of copper and that of iron.

Description: Background of the Invention Field of the Invention: The present invention relates to a coating material for an armature coil of a motor for electrical equipment. The motor can be, for example, a starter motor, a wiper motor, a power window motor, a power seat motor or a sunroof motor. Description of the Related Art: In the above-described type of motors for electrical equipment, a copper armature core, which is wound around a slot formed in an iron armature core, is fixed to the armature core by coating a resin coating material (fillers) on the armature coil by impregnation. Consequently, in such a motor, even when the armature is rotated at a high speed, abrasion of the armature coil or projection of the armature coil from the slot is eliminated, thus eliminating breakage of the coil or peeling-off of an insulating film which impairs the insulation property. Therefore, a reliable motor is provided. Motors for the electrical equipment may be installed near an engine, such as a starter motor. Such motors are heated to 150 °C or above when the engine heated to a high temperature. The vehicle may be parked in a severe cold region where the temperature may fall to -40 °C or below. Thus, the requirement of the motor is that the motor can withstand such a great temperature difference. However, it is difficult for the conventional motor to withstand such a great temperature difference. Consequently, the coating material may be cracked, making the motor unreliable. Hence, the present inventors made intensive studies regarding the reasons for crack generation, found that crack generation has a relation with the coefficient of thermal expansion of the coating material, and completed the present invention on the basis of the obtained knowledges. US-A-2846599 proposed using a sealing material which had substantially the same temperature coefficient of expansion as the metals of the core and coil. Summary of the Invention In view of the aforementioned problems of the prior art, an object of the present invention is to provide a coating material for an armature coil for a motor for electrical equipment which is capable of overcoming the aforementioned problems. According to the present invention there is provided a coating material for an armature coil of a motor for electrical equipment in which the armature coil is made of copper and wound around a slot formed in an armature core made of iron wherein said coating material is coated on said armature coil by impregnation to fix said armature coil to said armature core, characterised in that said coating material is made of a resin which is cross-linked to adjust the coefficient of thermal expansion to a value which is between the coefficient of thermal expansion of copper and the coefficient of thermal expansion of iron. The invention also provides a method for forming an armature coil using such a material. It is therefore possible according to the present invention to effectively eliminate generation of cracks in the coating material due to a great temperature difference. The invention will be described now by way of example only, with reference to the accompanying drawings. In the drawings: Fig. 1 is a front view, with part broken away, of an armature core, and Fig. 2 is a B-B cross section of an armature core. Description of the Preferred Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawing. In the figure, reference numeral 1 denotes an armature core which constitutes a motor for the electrical equipment. The armature core 1 is an assembly of a plurality of thin plat-like laminations of a core material made of iron. An armature coil 2 made of copper is wound around a slot la formed in the armature core 1. A resin coating material is coated on the armature core 1 with the armature coil 2 wound around by impregnation to fix the armature coil 2 to the armature core 1. The present inventors conducted experiments in the manner described below to examine the relation between the coefficient of thermal expansion and crack generation. That is, the present inventors carried out the simulation test in the manner described below. First, the armature cores 1 were manufactured. These armature cores 1 were coated by impregnation with substantially the same amount of coating materials 3 having different coefficients of thermal expansion shown below under substantially the same conditions. Each of the manufactured armature cores 1 was rotated at a speed of 2000 revolutions/min (rpm) while the temperature of the atmosphere thereof was raised from -50 °C to 200 °C in 10 minutes. At 200 °C, the armature core 1 was rotated for another 20 minutes. After the rotation of the armature core 1 was stopped, the temperature of the atmosphere was cooled from 200 °C to -50 °C in 30 minutes, and was then maintained to -50 °C for 20 minutes. A series of the above-described operations were repeated 20 times. Thereafter, the armature core 1 was removed to observe incidence of crack generation in the coating material 3. The coating materials 3 selected in the above-described simulation test were diallyl phthalate impregnated with 70% of glass fiber. Four types of coating materials respectively having coefficients of thermal expansion (which are coefficients of linear expansion) of 2.55 x 10 -5 (comparative example 1), 1.96 x 10 -5 (comparative example 2), 1.51 x 10 -5 (example 1) and 1.36 x 10 -5 (example 2) were prepared. The coefficient of thermal expansion of each of the coating materials was adjusted by crosslinking (bridging) of styrene oligomer. To take variations in the tests into account, three coating material samples were used in each of the tests. Table 1 shows the results of the tests. Crack generation was evaluated by visually observing the sliced two surfaces of a coil end portion A of the armature core 1, the sliced two surfaces of a core portion B thereof, and the two axially cut surfaces of an armature core portion C. Sample No. Coefficient of Thermal Expansion (x 10 -5 ) Incidence of Crack Generation Portion A Portion B Portion C Example 1 1 1.51 Non Non Slightly Generated 2 1.51 Non Non Non 3 1.51 Slightly Generated Non Non Example 2 1 1.36 Non Non Non 2 1.36 Non Non Non 3 1.36 Non Non Non Comparative Example 1 1 2.55 High Occurence High Occurence High Occurence 2 2.55 High Occurence Moderate Occurence High Occurence 3 2.55 Moderate Occurence High Occurence High Occurence Comparative Example 2 1 1.96 High Occurence Slight Occurence Slight Occurence 2 1.96 Moderate Occurence Slight Occurence Moderate Occurence 3 1.96 Moderate Occurence Slight Occurence High Occurence It is clear from Table 1 that crack generation was observed more or less in Comparative Examples 1 and 2 in which the coating materials 3 had a high coefficient of thermal expansion and that no crack was generated at all or cracks were generated at a low level that does not matter at all in Examples 1 and 2. That is, the coefficient of thermal expansion of iron which is the material of the armature core 1 is about 1.15 x 10 -5 . The coefficient of linear expansion of copper which is the material of the armature coil 2 ranges from 1.54 x 10 -5 to 1.62 x 10 -5 . In Examples 1 and 2 in which substantially no crack was generated, the coefficients of thermal expansion of the coating materials 3 were 1.51 x 10 -5 and 1.36 x 10 -5 , which were between the coefficient of thermal expansion of iron and that of copper. It can therefore be inferred from the above-mentioned results that generation of cracks in the coating material 3 due to a temperature difference is greatly affected by the coefficient of thermal expansion thereof which differs in materials. Thus, even in the motor which is disposed at a site where there is a great temperature difference, generation of cracks can be effectively avoided by using the coating material 3 having a coefficient of thermal expansion which is between the coefficient of thermal expansion of iron and that of copper, like the above-described examples. As a result, the reliability of the motor is improved. Besides a diallyl phthalate resin, an unsaturated polyester resin or an epoxy resin can also be used as the main component of the coating material. Such a resin is crosslinked (bridged) using a crosslinking (bridging) agent, such as styrene oligomer or allyl oligomer, to adjust the coefficient of thermal expansion thereof to a value between the coefficient of thermal expansion of iron and that of copper. The present inventors conducted the same experiments as the above-described ones using such coating materials, and obtained the same results. As will be understood from the foregoing description, generation of cracks due to a temperature difference can be effectively avoided by using the coating material having a coefficient of thermal expansion which is between the coefficient of thermal expansion of iron and that of copper. Consequently, even when the motor is used at a site where there is a great temperature difference, it can be used reliably.

Claims: A coating material for an armature coil of a motor for electrical equipment in which the armature coil (2) is made of copper and wound around a slot formed in an armature core (1) made of iron, wherein said coating material is coated on said armature coil (2) by impregnation to fix said armature coil to said armature core (1), characterised in that said coating material is made of a resin which is cross-linked to adjust the coefficient of thermal expansion to a value which is between the coefficient of thermal expansion of copper and the coefficient of thermal expansion of iron. A coating material according to claim 1, wherein said resin coating material prevents projection of said armature coil from said armature core due to centrifugal force generated when said armature core is rotation at high speeds. A coating material according to claim 1, wherein said resin coating material prevents cracking of said armature core after said armature core is repeatedly exposed to high temperature differentials and rotation at high speeds. A coating material according to claim 1, wherein said resin coating material is impregnated into said armature core and on a connecting portion of said armature coil, said connecting portion electrically connecting said armature coil to a commutator of said electrical motor. A method of forming an armature coil for a motor for use in electrical equipment comprising winding an armature coil made of copper around a slot in an armature core made of iron and coating the armature coil with a coating material to fix the armature coil to said armature core, characterised in that the coating material is made of a resin which is cross-linked to adjust the coefficient of thermal expansion to a value which is between that of copper and iron.

Inventors: ONODERA TSUGIO, ONODERA, TSUGIO
Applicants: MITSUBA ELECTRIC MFG CO, MITSUBA ELECTRIC MANUFACTURING CO., LTD.
Application year: 1993
Main classification: H02K3
IPC codes: H02K3, H02K15