CA2043519C - Motor casing made of resin and method of manufacturing the same - Google Patents
Motor casing made of resin and method of manufacturing the sameInfo
- Publication number
- CA2043519C CA2043519C CA002043519A CA2043519A CA2043519C CA 2043519 C CA2043519 C CA 2043519C CA 002043519 A CA002043519 A CA 002043519A CA 2043519 A CA2043519 A CA 2043519A CA 2043519 C CA2043519 C CA 2043519C
- Authority
- CA
- Canada
- Prior art keywords
- bearing
- resin material
- thermoplastic resin
- motor casing
- temperature
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
- 229920005989 resin Polymers 0.000 title claims abstract description 53
- 239000011347 resin Substances 0.000 title claims abstract description 53
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 16
- 239000000463 material Substances 0.000 claims abstract description 68
- 230000009477 glass transition Effects 0.000 claims abstract description 23
- 229920005992 thermoplastic resin Polymers 0.000 claims description 44
- 238000000034 method Methods 0.000 claims description 19
- 238000000465 moulding Methods 0.000 claims description 18
- 238000001953 recrystallisation Methods 0.000 claims description 13
- 238000001816 cooling Methods 0.000 claims description 7
- -1 polyethylene terephthalate Polymers 0.000 claims description 7
- 229920000139 polyethylene terephthalate Polymers 0.000 claims description 7
- 239000005020 polyethylene terephthalate Substances 0.000 claims description 7
- 238000003780 insertion Methods 0.000 claims description 6
- 230000037431 insertion Effects 0.000 claims description 6
- 238000003303 reheating Methods 0.000 claims 1
- 230000002093 peripheral effect Effects 0.000 description 18
- 238000003825 pressing Methods 0.000 description 10
- 238000002425 crystallisation Methods 0.000 description 5
- 230000008025 crystallization Effects 0.000 description 5
- 230000006872 improvement Effects 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 230000009471 action Effects 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 239000012779 reinforcing material Substances 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 238000005336 cracking Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 239000003365 glass fiber Substances 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
- F16B4/00—Shrinkage connections, e.g. assembled with the parts at different temperature; Force fits; Non-releasable friction-grip fastenings
- F16B4/006—Shrinkage connections, e.g. assembled with the parts being at different temperature
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
- B29C45/0053—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor combined with a final operation, e.g. shaping
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C65/00—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor
- B29C65/66—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by liberation of internal stresses, e.g. shrinking of one of the parts to be joined
- B29C65/665—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by liberation of internal stresses, e.g. shrinking of one of the parts to be joined using shrinking during cooling
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C66/00—General aspects of processes or apparatus for joining preformed parts
- B29C66/50—General aspects of joining tubular articles; General aspects of joining long products, i.e. bars or profiled elements; General aspects of joining single elements to tubular articles, hollow articles or bars; General aspects of joining several hollow-preforms to form hollow or tubular articles
- B29C66/51—Joining tubular articles, profiled elements or bars; Joining single elements to tubular articles, hollow articles or bars; Joining several hollow-preforms to form hollow or tubular articles
- B29C66/53—Joining single elements to tubular articles, hollow articles or bars
- B29C66/532—Joining single elements to the wall of tubular articles, hollow articles or bars
- B29C66/5324—Joining single elements to the wall of tubular articles, hollow articles or bars said single elements being substantially annular, i.e. of finite length
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C66/00—General aspects of processes or apparatus for joining preformed parts
- B29C66/50—General aspects of joining tubular articles; General aspects of joining long products, i.e. bars or profiled elements; General aspects of joining single elements to tubular articles, hollow articles or bars; General aspects of joining several hollow-preforms to form hollow or tubular articles
- B29C66/61—Joining from or joining on the inside
- B29C66/612—Making circumferential joints
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C35/00—Rigid support of bearing units; Housings, e.g. caps, covers
- F16C35/02—Rigid support of bearing units; Housings, e.g. caps, covers in the case of sliding-contact bearings
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K15/00—Methods or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines
- H02K15/14—Casings; Enclosures; Supports
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K5/00—Casings; Enclosures; Supports
- H02K5/04—Casings or enclosures characterised by the shape, form or construction thereof
- H02K5/08—Insulating casings
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C66/00—General aspects of processes or apparatus for joining preformed parts
- B29C66/01—General aspects dealing with the joint area or with the area to be joined
- B29C66/05—Particular design of joint configurations
- B29C66/10—Particular design of joint configurations particular design of the joint cross-sections
- B29C66/12—Joint cross-sections combining only two joint-segments; Tongue and groove joints; Tenon and mortise joints; Stepped joint cross-sections
- B29C66/124—Tongue and groove joints
- B29C66/1244—Tongue and groove joints characterised by the male part, i.e. the part comprising the tongue
- B29C66/12441—Tongue and groove joints characterised by the male part, i.e. the part comprising the tongue being a single wall
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C66/00—General aspects of processes or apparatus for joining preformed parts
- B29C66/70—General aspects of processes or apparatus for joining preformed parts characterised by the composition, physical properties or the structure of the material of the parts to be joined; Joining with non-plastics material
- B29C66/71—General aspects of processes or apparatus for joining preformed parts characterised by the composition, physical properties or the structure of the material of the parts to be joined; Joining with non-plastics material characterised by the composition of the plastics material of the parts to be joined
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C66/00—General aspects of processes or apparatus for joining preformed parts
- B29C66/70—General aspects of processes or apparatus for joining preformed parts characterised by the composition, physical properties or the structure of the material of the parts to be joined; Joining with non-plastics material
- B29C66/73—General aspects of processes or apparatus for joining preformed parts characterised by the composition, physical properties or the structure of the material of the parts to be joined; Joining with non-plastics material characterised by the intensive physical properties of the material of the parts to be joined, by the optical properties of the material of the parts to be joined, by the extensive physical properties of the parts to be joined, by the state of the material of the parts to be joined or by the material of the parts to be joined being a thermoplastic or a thermoset
- B29C66/731—General aspects of processes or apparatus for joining preformed parts characterised by the composition, physical properties or the structure of the material of the parts to be joined; Joining with non-plastics material characterised by the intensive physical properties of the material of the parts to be joined, by the optical properties of the material of the parts to be joined, by the extensive physical properties of the parts to be joined, by the state of the material of the parts to be joined or by the material of the parts to be joined being a thermoplastic or a thermoset characterised by the intensive physical properties of the material of the parts to be joined
- B29C66/7311—Thermal properties
- B29C66/73117—Tg, i.e. glass transition temperature
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
- B29L2031/00—Other particular articles
- B29L2031/748—Machines or parts thereof not otherwise provided for
- B29L2031/749—Motors
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C2226/00—Joining parts; Fastening; Assembling or mounting parts
- F16C2226/30—Material joints
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C2380/00—Electrical apparatus
- F16C2380/26—Dynamo-electric machines or combinations therewith, e.g. electro-motors and generators
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Power Engineering (AREA)
- Motor Or Generator Frames (AREA)
- Injection Moulding Of Plastics Or The Like (AREA)
- Manufacture Of Motors, Generators (AREA)
Abstract
Disclosed are a motor casing made of a resin and a method of manufacturing such a motor casing. A bearing for rotatably supporting a core shaft of a rotor core is inserted into a small-diameter portion of the motor casing when the temperature of the resin material which forms the small-diameter portion is substantially at the glass transition temperature thereof or above, the resin material being then cooled to a room temperature.
Description
~ 2 0 Li 3 5 ~ !~
MOTOR CASING MADE OF RESIN AND
METHOD OF MANUFACTURING THE SAME
BACKGROUND OF THE INVENTION
Field of the Invention:
The present invention relates to a motor casing made of a resin, for use in the vehicle-mounted electric equipment or the like, and a method of manufacturing the same.
Description of the Related Art:
It has been proposed to form a light-weight motor casing (a motor housing) by molding using a crystallizable thermoplastic resin material. However, such a motor casing made of a resin suffers from a drawback in that the processing accuracy is lower than that of a metal one. In such a motor casing, the portion into which a bearing for rotatably supporting a motor shaft is pressingly inserted therefore has an inner peripheral surface which is not round. This allows an excessive amount of pressing force to be locally act on the bearing, causing deformation thereof and hence reduction in the bearing accuracy. Furthermore, a bearing 6 is inserted into a bearing inserting portion lla of a small-diameter portion 11 of a casing 10 made of a resin which has a diameter smaller than the outer diameter of the bearing 6, as shown in Fig. 5. With such a casing, the inner diameter of the bearing inserting portion may be increased to such an extent that a required bearing pressing ~' 2G~3~ 3 force cannot be obtained due to the deteriorated processing accuracy. In that case, the bearing may come off from the bearing inserting portion lla.
Motors mounted on a vehicle, such as an automobile, are known. In a motor casing for use in such a motor, the temperature range in which the motor casing is used must be enlarged toward the high temperature. However, since the coefficient of thermal expansion of the resin material which forms the motor casing is larger than that of the metal which forms the bearing, the inner diameter of the bearing inserting portion lla may become larger than the outer diameter of the bearing at high temperatures. A combination of this expansion and creeping of the resin material leads to reduction in the pressing force of the bearing, thus causing coming-off of the bearing from the small-diameter portion. It has therefore been proposed to reduce the inner diameter of the bearing inserting portion so as to ensure the required pressing force at high temperatures. However, this makes the pressing force too large in a normal temperature state, generating galling between the inner peripheral surface of the bearing inserting portion and the bearing, which may lead to planing of the inner peripheral surface of the small-diameter portion or to cracking of the bearing insert portion.
In the above-described type of motor casing, a h a ~ ~ s 1 9 reinforcing material, such as glass fiber, may be mixed in order to increase the mechanical strength of the casing. As the reinforcing material has a fiber-like shape and is elongated, an ejected resin material may have a directional property, and have different shrinkage factors in the longitudinal and lateral directions. This increases tendency in which changes in the dimension are increased.
Accordingly, attempts have been made to improve the accuracy of the resin casing by maintaining the temperature of the mold used for molding substantially to the recrystallization temperature of the resin material over many hours until the crystallization of the resin material reaches substantially a saturated state, the resin being then cooled. This is effective to restrict changes (shrinkages) in the dimensions caused by the recrystallization of the resin product. However, to obtain a saturated state of crystallization, the temperature must be maintained constant over many hours. This is therefore unpractical as the manufacturing method of the casing in which casings are mass produced in a short period of time.
In another conventional manufacturing method, a resin material is injected into a mold heated to a lower temperature so as to achieve quick cooling of the resin material and thereby shorten the molding time. However, in this method, amorphous portions may be generated in the ~ 6~ ~ 1 9 resin material due to quick cooling. Such amorphous portions may be recrystallized when the casing is used in the vicinity of the glass transition temperature, such as that used for electrical equipment mounted on a vehicle, thus generating changes in the dimensions.
Accordingly, it has been proposed to prevent generation of the amorphous portions by controlling the speed at which the temperature of the mold is lowered using a temperature adjusting device mounted on the mold and to use a mold which is slightly elliptical or eccentric with changes in the dimensions caused by molding taken into consideration.
Deformation caused by molding may make the resin round.
However, in this method, the relation between the temperature lowering speed and changes in the dimensions of the product and the shape of the mold must be measured using the highly accurate measuring technique. Also, since a very sophisticated expensive temperature lowering device and accurate mold processing technique are required, a great loss is generated in both time and cost. When the shape of the molded product is complicated, like the motor casing, estimation of changes in the dimensions caused by molding is difficult. Also, reproducibility is poor.
In another manufacturing methods, accuracy of the bearing inserting portion is improved by increasing the wall thickness of the bearing so that the pressing force does not 2 ~
cause deformation of the bearing or by reducing the inserting margin of the bearing. In the former method, the diameter of the motor casing increases by a degree at which the bearing is made thick, thus increasing the overall size of the motor casing. In the latter method, since the inserting margin is small, the bearing easily comes off.
Consequently, the bearing supporting strength is reduced.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a motor casing made of a resin and a method of manufacturing such a motor casing which are capable of overcoming the aforementioned problems of the conventional motor casing.
To achieve this object, the present invention provides a method of manufacturing a motor casing which is characterized in that when the motor casing is formed by molding in which a thermoplastic resin material is injected into a mold, a bearing for rotatably supporting a core shaft of a rotor core is inserted into a small-diameter portion of the motor casing before the temperature of the resin material is substantially lowered to the glass transition temperature, the resin material being then cooled to the room temperature.
The present invention further provides a motor casing made of a resin, which is characterized in that when the ~ Q ~ 3 5 ~ ~
motor casing is manufactured by molding in which a thermoplastic resin is injected into a mold, a bearing for rotatably supporting a core shaft of a rotor core is inserted into a small-diameter portion of the motor casing before the temperature of the resin material which forms the small-diameter portion substantially lowers to the glass transition temperature, the resin material being then cooled to a room temperature.
The present invention further provides a method for manufacturing a motor casing having a circular bear seat portion for supporting a bearing, which comprises the steps of:
injecting a heated thermoplastic resin material into a mold thereby forming a motor casing by molding;
inserting a bearing, the bearing rotatably supporting a core shaft of a rotor core such that an axis of the bearing is substantially parallel to an axis of the core shaft, into the bearing seat portion while a temperature of the thermoplastic resin material is below a recrystallization temperature of the thermoplastic resin material and above a glass transition temperature of the thermoplastic resin material; and cooling the thermoplastic resin material to room temperature to obtain a bearing seat portion that is substantially completely round.
The present invention further provides a method for manufacturing a motor casing having a circular bearing seat portion for supporting a bearing, which comprises the steps of:
injecting a thermoplastic resin material into a mold thereby forming a motor casing by molding;
~o~5 19 successively removing an inner mold section to expose the bearing seat portion and inserting a bearing, the bearing rotatably supporting a core shaft of a rotor, into the bearing seat portion such that an axis of the bearing is substantially parallel to an axis of the core shaft, while a temperature of the thermoplastic resin material is below a recrystallization temperature of the thermoplastic resin material and above a glass transition temperature of the thermoplastic resin material; and cooling the thermoplastic resin material to room temperature to obtain a bearing seat portion that is substantially completely round.
In the present invention, although the motor casing is made of a resin, the circularity of the bearing inserting portion can be greatly improved. Furthermore, shifting of the bearing inserted into the bearing inserting portion formed in the motor casing is prevented.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic cross-sectional view of a motor, showing an embodiment of a motor casing according to the present invention;
Fig. 2 is an enlarged cross-sectional view of the essential parts of the casing of Fig. l;
Fig. 3 is a cross-sectional view of the motor;
Fig. 4 is an enlarged cross-sectional view of a front frame of Fig. 3;
Fig. 5 is an enlarged cross-sectional view of a front frame of a conventional motor casing;
~- ~ 2~ ~ 3~ 1 g Fig. 6 is a graph in which changes in the temperature of the inner peripheral surface of a bearing inserting portion when the molded product is removed from a mold and changes in the circularity of the inserted bearing are plotted; and Fig. 7 is a graph in which changes in the temperature of the inner peripheral surface of a bearing inserting .
-7a-portion when the molded product is removed from a mold and changes in the circularity of the inserted bearing are plotted.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of the present invention will be described in detail with reference to the accompanying drawings. In Figs. 1 to 4, a motor casing 1 has a permanent magnet 2 fixed to the inner peripheral surface thereof. The motor casing 1 incorporates a rotor core 3. Brush holders 5 are integrally formed with a brush chamber ~ formed on the inner peripheral surface of the casing 1. Brushes 5a elastically mounted on the brush holders 5 are slidably in contact with a commutator 3a of the rotor core 3.
The motor casing 1 has a small-diameter portion, that is, an inserting portion 7, for rotatably supporting a core shaft 3b of the rotor core 3 through a bearing 6. The present invention is carried on this inserting portion 7.
That is, in a first embodiment, the inserting portion 7 is manufactured in the manner described below by injecting a molten thermoplastic resin, such as polyethylene terephthalate, between an outer mold H which defines the outer periphery of the inserting portion 7 and an inner mold I which defines the inner periphery thereof. First, both the molds H and I are heated to about 110 C which is the recrystallization temperature of the resin material. At ~ a ~ s that time, adjustment of the surface temperature of the inner mold I alone may be conducted using a temperature adjusting device connected to the inner mold I. In that state, a molten resin material is injected between the two molds, and then the resin is gradually cooled. When the temperature of the inner mold I has been cooled to a value which is higher than the glass transition point of the resin and at which the resin is in an activated state and crystallization thereof is in a progress, the inner mold I
alone is removed, and the bearing 6 is inserted into the inserting portion 7 before the temperature of the inner peripheral surface thereof lowers to the glass transition temperature of the resin or below. Thereafter, the bearing inserting portion 7 is cooled to the ambient temperature to obtain the casing 1.
In a second embodiment, the bearing inserting portion 7 is manufactured in the manner described below. First, the casing is formed by injecting a molten thermoplastic resin, such as polyethylene terephthalate, between the outer mold H
which defines the outer periphery of the inserting portion 7 and the inner mold I which defines the inner periphery thereof. After the casing 1 is cooled to the ambient temperature, it is heated to a temperature which is not less than the glass transition temperature thereof, and the bearing 6 is inserted into the bearing inserting portion 7 ~ 204~5~9 which is in a heated state. Thereafter, the inserting portion 7 is cooled to the ambient temperature to obtain the casing 1.
In either of the above-described embodiments, when the bearing 6 is inserted into the bearing inserting portion 7 during the molding of the casing 1, it is inserted before the temperature of the bearing inserting portion 7 lowers to the glass transition temperature thereof or below, i.e., at a temperature at which crystallization of the resin is in a progress but at which the resin is in an activated state which allows for deformation thereof, as stated above.
Consequently, in a subsequent temperature lowering process, the inserting portion 7 gradually shrinks in the form of the bearing 6 inserted thereinto. As a result, the inner peripheral surface of the bearing inserting portion 7 is substantially completely round and is in surface contact with the outer peripheral surface of the bearing 6.
Therefore, action of the local pressing force on the bearing 6 can be eliminated, and deformation of the bearing 6 can thus be prevented effectively. This allows for mounting of the bearing with a high degree of accuracy and leads to an increase in the quality and performance of the motor.
Such a highly accurate mounting of the bearing can be accomplished without repeating correction of the shape of the mold used for molding the bearing inserting portion 7 using an expensive measuring device and a sophisticated processing technique. This is a great improvement in workability.
Furthermore, the bearing inserting portion 7 has a diameter smaller than the outer diameter of the bearing 6 at positions which face the front and rear end portions of the bearing 6 due to shrinkage of the resin material, and the inner peripheral surface of the bearing inserting portion 7 supports the front and rear end portions of the bearing 6 in an undercut state. Consequently, coming off of the bearing 6 in an axial direction thereof is reliably prevented, and reliability of the casing is greatly improved.
The advantages of the first embodiment will further be described below using an example. In the following example, the motor casing 1 was actually manufactured by molding using polyethylene terephthalate having a melting point of 260 C, a recrystallization temperature of about llO C and the glass transition temperature of about 55 C.
In the above motor casing 1, bearings X and Y
respectively having an outer diameter of 9 mm and 12 mm were inserted. Fig. 6 shows a graph in which changes in the temperature of the inner peripheral surface of the bearing inserting portion 7 when the molded article is removed from the mold and changes in the circularity (the maximum deflection in the radial direction from an ideal circle, a ~
measured twenty hour hours after the bearing inserting portion 7 has been removed from the mold) of the bearing 5 inserted into the bearing inserting portion at a given surface temperature are plotted. As can be seen from Fig.
6, changes in the circularity of the bearing inserted before the surface temperature lowers substantially to the glass transition temperature is less. The lower the surface temperature when the bearing is inserted, the worse the circularity is. This shows how advantageous the first embodiment is.
With respect to the bearing X, it was observed that the circularity thereof inserted into the bearing inserting portion, which was removed from the mold twenty four hours (one thousand four hundred forty minutes) ago, changed by 17.5 ~m, whereas that of the bearing inserted in the vicinity of the glass transition temperature changed about S
~m. With respect to the bearing Y, changes in the circularity decreased from 37.5 ~m to 9 ~m. In both cases, the circularity improved by 70% or above.
Next, the advantages of the second embodiment will be described. In this example, the same bearings were used.
After the manufactured casing 1 was left at the room temperature for twenty four hours, the casing 1 was heated to a selected temperature, and the bearing 6 was inserted into the bearing inserting portion 7 having that 2~435~t!~
temperature. Thereafter, the casing 1 was left at the room temperature for forty eight hours. Fig. 7 is a graph in which the temperature of the bearing inserting portion when the bearing is inserted and changes in the circularity (maximum deflection in the radial direction relative to the ideal circle) of the inserted bearing 6 are plotted. As can be seen from Fig. 7, when the heating temperature was higher than the glass transition temperature, a great improvement in the circularity of the bearing was observed, as in the first embodiment.
That is, with respect to the bearing X, it was observed the circularity thereof inserted at the room temperature changed by 17.5 ~m, whereas that of the bearing inserted near the glass transition temperature and then cooled changed by about 6 ~m. Change in the circularity decreases as the heating temperature increases to the recrystallization temperature. Similar phenomenon was observed with respect to the bearing Y. These prove how advantageous the second embodiment is.
In the first embodiment, the mold was removed at a temperature higher than the recrystallization point, and the bearing was inserted into the bearing inserting portion having that temperature. Forty eight hours after the mold was removed, the circularity of the inserted bearing was measured in the similar manner. Great change in the 2~43S~9 circularity was observed. As the temperature at which the bearing was inserted rises, the resin material which forms the inserting portion is softened, making insertion difficult. Particularly, at 200 C or above, the resin material cannot maintain its original shape. Therefore, the temperature of the inner peripheral surface of the inserting portion at which the bearing is inserted should be a value which ensures that the resin material can maintain its shape after the mold was removed therefrom. When the temperature of the inner peripheral surface is lower than the recrystallization temperature, recrystallization of the resin material which forms the inner peripheral surface of the bearing inserting portion is in a progress and the resin material is stable. As a result, deformation of the bearing inserting portion caused by the insertion is eliminated.
In the second embodiment, the bearing was inserted in a state in which the bearing inserting portion was heated to a temperature higher than the recrystallization temperature, as in the first embodiment. It was observed that the circularity greatly changed.
It is possible to provide a better casing using the above-described procedures. In this embodiment, the casing 1 made of a resin is divided into a yoke la and a front bracket lb, and mounting of the bearing in the front bracket lb is specifically examined. That is, the front bracket lb has an inserting portion 7 for rotatably supporting a rotor shaft 3b of the rotor core 3. This inserting portion rotatably supports the rotor shaft 3b through the bearing 6 and has the following inner peripheral surface. More specifically, the inserting portion 7 has a bearing introducing portion 7a which protrudes toward the brush chambers 4. The introducing portion 7a has an inner diameter A which is slightly larger than the outer diameter B of the bearing 6 (A > B) so that it can temporarily hold the bearing 6 in a state in which the bearing 6 is centered.
A bearing inserting portion 7b is formed on the distal end side of the bearing introducing portion 7a. A small-diameter coming-off preventing portion 7c is formed between the introducing portion 7a and the bearing inserting portion 7b to prevent coming-off of the inserted bearing.
Since the front bracket lb is made of a resin, it has an coefficient of expansion very larger than that of the metal which forms the bearing 6. Therefore, the inner diameter C
of the coming-off preventing portion 7c is made smaller than the outer diameter B of the bearing 6 at room temperatures.
Furthermore, B' > C' where B' (B < B') is the outer diameter of the expanded bearing 6 at the upper value in the temperature range in which the motor is used and C'(C < C') is the inner diameter of the expanded coming-off preventing portion 7c.
~ g In this embodiment, when the bearing 6 is inserted into the bearing inserting portion 7b, it is first retained in the introducing portion 7a temporarily, and then forcibly inserted into the bearing inserting portion 7b. The inserted bearing 6 is reliably prevented from coming off by the presence of the small-diameter coming-off preventing portion 7c formed between the introducing portion 7a and the bearing inserting portion 7b.
More specifically, even when the pressing force of the bearing 6 inserted in the bearing inserting portion 7b is smaller than a required one, the bearing 6 is prevented from coming off by the small-diameter coming-off preventing portion 7c formed at the inlet of the bearing inserting portion 7b. Consequently, reliability of the motor is greatly improved, and troubles caused by coming-off of the bearing 6 can thus be eliminated.
Furthermore, coming-off of the bearing 6, which would occur when the motor is heated to a high temperature, can be prevented. That is, since the inner diameter of the coming-off preventing portion 7c remains smaller than the outer diameter of the expanded bearing 6 at high temperatures, coming-off of the bearing 6 from the bearing inserting portion 7b is prevented at those high temperatures. This further improves reliability of the motor.
In this embodiment, when the bearing 6 is inserted into ~ L 3 ~
the bearing inserting portion 7b, it is passed through the narrow coming-off preventing portion 7c. At that time, the bearing 6 is first inserted into the introducing portion 7a formed on the inlet side of the coming-off preventing portion 7b and temporarily held therein in a centered state before being forcibly pushed into the bearing inserting portion 7b. Consequently, offset of the bearing 6 with respect to the small-diameter coming-off preventing portion 7c does not occur when it is forcibly inserted into the bearing inserting portion 7b. In this embodiment, the adjoining portion between the introducing portion 7a and the coming-off preventing portion 7c is tapered so as to make movement of the bearing 6 from the introducing portion 7a to the coming-off preventing portion 7c smooth.
When the bearing 6 passes through the small-diameter coming-off preventing portion 7c, expanding loads are applied to the coming-off preventing portion 7c. However, the coming-off preventing portion 7c is made of a resin exhibiting an elasticity. Therefore, if the expanding loads are within the elastic limitation of the coming-off preventing portion 7c, passage of the bearing 6 causes forcible expansion of the coming-off preventing portion 7c but does not cause any trouble. The coming-off preventing portion 7c recovers its original shape after the bearing 6 has passed therethrough.
Z~ ~3~ ~
As will be understood from the foregoing description, in the present invention, the bearing is inserted into the bearing inserting portion of the motor casing made of a thermoplastic resin while crystallization of the resin material is in a progress and the resin material is thus in an activated state. Therefore, in a subsequent temperature lowering process, the inserting portion 7 gradually shrinks in the form of the bearing inserted thereinto. As a result, the inner peripheral surface of the bearing inserting portion is substantially completely round and is in surface contact with the outer peripheral surface of the bearing.
Therefore, action of the local pressing force on the bearing 6 can be eliminated, and deformation of the bearing 6 can thus be prevented effectively. This allows for mounting of the bearing with a high degree of accuracy and leads to an increase in the quality and performance of the motor. Such a highly accurate mounting of the bearing can be accomplished without repeating correction of the shape of the mold used for molding the bearing inserting portion using an expensive measuring device and a sophisticated processing technique. This is a great improvement in workability.
Furthermore, even when the pressing force of the bearing inserted into the bearing inserting portion is looser than a set one, the bearing is prevented from coming 3 ~ ~ ~
off by the small-diameter coming-off preventing portion formed on the inlet side of the inserting portion.
Therefore, accidental coming-off of the bearing from the bearing inserting portion made of a resin can reliably be avoided, and reliability of the motor can thus be greatly improved while the trouble involving coming-off of the bearing can be avoided.
~ urthermore, when the bearing is inserted into the bearing inserting portion by forcibly passing it through the small-diameter coming-off preventing portion, it is temporarily held in a centered stated by the bearing introducing portion having a diameter larger than the outer diameter of the bearing and formed on the inlet side of the coming-off prevention portion. Consequently, a troublesome centering task can be eliminated when the bearing is pushed into the coming-off preventing portion, thus greatly improving workability.
Furthermore, since the inner diameter of the coming-off preventing portion is made smaller than the outer diameter of the bearing at the upper limit of the temperature range in which the motor is used, coming-off of the bearing is reliably prevented at the high temperatures which ensure different degrees of expansion. Therefore, reliability of the motor casing can greatly be improved even when the casing is used for a motor operated at high temperatures, 2 ~ 'J _ g such as that for the electrical equipment.
MOTOR CASING MADE OF RESIN AND
METHOD OF MANUFACTURING THE SAME
BACKGROUND OF THE INVENTION
Field of the Invention:
The present invention relates to a motor casing made of a resin, for use in the vehicle-mounted electric equipment or the like, and a method of manufacturing the same.
Description of the Related Art:
It has been proposed to form a light-weight motor casing (a motor housing) by molding using a crystallizable thermoplastic resin material. However, such a motor casing made of a resin suffers from a drawback in that the processing accuracy is lower than that of a metal one. In such a motor casing, the portion into which a bearing for rotatably supporting a motor shaft is pressingly inserted therefore has an inner peripheral surface which is not round. This allows an excessive amount of pressing force to be locally act on the bearing, causing deformation thereof and hence reduction in the bearing accuracy. Furthermore, a bearing 6 is inserted into a bearing inserting portion lla of a small-diameter portion 11 of a casing 10 made of a resin which has a diameter smaller than the outer diameter of the bearing 6, as shown in Fig. 5. With such a casing, the inner diameter of the bearing inserting portion may be increased to such an extent that a required bearing pressing ~' 2G~3~ 3 force cannot be obtained due to the deteriorated processing accuracy. In that case, the bearing may come off from the bearing inserting portion lla.
Motors mounted on a vehicle, such as an automobile, are known. In a motor casing for use in such a motor, the temperature range in which the motor casing is used must be enlarged toward the high temperature. However, since the coefficient of thermal expansion of the resin material which forms the motor casing is larger than that of the metal which forms the bearing, the inner diameter of the bearing inserting portion lla may become larger than the outer diameter of the bearing at high temperatures. A combination of this expansion and creeping of the resin material leads to reduction in the pressing force of the bearing, thus causing coming-off of the bearing from the small-diameter portion. It has therefore been proposed to reduce the inner diameter of the bearing inserting portion so as to ensure the required pressing force at high temperatures. However, this makes the pressing force too large in a normal temperature state, generating galling between the inner peripheral surface of the bearing inserting portion and the bearing, which may lead to planing of the inner peripheral surface of the small-diameter portion or to cracking of the bearing insert portion.
In the above-described type of motor casing, a h a ~ ~ s 1 9 reinforcing material, such as glass fiber, may be mixed in order to increase the mechanical strength of the casing. As the reinforcing material has a fiber-like shape and is elongated, an ejected resin material may have a directional property, and have different shrinkage factors in the longitudinal and lateral directions. This increases tendency in which changes in the dimension are increased.
Accordingly, attempts have been made to improve the accuracy of the resin casing by maintaining the temperature of the mold used for molding substantially to the recrystallization temperature of the resin material over many hours until the crystallization of the resin material reaches substantially a saturated state, the resin being then cooled. This is effective to restrict changes (shrinkages) in the dimensions caused by the recrystallization of the resin product. However, to obtain a saturated state of crystallization, the temperature must be maintained constant over many hours. This is therefore unpractical as the manufacturing method of the casing in which casings are mass produced in a short period of time.
In another conventional manufacturing method, a resin material is injected into a mold heated to a lower temperature so as to achieve quick cooling of the resin material and thereby shorten the molding time. However, in this method, amorphous portions may be generated in the ~ 6~ ~ 1 9 resin material due to quick cooling. Such amorphous portions may be recrystallized when the casing is used in the vicinity of the glass transition temperature, such as that used for electrical equipment mounted on a vehicle, thus generating changes in the dimensions.
Accordingly, it has been proposed to prevent generation of the amorphous portions by controlling the speed at which the temperature of the mold is lowered using a temperature adjusting device mounted on the mold and to use a mold which is slightly elliptical or eccentric with changes in the dimensions caused by molding taken into consideration.
Deformation caused by molding may make the resin round.
However, in this method, the relation between the temperature lowering speed and changes in the dimensions of the product and the shape of the mold must be measured using the highly accurate measuring technique. Also, since a very sophisticated expensive temperature lowering device and accurate mold processing technique are required, a great loss is generated in both time and cost. When the shape of the molded product is complicated, like the motor casing, estimation of changes in the dimensions caused by molding is difficult. Also, reproducibility is poor.
In another manufacturing methods, accuracy of the bearing inserting portion is improved by increasing the wall thickness of the bearing so that the pressing force does not 2 ~
cause deformation of the bearing or by reducing the inserting margin of the bearing. In the former method, the diameter of the motor casing increases by a degree at which the bearing is made thick, thus increasing the overall size of the motor casing. In the latter method, since the inserting margin is small, the bearing easily comes off.
Consequently, the bearing supporting strength is reduced.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a motor casing made of a resin and a method of manufacturing such a motor casing which are capable of overcoming the aforementioned problems of the conventional motor casing.
To achieve this object, the present invention provides a method of manufacturing a motor casing which is characterized in that when the motor casing is formed by molding in which a thermoplastic resin material is injected into a mold, a bearing for rotatably supporting a core shaft of a rotor core is inserted into a small-diameter portion of the motor casing before the temperature of the resin material is substantially lowered to the glass transition temperature, the resin material being then cooled to the room temperature.
The present invention further provides a motor casing made of a resin, which is characterized in that when the ~ Q ~ 3 5 ~ ~
motor casing is manufactured by molding in which a thermoplastic resin is injected into a mold, a bearing for rotatably supporting a core shaft of a rotor core is inserted into a small-diameter portion of the motor casing before the temperature of the resin material which forms the small-diameter portion substantially lowers to the glass transition temperature, the resin material being then cooled to a room temperature.
The present invention further provides a method for manufacturing a motor casing having a circular bear seat portion for supporting a bearing, which comprises the steps of:
injecting a heated thermoplastic resin material into a mold thereby forming a motor casing by molding;
inserting a bearing, the bearing rotatably supporting a core shaft of a rotor core such that an axis of the bearing is substantially parallel to an axis of the core shaft, into the bearing seat portion while a temperature of the thermoplastic resin material is below a recrystallization temperature of the thermoplastic resin material and above a glass transition temperature of the thermoplastic resin material; and cooling the thermoplastic resin material to room temperature to obtain a bearing seat portion that is substantially completely round.
The present invention further provides a method for manufacturing a motor casing having a circular bearing seat portion for supporting a bearing, which comprises the steps of:
injecting a thermoplastic resin material into a mold thereby forming a motor casing by molding;
~o~5 19 successively removing an inner mold section to expose the bearing seat portion and inserting a bearing, the bearing rotatably supporting a core shaft of a rotor, into the bearing seat portion such that an axis of the bearing is substantially parallel to an axis of the core shaft, while a temperature of the thermoplastic resin material is below a recrystallization temperature of the thermoplastic resin material and above a glass transition temperature of the thermoplastic resin material; and cooling the thermoplastic resin material to room temperature to obtain a bearing seat portion that is substantially completely round.
In the present invention, although the motor casing is made of a resin, the circularity of the bearing inserting portion can be greatly improved. Furthermore, shifting of the bearing inserted into the bearing inserting portion formed in the motor casing is prevented.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic cross-sectional view of a motor, showing an embodiment of a motor casing according to the present invention;
Fig. 2 is an enlarged cross-sectional view of the essential parts of the casing of Fig. l;
Fig. 3 is a cross-sectional view of the motor;
Fig. 4 is an enlarged cross-sectional view of a front frame of Fig. 3;
Fig. 5 is an enlarged cross-sectional view of a front frame of a conventional motor casing;
~- ~ 2~ ~ 3~ 1 g Fig. 6 is a graph in which changes in the temperature of the inner peripheral surface of a bearing inserting portion when the molded product is removed from a mold and changes in the circularity of the inserted bearing are plotted; and Fig. 7 is a graph in which changes in the temperature of the inner peripheral surface of a bearing inserting .
-7a-portion when the molded product is removed from a mold and changes in the circularity of the inserted bearing are plotted.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of the present invention will be described in detail with reference to the accompanying drawings. In Figs. 1 to 4, a motor casing 1 has a permanent magnet 2 fixed to the inner peripheral surface thereof. The motor casing 1 incorporates a rotor core 3. Brush holders 5 are integrally formed with a brush chamber ~ formed on the inner peripheral surface of the casing 1. Brushes 5a elastically mounted on the brush holders 5 are slidably in contact with a commutator 3a of the rotor core 3.
The motor casing 1 has a small-diameter portion, that is, an inserting portion 7, for rotatably supporting a core shaft 3b of the rotor core 3 through a bearing 6. The present invention is carried on this inserting portion 7.
That is, in a first embodiment, the inserting portion 7 is manufactured in the manner described below by injecting a molten thermoplastic resin, such as polyethylene terephthalate, between an outer mold H which defines the outer periphery of the inserting portion 7 and an inner mold I which defines the inner periphery thereof. First, both the molds H and I are heated to about 110 C which is the recrystallization temperature of the resin material. At ~ a ~ s that time, adjustment of the surface temperature of the inner mold I alone may be conducted using a temperature adjusting device connected to the inner mold I. In that state, a molten resin material is injected between the two molds, and then the resin is gradually cooled. When the temperature of the inner mold I has been cooled to a value which is higher than the glass transition point of the resin and at which the resin is in an activated state and crystallization thereof is in a progress, the inner mold I
alone is removed, and the bearing 6 is inserted into the inserting portion 7 before the temperature of the inner peripheral surface thereof lowers to the glass transition temperature of the resin or below. Thereafter, the bearing inserting portion 7 is cooled to the ambient temperature to obtain the casing 1.
In a second embodiment, the bearing inserting portion 7 is manufactured in the manner described below. First, the casing is formed by injecting a molten thermoplastic resin, such as polyethylene terephthalate, between the outer mold H
which defines the outer periphery of the inserting portion 7 and the inner mold I which defines the inner periphery thereof. After the casing 1 is cooled to the ambient temperature, it is heated to a temperature which is not less than the glass transition temperature thereof, and the bearing 6 is inserted into the bearing inserting portion 7 ~ 204~5~9 which is in a heated state. Thereafter, the inserting portion 7 is cooled to the ambient temperature to obtain the casing 1.
In either of the above-described embodiments, when the bearing 6 is inserted into the bearing inserting portion 7 during the molding of the casing 1, it is inserted before the temperature of the bearing inserting portion 7 lowers to the glass transition temperature thereof or below, i.e., at a temperature at which crystallization of the resin is in a progress but at which the resin is in an activated state which allows for deformation thereof, as stated above.
Consequently, in a subsequent temperature lowering process, the inserting portion 7 gradually shrinks in the form of the bearing 6 inserted thereinto. As a result, the inner peripheral surface of the bearing inserting portion 7 is substantially completely round and is in surface contact with the outer peripheral surface of the bearing 6.
Therefore, action of the local pressing force on the bearing 6 can be eliminated, and deformation of the bearing 6 can thus be prevented effectively. This allows for mounting of the bearing with a high degree of accuracy and leads to an increase in the quality and performance of the motor.
Such a highly accurate mounting of the bearing can be accomplished without repeating correction of the shape of the mold used for molding the bearing inserting portion 7 using an expensive measuring device and a sophisticated processing technique. This is a great improvement in workability.
Furthermore, the bearing inserting portion 7 has a diameter smaller than the outer diameter of the bearing 6 at positions which face the front and rear end portions of the bearing 6 due to shrinkage of the resin material, and the inner peripheral surface of the bearing inserting portion 7 supports the front and rear end portions of the bearing 6 in an undercut state. Consequently, coming off of the bearing 6 in an axial direction thereof is reliably prevented, and reliability of the casing is greatly improved.
The advantages of the first embodiment will further be described below using an example. In the following example, the motor casing 1 was actually manufactured by molding using polyethylene terephthalate having a melting point of 260 C, a recrystallization temperature of about llO C and the glass transition temperature of about 55 C.
In the above motor casing 1, bearings X and Y
respectively having an outer diameter of 9 mm and 12 mm were inserted. Fig. 6 shows a graph in which changes in the temperature of the inner peripheral surface of the bearing inserting portion 7 when the molded article is removed from the mold and changes in the circularity (the maximum deflection in the radial direction from an ideal circle, a ~
measured twenty hour hours after the bearing inserting portion 7 has been removed from the mold) of the bearing 5 inserted into the bearing inserting portion at a given surface temperature are plotted. As can be seen from Fig.
6, changes in the circularity of the bearing inserted before the surface temperature lowers substantially to the glass transition temperature is less. The lower the surface temperature when the bearing is inserted, the worse the circularity is. This shows how advantageous the first embodiment is.
With respect to the bearing X, it was observed that the circularity thereof inserted into the bearing inserting portion, which was removed from the mold twenty four hours (one thousand four hundred forty minutes) ago, changed by 17.5 ~m, whereas that of the bearing inserted in the vicinity of the glass transition temperature changed about S
~m. With respect to the bearing Y, changes in the circularity decreased from 37.5 ~m to 9 ~m. In both cases, the circularity improved by 70% or above.
Next, the advantages of the second embodiment will be described. In this example, the same bearings were used.
After the manufactured casing 1 was left at the room temperature for twenty four hours, the casing 1 was heated to a selected temperature, and the bearing 6 was inserted into the bearing inserting portion 7 having that 2~435~t!~
temperature. Thereafter, the casing 1 was left at the room temperature for forty eight hours. Fig. 7 is a graph in which the temperature of the bearing inserting portion when the bearing is inserted and changes in the circularity (maximum deflection in the radial direction relative to the ideal circle) of the inserted bearing 6 are plotted. As can be seen from Fig. 7, when the heating temperature was higher than the glass transition temperature, a great improvement in the circularity of the bearing was observed, as in the first embodiment.
That is, with respect to the bearing X, it was observed the circularity thereof inserted at the room temperature changed by 17.5 ~m, whereas that of the bearing inserted near the glass transition temperature and then cooled changed by about 6 ~m. Change in the circularity decreases as the heating temperature increases to the recrystallization temperature. Similar phenomenon was observed with respect to the bearing Y. These prove how advantageous the second embodiment is.
In the first embodiment, the mold was removed at a temperature higher than the recrystallization point, and the bearing was inserted into the bearing inserting portion having that temperature. Forty eight hours after the mold was removed, the circularity of the inserted bearing was measured in the similar manner. Great change in the 2~43S~9 circularity was observed. As the temperature at which the bearing was inserted rises, the resin material which forms the inserting portion is softened, making insertion difficult. Particularly, at 200 C or above, the resin material cannot maintain its original shape. Therefore, the temperature of the inner peripheral surface of the inserting portion at which the bearing is inserted should be a value which ensures that the resin material can maintain its shape after the mold was removed therefrom. When the temperature of the inner peripheral surface is lower than the recrystallization temperature, recrystallization of the resin material which forms the inner peripheral surface of the bearing inserting portion is in a progress and the resin material is stable. As a result, deformation of the bearing inserting portion caused by the insertion is eliminated.
In the second embodiment, the bearing was inserted in a state in which the bearing inserting portion was heated to a temperature higher than the recrystallization temperature, as in the first embodiment. It was observed that the circularity greatly changed.
It is possible to provide a better casing using the above-described procedures. In this embodiment, the casing 1 made of a resin is divided into a yoke la and a front bracket lb, and mounting of the bearing in the front bracket lb is specifically examined. That is, the front bracket lb has an inserting portion 7 for rotatably supporting a rotor shaft 3b of the rotor core 3. This inserting portion rotatably supports the rotor shaft 3b through the bearing 6 and has the following inner peripheral surface. More specifically, the inserting portion 7 has a bearing introducing portion 7a which protrudes toward the brush chambers 4. The introducing portion 7a has an inner diameter A which is slightly larger than the outer diameter B of the bearing 6 (A > B) so that it can temporarily hold the bearing 6 in a state in which the bearing 6 is centered.
A bearing inserting portion 7b is formed on the distal end side of the bearing introducing portion 7a. A small-diameter coming-off preventing portion 7c is formed between the introducing portion 7a and the bearing inserting portion 7b to prevent coming-off of the inserted bearing.
Since the front bracket lb is made of a resin, it has an coefficient of expansion very larger than that of the metal which forms the bearing 6. Therefore, the inner diameter C
of the coming-off preventing portion 7c is made smaller than the outer diameter B of the bearing 6 at room temperatures.
Furthermore, B' > C' where B' (B < B') is the outer diameter of the expanded bearing 6 at the upper value in the temperature range in which the motor is used and C'(C < C') is the inner diameter of the expanded coming-off preventing portion 7c.
~ g In this embodiment, when the bearing 6 is inserted into the bearing inserting portion 7b, it is first retained in the introducing portion 7a temporarily, and then forcibly inserted into the bearing inserting portion 7b. The inserted bearing 6 is reliably prevented from coming off by the presence of the small-diameter coming-off preventing portion 7c formed between the introducing portion 7a and the bearing inserting portion 7b.
More specifically, even when the pressing force of the bearing 6 inserted in the bearing inserting portion 7b is smaller than a required one, the bearing 6 is prevented from coming off by the small-diameter coming-off preventing portion 7c formed at the inlet of the bearing inserting portion 7b. Consequently, reliability of the motor is greatly improved, and troubles caused by coming-off of the bearing 6 can thus be eliminated.
Furthermore, coming-off of the bearing 6, which would occur when the motor is heated to a high temperature, can be prevented. That is, since the inner diameter of the coming-off preventing portion 7c remains smaller than the outer diameter of the expanded bearing 6 at high temperatures, coming-off of the bearing 6 from the bearing inserting portion 7b is prevented at those high temperatures. This further improves reliability of the motor.
In this embodiment, when the bearing 6 is inserted into ~ L 3 ~
the bearing inserting portion 7b, it is passed through the narrow coming-off preventing portion 7c. At that time, the bearing 6 is first inserted into the introducing portion 7a formed on the inlet side of the coming-off preventing portion 7b and temporarily held therein in a centered state before being forcibly pushed into the bearing inserting portion 7b. Consequently, offset of the bearing 6 with respect to the small-diameter coming-off preventing portion 7c does not occur when it is forcibly inserted into the bearing inserting portion 7b. In this embodiment, the adjoining portion between the introducing portion 7a and the coming-off preventing portion 7c is tapered so as to make movement of the bearing 6 from the introducing portion 7a to the coming-off preventing portion 7c smooth.
When the bearing 6 passes through the small-diameter coming-off preventing portion 7c, expanding loads are applied to the coming-off preventing portion 7c. However, the coming-off preventing portion 7c is made of a resin exhibiting an elasticity. Therefore, if the expanding loads are within the elastic limitation of the coming-off preventing portion 7c, passage of the bearing 6 causes forcible expansion of the coming-off preventing portion 7c but does not cause any trouble. The coming-off preventing portion 7c recovers its original shape after the bearing 6 has passed therethrough.
Z~ ~3~ ~
As will be understood from the foregoing description, in the present invention, the bearing is inserted into the bearing inserting portion of the motor casing made of a thermoplastic resin while crystallization of the resin material is in a progress and the resin material is thus in an activated state. Therefore, in a subsequent temperature lowering process, the inserting portion 7 gradually shrinks in the form of the bearing inserted thereinto. As a result, the inner peripheral surface of the bearing inserting portion is substantially completely round and is in surface contact with the outer peripheral surface of the bearing.
Therefore, action of the local pressing force on the bearing 6 can be eliminated, and deformation of the bearing 6 can thus be prevented effectively. This allows for mounting of the bearing with a high degree of accuracy and leads to an increase in the quality and performance of the motor. Such a highly accurate mounting of the bearing can be accomplished without repeating correction of the shape of the mold used for molding the bearing inserting portion using an expensive measuring device and a sophisticated processing technique. This is a great improvement in workability.
Furthermore, even when the pressing force of the bearing inserted into the bearing inserting portion is looser than a set one, the bearing is prevented from coming 3 ~ ~ ~
off by the small-diameter coming-off preventing portion formed on the inlet side of the inserting portion.
Therefore, accidental coming-off of the bearing from the bearing inserting portion made of a resin can reliably be avoided, and reliability of the motor can thus be greatly improved while the trouble involving coming-off of the bearing can be avoided.
~ urthermore, when the bearing is inserted into the bearing inserting portion by forcibly passing it through the small-diameter coming-off preventing portion, it is temporarily held in a centered stated by the bearing introducing portion having a diameter larger than the outer diameter of the bearing and formed on the inlet side of the coming-off prevention portion. Consequently, a troublesome centering task can be eliminated when the bearing is pushed into the coming-off preventing portion, thus greatly improving workability.
Furthermore, since the inner diameter of the coming-off preventing portion is made smaller than the outer diameter of the bearing at the upper limit of the temperature range in which the motor is used, coming-off of the bearing is reliably prevented at the high temperatures which ensure different degrees of expansion. Therefore, reliability of the motor casing can greatly be improved even when the casing is used for a motor operated at high temperatures, 2 ~ 'J _ g such as that for the electrical equipment.
Claims (12)
1. A method of manufacturing a motor casing from a resin, characterized in that when the motor casing is formed by molding in which a thermoplastic resin material is injected into a mold, a bearing for rotatably supporting a core shaft of a rotor core is inserted into a small-diameter portion of the motor casing before a temperature of the thermoplastic resin material which forms the small-diameter portion substantially lowers to a glass transition temperature of the thermoplastic resin material, the thermoplastic resin material being then cooled to a room temperature.
2. A method of manufacturing a motor casing from a resin according to claim 1, wherein the insertion is conducted after the thermoplastic resin material is removed from the mold and before the thermoplastic resin material is cooled substantially to the glass transition temperature.
3. A method of manufacturing a motor casing from a resin according to claim 1, wherein the insertion is conducted after the motor casing cooled to the room temperature is heated substantially to the glass transition temperature of the thermoplastic resin material or above, the resin material being then cooled to the room temperature.
4. A motor casing made of a resin characterized in that when the motor casing is manufactured by molding in which a thermoplastic resin material is injected into a mold, a bearing for rotatably supporting a core shaft of a rotor core is inserted into a small-diameter portion of the motor casing before a temperature of the thermoplastic resin material which forms the small-diameter portion substantially lowers to a glass transition temperature of the thermoplastic resin material, the thermoplastic resin material being then cooled to a room temperature.
5. A motor casing according to claim 4, wherein the insertion is conducted after the thermoplastic resin material is removed from the mold and before the resin material is cooled substantially to the glass transition temperature.
6. A motor casing according to claim 4, wherein the insertion is conducted after the motor casing cooled to the room temperature is heated substantially to the glass transition temperature of the thermoplastic resin material or above.
7. A method for manufacturing a motor casing having a circular bear seat portion for supporting a bearing, comprising the steps of:
injecting a heated thermoplastic resin material into a mold thereby forming a motor casing by molding;
inserting a bearing, the bearing rotatably supporting a core shaft of a rotor core such that an axis of the bearing is substantially parallel to an axis of the core shaft, into the bearing seat portion while a temperature of the thermoplastic resin material is below a recrystallization temperature of the thermoplastic resin material and above a glass transition temperature of the thermoplastic resin material; and cooling the thermoplastic resin material to room temperature to obtain a bearing seat portion that is substantially completely round.
injecting a heated thermoplastic resin material into a mold thereby forming a motor casing by molding;
inserting a bearing, the bearing rotatably supporting a core shaft of a rotor core such that an axis of the bearing is substantially parallel to an axis of the core shaft, into the bearing seat portion while a temperature of the thermoplastic resin material is below a recrystallization temperature of the thermoplastic resin material and above a glass transition temperature of the thermoplastic resin material; and cooling the thermoplastic resin material to room temperature to obtain a bearing seat portion that is substantially completely round.
8. The method of claim 7, wherein the thermoplastic resin material is polyethylene terephthalate and the bearing is inserted into the bearing seat portion while the temperature of the polyethylene terephthalate material is between 55° C. and 80° C
9. The method of claim 7, further comprising the step of:
removing the thermoplastic resin material from the mold before the step of inserting the bearing.
removing the thermoplastic resin material from the mold before the step of inserting the bearing.
10. The method of claim 7, further comprising, before the step of inserting the bearing, the steps of:
cooling the thermoplastic resin material; and reheating the thermoplastic resin material.
cooling the thermoplastic resin material; and reheating the thermoplastic resin material.
11. A method for manufacturing a motor casing having a circular bearing seat portion for supporting a bearing, comprising the steps of:
injecting a thermoplastic resin material into a mold thereby forming a motor casing by molding;
successively removing an inner mold section to expose the bearing seat portion and inserting a bearing, the bearing rotatably supporting a core shaft of a rotor, into the bearing seat portion such that an axis of the bearing is substantially parallel to an axis of the core shaft, while a temperature of the thermoplastic resin material is below a recrystallization temperature of the thermoplastic resin material and above a glass transition temperature of the thermoplastic resin material; and cooling the thermoplastic resin material to room temperature to obtain a bearing seat portion that is substantially completely round.
injecting a thermoplastic resin material into a mold thereby forming a motor casing by molding;
successively removing an inner mold section to expose the bearing seat portion and inserting a bearing, the bearing rotatably supporting a core shaft of a rotor, into the bearing seat portion such that an axis of the bearing is substantially parallel to an axis of the core shaft, while a temperature of the thermoplastic resin material is below a recrystallization temperature of the thermoplastic resin material and above a glass transition temperature of the thermoplastic resin material; and cooling the thermoplastic resin material to room temperature to obtain a bearing seat portion that is substantially completely round.
12. The method of claim 11, wherein the thermoplastic resin material is polyethylene terephthalate and the bearing is inserted into the bearing seat portion while the temperature of the polyethylene terephthalate material is between 55 °C. and 80° C.
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2-142679 | 1990-05-31 | ||
| JP2142679A JP2577266B2 (en) | 1990-05-31 | 1990-05-31 | Bearing mounting structure for motor shaft |
| JP2-157283 | 1990-06-15 | ||
| JP15728390A JPH0645208B2 (en) | 1990-06-15 | 1990-06-15 | Resin motor casing and method of manufacturing the same |
| JP2-157284 | 1990-06-15 | ||
| JP2157284A JPH07118890B2 (en) | 1990-06-15 | 1990-06-15 | Method of manufacturing resin motor casing |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2043519A1 CA2043519A1 (en) | 1991-12-01 |
| CA2043519C true CA2043519C (en) | 1998-11-24 |
Family
ID=27318488
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002043519A Expired - Fee Related CA2043519C (en) | 1990-05-31 | 1991-05-30 | Motor casing made of resin and method of manufacturing the same |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA2043519C (en) |
| DE (1) | DE4117763C2 (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IT1261204B (en) * | 1993-03-02 | 1996-05-09 | Pellegrino Giuseppe | PROCEDURE FOR PRODUCING A COVER FOR APPLIANCES IN GENERAL THAT EXPLOITS THE RECOVERY PROPERTY OF THE HEATED PLASTIC MATERIAL THAT CONSTITUTES THE COVER FRAME. |
| US5476423A (en) * | 1994-11-14 | 1995-12-19 | Occidental Chemical Corporation | Plastic wheel assembly |
| DE29805027U1 (en) | 1998-03-19 | 1998-07-23 | TRW Airbag Systems GmbH & Co. KG, 84544 Aschau | Gas generator with plastic housing |
| DE19902430C2 (en) * | 1999-01-22 | 2001-09-06 | Mannesmann Vdo Ag | Process for manufacturing a plastic container |
| FR2796425B1 (en) * | 1999-07-13 | 2001-10-19 | Aerospatiale Matra Ccr | METHOD OF INTRODUCING A METAL RING INTO A PART OF COMPOSITE MATERIAL WITH ORGANIC MATRIX AND PART OBTAINED BY THIS PROCESS |
| DE10010838B4 (en) * | 2000-03-09 | 2011-07-07 | ThyssenKrupp Presta SteerTec GmbH, 40476 | Method for producing a transmission and steering gear for a motor vehicle |
| JP5575329B2 (en) | 2010-04-22 | 2014-08-20 | コンチネンタル オートモーティブ システムズ インコーポレイテッド | Idle air control valve with plastic casing and holding mechanism |
| DE102020107584A1 (en) | 2020-03-19 | 2021-09-23 | KSB SE & Co. KGaA | Centrifugal pump with canned motor |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1938496A1 (en) * | 1969-07-29 | 1971-02-11 | Wintergerst Prof Dr Ing Siegmu | Prevention of residual stresses and orienta- - tion in thermoplastic injection mouldings |
-
1991
- 1991-05-30 CA CA002043519A patent/CA2043519C/en not_active Expired - Fee Related
- 1991-05-31 DE DE4117763A patent/DE4117763C2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| DE4117763A1 (en) | 1991-12-05 |
| DE4117763C2 (en) | 1995-11-30 |
| CA2043519A1 (en) | 1991-12-01 |
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| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |