JPH0447929A - Resinous motor casing and production thereof - Google Patents

Abstract

PURPOSE:To drastically enhance the roundness of a bearing pressure insertion part in spite of a motor casing made of a resin by carrying out the insertion of a bearing under pressure before the temp. of the resin material injected in a mold lowers to the glass transition temp. thereof after the detachment of the resin material from the mold. CONSTITUTION:A resin material is detached from an inside mold B by pulling during a period when the temp. of the mold is higher than the glass transition temp. of the resin material and the resin material is yet in an activated state and advanced in crystallization and a bearing 5 is inserted in a bearing pressure insertion part 6 before the temp. of the inner peripheral surface of said insertion part 6 become lower than the glass transition temp. and, thereafter, the resin material is cooled to room temp. to mold a casing 1. In the temp. lowering process after the pressure insertion of the bearing, the resin material is molded and shrunk while it gradually follows the shape of the bearing so as to conform to the surface of the bearing inserted under pressure and, as a result, the inner peripheral surface of the bearing pressure insertion part 6 becomes a state near to roundness almost coming into contact with the outer peripheral surface of the bearing 5 and no locally offset pressure insertion stress is applied to the bearing 5 and the deformation of the bearing 5 can be effectively avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to a resin motor casing used in electrical components for vehicles and a method for manufacturing the same.

[Prior Art and Problems to be Solved by the Invention] Today, in order to reduce the weight of motors, it is possible to use a crystalline thermoplastic resin material for the motor casing (motor housing) and form it by molding. is being attempted. However, since the formed motor casing is made of resin, its processing accuracy is inevitably poorer than that of a metal casing.

If this is a press-fitted part of a bearing that supports a motor shaft, the back opening of the inner circumferential surface will be significantly impaired, and as a result, excessive press-fitting stress will act locally on the bearing, causing deformation of the bearing. Therefore, a problem arises in that the bearing accuracy decreases.

Moreover, in the case of such a resin casing, 1. In order to increase the mechanical strength, a strong fat material such as glass fiber is mixed in, but since these reinforcing materials are fibrous and elongated, the resin material During injection, there is inevitably a directionality in the direction of the fibers, which results in different molding shrinkage rates in the longitudinal and transverse directions, which tends to increase the difference in layer size carbonization. .

Therefore, there have been several attempts to improve the accuracy of resin casings. As one attempt, we focused on the temperature of the mold during resin molding, and used this temperature to suppress dimensional changes (molding shrinkage) due to recrystallization of the resin when the product is manufactured.

There is a method in which the mold temperature is set approximately at the recrystallization temperature of the resin material for a long period of time until the crystallinity of the resin material reaches a nearly saturated state, and then the mold temperature is cooled down to ensure the accuracy of the press-fitted bearing part. However, a long period of constant temperature curing is required to bring the crystallinity close to saturation, so it is not realistic to use this method as a manufacturing process for casings that need to be mass-produced in the shortest possible time. do not have.

On the other hand, there is a method to shorten the molding time by setting the mold temperature low and rapidly cooling the injected resin material. ) parts are formed, and in products such as electrical components for vehicles that are subjected to thermal history during use at high temperatures close to or exceeding the glass transition point, when the high temperature conditions are reached, amorphous This cannot be used at all, as the portions will recrystallize, resulting in dimensional changes over time.

Therefore, we installed a temperature control device on the mold to control the cooling rate of the mold to prevent the formation of amorphous parts as much as possible, and for the bearing press-fit part, we changed the shape of the mold to control the flow of reinforcing material. In anticipation of dimensional changes after molding, including
Shift it from a right circular shape to, for example, an ellipse or an eccentric circular shape,
Attempts have also been made to make the shape closer to a perfect circle by deforming it after molding. However, in this case, it is necessary to measure the relationship between the temperature cooling rate, the dimensional change of the molded product, and the mold shape using 14N precise measurement technology, and also requires advanced temperature cooling technology, which requires the cooling device itself. It is not a fake that is expensive,
There is a problem in that this requires precise machining technology for the mold, resulting in a huge loss in time and cost. The reality is that as the shape of the motor casing becomes more and more wasteful, it becomes more difficult to predict dimensional changes after molding, and reproducibility becomes poorer.

On the other hand, attempts have been made to improve the accuracy of the press-fitted part of the bearing without using such a method, such as making the bearing thicker so that the press-fitting stress does not affect the deformation of the inner diameter of the bearing. There are attempts to reduce the press-fitting allowance so as not to affect the deformation of the inner diameter of the bearing, but in the former case, the thicker the bearing, the larger the diameter of the motor casing and the heavier it becomes. This goes against the original purpose of using a resin material to reduce weight, and it also has the disadvantage of increasing the size.In the latter case, the press-fitting allowance is small, so the bearing can easily come out, and the intended bearing support cannot be achieved. It has the disadvantage that it is difficult to ensure strength, so it cannot be used in any case.

[Means for Solving the Problems] In view of the above-mentioned circumstances, the present invention was devised for the purpose of providing a resin motor casing and a method for manufacturing the same that can eliminate these drawbacks. The first invention is to form a motor casing by a molding method in which a thermoplastic resin material is injected into a mold, and a bearing that rotatably supports the core shaft of a rotor core is press-fitted into a small diameter part of the motor casing. During assembly, the bearing is press-fitted after the resin material injected into the mold is removed from the mold until the temperature of the resin material drops to the glass transition temperature, and then the temperature is lowered to room temperature. It is characterized by being cooled.

Further, a second invention provides a motor casing formed by a molding method in which a thermoplastic resin material is injected into a mold, and a bearing rotatably supports a core shaft of a rotor core in a small diameter portion of the motor casing. The bearing is press-fitted within a temperature range until the temperature of the resin material falls to the glass transition temperature.

With these configurations, the present invention makes it possible to dramatically improve the roundness of the bearing press-fit portion even though the motor casing is made of resin.

[Example] Next, an example of the present invention is explained based on the drawings. In drawing 1, 1 is a motor casing formed by molding polyethylene terephthalate, which is a thermoplastic resin material. The casing 1 has a magnet 2 attached to its inner peripheral surface, a large diameter part 4 in which a rotor core 3 is housed, and a core shaft 3 of the rotor core 3.
A small diameter portion, ie, a bearing press-fit portion 6, which supports the bearing 5 through the bearing 5 is formed, and the present invention is implemented in this bearing press-fit portion 6.

In other words, in this embodiment, a thermoplastic resin such as polyethylene terephthalate is used, and the resin material is injected between an outer mold A that defines the outer periphery of the bearing press-fit portion 6 and an inner mold B that defines the inner periphery. However, the procedure is to first raise the temperature of molds A and B to around 110°C, which is the recrystallization temperature of the resin material, and for inner mold B, turn on the temperature adjustment device. It is preferable to connect and control the surface temperature, and in this state, the resin material is injected and the temperature is gradually lowered, and molding is performed in this manner. Regarding the inner mold B.

When the mold temperature is higher than the glass transition temperature and the resin material is still in an activated state and crystallization is progressing, remove it by pulling it out, etc., and the inner circumferential surface temperature of the bearing press-fit part 6 does not fall below the glass transition temperature. During this time, the bearing 5 is press-fitted, and then the casing 1 is formed by cooling it to room temperature.

The bearing 5 is already press-fitted into the bearing press-fit part 6 of the casing 1 molded in this way, but the press-fitting operation of the bearing 5 is performed at a temperature that does not become lower than the glass transition temperature, as described above. In other words, the crystallization of the resin material has progressed to a certain extent, but it is still in an activated state that allows some deformation. The molding shrinks while gradually following the shape of the bearing so that it fits into the bearing surface, and as a result, the inner circumferential surface of the bearing press-fit portion 6 becomes a nearly perfect circle with almost surface contact with the outer circumferential surface of the bearing 5. As a result, locally uneven press-fitting stress does not act on the bearing 5, and deformation of the bearing 5 can be effectively avoided, allowing high-precision bearing installation, which greatly contributes to improving the quality and performance of the motor. It will be possible.

In addition, in order to install such a high-precision bearing, there is no need to constantly repeat the process of correcting the mold shape of the bearing press-fit part 6 using expensive measuring equipment and advanced processing technology, as in the past. As a result, work efficiency can be significantly improved.

Furthermore, the inner peripheral surface of the bearing press-fit portion 6 has a smaller diameter than the outer diameter of the bearing S at both front and rear ends of the bearing 5 due to molding shrinkage of the resin material, supporting both front and rear ends of the bearing S in a so-called undercut state. As a result, the bearing 5 is reliably prevented from coming off in the axial direction, and its reliability is greatly improved.

Incidentally, to see how effective the present invention is, the motor casing 1 was actually molded using polyethylene terephthalate, which has a melting point of 260°C, a recrystallization temperature of approximately 110°C, and a glass transition point of approximately 55°C. Further explanation will be given by taking the case of molding as an example.

In this case, the case where bearings X and Y with outer diameters of 9 m and 12 mm were press-fitted was studied. Figure 3 shows the change in surface temperature of the inner peripheral surface of the press-fitted bearing 6 when the molded product is removed from the mold, and the change in the roundness (ideal circle) of the press-fitted bearing 5 at a selected arbitrary surface temperature. This is a plot of the maximum deviation in the radial direction from 24 hours after removal from the mold), and it shows that until the surface temperature drops to approximately the glass transition temperature. For bearings press-fitted between 1. It was observed that the change in roundness was slight, and that the roundness decreased as the surface temperature at the time of press-fitting became lower than the glass transition temperature, demonstrating how effective the present invention is.

In other words, for bearing X, when the bearing is press-fitted after 24 hours (1440 minutes), the roundness change is 17.
5μs was also observed, but in the case of press-fitting near the glass transition temperature, the time was only 5μs. It was observed that the
In addition, for bearing Y, from the same <37.5n to 91Jm
The roundness was improved by more than 70% in all cases, demonstrating how effective the present invention is.

In addition, in the above example, the mold was removed at a temperature higher than the recrystallization temperature, and the bearing was attempted to be press-fitted, and after 48 hours had passed after the mold was released, the bearing was press-fitted in the same manner as described above. The roundness of the bearing was measured, and a significant change in roundness was observed in this bearing as well. However, the higher the temperature during bearing press-fitting, the softer the resin material itself in the press-fitting part becomes, making the press-fitting process more difficult.In particular, when the temperature exceeds 200℃, the resin material loses its original shape after being released from the mold. From this point of view, the temperature of the inner circumferential surface of the press-fitted part during press-fitting of the bearing should be at least below the temperature at which the resin material does not overlap with the mold even after the mold is released. In particular, if this temperature is lower than the recrystallization temperature, the resin material on the inner peripheral surface of the press-fit part has already begun to recrystallize and is stabilized, so the press-fit part side of the bearing will be deformed by press-fitting. It is preferable because it does not cause any problems.

[Operations and Effects] In summary, the present invention is configured as described above, and although the motor casing is formed by molding using a thermoplastic resin material, press fitting of the bearing is not possible using the resin material. This is done in the activated state where crystallization is progressing, so during the temperature cooling process after press-fitting the bearing,
The resin material shrinks during molding while following the shape of the bearing so that it conforms to the surface of the press-fitted bearing.As a result, the inner circumferential surface of the press-fitted part of the bearing is almost a perfect circle that makes almost surface contact with the outer circumferential surface of the bearing. This prevents locally uneven press-fitting stress from acting on the bearing, effectively avoiding deformation of the bearing, enabling high-precision bearing installation, and significantly improving the quality and performance of the motor. You will be able to contribute. Furthermore, this kind of high-precision bearing mounting eliminates the need to constantly modify the mold shape of the bearing press-fit part using expensive measuring equipment and advanced processing technology, as was the case in the past. , which can be easily performed by molding, resulting in a significant improvement in workability.

Furthermore, the inner circumferential surface of the bearing press-fit part becomes smaller in diameter than the outer diameter of the bearing at both the front and rear ends of the bearing due to molding shrinkage of the resin material, supporting both the front and rear ends of the bearing in a so-called undercut state. This ensures that the bearing is not pulled out in the axial direction, greatly improving reliability.

[Brief explanation of the drawing]

The drawings show an embodiment of the resin motor casing and the manufacturing method thereof according to the present invention, and are
2 is a sectional view of the main part of the motor casing, FIG. 2 is a sectional view of the bearing press-fit part, and FIG. 3 is the change in surface temperature of the inner peripheral surface of the bearing press-fit part over time when the molded product is removed from the mold. FIG. 3 is a graph plotting changes in roundness of a press-fitted bearing. In the figure, 1 is a motor casing, 5 is a bearing, and 6 is a bearing press-fit part.

Claims (1)

[Claims] 1) When forming a motor casing by a molding method in which a thermoplastic resin material is injected into a mold,
When press-fitting a bearing that rotatably supports the core shaft of the rotor core into the small diameter portion of the motor casing, the bearing is press-fitted by removing the resin material injected into the mold from the mold.
A method for producing a resin motor casing, characterized in that the process is carried out until the glass transition temperature is lowered, and then cooled to room temperature. 2) In a motor casing formed by a molding method in which thermoplastic resin material is injected into a mold,
When a bearing that rotatably supports the core shaft of the rotor core is press-fitted into the small diameter portion of the motor casing, the bearing is
A resin motor casing characterized by being press-fitted within a temperature range until the temperature of the resin material drops to the glass transition temperature.