JP2008178161A - Motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor whose gear holding torque in the axial direction becomes large while reducing a press-insertion force in the axial direction at the press-insertion of a rotating shaft and a gear. <P>SOLUTION: Since a plurality of crests 11a are formed in the circumferential direction at equal intervals to form flat knurling at the external periphery of the rotating shaft 11, only the crests 11a of the rotating shaft 11 abut on the internal periphery of an opening 17b of the bear 17 and slide when press-inserting the gear 17 into the rotating shaft 11, and thereby the press-insertion force can be reduced compared with the case that a simple cylindrical column is press-inserted, thus suppressing the breakage of the gear 17 even if the gear is composed of an iron system sintered material. When the gear 17 is engaged with the rotating shaft 11, the internal periphery of the opening 17b of the gear 17 is minutely deformed elastically by being pressed by the crests 11a of the rotating shaft 11, the relative rotation of the rotating shaft 11 and the gear 17 are suppressed by this deformation, and proper torque transmission can be performed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to improvements in general industrial motors and motors used in automobiles, outboard motors, and the like.

Conventionally, the torque of the rotating shaft of an electric motor is often output after the gear attached to the tip of the rotating shaft is engaged with another gear and decelerated or increased by such a gear set. Here, as shown in Patent Documents 1 and 2, the rotation shaft of the electric motor and the gear are coupled by press-fitting both into a simple cylinder with the rotation shaft shape of the electric motor as a simple cylinder. is there.
JP 2002-370109 A JP 2000-32708 A

  By the way, in general, in press-fitting between a cylindrical shaft and a gear cylindrical portion, the assembly strength is determined by the interference between the shaft outer diameter and the gear inner diameter, which are in a press-fitting relationship. For example, in the case of a gear that is press-fitted into the tip of the motor and its rotating shaft, it is necessary to prevent the press-fitting portion from loosening in order to reliably transmit the torque generated by the motor to the outside. In order to obtain a large pressure input when the torque is large, it is necessary to have a fitting relationship for obtaining a strong press-fitting relationship. The pressure input during assembly and the torque holding force of the fitting portion are in a proportional relationship.

  On the other hand, electric motors are required to keep the output shaft in a shape with as little mass as possible in order to keep the moment of inertia of the rotating part as low as possible, and the outside diameter is often kept small. As a result, the diameter dimension of the fitting portion between the rotating shaft and the gear tends to be reduced, and the pressure input must be reduced accordingly. In addition, when assembling a gear with a large tightening allowance (large press-fit load) to the rotating shaft of an electric motor, which is often formed thin and long, the output shaft will not be deformed, or in the worst case, will not buckle. In addition, the pressure input is limited.

  In addition, the press-fitted gear is generally formed of metal when there is a restriction on the strength of the gear, but in the case of using a metal gear, iron-based sintering is often used because of cost problems. . However, the iron-based sintered gear has a problem that its strength against press-fitting is low as compared with general steel materials. Therefore, increasing the press-fitting allowance between the rotating shaft and the gear and increasing the press-fit has a limitation in terms of the material of the gear.

  The present invention has been made in view of the problems of the prior art, and an electric motor in which the axial holding force during press-fitting of the rotating shaft and the gear is kept small while the gear holding torque in the rotating direction is increased. The purpose is to provide.

The electric motor of the present invention is an electric motor having a rotating shaft and a gear press-fitted to the rotating shaft.
The gear is formed of an iron-based sintered material, and the inner periphery of the gear with which the rotating shaft is fitted has a cylindrical shape,
A plurality of valleys and peaks are alternately formed in the circumferential direction on the outer periphery of the rotating shaft.

  According to the electric motor of the present invention, since a plurality of valleys and peaks are alternately formed in the circumferential direction on the outer periphery of the rotating shaft, when the gear is press-fitted into the rotating shaft, Since only the mountain slides in contact with the inner periphery of the gear, the pressure input can be reduced compared to the case of press-fitting a simple cylinder, so even if the gear is formed from an iron-based sintered material, The damage can be suppressed. On the other hand, after the gear meshes with the rotating shaft, the crest of the rotating shaft is elastically deformed, and the inner periphery of the gear is also elastically deformed slightly by being pushed by the crest, and the rotation is caused by the drag generated thereby. Relative rotation between the shaft and the gear can be suppressed and appropriate torque transmission can be performed.

  In general, the pressure input between members having a simple cylinder and a circular opening is determined by the contact surface pressure of the fitting tightening margin of the member having the cylinder and the opening. A proportional relationship is established between the contact surface pressure and the pressure input. Further, the pressure input has a proportional relationship with the holding torque (force against relative sliding) between the two in the press-fitting relationship. Therefore, when a large holding torque is required, a large tightening margin is relatively provided. On the other hand, when the rotary shaft with a plurality of valleys and peaks is press-fitted into a member having a circular opening, only the holding torque can be increased without depending on the pressure input during assembly.

  A knurling is formed on the outer periphery of the rotary shaft, and a radial interference between the outer diameter of the knurling and the inner diameter of the gear is preferably 10 μm to 100 μm.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of the electric motor according to the present embodiment, and FIG. 2 is a view of the configuration of FIG. 1 viewed in the direction of arrow II. In the electric motor 10 shown in FIG. 1, the rotating shaft 11 is rotatably supported by bearings 13 and 14 in a hollow cylindrical housing 12. A rotor 15 is disposed at the center of the rotating shaft 11, and a stator (magnet) 16 is disposed on the inner periphery of the housing 12 so as to face the rotor 15. A gear 17 is attached to the end of the rotating shaft 11 protruding from the housing 12. As shown in FIG. 2, the gear 17 formed of an iron-based sintered material has gear teeth 17a on the outer periphery and a cylindrical opening 17b in the center. The electrical configuration and operation of the motor are well known and will not be described in detail.

  FIG. 3 is a side view of the rotating shaft 11, and FIG. 4 is a view of the rotating shaft of FIG. A plurality of peaks 11 a extending in the axial direction and valleys 11 b arranged between adjacent peaks 11 a are formed on the outer periphery of the rotating shaft 11. The plurality of peaks 11a are arranged at equal intervals in the circumferential direction to form a so-called flat knurling. In addition, it is preferable that the radial interference between the outer diameter D of the flat knurling (the outer diameter of the circle connecting the vertices of the peaks 11a: see FIG. 4) and the inner diameter of the opening 17b of the gear 17 is 10 μm to 100 μm.

  FIG. 5 is a diagram illustrating a process of press-fitting the gear 17 into the rotating shaft 11 of the electric motor 10. In FIG. 5, the electric motor 10 assembled except for the gear 17 is held perpendicular to the rigid body G, and the lower end of the rotating shaft 11 is brought into contact with the rigid body G. In this state, the gear 17 is press-fitted into the upper end of the rotating shaft 11.

  At this time, since a plurality of peaks 11a are formed at equal intervals in the circumferential direction to form a flat knurling on the outer periphery of the rotary shaft 11, when the gear 17 is press-fitted into the rotary shaft 11, the peaks of the rotary shaft 11 are formed. Since only 11a abuts on the inner periphery of the opening 17b of the gear 17 and slides in the axial direction, the pressure input can be reduced as compared with the case of press-fitting a simple cylinder. Even if formed from a material, the breakage can be suppressed. On the other hand, after the gear 17 meshes with the rotating shaft 11, the inner periphery of the opening 17b of the gear 17 is pushed by the mountain 11a of the rotating shaft 11, and the inner periphery of the mountain 11a and the opening 17b is slightly elastically deformed. Thus, the relative rotation between the rotating shaft 11 and the gear 17 can be suppressed, and appropriate torque transmission can be performed.

  FIG. 6 is a graph showing the relationship between the press-fit allowance and the press-fit obtained by the present inventors. In FIG. 6, a broken line indicates a pressure input when a simple column is press-fitted into a gear having a cylindrical opening, and a solid line indicates a pressure when a shaft having the same outer diameter and flat knurling is pressed into a gear having the same cylindrical opening. Although the input is shown, the reference outer diameter of the rotating shaft to which the flat knurling is applied is the outer diameter of the knurling peak. As is clear from FIG. 6, the press input when the flat knurled shaft is press-fitted into the gear having the cylindrical opening is about 1 with respect to the press input when the simple column is press-fitted into the gear having the cylindrical opening. A pressure input of about 5 to 1/6 is sufficient.

  FIG. 7 is a graph showing the relationship between the press-fit allowance obtained by the inventors and the holding torque. In FIG. 7, circles indicate holding torque when a simple column is press-fitted into a gear having a cylindrical opening, and a solid line indicates a state where a flat knurled shaft is pressed into a gear having the same cylindrical opening. The holding torque at is shown. As is clear from FIG. 7, if the press-fitting allowance, that is, the tightening allowance is the same level, the holding torque when the flat knurled shaft is press-fitted into the gear having the cylindrical opening is press-fitted into the gear having the cylindrical opening. It is more than the holding torque at the time.

  From the results shown in FIG. 6 and FIG. 7, when the combination of a flat knurled shaft and a gear having a cylindrical opening is compared with the combination of a simple column and a gear having a cylindrical opening, The combination of a flat knurled shaft and a gear having a cylindrical opening gives a lower pressure input, but the holding torque in the press-fitted member (gear) is the same as that of a flat knurled shaft and a gear having a cylindrical opening. It became clear that the combination of became larger. Note that the lower limit of the press-fitting allowance is 10 μm in the fitting of the shaft formed with the flat knurling and the gear, and the effect of the flat knurling becomes less below that, while the upper limit is set to 100 μm. This is because the stress concentration on the inner diameter of the gear becomes excessive, and the gear itself may be damaged.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate.

It is a schematic sectional drawing of the electric motor concerning this Embodiment. It is the figure which looked at the structure of FIG. 1 in the arrow II direction. 3 is a side view of a rotating shaft 11. FIG. It is the figure which looked at the rotating shaft of FIG. 3 in the arrow IV direction. FIG. 4 is a diagram illustrating a process of press-fitting a gear 17 into the rotating shaft 11 of the electric motor 10. It is the graph which showed the relationship between the press fit allowance calculated | required by the present inventors and press input. It is the graph which showed the relationship between the press fitting allowance calculated | required by the present inventors and holding torque.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electric motor 11 Rotating shaft 11a Mountain 12 Housing 13, 14 Bearing 15 Rotor 16 Stator 17 Gear 17a Gear tooth 17b Opening

Claims (2)

In an electric motor having a rotating shaft and a gear press-fitted to the rotating shaft,
The gear is formed of an iron-based sintered material, and the inner periphery of the gear with which the rotating shaft is fitted has a cylindrical shape,
A motor having a plurality of valleys and peaks alternately formed in a circumferential direction on an outer periphery of the rotating shaft.   2. The electric motor according to claim 1, wherein a knurling is formed on an outer periphery of the rotating shaft, and a radial interference between an outer diameter of the knurling and an inner diameter of the gear is 10 μm to 100 μm. .

Images