GB2391118A

GB2391118A - Miniature motor with sleeved shaft

Info

Publication number: GB2391118A
Application number: GB0303341A
Authority: GB
Inventors: Takaichi Mabuchi; Etsuo Mayumi
Original assignee: Mabuchi Motor Co Ltd
Current assignee: Mabuchi Motor Co Ltd
Priority date: 2002-02-22
Filing date: 2003-02-13
Publication date: 2004-01-28
Also published as: CN1440108A; JP2003319629A; CN1252896C; GB0303341D0

Abstract

The present invention minimizes flexural vibrations transmitted to a commutator terminal 5 and prevents breakage of a connected coil by mounting a metallic sleeve 20 on a shaft 2 between the mounting portion of a commutator 4 and the end face of a laminated core 3. Also, insulation coating is applied not only onto the laminated core 3 but also onto the metallic sleeve 20 to fix the metallic sleeve 20 to the laminated core 3. Thereby, deflection is prevented from being transmitted to a connecting portion of the coil and the commutator terminal. Wire breakage is prevented and the positioning of the commutator on the rotor shaft is made easy.

Description

23911 18

ROTOR The present invention relates to a rotor for a miniature motor, for example a motor used for elevating an automotive window glass or the like.

FIG. 5 shows a publicly known conventional miniature motor with worm 5 speed reducer (see Patent Publication No. 2636958). In this figure, a motor section is connected to a speed reducing section via screws. A motor shaft 2 is fixedly mounted with a worm 7, and the tip end portion thereof is pivotally carried on a bearing 9. The worm 7 is engaged with a helical gear 10 constituting a worm wheel so that driving torque outputted from the motor 10 section is transmitted to the worm 7 through the motor shaft 2, from the worm 7 to the helical gear 10 in the speed reducing section, and is taken out from an output shaft 12 to the outside.

A construction of a coil connection for the above-described miniature motor with worm speed reducer will be described with reference to FIG. 6.

15 FIG. 6 shows a rotor assembly for a general miniature motor of the prior art.

The motor shaft 2 is fixedly mounted with a laminated core 3, and a coil 6 is wound on the laminated core 3. The shaft 2 is also fixedly mounted with a commutator 4 at a predetermined position, and each commutator terminal 5 of the commutator 4 is connected with an end portion of the coil 6 constituting a 20 rotor magnetic pole. As described above, the worm 7 is fixed on the output side of the shaft 2. A bearing 8 may be mounted in advance between the laminated core 3 and the worm 7 depending on the relation of assembly of the motor section and the speed reducing section.

When such a miniature motor with worm speed reducer is used for 25 elevating an automotive window glass, for example, it is desirable to miniaturize the motor to the utmost because of limited mounting space etc. , and a shaft 2 having a diameter of about 3 mm is commonly used. For a motor for elevating an automotive window glass, however, since a high

( reaction force is applied to the shaft 2 from the worm speed reducing section, when the conventionally used shaft 2 having a diameter of about 3 mm is adopted, the whole shaft is deflected at the time when a load is applied, and a deflection force is transmitted to a portion of the commutator terminal 5 to 5 which the coil 6 is connected. As a result, the rotor rotates while being deflected, so that the connecting portion of coil expands and contracts, causing vibrations. Thereby, a problem occurs such that the coil 6 is liable to break at that portion. Also, there arises a problem in that a loud noise is produced by resonance of the vibrations with the natural frequency of a motor 1 0 casing.

To overcome these problems, an adhesive covering the whole of the connecting portion has conventionally been applied to protect a portion of the coil 6 and the commutator terminal 5 and to restrain deflection and resonance.

An epoxy adhesive may be used because it must adhere to the connecting 15 portion in such a manner as to penetrate into the coil 6 and wrap the coil 6.

However, since the application of the adhesive requires control of its spread and much manpower and time for drying, it is unsuitable for mass production whilst ensuring a reliable and stable quality. In particular, the requirement for the drying to interrupt production lines and conduct batch 20 processing, and, the difficulty in controlling the spread of adhesive presents a problem of difficulty in assuring the reliability.

Further, the commutator 4 cannot easily be positioned and fixed on the motor shaft 2, so that the commutator 4 is fixed by extending a commutator insulating cylinder on the laminated core side of the commutator 4 in such a 25 manner as strike the laminated core. Thus, a troublesome process has conventionally been needed to position such a commutator 4.

Also, when the miniature motor is used as a throttle valve driving motor, there arises a problem in that the vibrations of the engine resonate with mu

( the natural frequency of the motor casing and hence a loud noise is produced, or the shaft is deflected and hence the coil is broken. The throttle valve driving motor is a motor that is used when the opening/closing operation of the throttle valve of the engine is performed by electrical control. The throttle 5 valve driving motor is provided on a throttle body for performing the opening/closing operation of throttle valve, and the throttle body is directly installed on the engine, so that the vibrations of the engine are transmitted directly, which causes the above-described problems.

The problem of vibrations due to the deflection of the shaft 2 can be 10 solved by increasing the shaft diameter as a whole or by using a special shaft in which a part thereof in the axial direction is partially increased (what is called a stepped shaft). However, the increase in shaft diameter or the use of the special shaft is disadvantageous in meeting the requirement for miniaturization. Also, the change of shaft diameter causes a problem of 15 increased cost because all parts such as the laminated core, bearing, and commutator which relate to the shaft diameter must be changed. As a matter of course, the change itself to the stepped shaft increases the cost. Machine loss is increased in relation to larger parts, and there arises a situation in which the motor characteristics cannot be achieved fully.

20 According to the present invention, a rotor for a miniature motor having a laminated core and a commutator, which are fixed on a shaft, a coil wound on the laminated core, and a commutator terminal connected with an end portion of the coil, wherein a metallic sleeve is mounted on the shaft between the end face of the laminated core and the commutator.

25 The present invention helps to prevent vibrations and wire breakage due to deflection by preventing deflection from being transmitted to a connecting portion of a coil and a commutator terminal while the motor characteristics are achieved fully without the increase in shaft diameter or the

use of a special shaft and without the need for an adhesive applying process that is unsuitable for mass production.

The present invention also assists in the positioning of a communicator on a motor shaft, and helps to prevent vibrations from the outside of motor 5 from resonating with the natural frequency of a motor casing as in the case where the motor is used as a throttle valve driving motor.

Preferably, an insulation coating is applied not only onto the laminated core but also onto the metallic sleeve to fix the metallic sleeve to the laminated core.

10 Advantageously, the positioning of commutator of a rotor assembly is made easy by mounting the metallic sleeve.

The present invention will be described, by way of example, with reference to the accompanying drawings, in which: FIG. 1 is a view for detailedly illustrating a coil connecting portion of a 15 rotor of a miniature motor; FIG. 2 is a view showing a rotor of a miniature motor before a coil is FIG. 3 is a view showing examples of metallic sleeve capable of being used in the present invention; 20 FIG. 4 is a view showing a state in which an iron core consisting of a laminated core and a metallic sleeve are mounted on a rotor shaft; FIG. 5 is a view showing a miniature motor with worm speed reducer of the prior art;

FIG. 6 is a view showing a rotor assembly of the prior art;

( FIG. 7 is a diagram showing an experimental result indicating the effect of countermeasures against resonance of the present invention; and FIG. 8 is a schematic view showing an example in which a motor in accordance with the present invention is used for driving a throttle valve.

5 FIG. 1 is a view detailedly showing a coil connecting portion of a rotor assembly of a miniature motor, and FIG. 2 is a view showing a rotor assembly before a coil is wound. FIG. 3 is a sectional view showing two examples of a metallic sleeve 20. FIG. 4 is a view showing a state in which only a laminated core 3 and a metallic sleeve 20 are mounted on a shaft. The miniature motor 10 to which the present invention is applied can have an ordinary construction that is publicly known, except for the metallic sleeve 20 provided on the shaft 2 and a construction relating thereto. The rotor assembly shown in FIG. 1 usually has a laminated core 3 and a commutator 4 that are fixed on the shaft 2, a coil 6 wound on the laminated core 3, and a commutator terminal 5 to 15 which an end portion of each coil 6 is connected. In the construction shown in the figures, the metallic sleeve 20 is mounted on the shaft 2 between the end face of the laminated core 3 and the commutator 4.

The metallic sleeve 20 can be constructed so as to have a pipe shape as shown in FIG. 3(a) or so as to have an eyelet shape having a collar on one 20 end side of a pipe as shown in FIG. 3(b). The material of the metallic sleeve 20 may be iron, iron alloy (including stainless steel), or copper alloy such as brass. From the viewpoint of cost and workability and further since an insulation coating must adhere to the metallic sleeve properly, the material is preferably iron or iron alloy.

25 As shown in FIG. 4, the metallic sleeve 20 is pressed onto the shaft 2 on the side on which the commutator 4 is mounted in a state in which the laminated core 3 is pressed and fixed onto the shaft 2, and is brought into contact with the end face of the laminated core 3 (working example (1)).

( Although this metallic sleeve 20 is formed into an eyelet shape, and the collar of the eyelet is brought into contact with the end face of the laminated core 3 in FIG. 4, the collar may be brought into contact with the commutator 4 side.

Further, a metallic sleeve 20 of a pipe shape as shown in FIG. 3(a) may be 5 used. A portion in which the commutator 4 is mounted on the shaft 2 can be provided with knurls 11 in advance.

Usually, insulation coating is applied onto the laminated core 3 by using an insulating material such as epoxy powder to provide insulation between the laminated core 3 and the coil 6. In the construction shown in 10 FIG. 4, insulation coating is applied not only to the slot portions and both end faces of the laminated core 3 but also onto the metallic sleeve 20. By this insulation coating, the metallic sleeve 20 is firmly fixed to the laminated core 3 and the shaft 2. Most desirably, the collar of the eyelet-shaped metallic sleeve 20 is brought into contact with the end face of the laminated core 3, 15 and the insulation coating is applied, by which the metallic sleeve 20 pressed onto the shaft 2 is fixed firmly.

Also, a second metallic sleeve having the same construction may be provided, being brought into contact with the opposite end face of the laminated core and insulation coating is applied (working example (2)). This 20 configuration has an effect of further increasing the stiffness of the shaft 2.

Subsequently, the commutator 4 is pressed and fixed onto the shaft 2 so as to come into contact with the metallic sleeve 20 as shown in FIG. 2.

The position of the commutator 4 relative to the laminated core 3 is determined by the length in the axial direction of the metallic sleeve 20. Then, 25 the coil 6 is wound on the laminated core 3 as shown in FIG. 1, and each coil end is connected to the commutator terminal 5 of the commutator 4.

FIG. 7 is a diagram showing an experimental result indicating the effect of countermeasures against resonance of the present invention. Resonance

( (G) was measured by increasing the voltage from 9 V to 15.5 V. In FIG. 7, "prior art" designates the construction in which the whole of the connecting

portion of the coil 6 and the commutator terminal 5 is covered with an adhesive as explained with reference to FIG. 6, working example (1) 5 designates the construction in which the metallic sleeve 20 is provided on the commutator side only, working example (2) designates the construction in which the metallic sleeve is provided on both sides of the laminated core, and Uno countermeasures" designates a construction in which no countermeasures against resonance are taken. Two triangles in the figure 10 designate cases where measurement was made by rotating the motor in the clockwise (COO) direction and counterclockwise (CCW) direction. Also, each apex of triangle designates the maximum, average, and minimum of resonance (G) in that order from the upside.

As is apparent from FIG. 7, according to the present invention, both 15 working examples (1) and (2) have a remarkable effect of restraining vibrations despite a simple construction. The prior art explained with

reference to FIG. 6 also has a great effect of restraining vibrations. However, as described before, this art requires control of adhesive spread and much manpower for drying, and also requires an adhesive applying process that is 20 unsuitable for mass production achieved with stable quality being secured.

Both working example (1) and working example (2) can be constructed so that resonance does not occur at a service voltage of motor (about 12 V), and thereby noise can be restrained.

FIG. 8 is a schematic view showing an example in which the motor in 25 accordance with the present invention is used for driving a throttle valve. The whole construction for controlling the opening/closing operation of the throttle valve 34 is referred to as a throttle body 35. An electronic control unit controls a throttle valve driving motor based on a detection signal corresponding to the

l stroke of an accelerator pedal, which is outputted from an accelerator operating unit, and a throttle valve opening signal sent from a throttle sensor.

The throttle valve driving motor 31 has a gear 32 fixed to a shaft thereof. The gear 32 rotates a shaft 33 for driving the throttle valve 34 via a speed reducing 5 section consisting of a plurality of gears, whereby the throttle valve 34 is opened and closed.

Since the throttle body 35 is installed directly to an engine for a motor vehicle, vibrations of the engine are transmitted directly to the driving motor 31. Thus, in an application in which vibrations are transmitted from the 10 outside of motor to the driving motor, by using the abovedescribed construction of working example (1) or working example (2), the metallic sleeve can restrain vibrations of shaft transmitted from the outside.

The present invention can prevent broken coil in the connecting portion due to flexural vibrations, which is caused by a small diameter of motor shah 15 relative to the load, and can reduce noise by restraining vibrations while enabling the miniaturization of motor without increasing the shaft diameter or using a special shaft and without changing the specifications of other parts by

mounting the metallic sleeve on the motor shaft.

Also, since the shaft has a small diameter relative to the load, the 20 present invention achieves the effects of miniaturizing of the bearing, reduction in machine loss due to the prevention of parts such as a bearing from being made large in size, reduction in the peripheral speed due to the use of a small-diameter commutator, restraint of sliding noise due to the reduction in the peripheral speed, power saving of motor due to the reduction 25 in machine loss and the use of small-size parts, reduction in cost due to the common use of parts of a motor without a worm.

( Also, the present invention can assure high reliability of coil connection because the coil connecting portion does not require an adhesive applying process that is unsuitable for mass production.

Also, the present invention achieves an effect of easy positioning of 5 commutator because the metallic sleeve is mounted.

Further, the present invention can prevent a problem in that vibrations form the outside of motor resonate with the natural frequency of the motor casing as in the case where the motor in accordance with the present invention is used for driving a throttle valve.

Claims

CLAIMS:

1. A rotor for a miniature motor having a laminated core and a commutator, which are fixed on a shaft, a coil wound on the laminated core, and a commutator terminal connected with an end portion of the coil, 5 whereina metallic sleeve is mounted on the shaft between the end face of the laminated core and the commutator.

2. The rotor according to claim 1, wherein an insulation coating is applied onto the laminated core and the metallic sleeve so that the metallic sleeve is fixed to the laminated core by the insulation coating.

10 3. The rotor according to claim 1 or 2, wherein the metallic sleeve is constructed so as to have a pipe shape or an eyelet shape.

4. The rotor according to any one of claims 1 to 3, wherein the metallic sleeve is made of iron or iron alloy.

5. The rotor according to any one of the preceding claims, wherein a 15 second metallic sleeve is mounted on the shaft so as to be brought into contact with the opposite end face of laminated core.

6. The rotor according to any one of the preceding claims, wherein a speed reducing section including a worm installed in a tip end portion of the shaft is integrally connected to a motor section.

20 7. A rotor for a miniature motor, substantially as shown in or as described with respect to any one of Figures 1 to 5 of the accompany drawings. 8. A miniature motor including a brush, and a rotor according to any one of the preceding claims.

9. A miniature motor according to claim 8 constructed as a throttle valve driving motor which opens and closes a throttle valve via a speed reducing section including a gear installed in a tip end portion of the shaft.

10. A miniature motor substantially as shown in or as described with 5 respect to any one of Figures 1 to 5 or 8 of the accompanying drawings.