GB2140217A

GB2140217A - Direct-current core-less motor

Info

Publication number: GB2140217A
Application number: GB08410703A
Authority: GB
Inventors: Naoyuki Matsumoto; Michiyasu Onda; Yasuhiro Fukushima
Original assignee: Seiko Instruments Inc
Current assignee: Seiko Instruments Inc
Priority date: 1983-05-19
Filing date: 1984-04-26
Publication date: 1984-11-21
Also published as: JPS59216456A; GB8410703D0

Abstract

A direct current core-less motor having a housing (14,21,22) within which is mounted a rotor (16,17,18) comprising a rotor coil (17), a commutator (16) and connector means (18) which electrically interconnect the rotor coil (17) and the commutator (16); and magnets (12a, 12b) which are disposed on opposite sides of the rotor coil (17): the connector means (18) being disposed on one side of the rotor coil (17) and the commutator (16) being disposed, at least in part, on the opposite side of the rotor coil (17). <IMAGE>

Description

SPECIFICATION Direct-current core-less motor The present invention relates to a direct-current core-less motor. Although the invention is not so restricted, it relates especially to a direct-current core-less motor which is small in diameter, thin, and at the same time shows excellent characteristics, and more particularly to a directcurrent core-less motor having a diameter of not more than 25 mm and a thickness of not more than 10 mm.

Although the present invention is primarily directed to any novel integer or step, or combination of integers or steps, as herein described and/or as shown in the accompanying drawings, nevertheless, according to one particular aspect of the present invention to which however, the invention is in no way restricted, there is provided a direct current core-less motor having a housing within which is mounted a rotor comprising a rotor coil, a commutator and connector means which electrically interconnect the rotor coil and the commutator, and magnets which are disposed on opposite sides of the rotor coil; the connector means being disposed on one side of the rotor coil and the commutator being disposed, at least in part, on the opposite side of the rotor coil.

Preferably, the housing comprises first and second housing members which are disposed on opposite sides of the rotor coil, and a sleeve which is non-integrally secured to the first and second housing members.

The said magnets preferably comprise first and second magnets which are carried respectively by said first and second housing members.

The connector means may comprise a printed circuit board and/or a ring varistor.

Preferably, the said part of the commutator is engaged by a brush carried directly or indirectly, by said second housing member.

The rotor preferably has a rotor shaft which is supported by an automatic centering bearing which is carried by said first housing member.

The motor preferably has a diameter not exceeding 25 mm and a thickness not exceeding 10 mm.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which: Figures 1 and 2 are respectively sectional views of known direct-current core-less motors, and Figures 3 and 4 are respectively sectional views showing direct-current core-less motors according to the present invention.

A known direct-current core-less motor is shown in Figure 1. The motor comprises a housing 1; a rotor 9 composed of a rotor shaft 2, a rotor coil 3, a ring varistor or a printed circuit board 4 and a commutator 5; an end bracket 10 provided with a yoke 6 and a brush 8; and a magnet 7.

With the recent trend toward the miniaturization of many devices, there is a need for a motor which is small in diameter, thin, and of high efficiency. In order to obtain high efficiency in the limited space provided within the motor, it is necessary to increase the magnetic flux density as much as possible in a gap where the rotor coil 3 is disposed. However, in a magnetic circuit in which the magnet 7 is disposed only on the end bracket 10 as shown in Figure 1, it is difficult to obtain enough magnetic flux density in the gap because a magnetic leakage occurrs.

Another known motor is shown in Figure 2. In this case, in order to reduce the magnetic flux leakage as much as possible, the magnet 7 of Figure 1 is divided into two portions 7a, 7b one portion 7a of which is mounted within and secured to the housing 1. As shown in Figure 2, the magnets 7a and 7b are secured to the housing 1 and the end bracket 1 Oa respectively so that the magnets 7a, 7b are disposed on opposite sides of the rotor coil 3.BY adopting this construction, although the motor can be given satisfactory characteristics, the thickness of the motor at the end bracket 1 Oa is increased since the ring varistor or the printed circuit board 4 for connecting the rotor coil 3 and the commutator 5 is housed on the same side of the rotor coil 3 as the end bracket 1 0a. Further, it is difficult to magnetize the magnet 7a after securing it to the housing 1. In addition, the thickness of the cylindrical portion of the housing 1 is greater than is desirable since the cylindrical portion is machined in one body with the yoke 6, resulting in the motor having an unnecessarily large diameter.

As described above, in this construction, it is difficult to reduce the diameter and the thickness, although excellent characteristics can be obtained.

Hereinafter, two embodiments of the present invention will be described with reference to Figures 3 and 4 respectively of the drawings.

As shown in Figure 3, a direct-current core-less motor has a housing which comprises a top bracket or first housing member 21 composed of a yoke 11 a and a bearing 20a; a sleeve 14 serving as a cylindrical portion of the housing; and an end bracket or second housing member 22 composed of a yoke 11 b, a brush 1 3 and a bearing 20b, the sleeve 1 4 being non-integrally secured to the first and second housing members 21,22.

The motor has a rotor 23 composed of a rotor shaft 1 5, a commutator 16, a rotor coil 17, and a printed circuit board 18 and a ring varistor 19 which electrically interconnect the rotor coil 1 7 and the commutator 16. Magnets 1 2a and 1 2b are secured to the top bracket 21 and the end bracket 22 respectively so as to be disposed on opposite sides of the rotor coil 1 7. In the rotor 23, a part of the commutator 1 6 is disposed on the side of the rotor coil 17 facing the end bracket 22, while the printed circuit board 1 8 and ring varistor 1 9 are disposed on the side of the rotor coil 1 7 facing the top bracket 21.By adopting this rotor construction, the space around the magnets 1 2a and 1 2b can be used efficiently. Further, since the housing is composed of a plurality of pieces, they can be machined by conventional machining technology.

Figure 4 shows another embodiment of the present invention in which an automatic centering bearing 20c is mounted on the top bracket 21.

The constructions shown in Figures 3 and 4 provide the following remarkable advantages: (1) The magnets 12a,12b secured to the top bracket 21 and the end bracket 22, and thus on opposite sides of the rotor coil 1 7, can be magnetized easily after they are assembled, resulting in higher productivity.

(2) The diameter of the motor can be made smaller since the housing is composed of a plurality of pieces, namely a yoke 11 a whose thickness must be sufficient to prevent magnetic saturation and a sleeve 14 whose thickness need only be great enough to satisfy mechanical strength.

(3) By adopting a magnetic circuit in which magnets 12a,12b are disposed on opposite sides of the rotor coil 17, excellent magnetic characteristics can be obtained without increasing the thickness of the motor.

Claims

1. A direct current core-less motor having a housing within which is mounted a rotor comprising a rotor coil, a commutator and connector means which electrically interconnect the rotor coil and the commutator; and magnets which are disposed on opposite sides of the rotor coil; the connector means being disposed on one side of the rotor coil and the commutator being disposed, at least in part, on the opposite side of the rotor coil.

2. A motor as claimed in claim 1 in which the housing comprises first and second housing members which are disposed on opposite sides of the rotor coil and a sleeve which is non-integrally secured to the first and second housing members.

3. A motor as claimed in claim 2 in which the said magnets comprise first and second magnets which are carried respectively by said first and second housing members.

4. A motor as claimed in any preceding claim in which the connector means comprises a printed circuit board and/or a ring varistor.

5. A motor as claimed in claim 2 or 3 in which the said part of the commutator is engaged by a brush carried, directly or indirectly, by said second housing member.

6. A motor as claimed in claim 2, 3 or 5 in which the rotor has a rotor shaft which is supported by an automatic centering bearing which is carried by said first housing member.

7. A motor as claimed in any preceding claim in which the motor has a diameter not exceeding 25 mm.

8. A motor as claimed in any preceding claim in which the motor has a thickness not exceeding 10 mm.

9. A direct current core-less motor substantially as hereinbefore described with reference to and as shown in Figure 3 or in Figure 4 of the accompanying drawings.

10. A direct-current core-less motor comprising a top bracket having a magnet; an end bracket having another magnet; a sleeve for connecting said top bracket and said end bracket so that they face each other; and a rotor composed of a commutator, a rotor coil and a means for connecting said commutator and said rotor coil, wherein said rotor is disposed between said top bracket and end bracket, and said commutator is disposed on the side of said rotor coil facing said end bracket, and said means for connecting said commutator and said rotor coil is disposed on the side of said rotor coil facing said top bracket.

11. Any novel integer or step; or combination of integers or steps, hereinbefore described and/or as shown in the accompanying drawings, irrespective of whether the present claim is within the scope of or relates to the same or a different invention from that of the preceding claims.