Electric motor and machine tool equipped with a terminal box

Abstract

Electric motor (10), comprising: a stator (22); a rotor (20) having a rotation axis (18) which is rotatable about an axis line (16) with respect to the stator (22); a bearing (12, 14) that keeps the axis of rotation (18) rotatable; a housing (26, 28, 30, 32, 34) that holds the bearing (12, 14) and defines a space (46, 48) that adjoins the bearings (46, 48) on the outside in the axial direction; and a terminal box (40) for a power line that is connected to the electric motor (10), wherein the interior of the terminal box (40) is fluidically connected to a clean environment and the interior of the terminal box (40) and the space (46) are connected to each other by a flow path (50) formed outside the stator (22) and the air in the clean environment in conjunction with the rotations of the rotor (20) automatically flows through the interior of the terminal box (40) and the flow path (50) into the space (46), so that air flowing out of a gap (44) adjacent to the bearing (12) and fluidically connected to an exterior of the electric motor (10) is replenished.

Description

Background of the invention 1. Field of the invention

[0001] The present invention relates to an electric motor provided with a terminal box, and to a machine tool provided with this electric motor. 2. Description of the state of the art

[0002] In electric motors (rotary electric machines) equipped with a stator and a rotor, there are motors that have a structure to prevent moisture or foreign matter from entering the motor interior. In this regard, techniques are known in which the internal pressure inside an electric motor is increased or an air flow is forced using an air purge structure (an air supply device) to prevent foreign matter from entering (see, for example, Patent Application Laid-Open No. JP 2013-236473 A, Patent Application No. JP 5765486 B2, or Patent Application Laid-Open No. JP 2015-223022 A).

[0003] A technique is also known that utilizes fluidized air generated by the rotation of the rotor, which is intended to prevent the ingress of moisture or the like into the interior of an electric motor (see, for example, Patent Application Laid-Open No. 2006-353053 A).

[0004] When an air purge assembly is used, it is necessary to construct a separate air supply device or the like, which increases the cost of the entire machine including the electric motor (see, for example, DE 10 2017 001 530 A1). On the other hand, without using an air supply device, it is difficult to construct a flow path assembly that can reliably prevent foreign matter from entering the interior of an electric motor. Furthermore, such a flow path assembly can become complicated, resulting in an increase in the cost of the electric motor. Brief description of the invention

[0005] One form of the present disclosure is an electric motor including a stator; a rotor having a rotation axis rotatable with respect to the stator about an axis line; a bearing rotatably supporting the rotation axis; a housing supporting the bearing and defining a space adjacent to the bearing on the outside in the axis line direction;and a terminal box for a power line that is connected to the electric motor, wherein the interior of the terminal box is fluidically connected to a clean environment, and the interior of the terminal box and the space are connected to each other by a flow path formed outside the stator, and the air in the clean environment automatically flows through the interior of the terminal box and the flow path into the space in conjunction with the revolutions of the rotor, so that air flowing out of a gap that is adjacent to the bearing and fluidically connected to an exterior of the electric motor is supplemented.;

[0006] Another form of the present disclosure is a machine tool including an electric motor as recited above, wherein the electric motor is disposed inside the machine tool and the terminal box is fluidly connected to an exterior of the machine tool. Simple explanation of the drawings

[0007] The objects, features and advantages of the present invention will become more apparent from the following explanation of an embodiment in conjunction with the accompanying drawings. In the drawings is Fig. 1 is a view showing the schematic structure of an electric motor according to an ideal embodiment; and is Fig. 2 a partial enlargement of the area around the output shaft of the electric motor in Fig. 1. Detailed explanation

[0008] Fig. Fig. 1 is a sectional view along the axial direction showing the schematic structure of an electric motor (rotary electric machine) 10 according to an ideal embodiment, and Fig. 2 is a partial enlargement of the front portion (the vicinity of the output shaft) of the electric motor 10. The electric motor 10 is arranged inside a schematically illustrated machine 8 such as a machine tool and includes a rotation axis (shaft) 18 supported rotatably about an axis line 16 by a first bearing (front bearing) 12 and a second bearing (rear bearing) 14, a rotor 20 fitted on the outer peripheral surface of the rotation axis 18 and rotating integrally with the rotation axis 18, and a generally tubular stator 22 extending along the axis line 16 so as to surround the rotor 20.The interior of the machine 8 refers to a space where the air environment is worse (the degree of pollution is higher) than outside the machine, such as the machining chamber of a machine tool. Specifically, this refers to a space containing air in which cutting fluid or the like is dispersed in a mist-like manner, and whose penetration into the interior of the electric motor is undesirable. In contrast, the exterior of the machine 8 refers to a space where the degree of air purity is higher than inside the machine 8. The penetration of air from outside the machine 8 into the interior of the electric motor does not cause problems such as machine defects or the like.

[0009] The front bearing 12 is disposed near a front end 18a of the rotation axis 18 and is held by a front flange 26 fixed to a front end surface 24a of a core (stator core) 24 of the stator by screw fastening or the like. The front flange 26 extends from the front end surface 24a of the stator core 24 toward the front end 18a of the rotation axis 18 and holds a portion of the rotation axis 18 and the front bearing 12 (its outer ring). A generally annular front cover 28 is attached to the front flange 26. The front end 18a of the rotation axis 18 protrudes from the front flange 26 and the front cover 28, and the rotation axis 18 functions as an output shaft connected directly or indirectly to a main shaft of the machine tool, such as a lathe or a machining center.

[0010] For convenience, the output shaft side (left in the figure) is used in this description. Fig. 1) is called “front”, and the opposite side (right in Fig. 1) is referred to as "rear." Furthermore, the "axis line direction" or "axis direction" refers to the direction parallel to the rotation axis direction.

[0011] The rear bearing 14 is arranged near the rear end 18b of the rotation axis 18, which is positioned on the opposite side to the front end 18a of the rotation axis 18. A rear flange 30 is fixed to a rear end surface 24a of the stator core 24 by a screw fastening or the like. A retaining ring 32 is fixed to the rear flange 30 by a screw fastening or the like, and the retaining ring 32 holds the rear bearing 14 (its outer ring). The rear end 18b of the rotation axis 18, projecting from the rear flange 30, is surrounded by a rear cover 34 attached to the rear flange 30. An encoder 36 is attached to the rear end 18b of the rotation axis 18, which detects the rotational position and rotational speed, or the like, of the rotation axis 18.

[0012] The stator 22 includes the stator core 24 formed from a plurality of laminated magnetic steel sheets, and windings 28 wound around protrusions (not shown) formed on the inner peripheral surface of the stator core 24. The windings 38 are fixed to the stator core 24 by resin or the like. The windings 38 extend along the rotation axis line 16 so as to protrude from both ends of the stator core 24 and are connected to power lines (lead wires) (not shown) extending from the terminal box 40. The windings generate rotating magnetic fields by the current supplied via the power lines, and the rotor 20 rotates integrally with the rotation axis 16 due to the generated rotating magnetic fields.

[0013] The electric motor 10 may be used, coupled to the main shaft of a machine tool, in an environment (for example, the machining chamber of the machine tool) where solids such as dust or liquids such as cleaning fluid or cutting fluid, etc. (hereinafter referred to simply as "foreign matter") are scattered. If these foreign matters enter the interior of the electric motor, there is a risk of deterioration of the insulation of the windings or impairment of the holding effect of the bearings. Therefore, it is desirable to more securely prevent the intrusion of foreign matters.

[0014] As a means for preventing the intrusion of foreign matter, it is known to form a labyrinth structure near at least one of the front bearing 12 and the rear bearing (the front bearing 12 in the illustrated example). Specifically, a roughly annular labyrinth member 42 is fixed by press fitting or the like to a part (on the outer peripheral surface) of the rotational axis 18 on the front side of the front bearing 12 with respect to the axis line 16 (on the outside of the electric motor), and the labyrinth member 42 is configured to rotate integrally with the rotational axis 18. Furthermore, a gap 44 is formed between the front cover 28 and the labyrinth member 42 to prevent the two members from abutting against each other.Therefore, in the present embodiment, a front housing formed by the front flange 26 and the front housing 28, the front bearing 12, and the labyrinth member 42 defines a front space 46 on the outer side (the front side) forward of the front bearing 12 with respect to the axial direction. The front space 46 is adjacent to the front bearing 12 and has the gap 44 (a flow path) connected to the exterior of the electric motor. When the electric motor 10 does not have a labyrinth structure, the front space provided with the flow path (the gap between the front cover 28 and the rotation axis 18) is defined by the front housing and the front bearing 12.

[0015] When a labyrinth structure is also formed near the rear bearing 14, the approximately annular labyrinth element 42 is formed on a part (on the outer peripheral surface) of the rotation axis 18 on the rear side of the rear bearing 14 with respect to the axis line 16. As in the case of the front space 46, a rear space 48 may be defined for the rear bearing 14 on the outer side (the rear side) rearward of the rear bearing 14 with respect to the axial direction. This rear space 48 is adjacent to the rear bearing 14 and has a gap (a flow path) connected to the exterior of the electric motor. More specifically, a rear housing is formed by the retaining ring 32 and the rear cover 34, and the rear space provided with the gap (flow path) connected to the exterior of the electric motor is defined by the rear housing and the rear bearing 14.

[0016] However, the labyrinth structure described above may not be sufficient to reliably prevent the ingress of foreign matter. For example, when the labyrinth 42 rotates together with the rotation axis 18, the area surrounding the labyrinth 42 reaches a negative pressure, and air inside the electric motor is sucked out (according to Bernoulli's theorem). More specifically, an airflow is created that flows outward from the front space 46 through the gap 44 between the labyrinth 42 and the front cover 28, resulting in a situation where the pressure inside the electric motor is lower than outside.

[0017] While the rotational axis 18 (the labyrinth) rotates at a constant speed, the negative pressure condition inside the electric motor is maintained. However, when the rotation of the labyrinth stops, an airflow is generated, through which air flows from the gap 44 in the front chamber 46 to relieve the negative pressure condition. Since the area surrounding the labyrinth 42 is filled with air containing many foreign matter, foreign matter penetrates into the interior of the electric motor.

[0018] Now, in the present embodiment, as in Fig. 1 and Fig. 2, the interior of the terminal box 40 and the front space 46 are connected by a flow path formed outside the stator 22, and the air in the terminal box 40 automatically flows into the front space 46 through this flow path in conjunction with the rotation of the rotor 20. More specifically, a hollow pipe 50, such as a flexible hose or a rigid pipe, which fluidically connects the interior of the terminal box 40 and the outer surface of the front flange 26 (here, the peripheral surface) is formed to extend on the outside in the radial direction of the stator 22. In addition, a through hole 52 is formed which extends from the outer surface of the front flange 26 into the front space 46, and a flow path is formed by the hollow pipe 50 and the through hole 52 on the radially outer side of the stator 22.In this way, the interior of the terminal box 40 and the front space 46 are connected by a flow path that is fluidly isolated from the interior 54 of the machine 8, such as a machine tool. Furthermore, no connection opening extending from the vicinity of the front bearing 12 into the interior of the electric motor (into the space where the rotor 20 and the windings 38 are located) is formed in the electric motor 10.

[0019] The interior of the terminal box 40 is fluidly connected to the exterior of the machine 8 (a clean environment), and in the example of Fig. 1, the terminal box 40 is fluidically connected to an amplifier 56 formed outside the machine 8 via a hollow ventilation pipe 58 such as a flexible hose or a rigid line, and the ventilation pipe 58 can also be used as a conduit for introducing power lines 60 from the amplifier 56 into the interior of the terminal box.

[0020] The terminal box 40 itself normally has a tightly sealed structure and is not provided with an opening portion or the like opening to the interior 54 of the machine 8. On the other hand, the booster 56 normally does not have a tightly sealed structure, so the interior of the booster 56 is filled with air having generally the same degree of purity as that outside the machine 8 (the clean environment). Consequently, when the rotary shaft 18 rotates, the clean air inside the booster 56 automatically flows into the interior of the front space 46 through the pipe 58, the terminal box 40, the hose 50, and the through-hole 52 to supplement the air flowing out from the gap 44. Therefore, in the present embodiment, by utilizing the airflow formed by the rotations of the rotary shaft 18, clean air can be supplied into the interior of the front space 46 without using an air purge device.

[0021] Since, as described above, air flows at a constant rate from the terminal box 40 into the front chamber 46 during the rotation of the rotary shaft 18, no negative pressure is generated inside the front chamber 46 relative to the exterior of the electric motor. Consequently, since no contaminated air flows from the gap 44 into the front chamber 46 at the moment the rotary shaft 18 stops, the intrusion of foreign matter into the interior of the electric motor is prevented, and the interior of the electric motor is kept clean. A similar structure can also be designed for the rear chamber described above.

[0022] Thus, in the electric motor (rotary electric machine) 10 according to the present embodiment, in addition to the foreign matter intrusion prevention effect that the labyrinth 42 usually has, air can be automatically supplied into the front space 46 using the air flow associated with the rotation of the rotary shaft 18. Only clean air from the inside of the terminal box 40 can be used for the air supplied into the front space 46. Therefore, since it is not necessary to prepare a separate air purge device or the like, the manufacturing cost of the electric motor can be reduced.When such an electric motor is applied to a machine tool having a main shaft capable of rotating at a high speed (i.e., where the degree of contamination inside the machining chamber is comparatively high), such as an NC lathe or a machining center, a machine tool with high safety and low cost is obtained.

[0023] As an ideal modification, it is possible not to use a hollow conduit 50 such as a hose or a cable, but to connect the terminal box 40 directly to the front flange 26 (the through opening 52 formed therein). Fig.1, an amplifier 56 is shown as an example for the external structural element of the machine 8, which is connected to the terminal box 40 (supplies clean air to the terminal box 40), but it is also possible to use a different structural element. However, since an amplifier is an element with which an electric motor is normally provided, no other structural element needs to be used if the ventilation pipe 58 (which is also normally used as a conduit pipe) is used by the amplifier 56.

[0024] In the present disclosure, clean air can be automatically supplied to the interior of an electric motor without actively (forcibly) supplying air to the interior of the electric motor using an air purge device or the like. More specifically, even if the interior of the electric motor momentarily reaches a negative pressure due to the rotation of the rotor, clean air in the terminal box automatically flows into the interior of the electric motor to relieve this negative pressure. Since the interior of the terminal box is not connected to the interior of the machine tool but only to the exterior of the machine tool (a clean environment), contaminated air inside the machine tool does not flow into the interior of the electric motor.Since a constant amount of (clean) air flows into the interior of the electric motor during the rotor's rotation, air from the labyrinth's surroundings (from inside the machine tool) no longer penetrates into the interior due to negative pressure after the rotor's rotation stops. Consequently, an air purge device that increases the internal pressure inside the electric motor is no longer required, allowing the cost of the electric motor and a machine containing it (e.g., a machine tool) to be reduced.

[0025] According to the present disclosure, since clean air inside the terminal box automatically flows into the interior of the electric motor, the intrusion of contaminated air or foreign matter into the interior of the electric motor can be effectively suppressed even without using an air purge device.

Claims

[1] Electric motor (10), comprising: a stator (22); a rotor (20) having an axis of rotation (18) rotatable with respect to the stator (22) about an axis line (16); a bearing (12, 14) which rotatably supports the rotation axis (18); a housing (26, 28, 30, 32, 34) which holds the bearing (12, 14) and defines a space (46, 48) which is adjacent to the bearings (46, 48) on the outside in the axis line direction; and a terminal box (40) for a power line connected to the electric motor (10), wherein the interior of the terminal box (40) is fluidically connected to a clean environment, and the interior of the terminal box (40) and the space (46) are connected to one another by a flow path (50) formed outside the stator (22), and the air in the clean environment automatically flows through the interior of the terminal box (40) and the flow path (50) into the space (46) in conjunction with the revolutions of the rotor (20), so that air flowing out of a gap (44) adjacent to the bearing (12) and fluidically connected to an exterior of the electric motor (10) is supplemented. [2] The electric motor (10) according to claim 1, comprising a labyrinth member (42) mounted on a part of the rotation axis (18) located on the outside of the bearing (12) in the axis line direction and defining a part of the space (46), and wherein the gap (44) is defined between a front cover (28) and the labyrinth member (42). [3] Electric motor (10) according to claim 1 or 2, wherein a ventilation pipe (58), which is also used as a conduit for power lines, is connected to the terminal box (40). [4] Electric motor (10) according to one of claims 1 to 3, wherein the terminal box (40) is connected to a through opening (52) formed in the housing (26) via a hollow pipe (50) running on the outside of the stator (22). [5] A machine tool (8) including an electric motor (10) according to any one of claims 1 to 4, wherein the electric motor (10) is arranged inside the machine tool (8) and the terminal box (40) is fluidly connected to an exterior of the machine tool (8).

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