Patent Description:
In strain wave gearings and other gearing devices, a rotation-side member such as an input shaft or an output shaft is 20supported by a device housing or other secured-side member via bearings. A gap is formed between the rotation-side member and the secured-side member. Typically, the gap is sealed by an oil seal in order to prevent lubricant such as oil or grease with which the interior of the device is filled from leaking outside of the device or 25to other sites within the device through the gap.

Patent document <NUM> (<CIT>) proposes a lubricant sealing structure in which the sealing properties of an oil seal are enhanced. In this lubricant sealing structure, a fluorine-based grease having oil repellency with respect to lubricant is applied to portions of a rotating member that are sealed by an oil seal, and the sealing properties are enhanced.

Lubricant sealing structures in which labyrinth seals are used in lieu of oil seals are also known. Patent document <NUM> (<CIT>) proposes a roll bearing device provided with a labyrinth gap formed between a secured-side member and a rotation-side member, and an oil-repellent and water-repellent surface formed by coating the surfaces that form the labyrinth gap with an oil-repellent and water-repellent material. Patent document <NUM> (<CIT>) proposes a contactless sealing device provided with a labyrinth flow path that is incorporated between an axle and a casing of a gearing device for a railway vehicle, the labyrinth flow path defined by an oil-repellent treated surface.

Moreover, surface texturing, in which fine grooves, etc., are machined into a designated surface, is known as a technique for modifying surfaces such as sliding surfaces. Patent document <NUM> (<CIT>) proposes forming a periodic structure of recesses and protrusions in the form of a fine grating in a sliding surface, and preventing any increase in friction and any occurrence of burning caused by a deficiency of lubricant, through surface machining in which a femtosecond laser is used. Additionally, Patent document <NUM> (<CIT>) proposes interposing a lubricating fluid onto sliding surfaces between two members and forming very small grooves in the sliding surfaces through laser machining, thereby imparting a strong friction-reducing effect.

<CIT> discloses a mechanical seal provided with multiple end faces arranged between a moving ring and a stationary ring for realizing zero leakage and non-contact through the combined actions of micro concave cavities, gap channels and pumping slots. Micro concave cavities or pumping slots are respectively formed in different end faces of the mechanical seal friction pair; the dynamic pressure effect of the micro concave cavities and the pumping slots is utilized to realize the non-contact; the pressure of leaked medium is reduced by utilizing the gap channels (or provided with mazes) among different end faces; the leakage amount is reduced or the zero leakage is achieved by utilizing the pumping effect of the pumping slot.

<CIT> discloses a fluid machine including a stationary member, a rotary member and a labyrinth seal including a succession of stationary steps formed on the stationary member, and a succession of rotary steps formed on the rotary member. The labyrinth seal further includes a plurality of stationary recesses each formed in a radial wall portion of a respective stationary step, and a plurality of rotary recesses each formed in a radial wall portion of a respective rotary step. Each stationary step defines a stationary projection delimited by the stationary recess formed on said stationary step, and each rotary step defines a rotary projection delimited by the rotary recess formed on said rotary step. The axial width of each of the stationary recesses and of the rotary recesses substantially equals the axial width of each of the stationary projections and of the rotary projections.

It is an object of the present invention to provide a lubricant sealing structure with which it is possible, by using fine groove machining (surface texturing), to reliably prevent lubricant from leaking out through a gap portion between first and second members that rotate relative to one another.

According to the present invention, there is provided a lubricant sealing structure that prevents lubricant from leaking out, from an interior of a device provided with a first member and a second member that rotate relative to one another about a central axis, through a gap portion between the first and second members, wherein.

The labyrinth seal is provided with a first gap portion having a first gap dimension; and the first gap portion is formed with an oi1 reservoir having a second gap dimension that is larger than the first gap dimension, the oi1 reservoir being positioned at an intermediate section of the first gap portion in the leaking direction.

In the lubricant sealing structure according to the present invention, the oil-repellent surfaces in which a groove array pattern of fine grooves has been produced are formed in the first and second surface portions forming the labyrinth seal for sealing the gap between the first and second members. Additionally, the upstream-side oil-repellent surfaces are formed on the first and second upstream-side surface portions positioned further upstream than the labyrinth seal in the direction in which the lubricant leaks. The lubricant leaking through the gap deforms into spheroids after being repelled by the upstream-side oil-repellent surfaces. The dimensions of the gap in the labyrinth seal are made smaller than the size (diameter) of the spheroidal lubricant, whereby the flow of lubricant into the gap forming the labyrinth seal is suppressed. Additionally, because the labyrinth seal is formed by the oil-repellent surfaces, the flow of lubricant into the labyrinth seal is suppressed.

In the lubricant sealing structure according to the present invention, the oil-repelling effect produced by the upstream-side oil-repellent surface formed by implementing surface texturing through fine groove machining, the sealing effect produced by the labyrinth seal, and the oil-repelling effect produced by the oil-repellent surface that regulates the labyrinth seal operate synergistically, and exceptional sealing properties are achieved and maintained. The lubricant is thereby reliably prevented from leaking from the lubricant enclosure portions in the interior of the device to, inter alia, the exterior of the device.

Any of the following array patterns (<NUM>) to (<NUM>) can be employed as the groove array pattern for imparting oil repellency to the member surfaces. Additionally, a composite array pattern in which a plurality of array patterns selected from among these array patterns are combined can also be employed.

In the lubricant sealing structure according to the present invention, an oil reservoir having large gap dimensions can be formed in part of the gap portion constituting the labyrinth seal. Lubricant that has penetrated the gap portion of the labyrinth seal is trapped in the oil reservoir, whereby leakage of the lubricant can be reliably prevented.

In cases where the oil reservoir is formed, an oil absorber composed of a non-woven fabric or another porous material can be mounted in the oil reservoir. The lubricant can be reliably prevented from flowing downstream from the oil reservoir.

Additionally, the inner peripheral surface portion of the oil reservoir can be configured as an oleophilic surface provided with oleophilic properties with respect to the lubricant. This makes it possible to efficaciously prevent the lubricant that has collected in the oil reservoir from flowing downstream.

A gap portion in which the gap dimensions gradually decrease toward the direction in which the lubricant leaks can be formed in part of the gap portion constituting the labyrinth seal. For example, a gap portion having a wedge shape in cross-section can be formed. Suitably setting the gap dimensions of this gap portion makes it easier for the lubricant to be trapped in the gap portion and makes it possible to efficaciously prevent the lubricant from flowing downstream.

Embodiments of a lubricant sealing structure to which the present invention is applied are described below with reference to the accompanying drawings. The embodiments described below illustrate cases where the lubricant sealing structure according to the present invention is applied to a strain wave gearing and to an actuator provided with a strain wave gearing and a motor. The present invention also can similarly be applied to gear-type reducers and other rotation-transmitting devices other than strain wave gearings.

<FIG> is a schematic longitudinal cross-sectional view of a strain wave gearing according to embodiment <NUM> of the present invention. The strain wave gearing <NUM> is provided with: disc-form end plates <NUM> and <NUM> that face each other across a prescribed spacing in the direction of a central axis 1a; a hollow input shaft <NUM> that extends coaxially through central portions of the end plates <NUM>, <NUM>; and a wave gear mechanism <NUM> that is incorporated between the end plates <NUM>, <NUM> in a state of coaxially surrounding the hollow input shaft <NUM>. The hollow input shaft <NUM> is supported by the end plates <NUM>, <NUM>, with ball bearings <NUM>, <NUM> interposed therebetween, in a state that allows rotation. The wave gear mechanism <NUM> is provided with an annular rigid internally toothed gear <NUM>, a top-hat-shaped elastic externally toothed gear <NUM>, an ellipsoidally contoured wave generator <NUM>, and cross-roller bearing <NUM> that supports the internally toothed gear <NUM> and the externally toothed gear <NUM> in a state that allows relative rotation.

The externally toothed gear <NUM> is provided with a flexible cylindrical barrel part 9b on which external teeth 9a are formed, a disc-form diaphragm 9c that spreads radially outward from the end of the cylindrical barrel part 9b, and an annular rigid boss 9d formed integrally with the outer peripheral edge portion of the diaphragm 9c. The opening-end-side portion of the cylindrical barrel part 9b where the external teeth 9a are formed is disposed coaxially inside the internally toothed gear <NUM>. The wave generator <NUM> is coaxially fitted into the inner side of the opening-end-side portion of the cylindrical barrel part 9b. The wave generator <NUM> is provided with a plug part 10a formed integrally with the outer peripheral surface portion of the hollow input shaft <NUM>, and a wave bearing 10b mounted on the ellipsoidal outer peripheral surface of the plug part 10a. The cylindrical barrel part 9b of the externally toothed gear <NUM> is flexed into an ellipsoidal shape by the wave generator <NUM>, and portions of the external teeth 9a positioned at both long-axis ends of the ellipsoidal shape mesh with internal teeth 8a of the internally toothed gear <NUM>.

The boss 9d of the externally toothed gear <NUM> is sandwiched between the end plate <NUM> and an outer race <NUM> of the cross-roller bearing <NUM> from both sides along the central-axis 1a direction, and these three members are securely fastened in this state. The internally toothed gear <NUM> is sandwiched between the end plate <NUM> and an inner race <NUM> of the cross-roller bearing <NUM> from both sides along the central-axis 1a direction, and these three members are securely fastened in this state.

The hollow input shaft <NUM> is a rotation-inputting member linked to a motor, etc. When the hollow input shaft <NUM> rotates, the wave generator <NUM> rotates integrally therewith, and the positions where the externally toothed gear <NUM> meshes with the internally toothed gear <NUM> move in the circumferential direction. The two gears <NUM>, <NUM> undergo relative rotation that corresponds to the difference between the numbers of teeth of the two gears <NUM>, <NUM>. For example, the end plate <NUM> to which the externally toothed gear <NUM> is fastened is configured as a secured-side member, the end plate <NUM> to which the internally toothed gear <NUM> is fastened is configured as a rotation-outputting member, and relative rotation (reduced rotation) is outputted from the end plate <NUM>.

Examples of lubricated portions in the interior of the strain wave gearing <NUM> include the portions where the externally toothed gear <NUM> and the internally toothed gear <NUM> mesh, the portions where the externally toothed gear <NUM> and the wave generator <NUM> contact each other, sliding sections of the cross-roller bearing <NUM> and the wave bearing 10b of the wave generator <NUM>, and sliding sections of the ball bearings <NUM>, <NUM>. Lubricant sealing structures for preventing lubricant enclosed in or applied to these portions from leaking from the interior of the strain wave gearing <NUM> to the exterior are incorporated into the strain wave gearing <NUM>. The strain wave gearing <NUM> according to the present example is provided with a site 1B where a lubricant sealing structure provided with a labyrinth seal <NUM> is incorporated, a site 1C where a lubricant sealing structure provided with a labyrinth seal <NUM> is incorporated, and a site 1D where a lubricant sealing structure provided with a labyrinth seal <NUM> is incorporated.

The lubricant sealing structure provided with the labyrinth seal <NUM> at the site 1B creates a seal between the end plate <NUM> and one shaft end section 4a of the hollow input shaft <NUM>, and prevents lubricant from leaking out from a portion of the ball bearing <NUM> and from a lubricant enclosure portion <NUM> located between the hollow input shaft <NUM> and the externally toothed gear <NUM> between the end plates <NUM>, <NUM>. The lubricant sealing structure provided with the labyrinth seal <NUM> at the site 1C creates a seal between the end plate <NUM> and the other shaft end section 4b of the hollow input shaft <NUM>, and prevents lubricant from leaking out from a portion of the ball bearing <NUM> and from the lubricant enclosure portion <NUM>. The lubricant sealing structure provided with the labyrinth seal <NUM> at the site 1D creates a seal between the outer race <NUM> and the inner race <NUM> of the cross-roller bearing <NUM>, and prevents lubricant from leaking out from a portion of the cross-roller bearing <NUM> and from a lubricant enclosure portion <NUM> formed between the externally toothed gear <NUM>, the cross-roller bearing <NUM>, and the internally toothed gear.

<FIG> is an illustrative diagram of the lubricant sealing structure provided with the labyrinth seal <NUM> that creates a seal between the end plate <NUM> and the shaft end section 4a of the hollow input shaft <NUM>. The one shaft end section 4a of the hollow input shaft <NUM> is rotatably supported in the end plate <NUM> via the ball bearing <NUM>. The shaft end section 4a of the hollow input shaft <NUM> protrudes toward the exterior of the device through a central portion of the end plate <NUM>. A gap that allows communication from the ball-bearing <NUM> side (lubricant-enclosure-portion <NUM> side) to the exterior of the device is formed between the end plate <NUM> and the shaft end section 4a of the hollow input shaft <NUM>. The gap is sealed by the labyrinth seal <NUM>.

An annular member <NUM> is mounted in the gap between the end plate <NUM> and the shaft end section 4a of the hollow input shaft <NUM>. The annular member <NUM> is securely press-fitted onto an outer peripheral surface portion 4c of the shaft end section 4a of the hollow input shaft <NUM>. An annular protrusion 2a that protrudes inward is formed on the inner peripheral surface of the end plate <NUM> so as to face the annular member <NUM> in the axial direction. The labyrinth seal <NUM> is formed between a surface portion 2b on the annular-protrusion 2a side of the end plate <NUM> and a surface portion 22a on the annular-member <NUM> side of the hollow input shaft <NUM>, the surface portion 22a facing the surface portion 2b.

The labyrinth seal <NUM> according to the present example is an axial labyrinth seal and is such that gap portions 21a, 21c, 21e extending in the axial direction and gap portions 21b, 21d extending in the radial direction are alternatingly formed from the upstream side toward the downstream side in the direction in which lubricant leaks. The gap portions 21a to 21e are such that the downstream-side gap portions are narrower than the upstream-side gap portions. Furthermore, the radial-direction gap dimensions of the furthest-upstream gap portion 21a in the labyrinth seal <NUM> are set to values that are less than the diameter of lubricant grains, which are formed into spheroids after being repelled by an oil-repellent surface that shall be described below.

An oil-repellent surface provided with oil repellency with respect to the lubricant is formed on the surface portion 2b on the end-plate <NUM> side where the gap portions 21a to 21e are formed. In <FIG>, a dotted pattern is used to indicate the region on the surface portion 2b where the oil-repellent surface is formed. Oil-repellent surfaces are also formed on the surface portion 22a of the annular member <NUM> that faces the surface portion 2b on the end-plate <NUM> side, and on an outer peripheral surface portion 4d of the hollow input shaft <NUM>. A dotted pattern is also used to indicate the regions on the surface portion 22a and the outer peripheral surface portion 4d where the oil-repellent surfaces are formed. On the shaft end section 4a of the hollow input shaft <NUM>, oil-repellent surfaces (upstream-side oil-repellent surfaces) are formed not only on the outer peripheral surface portion 4d where the gap portion 21a is formed but also on an outer peripheral surface portion 4d1 (upstream-side surface portion) extending from the outer peripheral surface portion 4d to a site at which an outer race of the ball bearing <NUM> is mounted.

The oil-repellent surfaces according to the present example are provided with surface texturing in which fine grooves are formed in a prescribed groove array pattern so as to achieve oil repellency with respect to the enclosed lubricant. The fine grooves are provided with a groove width and a groove depth ranging from several microns to several tens of nanometers, and the groove array pattern is such that the fine grooves are arrayed at spacings ranging from several microns to several tens of nanometers. For example, fine grooves <NUM> that form the oil-repellent surface on the outer peripheral surface portion 4d of the hollow input shaft <NUM> extend in the circumferential direction and are arrayed at fixed intervals in the direction of the central axis 1a, as is schematically shown in <FIG>.

A variety of groove array patterns can be employed as the groove array pattern of the fine grooves <NUM> that form the oil-repellent surface. For example, it is possible to use a groove array pattern in which fine grooves <NUM> extending in a straight line, curve, or undulating form in a direction following the central axis 1a are formed at fixed intervals in the circumferential direction. The fine grooves <NUM> may form a groove array pattern in which fine grooves <NUM> extending in a straight line, curve, or undulating form in a circumferential direction centered on the central axis 1a are formed at fixed intervals in the central-axis 1a direction. It is also possible to employ a groove array pattern configured from fine grooves <NUM> extending in a straight line, curve, or undulating form in a direction that is inclined relative to the direction following the central axis 1a. It is additionally possible to employ a groove array pattern configured from fine grooves <NUM> extending in a spiral at a fixed pitch in the central-axis 1a direction. Furthermore, it is also possible to employ a reticulate groove array pattern in which fine grooves <NUM> extending in the central-axis 1a direction and fine grooves <NUM> extending in the circumferential direction intersect. It is moreover possible to employ a groove array pattern having a configuration in which the aforementioned groove array patterns overlap.

As described above, a seal is created between the hollow input shaft <NUM> and the end plate <NUM> by the labyrinth seal <NUM>, and the lubricant is prevented from leaking to the exterior of the device. Because the gap portions 21a to 21e constituting the labyrinth seal <NUM> are regulated by the oil-repellent surfaces, lubricant that has penetrated the labyrinth seal <NUM> is efficaciously prevented from flowing out toward the exterior of the device. Furthermore, the outer peripheral surface portion 4d1 of the hollow input shaft <NUM> is also configured as an oil-repellent surface (upstream-side oil-repellent surface). Lubricant flowing into the labyrinth seal <NUM> from the ball-bearing <NUM> side is repelled by this oil-repellent surface, and deforms into spheroidal grains just before penetrating the gap portion 21a of the labyrinth seal <NUM>. Because the radial-direction gap dimensions of the gap portion 21a are smaller than the diameter of the spheroidal lubricant grains thus formed, penetration of the lubricant into the gap portion 21a is suppressed. Additionally, because the downstream-side gap portions among the gap portions 21a to 21e constituting the labyrinth seal <NUM> are narrower than the upstream-side gap portions, lubricant that has penetrated the upstream-side gap portions is efficaciously prevented from flowing into the downstream-side gap portions.

In the present example, the gap dimensions at individual radial-direction positions are the same in each of the gap portions 21a, 21c, 21e extending in the axial direction. Additionally, the gap dimensions in the axial direction are the same in each of the gap portions 21b, 21d extending in the radial direction. It is also possible to use gap portions in which the gap dimensions gradually decrease from the interior of the device toward the exterior (i.e., gap portions having a wedge-shaped cross-section).

For example, as shown in <FIG>, the gap portion 21a can be configured such that the radial-direction gap dimensions thereof gradually decrease from the lubricant-enclosure-portion <NUM> side toward the exterior of the device. For example, an inner peripheral surface portion 2c on the surface portion 2b on the end-plate <NUM> side where the gap portion 21a is formed is to be configured as a tapered inner peripheral surface. In this case, at least the minimum gap dimensions of the gap portion 21a are to be set to values that are less than the diameter of the lubricant grains formed into spheroids on the oil-repellent surface. Gap portions in which the gap dimensions gradually decrease toward the downstream side can also be applied in a similar manner to the lubricant sealing structures described below and to lubricant sealing structures in embodiment <NUM> that shall be described later.

<FIG> is an illustrative diagram of the lubricant sealing structure provided with the labyrinth seal <NUM> that creates a seal between the end plate <NUM> and the other shaft end section 4b of the hollow input shaft <NUM>. The shaft end section 4b of the hollow input shaft <NUM> is rotatably supported in the end plate <NUM> via the ball bearing <NUM>. The shaft end section 4b of the hollow input shaft <NUM> protrudes toward the exterior of the device through a central portion of the end plate <NUM>. A gap that allows communication from the ball-bearing <NUM> side (lubricant-enclosure-portion <NUM> side) to the exterior of the device is formed between the end plate <NUM> and the shaft end section 4b of the hollow input shaft <NUM>. The gap is sealed by the labyrinth seal <NUM>.

An annular member <NUM> is mounted in the gap between the end plate <NUM> and the shaft end section 4b of the hollow input shaft <NUM>. The annular member <NUM> is securely press-fitted onto an outer peripheral surface portion 4e of the shaft end section 4b of the hollow input shaft <NUM>. An annular protrusion 3a that protrudes inward is formed on the inner peripheral surface of the end plate <NUM> so as to face the annular member <NUM> in the axial direction. The labyrinth seal <NUM> is formed between a surface portion 3b on the annular-protrusion 3a side of the end plate <NUM> and a surface portion 32a on the annular-member <NUM> side, the surface portion 32a facing the surface portion 3b.

In the labyrinth seal <NUM> according to the present example, gap portions 31a, 31c, 31e extending in the axial direction and gap portions 31b, 31d extending in the radial direction are alternatingly formed from the upstream side toward the downstream side in the direction in which lubricant leaks. The gap portions 31a to 31e are such that the downstream-side gap portions are narrower than the upstream-side gap portions. Furthermore, the radial-direction gap dimensions of the furthest-upstream gap portion 31a in the labyrinth seal <NUM> are set to values that are less than the diameter of lubricant grains, which are formed into spheroids after being repelled by an oil-repellent surface that shall be described below.

The surface portion 3b on the end-plate <NUM> side where the gap portions 31a to 31e are formed is an oil-repellent surface provided with oil repellency with respect to the lubricant. In <FIG>, a dotted pattern is used to indicate the range over which the oil-repellent surface is formed. The surface portion 32a of the annular member <NUM> that faces the surface portion 3b is also configured as an oil-repellent surface. A dotted pattern is also used to indicate the range over which the oil-repellent surface on the surface portion 32a is formed. On the shaft end section 4b of the hollow input shaft <NUM>, an oil-repellent surface (upstream-side surface portion) is also formed on part of an outer peripheral surface portion 4f at which the ball bearing <NUM> is mounted. The oil-repellent surfaces have the same configurations as the oil-repellent surfaces of the labyrinth seal <NUM> described above, and therefore are not described here.

An oil reservoir is formed in the gap portion 31a of the labyrinth seal <NUM>. Specifically, a groove 32b of rectangular cross-section that extends in the circumferential direction is formed in the inner peripheral surface of the annular protrusion 3a of the end plate <NUM>. The oil reservoir, in which the radial-direction gap dimensions are greater than those at other portions in the gap portion 31a, is formed by the groove 32b. The groove 32b is filled with a porous material, such as an oil absorber <NUM> composed of a non-woven fabric. Furthermore, a bottom surface portion and both inner peripheral side surface portions of the groove 32b are subjected to surface treatment and configured as oleophilic surfaces provided with oleophilic properties with respect to the lubricant. In <FIG>, cross-hatching is used to indicate the range over which the oleophilic surfaces are formed.

The lubricant flows out from the ball-bearing <NUM> side in the interior of the device to the gap between the hollow input shaft <NUM> and the end plate <NUM>. The lubricant is prevented from leaking to the exterior of the device by the labyrinth seal <NUM>. Additionally, because the downstream-side gap portions among the gap portions 31a to 31e constituting the labyrinth seal <NUM> are narrower than the upstream-side gap portions, lubricant that has penetrated the upstream-side gap portions is efficaciously prevented from flowing into the downstream-side gap portions. Furthermore, because the gap portions 31a to 31e constituting the labyrinth seal <NUM> are regulated by the oil-repellent surfaces, lubricant that has penetrated the labyrinth seal <NUM> is efficaciously prevented from flowing out toward the exterior of the device. Moreover, lubricant flowing from the ball-bearing <NUM> side toward the labyrinth seal <NUM> is repelled by the oil-repellent surface formed on the outer peripheral surface portion 4f of the shaft end section 4b of the hollow input shaft <NUM>, and deforms into spheroidal grains just before penetrating the gap portion 31a of the labyrinth seal <NUM>. Because the radial-direction gap dimensions of the gap portion 31a are smaller than the diameter of the spheroidal lubricant grains thus formed, the flow of the lubricant into the gap portion 31a is suppressed.

The oil reservoir filled with the oil absorber <NUM> is formed in the gap portion 31a of the labyrinth seal <NUM>. Lubricant that has penetrated the labyrinth seal <NUM> is trapped in the oil reservoir and prevented from flowing out toward the downstream side (toward the exterior of the device). Because the inner peripheral surface portions of the groove forming the oil reservoir are configured as oleophilic surfaces, the lubricant trapped in the oil reservoir is efficaciously prevented from flowing out toward the downstream side by this configuration as well. Thus, the sealing effect produced by the labyrinth seal <NUM>, the effect produced by the oil-repellent surface, and the effect produced by the oil reservoir provided with the oil absorber and the oleophilic surfaces make it possible to reliably prevent the lubricant from leaking to the exterior of the device.

The lubricant sealing structure provided with the labyrinth seal <NUM> that seals a gap between the outer race <NUM> and the inner race <NUM> of the cross-roller bearing <NUM> is described next. <FIG> is an illustrative diagram of the lubricant sealing structure provided with the labyrinth seal <NUM> that creates a seal between the outer race <NUM> and the inner race <NUM>. A gap that allows communication from a raceway groove <NUM> to the exterior of the device is formed between outer race <NUM> and the inner race <NUM>. The gap is sealed by the labyrinth seal <NUM>. The labyrinth seal <NUM> is formed between an inner-peripheral-side surface portion 12a of the outer race <NUM> and an outer-peripheral-side surface portion 13a of the inner race <NUM>, the outer-peripheral-side surface portion 13a facing the inner-peripheral-side surface portion 12a.

In the labyrinth seal <NUM>, gap portions 41a, 41c, 41e extending in the axial direction and gap portions 41b, 41d extending in the radial direction are alternatingly formed along the direction from the lubricant-enclosure-portion side toward the exterior of the device. The gap portions 41a to 41e are such that the downstream-side gap portions are narrower than the upstream-side gap portions.

The inner-peripheral-side surface portion 12a of the outer race <NUM> where the gap portions 41a to 41e are formed is an oil-repellent surface provided with oil repellency with respect to the lubricant. In <FIG>, a dotted pattern is used to indicate the range over which the oil-repellent surface is formed. The outer-peripheral-side surface portion 13a of the inner race <NUM> that faces the inner-peripheral-side surface portion 12a is also configured as an oil-repellent surface. In <FIG>, a dotted pattern is also used to indicate the range over which the oil-repellent surface on the outer-peripheral-side surface portion 13a is formed. The oil-repellent surfaces are configured in the same manner as the oil-repellent surfaces of the labyrinth seal <NUM> described above, and therefore are not described here.

The lubricant flows out from the raceway-groove <NUM> side of the cross-roller bearing <NUM> in the interior of the device to the gap between the outer race <NUM> and the inner race <NUM>. The lubricant is prevented from leaking to the exterior of the device by the labyrinth seal <NUM>. Additionally, because the downstream-side gap portions among the gap portions 41a to 41e constituting the labyrinth seal <NUM> are narrower than the upstream-side gap portions, lubricant that has penetrated the upstream-side gap portions is efficaciously prevented from flowing into the downstream-side gap portions. Furthermore, because the gap portions 41a to 41e constituting the labyrinth seal <NUM> are regulated by the oil-repellent surfaces, lubricant that has penetrated the labyrinth seal <NUM> is efficaciously prevented from flowing out toward the exterior of the device. Thus, the sealing effect produced by the labyrinth seal <NUM> and the oil-repelling effect produced by the oil-repellent surface make it possible to reliably prevent the lubricant from leaking to the exterior of the device via the gap.

<FIG> is a schematic longitudinal cross-sectional view of an actuator provided with the lubricant sealing structure according to the present invention. The actuator <NUM> is a hollow actuator provided with a hollow section extending through the center thereof, and is provided with a motor <NUM> and a strain wave gearing <NUM>. The motor <NUM> is provided with a hollow motor shaft <NUM>, a rotor <NUM> attached to the outer peripheral surface of the hollow motor shaft <NUM>, and a stator <NUM> that coaxially surrounds the rotor <NUM>. The hollow motor shaft <NUM> is rotatably supported, at both ends thereof, by a motor housing <NUM> with ball bearings interposed therebetween (only one ball bearing <NUM> is shown in the drawings).

The motor housing <NUM> is provided with a large-diameter attachment flange <NUM> at the front end thereof. The strain wave gearing <NUM> is coaxially attached to the front surface of the attachment flange <NUM>. The strain wave gearing <NUM> is provided with a rigid internally toothed gear <NUM>, a top-hat-shaped flexible externally toothed gear <NUM>, a wave generator <NUM>, a cross-roller bearing <NUM> that supports the internally toothed gear <NUM> and the externally toothed gear <NUM> in a state that allows relative rotation, and a disc-form output shaft <NUM>.

The wave generator <NUM> is provided with a hollow input shaft <NUM> that is coaxially linked to the hollow motor shaft <NUM>, and an ellipsoidally contoured plug <NUM> being formed integrally with the outer peripheral surface of the hollow input shaft <NUM>. A wave bearing <NUM> is mounted on the ellipsoidal outer peripheral surface of the plug <NUM>. A cylindrical barrel part of the externally toothed gear <NUM>, on which external teeth 122a are formed, is flexed into an ellipsoidal shape by the wave generator <NUM>, and the external teeth partially meshes with internal teeth 121a of the internally toothed gear <NUM>.

An annular boss 122c of the externally toothed gear <NUM> is sandwiched between the attachment flange <NUM> and an outer race 124a of the cross-roller bearing <NUM>, and these three members are securely fastened in this state. The internally toothed gear <NUM> is sandwiched between an inner race 124b of the cross-roller bearing <NUM> and the output shaft <NUM>, and these three members are securely fastened in this state. Output rotation of the motor <NUM> is inputted from the hollow motor shaft <NUM> to the wave generator <NUM>. When the wave generator <NUM> rotates, the internally toothed gear <NUM> rotates at a reduced speed, and reduced-speed rotation is outputted from the output shaft <NUM> linked to the internally toothed gear <NUM> to a load side (not shown).

Examples of lubricated portions in the interior of the strain wave gearing <NUM> include the portions where the externally toothed gear <NUM> and the internally toothed gear <NUM> mesh, the portions where the externally toothed gear <NUM> and the wave generator <NUM> contact each other, and the cross-roller bearing <NUM> and the wave bearing <NUM> of the wave generator <NUM>. A site 2B of a lubricant sealing structure provided with a labyrinth seal <NUM>, a site 2C of a lubricant sealing structure provided with a labyrinth seal <NUM>, and a site 2D of a lubricant sealing structure provided with a labyrinth seal <NUM> are incorporated into the strain wave gearing <NUM> in order to prevent lubricant from leaking from lubricant enclosure portions <NUM>, <NUM> in the interior of the strain wave gearing <NUM> to the exterior of the device or toward the motor <NUM>.

<FIG> is an illustrative diagram of the site of the lubricant sealing structure provided with the labyrinth seal <NUM> that creates a seal between the hollow input shaft <NUM> and the output shaft <NUM>. The space between the hollow input shaft <NUM>, which rotates at high speed, and the output shaft <NUM>, which rotates at a reduced speed, is sealed by the lubricant sealing structure provided with the labyrinth seal <NUM>. An internal space in the externally toothed gear <NUM> in which the wave bearing <NUM> is disposed is a lubricant enclosure portion <NUM> (refer to <FIG>) in which is enclosed lubricant supplied, inter alia, to the wave bearing <NUM> or to sliding portions between the wave bearing <NUM> and the externally toothed gear <NUM>. A gap that passes through from the wave bearing <NUM> positioned toward the interior of the device to the exterior of the device is formed between the hollow input shaft <NUM> and the output shaft <NUM>. The gap is sealed by the labyrinth seal <NUM>. The labyrinth seal <NUM> is formed between an inner-peripheral-side surface portion 125a of the output shaft <NUM> and a shaft-end-side surface portion 126a of the hollow input shaft <NUM>, the shaft-end-side surface portion 126a facing the inner-peripheral-side surface portion 125a.

The labyrinth seal <NUM> is an axial labyrinth seal and is such that gap portions 141a, 141c, 141e extending in the radial direction and gap portions 141b, 141d, 141f extending in the axial direction are alternatingly formed along the direction from the lubricant sealing structure toward the exterior of the device. The gap portions 141a to 141e are such that the downstream-side gap portions are narrower than the upstream-side gap portions. Furthermore, the axial-direction gap dimensions of the furthest-upstream gap portion 141a in the labyrinth seal <NUM> are set to values that are less than the diameter of lubricant grains, which are formed into spheroids after being repelled by an oil-repellent surface that shall be described below.

An oil-repellent surface provided with oil repellency with respect to the lubricant is formed on the inner-peripheral-side surface portion 125a of the output shaft <NUM> where the gap portions 141a to 141f are formed. Additionally, an oil-repellent surface (upstream-side oil-repellent surface) is also formed on an outer peripheral surface portion 125b (upstream-side surface portion) that is connected to the inner side of the device (upstream side in the direction in which lubricant leaks) with respect to the gap portion 141a. Furthermore, an oil-repellent surface is additionally formed on the surface portion 126a of the hollow input shaft <NUM>. In <FIG>, a dotted pattern is applied along surface portions where the oil-repellent surfaces are formed in order to indicate these surface portions. The oil-repellent surfaces are surface portions in which fine grooves are formed in a prescribed groove array pattern in the same manner as with the oil-repellent surfaces on the labyrinth-seal <NUM> side in embodiment <NUM> described above, and therefore are not described here.

The lubricant flows out from the interior of the device to the gap between the hollow input shaft <NUM> and the output shaft <NUM>. Because the lubricant is sealed by the labyrinth seal <NUM>, the lubricant is prevented from leaking to the exterior of the device. Additionally, because the downstream-side gap portions among the gap portions 141a to 141f constituting the labyrinth seal <NUM> are narrower than the upstream-side gap portions, lubricant that has penetrated the upstream-side gap portions is efficaciously prevented from flowing into the downstream-side gap portions. Furthermore, because the gap portions 141a to 141f are regulated by the oil-repellent surfaces, lubricant that has penetrated the labyrinth seal <NUM> is efficaciously prevented from flowing out toward the exterior of the device. Moreover, lubricant flowing into the labyrinth seal <NUM> is repelled by the oil-repellent surface formed on the outer peripheral surface portion 125b of the output shaft <NUM>, and deforms into spheroidal grains just before penetrating the gap portion 141a of the labyrinth seal <NUM>. Because the axial-direction gap dimensions of the gap portion 141a are smaller than the diameter of the spheroidal lubricant grains thus formed, the flow of the lubricant into the gap portion 141a is suppressed.

Thus, the oil-repelling effect produced by the upstream-side oil-repellent surface, the sealing effect produced by the labyrinth seal <NUM>, and the oil-repelling effect produced by the oil-repellent surface that regulates the labyrinth seal <NUM> make it possible to reliably prevent the lubricant from leaking to the exterior of the device.

<FIG> is an illustrative diagram of the site of the lubricant sealing structure provided with the labyrinth seal <NUM> that creates a seal between the strain wave gearing <NUM> and the motor <NUM>. The lubricant is prevented from leaking from the strain-wave-gearing <NUM> side toward the motor <NUM> side by this lubricant sealing structure. The ball bearing <NUM> is mounted between an inner peripheral edge section 117a of the attachment flange <NUM> and a shaft end section 111a of the hollow motor shaft <NUM>, the shaft end section 111a facing the inner peripheral edge section 117a. The distal end of the shaft end section 111a of the hollow motor shaft <NUM> protrudes toward the strain-wave-gearing <NUM> side through the attachment flange <NUM>. The hollow input shaft <NUM> of the strain wave gearing <NUM> is securely linked in a coaxial manner to the shaft end section 111a of the hollow motor shaft <NUM>.

A gap is formed between the inner peripheral edge section 117a of the attachment flange <NUM> and the hollow input shaft <NUM> that faces the inner peripheral edge section 117a. The gap is sealed by the labyrinth seal <NUM>. The labyrinth seal <NUM> is formed between a surface portion 117b of the inner peripheral edge section 117a of the attachment flange and a surface portion 126c of the hollow input shaft <NUM>, the surface portion 126c facing the surface portion 117b from the axial direction.

In the labyrinth seal <NUM>, gap portions 151a, 151c, 151e extending in the radial direction and gap portions 151b, 151d extending in the axial direction are alternatingly formed along the direction from the strain-wave-gearing <NUM> side toward the motor <NUM> side. The gap portions 151a to 151e are such that the downstream-side gap portions are narrower than the upstream-side gap portions. Furthermore, the axial-direction gap dimensions of the furthest-upstream gap portion 151a in the labyrinth seal <NUM> are set to values that are less than the diameter of lubricant grains, which are formed into spheroids after being repelled by an oil-repellent surface that shall be described below.

An oil-repellent surface provided with oil repellency with respect to the lubricant is formed on the surface portion 117b of the inner peripheral edge section 117a of the attachment flange where the gap portions 151a to 151e are formed. Additionally, an oil-repellent surface is also formed on the surface portion 126c on the shaft end of the hollow input shaft <NUM> that faces the surface portion 117b. Furthermore, an oil-repellent surface (upstream-side oil-repellent surface) is additionally formed on an outer peripheral surface portion 126d (upstream-side surface portion) on the inner side of the device with respect to the gap portion 151a. In <FIG>, a dotted pattern is applied along surface portions where the oil-repellent surfaces are formed in order to indicate these surface portions. The oil-repellent surfaces are surface portions in which fine grooves are formed in a prescribed groove array pattern in the same manner as with the oil-repellent surfaces on the labyrinth-seal <NUM> side in embodiment <NUM> described above, and therefore are not described here.

The lubricant flows out from the interior of the device to the gap between the hollow input shaft <NUM> and the inner peripheral edge section 117a of the attachment flange. Because the lubricant is sealed by the labyrinth seal <NUM>, the lubricant is prevented from leaking to the exterior of the device. Additionally, because the downstream-side gap portions among the gap portions 151a to 151e constituting the labyrinth seal <NUM> are narrower than the upstream-side gap portions, lubricant that has penetrated the upstream-side gap portions is efficaciously prevented from flowing into the downstream-side gap portions. Furthermore, because the gap portions 151a to 151e are regulated by the oil-repellent surfaces, lubricant that has penetrated the labyrinth seal <NUM> is efficaciously prevented from flowing out toward the exterior of the device. Moreover, lubricant flowing into the labyrinth seal <NUM> is repelled by the oil-repellent surface formed on the outer peripheral surface portion 126d on the shaft end of the hollow input shaft <NUM>, and deforms into spheroidal grains just before penetrating the gap portion 151a of the labyrinth seal <NUM>. Furthermore, because the axial-direction gap dimensions of the gap portion 151a are smaller than the diameter of the spheroidal lubricant grains thus formed, the flow of the lubricant into the gap portion 151a is suppressed.

Thus, the oil-repelling effect produced by the upstream-side oil-repellent surface of the labyrinth seal <NUM>, the sealing effect produced by the labyrinth seal <NUM>, and the oil-repelling effect produced by the oil-repellent surface that regulates the labyrinth seal <NUM> make it possible to reliably prevent the lubricant from leaking to the exterior of the device.

<FIG> is an illustrative diagram of the site of the lubricant sealing structure between the outer race 124a and the inner race 124b of the cross-roller bearing <NUM>. The site 2D of the lubricant sealing structure provided with the labyrinth seal <NUM> is disposed at a portion of the cross-roller bearing <NUM> that supports the externally toothed gear <NUM> and the internally toothed gear <NUM> in a state that allows relative rotation. Specifically, the lubricant sealing structure is disposed in order to seal a gap portion between the outer race 124a and the inner race 124b of the cross-roller bearing <NUM>. This lubricant sealing structure is substantially identical to the lubricant sealing structure in which the labyrinth seal <NUM> is used, which is shown in <FIG> within embodiment <NUM>.

Claim 1:
A lubricant sealing structure which prevents lubricant from leaking out, from an interior of a device provided with a first member (<NUM>) and a second member (<NUM>) that rotate relative to one another about a central axis (1a), through a gap portion (21a-21e, 31a-31e, 41a-41e, 141a-141f) between the first and second members (<NUM>), the lubricant sealing structure comprising:
a labyrinth seal (<NUM>; <NUM>; <NUM>) for sealing the gap portion (21a-21e, 31a-31e, 41a-41e, 141a-141f), the labyrinth seal (<NUM>; <NUM>; <NUM>) being formed between a first surface portion on a first-member side and a second surface portion on a second-member side, the first and second surface portions facing each other;
oil-repellent surfaces provided with oil repellency with respect to the lubricant, the oil-repellent surfaces being formed on each of the first and second surface portions; and
an upstream-side oil-repellent surface provided with oil repellency, the upstream-side oil-repellent surface being formed on at least one of a first upstream-side surface portion and a second upstream-side surface portion, the first upstream-side surface portion being connected to the first surface portion and located on an upstream side in a leaking direction in which the lubricant leaks, and the second upstream-side surface portion being connected to the second surface portion and located on an upstream side in the leaking direction,
wherein each of the oil-repellent surfaces and the upstream-side oil-repellent surface is provided with surface texturing in which fine grooves are formed in a prescribed groove array pattern;
the fine grooves are provided with a groove width and a groove depth ranging from several microns to several tens of nanometers; and
the groove array pattern is such that the fine grooves are arrayed at spacings ranging from several microns to several tens of nanometers
characterized in that
the labyrinth seal (<NUM>; <NUM>; <NUM>) is provided with a first gap portion (21a-21e, 31a-31e, 41a-41e, 141a-141f) having a first gap dimension; and,
the first gap portion (21a-21e, 31a-31e, 41a-41e, 141a-141f) is formed with an oil reservoir having a second gap dimension that is larger than the first gap dimension, the oil reservoir being positioned at an intermediate section of the first gap portion (21a-21e, 31a-31e, 41a-41e, 141a-141f) in the leaking direction.