TRANSMISSION

A transmission according to the disclosure includes: a case; a carrier housed inside the case and configured to rotate relative to the case; and a seal mechanism provided between the case and the carrier. The seal mechanism includes a seal lip portion having a lip end for sealing, the lip end being in linear contact with an outer circumferential surface of the carrier along a circumferential direction of the carrier.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims the benefit of priority from Japanese Patent Application Serial No. 2022-154776 (filed on Sep. 28, 2022), the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to a transmission.

BACKGROUND

A speed reducer and a transmission includes a seal mechanism provided between a case and a carrier that rotate relative to each other (e.g., Japanese Patent Application Publication No. 2015-083329).

In recent years, the load on a transmission has been higher due to the increased rotation speed and higher temperatures resulting from high-speed operation. This causes an insufficient sealing performance between the case and the carrier, which was sufficient in the past.

SUMMARY

One object of the present disclosure is to provide a transmission having an improved sealing performance.

(1) A transmission according to one aspect of the disclosure includes: a case; a carrier housed inside the case and configured to rotate relative to the case; and a seal mechanism provided between the case and the carrier. The seal mechanism includes a seal lip portion having a lip end for sealing, the lip end being in linear contact with an outer circumferential surface of the carrier along a circumferential direction of the carrier.

With the configuration as described in (1) above, the fluid feed rate accomplished by the seal mechanism can be increased even when the temperature of the transmission rises during high circumferential speed rotation. Thus, the sealing performance can be improved. When high-speed rotation is not reached, the temperature rise in the transmission is inhibited to such a degree as not to affect the sealing performance. Therefore, there is no need to use the seal mechanism of the disclosure to improve the sealing performance. The fluid feed rate refers to the amount of fluid fed by the seal mechanism from the atmospheric side outside the seal mechanism to the sealed side inside the seal mechanism while the carrier is rotating. In practice, the fluid feed rate is replaced with (calculated as) the amount of fluid flowing out from the inside of the transmission toward the outside measured when the sealing mechanism is installed to face the opposite direction. This measured value indicates the degree of sealing performance. When the seal mechanism is installed in the proper forward direction, the air is fed from the outside of the transmission to the inside. Therefore, a larger value of the feed rate means a smaller amount of fluid outflow (i.e., fluid leakage) from the inside of the transmission to the outside. This inhibits the oil or other lubricant from leaking out from the inside of the transmission toward the outside. In other words, the sealing performance in the transmission can be improved. The improvement of the sealing performance is less likely to be affected by temperature rise in the transmission. Therefore, it is possible to maintain the sealing performance regardless of temperature changes in the transmission caused by high speed rotation.

(2) The seal mechanism may include a suction-increasing portion, the suction-increasing portion being configured to increase, in accordance with a circumferential speed of the carrier, a feed rate of fluid fed from an outside of the seal lip portion toward an inside of the seal lip portion through an interstice between the lip end and the outer circumferential surface of the carrier.

(3) The carrier may rotate relative to the case such that a circumferential speed of the outer circumferential surface of the carrier is 70 mm/sec or higher.

(4) The suction-increasing portion may have a plurality of ribs extending from the lip end toward an outside of the seal lip portion along an axial direction of the carrier, so as to be inclined relative to the axial direction.

(5) The suction-increasing portion may include a plurality of rib regions arranged along a circumferential direction of the lip end. In the plurality of rib regions, the plurality of ribs are disposed in parallel to each other along the circumferential direction of the lip end. The “rib regions” refers to the regions formed in the circumferential direction of the lip end by the ends of the ribs contacting the lip end. Even if the ends of the ribs do not contact the lip end, the “rib regions” refers to the regions formed by the extended ribs contacting the lip end. In other words, the extent of the rib regions is defined by their lengths along the circumferential direction of the lip end.

(6) An axial dimension W of the plurality of rib regions along an axial direction of the carrier may satisfy a following condition: W≥{(WR2−Wr2)/2}/tan φ where WR2 is an outer diameter of the outer circumferential surface of the carrier, Wr2 is an inner diameter of the seal lip portion, and φ is a lip angle of the seal lip portion. The axial dimension of the rib regions refers to the length of the ribs along the axial direction of the carrier.

(7) Prior to assembly of the seal mechanism, the plurality of ribs protruding from the lip end along a radial direction of the lip end may have a height of 0.01 mm to 0.10 mm, and the plurality of ribs may have a width of 0.05 mm to 0.30 mm along the lip end.

(8) At a position where the seal mechanism is installed, a dimensional difference between an inner diameter of the case and an outer diameter of the seal mechanism before assembly may be larger than 5% and smaller than 20% of an original width, or a radial dimension of the seal mechanism before assembly. The dimensional difference refers to the tightening margin between the case and the sealing mechanism.

(9) For any two of the plurality of rib regions adjacent to each other in the circumferential direction of the lip end, the plurality of ribs may be formed to be inclined in opposite directions. The opposite direction of inclination of the ribs means that the angles between the ribs and the lip end are values with inverted signs, positive or negative.

(10) The plurality of rib regions may be spaced intermittently along the circumferential direction of the lip end. The suction-increasing portion includes inter-rib regions disposed between any two of the plurality of rib regions adjacent to each other in the circumferential direction of the lip end, the inter-rib regions having no ribs. The “inter-rib region” refers to the region interposed, in the circumferential direction of the lip end, between the rib located at the end of a rib region and the rib located at the end of another rib region adjacent thereto. Even if the ends of the ribs do not contact the lip end, the “inter-rib region” likewise refers to the region interposed, in the circumferential direction of the lip end, between the positions at which the extended ribs at the ends of the rib regions contact the lip end. In other words, the extent of the inter-rib regions is defined by their lengths along the circumferential direction of the lip end.

(11) A total of circumferential lengths of the plurality of rib regions may be within a range of 30% to 80% of an entire length of the lip end along the circumferential direction.

(12) In the suction-increasing portion, the plurality of ribs may have an inclination angle of 20° to 30°. The inclination angle of the ribs refers to the angle between the ribs and the lip end.

(13) In the plurality of rib regions, an interval between any two of the plurality of ribs adjacent to each other along the circumferential direction of the lip end may be within a range of 0.1 mm to 5 mm. The interval between the ribs refers to the distance between the ribs adjacent to each other along the circumferential direction of the lip end.

(14) The suction-increasing portion may be set such that the feed rate of fluid is 0.2 mL/h to 30 mL/h.

(15) A transmission according to another aspect of the disclosure includes: a case; an internal gear provided in the case and having internal teeth; an oscillating gear having external teeth meshing with the internal teeth of the internal gear, the oscillating gear being configured to be oscillatorily rotated; a crankshaft having an eccentric portion that rotatably supports the oscillating gear, the crankshaft being configured to transmit a rotational force of a drive source to the oscillating gear; a carrier configured to receive the rotational force from the oscillating gear and rotate relative to the case; and a seal mechanism provided between the case and the carrier. The seal mechanism includes: a seal lip portion having a lip end for sealing, the lip end being in linear contact with an outer circumferential surface of the carrier along a circumferential direction of the carrier; and a suction-increasing portion configured to increase a feed rate of fluid fed from an outside of the seal lip portion toward an inside of the seal lip portion through an interstice between the lip end and the outer circumferential surface of the carrier. The suction-increasing portion includes: a plurality of ribs extending from the lip end toward an outside of the seal lip portion along an axial direction of the carrier and extending at an angle to the axial direction; and forward rib regions, inter-rib regions, and reverse rib regions arranged along a circumferential direction of the lip end. In the forward rib regions and the reverse rib regions, the plurality of ribs are arranged in parallel to each other along the circumferential direction of the lip end. For the forward rib regions and the reverse rib regions, the plurality of ribs are formed to be inclined in opposite directions. The suction-increasing portion rotates relative to the case such that a circumferential speed of the outer circumferential surface of the carrier is 70 mm/sec or higher. The suction-increasing portion is set such that the feed rate of fluid is 30 to 300 times as high as in a case where the suction-increasing portion is not provided.

With this configuration, the fluid feed rate accomplished by the seal mechanism can be increased even when the temperature of the transmission rises during high-speed rotation at a circumferential speed of 70 mm/sec or higher, resulting in an improved sealing performance. Thus, it is possible to prevent leakage of liquid from the inside of the transmission to the outside.

The present disclosure can provide a transmission having an improved sealing performance between a case and a shaft even for an increased rotation speed.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

The following describes a transmission relating to a first embodiment of the disclosure with reference to the accompanying drawings.FIG.1is a schematic view showing the transmission relating to the embodiment.FIG.2is a schematic view of a seal mechanism shown inFIG.1. This seal mechanism, which is not yet assembled to the transmission, is viewed from the axial direction.FIG.3shows a partial cross-sectional view of the seal mechanism shown inFIG.1. This seal mechanism is not yet assembled to the transmission.FIG.4is a schematic view showing the sealing in the seal mechanism shown inFIG.1.

As shown inFIGS.1to4, the transmission100relating to the embodiment includes a cylindrical case20, a carrier30, and a seal mechanism50. In the transmission100, the case20and the carrier30are configured to rotate relative to each other with respect to the rotation axis F0. The case20and the carrier30are assembled together for relative rotation via bearings26.

In this embodiment, the direction along the rotation axis F0 may be referred to simply as the axial direction. Furthermore, in plan view along the axial direction, the directions intersecting the rotation axis F0 are referred to as the radial directions, and the direction circling around the rotation axis F0 is referred to as the circumferential direction. Furthermore, of the radial directions, the direction toward the rotation axis F0 is referred to as the radially inward direction, and the direction away from the rotation axis F0 is referred to as the radially outward direction.

The transmission100changes the speed of the rotational driving force input from the input section (not shown), and outputs the rotational driving force from one of the case20or the carrier30. The other of the case20or the carrier30serves as a fixed portion. The components for fixing the fixed portion to other external components are not illustrated or described for this embodiment.

The internal space V of the transmission100is filled with a lubricant such as an oil. The internal space V is sealed by the seal mechanism50. The seal mechanism50is disposed between the inner circumferential surface20aof the case20and the outer circumferential surface30aof the carrier30. The inner circumferential surface20aand the outer circumferential surface30aare opposed to each other in the radial direction of the case20. The inner circumferential surface20aand the outer circumferential surface30ahave coaxial circular shape around the rotation axis F0. The inner circumferential surface20ais disposed radially outside the outer circumferential surface30a.

In this embodiment, the inner circumferential surface20aof the case20and the outer circumferential surface30aof the carrier30are flat in the vicinity of the seal mechanism50. Therefore, the inner circumferential surface20aof the case20and the outer circumferential surface30aof the carrier30may have various radial dimensions, axial dimensions, or surface shapes, for example, in accordance with the configuration of the other components of the transmission100excluding the seal mechanism50.

The seal mechanism50seals between the internal space V of the transmission100and the external space A. Sealing the internal space V of the transmission100means that no fluid, or lubricant such as oil, leaks from the internal space V of the transmission100toward the external space A. In order to keep the internal space V sealed such that no fluid leaks toward the external space A, the seal mechanism50is capable of sucking fluid from the external space A toward the internal space V.

The seal mechanism50is what is called an oil seal. The seal mechanism50includes a metal core52, a seal member53, a garter spring (spring)58, and a suction-increasing portion56. The seal member53is made of rubber or other elastic material and adhered to the core52by vulcanization adhesion. The core52has an annular shape formed by pressing or otherwise processing a steel plate such as SPCC, for example. The core52includes a first cylindrical portion52aand a first annular portion52b. The first cylindrical portion52ahas a cylindrical shape and extends in parallel with the inner circumferential surface20aof the case20, and the first annular portion52bextends radially inward from one end of the first cylindrical portion52a. The first annular portion52bis formed on the end of the first cylindrical portion52apositioned on the external space A side in the axial direction. Thus, the core52has an L-shaped cross section formed of the first cylindrical portion52aand the first annular portion52b.

The seal member53includes a base body portion (fitting portion)54, a seal lip portion55that serves as a main lip, and an auxiliary lip portion (dust lip portion)57. The base body portion54is bonded to the outer circumferential surface of the core52so that it covers the entirety of the core52. Specifically, the base body portion54is bonded along the outer circumferential surface of the first cylindrical portion52aof the core52, and extends round the end surface of the first cylindrical portion52apositioned on the inner space V side, and then is bonded along the inner circumferential surface of the first cylindrical portion52a. Furthermore, the base body portion54is bonded along the side surface of the first annular portion52bpositioned on the external space A side and connected to the outer circumferential surface of the first cylindrical portion52aof the core52, and extends round the inner circumferential end of the first annular portion52bpositioned on the carrier30side, and then is bonded along the side surface of the first annular portion52bpositioned on the internal space V side. The base body portion54bonded to this side surface extends to the inner circumferential surface of the first cylindrical portion52a. The seal lip portion55is integrated with the base body portion54so as to extend from the inner circumferential end of the first annular portion52bof the core52toward the internal space V side. The auxiliary lip portion57is integrated with the base body portion54so as to extend from the inner circumferential end of the first annular portion52bof the core52toward the external space A side.

The base body portion54includes a second cylindrical portion54a, a second annular portion54b, a third cylindrical portion54c, and a third annular portion54d. The second cylindrical portion54acovers the inner circumferential surface of the first cylindrical portion52aof the core52. The second annular portion54bcovers the side surface of the first annular portion52bof the core52that is positioned on the internal space V side. The third cylindrical portion54ccovers the outer circumferential surface of the first cylindrical portion52aof the core52. The third annular portion54dcovers the side surface of the first annular portion52bof the core52that is positioned on the external space A side. In the base body portion54configured in this manner, the space enclosed by the second cylindrical portion54a, the second annular portion54b, and the seal lip portion55forms an annular recess59that is open toward the internal space V. The core52is press-fitted between the case20and the carrier30with the third cylindrical portion54cof the base body portion54in contact with the inner circumferential surface20aof the case20. The entire seal mechanism50is thus fixed to the inner circumferential surface20aof the case20.

The auxiliary lip portion57has its proximal end at the inner circumferential end of the first annular portion52bof the core52and extends toward the external space A side in the radially inward direction. The auxiliary lip portion57is thinner toward its distal end and slidably contacts the outer circumferential surface30aof the carrier30. The auxiliary lip portion57is positioned at a distance from the seal lip portion55along the axial direction toward the external space A side. The auxiliary lip portion57serves as a dust lip for previously preventing dust likely to enter from the external space A toward the internal space V side from reaching the seal lip portion55.

The seal lip portion55has an annular shape extending along the circumferential direction. The seal lip portion55has its proximal end at the inner circumferential end of the first annular portion52bof the core52and extends along the axial direction from the external space A side toward the internal space V side.

The seal lip portion55is a main lip for sealing between the internal space V and the external space A. The seal lip portion55has a lip end (linear seal position)51in linear contact along the circumferential direction with the outer circumferential surface30aof the carrier30. The seal lip portion55seals between the interior space V and the exterior space A using the lip end51. The lip end51serves as a linear main lip that slidingly contacts the outer circumferential surface30aof the carrier30. The inner circumferential portion of the seal lip portion55is shaped such that the portions on the axially opposite sides of the lip end51are sloped so as to be separated from the outer circumferential surface30aof the carrier30toward the axial directions away from the lip end51.

Specifically, the inner circumferential portion of the seal lip portion55has an inside sloping surface (internal space-side sloping surface)511and an outside sloping surface (external space-side sloping surface)512. The inside sloping surface511is axially positioned on the internal space V side of the lip end51and faces the internal space V. The inside sloping surface511is sloped from the lip end51to increase its diameter gradually. The outside sloping surface512is axially positioned on the external space A side of the lip end51and faces the external space A. The outside sloping surface512is sloped from the lip end51to increase its diameter gradually. Since the auxiliary lip portion57is positioned on the external space A side of the outside sloping surface512, the outside sloping surface512does not face the external space A in a strict sense. However, since the auxiliary lip portion57is not essential and may not be formed, the outside sloping surface512is defined as facing the external space A.

Since the inside sloping surface511and the outside sloping surface512are positioned on opposite sides of the lip end51, the inner circumferential portion of the seal lip portion55has a mountain-shaped cross section with the lip end51as the apex. InFIG.4, the seal lip portion55is pressed against the outer circumferential surface30aof the carrier30, and thus the lip end51contacts the outer circumferential surface30awith a predetermined width (seal width).

A garter spring (spring)58is attached to the outer circumferential portion of the seal lip portion55to tighten (press) the seal lip portion55radially inward to enhance sealing. The seal lip portion55seals between the internal space V and the external space A by slidingly contacting the outer circumferential surface30aof the carrier30. Thus, the seal lip portion55prevents the oil or other fluid filled in the internal space V from leaking out through the space between the carrier30and the case20into the external space A.

The suction-increasing portion56increases the feed rate of fluid fed from the external space A, which is positioned axially outside of the lip end51, into the internal space V, which is positioned axially inside of the lip end51. The suction-increasing portion56is set so that when the circumferential speed of the outer circumferential surface30aof the carrier30relative to the seal lip portion55is 70 mm/sec to 5000 mm/sec, the feed rate of fluid is 30 to 300 times as high as in the case where the suction-increasing portion is not provided. More preferably, the suction-increasing portion56is set so that when the circumferential speed of the outer circumferential surface30aof the carrier30relative to the seal lip portion55is 70 mm/sec to 1000 mm/sec, the feed rate of fluid is 30 to 200 times as high as in the case where the suction-increasing portion is not provided. The feed rate of fluid will be described later.

As shown inFIGS.2to4, the suction-increasing portion56has a plurality of ribs56aformed on the outside sloping surface512. The plurality of ribs56aextend along the axial direction from the lip end51toward the external space A side and are inclined with respect to the rotation axis F0. As will be described later, the presence of the plurality of ribs56aincreases the feed rate of fluid fed from the external space A, which is positioned outside of the lip end51, into the internal space V, which is positioned inside of the lip end51.

The suction-increasing portion56has a plurality of rib regions56rspaced along the circumferential direction of the lip end51. Each of the plurality of rib regions56rhas a plurality of ribs56ainclined with respect to the rotation axis F0 and arranged parallel to each other. Each of the plurality of rib regions56rextends along the circumferential direction of the lip end51. As will be described later, the presence of the rib regions56rincreases the feed rate of fluid fed from the external space A, which is positioned outside of the lip end51, into the internal space V, which is positioned inside of the lip end51.

The plurality of rib regions56rof the suction-increasing portion56include forward rib regions56r1and reverse rib regions56r2. The forward rib regions56r1and the reverse rib regions56r2are arranged alternately along the circumferential direction of the lip end51so as to be adjacent to each other. The plurality of ribs56aare inclined in opposite directions in the forward rib regions56r1and the reverse rib regions56r2. As will be described later, the presence of the forward rib regions56r1and the reverse rib regions56r2increases the feed rate of fluid fed from the external space A, which is positioned outside of the lip end51, into the internal space V, which is positioned inside of the lip end51, irrespective of whether the rotation of the carrier30relative to the case20is in the forward or reverse direction.

As mentioned above, the plurality of rib regions56rare spaced intermittently along the circumferential direction of the lip end51. As a result, the suction-increasing portion56has inter-rib regions56npositioned between the rib regions56radjacent to each other in the circumferential direction. The presence of the inter-rib regions56nallows the forward rib regions56r1and the reverse rib regions56r2to be formed with a sufficient length on the lip end51.

An inter-rib region56nis defined by the lengthwise position along the lip end51from a connection point in one rib region56rto a connection point in another rib region56radjacent to the one rib region56r. These rib regions56rhave the ribs56aconnected to the lip end51at regular intervals. At the connection point in the one rib region56r, the rib56aforming the end of the one rib region56ris connected to the lip end51, and at the connection point in the other rib region56r, the rib56aforming the end of the other rib region56ris connected to the lip end51. For a forward rib region56r1and a reverse rib region56r2adjacent to each other in the circumferential direction, the inter-rib region56nis defined as the region between the connection point at which the rib56apositioned at the end of the forward rib region56r1is connected to the lip end51and the connection point at which the rib56apositioned at the end of the reverse rib region56r2is connected to the lip end51.

In other words, the inter-rib region56nis defined by a length along the lip end51between the connection point at which the rib56apositioned at the end of one rib region56ris connected to the lip end51and the connection point at which the rib56apositioned at the end of another rib region56radjacent to the one rib region56ris connected to the lip end51. The length of the inter-rib region56nis larger than the intervals between the plurality of ribs56ain each rib region56r. The rib regions56rand the inter-rib regions56nare defined by the circumferential length corresponding to the connection points at which the ribs56aare connected to the lip end51, regardless of the inclination angle of the ribs56aor the like. Therefore, the rib regions56rand the inter-rib regions56nare defined only by their circumferential length, although they are called regions (seeFIG.3).

The suction-increasing portion56is formed so that the total of the circumferential lengths of all rib regions56ris within the range of 30% to 80% of the entire length of the lip end51along the circumferential direction. In other words, the suction-increasing portion56is formed such that the total of the circumferential lengths of all inter-rib regions56nis within the range of 70% to 20% of the entire length of the lip end51along the circumferential direction. The suction-increasing portion56formed so that the total of the circumferential lengths of the rib regions56ris within the range of 30% to 80% of the entire circumferential length of the lip end51can increase the feed rate of fluid fed from the external space A, which is positioned outside of the lip end51, into the internal space V, which is positioned inside of the lip end51.

In the suction-increasing portion56, the angle θ of the ribs56a, which are inclined with respect to the rotation axis F0, is set at 20° to 30°. In other words, on the outside sloping surface512, the angle θ between the lip end51and the ribs56ais set at 20° to 30°. The suction-increasing portion56formed so that the angle θ between the lip end51and the ribs56ais within the range of 20° to 30° can increase the feed rate of fluid fed from the external space A, which is positioned outside of the lip end51, into the internal space V, which is positioned inside of the lip end51.

In the rib regions56r, the intervals between the ribs56aadjacent to each other along the circumferential direction are within the range of 0.1 mm to 5 mm. In other words, the intervals along the lip end51between the connection points at which the ribs56aadjacent to each other along the circumferential direction are connected to the lip end51are within the range of 0.1 mm to 5 mm. The suction-increasing portion56formed so that the intervals along the lip end51between the plurality of ribs56aare within the range of 0.1 mm to 5 mm can increase the feed rate of fluid fed from the external space A, which is positioned outside of the lip end51, into the internal space V, which is positioned inside of the lip end51.

The suction-increasing portion56is formed so that the dimension W of the rib region56ralong the axial direction satisfies the following equation:

where WR2 is the outer diameter of the outer circumferential surface30aof the carrier30(seeFIG.1), Wr2 is the inner diameter of the seal lip portion55of the seal mechanism50(seeFIG.2), φ is the lip angle of the seal lip portion55(seeFIG.4).

As shown inFIG.4, the lip angle φ is the angle between the outside sloping surface512and the outer circumferential surface30aof the carrier30. The inner diameter Wr2 and the outer diameter of the seal lip portion55are the dimensions in the seal mechanism50yet to be assembled.

Thus, in the inter-rib region56n, which is the boundary between the forward rib region56r1and the reverse rib region56r2, the ends of the ribs56athat are positioned on the opposite side in the axial direction to the lip end51are connected to each other. In other words, in the inter-rib region56n, which is the boundary between the forward rib region56r1and the reverse rib region56r2, a triangular shape is formed by connection between the ends of the adjacent rib regions56a. This increases the feed rate of fluid fed from the external space A, which is positioned outside of the lip end51, into the internal space V, which is positioned inside of the lip end51.

Prior to assembly of the seal mechanism50, the ribs56ahave a height of 0.01 mm to 0.10 mm along the radial direction. The height of the ribs56acorresponds to the protruding dimension of the ribs56aprotruding from the lip end51toward the inside in the radial direction. Furthermore, prior to assembly of the seal mechanism50, the ribs56ahave a width of 0.05 mm to 0.30 mm along the circumferential direction. The width of the ribs56acorresponds to the length of the ribs56aextending along the lip end51in the circumferential direction. The ribs56aformed to have a height along the radial direction and a width along the circumferential direction within the above ranges increases the feed rate of fluid fed from the external space A, which is positioned outside of the lip end51, into the internal space V, which is positioned inside of the lip end51.

Each of the plurality of ribs56amay be formed to have the same height along the radial direction and the same width along the circumferential direction. Alternatively, each of the plurality of ribs56amay be formed to have different dimensions, as long as the height along the radial direction and the width along the circumferential direction are within the above ranges. In the pre-assembly state (free state) of the seal mechanism50, the inner diameter of the lip end51is the same as or smaller than the outer diameter of the outer circumferential surface30aof the carrier30.

When the inner diameter of the lip end51is the same as the outer diameter of the outer circumferential surface30aof the carrier30, it follows, for example, that these diameters are equal to each other without considering the height of the ribs56a. Also, when the carrier30is inserted inside the seal lip portion55, and the lip end51is in sliding contact with the outer circumferential surface30aof the carrier30(only the ribs56aare squeezed) while being elastically deformed, the inner diameter of the lip end51and the outer diameter of the outer circumferential surface30aof the carrier30are the same. The inner diameter of the lip end51and the outer diameter of the outer circumferential surface30acan be set appropriately to have a predetermined dimensional difference from the state where only the ribs56aare squeezed. When the inner diameter of the lip end51and the outer diameter of the outer circumferential surface30ahave a predetermined dimensional difference, the seal lip portion55is elastically deformed toward the outside in the radial direction. This allows the sealing performance and the feed rate of fluid to be set as desired.

In the transmission100according to this embodiment, the seal width WR (seeFIG.1) along the radial direction sealed by the seal mechanism50installed between the inner circumferential surface20aof the case20and the outer circumferential surface30aof the carrier30is smaller than the original seal width Wr (seeFIG.2) of the seal mechanism50before assembly (seeFIG.2). In other words, the seal width WR of the seal mechanism50after assembly is smaller than the original seal width Wr (the difference between the inner and outer diameters of the seal mechanism50) of the seal mechanism50before assembly.

Furthermore, in the transmission100according to this embodiment, the dimensional difference between the inner diameter WR1 (seeFIG.1) of the inner circumferential surface20aof the case20and the outer diameter Wr1 (seeFIG.2) of the seal mechanism50before assembly, at the position where the seal mechanism50is installed, is larger than 5% and smaller than 20% of the original seal width (original width) Wr (seeFIG.2) of the seal mechanism50before assembly. This allows the seal mechanism50to be squeezed with a sufficient tightening margin, thus achieving sufficient sealing performance and a sufficient fluid feed rate.

The foregoing described the settings of the structure of the ribs56a, the positional relationship between the rib regions56rand the inter-rib regions56n, the positional relationship between the forward rib regions56r1and the reverse rib regions56r2, and the dimension W of the rib regions56ralong the axial direction, in the suction-increasing portion56according to this embodiment. These settings allow the fluid feed rate to be 0.2 mL/h to 30 mL/h. This increases the feed rate of fluid fed from the external space A, which is positioned outside of the lip end51, into the internal space V, which is positioned inside of the lip end51, thus achieving a sufficient sealing performance.

As shown inFIG.4, when the carrier30is inserted into the inner circumference of the seal lip portion55, the end of the seal lip portion55positioned in the internal space V moves elastically toward the outside in the radial direction. This causes the end positioned in the internal space V and the lip end51to deform elastically so as to slightly expand in diameter.FIG.4shows that the carrier30is inserted into the inner circumference of the seal lip portion55, so that the lip end51elastically deforms to slidingly contact the outer circumferential surface30aof the carrier30.

In this embodiment, it was described that only one seal mechanism50is provided between the inner circumferential surface20aof the case20and the outer circumferential surface30aof the carrier30, but this example is not limitative. For example, two seal mechanisms50may be arranged in the axial direction between the inner circumferential surface20aof the case20and the outer circumferential surface30aof the carrier30. In this case, an annular space extending in the circumferential direction can be formed by the recess59of the first-stage seal mechanism50, the third annular portion54dof the second-stage seal mechanism50, and the outer circumferential surface30aof the carrier30.

The following describes the increase of the fluid feed rate.

FIG.5is a schematic view for explaining the fluid feed rate in the seal mechanism50. In the following description, the effect of the auxiliary lip portion57is not considered.

As described above, the seal mechanism50is an oil seal with ribs (thread ribs)56aformed on the lip end51of the seal lip portion55, and the ribs56aexert a fluid pumping effect. This serves to improve the sealing performance of the transmission100with respect to oil or other sealing fluids. In the case where the carrier30, which is the mating sliding member, rotates in both forward and reverse directions around the rotation axis F0, the ribs (bidirectional thread ribs)56aare formed on the outside sloping surface512of the seal lip portion55to extend from the lip end51, as shown inFIG.3.

The suction-increasing portion56includes the forward rib regions56r1that exert a sealing action by pumping when the carrier30rotates in the forward direction and the reverse rib regions56r2that exert a sealing action by pumping when the carrier30rotates in the reverse direction. In the forward rib regions56r1and the reverse rib regions56r2, the directions of the plurality of ribs56arranged circumferentially are opposite. In both the forward rib regions56r1and the reverse rib regions56r2, the ribs56ahave a triangular cross section with a pointed tip (apex).

Specifically, the ribs56aare inclined in opposite directions in the forward rib regions56r1and the reverse rib regions56r2. Furthermore, the pointed tips of the ribs56aextend to the lip end51, which corresponds to the tip apex of the seal lip portion55, and also intersects the lip end51.

To evaluate the lubrication characteristics and the sealing characteristics of the seal lip portion55of the seal mechanism50, which is an oil seal, friction characteristics were verified. In the verification, the seal mechanism50was mounted on a test machine that simulates the transmission100. The test machine simulating the transmission100includes a carrier that has the same diameter as the outer circumferential surface30aof the carrier30and the same surface conditions as the outer circumferential surface30a. Furthermore, the test machine simulating the transmission100includes a case that has the same diameter as the inner circumferential surface20aof the case20and the same surface conditions as the inner circumferential surface20a. The surface conditions are the surface characteristics that affect the friction characteristics, such as macroscopic and microscopic unevenness, or the directions of protrusions.

The relationship between the dimensionless characteristic number G, which is determined by the shape and the service conditions of the seal mechanism50(hereinafter also referred to as the oil seal50), and the friction coefficient fat that time is expressed as the Formula (1) that follows.

The symbols f, Φ, and G in Formula (1) indicate the following.f=friction coefficientΦ=constant determined by oil film conditionsG=dimensionless characteristic number (=μ*u*b/Pr)
Furthermore, the symbols μ, u, b, and Pr indicate the following.μ=viscosity of sealing fluid (N·sec/cm2[kgf·sec/cm2])u=circumferential speed (cm/sec)b=contact width of seal lip portion55in the axial direction (cm)Pr=tension force of the seal lip portion55(N [kgf])

A graph with the friction coefficient f on the vertical axis and the dimensionless characteristic number G on the horizontal axis shows that the friction coefficient f is constant up to a given range of the dimensionless characteristic number G, but beyond that range, the friction coefficient f increases monotonically. The phenomenon in the region of the dimensionless characteristic number G that forms a positive gradient is described in lubrication theory as a characteristic of fluid lubrication. In such lubrication conditions, similar to the characteristics in bearings, the friction characteristics of the oil seal50are governed by the viscosity of the fluid and the sliding speed, and an oil film is present in the sliding parts. In other words, the two surfaces sliding between the oil seal50and the outer circumferential surface30aof the carrier30are in sliding motion in a fluid-lubricated condition macroscopically separated by the oil film, and the friction force of the oil seal50is maintained low.

The sealing mechanism of the oil seal50results from the movement of oil on the two sliding surfaces, i.e., the movement of oil within the sliding contact surfaces of the oil seal50. In other words, the sealing performance of the oil seal50results from the movement of oil within the lip end51, which is in linear contact with the outer circumferential surface30aof the carrier30with a predetermined width in the axial direction. The movement of oil is circulating from the external space A side to the internal space V side and from the internal space V side to the external space A side within the contact area of the lip end51. In the contact area of the lip end51, the oil circulation provides excellent lubrication on the sliding contact surfaces and prevents the progression of wear of the oil seal50. Furthermore, oil will not leak from the internal space V to the external space A. This is because the circulation of oil causes fluid, either oil or air, to be fed from the external space A side toward the internal space V side.

The mechanism of sealing by feeding fluid toward the internal space V is determined by the uneven shapes and unevenness distributions of the lip end51and the outer circumferential surface30ain contact with the lip end51, and by the pressure distribution generated between the lip end51and the outer circumferential surface30a. In other words, a high fluid feed rate in the oil seal50increases the sealing performance, while a low fluid feed rate relatively reduces the sealing performance.

It is difficult to directly measure the fluid feed rate in the oil seal50. Therefore, as shown inFIG.5, oil is filled into the internal space V in the reverse installation state, where the oil seal50is installed so that the seal lip portion55is positioned on the external space A side. Then, in this reverse installation state, the flow rate of oil flowing out from the internal space V side to the external space A side is measured. This method provides the fluid feed rate in the normal installation state (seeFIG.4) in which the oil seal50is installed so that the seal lip portion55is positioned on the internal space V side.

FIG.4shows the oil sealing of the internal space V in the normal installation state of the oil seal50. InFIG.4, the arrow Ain indicates the state in which the air is fed from the external space A to the internal space V.FIG.5shows oil leakage from the internal space V in the reverse installation state of the oil seal50. InFIG.5, the arrow Oout indicates the oil leaking from the internal space V toward the external space A.

In the reverse installation state shown inFIG.5, the amount of oil leaking to the external space A side is measured per unit time, so as to quantitatively determine the amount of oil corresponding to the fluid feed rate in the normal installation state shown inFIG.4. In other words, the amount of oil leaking to the external space A side in the reverse installation state is measured to quantitatively determine the sealing performance of the oil seal50.

The lip end51in the seal lip portion55is an important factor in forming the unevenness of the sliding surface of the oil seal50. The contact pressure distribution at the lip end51is identical in the circumferential direction, and the following description compares to an oil seal50formed with different heights of fine unevenness at the lip end51.

As the number of fine irregularities at the lip end51is larger, the amount of oil that leaks out in the reverse installation state is larger. Therefore, in the normal installation state, the ability to feed fluid from the external space A toward the internal space V is higher. Alternatively, the fluid feed rate can be varied by changing the macroscopic state of contact of the lip end51with the outer circumferential surface30aand the contact pressure distribution of the lip end51contacting the outer circumferential surface30a.

Thus, the two factors governing the sealing mechanism of the oil seal50, the lubrication characteristics and the sealing mechanism, are controlled by two factors: the material forming the seal lip portion55and the shape near the lip end51. From a microscopic point of view, it is necessary to set the material characteristics in consideration of the average film thickness control in the suction and discharge regions of the circulating flow in the sliding surface where the lip end51and the outer circumferential surface30aare in contact with each other.

To control these, the rib regions56rare formed on the outside sloping surface512of the seal lip portion55in this embodiment. In order to control the sealing characteristics, it is necessary to consider the operating conditions of the transmission100. In other words, only when the transmission100operates in operating conditions in which the circumferential speed of the outer circumferential surface30aof the carrier30is within a predetermined range, it is possible to perform the average film thickness control in the suction and discharge regions of the circulating flow in the sliding surface described above.

Therefore, in this embodiment, the suction-increasing portion56is set so that when the circumferential speed of the outer circumferential surface30aof the carrier30relative to the seal lip portion55is 70 mm/sec to 5000 mm/sec, the feed rate of fluid is 30 to 300 times as high as in the case where the suction-increasing portion56is not provided.

When the circumferential speed of the outer circumferential surface30aof the carrier30relative to the seal lip portion55is 70 mm/sec or higher, the transmission100is likely to rotate at a high speed, depending on the size of the transmission100. When the transmission100rotates at a high speed, the surface temperature rises. In this case, the seal width WR may change, and the sealing performance of the seal mechanism50may decrease. The Inventors are aware that the operational stability of the transmission100cannot be ensured when the surface temperature of the transmission100is 60° C. or higher.

In this respect, this embodiment has the suction-increasing portion56provided in the seal mechanism50, so that sealing performance can be maintained even when the seal mechanism50has a higher surface temperature. In other words, according to the transmission100of this embodiment, the effect of temperature rise caused by high-speed rotation can be canceled, and a high sealing performance can be maintained.

When the circumferential speed is 70 mm/sec or lower, the surface temperature of the transmission100will not exceed 60° C. However, in a conventional seal mechanism, the sealing performance would be reduced, and oil or other lubricant could leak out of the transmission100. By contrast, the oil seal50having a suction-increasing portion56as in the present embodiment can maintain sufficient sealing performance.

In the transmission100of this embodiment, the fluid feed rate accomplished by the seal mechanism50can be increased even when the temperature rises during high-speed rotation at the circumferential speed of 70 mm/sec or higher. This inhibits the oil or other lubricant from leaking out of the internal space V of the transmission100toward the external space A. In other words, the sealing performance in the transmission100can be improved. This improvement of the sealing performance is less likely to be affected by temperature rise. Therefore, it is possible to maintain the sealing performance regardless of temperature changes in the transmission100caused by high speed rotation or other conditions.

Furthermore, the presence of the ribs56aimproves the lip rigidity of the seal lip portion55. Therefore, the seal resistance can be increased against attacks by sludge on the seal lip portion55and the outer circumferential surface30aof the carrier30. In addition, the smaller contact area of the seal lip portion55to the outer circumferential surface30aof the carrier30reduces heat generation.

Second Embodiment

The following describes a transmission relating to a second embodiment of the disclosure with reference to the accompanying drawings.FIG.6is a sectional view showing the transmission (speed reducer) relating to this embodiment along a rotation axis.FIG.7is a sectional view viewed along the arrows VII-VII inFIG.6.

As shown inFIGS.6and7, the transmission (speed reducer)100in this embodiment functions as an eccentric oscillation speed reducer. The transmission100includes a case202, a carrier204, and a seal mechanism50. The case202corresponds to the case20in the first embodiment. The carrier204corresponds to the carrier30in the first embodiment. The case202includes a case body202cand a case flange202f.

In this embodiment, the direction along the rotation axis F0 of the case body202cmay be referred to simply as the axial direction. Furthermore, in plan view along the axial direction, the directions intersecting the rotation axis F0 are referred to as the radial directions, and the direction circling around the rotation axis F0 is referred to as the circumferential direction. Furthermore, of the radial directions, the direction toward the rotation axis F0 is referred to as the radially inward direction, and the direction away from the rotation axis F0 is referred to as the radially outward direction. The term “input side” refers to the internal space V side on which the transmission100is connected to the drive source, and the term “output side” refers to the external space A side on which the output of the transmission100is received. The transmission100transmits a driving force while changing the rotation speed at a predetermined rotation-speed ratio between the drive source and the output side member. In this embodiment, one of the case202and the carrier204serves as an output portion, and the other serves as a fixed portion. In other words, one of the case202and carrier204, which rotate relative to each other, is connected to a fixed member for fixing the transmission100, and the other is connected to an output side member that rotates.

The case body (outer tube)202chas a tubular shape centered on the rotation axis F0. The case body202c, which is an example of a first tube, is open toward the external space A. The opening of the case body202chouses the carrier204so as to be rotatable. The case flange202fis formed to extend radially outward from the case body202cand is connected to the fixed member or the output side member. The case flange202fis formed integrally with the portion of the case body202cthat is located on the input side. The transmission100has, on the output side thereof, a plurality of (for example, three) transmission gears220and input gears220a, and these gears are exposed.

The transmission100includes the case body202cof the case202, the carrier204as an example of a rotating member, an input shaft208, a plurality of (e.g., three) crankshafts210A, a first oscillating gear214, a second oscillating gear216, and the plurality of transmission gears220.

In the transmission100, as the input shaft208corresponding to the input gears220ais rotated, the crankshafts210A are resultantly rotated. With such arrangement, as the eccentric portions210aand210bof the crankshafts210A rotate, the oscillating gears214and216can resultantly oscillatorily rotate. In this way, the transmission100can reduce rotation input thereto and output the reduced rotation. The input gears220aor the transmission gears220constitute the input section.

The case202forms the outer surface of the transmission100and has a substantially cylindrical shape. A plurality of pin grooves202bare formed in the inner circumferential surface of the case202. Each pin groove202bextends in the axial direction of the case202and has a semicircular cross-sectional shape along the plane orthogonal to the axial direction. The pin grooves202bare arranged at equal intervals in the circumferential direction on the inner circumferential surface of the case body202c. The inner circumferential surface202aof the case202is located on the input side of the inner circumferential surface20aalong the axial direction, and the seal mechanism50described in the first embodiment is installed on the inner circumferential surface20a. In the illustrated example, the inner circumferential surface202aand the inner circumferential surface20ahave different diameters, but this example is not limitative.

The case202has a plurality of internal tooth pins203. The internal tooth pins203are attached in the pin grooves220b. More specifically, each internal tooth pin203is fitted in the corresponding pin groove202band retained therein such that it extends in the axial direction of the case202. In this manner, the plurality of internal tooth pins203are arranged at regular intervals along the circumference of the case202. The internal tooth pins203mesh with first external teeth214aof the first oscillating gear214and second external teeth216aof the second oscillating gear216.

The carrier204is aligned coaxially with the case202and is housed within the case202. The carrier204is rotatable relative to the case202about the same axis. More specifically, the carrier204is disposed on the radially inner side of the case202. The carrier204is supported by a pair of main bearings206(26), which are spaced away from each other in the axial direction, so as to be rotatable relative to the case202.

The carrier204includes a base portion and an end plate (flange)204b. The base portion includes a base plate204aand a plurality of (for example, three) shaft portions204c. The base plate204ais disposed on the output side within the case202. The base plate204ahas a through hole204dformed at the center thereof. A plurality of (for example, three) crankshaft mounting holes204e(hereinafter referred to simply as “mounting holes204e”) are arranged at equal intervals in the circumferential direction around the through hole204d.

The end plate204bis spaced away from the base plate204ain the axial direction and positioned on the input side within the case202. The end plate204bhas a through hole204fat the center thereof. A plurality of (for example, three) crankshaft mounting holes204g(hereinafter referred to simply as “mounting holes204g”) are arranged at equal intervals in the circumferential direction around the through hole204f. The plurality of mounting holes204gare positioned to be opposed to the plurality of mounting holes204ein the axial direction. Inside the case202, a closed space is defined by the inner surfaces of the end plate204band the base plate204aand the inner circumferential surface202aof the case202.

The three shaft portions204care integrated with the base plate204aand extend linearly from the base plate204atoward the end plate204b. The three shaft portions204care arranged at regular intervals in the circumferential direction (seeFIG.7). The shaft portions204care fastened to the end plate204bwith bolts204h(seeFIG.6). In this manner, the base plate204a, the shaft portions204c, and the end plate204btogether constitute a single integral piece.

The input shaft208serves as an input section for receiving a driving force input thereto from a driving motor (not shown). The input shaft208runs through the through hole204fformed in the end plate204band the through hole204dformed in the base plate204a. The input shaft208is disposed such that its axis is aligned with the rotation axis F0, the axis of the case202and the carrier204, and the input shaft208is rotatable about the rotation axis F0. An input gear208ais provided on the outer circumferential surface of the distal end of the input shaft208.

The three crankshafts210A are arranged around the input shaft208within the case202(seeFIG.7). The three crankshafts210A are arranged at regular intervals in the circumferential direction of the input shaft208. The crankshafts210A are each supported by a pair of crank bearings212aand212bso as to be rotatable relative to the carrier204(seeFIG.6). Specifically, the first crank bearing212ais mounted in the corresponding mounting hole204eformed in the base plate204a. On the other hand, the second crank bearing212bis mounted in the corresponding mounting hole204gformed in the end plate204b. The crankshafts210A are rotatably supported by the base plate204aand the end plate204bvia the first crank bearing212aand the second crank bearing212b.

Each crankshaft210A includes a shaft body212c, and a first eccentric portion210aand a second eccentric portion210bformed integrally with the shaft body212c. The first and second eccentric portions210a,210bare arranged in the axial direction between the first crank bearing212aand the second crank bearing212b. The first and second eccentric portions210aand210bare each shaped like a circular cylinder. The first and second eccentric portions210aand210bproject radially outward from the shaft body212cwhile being eccentrically arranged relative to the central axis of the shaft body212c. The first and second eccentric portions210aand210bare eccentric from the axis of the shaft body212cby a predetermined amount of eccentricity. The first and second eccentric portions210aand210bhave a phase difference of a predetermined angle from each other.

The portion of the crankshaft210A located on the output side of the mounting hole204eis provided with a mating portion210c. The transmission gear220is mounted to the mating portion210c. The transmission100relating to the present embodiment is not limited to the example case shown inFIGS.6and7. For example, in the transmission100, the crankshafts210A may be oriented oppositely in the axial direction. This is the opposite arrangement, in which the mating portions210care located on the input side of the mounting holes204g.

The first oscillating gear214is located in the closed space within the case202and is attached to the first eccentric portion210aof each crankshaft210A via a first roller bearing218a. As each crankshaft210A rotates, the first eccentric portion210aeccentrically rotates. This eccentric rotation results in the first oscillating gear214oscillatorily rotating while meshing with the internal tooth pins203.

The first oscillating gear214has an outer diameter slightly smaller than the inner diameter of the case202. The first oscillating gear214has first external teeth214a, a central through hole214b, a plurality of (for example, three) first eccentric portion insertion holes214c, and a plurality of (for example, three) shaft portion insertion holes214d. The first external teeth214aare shaped like smooth and continuous waves along the entire circumference of the oscillating gear214.

The central through hole214bis formed at the center of the first oscillating gear214. The central through hole214breceives therein the input shaft208with a clearance therebetween.

The three first eccentric portion insertion holes214care formed in the first oscillating gear214and arranged at regular intervals in the circumferential direction around the central through hole214b. The first eccentric portions210aof the crankshafts210A are inserted in the first eccentric portion insertion holes214c, via the first rolling bearings218ainterposed therebetween.

The three shaft portion insertion holes214dare formed in the first oscillating gear214and arranged at regular intervals in the circumferential direction around the central through hole214b. The shaft portion insertion holes214dare positioned between the first eccentric portion insertion holes214cnext to each other in the circumferential direction. The shaft portion insertion holes214dreceive therein the corresponding shaft portions204cwith a clearance therebetween.

The second oscillating gear216is located in the closed space within the case202and is attached to the second eccentric portion210bof each crankshaft210A via a second roller bearing218b. The first and second oscillating gears214and216are arranged in the axial direction so as to correspond to the first and second eccentric portions210aand210b. As each crankshaft210A rotates, the second eccentric portion210beccentrically rotates. This eccentric rotation results in the second oscillating gear216oscillatorily rotating while meshing with the internal tooth pins203.

The second oscillating gear216has an outer diameter slightly smaller than the inner diameter of the case202. The second oscillating gear216has second external teeth216a, a central through hole216b, a plurality of (for example, three) second eccentric portion insertion holes216c, and a plurality of (for example, three) shaft portion insertion holes216d. These are designed in the same manner as the first external teeth214a, the central through hole214b, the first eccentric portion insertion holes214c, and the shaft portion insertion holes214dof the first oscillating gear214. The second eccentric portions210bof the crankshafts210A are inserted in the second eccentric portion insertion holes216c, via the second rolling bearings218binterposed therebetween.

Each transmission gear220transmits the rotation of the input gear208ato the corresponding one of the crankshafts210A. Each transmission gear220is fitted onto the mating portion210cof the corresponding crankshaft210A. Each transmission gear220is rotatable integrally with the corresponding crankshaft210A around the same axis as the corresponding crankshaft210A. Each transmission gear220has the input gear220ameshing with the input gear208a.

The transmission100is a gear device configured to transmit a driving force while changing the rotation speed at a predetermined rotation-speed ratio between the drive source (first member) and the rotating member (second member). The transmission100includes an eccentric portion (210a,210b), an oscillating gear (214,216) having insertion holes (214c,216c) through which the eccentric portion is inserted and teeth (214a,216a), a first tube (case202) mountable on one of the first and second members, and a second tube (carrier204) mountable on the other of the first and second members. The first tube (202) has internal tooth pins (203) meshing with the teeth of the oscillating gears. The second tube is positioned inside the first tube in the radial direction while holding the oscillating gears. The first and second tubes are concentrically arranged and rotatable relative to each other when acted upon by oscillation of the oscillating gears caused by rotation of the eccentric portions in the reduction mechanism portion.

The transmission100relating to the embodiment includes the seal mechanism50disposed between the case202and the carrier204. The seal mechanism50is disposed between the case202and the carrier204at a position on the external space A side. Therefore, the portion of the annular gap formed between the case202and the carrier204positioned on the external space A side is sealed by the seal mechanism50. The seal mechanism50seals between the internal space V and the external space A.

The seal mechanism50is disposed between the inner circumferential surface20aof the case202and the outer circumferential surface30aof the carrier204. In this embodiment, the seal mechanism50is exposed to the external space A, but this configuration is not limitative. The seal mechanism50is disposed on the external space A side of the main bearings206. Therefore, in the gap between the case202and the carrier204, members are arranged from the external space A side toward the internal space V side along the rotation axis F0 in the order of the seal mechanism50, the main bearing206, the pin grooves202band the internal tooth pins203, and the main bearing206.

The seal mechanism50has the same configuration as described for the first embodiment. Accordingly, the seal mechanism50of this embodiment has the core52, the garter spring58, and the seal member53, as shown inFIGS.3and6. The seal member53includes the base body portion54, the seal lip portion55, and the auxiliary lip portion57. The seal mechanism50has the suction-increasing portion56formed on the outside sloping surface512located on the external space A side of the lip end51of the seal lip portion55. The suction-increasing portion56has the forward rib regions56r1, the reverse rib regions56r2, and the inter-rib regions56n. Each of the rib regions56rhas a plurality of ribs56aspaced parallel to each other. Furthermore, appropriate settings are provided for the length and arrangement of the rib regions56rrelative to the lip end51, the angle θ of the ribs56a, the height of the ribs56aalong the radial direction, the seal width of the ribs56aalong the circumferential direction, and the tightening margin of the seal mechanism50.

In this embodiment, the suction-increasing portion56is set so that when the circumferential speed of the outer circumferential surface30aof the carrier204relative to the seal lip portion55is 70 mm/sec to 5000 mm/sec, the feed rate of fluid is 30 to 300 times as high as in the case where the suction-increasing portion56is not provided. More preferably, the suction-increasing portion56is set so that when the circumferential speed of the outer circumferential surface30aof the carrier204relative to the seal lip portion55is 70 mm/sec to 1000 mm/sec, the feed rate of fluid is 30 to 200 times as high as in the case where the suction-increasing portion56is not provided.

In the transmission100, the rotation speed in the relative rotation between the case202and the carrier204and the circumferential speed of the outer circumferential surface30aof the carrier204are correlated. By way of an example, consider a case in which the case202serves as the fixed side and the carrier204serves as the output side that rotates relative to the case202. In this case, the following is an example of the relationship between the rotation speed of the carrier204and the circumferential speed of the outer circumferential surface30aof the carrier204.

In transmission100, the fluid feed rate was measured using a seal mechanism not provided with the suction-increasing portion56. As a result, it was confirmed that the fluid feed rate was almost unchanged, irrespective of the rotation speed of the carrier204. In contrast, the fluid feed rate [mL/h] was measured using the seal mechanism50with the suction-increasing portion56. As a result, it was confirmed that as the rotation speed of the carrier204increases, the fluid feed rate in the seal mechanism50with the suction-increasing portion56also increases. Furthermore, it was confirmed that the increase of the fluid feed rate in the seal mechanism50with the suction-increasing portion56is exponential with respect to the increase of the rotation speed of the carrier204, and that the fluid feed rate increases drastically with the increasing rotation speed. The fluid feed rate was within the range of 0.2 mL/h to 30 mL/h.

Here, in the transmission100, the values of the ratio of the fluid feed rate measured using the seal mechanism50with the suction-increasing portion56to the fluid feed rate measured using the seal mechanism not provided with the suction-increasing portion56were determined, so as to correspond to the rotation speed and the circumferential speed. These values of the ratio are shown below.

In addition, the temperature [° C.] of the surface of the transmission100and the presence of oil leaking into the external space A were examined under these conditions. The results showed that the temperature may be higher than 60° C. at circumferential speeds of 70 [mm/sec] or higher. It was also confirmed that no oil was leaking in any of the cases using the seal mechanism50with the suction-increasing portion56.

In the transmission100of this embodiment, the fluid feed rate accomplished by the seal mechanism50can be increased even when the temperature rises during high-speed rotation at the circumferential speed of 70 mm/sec or higher. This inhibits the oil or other lubricant from leaking out of the internal space V of the transmission100toward the external space A. In other words, the sealing performance in the transmission100can be improved. This improvement of the sealing performance is less likely to be affected by temperature rise. Therefore, it is possible to maintain the sealing performance regardless of temperature changes in the transmission100caused by high speed rotation or other conditions.

Accordingly, this embodiment produces the same advantageous effects as the first embodiment. Furthermore, the presence of the ribs56aimproves the lip rigidity of the seal lip portion55. Therefore, the seal resistance can be increased against attacks by sludge on the seal lip portion55and the outer circumferential surface30aof the carrier204. In addition, the smaller contact area of the seal lip portion55to the outer circumferential surface30aof the carrier204reduces heat generation.

Third Embodiment

The following describes a transmission relating to a third embodiment of the disclosure with reference to the accompanying drawings.FIG.8is a sectional view showing the transmission relating to the embodiment.

As shown inFIG.8, the transmission (speed reducer)100of the embodiment operates as a center-crank speed reducer. The transmission100includes a case (outer tube)3310, an outer wall3740, a carrier3400C, a crankshaft assembly3500C, a gear unit3600C, two main bearings3710C (26) and3720C (26), an input gear3730C, and the seal mechanism50.

The output axis3C1corresponds to a central axis (rotation axis F0) of the two main bearings3710C,3720C and the input gear3730C. The outer tube3310and the carrier3400C are relatively rotatable about the rotation axis F0.

The driving force generated by a motor (not shown) or any other drive source (not shown) is inputted to the crankshaft assembly3500C through the input gear3730C extending along the output axis3C1. The driving force inputted to the crankshaft assembly3500C is transmitted to the gear unit3600C disposed in an internal space surrounded by the outer tube3310and the carrier3400C. The output axis3C1is the output axis from the motor and is also the input axis to the transmission100. The two main bearings3710C,3720C are disposed in an annular space formed between the outer tube3310and the carrier3400C. The outer tube3310or the carrier3400C is rotatable about the output axis3C1by the driving force transmitted to the gear unit3600C.

The carrier3400C includes a base portion (first carrier)3410C and an end plate (second carrier)3420C. The carrier3400C as a whole is shaped like a cylinder. The end plate3420C has a substantially disc-like shape. The outer circumferential surface of the end plate3420C is partially surrounded by a second cylindrical portion3312on the radially outer side. The main bearing3720C is fitted into a ring-shaped gap between the second cylindrical portion3312and the circumferential surface of the end plate3420C. The outer circumferential surface of the end plate3420C is formed such that the rollers of the main bearing3720C can roll directly on the end plate3420C.

The base portion3410C includes a base plate3411C and a plurality of shaft portions3412C. The outer circumferential surface of the base plate3411C is partially surrounded by a third cylindrical portion3313on the radially outer side. The main bearing3710C may be fitted into a ring-shaped gap between the third cylindrical portion3313and the outer circumferential surface of the base plate3411C. The outer circumferential surface of the base plate3411C is formed such that the rollers of the main bearing3710C can roll directly on the outer circumferential surface of the base plate3411C. The base plate3411C is spaced apart from the end plate3420C along the output axis3C1. The base plate3411C is coaxial with the end plate3420C. Thus, the output axis3C1corresponds to the central axis of the base plate3411C and the end plate3420C.

The base plate3411C includes an inner surface3415C and an outer surface3416C on the opposite side to the inner surface3415C. The inner surface3415C faces the gear unit3600C in the axial direction. The inner surface3415C and the outer surface3416C are located to extend along an imaginary plane (not shown) orthogonal to the output axis3C1. A central through hole3417C is formed through the base plate3411C. The central through hole3417C extends between the inner surface3415C and the outer surface3416C along the output axis3C1. The output axis3C1corresponds to the central axis of the central through hole3417C.

The end plate3420C includes an inner surface3421C and an outer surface3422C on the opposite side to the inner surface3421C. The inner surface3421C faces the gear unit3600C in the axial direction. The inner surface3421C and the outer surface3422C are located to extend along an imaginary plane (not shown) orthogonal to the output axis3C1. A central through hole3423C is formed through the end plate3420C. The central through hole3423C extends between the inner surface3421C and the outer surface3422C along the output axis3C1. The output axis3C1corresponds to the central axis of the central through hole3423C.

Each of the plurality of shaft portions3412C extends from the inner surface3415C of the base plate3411C toward the inner surface3421C of the end plate3420C. The end plate3420C has a plurality of second junction surfaces3421B connected to first junction surfaces3412B located at the distal ends of the plurality of shaft portions3412C. The end plate3420C may be connected to the end surfaces of the plurality of shaft portion3412C by a fastening portion3050, which is constituted by an internally threaded portion3056and a bolt3051having an externally thread portion3053, a positioning pin and the like. The first junction surfaces3412B of the shaft portions3412C and the second junction surfaces3421B of the end plate3420C are connected by bolts3051so as to be pressed against each other.

The gear unit3600C is disposed between the inner surface3415C of the base plate3411C and the inner surface3421C of the end plate3420C. The shaft portions3412C extend through the gear unit3600C and are connected to the end plate3420C. The gear unit3600C includes two oscillating gears3610C,3620C. The oscillating gear3610C is disposed between the end plate3420C and the oscillating gear3620C. The oscillating gear3620C is disposed between the base plate3411C and the oscillating gear3610C.

The oscillating gears3610C,3620C may be formed based on a common design drawing. Each of the oscillating gears3610C,3620C may be a trochoidal gear or a cycloidal gear. The principle of this embodiment is not limited to a particular type of gears used as the oscillating gears3610C,3620C.

Each of the oscillating gears3610C,3620C is meshed with a plurality of internal tooth pins3320. When the crankshaft assembly3500C rotates about the output axis3C1, the oscillating gears3610C,3620C perform circling movement (namely, oscillatory rotation) within a case3310while being meshed with the internal tooth pins3320. During this movement, respective centers of the oscillating gears3610C,3620C circle about the output axis3C1. Relative rotation between the outer tube3310and the carrier3400C is caused by the oscillatory rotation of the oscillating gears3610C,3620C.

Each of the oscillating gears3610C,3620C has a through hole formed at the respective center. The crankshaft assembly3500C is fitted into the through holes formed in the oscillating gears3610C,3620C. Each of the oscillating gears3610C,3620C has a plurality of through holes formed so as to correspond to the plurality of shaft portions3412C disposed around the output axis3C1. The plurality of shaft portions3412C are inserted into these through holes, respectively. These through holes have such a size that no interference occurs between the plurality of shaft portions3412C and the oscillating gears3610C,3620C.

The crankshaft assembly3500C includes a crankshaft3520C, two journal bearings3531C,3532C, and two crank bearings3541C,3542C. The crankshaft3520C includes a first journal3521C, a second journal3522C, a first eccentric portion3523C, and a second eccentric portion3524C. The first journal3521C extends along the output axis3C1and is inserted into the central through hole3423C of the end plate3420C. The second journal3522C, which is disposed on the opposite side to the first journal3521C, extends along the output axis3C1and is inserted into the central through hole3417C of the base plate3411C.

The journal bearing3531C is fitted into an annular space between the first journal3521C and the inner wall of the central through hole3423C formed in the end plate3420C. As a result, the first journal3521C is joined to the end plate3420C. The journal bearing3532C is fitted into an annular space between the second journal3522C and the inner wall of the central through hole3417C formed in the base plate3411C. As a result, the second journal3522C is joined to the base plate3411C. In this manner, the carrier3400C can support the crankshaft assembly3500C.

The first eccentric portion3523C is positioned between the first journal3521C and the second eccentric portion3524C. The second eccentric portion3524C is positioned between the second journal3522C and the first eccentric portion3523C. The crank bearing3541C is fitted into the through hole formed at the center of the oscillating gear3610C and is joined to the first eccentric portion3523C. As a result, the oscillating gear3610C is mounted to the first eccentric portion3523C. The crank bearing3542C is fitted into the through hole formed at the center of the oscillating gear3620C and is joined to the second eccentric portion3524C. As a result, the oscillating gear3620C is mounted to the second eccentric portion3524C.

The first journal3521C is coaxial with the second journal3522C and rotates about the output axis3C1. Each of the first and second eccentric portions3523C and3524C is formed in a columnar shape and positioned eccentrically from the output axis3C1. The first eccentric portion3523C and the second eccentric portion3524C eccentrically rotate with respect to the output axis3C1and impart oscillatory rotation to the oscillating gears3610C,3620C, respectively. In this embodiment, one of the first and second eccentric portions3523C and3524C may be an example of the eccentric portion.

When the outer tube3310is fixed, since the oscillating gears3610C and3620C are meshed with the plurality of internal tooth pins3320of the outer tube3310, the oscillatory rotation of the oscillating gears3610C and3620C is converted into circling motion of the crankshaft3520C and rotation of the base plate3411C about the output axis3C1. The end plate3420C and the base plate3411C are joined to the first journal3521C and the second journal3522C, respectively, and thus circling motion of the crankshaft3520C is converted into rotational motion of the end plate3420C and the base plate3411C about the output axis3C1via the shaft portions3412C. The phase difference in the circling movement between the oscillating gears3610C,3620C is determined by a difference in eccentricity direction between the first eccentric portion3523C and the second eccentric portion3524C.

When the carrier3400C is fixed, since the oscillating gears3610C and3620C are meshed with the plurality of internal tooth pins3320of the outer tube3310, oscillatory rotation of the oscillating gears3610C and3620C is converted into rotational motion of the outer tube3310about the output axis3C1. The input gear3730C extends along the output axis3C1through a support wall3742. The input gear3730C extends through a space3750in the internal space V surrounded by the outer wall3740. The crankshaft3520C has a through hole3525extending along the output axis3C1. The distal end portion of the input gear3730C is inserted into the through hole3525.

A key groove3732is formed at the distal end portion of the input gear3730C. Another key groove3526is formed in the inner wall surface of the through hole3525formed in the crankshaft3520C. The key grooves3732,3526extend substantially parallel to the output axis3C1. A key3733is inserted into the key grooves3732,3526. As a result, the input gear3730C is joined to the crankshaft3520C. When the input gear3730C rotates about the output axis3C1, the crankshaft3520C rotates about the output axis3C1. As a result, oscillatory rotation of the oscillating gears3610C,3620C occurs.

The central through hole3417C formed through the base plate3411C includes a first hollow portion3491and a second hollow portion3492. The first hollow portion3491and the second hollow portion3492both have a circular cross section. The first hollow portion3491is smaller in cross section than the second hollow portion3492. The second journal3522C and the journal bearing3532C are disposed in the first hollow portion3491. The outer surface3416C of the base plate3411C is pressed against a mating member (not shown), irrespective of whether the mating member is the fixed side or the output side.

A flange portion3314is formed all around the periphery of the case3310and is connected to the outer wall3740. The outer wall3741has a flat end3741a. The end3741aof the outer wall3741has internally threaded portions3250, which serve as mounting-fastening portions150. The flange portion3314has through holes3315that are located on the outer circumference of the case3310and extend through the flange portion3314along the rotation axis F0. The through holes3315are arranged at intervals in the circumferential direction.

The through holes3315serve as fastening holes penetrated by the bolts3151that fasten the transmission100and the outer wall3740, which is a part of the component that is either the fixed side or the output side. The through holes3315are penetrated by the bolts3151, which serve as fastening members. The internally threaded portions3250of the outer wall3740and the bolts3151constitute the mounting-fastening portions.

The internal space V that serves as a space surrounded by the outer wall3740and the case3310is sealed by the seal mechanism50. The transmission100relating to the embodiment includes the seal mechanism50disposed between the case3310and the carrier3400C at a position closest to the external space A. In other words, the portion of the annular gap between the case3310and the carrier3400C positioned on the external space A side is sealed by the seal mechanism50. The seal mechanism50seals between the internal space V and the external space A.

The seal mechanism50is disposed between the inner circumferential surface20aof the case3310and the outer circumferential surface30aof the carrier3400C. The seal mechanism50is disposed to be exposed to the external space A, but this configuration is not limitative. The seal mechanism50is disposed on the external space A side of the main bearing3710C. In the gap between the case3310and the carrier3400C, members are arranged from the external space A side toward the internal space V side along the rotation axis F0 in the order of the seal mechanism50, the main bearing3710C, the internal tooth pins3320, and the main bearing3720C.

The seal mechanism50has the same configuration as described for the first embodiment. Accordingly, the seal mechanism50of this embodiment has the core52, the garter spring58, and the seal member53, as shown inFIGS.3and8. The seal member53includes the base body portion54, the seal lip portion55, and the auxiliary lip portion57. The seal mechanism50has the suction-increasing portion56formed on the outside sloping surface512located on the external space A side of the lip end51of the seal lip portion55. The suction-increasing portion56has the forward rib regions56r1, the reverse rib regions56r2, and the inter-rib regions56n. Each of the rib regions56rhas a plurality of ribs56aspaced parallel to each other. Furthermore, appropriate settings are provided for the length and arrangement of the rib regions56rrelative to the lip end51, the angle θ of the ribs56a, the height of the ribs56ain the radial direction, the seal width of the ribs56ain the circumferential direction, and the tightening margin of the seal mechanism50.

In this embodiment, the suction-increasing portion56is set so that when the circumferential speed of the outer circumferential surface30aof the carrier3400C relative to the seal lip portion55is 70 mm/sec to 5000 mm/sec, the feed rate of fluid is 30 to 300 times as high as in the case where the suction-increasing portion56is not provided. More preferably, the suction-increasing portion56is set so that when the circumferential speed of the outer circumferential surface30aof the carrier3400C relative to the seal lip portion55is 70 mm/sec to 1000 mm/sec, the feed rate of fluid is 30 to 200 times as high as in the case where the suction-increasing portion56is not provided.

The carrier3400C of the transmission100in this embodiment accomplishes a larger number of rotations, or higher-speed rotation, than in the configuration described for the second embodiment.

In the transmission100of this embodiment, the fluid feed rate accomplished by the seal mechanism50can be increased even when the temperature rises during high-speed rotation at the circumferential speed of 70 mm/sec or higher. This inhibits the oil or other lubricant from leaking out of the internal space V of the transmission100toward the external space A. In other words, the sealing performance in the transmission100can be improved. This improvement of the sealing performance is less likely to be affected by temperature rise. Therefore, it is possible to maintain the sealing performance regardless of temperature changes in the transmission100caused by high speed rotation or other conditions.

Accordingly, this embodiment produces the same advantageous effects as the first and second embodiments. Furthermore, the presence of the ribs56aimproves the lip rigidity of the seal lip portion55. Therefore, the seal resistance can be increased against attacks by sludge on the seal lip portion55and the outer circumferential surface30aof the carrier3400C. In addition, the smaller contact area of the seal lip portion55to the outer circumferential surface30aof the carrier3400C reduces heat generation.

In the embodiments disclosed herein, a member formed of multiple components may be integrated into a single component, or conversely, a member formed of a single component may be divided into multiple components. Irrespective of whether or not the components are integrated, they are acceptable as long as they are configured to attain the object of the invention.