Search

EP-4134573-B1 - LUBRICANT SEALING STRUCTURE, WAVE-MOTION GEAR DEVICE, AND ACTUATOR

EP4134573B1EP 4134573 B1EP4134573 B1EP 4134573B1EP-4134573-B1

Inventors

  • ORII, DAISUKE
  • KOBAYASHI, SYUHEI

Dates

Publication Date
20260513
Application Date
20200410

Claims (6)

  1. A lubricant sealing structure that prevents a lubricant from leaking out, from an interior of a device (1; 100) provided with a first member and a second member that rotate relative to one another about a central axis (1a; 100a), through a gap portion (41) between the first and second members, the lubricant sealing structure comprising: a first surface portion of the first member and a second surface portion of the second member, between which the gap portion (21, 41; 121; 141) is formed; an oil seal (20, 40, 140, 150) that is secured to the first surface portion and that seals the gap portion (21, 41; 121; 141, 151a) while slidably being in contact with the second surface portion; an oil-repellent surface that is formed on at least one of the first surface portion and the second surface portion, and that is positioned at a side of the interior of the device (1; 1ßß) with respect to the oil seal (20, 40, 140, 150); and an oil film formation surface formed on at least one of a distal-end surface portion of the oil seal (20, 40, 140, 150) that comes into contact with the second surface portion and a site on the second surface portion with which the distal-end surface portion comes into contact, the oil-repellent surface being provided with a surface texture in which first fine grooves (23, 43) extending in a direction along the central axis (1a; 100a) are formed across an entire circumference of the at least one of the first surface portion and the second surface portion at fixed intervals so as to achieve an oil-repelling effect with respect to the lubricant, the first fine grooves (23, 43) being provided with a groove width and a groove depth ranging from several microns to several tens of nanometers, and being formed in the oil-repellent surface at intervals ranging from several microns to several tens of nanometers, the oil film formation surface being provided with a surface texture in which second fine grooves (24, 44) extending in a circumferential direction centered on the central axis (1a; 100a) are formed at fixed intervals in the central axis direction (1a) so as to achieve an oil film formation effect, and the second fine grooves (24, 44) being provided with a groove width and a groove depth ranging from several microns to several tens of nanometers, and being formed in the oil film formation surface at intervals ranging from several microns to several tens of nanometers; and wherein a very small gap portion (22, 42; 122, 142, 152b) is formed in the gap portion (21, 41; 121; 141, 151a) and is located at a side of the interior of the device (1) with respect to the oil seal (20); and in at least one of the first and second surface portions, the oil-repellent surface is formed on a surface portion extending from a position located at a site further toward the interior of the device (1) than the very small gap portion (22, 42; 122, 142, 152b) to the very small gap portion (22, 42; 122, 142, 152b) and is formed on a surface portion forming the very small gap portion (22, 42; 122, 142, 152b), the very small gap portion being of a size to hinder lubricant from flowing into the very small gap portion.
  2. The lubricant sealing structure according to claim 1, wherein the oil film formation surface is: a surface in which the second fine grooves (24, 44) are formed entirely or partially on a circumference thereon; or a surface in which a grooved surface portion where the second fine grooves (24, 44) are formed and a non-grooved surface portion where the second fine grooves (24, 44) are not formed, are formed in an alternating manner.
  3. A strain wave gearing (1), comprising: an input shaft (4); a wave gear mechanism (5) that reduces in speed of rotation of the input shaft (4) and output reduced-speed rotation; a device housing to support the input shaft (4) in a rotatable state via a bearing (6); the lubricant sealing structure according to claim 1 that prevents a lubricant from leaking out, from an interior to an exterior of the gearing (1), through a gap portion (21) formed between an inner peripheral surface potion of the device housing and an outer peripheral surface portion (4a) of the input shaft (4); wherein the device housing (2) is the first member and the inner peripheral surface portion (2a) thereof is the first surface portion; and the input shaft (4) is the second member and the outer peripheral surface portion (4a) thereof is the second surface portion.
  4. A strain wave gearing (1), comprising: a roller bearing (6) that supports a rigid internally toothed gear (8) and a flexible externally toothed gear (9) in a relatively rotatable state; a lubricant sealing structure according to claim 1 that prevents a lubricant from leaking out to an exterior of the gearing (1), through a gap portion formed between an inner peripheral surface potion of an outer race and an outer peripheral surface portion of an inner race of the roller bearing; wherein the outer race is the first member and the inner peripheral surface portion thereof is the first surface portion; and the inner race is the second member and the outer peripheral surface portion thereof is the second surface portion.
  5. A strain wave gearing (120) comprising: a motor (110); an input shaft (126) coaxially linked with the motor (110); a wave gear mechanism that reduces rotation of the input shaft (126); and an output shaft (125) that outputs reduced rotation; the strain wave gearing (120) comprising: a lubricant sealing structure according to claim 1 that prevents a lubricant from leaking out, from an interior of the strain wave gearing (120) to an exterior of the gearing (120), through a gap portion (141) formed between a first surface portion of the output shaft (125) and a second surface portion of the input shaft (126), the second surface portion facing the first surface portion.
  6. An actuator (100), comprising: a motor (110); a strain wave gearing (120) that is coaxially attached to a mounting flange (117) provided on a front end of the motor (110); a motor shaft (111) that penetrates through the mounting flange (117) and extends into an interior of the strain wave gearing (120); an input shaft (126) that is coaxially linked with a distal-end portion of the motor shaft (111) inside the strain wave gearing (120); a lubricant sealing structure according to claim 1 that prevents a lubricant from leaking out, from the strain wave gearing (120) to an interior of the gearing (120), through a gap portion (141) formed between a first surface portion of an inner peripheral edge part of the mounting flange and portions where the first surface portion faces, the portions including a motor shaft (111) and a second surface portion of the input shaft (126); an oil seal (140, 150) that is secured to the first surface portion and that seals the gap portion (141, 151a) while slidably being in contact with the second surface potion.

Description

TECHNICAL FIELD The present invention relates to a lubricant sealing structure used in a strain wave gearing, in an actuator that is provided with a strain wave gearing and a motor, and in other mechanical devices. More specifically, the present invention relates to a lubricant sealing structure that prevents a lubricant from leaking out from the interior of a device to the exterior through a space between a first member and a second member that rotate relative to one another about a central axis. BACKGROUND ART In strain wave gearings and other gearing devices, a rotating member such as an input shaft or an output shaft is disposed in a secured-side device housing with a gap interposed therebetween. Typically, an oil seal is used in order to prevent a lubricant such as oil or grease with which the interior of the device is filled from leaking outside of the device or to other sites within the device through the gap. The oil seal is provided with an annular seal element composed of an elastic material, the seal element being secured to the device housing, and a seal lip of the seal element being slidably pressed against the outer peripheral surface of the rotating member, whereby the gap is sealed such that the lubricant does not leak out. Patent literature 1 (JP 2006-258234 A) proposes a lubricant hermetic-sealing device in which the sealing properties of an oil seal are enhanced. In this lubricant hermetic-sealing device, a fluorine-based grease having oil repellency with respect to a lubricant is applied to portions of a rotating member that are sealed by an oil seal, and the sealing properties are enhanced. 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 Literature 2 (JP 2017-214996 A) 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 Literature 3 (JP 5465109 B) 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. PRIOR-ART LITERATURE PATENT LITERATURE Patent Literature 1: JP 2006-258234 APatent Literature 2: JP 2017-214996 APatent Literature 3: JP 5465109 B SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION EP 2 754 928 A1 discloses a lip seal-type shaft seal device that exhibits no leakage when at rest; operates under fluid lubrication and prevents leakage when rotating, including during initial rotation; and enables a balance between seal integrity and lubrication. A plurality of discontinuous pumping areas for generating pumping action via the relative rotational sliding of a lip seal and a rotating member is formed in the circumferential direction on the outer circumferential surface of a rotating member, the plurality of pumping areas being provided with suction portion of pumping areas operating in a direction in which a sealed fluid is drawn in and discharge portion of pumping areas operating in a direction in which the sealed fluid is expelled, a lip of the lip of the lip seal extending in an axial direction towards an atmosphere side, leaving part of the pumping areas uncovered on a sealed fluid side. US 2009/066033 A1 discloses barrier seal system that comprises a rotatable shaft disposed within an outer housing. The rotatable shaft axially extends from a high-pressure region to a low-pressure region within the outer housing. At least a portion of the rotatable shaft, typically the portion disposed adjacent to the low-pressure region, comprises an oleophobic surface. The system further comprises a barrier seal that radially extends from the outer housing to the rotatable shaft and defines a gap between the barrier seal and the rotatable shaft. A barrier gas injector is provided for injecting a barrier gas into the gap to flow from the high-pressure region to the low-pressure region. In order to maintain the sealing properties of an oil seal, it is necessary for a seal-lip grease film to be kept at a suitable thickness on a portion to be sealed using a seal lip, and for wear in the seal portion to be prevented. If a lubricant such as gear oil that is enclosed in the interior of a device penetrates and comes into contact with the seal portion, there is a concern that the wear resistance and sealing properties of the seal portion could decrease. It is an object of the present invention to provide a lubricant sealing structure with which it is possible to maintain the sealing properties of an oil seal using fine groove machining (surface texturing). MEANS OF SOLVING THE PROBLEMS The present invention provides a lubricant sealing structure th