Method of lubricating a wave generator device

Abstract

A wave gear device (1) is lubricated with non-hydrophobized powder (10A) enclosed in an internal space (9) before the end of running-in (aging), and the non-hydrophobized powder (10A) forms a firm lubricating film by transferring and adhering to each contact surface of the contact portions (B, C). During load running, the wave gear device (1) is lubricated with hydrophobized powder (10B) enclosed in the internal space (9) instead of the non-hydrophobized powder (10A). The powders (10A, 10B) used are powders of ionic crystal compounds (MoS2, WS2, etc.) having a layered crystal structure. By lubricating the wave gear device (1) during load running with the hydrophobized powder (10B), temporary efficiency reduction at the start of running can be suppressed, and stable running of the wave gear device (1) can be maintained.

Description

Technical Field

[0001] This invention relates to a wave gear device, and more particularly to a lubrication method for a wave gear device using a powder of an ionic crystalline compound having a layered crystalline structure as a solid lubricant. Background Technology

[0002] In Patent Documents 1 and 2, the inventors have proposed a lubrication method for a wave gear device using powdered solid lubricant. In Patent Document 1, a fine powder of an ionic crystalline compound having a layered crystalline structure is used to lubricate the wave gear device. During operation of the wave gear device, the fine powder is flattened between the contact surfaces of the object being lubricated, transferring and adhering to both contact surfaces to form a thin lubricating film. Furthermore, it is rolled thinner and further subdivided into a shape that easily penetrates between the contact surfaces. Lubrication is maintained by the shape-changing fine powder and the thin lubricating film formed on the contact surfaces. The transferred, adhered thin lubricating film and the rolled, subdivided fine powder are non-sticky, thus preventing viscous resistance loss and enabling high-efficiency operation in low-load and high-speed rotation regions. On the other hand, in Patent Document 2, a mechanism is assembled inside the wave gear device for efficiently guiding the fine powder of solid lubricant to the area being lubricated.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2016 / 084235

[0006] Patent Document 2: International Publication No. 2016 / 113847 Summary of the Invention

[0007] Here, the fine powder of solid lubricant filling the inner side of the external gear is introduced into the gap between the contact surfaces due to the splitting force, and is rolled thinner. Further subdivision results in torque loss, causing a temporary decrease in efficiency of the wave gear device. In particular, when using fine powder of ionic crystalline compounds (MoS2, WS2, etc.) with a layered crystalline structure, atmospheric moisture arranges on the surface of the layered crystals through hydrogen bonds, increasing friction. Furthermore, the agglomeration of the fine powder increases, leading to coarser aggregated particles. Thus, the fine powder filling the inner side of the external gear is affected by atmospheric moisture and is flattened between the contact surfaces during operation of the wave gear device. This efficiency reduction, especially when a large amount of powder is introduced into the tiny gaps inside the high-speed rotating wave generator, hinders the stable operation of the wave gear device.

[0008] The purpose of this invention is to provide a lubrication method for a wave gear device that can suppress temporary efficiency reduction caused by powder of an ionic crystalline compound with a layered crystalline structure used as a solid lubricant, and maintain a stable high-efficiency operation.

[0009] In the lubrication method of the wave gear device of the present invention, before the break-in operation (aging) of the wave gear device is completed, the contact surfaces of the object to be lubricated are lubricated using unhydrophobicated powder of an ionic crystalline compound with a layered crystalline structure. The powder of the ionic crystalline compound is then transferred and adhered to the contact surfaces to form a firm lubricating film. Then, the hydrophobicated body of the ionic crystalline compound with a layered crystalline structure is sealed or filled into the internal space of the wave gear device. During load operation, the wave gear device maintains the lubrication state of the contact surfaces through the lubricating film formed on the contact surfaces and the hydrophobicated powder of the ionic crystalline compound with a layered crystalline structure.

[0010] The ionic crystalline compounds with layered crystalline structures used are molybdenum disulfide, tungsten disulfide, etc. Regarding the hydrophobic powder of the ionic crystalline compound with a layered crystalline structure that is sealed or filled into the internal space of the wave gear device after break-in operation (aging), it is obtained, for example, by using cationic surfactants such as alkylamine acetates to hydrophobize tiny powders with an average particle size of less than 5 μm as determined by laser desorption / scattering, followed by further pulverization.

[0011] Invention Effects

[0012] By using hydrophobicated powder as the powder of the ionic crystalline compound encapsulated or filled within the internal space of the wave gear device, the rate of efficiency reduction in the wave gear device can be reduced, and its frequency can be suppressed, thereby maintaining a stable high-efficiency state over a long period. Furthermore, the torque loss is small, resulting in less heat generation. Attached Figure Description

[0013] Figure 1 This is a schematic longitudinal sectional view showing an example of a wave gear device.

[0014] Figure 2 This is a schematic flowchart illustrating an example of a lubrication method for the wave gear device of the present invention. Detailed Implementation

[0015] Hereinafter, embodiments of the lubrication method for the wave gear device of the present invention will be described with reference to the accompanying drawings. The embodiments described below apply the present invention to a cup-shaped wave gear device having a cup-shaped external gear; however, the present invention can also be applied to wave gear devices other than cup-shaped wave gear devices. For example, it can be applied to a top-hat type wave gear device having a top-hat shaped external gear, and a flat type wave gear device having a cylindrical external gear and two internal gears.

[0016] Figure 1 This is a schematic longitudinal sectional view showing an example of a cup-shaped wave gear device. The cup-shaped wave gear device 1 (hereinafter simply referred to as "wave gear device 1") includes: a rigid, annular internal gear 2, a flexible, cup-shaped external gear 3, and a wave generator 4 with an elliptical profile. The external gear 3 is coaxially disposed inside the internal gear 2. The wave generator 4 is mounted inside the external gear 3. The external gear 3, bent into an elliptical shape by the wave generator 4, meshes with the internal gear 2 at both ends of the ellipse's major axis.

[0017] The external gear 3 is cup-shaped, and external teeth 3b are formed on the outer peripheral surface of the cylindrical main body 3a, which is capable of flexing in the radial direction. A diaphragm 3c extending radially inward is formed from the opposite end of the cylindrical main body 3a. A rigid annular boss 3d is formed on the inner peripheral edge of the diaphragm 3c. The wave generator 4 includes: a rigid wave plug 4a; and a wave bearing 4b (wave generator bearing), which is mounted on the outer peripheral surface of the elliptical profile of the wave plug 4a. The wave generator 4 is mounted on the inner side of the portion of the external gear 3 where the external teeth 3b of the cylindrical main body 3a are formed.

[0018] Solid lubricant powder 10 is sealed or filled in an internal space 9, which is formed between the cylindrical main body 3a and boss 3d of the external gear 3 and the wave generator 4 mounted on the open end side of the external gear 3. As described later, the solid lubricant powder 10 uses unhydrophobic ionic crystalline compound powder 10A (hereinafter referred to as "unhydrophobic powder 10A") and hydrophobic ionic crystalline compound powder 10B (hereinafter referred to as "hydrophobic powder 10B"). The central opening 3e of the boss 3d is closed by a cover 12, and the central opening 4c of the wave generator 4 is closed by the head of a bolt 13 for fixing the input shaft (indicated by an imaginary line) and a flat washer 14. The solid lubricant powder 10 will not leak out through the aforementioned central openings 3e and 4c.

[0019] The main lubrication points of the wave gear device 1 are: the contact portion (tooth portion) A between the internal gear 2 and the external gear 3; the contact portion B between the inner circumferential surface 3f of the cylindrical main body 3a of the external gear 3 and the outer circumferential surface 4d of the wave generator 4; and the contact portion C inside the wave generator 4. The contact portion C inside the wave generator 4 includes: the contact portion between the wave plug 4a and the wave bearing 4b; and the contact portion between the components of the wave bearing 4b (inner ring, outer ring, and balls). Each contact surface of contact portion B (inner circumferential surface 3f, outer circumferential surface 4d) and each contact surface at contact portion C inside the wave generator 4 communicates with the internal space 9. Each contact surface of the aforementioned contact portions B and C is lubricated by powder 10 of a solid lubricant sealed or filled in the internal space 9. Furthermore, the lubrication of contact portion (tooth portion) A is performed by ordinary oil lubrication or grease lubrication.

[0020] When the wave gear device 1 is used as a speed reducer, the wave generator 4 rotates at high speed by a motor or the like (not shown). For example, the internal gear 2 is fixed to the housing 5, and the external gear 3 rotates at a reduced speed. The reduced speed is output to a rotation output member 6 that is coaxially connected to a rigid boss 3d formed on the external gear 3.

[0021] According to the experiments conducted by the inventors, it can be confirmed that in order to achieve the desired lubrication effect and smooth rotation of the wave generator 4, the powder 10 used as the solid lubricant is preferably a soft, fine powder with an average particle size of 15 μm or less and a Mohs hardness of 1.5 or less.

[0022] Furthermore, the powder 10 used as a solid lubricant can be an ionic crystalline compound with a layered crystalline structure, such as molybdenum disulfide, tungsten disulfide, graphite, boron nitride, etc. Two or more of these solid lubricant powders can also be used in combination. In particular, molybdenum disulfide and tungsten disulfide can be used.

[0023] Figure 2 This is a schematic flowchart illustrating an example of a lubrication method for the wave gear device 1 of the present invention. In this example, before the break-in operation (aging) of the wave gear device 1 is completed, the contact parts B and C are lubricated using unhydrophobic powder 10A as a solid lubricant powder 10. When subsequent load operation is performed, the contact parts B and C are lubricated using hydrophobic powder 10B as a solid lubricant powder 10.

[0024] Reference Figure 2The following explanation is provided. First, the external gear 3 and the wave generator 4 (ST1), which are components constituting the contact portions B and C in the wave gear device 1, are prepared. Their surfaces are shot-peened using non-hydrophobic powder 10A (non-hydrophobic molybdenum disulfide (MoS2) powder or non-hydrophobic tungsten disulfide (WS2) powder) (ST11). This transfers the non-hydrophobic powder 10A to the surface portion of the components that forms the contact surfaces of contact portions B and C, forming a lubricating coating. Alternatively, or in conjunction with shot-peening, the non-hydrophobic powder 10A can be applied to the surface of the components using a soft leather polishing material, thereby transferring the non-hydrophobic powder 10A to the contact surfaces of contact portions B and C to form a lubricating coating (ST12). The above steps (ST11, ST12) can also be omitted.

[0025] Next, in the assembly process of the components of the wave gear device 1, molybdenum disulfide (MoS2) powder or tungsten disulfide (WS2) powder is sealed or filled into the internal space 9 (ST2) of the cup-shaped external gear 3 as unhydrophobic powder 10A.

[0026] With the unhydrophobicated powder 10A sealed or filled in the internal space 9, the wave gear device 1 is subjected to break-in operation (aging) (ST3). During the break-in operation of the wave gear device 1, the unhydrophobicated powder 10A sealed or filled in the internal space 9 is flattened between the contact surfaces at each contact portion B and C, and transferred to the contact surfaces to form a firm, thin, lubricating film. In addition, the unhydrophobicated powder 10A is rolled thinner and further subdivided into micro-powders that can easily enter the contact surfaces.

[0027] The lubrication of the contact portions B and C is maintained by the micro-powder of the non-hydrophobic powder 10A, whose shape has been altered in this way, and the thin lubricating coating formed on each contact surface of the contact portions B and C. In addition, the thin lubricating coating adhering to the contact surface and the micro-powder of the non-hydrophobic powder 10A, which has been rolled and subdivided, are non-sticky, so there is no loss of viscous resistance.

[0028] To achieve lubrication and smooth operation from the initial stage of operation of the wave gear device 1, it is preferable to perform break-in operation (aging) under low load. Additionally, the unhydrophobicated powder 10A sealed or filled in the internal space 9 of the external gear 3 can be pre-rolled to form a thin flake shape. This results in smooth rotation of the wave generator 4, particularly during the initial stage of operation.

[0029] After the break-in period, the wave gear device 1 is temporarily disassembled. The disassembly is carried out to remove and recover the unhydrophobic powder 10A remaining in the internal space 9 of the cup-shaped external gear 3 (ST4).

[0030] Then, the components of the wave gear device 1 are reassembled. In the reassembly process, hydrophobic molybdenum disulfide powder or hydrophobic tungsten disulfide powder, which is the hydrophobic powder 10B, is sealed or filled into the internal space 9 (ST5) of the external gear 3, instead of the unhydrophobic powder 10A. For example, molybdenum disulfide powder is used as both the unhydrophobic powder 10A and the hydrophobic powder 10B. Alternatively, different types of solid lubricant powders can be prepared as the solid lubricant powder 10, with one powder kept as is and used as the unhydrophobic powder 10A, and the other powder treated with hydrophobicity to be used as the hydrophobic powder 10B.

[0031] In the hydrophobication treatment of solid lubricant powder 10 (powder of an ionic crystalline compound having a layered crystalline structure), a cationic surfactant, such as an alkylamine acetate, is diluted with a solvent at a ratio of approximately 1:100 to 1:200. Solid lubricant powder 10 with an average particle size of 5 μm or less is added to this diluted solution and stirred to achieve hydrophobication. This yields hydrophobicated powder 10B. As the cationic surfactant, the alkylamine acetate preferably has a C=10 to 15. Furthermore, the solid lubricant powder 10 and the cationic surfactant are preferably mixed at a molar ratio of 1:0.06 to 0.07.

[0032] As described above, a wave gear device 1 in which hydrophobic powder 10B is sealed or filled in the internal space 9 can be obtained. Under the load operation state (ST6) of the wave gear device 1, the lubrication state of the contact parts B and C is maintained by the hydrophobic powder 10B and the lubricating film formed on the contact surface during the break-in operation (ST3) and the preceding processes (ST11, ST12).

[0033] In this way, the solid lubricant powder 10 (powder of an ionic crystalline layered compound) sealed or filled in the internal space 9 of the wave gear device 1 during load operation is hydrophobically modified powder 10B. Compared with using the unhydrophobically modified powder 10A as is, the rate of efficiency reduction of the wave gear device 1 can be reduced, and its frequency can be suppressed. Therefore, a stable high-efficiency state of the wave gear device 1 can be maintained for a long time. In addition, the torque loss is smaller, so heat generation can also be suppressed.

Claims

1. A lubrication method for a wave gear device, using powder of an ionic crystalline compound having a layered crystalline structure, characterized in that, The wave gear device is run-in under the condition that the unhydrophobic powder is sealed or filled as the powder of the ionic crystalline compound into the internal space of the wave gear device communicating with the contact surface of the lubricated object. Through the break-in operation, the non-hydrophobic powder is transferred and adhered to the contact surface, thereby forming a lubricating film on the contact surface. After the break-in period, the unhydrophobicated powder remaining in the internal space is removed, and the hydrophobicated powder is sealed or filled into the internal space as the powder of the ionic crystalline compound. During operation under load, the lubrication of the contact surfaces is maintained by the lubricating coating and the hydrophobic powder encapsulated or filled in the internal space.

2. The lubrication method for the wave gear device according to claim 1, characterized in that, The ionic crystalline compound is molybdenum disulfide or tungsten disulfide.

3. The lubrication method for the wave gear device according to claim 2, characterized in that, The non-hydrophobic powder has an average particle size of less than 15 μm and a Mohs hardness of less than 1.

5.

4. The lubrication method for the wave gear device according to claim 3, characterized in that, The hydrophobicated powder is obtained by hydrophobizing the powder of the ionic crystalline compound with an average particle size of less than 5 μm using a cationic surfactant.

5. A wave gear device, comprising: The internal space, which is connected to the contact surface of the object being lubricated; Powdered solid lubricant, which is sealed or filled in the internal space; and A lubricating coating is formed on the contact surface. The solid lubricant powder is a powder of an ionic crystalline compound with a layered crystalline structure after hydrophobication. The lubricating coating is formed by transferring and adhering powder of an ionic crystalline compound with a layered crystalline structure that has not been hydrophobized to the contact surface.

6. The wave gear device according to claim 5, characterized in that, The ionic crystalline compound is molybdenum disulfide or tungsten disulfide.

7. The wave gear device according to claim 5, characterized in that, The hydrophobicated powder is obtained by hydrophobizing the powder of the ionic crystalline compound with an average particle size of less than 5 μm using a cationic surfactant.

8. The wave gear device according to claim 5, characterized in that, have: Rigid internal gears; A flexible external gear, disposed inside the internal gear; and A wave generator, mounted on the inner side of the external gear, bends the external gear into a non-circular shape to mesh with the internal gear, causing the meshing position of the two gears to move circumferentially. The internal space is the space surrounded by the external gear and the wave generator. The contact surface is the contact surface between the external gear and the wave generator, as well as the contact surface inside the wave generator.

Images