Bearing unit with optimized radial inner ring
By designing two different diameters on the shoulder of the radial inner ring, the problem of uneven grinding was solved, high-precision radial inner ring machining was achieved, and the scrap rate was reduced.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- AB SKF SKF PATENT DEPARTMENT
- Filing Date
- 2021-04-06
- Publication Date
- 2026-06-09
AI Technical Summary
The existing bearing unit has uneven grinding problem during the radial inner ring grinding process, which causes the roundness of the parts to not meet the tolerance and increases the scrap rate.
The shoulder of the radial inner ring is designed with two different diameters. The larger diameter portion is ground as a reference to ensure uniformity and precision and reduce asymmetrical force distribution.
Precision grinding of the radial inner ring was achieved, significantly reducing the scrap rate and improving the quality control effect of the machining process.
Smart Images
Figure CN113513537B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a bearing unit provided with elements for clamping a radial inner ring onto a rotating shaft. Because this bearing unit is simple and economical to manufacture, it is suitable for applications in manufacturing, and especially in agriculture. Background Technology
[0002] There is a known bearing unit: the bearing unit is provided with rolling elements and a system for clamping the bearing unit onto a rotating shaft.
[0003] A bearing unit is used to allow relative movement of one component or assembly relative to another. Typically, a bearing unit has a first element (e.g., an inner radial ring) and a second element (e.g., an outer radial ring), the first element being fixed to a first assembly (e.g., a rotating shaft), and the second element being fixed to a second assembly (e.g., a mounting base). Typically, as in the aforementioned example, the inner radial ring is rotatable while the outer radial ring is fixed; however, in many applications, the outer element rotates while the inner element is fixed. In any case, in a rolling bearing unit, the rotation of one ring relative to another is allowed by a plurality of rolling elements located between the cylindrical surfaces of one assembly and the cylindrical surfaces of the other assembly; these surfaces are commonly referred to as raceways. The rolling elements can be balls, cylindrical or tapered rollers, needle rollers, or similar rolling elements.
[0004] Bearing units with clamping elements for mounting on a rotating shaft are also known. For example, these elements can be a pair of so-called "grub screws," or headless screws, which, when inserted into suitable threaded through-holes formed in the axial end portion of the radial inner ring, stably lock the radial inner ring to the shaft. Typically, the angular interval between the two grub screws and their corresponding holes is 120°. This approach is simpler and more economical than two other approaches, specifically, compared to a method that forces the radial inner ring to the rotating shaft with an interference fit, and compared to another known approach that uses a clamping collar (which deforms the end portion of the ring by radially contracting it) to press it onto the rotating shaft.
[0005] Despite its simplicity, this approach has several drawbacks. It is well known that both the radially outer cylindrical and radially inner cylindrical surfaces of the bearing unit's radial inner ring require precise surface finishes, achieved through mechanical grinding. During the grinding of the diameter of the shoulder (radial outer surface) of the radial inner ring, the grinding machine uses the front surface of the radial inner ring as a reference surface, which has already been ground in a previous process. The diameter of the shoulder is then achieved through solid profile grinding.
[0006] The problem is that in each revolution of the radial inner ring, the solid profile grinding of the shoulder comes into contact with the threaded holes of the headless screw (usually two). These holes obviously alter the stiffness of the radial inner ring in their cross-section and surrounding area. This results in a different distribution of forces exchanged between the grinding and the shoulder during each revolution of the radial inner ring. This asymmetrical distribution of forces (twice per revolution) (i.e., once per hole) leads to uneven grinding of the diameter of the shoulder of the radial inner ring. The exchanged forces are stronger near the cross-section of the hole used for the locking screw, resulting in a larger amount of material being removed.
[0007] Then, this problem of uneven grinding escalates. This is because, in subsequent machining, the small surface of the shoulder of the radial inner ring is used as a reference for grinding the hole in the inner ring (in other words, the radially inner cylindrical surface of the inner ring). However, despite the well-known problem of asymmetrical force distribution near the threaded hole, the process of grinding the inner hole of the radial inner ring also produces an uneven surface in the hole. When the roundness of the inner hole diameter is checked, two "bumps" are seen at 120° intervals between the two threaded hole locations.
[0008] These "bulges" are a direct result of a stronger force that removes a significant amount of material from the cross-section of the hole used to lock the screw. Clearly, this leads to a substantial increase in the number of parts rejected by quality control when encountering roundness that does not meet permissible tolerances.
[0009] Therefore, it is necessary to design a bearing unit equipped with a clamping element for locking the radial inner ring to the rotating shaft, wherein the surface finish of the radial inner ring meets specified tolerances, thereby avoiding the problem of high scrap rate (percentage of rejected parts). Summary of the Invention
[0010] The object of the present invention is to provide a bearing unit provided with a clamping element for locking a radial inner ring to a rotating shaft, the bearing unit including a radial inner ring having shoulders with two different diameters (i.e., its radially outer cylindrical surface), thus avoiding the above-mentioned disadvantages.
[0011] According to the invention, the outer diameter of the radial inner ring at its axial end portion (including the portion containing the threaded hole for the flathead screw) is different from (in particular smaller than) the diameter of the remaining portion of the radial outer cylindrical surface of the radial inner ring (i.e., the surface including the raceway of the rolling element).
[0012] The concept involves giving a portion of the shoulder a smaller diameter at the end of the radial inner ring, where the rigidity is not constant—that is, the rigidity near the hole used for headless screws is not constant. Therefore, this surface with the smaller diameter will not be ground by solid profile grinding. Instead, the ground surface will be the shoulder with a larger outer diameter (in other words, the radially outer surface including the raceway), exhibiting material uniformity. This allows for precise grinding, resulting in the same precision on the radially inner cylindrical surface of the radial inner ring. Consequently, roundness checks on the inner hole of the radial inner ring will yield excellent results and potentially significantly reduce part scrap during the machining process.
[0013] Therefore, the scheme of forming a shoulder with a smaller diameter and having two different diameters in the radial inner circle makes it possible to significantly reduce the rejection rate during the manufacturing process.
[0014] Therefore, according to the present invention, a bearing unit is formed, the bearing unit including a radial inner ring, the radial inner ring being provided with shoulders having two different diameters, the shoulders including a first portion and a second portion of the radial inner ring, wherein the diameter of a first cylindrical surface radially outer of the first portion is smaller than the diameter of a second cylindrical surface radially outer of the second portion.
[0015] Furthermore, there is a step between the first cylindrical surface and the second cylindrical surface of the radial inner ring, and the height of the step is between 5% and 15% of the thickness of the second portion of the radial inner ring. Attached Figure Description
[0016] The invention will now be described with reference to the accompanying drawings, which illustrate some non-limiting examples of embodiments of the seat element, wherein:
[0017] - Figure 1 A cross-sectional view illustrates a bearing unit equipped with a locking system using a headless screw according to an embodiment of the present invention, and...
[0018] - Figure 2 A cross-sectional view is shown. Figure 1 The bearing unit has no locking system and is designed with a first part (end part) of the radial inner ring. Detailed Implementation
[0019] Embodiments of the bearing unit according to the present invention will now be described by way of example only with reference to the above-described figures.
[0020] Special reference Figure 1The bearing unit 10, used in agricultural and / or manufacturing applications (e.g., textiles, mining, motor vehicles, or food industries), may, for example, be located between a rotating shaft and a housing element, which is not part of the invention, and the bearing unit 10 comprises:
[0021] - Stationary radial outer ring 31,
[0022] - The radial inner ring 33 is capable of rotating about the central rotation axis X of the bearing unit 10.
[0023] - At least one row of rolling elements 32, located between the radial outer ring 31 and the radial inner ring 33, wherein in this example, the rolling elements 32 are balls.
[0024] - Cage 34, for receiving rolling elements to hold the rolling elements of the row of rolling elements 32 in place.
[0025] - Clamping element 20 for locking the radial inner ring onto the shaft.
[0026] Throughout the specification and claims, terms and expressions indicating position and orientation such as “radial” and “axial” shall be interpreted as relative to the central axis of rotation X of the bearing unit 30.
[0027] The outer radial ring 31 is provided with an outer radial raceway 31', while the inner radial ring 33 is provided with at least one inner radial raceway 33' to allow the rolling elements 32 arranged in a row between the outer radial ring 31 and the inner radial ring 33 to roll. For simplicity of illustration, reference numeral 32 will be applied to both a single ball and a row of balls. Also for simplicity, the term "ball" may be used by way of example in this specification and drawings in place of the more general term "rolling element" (and the same reference numerals will also be used). Some examples of embodiments and corresponding designs may provide the use of rolling elements other than balls (e.g., rollers) without departing from the scope of the invention.
[0028] The bearing unit 10 is also provided with a sealing element 35 for sealing the bearing unit from the external environment. In the following text, the sealing element 35 may even be more simply referred to as a seal 35, although this obviously refers to the same component.
[0029] As described above, the clamping element 20 functions to lock the first portion 36 (or end portion) of the radial inner ring 33 onto the rotating shaft. In this example, the clamping element 20 consists of two headless screws positioned at 120° to each other. These screws pass through corresponding through holes 21 formed in the first portion 36 of the radial inner ring. Figure 1In the example, the through hole 21 is threaded, and the headless screw 20 is screwed into the threaded through hole ( / threaded through hole) 21.
[0030] Reference Figure 2 The idea behind this invention is to form a shoulder with two diameters for the radial inner ring 33. More precisely, we can identify two parts forming the radial inner ring: a first part 36 (also called the end part) and the remaining second part 37. The first part 36 has two threaded through holes 21 for inserting a headless screw 20, and the second part 37 includes at least one raceway 33'. The first part 36 has a first radially outer cylindrical surface 38, and the second part 37 has a second cylindrical surface 39, also located radially outer.
[0031] Therefore, according to the present invention, material is removed from the first portion 36 of the radial inner ring 33, that is, from the portion including the threaded through hole 21, where the stiffness of the radial inner ring is not constant due to the presence of the hole. When this is done, the diameter of the first cylindrical surface 38 will be different from the diameter of the second cylindrical surface 39 belonging to the second portion 37 of the radial inner ring 33; in particular, the diameter of the first cylindrical surface 38 will be smaller than the diameter of the second cylindrical surface 39 belonging to the second portion 37 of the radial inner ring 33. Therefore, only the second cylindrical surface 39 of the second portion 37 can be ground, and the second cylindrical surface has material uniformity, thus enabling high precision to be achieved in machining. Therefore, since the second cylindrical surface 39 will be used as a reference to grind the radial inner cylindrical surface 40 of the radial inner ring 33 (in practice, the surface defining the inner hole), the radial inner cylindrical surface 40 will also obtain the same precision.
[0032] Advantageously, better results can be obtained by optimizing the design of the radial inner ring 33.
[0033] Specifically, the first important geometric parameter is the height A of the step 41 formed between the first cylindrical surface 38 and the second cylindrical surface 39. This height A must be between 5% and 15% of the thickness C of the second portion 37 of the radial inner ring 33. A larger value for the height A of the step 41 will excessively weaken the first portion 36 in terms of mechanical strength, since this portion 36 is used to bear the load transmitted by the locking screw 20. A smaller value for the height A of the step 41 will render the inventive idea of forming a shoulder with two diameters ineffective, thereby adversely affecting the accuracy of machine grinding. The preferred value for the height A of the step 41 is equal to 10% of the thickness C of the radial inner ring 33.
[0034] The second equally important geometric parameter is the axial length B of the first portion 36, which includes the threaded through hole 21. If D represents the distance of the axis Y of hole 21 from the front surface 42 of the radial inner ring 33, and E represents the diameter of hole 21, the axial length B must be greater than:
[0035] D + E / 2 + 1mm
[0036] In fact, the first part 36 must extend at least 1 mm beyond the inner edge of the hole 21; otherwise, the effect of material inhomogeneity caused by the hole 21 will also extend partly to the second part 37, thereby adversely affecting the quality of machine grinding on the second cylindrical surface 39.
[0037] Therefore, by forming shoulders with two different diameters on the radial inner ring 33, and preferably by following the design rules described above, a precise ground finish can be obtained on both the second cylindrical surface 39 and the radial inner cylindrical surface 40 of the radial inner ring. Subsequent quality control (especially the inspection of the roundness of the inner hole of the radial inner ring) will yield excellent results, and the rejection rate of parts during the machining process can be greatly reduced by approximately 50%.
[0038] In addition to the embodiments of the invention described above, it should be understood that many other variations exist. It should also be understood that the embodiments are provided by way of example only and do not limit the purpose of the invention or its application or possible constructions. Rather, although the description given above enables those skilled in the art to practice the invention based on at least one example of its construction, it should be understood that many variations of the described components are contemplated without departing from the purpose of the invention, as defined by the appended claims, interpreted literally and / or according to their legal equivalents.
Claims
1. A bearing unit (10), comprising: - Fixed radial outer ring (31). - A radial inner ring (33) is rotatable about the central rotation axis (X) of the bearing unit (10). The radial inner ring (33) is provided with at least one raceway (33') and at least one through hole (21) is provided in the first part (36) of the radial inner ring (33). - At least one row of rolling elements (32) is located between the radial outer ring (31) and the radial inner ring (33). - At least one clamping element (20) is accommodated in the through hole (21) to lock the radial inner ring (33) onto the rotating shaft. The bearing unit (10) is characterized in that the diameter of the first cylindrical surface (38) of the first portion (36) of the radial inner ring (33) is smaller than the diameter of the second cylindrical surface (39) of the second portion (37) of the radial inner ring (33). There is a step (41) between the first cylindrical surface (38) and the second cylindrical surface (39) of the radial inner ring (33), and the height (A) of the step (41) is between 5% and 15% of the thickness (C) of the second part (37) of the radial inner ring (33).
2. The bearing unit (10) according to claim 1, characterized in that, The height (A) of the step (41) is exactly 10% of the thickness (C) of the second part (37) of the radial inner circle (33).
3. The bearing unit (10) according to claim 1 or 2, characterized in that, The axial length (B) of the first portion (36) of the radial inner ring (33) is greater than: D + E / 2 + 1mm in, D is the distance from the axis (Y) of the at least one through hole (21) to the front surface (42) of the radial inner ring (33). E is the diameter of the at least one through hole (21).
4. The bearing unit (10) according to claim 1 or 2, characterized in that, The at least one clamping element (20) is configured as two headless screws 120° apart from each other, and the at least one through hole (21) is configured as two corresponding threaded through holes (21).
5. The bearing unit (10) according to claim 3, characterized in that, The at least one clamping element (20) is configured as two headless screws 120° apart from each other, and the at least one through hole (21) is configured as two corresponding threaded through holes (21).